DESCRIPTION
[Title of Invention]
OFDM TRANSMITTER DEVICE, OFDM TRANSMISSION METHOD,
OFDM RECEIVER DEVICE, AND OFDM RECEPTION METHOD
[Technical Field]
[0001]
The present invention relates to technology for transmitting a signal
multiplexed over a plurality of sub-carriers, and to technology for receiving a signal
in which are multiplexed a plurality of sub-carriers.
[Background Art]
[0002]
Presently, Orthogonal Frequency Division Multiplexing (OFDM) is a
transmission system widely user for various types of digital transmission, notably
including terrestrial digital broadcasting and IEEE 802.11a. The OFDM method
makes highly efficient use of frequencies by frequency-multiplexing a plurality of
narrowband digitally-modulated signals using mutually-orthogonll sub-carriers.
[0003]
Additionally, in the OFDM method, one symbol comprises a useful symbol
as well as a guard interval, both of which are signals. As such, a portion of the useful symbol is replicated as the guard interval to produce intra-symbol periodicity.
Thus, the influence of inter-symbol interference caused by multi-path interference is
reduced, in that such a scheme offers superb resistance to such interference.
[0004]
Analog television broadcasting is to cease around the world as worldwide
frequency reconfiguration is being carried out. In Europe, demand is growing for
HD (High Definition) broadcasting services in addition to the SD (Standard
Definition) broadcasting services using DVB-T (Digital Video Broadcasting for
Terrestrial) currently available. Thus the standardization of the second-generation

European digital terrestrial television broadcasting system, DVB-T2, has advanced.
The DVB-T2 broadcasting system is detailed in Non-Patent Literature 1.
[0005]
As shown in Fig. 50, the DVB-T2 broadcasting system uses DVB-T2
frames, the structure of which includes a P1 symbol (P1 signal), one or more P2
symbols, and data symbols.
[0006]
The P1 symbol is made to have an FFT (Fast Fourier Transform) size of 1k.
As shown in Fig. 51, guard intervals are arranged in front of and behind the useful
symbol. In Fig. 51, the P1 symbol is shown in the time domain. Hereinafter, the
guard interval arranged in front of the useful symbol interval is also termed the
leading guard interval, while the guard interval arranged behind the useful symbol is
also termed the trailing guard interval.
[0007]
The guard interval of the P1 symbol differs from the guard interval user in
the ISDB-T (Integrated Services Digital Broadcasting for Terrestrial) and DVB-T
broadcasting systems thus far. In the P1 symbol, the guard interval arranged in
front of the useful symbol (the leading guard interval) replicates the leading portion
(Tc = 59 μs) of the useful symbol (Ta = 112 μs). Similarly, the guard interval
arranged behind the useful symbol (the trailing guard interval) replicates the trailing
portion (Tb = 53 μs) of the useful symbol (Ta = 112 μs). As shown in Fig. 51 and
in Patent Literature 1, when these replicated portions are to be inserted, a
predetermined frequency shift fSH (equivalent to the sub-carrier spacing of the P1
symbol) is first applied to the signal to be replicated before insertion. This process
is expressed by the below-inscribed Math. 1.
[0008]
(Math. 1)


where pl(t) is the first P1 symbol, plA(t) is the useful symbol, +fsH is the
frequency shift, T is the time of one sample, post-IFFT, t is time, and the start time
of the first P1 symbol is 0. In the DVB-T2 broadcasting system, for a bandwidth of
8 MHz, T = 7/64 μs and the time span of the useful symbol (hereinafter, useful
symbol length)is1024T=112 μs.
[0009]
Also, as shown in Fig. 52, the P1 symbol as expressed in the frequency
domain is seen to be composed of a plurality of Active carriers and a plurality of
Null carriers (Unused carriers). Information is affixed to the Active carriers. For
convenience, Fig. 52 illustrates the Null carriers with dashed arrows. In reality, the
Null carriers carry no information and have no amplitude. As described in Patent
Literature 2, the Active carrier positions are given by a predetermined sequence.
That is, the positions are designated according to CSS (Complementary Sets of
Sequences).
[0010]
Fig. 53 shows the configuration of a typical P1 symbol demodulator 10001
demodulating the P1 symbol, as described by Non-Patent Literature 1. The P1 symbol demodulator 10001 includes a P1 position detector 10101, an FFT unit
10102, and a P1 decoder 10103.
[0011]
The P1 position detector 10101 detects the position of the P1 symbol in the
input signal (i.e., the P1 symbol demodulator 10001 input signal) and accordingly
outputs P1 symbol position information to the FFT unit 10102. Fig. 54 shows the
configuration of the P1 position detector 10101.
[0012]

The P1 position detector 10101 includes a multiplier 10201, a delayer
10202, a complex conjugate calculator 10203, a multiplier 10204, an integral
calculator 10205, a delayer 10206, a complex conjugate calculator 10207, a
multiplier 10208, an integral calculator 10209, a delayer 10210, a multiplier 10211,
and a peak detector 10212.
[0013]
The P1 position detector 10101 input signal is input to the multiplier 10201.
The multiplier 10201 multiplies the P1 position detector 10101 input signal by
exp(-y27rfSHt) in order to apply a frequency shift that is the inverse of the +fsH
frequency shift applied by the transmitter to the leading and trailing guard intervals
of the fIrst P1 symbol (applying a frequency shift of -fSH). The multiplier 10201
then outputs the result to the delayer 10202 and to the multiplier 10208. The
delayer 10202 delays the multiplier 10201 output signal by Tc (= 59 μs), a span
equivalent to the leading guard interval time span (hereinafter, the length of the
leading guard interval), and then outputs the signal so delayed to the complex
conjugate calculator 10203. The complex conjugate calculator 10203 calculates
the complex conjugate of the signal output by the delayer 10202 and outputs the
resulting complex conjugate signal to the multiplier 10204. The multiplier 10204
calculates a correlation by multiplying the P1 position detector 10101 input signal
and the complex conjugate calculator 10203 output signal, then outputs the
correlated value so calculated to the integral calculator 10205. The integral
calculator 10205 integrates the output signal from the multiplier 10204 over the
length Tc of the leading guard interval, and then outputs the result to the delayer
10210. Figs. 55A through 55C are schematic diagrams illustrating this signal
processing. As shown in Fig. 55A, the leading guard interval obtained by
frequency shifting the P1 position detector 10101 input signal by -fsH and then
delaying the result by the length Tc of the leading guard interval (shown in the lower
portion of Fig. 55A) is identical to the leading part of the useful symbol within the

P1 position detector 10101 (shown in the upper portion of Fig. 55A). A correlation
appears in this portion, as shown in Fig. 55B. Given that other parts of the signals
are not identical, no correlation appears therein. The peak shown in Fig. 55C is the
effect of integrating the correlated value shown in Fig. 55B over the length Tc of the
trailing guard interval.
[0014]
Meanwhile, the P1 position detector 10101 input signal is input to the
delayer 10206. The delayer 10206 delays the P1 position detector 10101 input
signal by Tb (= 53 μs), a span equivalent to the trailing guard interval time span
(hereinafter, the length of the trailing guard interval), and then outputs the result to
the complex conjugate calculator 10207. The complex conjugate calculator 10207
calculates the complex conjugate of the signal output by the delayer 10206 and
outputs the resulting complex conjugate signal to the multiplier 10208. The signal
input to the multiplier 10208 is the result of the multiplier 10201 multiplying the P1
position detector 10101 input signal by exp(-j2πfSHt). The multiplier 10208
calculates a correlation by multiplying the multiplier 10201 output signal (the P1
position detector 10101 input signal with a frequency shift of-fsH applied thereto)
and the complex conjugate calculator 10207 output signal, then outputs the
correlated value so calculated to the integral calculator 10209. The integral
calculator 10209 integrates the multiplier 10208 output signal over the length Tb of
the trailing guard interval, and then outputs the result to the multiplier 10211. Figs.
56A through 56C are schematic diagrams illustrating this signal processing. As
shown in Fig. 56A, the trailing guard interval obtained by frequency shifting the P1
position detector 10101 input signal by -fSH (shown in the upper portion of Fig.
56A) is identical to the useful symbol within the P1 position detector 10101 with the
trailing part delayed by the length Tb of the trailing guard interval (shown in the
lower portion of Fig. 56A). The correlation appears in this part, as shown in Fig.
56B. Given that other parts of the signals are not identical, no correlation appears

therein. The peak shown in Fig. 56C is the effect of integrating the correlated
value shown in Fig. 56B over the length Tb of the trailing guard interval.
[0015]
The signal output from the integral calculator 10205 is input to the delayer
10210. The delayer 10210 delays the signal output from the integral calculator
10205 to the match in the signal output from the integral calculator 10209 for output
to the multiplier 10211. The multiplier 10211 multiplies the signal output from the
integral calculator 10209 by the signal output from the delayer 10210, and then
outputs the product to the peak detector 10212. Thus, the peaks are made more
prominent by matching the peaks in the correlated value integral taken for the
leading guard interval to the peaks in the correlated value integral taken for the
trailing guard interval. The peak detector 10212 detects the position of the P1
symbol within the P1 position detector 10101 input signal (i.e., the signal input to
the P1 symbol demodulator 10001) by detecting the peak position in the signal
output from the multiplier 10211. The peak detector 10212 accordingly outputs
position information for the P1 symbol to the FFT unit 10102 shown in Fig. 53.
Given the presence of a delayed wave, a peak correlation appears in correspondence
to the level and position of the delay.
[0016]
The FFT unit 10102 shown in Fig. 53 performs a FFT (Fast Fourier
Transform) on the signal input from the P1 symbol demodulator 10001 (a
time-domain signal) in accordance with the P1 symbol position information, thus
obtaining a converted frequency-domain signal for output to the P1 decoder 10103.
The P1 decoder 10103 executes a decoding process on the P1 symbol using the
Active carriers in the frequency-domain signal, calculates the values of the S1 and
S2 signals added to the P1 symbol to discern information therefrom, such as the FFT
size and MISO/SISO information.
[0017]

Incidentally, the DVB-T2 broadcasting system includes FEF (Future
Extension Frames) so that future broadcasting systems can broadcast using time
multiplexing. Accordingly, broadcasting systems other than DVB-T2 are made
possible. Fig. 57 shows the positional relationship between FEF and DVB-T2
frames. The head of an FEF part is a P1 symbol, much like that of a DVB-T2
frame. However, the information affixed to the P1 symbol is different from that user in the DVB-T2 broadcasting system. Therefore, a receiver implementing the
DVB-T2 broadcasting system (hereinafter, a DVB-T2 receiver) demodulates the P1
symbol of the FEF part with the P1 symbol demodulator 10001, and can then
acknowledge the presence of an FEF part by using the information affixed to the
symbol.
[Citation List]
[Patent Literature]
[0018]
[Patent Literature 1]
International Application Publication No. WO2009/060183
[Patent Literature 2]
International Application Publication No. WO2009/074693
[Non-Patent Literature]
[0019]
[Non-Patent Literature 1]
DVB Bluebook Document A133; Implementation guidelines for a
second-generation digital terrestrial television broadcasting system (DVB-T2)
[Summary of Invention]
[Technical Problem]
[0020]
Recently, worldwide debates on next-generation methods are taking place in
consideration of DVB-S2 and the above-described DVB•T2. This concerns

plausible services that make use of the FEF part. In such services, the information
that can be transmitted by the P1 symbol at the head of the FEF part can only be 7
bits, and must further indicate the presence of the FEF part. This imposes
considerable restrictions on the information. Transmitting an additional P1 symbol
in the FEF part seems plausible for a new transmission system. However, the
following problems arise in transmitting multiple P1 symbols in the FEF part as part
of the same transmission format. For simplicity, the transmission of two P1
symbols considered, below.
[0021]
In order to demodulate the P1 symbol, as described-above, a
transmitter-imparted frequency shift is reversed, then a guard correlation is obtained,
and peaks are detected therein. Here, the guard correlation appears for both P1
symbols. In the guard correlation, it is difficult to distinguish whether two detected
peaks belong to separate P1 symbols, or whether one peak is a delayed wave of the
other. This makes P1 symbol demodulation rather problematic. In the DVB-T2
broadcasting system, the maximum guard interval length for P2 symbols and data
symbols, in some cases, 4864 samples (for an FFT size of 32k and a guard interval
ratio of 19/128). There thus appears to be an upper limit of 2098 samples for the P1 symbol, imposed by the delayed waves that can be tolerated by the guard
intervals of the P2 symbols and the data symbols. For these reasons, there is a
pressing need to distinguish a P1 symbol from a delayed wave of an
already-detected peak from another P1 symbol. Also, in existing DVB-T2
receivers, demodulation is predicated on the expectation that only one P1 symbol
per frame will be received. A problem thus arises in that demodulation operations
are adversely affected when such DVB-T2 receivers receive the second P1 symbol,
which renders reception of the DVB-T2 broadcasting system itself impossible.
[0022]
In addition, both P1 symbols are transmitted using the same sub-carrier

locations (with the same sub-carriers arranged as Active carriers). Thus, in the
presence of a delayed wave, interference arises between the two P1 symbols because
of the electric power concentration in the P1 symbol Active carriers. This
interference is greater than that arising between the P1 symbols and typical data
symbols. For example, as shown in Fig. 58, when interference arises between the P1 symbol and a delayed wave of a typical data symbol, the P1 symbol is affected in
the Null carriers as well as the Active carriers because the data symbol has nearly no
Null carriers. In contrast, as shown in Fig. 59, when interference arises between
two P1 symbols, Active carriers are intensely affected. Given that the P1 symbol
has many Null carriers, the electric power of the Active carriers is greater than that
of a single sub-carrier for a typical data symbol. The same electric power in a
delayed wave causes greater interference at the Active carrier level than the data
symbol. As such, transmitting two P1 symbols using the same sub-carrier locations
leads to a problem in that, in a delayed environment, P1 symbol demodulation can
be erroneous, making correct reception impossible.
[0023]
Therefore, an atm of the present invention is to provide an OFDM
transmitter, an OFDM transmission method, an integrated circuit, and an OFDM
transmission program that generate multiple control symbols that, without affecting
existing DVB-T2 receivers, allow multiple control symbols (such as P1 symbols) to
be reliably distinguished, or such that demodulation thereof is reliably possible in a
delayed environment. Another aim ofthe present invention is to provide an OFDM
receiver, an OFDM reception method, an integrated circuit, and an OFDM reception
program that accurately receive the control symbols so transmitted.
[Solution to Problem]
[0024]
In order to achieve the above-stated goal, the present invention provides an
OFDM transmitter, comprising: a first symbol generator generating N (N being an

integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal; a
second symbol generator generating a plurality of symbols different from the control
symbols; and a symbol inserter inserting the N control symbols into the plurality of
symbols generated by the second symbol generator, wherein in each of the control
symbols, the guard interval time-domain signal is identical to a signal in which at
least a portion of the useful symbol time-domain signal has been frequency-shifted
by an amount different from any other control symbols.
[0025]
The present invention also seeks to provide an OFDM receiver, comprising:
a first symbol demodulator demodulating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain
signal and a guard interval time-domain signal; and a second symbol demodulator
demodulating symbols other than the control symbols according to results from the
first symbol demodulator, wherein in each of the control symbols, the guard interval
time-domain signal is identical to a signal in which at least a portion of the useful
symbol time-domain signal has been frequency-shifted by an amount different from
any other control symbols.
[Advantageous Effects of Invention]
[0026]
Accordingly, when transmitting N control symbols, the receiver can easily
and reliably distinguish whether two control symbols are distinct, or whether one
symbol is a delayed wave of the other. In addition, reliable reception is assured
when N control symbols are transmitted in the FEF part for reception by existing
DVB-T2 receivers.
[Brief Description of Drawings]

[0027]
Fig. 1 is a block diagram showing the configuration of an OFDM
transmitter 1 pertaining to Embodiment 1 of the present invention.
Fig. 2 is a block diagram showing the configuration of a P1 symbol
generator 11 from Fig. 1.
Fig. 3 is a block diagram showing the configuration of a first P1 symbol
generator 100 from Fig. 2.
Fig. 4 shows sub-carrier numbers for Active carriers.
Fig. 5 shows an MSS conversion sequence for the values of S1 and S2
signals.
Fig. 6 is a schematic diagram illustrating a first P1 symbol with guard
intervals inserted by a guard interval inserter 107 (time domain shown).
Fig. 7 is a block diagram showing the configuration of a second P1 symbol
generator 200 from Fig. 2.
Fig. 8 is a schematic diagram illustrating a second P1 symbol with guard
intervals inserted by a guard interval inserter 207 (time domain shown).
Fig. 9 is a schematic diagram illustrating a transmission system frame
structure that uses first and second P1 symbols.
Fig. 10 is a block diagram showing the configuration of an OFDM receiver
2 pertaining to Embodiment 1 of the present invention.
Fig. 11 is a block diagram showing the configuration of a P1 symbol
demodulator 26 from Fig. 10.
Fig. 12 is a block diagram showing the configuration of a first P1 symbol
demodulator300 from Fig.11.
Fig. 13 is a block diagram showing the configuration of a P1 position
detector 301from Fig.12.
Fig. 14 is a block diagram showing the configuration of a second P1 symbol
demodulator 400.

Fig. 15 is a block diagram showing the configuration of a P1 position
detector 401 from Fig.14.
Figs. l6A, l6B, and l6C are schematic diagrams illustrating correlations
taken in the leading portion of the second P1 symbol by the P1 position detector 401
from Fig. 15.
Figs. 17A, 17B, and 17C are schematic diagrams illustrating correlations
taken in the trailing portion of the second P1 symbol by the P1 position detector 401
from Fig. 15.
Figs. 18A, 18B, and 18C are schematic diagrams illustrating correlations
taken in the leading portion of the second P1 symbol by the P1 position detector 301
of the first P1 symbol demodulator 300.
Figs. 19A, 19B, and 19C are schematic diagrams illustrating correlations
taken in the trailing portion of the second P1 symbol by the P1 position detector 30I
of the first P1 symbol demodulator 300.
Fig. 20 is a block diagram showing the configuration of a P1 symbol
generator 11A in an OFDM transmitter pertaining to Embodiment 2 of the present
invention.
Fig. 21 is a block diagram showing the configuration of a second P1 symbol
generator 200A from Fig. 20.
Fig. 22 is a schematic diagram illustrating the second P1 symbol with guard
intervals inserted by a guard interval inserter 207A (time domain shown).
Fig. 23 is a block diagram showing the configuration of a P1 symbol
demodulator 26A in the OFDM receiver pertaining to Embodiment 2 of the present
invention.
Fig. 24 is a block diagram showing the configuration of a second P1 symbol
demodulator 400A from Fig. 23.
Fig. 25 is a block diagram showing the configuration of a P1 position
detector 401A from Fig. 24.

Figs. 26A, 26B, and 26C are schematic diagrams illustrating correlations
taken in the leading portion of the second P1 symbol by the P1 position detector
40IA from Fig.25.
Figs. 27A, 27B, and 27C are schematic diagrams illustrating correlations
taken in the trailing portion of the second P1 symbol by the P1 position detector
40IAfromFig.25.
Figs. 28A, 28B, and 28C are schematic diagrams illustrating correlations
taken in the leading portion of the second P1 symbol by the P1 position detector 301
of the first P1 symbol demodulator 300 (from Fig. 13).
Figs. 29A, 29B, and 29C are schematic diagrams illustrating correlations
taken in the trailing portion of the second P1 symbol by the P1 position detector 301
of the first P1 symbol demodulator 300 (from Fig. 13).
Fig. 30 is a block diagram showing the configuration of a P1 symbol
generator 11B in the OFDM transmitter pertaining to Embodiment 3 of the present
invention.
Fig. 31 is a block diagram showing the configuration of a second P1 symbol
generator 200B from Fig. 30.
Fig. 32 is a schematic diagram illustrating a second P1 symbol with guard
intervals inserted by a guard interval inserter 207B (time domain shown).
Fig. 33 is a block diagram showing the configuration of a P1 symbol
demodulator 26B in the OFDM receiver pertaining to Embodiment 3 of the present
invention.
Fig. 34 is a block diagram showing the configuration of a second P1 symbol
demodulator 400B from Fig. 33.
Fig. 35 is a block diagram showing the configuration of a P1 position
detector 40IB from Fig. 34.
Fig. 36 is a block diagram showing the configuration of a P1 symbol
generator 11C in the OFDM transmitter pertaining to Embodiment 4 of the present

invention.
Fig. 37 is a block diagram showing the configuration of a second P1 symbol
generator 200C from Fig. 36.
Figs. 38A and 38B are schematic diagrams illustrating sample sub-carrier
locations for the first and second P1 symbols when a carrier location sequence a[j]
and another carrier location sequence b[j] are orthogonal (uncorrected) (frequency
domain shown).
Figs. 39A and 39B are schematic diagrams illustrating sample sub-carrier
locations for the first and second P1 symbols when a subset of the Null carriers of
the first P1 symbol are made the Active carriers of the second P1 symbol (frequency
domain shown).
Fig. 40 is a block diagram showing the configuration of a P1 symbol
demodulator 26C in the OFDM receiver pertaining to Embodiment 4 of the present
invention.
Fig. 41 is a block diagram showing the configuration of a second P1 symbol
demodulator 26C.
Fig. 42 is a schematic diagram illustrating interference between the first and
second P1 symbols in a delayed environment.
Fig. 43 is a schematic diagram showing a variation on the frame structure
from Fig. 9.
Fig. 44 is a schematic diagram showing a variation on the frame structure
from Fig. 9.
Fig. 45 is a block diagram showing the configuration of another P1 symbol
demodulator 26D.
Fig. 46 is a block diagram showing the configuration of another P1 symbol
demodulator 26E.
Fig. 47 is a block diagram showing the configuration of a P1 correlation
calculator 30IE from Fig. 46.

Fig. 48 is a block diagram showing the configuration of a P1 correlation
calculator 40lE from Fig. 46.
Fig. 49A is a schematic diagram illustrating the transmission format of the
firt P1 symbol in the time dimension, while Fig. 49B is a schematic diagram
illustrating the transmission format of the second P1 symbol in the time dimension.
Fig. 50 is a schematic diagram illustrating the frame structure of the
DVB-T2 broadcasting format.
Fig. 51 is a schematic diagram illustrating the transmission format of the P1
symbol in the time dimension.
Fig. 52 is a schematic diagram illustrating the transmission format of the P1
symbol in the frequency dimension.
Fig. 53 is a block diagram showing the configuration of a P1 symbol
demodulator 10001 according to Non-Patent Literature 1.
Fig. 54 is a block diagram showing the configuration of a P1 position
detector 10101 from Fig. 53.
Figs. 55A, 55B, and 55C are schematic diagrams illustrating correlations
taken in the leading portion of the P1 symbol by the P1 position detector 10101 from
Fig. 54.
Figs. 56A, 56B, and 56C are schematic diagrams illustrating correlations
taken in the trailing portion of the P1 symbol by the P1 position detector 10101 from
Fig. 54.
Fig. 57 is a schematic diagram illustrating the structure of FEF and DVB-T2
frames.
Fig. 58 is a schematic diagram illustrating interference between the P1
symbol and data symbols in a delayed environment.
Fig. 59 is a schematic diagram illustrating interference between the P1
symbol and another P1 symbol in a delayed environment.
[Description of Embodiments]

[0028]
According to one aspect of the present invention, a first OFDM transmitter
comprises: a first symbol generator generating N (N being an integer satisfying N ≥
2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain
signal and a guard interval time-domain signal; a second symbol generator
generating a plurality of symbols different from the control symbols; and a symbol
inserter inserting the N control symbols into the plurality of symbols generated by
the second symbol generator, wherein in each of the control symbols, the guard
interval time-domain signal is identical to a signal in which at least a portion of the useful symbol time-domain signal has been frequency-shifted by an amount
different from any other control symbols.
[0029]
According to another aspect of the present invention, an OFDM
transmission method comprises a first symbol generation step of generating N (N
being an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal; a
second symbol generation step of generating a plurality of symbols different from
the control symbols; and a symbol insertion step of inserting the N control symbols
into the plurality of symbols generated by the second symbol generator, wherein in
each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols.
[0030]
According a further aspect of the present invention, an integrated circuit
comprises a first symbol generation circuit generating N (N being an integer
satisfying N ≥ 2) control symbols in which a plurality of mutually-orthogonal

sub-carriers are multiplexed, the control symbols being made up of a useful symbol
time-domain signal and a guard interval time-domain signal; a second symbol
generation circuit generating a plurality of symbols different from the control
symbols; and a symbol insertion circuit inserting the N control symbols into the
plurality of symbols generated by the second symbol generator, wherein in each of
the control symbols, the guard interval time-domain signal is identical to a signal in
which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols.
[0031]
According to an alternative aspect of the present invention, an OFDM
transmission program executed by an OFDM transmitter comprises: a first symbol
generation step of generating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed,
the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; a second symbol generation step of generating a
plurality of symbols different from the control symbols; and a symbol insertion step
of inserting the N control symbols into the plurality of symbols generated by the
second symbol generator, wherein in each of the control symbols, the guard interval
time-domain signal is identical to a signal in which at least a portion of the useful
symbol time-domain signal has been frequency-shifted by an amount different from
any other control symbols.
[0032]
Accordingly, when transmitting N control symbols, the receiver can easily
and reliably distinguish whether two control symbols are distinct, or whether one
symbol is a delayed wave of the other. In addition, reliable reception is assured
when N control symbols are transmitted in the FEF part without interfering with
reception by existing DVB-T2 receivers.
[0033]

In a further aspect of the present invention, a second OFDM transmitter
based on the first OFDM transmitter has the first symbol generator include: an
inverse orthogonal transformer generating the useful symbol time-domain signal
through an inverse orthogonal transformation from the frequency domain to the time
domain, performed for each of the N control symbols; and a guard interval inserter
(i) generating the guard interval time-domain signal by frequency-shifting at least a
portion of the useful symbol time-domain signal by a given amount different from
any other control symbols, and (ii) inserting the guard interval time-domain signal
so generated to the useful symbol time-domain signal, for each of the N control
symbols.
[0034]
Accordingly, N control symbols can easily be generated.
[0035]
According to an alternative aspect of the present invention, a third OFDM
transmitter based on the second OFDM transmitter has the guard interval inserter
generate the guard interval time-domain signal by frequency shifting one or both of
a portion and a span of the useful symbol time-domain signal different from any
other control symbols by the given amount.
[0036]
Accordingly, when transmitting N control symbols, the receiver can easily
and reliably distinguish whether two control symbols are distinct, or whether one
symbol is a delayed wave of the other. In addition, reliable reception is assured
when N control symbols are transmitted in the FEF part without interfering with
reception by existing DVB-T2 receivers.
[0037]
According to a further aspect of the present invention, a fourth OFDM
transmitter based on the second OFDM transmitter has the plurality of sub-carriers
include a plurality of Active carriers and a plurality of Null carriers, for each of the

N control symbols, a carrier location sequence used to distinguish between the
Active carriers and the Null carriers among the plurality of sub-carriers differs from
another carrier location sequence for other control symbols, and the first symbol
generator further includes a carrier locator generating the frequency-domain signal
by mapping control information data to each of the Active carriers in accordance
with the carrier location sequence, for each of the N control symbols.
[0038]
Accordingly, when N control symbols are transmitted, reliable reception is
made possible even when the receiver is in a delayed environment, with minimal
interference occurring between control symbols due to delayed waves.
[0039]
According to another alternative aspect of the present invention, a fifth
OFDM transmitter based on the first OFDM transmitter has N be equal to 2.
[0040]
According to an alternative aspect of the present invention, a sixth OFDM
transmitter based on the fifth OFDM transmitter has a frequency shift applied to a
first one of the control symbols and a frequency shift applied to a second one of the
control symbols are equal in absolute value while being opposite in sign.
[0041]
In this example, N equals two, and a sample frequency shift is provided for
each of the two control symbols.
[0042]
According to another aspect of the present invention, a seventh OFDM
transmitter comprises: a first symbol generator generating N (N being an integer
satisfying N ≥ 2) control symbols in which a plurality of mutually-orthogonal
sub-carriers are multiplexed, the control symbols being made up of a useful symbol
time-domain signal and a guard interval time-domain signal; a second symbol
generator generating a plurality of symbols different from the control symbols; and a

symbol inserter inserting the N control symbols into the plurality of symbols
generated by the second symbol generator, wherein for each of the control symbols,
the guard interval time-domain signal is identical to one or both of a portion and a
span of the useful symbol time-domain signal different from any other control
symbols frequency-shifted by a predetermined amount.
[0043]
Also, a second OFDM transmission method comprises: a first symbol
generation step of generating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed,
the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; a second symbol generation step of generating a
plurality of symbols different from the control symbols; and a symbol insertion step
of inserting the N control symbols into the plurality of symbols generated by the
second symbol generator, wherein in each of the control symbols, the guard interval
time-domain signal is identical to a signal in which at least a portion of the useful
symbol time-domain signal has been frequency-shifted by an amount different from
any other control symbols.
[0044]
Furthermore, a second integrated circuit comprises: a first symbol
generation circuit generating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed,
the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; a second symbol generation circuit generating a
plurality of symbols different from the control symbols; and a symbol insertion
circuit inserting the N control symbols into the plurality of symbols generated by the
second symbol generator, wherein in each of the control symbols, the guard interval
time-domain signal is identical to a signal in which at least a portion of the useful
symbol time-domain signal has been frequency-shifted by an amount different from

any other control symbols.
[0045]
In addition, a second OFDM transmission program executed by an OFDM
transmitter comprises: a first symbol generation step of generating N (N being an
integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal; a
second symbol generation step of generating a plurality of symbols different from
the control symbols; and a symbol insertion step of inserting the N control symbols
into the plurality of symbols generated by the second symbol generator, wherein in
each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols.
[0046]
Accordingly, when transmitting N control symbols, the receiver can easily
and reliably distinguish whether two control symbols are distinct, or whether one
symbol is a delayed wave of the other. In addition, reliable reception is assured
when N control symbols are transmitted in the FEF part without interfering with
reception by existing DVB-T2 receivers.
[0047]
According to an alternative aspect of the present invention, an eighth
OFDM transmitter based on the seventh OFDM transmitter has the first symbol
generator include: an inverse orthogonal transformer generating the useful symbol
time-domain signal through an inverse orthogonal transformation from the
frequency domain to the time domain, performed for each of the N control symbols;
and a guard interval inserter (i) generating the guard interval time-domain signal by
frequency-shifting one or both of a portion and a span different from any other
control symbols of the useful symbol time-domain signal by the predetermined

amount and (ii) inserting the guard interval time-domain signal so generated to the
useful symbol time-domain signal, for each of the N control symbols.
[0048]
Accordingly, N control symbols can easily be generated.
[0049]
In yet a further aspect of the present invention, a ninth OFDM transmitter
comprises: a first symbol generator generating N (N being an integer satisfying N ≥
2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain
signal and a guard interval time-domain signal; a second symbol generator
generating a plurality of symbols different from the control symbols; and a symbol
inserter inserting the N control symbols into the plurality of symbols generated by
the second symbol generator, wherein the plurality of sub-carriers include a plurality
of Active carriers and a plurality of Null carriers, for each of the N control symbols,
a carrier location sequence user to distinguish between the Active carriers and the
Null carriers among the plurality of sub-carriers differs from another carrier location
sequence for other control symbols, and control information data is mapped to each
of the Active carriers in accordance with the carrier location sequence for each of
the N control symbols.
[0050]
According to an alternative aspect of the present invention, a third OFDM
transmission method has comprises: a first symbol generation step of generating N
(N being an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal; a
second symbol generation step of generating a plurality of symbols different from
the control symbols; and a symbol insertion step of inserting the N control symbols
into the plurality of symbols generated by the second symbol generator, wherein the

plurality of sub-carriers include a plurality of Active carriers and a plurality of Null
carriers, for each of the N control symbols, a carrier location sequence user to
distinguish between the Active carriers and the Null carriers among the plurality of
sub-carriers differs from another carrier location sequence for other control symbols,
and control information data is mapped to each of the Active carriers in accordance
with the carrier location sequence for each of the N control symbols.
[0051]
According to an alternative aspect of the present invention, a third
integrated circuit comprises: a first symbol generation circuit generating N (N being
an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal; a
second symbol generation circuit generating a plurality of symbols different from
the control symbols; and a symbol insertion circuit inserting the N control symbols
into the plurality of symbols generated by the second symbol generator, wherein the
plurality of sub-carriers include a plurality of Active carriers and a plurality of Null
carriers, for each of the N control symbols, a carrier location sequence user to
distinguish between the Active carriers and the Null carriers among the plurality of
sub-carriers differs from another carrier location sequence for other control symbols,
and control information data is mapped to each of the Active carriers in accordance
with the carrier location sequence for each of the N control symbols.
[0052]
According to an alternative aspect of the present invention, a third program
OFDM transmission program executed by an OFDM transmitter, comprises: a first
symbol generation step of generating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed,
the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; a second symbol generation step of generating a

plurality of symbols different from the control symbols; and a symbol insertion step
of inserting the N control symbols into the plurality of symbols generated by the
second symbol generator, wherein the plurality of sub-carriers include a plurality of
Active carriers and a plurality of Null carriers, for each of the N control symbols, a
carrier location sequence user to distinguish between the Active carriers and the
Null carriers among the plurality of sub-carriers differs from another carrier location
sequence for other control symbols, and control information data is mapped to each
of the Active carriers in accordance with the carrier location sequence for each of
the N control symbols.
[0053]
Accordingly, when N control symbols are transmitted, reliable reception is
made possible even when the receiver is in a delayed environment, with minimal
interference occurring between control symbols due to delayed waves. In addition,
reliable reception is assured when N control symbols are transmitted in the FEF part
without interfering with reception by existing DVB-T2 receivers.
[0054]
According to a further aspect of the present invention, a tenth OFDM
transmitter based on the ninth OFDM transmitter has the first symbol generator
include: a carrier locator generating the frequency-domain signal by mapping the
control information data to each of the Active carriers in accordance with the carrier
location sequence, for each of the N control symbols; an inverse orthogonal
transformer generating the useful symbol time-domain signal through an inverse
orthogonal transformation from the frequency domain to the time domain,
performed for each of the N control symbols; and a guard interval inserter (i)
generating the guard interval time-domain signal by frequency-shifting at least a
portion of the useful symbol time-domain signal by a predetermined amount and (ii)
inserting the guard interval time-domain signal so generated to the useful symbol
time-domain signal, for each of the N control symbols.

[0055]
Accordingly, N control symbols can easily be generated.
[0056]
According to a further aspect of the present invention, an eleventh OFDM
transmitter based on the ninth OFDM transmitter has the carrier location sequence user for each of the N control symbols be orthogonal to the other carrier location
sequence user for any other control symbols.
[0057]
According to yet a further aspect of the present invention, a twelfth OFDM
transmitter based on the ninth OFDM transmitter has the Active carriers in the
carrier location sequence user for each of the N control symbols be the Null carriers
in the other carrier location sequence user for any other control symbols.
[0058]
This provides a sample carrier location sequence for each of the N control
symbols.
[0059]
According to an aspect of the present invention, a first OFDM receiver
comprises: a first symbol demodulator demodulating N (N being an integer
satisfying N ≥ 2) control symbols in which a plurality of mutually-orthogonal
sub-carriers are multiplexed, the control symbols being made up of a useful symbol
time-domain signal and a guard interval time-domain signal; and a second symbol
demodulator demodulating symbols other than the control symbols according to
results from the first symbol demodulator, wherein in each of the control symbols,
the guard interval time-domain signal is identical to a signal in which at least a
portion of the useful symbol time-domain signal has been frequency-shifted by an
amount different from any other control symbols.
[0060]
According to another aspect of the present invention, a first OFDM

reception method comprises: a first symbol demodulation step of demodulating N
(N being an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation step of demodulating symbols other than the
control symbols according to results of the first symbol demodulation step, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols.
[0061]
According to a further aspect of the present invention, a fourth integrated
circuit, comprises: a first symbol demodulation circuit demodulating N (N being an
integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation circuit demodulating symbols other than the
control symbols according to results from the first symbol demodulation circuit,
wherein in each of the control symbols, the guard interval time-domain signal is
identical to a signal in which at least a portion of the useful symbol time-domain
signal has been frequency-shifted by an amount different from any other control
symbols.
[0062]
According to yet another aspect of the present invention, a first OFDM
reception program comprises a first symbol demodulation step of demodulating N
(N being an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation step of demodulating symbols other than the

control symbols according to results of the first symbol demodulation step, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols.
[0063]
Accordingly, the receiver can easily and reliably distinguish whether two
control symbols are distinct, or whether one symbol is a delayed wave of the other.
[0064]
According to yet a further aspect of the present invention, a second OFDM
receiver based on the first OFDM receiver has the first symbol demodulator
demodulate the N control symbols by detecting a position of at least one
predetermined control symbol among the N control symbols in a received signal.
[0065]
Accordingly, control symbol positions are detected for demodulation.
[0066]
According to another further aspect of the present invention, a third OFDM
receiver based on the second OFDM receiver has the first symbol demodulator
detect the control symbol position by calculating a correlation between (i) the
received signal, and (ii) a signal obtained by frequency-shifting the received signal
by the inverse of the frequency shift applied by a transmitter to the control symbol
undergoing position detection.
[0067]
Accordingly, the frequency shift applied by the transmitter is taken into
consideration for control symbol position detection.
[0068]
According to another aspect of the present invention, a fourth OFDM
receiver comprises: a first symbol demodulator demodulating N (N being an integer
satisfying N ≥ 2) control symbols in which a plurality of mutually-orthogonal

sub-carriers are multiplexed, the control symbols being made up of a useful symbol
time-domain signal and a guard interval time-domain signal; and a second symbol
demodulator demodulating symbols other than the control symbols according to
results from the first symbol demodulator, wherein for each of the control symbols,
the guard interval time-domain signal is identical to one or both of a portion and a
span of the useful symbol time-domain signal different from any other control
symbols frequency-shifted by a predetermined amount.
[0069]
According to still another aspect of the present invention, a second OFDM
reception method comprises: a first symbol demodulation step of demodulating N
(N being an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation step of demodulating symbols other than the
control symbols according to results of the first symbol demodulation step, wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal
different from any other control symbols frequency-shifted by a predetermined
amount.
[0070]
According to a further aspect of the present invention, a fifth integrated
circuit comprises: a first symbol demodulation circuit demodulating N (N being an
integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation circuit demodulating symbols other than the
control symbols according to results from the first symbol demodulation circuit
wherein for each of the control symbols, the guard interval time-domain signal is

identical to one or both of a portion and a span of the useful symbol time-domain
signal different from any other control symbols frequency-shifted by a
predetermined amount.
[0071]
According to still another further aspect of the present invention, a second
OFDM reception program executed by an OFDM receiver comprises: a first symbol
demodulation step of demodulating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed,
the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and a second symbol demodulation step of
demodulating symbols other than the control symbols according to results of the first
symbol demodulation step, wherein for each of the control symbols, the guard
interval time-domain signal is identical to one or both of a portion and a span of the useful symbol time-domain signal different from any other control symbols
frequency-shifted by a predetermined amount.
[0072]
Accordingly, the receiver can easily and reliably distinguish whether two
control symbols are distinct, or whether one symbol is a delayed wave of the other,
thus enabling stable reception.
[0073]
According to still another aspect of the present invention, a fifth OFDM
receiver based on the fourth OFDM receiver has the first symbol demodulator
demodulate the N control symbols by detecting the position of at least one
predetermined control symbol among the N control symbols in a received signal.
[0074]
Accordingly, control symbol positions are detected for demodulation.
[0075]
According to another aspect of the present invention, a sixth OFDM

receiver based on the fifth OFDM receiver has the first symbol demodulator detects
the control symbol position by calculating a correlation between (i) the received
signal and (ii) a signal obtained by frequency-shifting the received signal by the
inverse of the frequency shift applied by a transmitter to the control symbol
undergoing position detection according to one or both of a portion and a span of the
control symbol.
[0076]
Accordingly, the frequency shift applied by the transmitter during
generation and the original signal are taken into consideration for control symbol
position detection.
[0077]
According an aspect of the present invention, a seventh OFDM receiver
comprises a first symbol demodulator demodulating N (N being an integer satisfying
N ≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain
signal and a guard interval time-domain signal; and a second symbol demodulator
demodulating symbols other than the control symbols according to results from the
first symbol demodulator, wherein the plurality of sub-carriers includes a plurality of
Active carriers and a plurality of Null carriers, for each of the N control symbols, a
carrier location sequence user to distinguish between the Active carriers and the
Null carriers among the plurality of sub-carriers differs from another carrier location
sequence for other control symbols, and control information data is mapped to each
of the Active carriers in accordance with the carrier location sequence for each of
the N control symbols.
[0078]
According to an alternate aspect of the present invention, a third OFDM
reception method comprises: a first symbol demodulation step of demodulating N
(N being an integer satisfying N ≥ 2) control symbols in which a plurality of

mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation step of demodulating symbols other than the
control symbols according to results of the first symbol demodulation step, wherein
the plurality of sub-carriers includes a plurality of Active carriers and a plurality of
Null carriers, for each of the N control symbols, a carrier location sequence user to
distinguish between the Active carriers and the Null carriers among the plurality of
sub-carriers differs from another carrier location sequence for other control symbols,
and control information data is mapped to each of the Active carriers in accordance
with the carrier location sequence for each of the N control symbols.
[0079]
According to another alternate aspect of the present invention, a sixth
integrated circuit comprises a first symbol demodulation circuit demodulating N (N
being an integer satisfying N ≥ 2) control symbols in which a plurality of
mutually-orthogonal sub-carriers are multiplexed, the control symbols being made
up of a useful symbol time-domain signal and a guard interval time-domain signal;
and a second symbol demodulation circuit demodulating symbols other than the
control symbols according to results from the first symbol demodulation circuit,
wherein the plurality of sub-carriers includes a plurality of Active carriers and a
plurality of Null carriers, for each of the N control symbols, a carrier location
sequence user to distinguish between the Active carriers and the Null carriers
among the plurality of sub-carriers differs from another carrier location sequence for
other control symbols, and control information data is mapped to each of the Active
carriers in accordance with the carrier location sequence for each of the N control
symbols.
[0080]
According to a further alternate aspect of the present invention, a third
OFDM reception program executed by an OFDM receiver, comprising: a first

symbol demodulation step of demodulating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain
signal and a guard interval time-domain signal; and a second symbol demodulation
step of demodulating symbols other than the control symbols according to results of
the first symbol demodulation step, wherein the plurality of sub-carriers includes a
plurality of Active carriers and a plurality of Null carriers, for each of the N control
symbols, a carrier location sequence user to distinguish between the Active carriers
and the Null carriers among the plurality of sub-carriers differs from another carrier
location sequence for other control symbols, and control information data is mapped
to each of the Active carriers in accordance with the carrier location sequence for
each of the N control symbols.
[0081]
Accordingly, the receiver can easily and reliably distinguish whether two
control symbols are distinct, or whether one symbol is a delayed wave of the other,
thus enabling stable reception.
[0082]
Embodiments of the present invention are described below with reference to
the drawings.
[0083]
[Embodiment 1]
An OFDM transmitter 1 and an OFDM receIver 2 pertaining to
Embodiment 1 of the present invention are described below with reference to the
drawings. In Embodiment 1, as well as in the later-described Embodiments 2
though 4, examples are given using DVB-T2, which is the second-generation digital
terrestrial television broadcasting system user in Europe, and further describe the use of a P1 symbol in the FEF part.
[0084]

(OFDM Transmitter)
Fig. 1 is a block diagram showing the configuration of the OFDM
transmitter 1 pertaining to Embodiment 1. The OFDM transmitter 1 includes a P1
symbol generator 11, a data symbol generator 12, and a P1 symbol inserter 13. The P1 symbol generator 11 generates two P1 symbols, as will be described later with
reference to the drawings, then outputs the generated P1 symbols to the P1 symbol
inserter 13. The data symbol generator 12 generates a plurality of data symbols,
which are distinct from the P1 symbols, by performing encoding, modulation, P1lot
insertion, guard interval insertion, and other processes on input data (e.g., data other
than the data to be transmitted in the P1 symbols). The generated data symbols are
then output to the P1 symbol inserter 13. The P1 symbol inserter 13 inserts each of
the P1 symbols generated by the P1 symbol generator 11 between the data symbols
generated by the data symbol generator 12 for output. The signals output by the P1
symbol inserter 13 are transmitted after further processing by a non-diagrammed
processor within the OFDM transmitter 1, such as digital-to-analog conversion and
up-conversion to the transmission frequency band. The P1 symbol generator 11
characterizes the OFDM transmitter 1. Other components thereof may be modified
or removed as required, and other structures may also be implemented (the same
applies to other OFDM transmitters pertaining to the present invention). For
example, the data symbol generator 12 may be replaced with a symbol generator that
generates other symbols distinct from the P1 symbols, and these other symbols may
partly consist of data symbols.
[0085]
(P1 Symbol Generator)
Fig. 2 is a block diagram showing the configuration of the P1 symbol
generator 11 shown in Fig. 1. The P1 symbol generator 11 includes a first P1
symbol generator 100 and a second P1 symbol generator 200.
[0086]

As will be described with reference to later figures, the first symbol
generator 100 generates a P1 symbol (hereinafter, first P1 symbol) for output to the P1 symbol inserter 13 from Fig. 1. As will be similarly described with reference to
later figures, the second symbol generator 200 generates another P1 symbol
(hereinafter, second P1 symbol) for output to the P1 symbol inserter 13 from Fig. 1.
[0087]
(First P1 Symbol Generator)
Fig. 3 is a block diagram showing the configuration of the first P1 symbol
generator 100 from Fig. 2. In this example, the first P1 symbol is a P1 symbol user
in the DVB-T2 broadcasting system and the FEF part. However, the P1 symbol is
not limited as such.
[0088]
The first P1 symbol generator 100 includes a carrier location sequence
generator 101, an MSS converter 102, a DBPSK converter 103, a data scrambler 104,
a carrier locator 105, an IFFT unit 106, and a guard interval inserter 107. MSS is
the abbreviation of Modulation Signaling Sequence.
[0089]
The carrier location sequence generator 101 generates or stores a carrier
location sequence affl such that, as shown in Fig. 4, a[j] = 1 (indicating Active
carriers) for a sub-carrier number j and a[j] = 0 (indicating Null carriers) for all other
sub-carriers. The carrier location sequence generator 101 then outputs the carrier
location sequence a[j] to the carrier locator 10S.
[0090]
The values of an S1 signal and an S2 signal, which indicate transmission
parameter information, are input to the MSS converter 102. The MSS converter
102 converts the values of the S1 signal and the S2 signal input thereto into the
sequence shown in Fig. 5, then outputs the resulting sequence to the DBPSK
converter 103. In Fig. S, the "Value" column indicates the values input to the MSS

converter 102, while the "Sequence (hexadecimal)" column indicates the converted
sequences (the sequences output by the MSS converter 102).
[0091]
The DBPSK converter 103 performs DBPSK (Differential Binary Phase
Shift Keying) on the sequence input thereto from the MSS converter 102, then
outputs the resulting sequence to the data scrambler 104.
[0092]
The data scrambler 104 uses a Pseudorandom Binary Sequence (PRBS) to
scramble the sequence input by the DBPSK converter 103, and then outputs the
resulting scrambled sequence to the carrier locator 105.
[0093]
The carrier locator 105 maps the sequence data input thereto from the data
scrambler 104 to the sub-carriers having a sub-carrier number with the value 1 (i.e.,
the Active carriers) in the carrier location sequence input thereto from the carrier
location sequence generator 101, then outputs the resulting map to the IFFT unit
106.
[0094]
Once the data have been mapped to the Active carriers by the carrier locator
105, the IFFT unit 106 converts the signal output by the carrier locator 105 (a
frequency-domain signal) into a useful symbol, which is a signal in the time domain,
by applying an IFFT (Inverse Fast Fourier Transform) thereto. The IFFT unit 106
then outputs the useful symbol so obtained to the guard interval inserter 107.
[0095]
The guard interval inserter 107 inserts a leading guard interval and a trailing
guard interval, which are time-domain signals, into the signal output by the IFFT
unit 106 (the signal with a useful symbol interval in the time domain), thus
generating the first P1 symbol. The guard interval inserter 107 then outputs the
first P1 symbol to the P1 symbol inserter 13 shown in Fig. 1.

[0096]
Fig. 6 is a schematic diagram illustrating the first P1 symbol with guard
intervals inserted by the guard interval inserter 107 (time domain shown). As
shown, the guard interval inserter 107 generates the leading guard interval by
frequency-shifting the leading portion (Tc = 59 μs) of the useful symbol (Ta = 112
lis) by +fsH (equivalent to the sub-carrier spacing in the first P1 symbol). The
guard interval inserter 107 then inserts the leading guard interval so generated at the
head of the useful symbo1. The above are all time-domain signals. Similarly, the
guard interval inserter 107 generates the trailing guard interval by frequency-shifiing
the trailing portion (Tb = 53 μs) of the useful symboll by +fsH• The guard interval
inserter 107 then inserts the trailing guard interval so generated at the tail of the useful symbol interva1. The above are all time-domain signals. The first P1
symbol is thereby generated. This process is expressed in the below-inscribed
Math. 2.
[0097]
(Math. 2)

where pllst(t) is the first P1 symbol, pllstA(t) is the useful symbol, +fsH is
the frequency shift, T is the time of one sample, post-IFFT, t is time, and the start
time of the first P1 symbol is 0. In the DVB-T2 broadcasting system, for a
bandwidth of8 MHz, T is 7/64 μs and the useful symbol length is 1024T = 112 μs.
[0098]
(Second P1 Symbol Generator)
Fig. 7 is a block diagram showing the configuration of the second P1
symbol generator 200 from Fig. 2.

[0099]
The second P1 symbol generator 200 includes a carrier location sequence
generator 201, an MSS converter 202, a DBPSK converter 203, a data scrambler 204,
a carrier locator 205, an IFFT unit 206, and a guard interval inserter 207.
[0100]
The carrier location sequence generator 201 generates or stores a carrier
location sequence aft such that, as shown in Fig. 4, a[j] = 1 (indicating Active
carriers) for a sub-carrier number j and a[j] = 0 (indicating Null carriers) for all other
sub-carriers. The carrier location sequence generator 101 then outputs the carrier
location sequence aQ] to the carrier locator 205. The carrier location sequence
generator 201 outputs a carrier location sequence identical to that output by the
carrier location sequence generator 101 of the first P1 symbol generator 100.
[0101]
The values of the S1 signal and the S2 signal, which indicate transmission
parameter information, are input to the MSS converter 202. The MSS converter
202 converts the values of the S1 signal and the S2 signal input thereto into the
sequence shown in Fig. 5, then outputs the resulting sequence to the DBPSK
converter 203. In Fig. 5, the "Value" column indicates the values input to the MSS
converter 202, while the "Sequence (hexadecimal)" column indicates the converted
sequences (the sequences output by the MSS converter 202). The transmission
parameter information input to the first P1 symbol generator 100 is not the same as
the transmission parameter information input to the second P1 symbol generator 200
(which receives more information). However, the same information may also be
input to both generators (improving information reliability through multiple
transmissions).
[0102]
The DBPSK converter 203 performs DBPSK on the sequence input thereto
from the MSS converter 202, and then outputs the resulting sequence to the data

scrambler 204.
[0103]
The data scrambler 204 uses a PBRS to scramble the sequence input thereto
by the DBPSK converter 203, and then outputs the resulting scrambled sequence to
the carrier locator 205.
[0104]
The carrier locator 205 maps the sequence data input thereto from the data
scrambler 204 to the sub-carriers having a sub-carrier number with a value of 1 (i.e.,
the Active carriers) in the carrier location sequence input thereto from the carrier
location sequence generator 201 , then outputs the resulting map to the IFFT unit
206.
[0105]
In this example, the structure of the carrier location sequence 201 through
the carrier locator 205 is described as identical to that of the corresponding
components of the first P1 symbol generator 100. However, this is not intended as
a restriction. That is, information may be modulated without using MSS
conversion beforehand, and the modulation need not necessarily be DBPSK.
Furthermore, a structure without carrier location sequences, such as the ISDB-T
broadcasting system or the DVB-T broadcasting system in which the central useful
sub-carriers are all user, is also applicable.
[0106]
Once the data have been mapped to the Active carriers by the carrier locator
205, the IFFT unit 206 converts the signal output by the carrier locator 205 (a
frequency-domain signal) into a signal with a useful symbol in the time domain by
applying an IFFT thereto. The IFFT unit 106 then outputs the useful symbol so
obtained to the guard interval inserter 207.
[0107]
The guard interval inserter 207 inserts a leading guard interval and a trailing

guard interval, which are time-domain signals, into the signal output by the IFFT
unit 206 (the signal with a useful symbol interval in the time domain), thus
generating the first P1 symbol. The guard interval inserter 207 then outputs the
second P1 symbol to the P1 symbol inserter 13 shown in Fig. 1.
[0108]
Fig. 8 is a schematic diagram illustrating the second P1 symbol with guard
intervals inserted by the guard interval inserter 207 (time domain shown). As
shown, the guard interval inserter 207 generates the leading guard interval by
frequency-shifting the leading portion (Tc = 59 μs) of the useful symbol (Ta = 112 μs) by -fSH. The guard interval inserter 207 then inserts the leading guard interval
so generated at the head of the useful symbol. The above are all time-domain
signals. Similarly, the guard interval inserter 207 generates the trailing guard
interval by frequency-shifting the trailing portion (Tb = 53 μs) of the useful symbol
by -fSH. The guard interval inserter 207 then inserts the trailing guard interval so
generated at the tail of the useful symbol interval. The above are all time-domain
signals. The second P1 symbol is thereby generated. This process is expressed in
the below-inscribed Math. 3.
[0109]

where p12nd(f) is the second P1 symbol, P12ndA(t') is the useful symbol, -fSH
is the frequency shift, T is the time of one sample, post-IFFT, t' is time, and the start
time of the second P1 symbol is 0. In the DVB-T2 broadcasting system, for a
bandwidth of 8 MHz, T = 7/64 μs and the useful symbol length is 1024T = 112 μs.
[0110]

As described above, the leading guard interval and the trailing guard
interval of the first P1 symbol are time-domain signals obtained by
frequency-shifting a given portion of the useful symbol in the time domain by +fsH
(* 0) (see Fig. 6). In contrast, the leading guard interval and the trailing guard
interval of the second P1 symbol are time-domain signals obtained by
frequency-shifting a given portion of the useful symbol in the time domain by -fSH
(equal in absolute value but opposite in sign to fsH) (see Fig. 8). Thus, the first and
second P1 symbols differ in terms of the frequency shift applied to the appropriate
portion of the useful symbol in the time domain in order to generate the guard
intervals. The same portion and span (length) of the useful symbol in the time
domain is user to generate the leading guard interval for both the first P1 symbol
and the second P1 symbol. Likewise, the same portion and span (length) of the useful symbol in the time domain is user to generate the trailing guard interval for
both the first P1 symbol and the second P1 symbol (see Figs. 6 and 8).
[0111]
The P1 symbol inserter 13 from Fig. 1 inserts the first and second P1
symbols, generated as described above, into the group of data symbols generated by
the data symbol generator 11 from Fig. 1. As shown in Fig. 9, the structure of a
frame is as follows: the first P1 symbol (labeled "1st P1 symbol" in Fig. 9) is
arranged at the head of the frame, immediately followed by the second P1 symbol
(labeled "2nd P1 symbol" in Fig. 9), and the data symbols are arranged after the
second P1 symbol to complete the frame. Thus, the main symbols (i.e., the data
symbols) can be demodulated according to the transmission parameter information
added to the first and second P1 symbols.
[0112]
(OFDM Receiver)
Fig. 10 is a block diagram showing the configuration of the OFDM receiver
2 pertaining to Embodiment 1. The OFDM receiver 2 includes an antenna 21, a

tuner 22, and a demodulator 23.
[0113]
The antenna 21 receives transmission waves from the OFDM transmitter 1
shown in Fig. 1, and then outputs the received transmission waves (received waves)
to the tuner 22. The tuner 22 selects a desired received wave among the multiple
received waves input thereto by the antenna 21, converts the selected wave from the
RF (Radio Frequency) band to the IF (Intermediate Frequency) band, and then
outputs the resulting IF-band wave to the demodulator 23.
[0114]
The demodulator 23 includes an ADC (analog-to-digital converter) 24, a
quadrature transformer 25, a P1 symbol demodulator 26, and a data symbol
demodulator 27. The ADC 24 converts the received IF-band waves from analog
signals to digital signals for output. The quadrature transformer 25 then performs a
quadrature transformation on the signals output by the ADC 24 to obtain complex
baseband signals for output. As will be described later with reference to the
drawings, the P1 symbol demodulator 26 demodulates the P1 symbols (the first and
second P1 symbols) included in the signal output by the quadrature transformer 25.
The data symbol demodulator 27 demodulates the multiple data symbols included in
the signal output by the quadrature transformer 25 according to the results of P1
symbol demodulation by the P1 symbol demodulator 26 (that is, according to the
transmission parameter information obtained by demodulating the P1 symbols).
The P1 symbol demodulator 26 characterizes the OFDM receiver 2. Other
components thereof may be modified or removed as required, and other structures
may also be implemented (the same applies to other OFDM receivers pertaining to
the present invention). For example, the data symbol demodulator 27 may be
replaced by a symbol demodulator that demodulates other symbols distinct from the P1 symbols, and these other symbols may partly consist of data symbols.
[0115]

(P1 Symbol Demodulator)
Fig. 11 is a block diagram showing the configuration of the P1 symbol
demodulator 26 shown in Fig. 10. The P1 symbol demodulator 26 includes a first P1 symbol demodulator 300 and a second P1 symbol demodulator 400.
[0116]
As will be described later with reference to the drawings, the first P1
symbol demodulator 300 demodulates the first P1 symbol while the second P1
symbol demodulator 400 demodulates the second P1 symbol.
[0117]
(First P1 Symbol Demodulator)
Fig. 12 is a block diagram showing the configuration of the first P1 symbol
demodulator 300 shown in Fig. 11. The first P1 symbol demodulator 300 includes
a P1 position detector 301, an FFT unit 302, and a P1 decoder 303.
[0118]
The P1 position detector 301 detects the position of the first P1 symbol in
the time-domain signal input thereto (i.e., in the first P1 symbol demodulator 300
input signal) and outputs the first P1 symbol position information so obtained to the
FFT unit 302. Fig. 13 shows the structure of the P1 position detector 301.
[0119]
The P1 position detector 301 includes a multiplier 311, a delayer 312, a
complex conjugate calculator 313, a multiplier 314, an integral calculator 315, a
delayer 316, a complex conjugate calculator 317, a multiplier 318, an integral
calculator 319, a delayer 320, a multiplier 321, and a peak detector 322.
[0120]
The P1 position detector 301 input signal is input to the multiplier 311.
The multiplier 311 multiplies the P1 position detector 301 input signal by
exp(-jπrfSHt) in order to apply a frequency shift that is the inverse of the +fsH
frequency shift applied by the transmitter to the time-domain signals of the leading

and trailing guard intervals of the first P1 symbol (applying a frequency shift of
-fSH). The multiplier 311 then outputs the result to the delayer 312 and to the
multiplier 318. The delayer 312 delays the signal output by the multiplier 311 by a
span equivalent to the length of the first P1 symbol leading guard interval (Tc = 59 μs), then outputs the delayed signal to the complex conjugate calculator 313. The
complex conjugate calculator 313 calculates the complex conjugate of the signal
output by the delayer 312 and outputs the resulting complex conjugate signal to the
multiplier 314. The multiplier 314 calculates a correlation by multiplying the P1
position detector 301 input signal and the complex conjugate calculator 313 output
signal, then outputs the correlated value so calculated to the integral calculator 315.
The integral calculator 315 integrates the output signal from the multiplier 314 over
the length Tc of the leading guard interval of the first P1 symbol, and then outputs
the result to the delayer 320. This signal processing is also illustrated by Figs. 55A
through 55C.
[0121]
Meanwhile, the P1 position detector 301 input signal is input to the delayer
316. The delayer 316 delays the P1 position detector 301 input signal by a span
equivalent to the length of the first P1 symbol trailing guard interval (Tb = 53 μs),
then outputs the delayed signal to the complex conjugate calculator 317. The
complex conjugate calculator 317 calculates the complex conjugate of the signal
output by the delayer 316 and outputs the resulting complex conjugate signal to the
multiplier 318. The signal input to the multiplier 318 is the result of the multiplier
311 multiplying the P1 position detector 301 input signal by exp(-j2πfSHt). The
multiplier 318 calculates a correlation by multiplying the signal output by the
multiplier 311 (the P1 position detector 301 input signal with a frequency shift of
-fSH applied thereto) and the complex conjugate calculator 317 output signal, then
outputs the correlated value so calculated to the integral calculator 319. The
integral calculator 319 integrates the output signal from the multiplier 318 over the

length Tb of the trailing guard interval of the first P1 symbol, and then outputs the
result to the multiplier 321. This signal processing is also illustrated by Figs. 56A
through 56C.
[0122]
The signal output from the integral calculator 315 is input to the delayer 320.
The delayer 320 delays the signal output from the integral calculator 315 to match
the signal output from the integral calculator 319 for output to the multiplier 321.
The delayer 320 applies a delay of 2xTb. The multiplier 321 multiplies the signal
output from the integral calculator 319 by the signal output from the delayer 320,
and then outputs the product to the peak detector 322. Thus, the peaks are made
more prominent by matching the peaks in the correlated value integral taken for the
leading guard interval to the peaks in the correlated value integral taken for the
trailing guard interval. The peak detector 322 detects the position of the first P1
symbol within the P1 position detector 301 input signal (i.e., the signal input to the
first P1 symbol demodulator 300) by detecting the peak position in the signal output
from the multiplier 321. The peak detector 322 then accordingly outputs position
information for the first P1 symbol to the FFT unit 302 shown in Fig. 12. Given
the presence of a delayed wave, a peak correlation appears in correspondence to the
level and position of the delay.
[0123]
The FFT unit 302 shown in Fig. 12 performs an FFT on the signal input
from the first P1 symbol demodulator 300 (a time-domain signal) in accordance with
the first P1 symbol position information, thus obtaining a converted
frequency-domain signal for output to the P1 decoder 303. The P1 decoder 303
generates or stores a carrier location sequence aft such that, as shown in Fig. 4, a[j]
= 1 (indicating the Active carriers) for a sub-carrier number j, and a[j] = 0
(indicating the Null carriers) for all other sub-carriers. The P1 decoder 303 then, in
accordance with the carrier location sequence a[j], uses the Active carrier in the

frequency-domain signal to perform a decoding process on the first P1 symbol,
calculates the values of the S1 and S2 signals that were added to the first P1 symbol,
and discerns the transmission parameter information (e.g., the FFT size, MISO/SISO
information, and so on) according to these values.
[0124]
(Second P1 Symbol Demodulator)
Fig. 14 is a block diagram showing the configuration of the second P1
symbol demodulator 400 shown in Fig. 11. The second P1 symbol demodulator
400 includes a P1 position detector 401, an FFT unit 402, and a P1 decoder 403.
[0125]
The P1 position detector 401 detects the position of the second P1 symbol in
the time-domain signal input thereto (i.e., in the second P1 symbol demodulator 400
input signal) and outputs the second P1 symbol position information so obtained to
the FFT unit 402. Fig. 15 shows the structure of the P1 position detector 401.
[0126]
The P1 position detector 401 includes a multiplier 411, a delayer 412, a
complex conjugate calculator 413, a multiplier 414, an integral calculator 415, a
delayer 416, a complex conjugate calculator 417, a multiplier 418, an integral
calculator 419, a delayer 420, a multiplier 421, and a peak detector 422.
[0127]
The P1 position detector 401 input signal is input to the multiplier 411.
The multiplier 411 multiplies the P1 position detector 401 input signal by
exp(+jπfSHt) in order to apply a frequency shift that is the inverse of the -fSH
frequency shift applied by the transmitter to the time-domain signals of the leading
and trailing guard intervals of the second P1 symbol (applying a frequency shift of
+fsH). The multiplier 411 then outputs the result to the delayer 412 and to the
multiplier 418. The delayer 412 delays the signal output by the multiplier 411 by a
span equivalent to the length of the second P1 symbol leading guard interval (Tc =

59 μs), then outputs the delayed signal to the complex conjugate calculator 413.
The complex conjugate calculator 413 calculates the complex conjugate of the signal
output by the delayer 412 and outputs the resulting complex conjugate signal to the
multiplier 414. The multiplier 414 calculates a correlation by multiplying the P1
position detector 401 input signal and the complex conjugate calculator 413 output
signal, then outputs the correlated value so calculated to the integral calculator 415.
The integral calculator 415 integrates the output signal from the multiplier 414 over
the length Ic of the leading guard interval of the second P1 symbol, and then
outputs the result to the delayer 420. Figs. 16A through 16C are schematic
diagrams illustrating this signal processing. As shown in Fig. 16A, the leading
guard interval obtained by frequency shifting the P1 position detector 401 input
signal by +fsH and then delaying the result by the length Tc of the leading guard
interval (shown in the lower portion of Fig. 16A) is identical to the leading part of
the useful symbol within the P1 position detector 401 (shown in the upper portion
of Fig. 16A). The correlation appears in this part, as shown in Fig. 16B. Given
that other parts of the signals are not identical, no correlation appears therein. The
peak shown in Fig. 16C is the effect of integrating the correlated value shown in Fig.
16B over the length Tc of the leading guard interval.
[0128]
Meanwhile, the P1 position detector 401 input signal is input to the delayer
416. The delayer 416 delays the P1 position detector 401 input signal by a span
equivalent to the length of the second P1 symbol trailing guard interval (Tb = 53 μs),
then outputs the delayed signal to the complex conjugate calculator 417. The
complex conjugate calculator 417 calculates the complex conjugate of the signal
output by the delayer 416 and outputs the resulting complex conjugate signal to the
multiplier 418. The signal input to the multiplier 418 is the result of the multiplier
411 multiplying the P1 position detector 401 input signal by exp(+j2πfsHt). The
multiplier 418 calculates a correlation by multiplying the signal output by the

multiplier 411 (the P1 position detector 401 input signal with a frequency shift of
+fsH applied thereto) and the complex conjugate calculator 417 output signal, then
outputs the correlated value so calculated to the integral calculator 419. The
integral calculator 419 integrates the output signal from the multiplier 418 over the
length Tb of the trailing guard interval of the second P1 symbol, and then outputs
the result to the multiplier 421. Figs. 17A through 17C are schematic diagrams
illustrating this signal processing. As shown in Fig. 17A, the trailing guard interval
obtained by frequency shifting the P1 position detector 401 input signal by +fsH
(shown in the upper portion of Fig. 17A) is identical to the trailing part of the useful
symbol within the P1 position detector 401 delayed by the length Tb of the trailing
guard interval (shown in the lower portion of Fig. 17A). The correlation appears in
this part, as shown in Fig. l7B. Given that other parts of the signals are not
identical, no correlation appears therein. The peak shown in Fig. 17C is the effect
of integrating the correlated value shown in Fig. 17B over the length Tb of the
trailing guard interval.
[0129]
The signal output from the integral calculator 415 is input to the delayer 420.
The delayer 420 delays the signal output from the integral calculator 415 to match
the signal output from the integral calculator 419 for output to the multiplier 421.
The delayer 420 applies a delay of 2xTb. The multiplier 421 multiplies the signal
output from the integral calculator 419 by the signal output from the delayer 420,
and then outputs the product to the peak detector 422. Thus, the peaks are made
more prominent by matching the peaks in the correlated value integral taken for the
leading guard interval to the peaks in the correlated value integral taken for the
trailing guard interval. The peak detector 422 detects the position of the second P1
symbol within the P1 position detector 401 input signal (i.e., the signal input to the
second P1 symbol demodulator 400) by detecting the peak position in the signal
output from the multiplier 421. The peak detector 422 then accordingly outputs

position information for the second P1 symbol to the FFT unit 402 shown in Fig. 14.
Given the presence of a delayed wave, a peak correlation appears in correspondence
to the level and position of the delay.
[0130]
The FFT unit 402 shown in Fig. 14 performs an FFT on the signal input
from the second P1 symbol demodulator 400 (a time-domain signal) in accordance
with the second P1 symbol position information, thus obtaining a converted
frequency-domain signal for output to the P1 decoder 403. The P1 decoder 403
generates or stores a carrier location sequence a[j] such that, as shown in Fig. 4, a[j]
= 1 (indicating the Active carriers) for a sub-carrier number j, and a[j] = 0
(indicating the Null carriers) for all other sub-carrier. The P1 decoder 403 then, in
accordance with the carrier location sequence aft, uses the Active carrier in the
frequency-domain signal to perform a decoding process on the second P1 symbol,
calculates the values of the S1 and S2 signals that were added to the second P1
symbol, and discerns the transmission parameter information according to these
values.
[0131]
As described above, the P1 position detector 301 in the first P1 symbol
demodulator 300 frequency-shifts the input signal by -fsH and calculates a
correlation in order to detect the first P1 symbol. Similarly, the P1 position
detector 401 in the second P1 symbol demodulator 400 frequency-shifts the input
signal by +fSH and calculates a correlation in order to detect the second P1 symbol.
[0132]
(P1 Position Detector of First P1 Symbol Demodulator Operations on Second P1
Symbol)
Figs. 18A through 18C are schematic diagrams showing a correlation of the
leading portion of the second P1 symbol taken by the P1 position detector 301 of the
first P1 symbol demodulator 300.

[0133]
In the second P1 symbol as transmitted, the leading and trailing guard
intervals are portions of the useful symbol that have been frequency shifted by -fSH
(see Fig. 8). As such, in the P1 position detector 301 of the first P1 symbol
demodulator 300, the input signal frequency-shifted by -fsH and delayed by the
length Tc of the leading guard interval (the lower portion of Fig. l8A) comes to
have leading and trailing guard interval signals that are frequency-shifted by -2fsH
while having a useful symbol that is frequency-shifted by -fSH. Thus, the leading
guard interval signal shown in the lower portion of Fig. l8A does not appear
identical to the leading part of the useful symbol of the P1 position detector 301
input signal (the upper portion of Fig. l8A). As shown in Fig. l8B, no correlation
appears. While the trailing part of the useful symbol within the signal shown in the
lower portion of Fig. 18A is identical to the trailing guard interval signal shown in
the upper portion of Fig. l8A, no correlation appears because the two signals are not
input to the multiplier 314 at the same time. For this reason, even if an integral of
the correlated values shown in Fig. l8B is taken over the length Tb of the leading
guard interval, no prominent peaks are produced as can be seen in Fig. l8C.
[0134]
Figs. 19A through 19C are schematic diagrams showing a correlation of the
trailing portion of the second P1 symbol taken by the P1 position detector 301 of the
first P1 symbol demodulator 300.
[0135]
In the second P1 symbol as transmitted, the leading and trailing guard
intervals are portions of the useful symbol that have been frequency shifted by -fSH
(see Fig. 8). As such, in the P1 position detector 301 of the first P1 symbol
demodulator 300, the input signal frequency-shifted by -fsH (the upper portion of
Fig. 19A) comes to have leading and trailing guard intervals that are
frequency-shifted by -2fSH while having a useful symbol that is frequency-shifted by

-fSH. Thus, the trailing guard interval shown in the upper portion of Fig. 19A does
not appear identical to the trailing part of the useful symbol of the P1 position
detector 301 input signal with the trailing part delayed by the length Tb of the
trailing guard interval (the lower portion of Fig. 19A). As shown in Fig. 19B, no
correlation appears. While the leading part of the useful symbol in the signal
shown in the upper portion of Fig. 19A is identical to the leading guard interval
shown in the lower portion of Fig. 19A, no correlation appears because the two
signals are not input to the multiplier 318 at the same time. This is shown in Fig.
19B. For this reason, even if an integral of the correlated values shown in Fig. 19B
is taken over the length Tb of the trailing guard interval, no prominent peaks are
produced as can be seen in Fig. 19C.
[0136]
As described above, the first P1 symbol demodulator 300 does not produce
peaks in the second P1 symbol, being able to detect the first P1 symbol only.
Similarly, the second P1 symbol demodulator 400 does not produce peaks in the first P1 symbol, being able to detect the second P1 symbol only.
[0137]
(Effects)
According to the above-described Embodiment 1, in the generation of the
leading and trailing guard intervals by the transmitter, portions of the first P1 symbol
are taken from the useful symbol with a frequency shift of+fsH applied thereto (see
Fig. 6) while the frequency shift applied for the second P1 symbol is of -fSH
(producing a frequency shift with the same absolute value but the opposite sign as
that applied to the first P1 symbol) (see Fig. 8). Accordingly, when the receiver
detects a plurality of peaks, the receiver can identify whether the peaks belong to
different symbols, or whether one peak is a delayed wave of the other, thus enabling
stable reception. In addition, when two P1 symbols are transmitted for the FEF
part (i.e., the first P1 symbol and the second P1 symbol), the first P1 symbol is made

the leading symbol of the FEF part. Thus, a DVB-T2 receiver equipped only with
a demodulator for demodulating the first P1 symbol is unaffected by the second P1
symbo1. This secures compatibility with existing DVB-T2 receivers.
[0138]
[Embodiment 2]
An OFDM transmitter and an OFDM receiver pertaining to Embodiment 2
of the present invention are described below with reference to the drawings. In the
present Embodiment, components having a structure substantially similar to their
counterparts in Embodiment 1 use the same reference signs thereas. Explanations
of such components are hereinafter simplified or omitted where appropriate.
[0139]
(OFDM Transmitter)
The OFDM transmitter of the present Embodiment includes a P1 symbol
generator 11A that differs from the P1 symbol generator 11 of Embodiment 1. The P1 symbol generator 11A is described below.
[0140]
(P1 Symbol Generator)
Fig. 20 is a block diagram showing the configuration of the P1 symbol
generator 11A in the OFDM transmitter pertaining to Embodiment 2. As shown,
the P1 symbol generator llA includes a first P1 symbol generator 100, which
generates a first P1 symbol by performing the process described for Embodiment 1,
and a second P1 symbol generator 200A. The second P1 symbol generator 200A
generates a second P1 symbol for output, and differs from the second P1 symbol
generator 200 of Embodiment 1 in the guard interval insertion method employed.
The second P1 symbol generator 200A is described below.
[0141]
(Second P1 Symbol Generator)
Fig. 21 is a block diagram showing the configuration of the second P1

symbol generator 200A from Fig. 20. In the second P1 symbol generator 200A,
the guard interval inserter 207 of the second P1 symbol generator 200 has been
replaced with a guard interval inserter 207A.
[0142]
The guard interval inserter 207A inserts a leading guard interval and a
trailing guard interval, which are time-domain signals, into the signal output by the
IFFT unit 206 (the useful symbol in the time domain), thus generating the second P1
symbol.
[0143]
Fig. 22 is a schematic diagram illustrating the second P1 symbol with guard
intervals inserted by the guard interval inserter 207A (time domain shown). As
shown, the guard interval inserter 207A generates the leading guard interval by
frequency-shifting the leading portion (Tb = 53 μs) of the useful symbol (Ta = 112
μs) by +fSH. The guard interval inserter 207 then inserts the leading guard interval
so generated at the head of the useful symbol. The above are all time-domain
signals. Similarly, the guard interval inserter 207A generates the trailing guard
interval by frequency-shifting the trailing portion (Tc = 59 μs) of the useful symbol
by +fsH. The guard interval inserter 207A then inserts the trailing guard interval so
generated at the tail of the useful symbol. The above are all time-domain signals.
This process is expressed in the below-inscribed Math. 4.
[0144]

where p12nd(t') is the second P1 symbol, Pl2ndA(t') is the useful symbol, +fsH
is the frequency shift, T is the time of one sample, post-IFFT, f is time, and the start

time of the second P1 symbol is 0. In the DVB-T2 broadcasting system, for a
bandwidth of 8 MHz, T = 7/64 μs and the useful symbol length is 1024T = 112 μs.
As shown in Figs. 6 and 22, the lengths of the guard intervals of the second P1
symbol are the opposite of those of the first P1 symbol (such that the leading guard
interval is of length Tb and the trailing guard interval is of length Tc). However,
no restriction is intended on this point.
[0145]
As described above, the leading guard interval and the trailing guard
interval of the first and second P1 symbols are time-domain signals obtained by
frequency-shifting a given portion of the useful symbol in the time domain by +fsH
(= 0), the same frequency shift being user in all cases (see Figs. 6 and 22). In
addition, the leading part of the useful symbol within the time domain is user to
generate the leading guard interval for both the first P1 symbol and the second P1
symbol, and the trailing part of the useful symbol in the time domain is user to
generate the trailing guard interval (see Figs. 6 and 22).
[0146]
However, the span of the useful symbol user to generate the time-domain
leading guard interval of the first P1 symbol has length Tc (= 59 μs) (see Fig. 6),
while the span of the useful symbol user to generate the time-domain leading guard
interval of the second P1 symbol has length Tb (= 53 μs) (see Fig. 22). The useful
symbol spans so user thus differ in length. Similarly, the span of the useful
symbol user to generate the time-domain trailing guard interval of the first P1
symbol has a length Tb (= 53 μs) (see Fig. 6), while the span of the useful symbol user to generate the time-domain trailing guard interval of the second P1 symbol has
a length Tc (= 59 μs) (see Fig. 22). The useful symbol spans so user thus differ in
length.
[0147]
(OFDM Receiver)

The OFDM receiver of the present Embodiment includes a P1 symbol
demodulator 26A that differs from the P1 symbol demodulator 26 of Embodiment 1.
The P1 symbol demodulator 26A is described below.
[0148]
(P1 Symbol Demodulator)
Fig. 23 is a block diagram showing the configuration of the P1 symbol
demodulator 26A in the OFDM receiver pertaining to Embodiment 2. The P1
symbol demodulator 26A includes a first P1 symbol demodulator 300, which
performs the same process previously described for Embodiment 1, and a second P1
symbol demodulator 400A. The second P1 symbol demodulator 400A
demodulates the second P1 symbol and is configured differently than the second P1
symbol demodulator 400 user in Embodiment 1. The second P1 symbol
demodulator 400A is described below.
[0149]
(Second P1 Symbol Demodulator)
Fig. 24 is a block diagram showing the configuration of the second P1
symbol demodulator 400A shown in Fig. 23. The second P1 symbol demodulator
400A includes a P1 position detector 401A, an FFT unit 402, and a P1 decoder 403.
[0150]
The P1 position detector 401A detects the position of the second P1 symbol
in the time-domain signal input thereto (i.e., in the signal input to the second P1
symbol demodulator 400A) and outputs the second P1 symbol position information
so obtained to the FFT unit 402. Fig. 25 shows the structure of the P1 position
detector 401A.
[0151]
The P1 position detector 401A includes a multiplier 451, a delayer 452, a
complex conjugate calculator 453, a multiplier 454, an integral calculator 455, a
delayer 456, a complex conjugate calculator 457, a multiplier 458, an integral

calculator 459, a delayer 460, a multiplier 461, and a peak detector 462.
[0152]
The P1 position detector 40lA input signal is input to the multiplier 451.
The multiplier 451 multipliss the P1 position detector 40lA input signal by
exp(-y27ifSHt) in order to apply a frequenyy shift that is the inverse of the +fSH
frequency shift applied by the transmitter to the time-domain signals of the leading
and trailing guard intervass of the second P1 symbol (applying a frequenyy shift of
-fSH). The multiplier 451 then outputs the result to the delayer 452 and to the
multiplier 458. The multiplier 451 handles the input signal in a different manner
than the multiplier 411 of the second P1 symbol demodulator 400 of Embodiment 1
(see Fig. 15) in applying the same frequenyy shift as the multiplier 311 of the first P1 symbol demodulator 300 (see Fig. 13). The delayer 452 delays the signal
output by the multiplier 451 by a span equivalent to the length of the second P1
symbol leading guard interval (Tb = 53 μs), then outputs the delayed signal to the
complex conjugaee calculator 453. The delay Tb (= 53 μs) applied by the delayer
452 differs from the delay Tc (= 59 μs) applied by the delayer 312 of the P1 position
detector 301 in the first P1 symbol demodulator 300 and from the delay Tc (= 59 μs)
applied by the delayer 412 of the P1 position detector 401 of the second P1 symbol
demodulator 400. The complex conjugaee calculator 453 calculates the complex
conjugate of the signal output by the delayer 452 and outputs the resulting complex
conjugate signal to the multiplier 454. The multiplier 454 calculates a correlaiion
by multiplying the P1 position detector 40lA input signal and the complex
conjugate calculator 453 output signal, then outputs the correlated value so
calculated to the integral calculator 455. The integral calculator 415 integrates the
output signal from the multiplier 414 over the length Tb of the leading guard interval
of the second P1 symbo,, and then outputs the result to the delayer 460. Figs. 26A
through 26C are schematic diagrams illustrating this signal processing. As shown
in Fig. 26A, the leading guard interval obtained by frequency shifting the P1

position detector 40lA input signal by -fSH and then delaying the result by the
length Tb of the leading guard interval (shown in the lower portion of Fig. 26A) is
identical to the leading part of the useful symbol within the P1 position detector
40lA (shown in the upper portion of Fig. 26A). The correlation appears in this
part, as shown in Fig. 26B. Given that other parts of the signals are not identical,
no correlation appears therein. The peak shown in Fig. 26C is the effect of
integrating the correlated value shown in Fig. 26B over the length Tb of the leading
guard interval.
[0153]
Meanwhile, the P1 position detector 40lA input signal is input to the
delayer 456. The delayer 456 delays the P1 position detector 40lA input signal by
a span equivalent to the length of the second P1 symbol trailing guard interval (Tc =
59 μs), then outputs the delayed signal to the complex conjugate calculator 457.
The delay Tc (= 59 μs) applied by the delayer 456 differs from the delay Tb (= 53 μs) applied by the delayer 316 of the P1 position detector 301 in the first P1 symbol
demodulator 300 and from the delay Tb (= 53 μs) applied by the delayer 426 of the P1 position detector 401 of the second P1 symbol demodulator 400. The complex
conjugate calculator 457 calculates the complex conjugate of the signal output by
the delayer 456 and outputs the resulting complex conjugate signal to the multiplier
458. The signal input to the multiplier 458 is the result of the multiplier 451
multiplying the P1 position detector 40lA input signal by exp(-y2^fSHt). The
multiplier 458 calculates a correlation by multiplying the signal output by the
multiplier 451 (the P1 position detector 401A input signal with a frequency shift of
-fsH applied thereto) and the complex conjugate calculator 457 output signal, then
outputs the correlated value so calculated to the integral calculator 459. The
integral calculator 459 integrates the output signal from the multiplier 458 over the
length Tc of the trailing guard interval of the second P1 symbol, and then outputs the
result to the multiplier 461. Figs. 27A through 27C are schematic diagrams

illustrating this signal processing. As shown in Fig. 27A, the trailing guard interval
obtained by frequency shifting the P1 position detector 401A input signal by -fSH
(shown in the upper portion of Fig. 27A) is identical to the trailing part of the useful
symbol delayed by the length Tc of the trailing guard interval within the P1 position
detector 401A (shown in the lower portion of Fig. 27A). The correlation appears in
this part, as shown in Fig. 27B. Given that other parts of the signals are not
identical, no correlation appears therein. The peak shown in Fig. 27C is the effect
of integrating the correlated value shown in Fig. 27B over the length Tc of the
trailing guard interval.
[0154]
The signal output from the integral calculator 455 is input to the delayer 460.
The delayer 460 delays the signal output from the integral calculator 455 to match
the signal output from the integral calculator 459 for output to the multiplier 461.
The delayer 460 applies a delay of 2xTc. The multiplier 461 multiplies the signal
output from the integral calculator 459 by the signal output from the delayer 460,
and then outputs the product to the peak detector 462. Thus, the peaks are made
more prominent by matching the peaks in the correlated value integral taken for the
leading guard interval to the peaks in the correlated value integral taken for the
trailing guard interval. The peak detector 462 detects the position of the second P1
symbol within the P1 position detector 40lA input signal (i.e., the signal input to the
second P1 symbol demodulator 401A) by detecting the peak position in the signal
output from the multiplier 461. The peak detector 422 then accordingly outputs
position information for the second P1 symbol to the FFT unit 402 shown in Fig. 24.
Given the presence of a delayed wave, a peak correlation appears in correspondence
to the level and position of the delay.
[0155]
(P1 Position Detector of First P1 Symbol Demodulator Operations on Second P1
Symbol)

Figs. 28A through 28C are schematic diagrams showing a correlation of the
leading portion of the second P1 symbol taken by the P1 position detector 301 of the
first P1 symbol demodulator 300 (see Fig. 13).
[0156]
In the second P1 symbol as transmitted, the leading and trailing guard
interval signals are portions of the useful symbol with a frequency shift of +fsH
applied thereto. The leading guard interval has length Tb (= 53 μs) and the trailing
guard interval has length Tc (= 59 μs) (see Fig. 22). As such, in the P1 position
detector 301 of the first P1 symbol demodulator 300, the leading guard interval
obtained from the input signal frequency-shifted by -fsH and delayed by the length
Tc (= 59 μs) of the leading guard interval of the first P1 symbol (the lower portion
of Fig. 28A) comes to have a frequency shift of 0 and thus matches the leading
portion of the useful symbol of the P1 position detector 301 input signal (the upper
portion of Fig. 28A). However, as shown in Fig. 28B, no correlation appears
because the two signals are not input to the multiplier 314 at the same time.
Similarly, the trailing portion of the useful symbol shown in the lower portion of Fig.
28A is input to the multiplier 314 at the same time as the trailing guard interval
shown in the upper portion of Fig. 28A. However, as shown in Fig. 28B, no
correlation appears due to the different frequency shifts applied. Therefore, as
shown in Fig. 28C, no prominent peaks appear in the correlated values shown in Fig.
28B when integrated over the length of the leading guard interval Tc of the first P1
symbol.
[0157]
Figs. 29A through 29C are schematic diagrams showing a correlation of the
trailing portion of the second P1 symbol taken by the P1 position detector 301 of the
first P1 symbol demodulator 300.
[0158]
In the second P1 symbol as transmitted, the leading and trailing guard

interval signals are portions of the useful symbol with a frequency shift of +fsH
applied thereto. The leading guard interval has length Tb (= 53 μs) and the trailing
guard interval has length Tc (= 59 μs) (see Fig. 22). As such, in the P1 position
detector 301 of the first P1 symbol demodulator 300, the trailing guard interval
obtained from the input signal frequency-shifted by -fsH (the upper portion of Fig.
29A) comes to have a frequency shift of 0 and thus matches the trailing portion of
the useful symbol of the P1 position detector 301 input signal delayed by the length
Tb (= 53 μs) of the trailing guard interval of the first P1 symbol (the lower portion
of Fig. 29A). However, as shown in Fig. 29B, the correlation is not significant
because the two signals are not input to the multiplier 318 at the same time.
Similarly, the leading portion of the useful symbol shown in the upper portion of Fig.
29A is input to the multiplier 318 at the same time as the leading guard interval
shown in the lower portion of Fig. 29A. However, different frequency shifts are
applied. Therefore, as shown in Fig. 29B, no correlation appears. For this reason,
as shown in Fig. 29C, no prominent peaks appear in the correlated values shown in
Fig. 29B when integrated over the length of the trailing guard interval Tb of the first P1 symbol.
[0159]
As described above, the first P1 symbol demodulator 300 does not produce
peaks in the second P1 symbol, being able to detect the first P1 symbol only.
Similarly, the second P1 symbol demodulator 400A does not produce peaks in the
first P1 symbol, being able to detect the second P1 symbol only.
[0160]
(Effects)
According to Embodiment 2 as described above, the transmitter generates
leading and trailing guard interval signals such that the first P1 symbol has a leading
guard interval of length Tc and a trailing guard interval of length Tb (see Fig. 6).
In contrast, the second P1 symbol has a leading guard interval of length Tb and a

trailing guard interval of length Tc (see Fig. 22). As such, the differing lengths of
the guard intervals in the first and second P1 symbols are employed in the structure
of the first and second P1 symbols so that the receiver can easily distinguish whether
or not the second P1 symbol is a delayed wave of the first P1 symbol, thereby
enabling secure reception. In addition, when two P1 symbols are user for the FEF
part (i.e., the first P1 symbol and the second P1 symbol), the first P1 symbol is made
the leading symbol of the FEF part. Thus, a DVB-T2 receiver equipped only with
a demodulator for demodulating the first P1 symbol is unaffected by the second P1
symbol. This ensures compatibility with existing DVB-T2 receivers.
[0161]
[Embodiment 3]
An OFDM transmitter and an OFDM receiver pertaining to Embodiment 3
of the present invention are described below with reference to the drawings. In the
present Embodiment, components having a structure substantially similar to their
counterparts in Embodiments 1 and 2 use the same reference signs thereas.
Explanations of such components are hereinafter simplified or omitted where
appropriate.
[0162]
(OFDM Transmitter)
The OFDM transmitter of the present Embodiment includes a P1 symbol
generator 11B that differs from the P1 symbol generator 11 of Embodiment 1. The P1 symbol generator lIB is described below.
[0163]
(P1 Symbol Generator)
Fig. 30 is a block diagram showing the configuration of the P1 symbol
generator 11B in the OFDM transmitter pertaining to Embodiment 3. As shown,
the P1 symbol generator 11B includes a first P1 symbol generator 100, which
generates a first P1 symbol by performing the process described for Embodiment 1,

and a second P1 symbol generator 200B. The second P1 symbol generator 200B
generates a second P1 symbol for output, and differs from the second P1 symbol
generators 200 and 200A of Embodiments 1 and 2 in the guard interval insertion
method employed. The second P1 symbol demodulator 200B is described below.
[0164]
(Second P1 Symbol Generator)
Fig. 31 is a block diagram showing the configuration of the second P1
symbol generator 200B from Fig. 30. In the second P1 symbol generator 200B, the
guard interval inserter 207 of the second P1 symbol generator 200 has been replaced
with a guard interval inserter 207B.
[0165]
The guard interval inserter 207B inserts a leading guard interval and a
trailing guard interval, which are time-domain signals, into the signal output by the
IFFT unit 206 (signal with a useful symbol in the time domain), thus generating the
second P1 symbol.
[0166]
Fig. 32 is a schematic diagram illustrating the second P1 symbol with guard
intervals inserted by the guard interval inserter 207B (time domain shown). As
shown, the guard interval inserter 207B generates the leading guard interval by
frequency-shifting the leading portion (Tb = 53 μs) of the useful symbol (Ta = 112
μs) by -fSH. The guard interval inserter 207 then inserts the leading guard interval
so generated at the head of the useful symbol. The above are all time-domain
signals. As similarly shown, the guard interval inserter 207B generates the trailing
guard interval by frequency-shifting the trailing portion (Tc = 59 μs) of the useful
symbol (Ta = 112 μs) by -fSH, and then inserting the trailing guard interval so
generated at the tail of the useful symbol. The above are all time-domain signals.
[0167]
As described above, for both the first P1 symbol and the second P1 symbol,

the leading part of the useful symbol in the time domain is user to generate the
leading guard interval, while the trailing part of the useful symbol in the time
domain is user to generate the trailing guard interval (see Figs. 6 and 32).
[0168]
However, the leading guard interval and the trailing guard interval of the
first P1 symbol are time-domain signals obtained by frequency-shifting a given
portion of the useful symbol in the time domain by +fSH (= 0) (see Fig. 6). In
contrast, the leading guard interval and the trailing guard interval of the second P1
symbol are time-domain signals obtained by frequency-shifting a given portion of
the useful symbol in the time domain by -fSH (equal in absolute value but opposite
in sign to +fSH) (see Fig. 32). Thus, the first and second P1 symbols differ in terms
of the frequency shift applied to the useful symbol in the time domain in order to
generate the guard intervals.
[0169]
Furthermore, the span of the useful symbol user to generate the
time-domain leading guard interval of the first P1 symbol has length Tc (= 59 μs)
(see Fig. 6), while the span of the useful symbol user to generate the time-domain
leading guard interval of the second P1 symbol has length Tb (= 53 μs) (see Fig. 32).
The useful symbol spans so user thus differ in length. Similarly, the span of the useful symbol user to generate the time-domain trailing guard interval of the first P1
symbol has length Tb (= 53 μs) (see Fig. 6), while the span of the useful symbol user to generate the time-domain trailing guard interval of the second P1 symbol has
length Tc (= 59 μs) (see Fig. 32). The useful symbol spans so user thus differ in
length.
[0170]
(OFDM Receiver)
The OFDM receiver of the present Embodiment includes a P1 symbol
demodulator 26B that differs from the P1 symbol demodulator 26 of Embodiment 1.

The P1 symbol demodulator 26B is described below.
[0171]
(P1 Symbol Demodulator)
Fig. 33 is a block diagram showing the configuration of the P1 symbol
demodulator 26B in the OFDM receiver pertaining to Embodiment 3. The P1
symbol demodulator 26B includes a first P1 symbol demodulator 300, which
performs the same process previously described for Embodiment 1, and a second P1
symbol demodulator 400B. The second P1 symbol demodulator 400B
demodulates the second P1 symbol and is configured differently than the second P1
symbol demodulators 400 and 400A user in Embodiments 1 and 2. The second P1
symbol demodulator 400B is described below.
[0172]
(Second P1 Symbol Demodulator)
Fig. 34 is a block diagram showing the configuration of the second P1
symbol demodulator 400B shown in Fig. 33. The second P1 symbol demodulator
400B includes a P1 position detector 401B, an FFT unit 402, and a P1 decoder 403.
[0173]
The P1 position detector 401B detects the position of the second P1 symbol
in the time-domain signal input thereto (i.e., in the signal input to the second P1
symbol demodulator 400B) and outputs the second P1 symbol position information
so obtained to the FFT unit 402. Fig. 35 shows the structure of the P1 position
detector 401B.
[0174]
The P1 position detector 401B includes a multiplier 501, a delayer 502, a
complex conjugate calculator 503, a multiplier 504, an integral calculator 505, a
delayer 506, a complex conjugate calculator 507, a multiplier 508, an integral
calculator 509, a delayer 510, a multiplier 511, and a peak detector 512.
[0175]

The P1 position detector 40lB input signal is input to the multiplier 501.
The multiplier 501 multiplies the P1 position detector 40lB input signal by
exp(+j2πfSHt) in order to apply a frequency shift that is the inverse of the -fSH
frequency shift applied by the transmitter to the time-domain signals of the leading
and trailing guard intervals of the second P1 symbol (applying a frequency shift of
+fsH). The multiplier 501 then outputs the result to the delayer 502 and to the
multiplier 508. The multiplier 501 applies a different frequency shift to the input
signal than the multiplier 311 of the first P1 symbol demodulator 300 (see Fig. 13),.
The delayer 502 delays the signal output by the multiplier 501 by a span equivalent
to the length of the second P1 symbol leading guard interval (Tb = 53 μs), then
outputs the delayed signal to the complex conjugate calculator 503. The delay Tb
(= 53 μs) applied by the delayer 502 differs from the delay Tc (= 59 μs) applied by
the delayer 312 of the P1 position detector 301 in the first P1 symbol demodulator
300. The complex conjugate calculator 503 calculates the complex conjugate of
the signal output by the delayer 502 and outputs the resulting complex conjugate
signal to the multiplier 504. The multiplier 504 calculates a correlation by
multiplying the P1 position detector 401B input signal and the complex conjugate
calculator 503 output signal, then outputs the correlated value so calculated to the
integral calculator 505. The integral calculator 505 integrates the output signal
from the multiplier 504 over the length Tb of the leading guard interval of the
second P1 symbol, and then outputs the result to the delayer 510.
[0176]
Meanwhile, the P1 position detector 40lB input signal is input to the
delayer 506. The delayer 506 delays the P1 position detector 401B input signal by
a span equivalent to the length of the second P1 symbol trailing guard interval (Tc =
59 μs), then outputs the delayed signal to the complex conjugate calculator 507.
The delay Tc (= 59 μs) applied by the delayer 506 differs from the delay Tb (= 53 μs) applied by the delayer 316 of the P1 position detector 301 in the first P1 symbol

demodulator 300. The complex conjugate calculator 507 calculates the complex
conjugate of the signal output by the delayer 506 and outputs the resulting complex
conjugate signal to the multiplier 508. The signal input to the multiplier 508 is the
result of the multiplier 501 multiplying the P1 position detector 401B input signal by
exp(+j2πfsHt). The multiplier 508 calculates a correlation by multiplying the signal
output by the multiplier 501 (the P1 position detector 401B input signal with a
frequency shift of+fsH applied thereto) and the complex conjugate calculator 507
output signal, then outputs the correlated value so calculated to the integral
calculator 509. The integral calculator 509 integrates the output signal from the
multiplier 508 over the length Tc of the trailing guard interval of the second P1
symbol, and then outputs the result to the multiplier 511.
[0177]
The signal output from the integral calculator 505 is input to the delayer 510.
The delayer 510 delays the signal output from the integral calculator 505 to match
the signal output from the integral calculator 509 for output to the multiplier 511.
The delayer 510 applies a delay of 2xTc. The multiplier 511 multiplies the signal
output from the integral calculator 519 by the signal output from the delayer 510,
and then outputs the product to the peak detector 512. Thus, the peaks are made
more prominent by matching the peaks in the correlated value integral taken for the
leading guard interval to the peaks in the correlated value integral taken for the
trailing guard interval. The peak detector 512 detects the position of the second P1
symbol within the P1 position detector 401B input signal (i.e., the signal input to the
second P1 symbol demodulator 401B) by detecting the peak position in the signal
output from the multiplier 511. The peak detector 512 then accordingly outputs
position information for the second P1 symbol to the FFT unit 402 shown in Fig. 34.
Given the presence of a delayed wave, a peak correlation appears in correspondence
to the level and position of the delay.
[0178]

(Effects)
According to Embodiment 3 as described above, the same results can be
obtained as for Embodiments 1 and 2. In this Embodiment, if, for example, the
process performed on the second P1 symbol by the P1 position detector 301 of the
first P1 symbol demodulator 300 produces mistaken results in the correlation or
integral calculated by components from the multiplier 311 through the integral
calculator 315 generating peaks in the trailing portion of the guard interval, or if
mistaken results in the correlation or integral calculated by components from the
multiplier 311 and the delayer 316 through the integral calculator 319 mistakenly
generate peaks in the leading portion of the guard interval, the peaks will be
eliminated through the multiplication performed by the multiplier 321. Thus, the
second P1 symbol position is not incorrectly detected as the first P1 symbol position.
Similarly, the P1 position detector 401B of the second P1 symbol demodulator 400B
does not incorrectly detect the first P1 symbol position as the second P1 symbol
position.
[0179]
A variation of Embodiment 3 in which, for the first P1 symbol, the leading
guard interval may have length Tel and the trailing guard interval may have length
TbI, while for the second P1 symbol, the leading guard interval may have length
Tc2 and the trailing guard interval may have length Tb2, such that the values ofTcl,
Tbl, Tc2, and Tb2 are distinct, is also possible. In such a case, the process
performed on the second P1 symbol by the P1 position detector 301 of the first P1
symbol demodulator 300 produces no peaks. Similarly, the process performed on
the first P1 symbol by the P1 position detector 401B of the second P1 symbol
demodulator 400B also produces no peaks.
[0180]
[Embodiment 4]
An OFDM transmitter and an OFDM receiver pertaining to Embodiment 4

of the present invention are described below with reference to the drawings. In the
present Embodiment, components having a structure substantially similar to their
counterparts in Embodiments 1 through 3 use the same reference signs thereas.
Explanations of such components are hereinafter simplified or omitted where
appropriate.
[0181]
(OFDM Transmitter)
The OFDM transmitter of the present Embodiment includes a P1 symbol
generator 11C that differs from the P1 symbol generator 11 of Embodiment 1. The P1 symbol generator IIC is described below.
[0182]
(P1 Symbol Generator)
Fig. 36 is a block diagram showing the configuration of the P1 symbol
generator IIC in the OFDM transmitter pertaining to Embodiment 4. As shown,
the P1 symbol generator 11C includes a first P1 symbol generator 100, which
generates a first P1 symbol by performing the process described for Embodiment 1,
and a second P1 symbol generator 200C. The second P1 symbol generator 200C
generates the second P1 symbol for output, using sub-carrier locations (Active and
Null carrier locations) unlike those user by the second P1 symbol generators 200,
200A, and 200B of Embodiments 1 through 3. The second P1 symbol generator
200C is described below.
[0183]
(Second P1 Symbol Generator)
Fig. 37 is a block diagram showing the configuration of the second P1
symbol generator 200C from Fig. 36. In the second P1 symbol generator 200C, the
carrier location sequence generator 201 of the second P1 symbol generator 200 has
been replaced with a carrier location sequence generator 201C.
[0184]

The carrier location sequence generator 20IC generates or saves a carrier
location sequence b[j] that differs from the carrier location sequence a[j] output to
the carrier locator 105 by the carrier location sequence generator 101 of the first P1
symbol generator 100, and outputs the carrier location sequence bD] to the carrier
locator 205. However, the sub-carrier number j of the Active carriers are set such
that bD] = 1 while the sub-carrier numbers j of the Null carriers are set such that bD]
= O. The carrier locator 205 maps data to the Active carrier using the carrier
location sequence bD] rather than the carrier location sequence a[j].
[0185]
The carrier location sequence a&] and the carrier location sequence bQ] are
defined so as to assure orthogonality (non-correspondence.. An example is shown
in Figs. 38A and 38B. Fig. 38A is a schematic diagram (in the frequency domain)
showing the first P1 symbol sub-carrier locations (the sub-carrier locations indicated
by the carrier location sequence afi]). Fig. 38B is a schematic diagram (in the
frequency domain) showing the second P1 symbol sub-carrier locations (the
sub-carrier locations indicated by the carrier location sequence bD]).
[0186]
Rather than making the carrier location sequence a[j] user for the first P1
symbol and the carrier location sequence bQ] user for the second P1 symbol
orthogonal, the following may be applied. The carrier location sequences au] and
bQ] may be made such that a subset of the multiple positions indicating 0 within the
carrier location sequence a[j] for the first P1 symbol are positions indicating 1 in the
carrier location sequence bD] for the second P1 symbol. That is, a subset of Null
carriers for the first P1 symbol (equal in number to the subset of Active carriers for
the second P1 symbol) may be user as Active carriers for the second P1 symbol.
An example is shown in Figs. 39A and 39B. Fig. 39A is a schematic diagram (in
the frequency domain) showing the first P1 symbol sub-carrier locations (the
sub-carrier locations indicated by the carrier location sequence a[j]). Fig. 39B is a

schematic diagram (in the frequency domain) showing the second P1 symbol
sub-carrier locations (the sub-carrier locations indicated by the carrier location
sequence b[i]).
[0187]
(OFDM Receiver)
The OFDM receiver of the present Embodiment includes a P1 symbol
demodulator 26C that differs from the P1 symbol demodulator 26 of Embodiment 1.
The P1 symbol demodulator 26C is described below.
[0188]
(P1 Symbol Demodulator)
Fig. 40 is a block diagram showing the configuration of the P1 symbol
demodulator 26C in the OFDM receiver pertaining to Embodiment 4. The P1
symbol demodulator 26C includes a first P1 symbol demodulator 300, which
performs the same process previously described for Embodiment 1, and a second P1
symbol demodulator 400C. The second P1 symbol demodulator 400C
demodulates the second P1 symbol and is configured differently than the second P1
symbol demodulators 400, 400A, and 400C user in Embodiments 1 through 3.
The second P1 symbol demodulator 400C is described below.
[0189]
(Second P1 Symbol Demodulator)
Fig. 41 is a block diagram showing the configuration of the second P1
symbol demodulator 400C from Fig. 40. In the second P1 symbol demodulator
400C, the P1 decoder 403 of the second P1 symbol demodulator 400 from
Embodiment 1 has been replaced with a P1 decoder 403C.
[0190]
The P1 decoder 403C generates or stores the carrier location sequence b[j]
and performs a decoding process for the second P1 symbol using the Active carriers
in the frequency domain according to the carrier location sequence b[j] so generated.

The P1 decoder 403C then calculates the values of the Sl and S2 signals added to
the second P1 symbol to obtain transmission parameter information therefrom.
[0191]
(Effects)
In the OFDM transmitter and the OFDM receiver described above, the
locations of the Active carriers for the first P1 symbol are different from the
locations of the Active carriers for the second P1 symbol (some (but not all) of the
Active carriers for the first P1 symbol have the same sub-carrier locations as some
(but not all) of the Active carriers for the second P1 symbol). Thus, as shown in
Fig. 42, interference is reduced in the delayed environment. By having the carrier
location sequence first and second P1 symbols be orthogonal, the quantity of carriers
affected by P1 symbol interference in the delayed wave is reduced by nearly half.
Also, by making only the Null carrier positions for the first P1 symbol into the
Active carrier positions for the second P1 symbol, the quantity of carriers affected
by interference falls to almost zero. Therefore, secure reception is assured even in
a delayed environment. Furthermore, when transmitting with an FEF part, the first P1 symbol comes to be at the head of the FEF part. Given that the carrier locations
of the second P1 symbol differ from those of the first P1 symbol, DVB-T2 receivers
can easily distinguish the first and second P1 symbols, thereby ensuring that the
second P1 symbol will not be made unreceivable.
[0192]
[Variations]
The present invention is not limited to the above-described Embodiments.
Any other Embodiment that accomplishes or supports the accomplishment of the
aims of the present invention is also possible, such as the following.
[0193]
(1) In Embodiment 1, when the leading and trailing guard interval signals are
generated, the first P1 symbol is frequency-shifted by +fsH (see Fig. 6) and the

second P1 symbol is frequency-shifted by -fsH (see Fig. 8). However, the
invention is not limited in this manner. For example, when the leading and trailing
guard intervals are generated, the first P1 symbol may be frequency-shifted by +fsH
while the second P1 symbol is frequency-shifted by +2fsH. Any frequency shift
may be user as long as the shifts applied to the first and second P1 symbols are
different. This includes cases where one frequency shift is zero while the other is a
non-zero value, as zero is also a possible frequency shift amount. When the second P1 symbol is frequency-shifted by +2fsH, the second P1 symbol demodulator 400 is
configured to calculate a correlation by applying a frequency shift of -2fsH
(multiplying the multiplier 411 input signal by exp(-2πfSHt)).
[0194]
(2) In Embodiment 1, the same frequency shift (+fsH) is applied to the leading
guard interval as well as the trailing guard interval of the first P1 symbol, and the
same frequency shift (-fSH) is applied to the leading guard interval as well as the
trailing guard interval of the first P1 symbol. However, the invention is not limited
in this manner. A different frequency shift may be applied to the leading and
trailing guard intervals of the first P1 symbol, and a different frequency shift may be
applied to the leading and trailing guard intervals of the second P1 symbol. In such
a case, the frequency shifts applied to the leading guard intervals of the first and
second P1 symbols should differ, as should the frequency shifts applied to the
trailing guard intervals of the first and second P1 symbols. Then, the P1 position
detector 301 shown in Fig. 13 is modified as follows, for example. The multiplier
311 applies a frequency shift to the input signal that is the inverse of the frequency
shift applied to the leading guard interval signal of the first P1 symbol, then outputs
the result to the delayer 312 (nothing is output to the multiplier 318). Furthermore,
a new multiplier is added to the P1 position detector. The newly-added multiplier
applies a frequency shift to the input signal that is the inverse of the frequency shift
applied to the trailing guard interval signal of the first P1 symbol, and then outputs

the result to the multiplier 318. Then, the P1 position detector 401 shown in Fig.
15 is modified as follows, for example. The multiplier 411 applies a frequency
shift to the input signal that is the inverse of the frequency shift applied to the
leading guard interval signal of the second P1 symbol, then outputs the result to the
delayer 412 (nothing is output to the multiplier 418). Furthermore, a new
multiplier is added to the P1 position detector. The newly-added multiplier applies
a frequency shift to the input signal that is the inverse of the frequency shift applied
to the trailing guard interval signal of the second P1 symbol, and then outputs the
result to the multiplier 418.
[0195]
(3) In Embodiment 1, two P1 symbols (the first P1 symbol and the second P1
symbol) are user. However, the invention is not limited in this manner. Three or
more P1 symbols may also be user. In such a case, when the leading and trailing
guard intervals are generated, the frequency shifts applied to each of the three or
more P1 symbols should preferably differ.
[0196]
(4) In Embodiment 1, the first and second P1 symbols correspond to the P1
symbol from the DVB-T2 specification, and as such, the first and second P1
symbols each have a leading guard interval of length Tc (= 59 μs) and a trailing
guard interval of length Tb (= 53μs). However, the invention is not limited in this
manner. The length of the leading guard interval of the first and second P1
symbols may be other than Tc (= 59 μs), and the length of the trailing guard interval
of multiple P1 symbols may be other than Tb (= 53 μs). The same applies to cases
with a plurality of P1 symbols. For instance, the length of the leading guard
interval of the first and second P1 symbols may be Tb (= 53 μs) and the length of
the trailing guard interval may be Tc (= 59 μs). Alternatively, the leading and
trailing guard intervals may be of equal length. In such a case, if, for example, the
process performed on the second P1 symbol by the P1 position detector 301 of the

fIrst P1 symbol demodulator 300 produces mistaken results in the correlation or
integral calculated by components from the multiplier 311 through the integral
calculator 315 generating peaks in the trailing portion of the guard interval, or if
mistaken results in the correlation or integral calculated by components from the
multiplier 311 and the delayer 316 through the integral calculator 319 mistakenly
generate peaks in the leading portion of the guard interval, the peaks will be
eliminated through the multiplication performed by the multiplier 321. Thus, the
second P1 symbol position is not mistakenly detected as the fIrst P1 symbol
position.
[0197]
(5) In Embodiments 1 through 3, the first and second P1 symbols correspond to
the P1 symbol from the DVB-T2 specifIcation, and as such, the sub-carrier locations
are indicated according to a carrier location sequence shown in Fig. 4 (in which the
Active sub-carrier locations are indicated). However, the invention is not limited
in this manner. Any type of carrier location sequence may be user. The Active
carriers need not be discrete. All of the sub-carriers may be Active, or a middle
portion of a plurality of sub-carriers may be user as the Active sub-carriers.
[0198]
(6) In Embodiments 1 through 4, the structure of the frames is, as shown in Fig.
9, such that the first P1 symbol is at the head of the frame, immediately followed by
the second P1 symbol. However, the invention is not limited in this manner. As
shown in Fig. 43, the fIrst P1 symbol may be arranged at the head of the frame while
the second P1 symbol is arranged farther back in the frame. Alternatively, as
shown in Fig. 44, the fIrst P1 symbol may be arranged at the head of the frame while
the second P1 symbol is arranged at the end of the frame. No particular restriction
is intended regarding frame structure. In Figs. 43 and 44, the label "1st P1 symbol"
shows the first P1 symbol and the label "2nd P1 symbol" shows the second P1
symbol. Furthermore, the second P1 symbol may appear only in alternate frames,

for example.
[0199]
(7) In Embodiments 1 through 4, a portion of the time-domain useful symbol is
rotated post-IFFT to generate the time-domain guard interval signal (the leading and
trailing guard intervals). However, the time-domain guard interval generation
method is not limited in this manner. The following is also possible. The
frequency-domain signal may be frequency-shifted pre-IFFT, so that the IFFT is
applied to the frequency-domain signal after the frequency shift, with a portion of
the post-IFFT time-domain signal being user as the time-domain signal of the guard
interval.
[0200]
(8) In Embodiments 1 through 4, the P1 symbol demodulators are configured
such that the first and second P1 symbol demodulators each include the P1 position
detector. However, the invention is not limited in this manner. The P1 symbol
demodulators may include either one of a P1 position detector for the first P1
symbol or a P1 position detector for the second P1 symbol (e.g., include only a P1
position detector for the first P1 symbol). In such a case, the P1 position detector
detects the position of one P1 symbol and estimates the position of the other P1
symbol according to that position and the relationship between the first and second P1 symbols in the transmission format being user. One FFT unit then performs an
FFT according to the detected position of one P1 symbol while the other FFT unit
performs an FFT according to the estimated position of the other P1 symbol. Thus,
the quantity of P1 position detectors is reduced, enabling the circuit scale to be
constrained.
[0201]
Fig. 45 shows an example configuration of a P1 symbol demodulator 26D
with a P1 position detector 301D user to detect the first P1 symbol, only. This
example describes a variation of the P1 symbol demodulator 26 from Embodiment 1.

However, the same variation is applicable to the P1 symbol demodulators 26A, 26B,
and 26C of Embodiments 2 through 4. The P1 position detector 30ID of the P1
symbol demodulator 26D is configured like the P1 position detector 30I shown in
Fig. 13, with the following additional functions. The P1 position detector 30ID uses the positional relationship between the first and second P1 symbols in the
transmission format to estimate the position of the second P1 symbol from the
position of the first P1 symbol detected by the peak detector 322, and then outputs
the resulting position information for the second P1 symbol to the FFT unit 402.
The FFT unit 402 performs an FFT on the P1 symbol demodulator 26D input signal
(a time-domain signal) according to the position information for the second P1
symbol from the P1 position detector 301D.
[0202]
IfM P1 symbols are user (where M is an integer, M ≥ 3), then P1 position
detectors may be included to detect each of the M P1 symbols. Alternatively, P1
position detectors may be included to detect each ofM-l P1 symbols.
[0203]
(9) In Embodiments I through 4, the P1 symbol demodulators are configured to
individually detect the first and second P1 symbol positions. However, the
invention is not limited in this manner. The P1 symbol demodulator may be
configured to find the positions of the first and second P1 symbols by delaying and
then multiplying the product of integrals taken for each half of the first P1 symbol
and the product of integrals taken for each half of the second P1 symbol, thereby
causing prominent peaks to appear.
[0204]
Fig. 46 shows an example configuration of a P1 symbol demodulator 26E.
This example describes a variation of the P1 symbol demodulator 26 from
Embodiment 1. However, the same variation is applicable to the P1 symbol
demodulators 26A, 26B, and 26C of Embodiments 2 through 4.

[0205]
The P1 symbol demodulator 26E includes a P1 correlation calculator 301E,
a P1 correlation calculator 401E, a delayer 601, a multiplier 602, a peak detector 603,
an FFT unit 302, a P1 decoder 303, an FFT unit 402, and a P1 decoder 403.
[0206]
As shown in Fig. 47, the multiplier 321 of the P1 correlation calculator
301E outputs multiplication results to the delayer 601. The P1 correlation
calculator 301E shown in Fig. 47 is configured identically to the P1 position detector
301 shown in Fig. 13, but lacks the peak detector 322. As shown in Fig. 48, the
multiplier 421 of the P1 correlation calculator 401E outputs multiplication results to
the multiplier 602. The P1 correlation calculator 401E shown in Fig. 48 is
configured identically to the P1 position detector 401 shown in Fig. 15, but lacks the
peak detector 422.
[0207]
The delayer 601 delays the signal output by the multiplier 321 of the P1
correlation calculator 301E to match the signal output by the multiplier 421 of the P1 correlation calculator 401E (applies delay adjustments to the first and second P1
symbols) and then outputs the result to the multiplier 602. The multiplier 602
multiplies the delayer 601 output signal by the signal output by the multiplier 421 of
the P1 correlation calculator 401E, and then outputs the product to the peak detector
603. The peak detector 603 detects peaks in the multiplier 602 output signal and
obtains the positions of the first and second P1 symbols in the P1 symbol
demodulator 27E input signal according to the detection results and the positional
relationship between the first and second P1 symbols in the transmission format.
Then, the peak detector 603 outputs the position information for the first P1 symbol
to the FFT unit 302. The FFT unit 302 applies an FFT based on this information.
The peak detector 603 outputs the position information for the second P1 symbol to
the FFT unit 402. The FFT unit 402 applies an FFT based on this information.

Thus, the precision of detection for the first and second P1 symbols is improved.
[0208]
(10) In Embodiments 1 through 4, the P1 symbol demodulators may reduce the
circuit scale by having the FFT unit and the decoder commonly realized, through
multi-processing or the like.
[0209]
(11) In Embodiments 1 through 4 and in the variations, the P1 position detectors
and the P1 correlation calculators of the variations are configured to apply a
frequency-shift that is the inverse of the frequency shift applied by the transmitter
(equal in absolute value but opposite in sign) and then obtain a correlation.
However, as long as the processes are mathematically similar, the frequency-shifting,
delaying, and correlation calculating (complex conjugation and multiplication)
processes may be performed in any order, and the direction of the frequency shift
may be adjusted as required.
[0210]
(12) In Embodiments 1 through 4, the transmitter applies an IFFT (an inverse
orthogonal transformation) while the receiver applies an FFT (an orthogonal
transformation). However, the invention is not limited in this manner. The
transmitterr may apply any of an inverse Fourier transform, an inverse cosine
transform, an inverse wavelet transform, an inverse Hadamard transform, or any
other inverse orthogonal transformation, while the receiver applies a Fourier
transform, a cosine transform, a wavelet transform, a Hadamard transform, or a
similar orthogonal transformation.
[0211]
(13) In Embodiment 2, as shown in Figs. 6 and 22, the span of the useful symbol user to generate the leading and trailing guard interval time-domain signals of the
first and second P1 symbols is given as an example. However, the invention is not
limited in this manner. The span of the useful symbol user to generate the leading

guard interval time-domain signals of the first and second P1 symbols may vary
(may be of a different length than the leading guard interval). Similarly, the span
of the useful symbol user to generate the trailing guard interval time-domain signals
of the first and second P1 symbols may vary (may be of a different length than the
trailing guard interval). In such a case, the length of the leading and trailing guard
intervals for the first P1 symbol mayor may not be equal. The same is true of the
leading and trailing guard intervals for the second P1 symbol.
[0212]
(14) In Embodiment 2, a frequency shift of +fsH (equivalent to the sub-carrier
spacing in the first and second P1 symbols) is user when generating the guard
intervals for the first and second P1 symbols. However, the invention is not limited
in this manner. A frequency shift of another value (including 0) may also be
applied.
[0213]
(15) The portion of the useful symbol user to generate the leading guard interval
time-domain signals of the first and second P1 symbols may vary, as may the
portion of the useful symbol user to generate the trailing guard interval time-domain
signals of the first and second P1 symbols. An example is shown in Figs. 49A and
49B. In the example shown, the guard interval inserter generates the leading guard
interval by applying a frequency shift of+fSH to the leading part of the useful symbol
for the first P1 symbol and to the trailing part of the useful symbol for the second P1
symbol, and then inserts the leading guard interval so generated at the head of the useful symbol. The above are all signals in the time-domain. Similarly, the guard
interval inserter generates the trailing guard interval by applying a frequency shift of
+fsH to the trailing part of the useful symbol for the first P1 symbol and to the
leading part of the useful symbol for the second P1 symbol, and then inserts the
trailing guard interval so generated at the tail of the useful symbol. These intervals
are all signals in the time-domain. In such a case, as shown in Fig. 25, the P1

position detector 40lA should adjust the delay imparted by the delayers 452, 456,
and 460 so as to calculate the correlation.
[0214]
The lengths of the leading and trailing guard intervals are given as an
example. The invention is not limited in this manner. Also, the frequency shift is
given as example, and the invention is not limited in this manner. A frequency
shift of another value (including 0) may also be applied rather than a frequency shift
of+fsH (equivalent to the sub-carrier spacing in the first and second P1 symbols).
[0215]
(16) In Embodiment 2, the method user to generate the guard intervals may be
combined with that described above for variation (15). That is, the portion and the
span of the useful symbol user to generate the time-domain leading guard interval of
the first P1 symbol and the portion and the span of the useful symbol user to
generate the time-domain leading guard interval of the second P1 symbol may differ
in length. Similarly, the portion and span of the useful symbol user to generate the
time-domain trailing guard interval of the first P1 symbol and the portion and span
of the useful symbol user to generate the time-domain trailing guard interval of the
second P1 symbol may differ in length.
[0216]
(17) In Embodiment 2 and in variations (15) and (16), two P1 symbols (the first
and second P1 symbols) are user. However, the invention is not limited in this
manner. Three or more P1 symbols may be user. In such a case, when the
leading and trailing guard intervals are generated, at least one of the span and
portion of the useful symbol user for each of the three or more P1 symbols should
preferably differ.
[0217]
(18) The variations described for Embodiments 1 and 2 may also be applied to
Embodiment 3, with regard to the span of the useful symbol, as well as the

frequency shift applied thereto, user to generate the leading and trailing guard
interval time-domain signals.
[0218]
(19) The method user to generate the guard intervals may be a combination of
those described above for Embodiments 1 and 2, and for variation (15). In other
words, the method user to generate the guard intervals may be that described above
for variation (15) may be combined in Embodiment 3.
[0219]
That is, the portion and the span of the useful symbol, as well as the
frequency shift, user to generate the time-domain leading guard interval of the first P1 symbol and the portion and the span of the useful symbol, as well as the
frequency shift, user to generate the time-domain leading guard interval of the
second P1 symbol may differ in all aspects. Similarly, the portion and span of the useful symbol, as well as the frequency shift, user to generate the time-domain
trailing guard interval of the first P1 symbol and the portion and span, as well as the
frequency shift, of the useful symbol user to generate the time-domain trailing guard
interval of the second P1 symbol may differ in all aspects.
[0220]
When three or more P1 symbols are user, the portion and span of the useful
symbol, as well as the frequency shift applied thereto, user to generate the
time-domain signal guard intervals of each P1 symbol (the leading and trailing guard
intervals) may vary.
[0221]
(20) In Embodiment 4, the method user to insert the guard intervals (in which
the frequency shift applied to each P1 symbol differs) was described as being
identical to that user in Embodiment 1. However, the invention is not limited in
this manner. The method described for Embodiments 2 through 4, or for variations
of Embodiments 1 through 4, may also be user to insert the guard intervals.

Furthermore, the span and portion of the useful symbol, as well as the frequency
shift, user to generate the leading and trailing guard interval time-domain signals of
the first and second P1 symbols may be the same.
[0222]
(21) In Embodiment 4, two P1 symbols are user (the first and second P1
symbols). However, the invention is not limited in this manner. Three or more P1 symbols may also be user. In such a case, the carrier location sequence user
for each of the three or more P1 symbols should differ.
[0223]
(22) In Embodiments 1 through 4, the P1 symbols correspond to the P1 symbols
from the DVB-T2 specification. However, the invention is not limited in this
manner. The P1 symbols need not necessarily correspond to the DVB-T2
specification. For example, the sub-carrier mapping carried out pre-IFFT may use
a different configuration, information may be appended to all sub-carriers, and
non-DBPSK differential modulation, or non-differential modulation, may be user.
The guard interval may come from either half of the useful symbol, taken alone (a
single guard interval signal may be generated from the entirety of the useful symbol,
or only from a portion thereof). Also, the FFT size of the first and second P1
symbols need not be lk, and the useful symbol need not have a length of 112 μs.
Furthermore, the frequency-dimension format of the first and second P1 symbols
need not be constant (in terms of MSS conversion, DBSK modulation, data
scrambling and so on).
[0224]
(23) The components of the above-described OFDM transmitters and OFDM
receivers may be realized as LSIs. In such a case, each component may be realized
on an individual chip. Alternatively, some or all of the components may be
realized on a single chip. Also, while LSIs are given as an example, ICs, system
LSIs, super LSIs, and ultra LSIs, which vary in terms of integration density, are also

plausible. Furthermore, the integrated circuit method is not limited to LSI, but may
also be realized as a private circuit or as a general-purpose processor. A FPGA
(Field Programmable Gate Array) or a reconfigurable processor, in which circuit cell
connections within the LSI can be reconfigured, may also be user. In addition1
developments in semiconductor technology or in other emerging technologies may
lead to LSls being replaced by other integrated circuit technology. Such
technology may, naturally, be user to integrate the functional blocks of the present
invention. Biotechnology applications are also plausible.
[0225]
(24) The order of operations for the above-described OFDM transmitters may be
at least partially written as a transmission program for execution by, for example, a
CPU (Central Processing Unit) reading the program from memory. The
aforementioned program may also be recorded on a recording medium for
distribution. The order of operations for the above-described OFDM receivers may
be at least partially written as a transmission program for execution by, for example,
a CPU reading the program from memory. The aforementioned program may also
be recorded on a recording medium for distribution.
[0226]
(25) The above-described OFDM transmitters may perform only a subset of the
transmission process presently explained. The above-described OFDM receivers
may perform only a subset of the transmission process presently explained.
[0227]
(26) Embodiments 1 through 4 and all variations thereon may be realized by any
combination of an OFDM transmitter, an OFDM transmission method, a transmitter
integrated circuit, an OFDM transmission program, an OFDM receiver, an OFDM
reception method, a receiver integrated circuit, an OFDM reception program
performing the above-described transmission or reception process. For example, a
portion of the OFDM transmitter described above in the Embodiments or variations

may be realized as an OFDM transmitter or as a transmitter integrated circuit, while
the order of operations for all remaining portions is written as an OFDM
transmission program for execution by, for example, a CPU reading the program
from memory. Similarly, a portion of the OFDM receiver described above in the
Embodiments or variations may be realized as an OFDM receiver or as a receiver
integrated circuit, while the order of operations for all remaining portions is written
as an OFDM reception program for execution by, for example, a CPU reading the
program from memory.
[0228]
(27) The above explanations describe control symbols user in the DVB-T2
format, called P1 symbols. However, the invention is not limited in this manner.
The information transmitted thereby need not necessarily consist of transmission
parameter information. Also, the above explanations are applicable to fields using
OFDM transmissions with a plurality of special symbols (control symbols) that
transmit control information like the P1 symbols, regardless of the presence of an
FEFpart.
[Industrill Applicabilit]
[0229]
The present invention is effective in the transmission and reception of
multiple characteristic control symbols.
[Reference Signs List]
[0230]
11 P1 symbol generator
12 Data symbol generator
13 P1 symbol inserter

26 P1 symbol demodulator
27 Data symbol demodulator
100 First P1 symbol generator

28 Carrier location sequence generator
29 MSS converter
30 DBPSK converter
31 Data scrambler
32 Carrier locator
33 IFFTunit
34 Guard interval inserter

200 Second P1 symbol generator
201 Carrier location sequence generator
202 MSS converter
203 DBPSK converter
204 Data scrambler
205 Carrier locator
206 IFFTunit
207 Guard interval inserter

300 First P1 symbol demodulator
301 P1 position detector
302 FFT unit
303 P1 decoder

400 Second P1 symbol demodulator
401 P1 position detector
402 FFT unit
403 P1 decoder

We claim:
1. An OFDM transmitter, comprising:
a first symbol generator generating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain
signal and a guard interval time-domain signal;
a second symbol generator generating a plurality of symbols different from the
control symbols; and
a symbol inserter inserting the N control symbols into the plurality of symbols
generated by the second symbol generator, wherein
in each of the control symbols, the guard interval time-domain signal is
identical to a signal in which at least a portion of the useful symbol time-domain
signal has been frequency-shifted by an amount different from any other control
symbols, and
the amount is non-zero for each ofthe control symbols.
2. The OFDM transmitter of Claim 1, wherein
the first symbol generator includes:
an inverse orthogonal transformer generating the useful symbol time-domain
signal through an inverse orthogonal transformation from the frequency domain to the time
domain, performed for each of the N control symbols; and
a guard interval inserter (i) generating the guard interval time-domain signal
by frequency-shifting at least a portion of the useful symbol time-domain signal by a given
amount different from any other control symbols, and (ii) inserting the guard interval time-
domain signal so generated to the useful symbol time-domain signal, for each of the N
control symbols.
3. The OFDM transmitter of Claim 2, wherein
the guard interval inserter generates the guard interval time-domain signal by

frequency shifting one or both of a portion and a span of the useful symbol time-domain
signal different from any other control symbols by the given amount.
4. The OFDM transmitter of Claim 2, wherein
the plurality of sub-carriers include a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
the first symbol generator further includes a carrier locator generating the frequency-
domain signal by mapping control information data to each of the Active carriers in
accordance with the carrier location sequence, for each of the N control symbols.
5. The OFDM transmitter of Claim 1, wherein
N equals 2.
6. The OFDM transmitter of Claim 5, wherein
a frequency shift applied to a first one of the control symbols and a frequency shift
applied to a second one of the control symbols are equal in absolute value while being
opposite in sign.
7. An OFDM transmitter, comprising:
a first symbol generator generating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the control
symbols being made up of a useful symbol time-domain signal and a guard interval time-
domain signal;
a second symbol generator generating a plurality of symbols different from the
control symbols; and
a symbol inserter inserting the N control symbols into the plurality of symbols
generated by the second symbol generator, wherein

for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symbols frequency-shifted by a predetermined amount, and
the predetermined amount is non-zero for each of the control symbols.
8. The OFDM transmitter of Claim 7, wherein
the first symbol generator includes:
an inverse orthogonal transformer generating the useful symbol time-domain
signal through an inverse orthogonal transformation from the frequency domain to the time
domain, performed for each of the N control symbols; and
a guard interval inserter (i) generating the guard interval time-domain signal
by frequency-shifting one or both of a portion and a span different from any other control
symbols of the useful symbol time-domain signal by the predetermined amount and (ii)
inserting the guard interval time-domain signal so generated to the useful symbol time-
domain signal, for each of the N control symbols.
9. An OFDM transmitter, comprising:
a first symbol generator generating N (N being an integer satisfying N ≥ 2) control
symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the control
symbols being made up of a useful symbol time-domain signal and a guard interval time-
domain signal;
a second symbol generator generating a plurality of symbols different from the
control symbols; and
a symbol inserter inserting the N control symbols into the plurality of symbols
generated by the second symbol generator, wherein
the plurality of sub-carriers include a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and

control information data is mapped to each of the Active carriers in accordance with
the carrier location sequence for each ofthe N control symbols.
10. The OFDM transmitter of Claim 9, wherein
the first symbol generator includes:
a carrier locator generating the frequency-domain signal by mapping the
control information data to each of the Active carriers in accordance with the carrier location
sequence, for each of the N control symbols.
an inverse orthogonal transformer generating the useful symbol time-domain
signal through an inverse orthogonal transformation from the frequency domain to the time
domain, performed for each of the N control symbols; and
a guard interval inserter (i) generating the guard interval time-domain signal
by frequency-shifting at least a portion of the useful symbol time-domain signal by a
predetermined amount and (ii) inserting the guard interval time-domain signal so generated
to the useful symbol time-domain signal, for each of the N control symbols.
11. The OFDM transmitter of Claim 9, wherein
the carrier location sequence user for each of the N control symbols is orthogonal to
the other carrier location sequence user for any other control symbols.
12. The OFDM transmitter of Claim 9, wherein
the Active carriers in the carrier location sequence user for each of the N control
symbols are the Null carriers in the other carrier location sequence user for any other control
symbols.
13. An OFDM transmission method, comprising:
a first symbol generation step of generating N (N being an integer satisfYing N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal;

a second symbol generation step of generating a plurality of symbols different from
the control symbols; and
a symbol insertion step of inserting the N control symbols into the plurality of
symbols generated by the second symbol generator, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each of the control symbols.
14. An OFDM transmission method, comprising:
a first symbol generation step of generating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal;
a second symbol generation step generating a plurality of symbols different from the
control symbols; and
a symbol insertion step of inserting the N control symbols into the plurality of
symbols generated by the second symbol generator, wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symbols frequency-shifted by a predetermined amount, and
the predetermined amount is non-zero for each of the control symbols.
15. An OFDM transmission method, comprising:
a first symbol generation step of generating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal;
a second symbol generation step of generating a plurality of symbols different from
the control symbols; and

a symbol insertion step of inserting the N control symboss into the plurality of
symbols generated by the second symbol generator, wherein
the plurality of sub-carriers include a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordanee with
the carrier location sequence for each of the N control symbols.
16. An integrated circuit, comprssing:
a first symbol generation circuit generaiing N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal;
a second symbol generation circuit generaiing a plurality of symboss different from
the control symbols; and
a symbol insertion circutt inserting the N control symboss into the plurality of
symbols generated by the second symbol generator, wherein
in each of the control symbos,, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each of the control symbols.
17. An integrated circuit, comprising:
a first symbol generation circuit generaiing N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domann signal;
a second symbol generation circuit generaiing a plurality of symboss different from

the control symbols; and
a symbol insertion circutt inserting the N control symboss into the plurality of
symbols generated by the second symbol generator, wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symboss frequency-shifted by a predetermined amoun,, and
the predetermined amount is non-zero for each of the control symbols.
18. An integrated circuit, comprising:
a first symbol generation circuit generaiing N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domann signal;
a second symbol generation circuit generaiing a plurality of symboss different from
the control symbols; and
a symbol insertion circutt inserting the N control symboss into the plurality of
symbols generated by the second symbol generator, wherein
the plurality of sub-carriers include a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordanee with
the carrier location sequence for each of the N control symbols.
19. An OFDM transmsssion program executed by an OFDM transmitter, comprising:
a first symbol generation step of generaiing N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domann signal;

a second symbol generation step of generating a plurality of symbols different from
the control symbols; and
a symbol insertion step of inserting the N control symbols into the plurality of
symbols generated by the second symbol generator, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each of the control symbols.
20. An OFDM transmission program executed by an OFDM transmitter, comprising:
a first symbol generation step of generating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal;
a second symbol generation step of generating a plurality of symbols different from
the control symbols; and
a symbol insertion step of inserting the N control symbols into the plurality of
symbols generated by the second symbol generator, wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symbols frequency-shifted by a predetermined amount, and
the predetermined amount is non-zero for each of the control symbols.
21. An OFDM transmission program executed by an OFDM transmitter, comprising:
a first symbol generation step of generating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal;
a second symbol generation step of generating a plurality of symbols different from
the control symbols; and

a symbol insertion step of inserting the N control symbols into the plurality of
symbols generated by the second symbol generator, wherein
the plurality of sub-carriers include a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordance with
the carrier location sequence for each of the N control symbols.
22. An OFDM receiver, comprising:
a first symbol demodulator demodulating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal; and
a second symbol demodulator demodulating symbols other than the control symbols
according to results from the first symbol demodulator, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each ofthe control symbols.
23. The OFDM receiver of Claim 22, wherein
the first symbol demodulator demodulates the N control symbols by detecting a
position of at least one predetermined control symbol among the N control symbols in a
received signal.
24. The OFDM receiver of Claim 23, wherein
the first symbol demodulator detects the control symbol position by calculating a
correlation between (i) the received signal, and (ii) a signal obtained by frequency-shifting

the received signal by the inverse of the frequency shift applied by a transmitter to the
control symbol undergoing position detection.
25. An OFDM receiver, comprising:
a first symbol demodulator demodulating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the
control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal; and
a second symbol demodulator demodulating symbols other than the control symbols
according to results from the first symbol demodulator, wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symbols frequency-shifted by a predetermined amount, and
the predetermined amount is non-zero for each of the control symbols.
26. The OFDM receiver of Claim 25, wherein
the first symbol demodulator demodulates the N control symbols by detecting the
position of at least one predetermined control symbol among the N control symbols in a
received signal.
27. The OFDM receiver of Claim 26, wherein
the first symbol demodulator detects the control symbol position by calculating a
correlation between (i) the received signal and (ii) a signal obtained by frequency-shifting the
received signal by the inverse of the frequency shift applied by a transmitter to the control
symbol undergoing position detection according to one or both of a portion and a span of the
control symbol.
28. An OFDM receiver, comprising:
a first symbol demodulator demodulating N (N being an integer satisfying N ≥ 2)
control symbols in which a plurality of mutually-orthogonal sub-carriers are multiplexed, the

control symbols being made up of a useful symbol time-domain signal and a guard interval
time-domain signal; and
a second symbol demodulator demodulating symbols other than the control symbols
according to results from the first symbol demodulator, wherein
the plurality of sub-carriers includes a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordance with
the carrier location sequence for each of the N control symbols.
29. An OFDM reception method, comprising:
a first symbol demodulation step of demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation step of demodulating symbols other than the control
symbols according to results of the first symbol demodulation step, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each of the control symbols.
30. An OFDM reception method, comprising:
a first symbol demodulation step of demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation step of demodulating symbols other than the control

symbols according to results of the first symbol demodulation step, wherein
for each of the control symbos,, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symboss frequency-shifted by a predetermined amoun,, and
the predetermined amount is non-zero for each of the control symbos..
31. An OFDM reception method, comprising:
a first symbol demodulation step of demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexe,, the control symboss being made up of a useful symbol time-domain signal and a
guard interval time-domain signa;; and
a second symbol demodulation step of demodulating symboss other than the control
symbols according to results of the first symbol demodulation step, wherein
the pluraltty of sub-carriers includes a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordanee with
the carrier location sequence for each of the N control symbols.
32. An integrated circuit, comprising:
a first symbol demodulation circuit demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation circuit demodulating symboss other than the control
symbols according to results from the first symbol demodulation circuit, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been

frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each ofthe control symbols.
33. An integrated circuit, comprising:
a first symbol demodulation circuit demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation circuit demodulating symbols other than the control
symbols according to results from the first symbol demodulation circuit wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symbols frequency-shifted by a predetermined amount, and
the predetermined amount is non-zero for each of the control symbols.
34. An integrated circuit, comprising:
a first symbol demodulation circuit demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation circuit demodulating symbols other than the control
symbols according to results from the first symbol demodulation circuit, wherein
the plurality of sub-carriers includes a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordance with
the carrier location sequence for each of the N control symbols.

35. An OFDM reception program executed by an OFDM receiver, comprising:
a first symbol demodulation step of demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation step of demodulating symbols other than the control
symbols according to results ofthe first symbol demodulation step, wherein
in each of the control symbols, the guard interval time-domain signal is identical to a
signal in which at least a portion of the useful symbol time-domain signal has been
frequency-shifted by an amount different from any other control symbols, and
the amount is non-zero for each of the control symbols.
36. An OFDM reception program executed by an OFDM receiver, comprising:
a first symbol demodulation step of demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation step of demodulating symbols other than the control
symbols according to results of the first symbol demodulation step, wherein
for each of the control symbols, the guard interval time-domain signal is identical to
one or both of a portion and a span of the useful symbol time-domain signal different from
any other control symbols frequency-shifted by a predetermined amount, and
the predetermined amount is non-zero for each of the control symbols.
37. An OFDM reception program executed by an OFDM receiver, comprising:
a first symbol demodulation step of demodulating N (N being an integer satisfying N
≥ 2) control symbols in which a plurality of mutually-orthogonal sub-carriers are
multiplexed, the control symbols being made up of a useful symbol time-domain signal and a
guard interval time-domain signal; and
a second symbol demodulation step of demodulating symbols other than the control

symbols according to results of the first symbol demodulation step, wherein
the plurality of sub-carriers includes a plurality of Active carriers and a plurality of
Null carriers,
for each of the N control symbols, a carrier location sequence user to distinguish
between the Active carriers and the Null carriers among the plurality of sub-carriers differs
from another carrier location sequence for other control symbols, and
control information data is mapped to each of the Active carriers in accordance with
the carrier location sequence for each of the N control symbols.

ABSTRACT

An OFDM transmitter and an OFDM receiver respectively transmit and
receive N (N ≥ 2, N is an integer) control symbols. For each control symbol, a
guard interval time-domain signal is, for example, identical to a signal obtained by
frequency-shifting at least a portion of a useful symbol time-domain signal by an
amount different from any other symbol, or to a signal obtained by
frequency-shifting one or both of a portion and a span of a useful symbol interval
time-domain signal different from any other symbol by a predetermined amount.