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DESCRIPTION
RECEIVING DEVICE, RECEIVING METHOD, PROGRAM, AND
RECEIVING SYSTEM
5 TECHNICAL FIELD
[0001]
The present technology relates to a receiving
device, a receiving method, a program, and a receiving
system capable of improving reception performance,
10 particularly in the case of receiving a signal with a
variable frequency band.
BACKGROUND ART
[0002]
15 In terrestrial digital broadcasting, for example,
channels (physical channels) are generally defined to be
spaced at constant frequency intervals so as to transmit
an independent signal with a bandwidth prescribed by laws
and regulations. In view of inter-channel interference
20 and so on, a guard band with a predetermined bandwidth is
established between channels.
[0003]
For example, in the case of DVB-T/T2 which is the
European terrestrial digital broadcasting standard, the
25 bandwidth of each channel is 8 MHz as illustrated in Fig.
1A. A receiver is to be designed on the premise that a
signal with such a predetermined bandwidth is transmitted.
[0004]
For example, in the event that interference wave
30 exists in a part of some channels (physical channels),
transmission operators that transmit signals using this
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kind of transmission system have chosen not to use an
entire band in which the interference wave exists. This
results in wasteful use of the frequency band.
[0005]
5 Meanwhile, DVB-C2, standardized in 2 010 as the
European second-generation cable digital broadcasting
standard, includes an arrangement configured to avoid
such a wasteful use of the frequency band (Non-Patent
Document 1).
10 [0006]
As illustrated in Fig. IB, DVB-C2 supports a
concept of data slice, and a predetermined number of such
data slices are combined to configure a C2 system. Each
data slice has a bandwidth of 3408 carriers or less and
15 is allowed to be freely combined as far as the conditions
specified by the standard are fulfilled.
[0007]
Further, DVB-C2 supports a concept of a notch. The
transmission operators define, as a notch, a band
20 unavailable due to external interference, etc., and the
C2 system may include information regarding the notch
position expressed in units of subcarriers.
[0008]
Fig. 2A is a diagram illustrating an example of a
25 DVB-T/T2 signal, and Fig. 2B is a diagram illustrating an
example of a DVB-C2 signal. In Fig. 2, a horizontal axis
indicates a frequency. A description will be given for
the signal of DVB-C2.
[0009]
30 As shown in parts enclosed by lines in Fig. 2B, the
C2 system includes a preamble symbol and a data symbol.
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According to the standard, one C2 system is a signal with
a bandwidth up to approximately 3.5 GHz.
[0010]
A preamble symbol is a symbol used to transmit
5 transmission control information called LI signaling part
2 data (LI information). The LI information will be
described later in detail. The same information is
repeatedly transmitted at the cycle of 3408 carriers
(cycle of 3408 subcarriers of OFDM (Orthogonal Frequency
10 Division Multiplex)) using the preamble symbol. The 3408
carriers corresponds to a 7.61 MHz frequency band.
[0011]
A data symbol is a symbol used to transmit TS
(Transport Streams) such as program data. The data
15 symbol is divided for each data slice. For example, data
slice 1 (DSl) and data slice 2 (DS2) transmit different
pieces of program data. The parameters relating to each
data slice, such as the number of data slices, are
contained in the Ll information.
20 [0012]
The portions painted in black in Fig. 2B indicate
the notches. The notches are frequency bands used for FM
broadcasting, police radio, military radio, etc. but not
used to transmit the C2 system signals. In a
25 transmission signal output from a transmitter, the notch
periods are signal-free periods. There are two types of
the notches, that is, a narrowband notch having less than
48 carriers in bandwidth and a broadband notch having 4 8
carriers or more in bandwidth. The parameters related to
30 the respective notches, such as the number of notches and
the bandwidth thereof, are contained in the Ll
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information.
[0013]
Thus, the DVB-C2 signal includes the "data slices"
and the "notches" that are variable in bandwidth. It is
5 necessary for the receiver to demodulate an OFDM signal
whose bandwidth is selected almost at discretion of the
transmitting side. In DVB-C2, there is a case where a
width of a desired data slice may be smaller than 3408
carriers. The carrier number of the desired data slice
10 is acquired from the LI information during channel scan.
[0014]
A receiving process in the receiver is conducted by
receiving a signal within a tuning window that has a
fixed bandwidth (3409 carriers) as illustrated in Fig. 3A.
15 The center position (center frequency) of the tuning
window suitable for receiving a signal of the desired
data slice is specified by the LI information from the
transmitting side.
[0015]
20 In the receiver, the OFDM signal is demodulated by
performing orthogonal demodulation using the signal with
the frequency specified by the transmitting side. The
program data is decoded based on the Ll information
obtained from the demodulation.
25
CITATION LIST
NON-PATENT DOCUMENT
[0016]
Non-Patent Document 1: DVB-C2 STANDARD [Digital Video
30 Broadcasting (DVB); Frame structure channel coding and
modulation for a second generation digital transmission
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system for cable systems (DVB-C2)] DVB Document A138
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
5 [0017]
In general, an OFDM signal of a desired data slice
may be demodulated by down-converting the OFDM signal to
a baseband signal whose frequency has been specified by
the transmitting side. This may be achieved by
10 demodulating a received signal and retrieving a necessary
portion, namely an OFDM signal, in accordance with
placement information of the OFDM signal contained in the
Ll information. The OFDM signal is used to transmit a
data symbol which constitutes a desired data slice.
15 [0018]
However, in the case where the desired data slice
is a dependent static DS of DVB-C2 and a notch (broadband
notch) is included in the band of the received signal,
demodulation sometimes may not be conducted. Here, an
20 expression "dependent static DS" refers to, so to speak,
a data slice which is a slave of other data slice because
the dependent static DS may be demodulated only after
obtaining the Ll information from the band of the other
data slice (DS).
25 [0019]
The dependent static DS is a data slice separate
from a group of other data slices, such as DS8
illustrated in Fig. 2B. The dependent static DS includes
sometimes one data slice and sometimes a group of data
30 slices including a plurality of data slices.
[0020]
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In the event of receiving the dependent static DS,
no matter how a tuning window is selected, there is a
broadband notch within the band of the received signal or
a portion outside the band of the C2 system as
5 illustrated in Fig. 3B. Even if the band including the
dependent static DS is received and demodulated, it is
not guaranteed that LI information can be decoded.
Meanwhile, it should be noted that, in DVB-C2, the
broadband notch is basically included in the band of the
10 received signal only in the case where the data slice to
be received is the dependent static DS.
[0021]
For example, demodulation may not be correctly
conducted in the case where the band of the dependent
15 static DS is located in a position biased to a highfrequency
band or a low frequency band in the band of the
received signal. As described later, when demodulating
the OFDM signal, GI correlation is calculated by using an
OFDM symbol to correct a carrier frequency error.
2 0 However, if there is any clock frequency error when the
band of the dependent static DS is in a biased position,
a correct correction value may not be obtained.
[0022]
The present technology has been provided in
25 consideration of the foregoing circumstances and is
directed to improving reception performance in the case
of receiving a signal with a variable frequency band.
SOLUTIONS TO PROBLEMS
30 [0023]
A receiving device according to an embodiment of
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the present technology includes a demodulation unit
configured to convert a received signal to a baseband
signal in the case where a first frequency differs from a
second frequency, wherein the first frequency is a center
5 frequency in a band of the received signal, the second
frequency is a center frequency in a band of a desired
signal contained in a part of the band of the received
signal, and a DC component of the baseband signal is to
be a frequency in the vicinity of the second frequency.
10 [0024]
The receiving device may be a piece of an IC chip,
a component including an IC chip, or a device including a
component including an IC chip.
[0025]
15 The band of the desired signal may include a band
of a signal to be received and a band of an adjacent
signal adjacent to the band of the signal to be received.
[0026]
In the case where the first frequency differs from
2 0 the second frequency, the demodulating unit may convert
the received signal to the baseband signal when either
one of both ends of the signal to be received is adjacent
to the adjacent signal.
[0027]
25 Further, a setting unit may be provided to specify
the first frequency and the second frequency based on
transmission control information contained in the
received signal and set a frequency which is to be the DC
component of the baseband signal. In this case, the
30 demodulation unit may convert the received signal in
accordance with the frequency set by the setting unit.
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[0028]
Further, a receiving unit may be provided to
receive a signal with a fixed bandwidth in a
predetermined frequency band which includes a bandwidth
5 of a signal used for transmitting the transmission
control information. In this case, the demodulation unit
may convert the received signal received by the receiving
unit to the baseband signal.
[0029]
10 Further, a processing-unit may be,provided to
suppress a signal in a band other than the band of the
desired signal. In this case, the demodulation unit may
convert the received signal, for which the signal has
been suppressed by the processing unit, to the baseband
15 signal.
[0030]
The band whose center frequency is the first
frequency may be a band of a DVB-C2 tuning window, and
the band of the desired signal may be a band of an OFDM
20 signal which includes, at least in part, an OFDM signal
of a data slice to be received.
[0031]
In the case where the band of the desired signal is
interposed between a band outside a C2 system and a band
25 of a notch, the demodulation unit may convert the
received signal to the baseband signal. A DC component
of the baseband signal is to be a frequency closer to the
band outside the C2 system than the center frequency in
the band of the desired signal.
30
EFFECTS OF THE INVENTION
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[0032]
The present technology may improve reception
performance in the case of receiving a signal with a
variable frequency band.
5
BRIEF DESCRIPTION OF DRAWINGS
[0033]
Fig. 1 is a diagram illustrating spectra of DVBT/
T2 and DVB-C2 signals.
10 Fig. 2 is a diagram illustrating examples of a C2
system.
Fig. 3 is a diagram illustrating examples of
received signals.
Fig. 4 is a block diagram illustrating a first
15 exemplary structure of a receiving device.
Fig. 5 is a diagram showing parameters included in
Ll information.
FIG 6 is a diagram illustrating examples of
received signals.
20 Fig. 7 is a diagram describing frequency transition
of a signal.
Fig. 8 is a diagram illustrating an example of a
transmitting signal.
Fig. 9 is a diagram illustrating an exemplary band
25 of a received signal.
Fig. 10 is a diagram illustrating another exemplary
band of the received signal.
Fig. 11 is a flowchart describing operation of the
receiving device.
30 Fig. 12 is a block diagram illustrating an
exemplary structure of the receiving device in detail.
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Fig. 13 is a block diagram illustrating an
exemplary structure of a GI correlation calculation unit.
Fig. 14 is a diagram illustrating examples of
signals observed at respective positions illustrated in
5 Fig. 13.
Fig. 15 is a diagram illustrating other examples of
signals observed at the respective positions illustrated
in Fig. 13.
Fig. 16 is a diagram illustrating OFDM signal
10 waveforms.
Fig. 17 is a diagram illustrating OFDM signal
waveforms without error.
Fig. 18 is a diagram illustrating OFDM signal
waveforms with carrier frequency errors.
15 Fig. 19 is a diagram illustrating OFDM signal
waveforms with clock frequency errors.
Fig. 20 is a diagram illustrating a relation
between frequency and phase difference.
Fig. 21 is another diagram illustrating the
2 0 relation between the frequency and the phase difference.
Fig. 22 is still another diagram illustrating the
relation between the frequency and the phase difference.
Fig. 23 is a block diagram illustrating a second
exemplary structure of the receiving device.
25 Fig. 24 is a block diagram illustrating a third
exemplary structure of the receiving device.
Fig. 25 is a diagram illustrating another example
of the band of the received signal.
Fig. 2 6 is a diagram illustrating an exemplary
30 structure of a receiving system.
FIG 27 is a diagram illustrating an exemplary
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structure of a computer.
MODES FOR CARRYING OUT THE INVENTION
[0034]
5 Hereinafter, the modes for carrying out the present
technology will be described. A description will be
given in the following order.
1. Configuration and Operation of Receiving Device
2. Effects
10 3. Modified Examples
[0035]

[Exemplary Structure of Receiving Device]
Fig. 4 is a block diagram illustrating a first
15 exemplary structure of a receiving device according to a
first embodiment of the present technology.
[0036]
A receiving device 1 illustrated in Fig. 4 is a
Low-IF receiver capable of receiving a DVB-C2 signal.
20 The receiving device 1 includes an RF tuner 11, a
demodulation unit 12, and an MPEG decoder 13.
[0037]
The RF tuner 11 includes a frequency conversion
unit 21, and an oscillator 22. The demodulation unit 12
25 includes an orthogonal demodulation unit 31, an
oscillator 32, an FFT calculation unit 33, an
equalization unit 34, an ECC processing unit 35, and a
frequency setting unit 36. An RF signal representing an
OFDM signal of DVB-C2 input to the receiving device 1 via
30 a cable circuit is input to the frequency conversion unit
21 in the RF tuner 11.
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[0038]
The frequency conversion unit 21 in the RF tuner 11
receives the input RF signal and converts the frequency
of the RF signal based on a signal supplied from the
5 oscillator 22. The frequency conversion unit 21 outputs,
to the orthogonal demodulation unit 31, the IF signal
obtained by the frequency conversion.
[0039]
The oscillator 22 generates a signal of a
10 predetermined frequency according to the tuning window to
output the signal to the frequency conversion unit 21.
[0040]
The orthogonal demodulation unit 31 in the
demodulation unit 12 orthogonally demodulates an IF
15 signal supplied from the frequency conversion unit 21
based on a signal supplied from the oscillator 32. The
orthogonal demodulation unit 31 outputs, to the FFT
calculation unit 33, a baseband signal obtained by
performing the orthogonal demodulation. The baseband
20 signal is the time-domain signal representing respective
symbols, such as preamble symbol and data symbol
configuring a C2 system.
[0041]
The oscillator 32 generates a signal of the
25 frequency set by the frequency setting unit 36 and
outputs the signal to the orthogonal demodulation unit 31
[0042]
The FFT calculation unit 33 performs FFT
calculation for the baseband signal supplied from the
30 orthogonal demodulation unit 31 and outputs a frequencydomain
signal to the equalization unit 34.
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[0043]
The equalization unit 34 extracts a pilot symbol
from the frequency-domain signal supplied from the FFT
calculation unit 33 and estimates transmitting channel
5 characteristics based on the extracted pilot symbol. The
equalization unit 34 removes distortion from the channel
based on the estimated transmitting channel
characteristics and equalizes the frequency-domain signal
supplied from the FFT calculation unit 33, and then
10 outputs the equalized signal to the ECC processing unit
35.
[0044]
The ECC processing unit 35 performs error
correction decoding for the data of each symbol based on
15 BCH and LDPC codes contained in the equalized signal
supplied from the equalization unit 34 and then outputs
the error correction decoded data. LI information and TS
data obtained by the error correction decoding are output
from the ECC processing unit 35 and supplied to the
20 frequency setting unit 36 and the MPEG decoder 13.
[0045]
For example, in the case where an OFDM signal is
included across the band of the received signal, the
frequency setting unit 3 6 outputs, to the oscillator 32,
25 the information of a center frequency of a desired data
slice based on the LI information supplied from the ECC
processing unit 35. The desired data slice is a data
slice to be received.
[0046]
30 Fig. 5 is a diagram illustrating parameters
included in the LI information. A description will be
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given for the major parameters.
[0047]
"START_FREQUENCY" in the third row represents the
frequency that serves as a start position of the C2
5 system. The start position is expressed by an absolute
frequency starting from 0 Hz. "C2_BANDWIDTH" in the
fourth row represents a bandwidth of the C2 system.
[0048]
"NUM_DSLICE" in the eighth row represents the
10 number of data slices contained in the C2 frame.
"NUM_NOTCH" in the ninth row represents the number of
notches contained in the C2 frame. The parameters from
the 10th to 45th rows are the parameters for the
respective data slices.
15 [0049]
"DSLICE_ID" in the 11th row represents an ID of the
data slice in the C2 system. "DSLICE_TUNE_POS" in the
12th row represents a center frequency of the data slice
based on the frequency represented by "START_FREQUENCY".
20 [0050]
The parameters from the 46th to 50th rows are given
for the respective notches. "NOTCH_START" in the 47th
row represents the position of the notch based on the
frequency represented by "START_FREQUENCY".
25 "NOTCH_WIDTH" in the 48th row represents the bandwidth of
the notch.
[0051]
The frequency setting unit 36 performs processes
such as specifying a center frequency of a desired data
30 slice to be received based on DSLICE_TUNE_POS.
[0052]
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The MPEG decoder 13 decodes the data stored in a TS
packet configuring the TS supplied from the ECC
processing unit 35 and outputs the decoded data to the
subsequent stage. The data stored in the TS packet is
5 compressed in a predetermined compression method, such as
MPEG2.
[0053]
[Regarding Frequency Transition of Signal]
Here, description will be given for frequency
10 transition of a received signal in the case where an OFDM
signal is included across a band.
[0054]
A received signal in the case where the OFDM signal
is included across the band is shown in Fig. 6A. In Fig.
15 6A, an axis along a trapezoid base indicates the
frequency, and an up-pointing arrow indicates a center
frequency in the band. In the band of the received
signal in Fig. 6A, only the OFDM signal is included and
no notch is included. The OFDM signal in Fig. 6A
20 includes an OFDM signal of a desired data slice.
[0055]
In the example in Fig. 4, the RF signal including
the OFDM signal across the band is input to the frequency
conversion unit 21. A frequency of the RF signal to be
25 input to the frequency conversion unit 21 is 666 MHz, for
example, and the RF signal has a predetermined bandwidth,
such as 8 MHz, having passed through a bandpass filter
(not shown) provided inside the RF tuner 11. The
frequency conversion unit 21 converts the RF signal at
30 666 MHz, for example, to an IF signal at 5 MHz and
outputs the IF signal to the orthogonal demodulation unit
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31. A description hereinafter will be given assuming
that a bandwidth of a tuning window, namely a bandwidth
of a received signal, is 8 MHz.
[0056]
5 In the case where an OFDM signal is included across
the band of the received signal, the frequency setting
unit 3 6 sets, in the oscillator 32, a frequency specified
by DSLICE_TUNE_POS in accordance with the DSLICE_TUNE_POS
of a desired data slice included in LI information.
10 [0057]
The orthogonal demodulation unit 31 orthogonally
demodulates the IF signal based on a signal generated by
the oscillator 32 and then down-converts the IF signal to
a baseband signal whose DC component is to be a center
15 frequency of the desired data slice. The orthogonal
demodulation unit 31 outputs the baseband signal obtained
by the orthogonal demodulation. In Fig. 4, the center
frequency of the signal to be output from the orthogonal
demodulation unit 31 is 0 MHz. This indicates that the
2 0 signal is the baseband signal.
[0058]
Thus, in the case where the OFDM signal is included
across the band of the received signal, demodulation is
performed so that the received signal is down-converted
25 to the baseband signal whose DC component is to be a
frequency specified by the DSLICE_TUNE_POS of the desired
data slice.
[0059]
Next, a description is given for frequency
30 transition of a received signal in the case where an OFDM
signal is included only in a part of the band.
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[0060]
A received signal in the case where the OFDM signal
is included only in a part of the band is shown in Fig.
6B. In the received signal illustrated in Fig. 6B, a
5 shaded portion represents a notch. In the received
signal in Fig. 6B, the notch is included in the band of a
frequency higher than the center frequency. The OFDM
signal included in the received signal in Fig. 6B is the
OFDM signal of a dependent static DS, and the OFDM signal
10 of the desired data slice is included at least in a part.
[0061]
As illustrated in Fig. 7, an RF signal including
the OFDM signal only in a part of the band is input to
the frequency conversion unit 21. The frequency of the
15 RF signal to be input to the frequency conversion unit 21
is 666 MHz. The frequency conversion unit 21 converts
the RF signal at 666 MHz to an IF signal at 5 MHz and
outputs the IF signal to the orthogonal demodulation unit
31.
20 [0062]
In the case where the OFDM signal is included only
in a part of the band of the received signal, the
frequency setting unit 36 specifies, based on LI
information, a center frequency of an entire band of the
25 OFDM signal included in the received signal. Hereinafter
a whole part of the OFDM signal of DVB-C2 included in the
received signal will be referred to as a desired OFDM
signal as appropriate.
[0063]
30 The frequency setting unit 36 sets, in the
oscillator 32, the specified center frequency of the
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desired OFDM signal.
[0064]
The orthogonal demodulation unit 31 orthogonally
demodulates an IF signal based on the signal generated by
5 the oscillator 32 and down-converts the IF signal to a
baseband signal whose DC component is to be the center
frequency in the band of the desired OFDM signal. The
orthogonal demodulation unit 31 outputs the baseband
signal obtained by the orthogonal demodulation. In the
10 baseband signal in Fig. 7, an arrow is up-pointed in the
center of the band of the desired OFDM signal excluding
the band of the notch. This indicates that the baseband
signal is a signal whose DC component is to be the center
frequency in the band of the desired OFDM signal.
15 [0065]
Thus, in the case where the OFDM is included only
in a part of the band of the received signal,
demodulation is performed so that the received signal is
down-converted to the baseband signal whose DC component
20 is to be the center frequency in the band of the desired
OFDM signal including the desired data slice, not the
frequency specified by the DSLICE_TUNE_POS of the desired
data slice.
[0066]
25 It may be considered that the transmitting side
sets, in the LI information, information related to an
optimal frequency for receiving each data slice. However,
the frequency considered to be optimal by the
transmitting side may be different from the frequency
30 optimal for demodulation. Therefore, it is preferable to
calculate the optimal frequency for demodulation in the
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receiving side and then perform the down-conversion using
the calculated frequency. In the receiving device 1, in
the case where the OFDM signal is included only in a part
of the band of the received signal, the optimal center
5 frequency is calculated as a center frequency in the band
of the desired OFDM signal so as to receive the signal
using the calculated optimal frequency.
[0067]
This results in improvement of reception
10 performance in the case where- the desired data slice is
included in all or a part of a dependent static DS and
the OFDM signal is included only in a part of the band of
the received signal. A description will be given later
for a reason why reception performance may be'improved by
15 down-converting the IF signal to the baseband signal
whose DC component is to be the center frequency in the
band of the desired OFDM signal, not the center frequency
in the band of the received signal.
[0068]
20 Meanwhile, it should be noted that the LI
information used in calculating the optimal center
frequency is the Ll information received at the time of
receiving the data slice (normal data slice) which is not
the dependent static DS. In DVB-C2, in the case where
25 the desired data slice is included in all or a part of
the dependent static DS, the normal data slice is
received first. At the time of receiving the normal data
slice, the Ll information may be decoded, and the
dependent static DS is received using the Ll information
30 obtained at the time of receiving the normal data slice.
As described above, the Ll information may not always be
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decoded even if the signal in the band including the
dependent static DS is received and demodulated.
[0069]
[Concrete Examples]
5 Some concrete examples of the demodulating process
will be described.
[0070]
Fig. 8 is a diagram illustrating an example of a
transmitting signal in the transmitting side.
10 [0071]
The transmitting signal in Fig. 8 is a signal with
8 MHz bandwidth, and there is dependent static DS
interposed between the broadband notches in the frequency
band of that signal. In the broadband notch located in
15 the low frequency band on one side of the dependent
static DS, local disturbance wave is included. Further,
in the broadband notch located in the high frequency band
on the other side of the dependent static DS, a signal of
other standard, such as DVB-C, is included as the
20 disturbance wave.
[0072]
In Fig. 8, the bandwidth of the dependent static DS
is 2 MHz and includes five data slices DS0 to DS4 having
the same bandwidth. The dependent static DS is added
25 with an LI block which is a preamble symbol block that
transmits the LI information. The LI information
obtained at the time of receiving the normal data slice
includes the information of frequencies fo to f4 which
are respectively the center frequencies of the data
30 slices DS0 to DS04.
[0073]
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A description will be given for the case where a
desired data slice to be received is the leftmost data
slice DSO. A left end of the data slice DSO contacts the
broadband notch and a right end thereof contacts a group
5 of the neighboring data slices, DSl to DS4. The center
frequency of the desired data slice will be different
from the center frequency in the band of the desired OFDM
signal including the desired data slice. The bandwidth
of the desired OFDM signal is 2 MHz.
10 [0074]
Fig. 9 is a diagram illustrating an example of the
received signal whose frequency has been shifted so that
the center frequency in the band of the received signal
may become the same as the center frequency of the
15 desired data slice DSO. In this case, the IF signal is
down-converted to the baseband signal whose DC component
is a frequency fo, namely the center frequency of DSO.
[0075]
The band of the desired OFDM signal in Fig. 9 is in
20 a position biased to the right side (high-frequency side)
in the band of the received signal.
[0076]
If the band of the desired OFDM signal is in a
biased position in the band of the received signal,
25 reception performance may be degraded. In the case where
an interference removing filter is provided to suppress
the OFDM signal of the data slice other than DSO as
illustrated in Fig. 9 in order to avoid the degradation
of reception performance caused by the biased position of
30 the desired OFDM signal, the number of obtainable
continual pilots will be reduced and it may be difficult
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to conduct demodulation itself. In the data symbol of
DVB-C2, a pilot symbol, such as a scattered pilot and the
continual pilot, is inserted and used to estimate
transmission channel characteristics at the time of
5 demodulation.
[0077]
Fig. 10 is a diagram illustrating an example of the
received signal whose frequency has been shifted so that
the center frequency in the band of the received signal
10 may become the same as the center frequency in the band
of the desired OFDM signal. In this case, the IF signal
is down-converted to a baseband signal whose DC component
is a frequency f2, namely the center frequency of DS2
included in the band of the desired OFDM signal.
15 [0078]
The band of the desired OFDM signal in Fig. 10 will
be positioned in the center of the band of the received
signal.
[0079]
20 This may avoid the degradation of reception
performance caused by the biased position of the desired
OFDM signal. Further, even if the interference removing
filter is set to suppress the signal other than the OFDM
signal of DS0 to DS4, it is possible to obtain as many
25 continual pilots as included in the 2 MHz band, and it
would not be difficult to conduct the demodulation itself
[0080]
As the center frequency in the band of the received
signal, it is also possible to use a frequency in the
30 vicinity of the center frequency of DS2 instead of the
center frequency of DS2. If the frequency is closer to
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the center frequency of DS2 than the center frequency of
DSO, the biased position of the OFDM signal in the band
of the received signal may be reduced.
[0081]
5 The band of the received signal may be shifted so
that the center frequency in the band of the received
signal would become the same as the center frequency in
the band of the desired OFDM signal only when the desired
data slice is included in the end portion of the band of
10 the desired OFDM signal as illustrated in Fig. 10, or
also when the desired data slice is included in a
position other than the end portion of the band of the
desired OFDM signal.
[0082]
15 [Operation of Receiving Device]
Here, a description will be given for how the
receiving device 1 operates to receive a dependent static
DS with reference to a flowchart illustrated in Fig. 11.
[0083]
20 In step Si, the receiving device 1 receives a
normal data slice in respective units. The signal
frequency transition in the respective units of the
receiving device 1 in this case is as described with
reference to Fig. 4.
25 [0084]
That is, the frequency conversion unit 21 in the RF
tuner 11 converts an RF signal to an IF signal. The
orthogonal demodulation unit 31 in the demodulation unit
12 orthogonally demodulates the IF signal based on a
30 signal supplied from the oscillator 32. As a subject to
be received is a normal data slice, orthogonal
24
SP321720WO00
demodulation by the orthogonal demodulation unit 31 is
conducted such that the IF signal is down-converted to a
baseband signal whose DC component is to be a center
frequency in a band of a received signal. Further, the
5 FFT calculation unit 33 performs FFT calculation for a
time-domain baseband signal. The equalization unit 34
equalizes a frequency-domain signal. The ECC processing
unit 35 performs error correction decoding for each of
the equalized symbol data and outputs the error
10 correction decoded data.
[0085]
In step S2, the frequency setting unit 3 6 acquires
LI information output from the ECC processing unit 35 as
the error correction decoded data at the time of
15 receiving the normal data slice.
[0086]
In step S3, the frequency setting unit 36
determines, as a center frequency in the band of the
desired OFDM signal, a center frequency in the band of
20 the received signal to receive a dependent static DS, as
has been described with reference to Fig. 10.
[0087]
In step S4, the receiving device 1 receives the
dependent static DS in the respective units. The signal
25 frequency transition in the respective units of the
receiving device 1 in this case is the same as has been
described with reference to Fig. 7.
[0088]
That is, the frequency conversion unit 21 in the RF
30 tuner 11 converts the RF signal to the IF signal. The
orthogonal demodulation unit 31 in the demodulation unit
25
SP321720WO00
12 orthogonally demodulates the IF signal based on a
signal supplied from the oscillator 32. As a subject to
be received is a dependent static DS, orthogonal
demodulation by the orthogonal demodulation unit 31 is
5 conducted such that the IF signal is down-converted to
the baseband signal whose DC component is to be a center
frequency in a band of a desired OFDM signal. Further,
the FFT calculation unit 33 performs FFT calculation for
a time-domain baseband signal. The equalization unit 34
10 equalizes a frequency-domain signal. The ECC processing
unit 35 performs error correction decoding for each of
the equalized symbol data and outputs the error
correction decoded data.
[0089]
15 With the above series of processes, the receiving
device 1 may improve the reception performance at the
time of receiving the dependent static DS.
[0090]

20 Here, a description is given for the reason why the
reception performance may be improved by shifting the
band of the received signal at time receiving the
dependent static DS as described above.
[0091]
25 Fig. 12 is a block diagram illustrating an
exemplary structure of the receiving device 1 in detail.
The components illustrated in Fig. 12 identical to those
illustrated in Fig. 4 are denoted by the same reference
numerals. Therefore, overlapping description will be
30 omitted as appropriate.
[0092]
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SP321720WO00
The demodulation unit 12 in Fig. 12 includes, in
addition to the components in Fig. 4, a clock frequency
correction unit 51, a carrier frequency correction unit
52, a GI correlation calculation unit 53, a carrier
5 frequency correction value generation unit 54, a clock
frequency error detection unit 55, and a clock frequency
correction value generation unit 56. The time-domain
OFDM signal, which is the baseband signal obtained by the
orthogonal demodulation in the orthogonal demodulation
10 unit 31, is supplied.to the clock frequency correction
unit 51. Further, the frequency-domain OFDM signal
obtained by the FFT calculation in the FFT calculation
unit 33 is supplied to the clock frequency error
detection unit 55.
15 [0093]
The clock frequency correction unit 51 corrects a
clock frequency error (sampling frequency error)
contained in the time-domain OFDM signal supplied from
the orthogonal demodulation unit 31 in accordance with
20 the clock frequency correction value supplied from clock
frequency correction value generation unit 56. The
received signal to be supplied to the clock frequency
correction unit 51 includes a real-axis component (I
component) and an imaginary-axis component (Q component).
25 The clock frequency correction unit 51 outputs, to the
carrier frequency correction unit 52, the time-domain
OFDM signal corrected by the clock frequency error
correction.
[0094]
30 The carrier frequency correction unit 52 corrects a
carrier frequency error contained in the time-domain OFDM
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signal supplied from the clock frequency correction unit
51 in accordance with a carrier frequency correction
value supplied from the carrier frequency correction
value generation unit 54. The carrier frequency
5 correction unit 52 outputs, to the FFT calculation unit
33 and the GI correlation calculation unit 53, the timedomain
OFDM signal corrected by the carrier frequency
error correction.
[0095]
10 The GI...correlation calculation unit 53 obtains, as
a GI correlation (autocorrelation), an average of time
duration corresponding to a GI length, for example. The
GI correlation is a value obtained by multiplying the
time-domain OFDM signal by a delay signal. The delay
15 signal is a signal delayed by a length of an effective
symbol of the time-domain OFDM signal supplied from the
carrier frequency correction unit 52. The GI correlation
thus obtained takes a peak value at the boundary between
the OFDM symbols.
20 [0096]
A phase of the GI correlation taking the peak value
becomes zero in the case where a carrier frequency used
for digital orthogonal demodulation perfectly matches a
center frequency of the OFDM signal (received OFDM
25 signal) to be digitally and orthogonally demodulated.
However, in the case where the carrier frequency used for
the digital orthogonal demodulation differs from the
center frequency of the OFDM signal to be digitally and
orthogonally demodulated, the phase of the GI correlation
30 taking the peak value is rotated accordingly.
[0097]
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SP321720WO00
Therefore, the phase of the GI correlation taking
the peak value is to represent an amount of difference
between the carrier frequency used for the digital
orthogonal demodulation and the center frequency of the
5 OFDM signal to be digitally and orthogonally demodulated.
The carrier frequency correction value generation unit 54
estimates a carrier frequency error based on a phase of
the GI correlation taking the peak value, and outputs the
estimated amount of the carrier frequency error to the
10 carrier frequency correction value generation unit 54.
[0098]
The carrier frequency correction value generation
unit 54 is an integrator which integrates the amount of
the carrier frequency error estimated by the GI
15 correlation calculation unit 53 and outputs, as a carrier
frequency correction value, the integration result to the
carrier frequency correction unit 52.
[0099]
The clock frequency error detection unit 55
20 estimates a clock frequency error contained in a
frequency-domain OFDM signal supplied from the FFT
calculation unit 33. The clock frequency error contained
in the frequency-domain OFDM signal is estimated based on,
for example, a phase difference between pilot symbols of
25 the OFDM.
[0100]
In the OFDM, respective subcarriers are arranged at
a predetermined frequency interval, and the larger the
subcarrier number, the higher the frequency. In the case
30 where there is no clock frequency error, only a phase
error caused by channel noise, etc. is included in the
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SP321720WO00
frequency-domain OFDM signal. Accordingly, the phase
error of each pilot carrier is substantially constant.
[0101]
Conversely, in the case where there is a clock
5 frequency error, the phase error caused by the clock
frequency error is included in the phase error of the
pilot carrier in addition to the phase error caused by
the channel noise, etc. The larger the subcarrier number
and the higher the frequency of the pilot carrier, the
10 larger the phase error caused by the clock frequency
error. That is, the phase error caused by the clock
frequency error is proportional to the subcarrier number.
[0102]
The clock frequency error detection unit 55 detects
15 the phase error proportional to the subcarrier number and
estimates the clock frequency error. The technology of
estimating the clock frequency error is disclosed, for
example, in Japanese Patent Application Laid-Open No.
2010-87749. The clock frequency error detection unit 55
20 outputs the estimated amount of the clock frequency error
to the clock frequency correction value generation unit
56.
[0103]
The clock frequency correction value generation
25 unit 56 is an integrator which integrates the amount of
the clock frequency error estimated by the clock
frequency error detection unit 55 and outputs, as a clock
frequency correction value, the integration result to the
clock frequency correction unit 51.
30 [0104]
Fig. 13 is a block diagram illustrating an
30
SP321720WO00
exemplary structure of the GI correlation calculation
unit 53.
[0105]
The GI correlation calculation unit 53 includes a
5 delay unit 61, a multiplication unit 62, a moving average
calculation unit 63, a peak detection unit 64, and an I/Q
phase difference calculation unit 65. The time-domain
OFDM signal output from the carrier frequency correction
unit 52 is input to the delay unit 61 and the
10 multiplication unit 62.
[0106]
The delay unit 61 delays the input time-domain OFDM
signal by the length of the effective symbol and then
outputs, to the multiplication unit 62, the delayed
15 signal transposed to complex conjugate (Conj).
[0107]
The multiplication unit 62 obtains a multiplication
value by multiplying the input time-domain OFDM signal by
the delayed signal delayed by the delay unit 61 and then
20 outputs the multiplication value to the moving average
calculation unit 63.
[0108]
The moving average calculation unit 63 obtains, as
the GI correlation, a moving average per time duration
25 corresponding to the GI length of the multiplication
value supplied from the multiplication unit 62 and, after
that, outputs the GI correlation to the peak detection
unit 64.
[0109]
30 The peak detection unit 64 detects a peak point of
the GI correlation and outputs information related to
31
SP321720WO00
phases of an I component and a Q component at the peak
point to the I/Q phase difference calculation unit 65.
The information related to the peak point is also
supplied to the FFT calculation unit 33 so that a subject
5 period for FFT calculation is set.
[0110]
The I/Q phase difference calculation unit 65
outputs, to the carrier frequency correction value
generation unit 54, information regarding the carrier
10 frequency error represented by a phase difference between
the I component and the Q component at the peak point
detected by the peak detection unit 64.
[0111]
A description will be given for influence of the
15 carrier frequency error.
[0112]
Fig. 14 is a diagram illustrating examples of
signals at respective positions A, B, and C in Fig. 13.
The position A is where an input signal is observed, and
20 the position B is where a delay signal is observed. The
position C is where a moving average of the GI
correlation is observed. A horizontal direction
represents the time direction.
[0113]
25 As illustrated in the upper portion of Fig. 14, one
OFDM symbol includes an effective symbol and a guard
interval (GI). The effective symbol is a signal period
during which an IFFT process is performed at the time of
transmission. The guard interval (GI) is a portion where
30 a partial wave in the latter part of the effective symbol
shown in shaded area is exactly copied at a head of the
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SP321720WO00
effective symbol.
[0114]
In Fig. 14, the upper portion shows an input signal,
and the middle portion shows a delay signal. In the case
5 where there is no carrier frequency error, the GI
correlation of the I component takes a peak point at the
boundary of the OFDM symbols in the input signal as
illustrated in the lower portion of Fig. 14.
[0115]
10 On the other hand, in the case where there is a
carrier frequency error Af, the GI correlation is
expressed by a formula (2) shown below in the case where
the input signal r(t) is expressed by an formula (1). t
represents the time. rB(t) in the formula (1) represents
15 the input signal in the case where there is no carrier
frequency error, and Tu in the formula (2) represents the
effective symbol length.
[Formula 1]
r(t) =rB(t)eJ2*Aft ••• (1)
2 0 [Formula 2]
r(t)-r*(t-Tu) =rB(t)ej27rAft-r;(t-Tu)e-j27rAf(t-Tu)
= |rB(t)|2e+J27rAfTu ... (2)
[0116]
According to e+j2"AfTu in the formula (2), it is
clear that rotation proportional to the carrier frequency
25 error Af occurs in the I component and the Q component at
the peak point of the GI correlation. Fig. 15 is a
diagram illustrating examples of signals in the case
where there is a carrier frequency error. As illustrated
33
SP321720WO00
in the lower portion of Fig. 15, the GI correlation takes
a peak also in the Q component.
[0117]
Next, a description will be given for influence of
5 the clock frequency error.
[0118]
Fig. 16 is a diagram illustrating OFDM signal
waveforms. The OFDM signal is considered as a group of
four sine waves of signals SI to S4. The signals SI to
10 S4 correspond to respective carriers.
[0119]
A period from time tl to t2 corresponds to a period
of the GI, and a period from time t2 to t3 corresponds to
a period of the effective symbol. In the period of the
15 effective symbol in the signal SI, one cycle of the sine
wave is included, and in the period of the effective
symbol in the signal S2, two cycles of the sine waves are
included. In the period of the effective symbol in the
signal S3, three cycles of the sine waves are included,
20 and in the period of the effective symbol in the signal
S4, four cycles of the sine waves are included.
[0120]
As shown by the arrows in Fig. 17, the GI
correlation corresponds to a value obtained by
25 multiplying a signal in a predetermined position of each
carrier by a signal which has been delayed by a length of
an effective symbol. Accordingly, in the case where
there is neither carrier frequency error nor clock
frequency error, there will be no phase difference
30 between the signals to be multiplied and the GI
correlation is generated only in the I component. In the
34
SP321720WO00
signal SI in Fig. 17, there is no phase difference
between the signal phase at a position PI and the signal
phase at a position P2. The position PI is the boundary
between the GI and the effective symbol, and the position
5 P2 is the end of the effective symbol.
[0121]
Fig. 18 is a diagram illustrating waves in the case
where there is a carrier frequency error of 0.25 carrier.
There is no clock frequency error.
10 [0122]
In this case, a fixed phase difference AG is
identically generated, in all carriers, between a phase
of a signal at a predetermined position and a phase of a
signal delayed by a length of an effective symbol. In
15 the period of the effective symbol in the signal Si, 1.25
cycles of the sine waves are included. In the period of
the effective symbol in the signal S2, 2.25 cycles of the
sine waves are included. In the period of the effective
symbol in the signal S3, 3.25 cycles of the sine waves
20 are included. In the period of the effective symbol in
the signal S4, 4.25 cycles of the sine waves are included.
[0123]
Fig. 19 is a diagram illustrating waves in the case
where there is a clock frequency error of 1/10 clock.
25 There is no carrier frequency error.
[0124]
In this case, a phase difference proportional to
the original carrier frequency is generated, in each
carrier, between the phase of the signal at the
30 predetermined position and the phase of the signal
delayed by the length of the effective symbol.
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SP321720WO00
[0125]
Assume that, in the signal SI, the phase difference
is A9 between the phase of the signal at the boundary
between the GI and the effective symbol and the phase of
5 the signal at the end of the effective symbol. In the
signal S2, the phase difference A9 x 2 is generated
between the phase of the signal at the boundary between
the GI and the effective symbol and the phase of the
signal at the end of the effective symbol. In the signal
10 S3, the phase difference A9 x 3 is generated between the
phase of the signal at the boundary between the GI and
the effective symbol and the phase of the signal at the
end of the effective symbol. Further, in the signal S4,
the phase difference A9 x 4 is generated between the
15 phase of the signal at the boundary between the GI and
the effective symbol and the phase of the signal at the
end of the effective symbol.
[0126]
In the period of the effective symbol in the signal
20 SI, 0.9 cycle of the sine wave is included, and in the
period of the effective symbol in the signal S2, 1.8
cycles of the sine wave are included. In the period of
the effective symbol in the signal S3, 2.7 cycles of the
sine waves are included, and in the period of the
25 effective symbol in the signal S4, 3.6 cycles of the sine
waves are included.
[0127]
Fig. 20 is a diagram illustrating a relation
between the frequency and the phase difference in the
30 case where there is only a clock frequency error. Fig.
20A is a diagram illustrating distribution of OFDM
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SP321720WO00
carriers. As illustrated in Fig. 20B, a phase difference
of the GI correlation is proportional to the carrier
frequency (carrier number).
[0128]
5 Assuming that a band of frequency fi to f-z in Fig.
20 is a band of DVB-C2 tuning window, in the case where
there is only the clock frequency error when the OFDM
signal is included across the band of the received signal,
a phase difference of the GI correlation proportional to
10 the carrier number is generated as illustrated in Fig.
20B.
[0129]
Now, let us consider a case where there is only the
clock frequency error when the OFDM signal is included
15 only in a part of band of the received signal. As
illustrated in Fig. 21A, in the case where the OFDM
signal is symmetrically distributed with respect to the
center frequency in the band of frequency fi to f2,
namely the band of the received signal, a phase
20 difference shown in a colored range of frequency fu to
fi2 in Fig. 21B is detected by the I/Q phase difference
calculation unit 65 and integrated by the carrier
frequency correction value generation unit 54. The
integration result by the carrier frequency correction
25 value generation unit 54 becomes zero, and it is
determined that there is no carrier frequency error.
[0130]
Here, the determination result by the carrier
frequency correction value generation unit 54 is correct
30 because the consideration is given to the case where
there is only the clock frequency error. In the carrier
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SP321720WO00
frequency correction unit 52, a suitable process is
performed in accordance with a current state of the
carrier frequency error. Specifically, no correction is
performed in the carrier frequency correction unit 52 as
5 the carrier frequency error is zero.
[0131]
Conversely, as illustrated in Fig. 22A, in the case
where the OFDM signal is not symmetrically distributed
with respect to the center frequency in the band of
10 frequency fi to fzr namely the band of the received
signal, and the band of the OFDM signal is in a biased
position, a phase difference shown in a colored range of
frequency f2i to f22 in Fig. 22B is detected by the
carrier frequency correction value generation unit 54 and
15 integrated by the carrier frequency correction value
generation unit 54.. The integration result by the
carrier frequency correction value generation unit 54
does not become zero, and it is determined that there are
as many carrier frequency errors as the results of the
20 integration.
[0132]
Here, the determination result in the carrier
frequency correction value generation unit 54 is not
correct because the case where there is only the clock
25 frequency error is considered. In the carrier frequency
correction unit 52, a process unsuitable to the current
state of the current carrier frequency error is performed.
Specifically, correction is performed in the carrier
frequency correction unit 52 to correct as many carrier
30 frequency errors as the results of the integration
although the actual carrier frequency error is zero.
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SP321720WO00
[0133]
In the case where the band of the OFDM signal is in
the biased position in the band of the received signal,
correction is thus performed not conforming to the actual
5 state of the carrier frequency error. This results in
degradation of reception performance by comparison to the
case where the band of the OFDM signal is not in a biased
position.
[0134]
10 In other words, in the case where the band of the
desired OFDM signal included in a part of the band of the
received signal is in a biased position, reception
performance may be improved by resolving the biased
position and performing down-conversion so that the band
15 of the desired OFDM signal may be symmetrically
positioned with reference to the center frequency in the
band of the received signal.
[0135]

20 Fig. 23 is a block diagram illustrating a second
exemplary structure of the receiving device 1.
[0136]
The components illustrated in Fig. 23 identical to
those illustrated in Fig. 4 are denoted by the same
25 reference numerals. Therefore, overlapping description
will be omitted as appropriate. The structure of the
receiving device 1 illustrated in Fig. 23 is a subsequent
stage of an orthogonal demodulation unit 31 and differs
from the structure illustrated in Fig. 4 in that a filter
30 processing unit 101 is provided in a previous stage of an
FFT calculation unit 33.
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SP321720WO00
[0137]
The orthogonal demodulation unit 31 in a
demodulation unit 12 orthogonally demodulates an IF
signal supplied from a frequency conversion unit 21 in an
5 RF tuner 11. The orthogonal demodulation unit 31 outputs,
to the filter processing unit 101, a time-domain baseband
signal obtained by the orthogonal demodulation.
[0138]
In the example illustrated in Fig. 23, a desired
10 OFDM signal is included in a part of a band of a. received
signal as described with reference to Fig. 7. A baseband
signal supplied from the filter processing unit 101 is a
signal obtained by down-converting the IF signal, and a
DC component of the baseband signal is to be a center
15 frequency in a band of the desired OFDM signal.
[0139]
The filter processing unit 101 suppresses, by a
low-pass filter, a signal in a band adjacent to the band
of the desired OFDM signal and other than the band of the
20 desired OFDM signal based on information related to the
desired OFDM signal supplied from a frequency setting
unit 36. The filter processing unit 101 outputs, to the
FFT calculation unit 33, the baseband signal for which
the signal in a band other than the band of the desired
25 OFDM signal has been suppressed.
[0140]
The FFT calculation unit 33 performs FFT
calculation to the baseband signal supplied from the
filter processing unit 101 and outputs the frequency-
30 domain baseband signal.
[0141]
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SP321720WO00
The frequency setting unit 3 6 specifies the band of
the OFDM signal included in the received signal based on
the LI information supplied from the ECC processing unit
35 and then outputs information related to the band of
5 the OFDM signal to the filter processing unit 101.
[0142]
It can be assumed that some disturbance exists
outside the band of the desired OFDM signal. Such
disturbance is preferably suppressed in advance by a
10 filtering process. .For example, in the case where•a
signal with high power exists as the disturbance and no
suppression has been carried out for such a signal,
overflow occurs in FFT calculation, and this may result
in degradation of reception performance. Accordingly, by
15 having suppressed the disturbance before the FFT
calculation, the overflow in the FFT calculation may be
avoided and the reception performance may be improved.
By down-converting a signal to be processed to the
baseband signal before the filtering process as described
2 0 above, the filtering process may be performed by using a
low-pass filter which adopts not a complex number
coefficient but a real number coefficient, and this
results in reduction of a circuit scale.
[0143]
25 The placement of the filter processing unit 101 may
be in a previous stage of the orthogonal demodulation
unit 31 in the demodulation unit 12, or may be in another
place, such as inside the RF tuner 11.
[0144]
30 Fig. 24 is a block diagram illustrating a third
exemplary structure of the receiving device 1. The
41
SP321720WO00
components illustrated in Fig. 24 identical to those
illustrated in Fig. 4 are denoted by the same reference
numerals. Therefore, overlapping description will be
omitted as appropriate.
5 [0145]
In the receiving device 1 in Fig. 24, in the case
where a band of a desired OFDM signal is included only in
a part of a band of a received signal, a process for
resolving a biased position of the band of the desired
10 OFDM signal is performed at the stage of converting an RF
signal to an IF signal.
[0146]
In the case where the desired OFDM signal is
included only in a part of the band of the received
15 signal, the frequency setting unit 36 specifies, based on
the LI information, a center frequency in the band of the
desired OFDM signal included in the band of the received
signal, and outputs information related to the center
frequency in the band of the desired OFDM signal to an
20 oscillator 22 in the RF tuner 11.
[0147]
The oscillator 22 in the RF tuner 11 generates a
signal of the frequency set by the frequency setting unit
3 6 and outputs the signal to the frequency conversion
25 unit 21.
[0148]
The frequency conversion unit 21 receives the input
RF signal and converts the frequency of the RF signal
based on the signal of the predetermined frequency
30 supplied from the oscillator 22. The frequency
conversion unit 21 outputs, to the orthogonal
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SP321720WO00
demodulation unit 31, an IF signal obtained from the
frequency conversion. The frequency of the IF signal is
the same as the center frequency in the band of the
desired OFDM signal.
5 [0149]
Thus, reception performance may also be improved by
resolving the biased position of the band of the OFDM
signal not in the stage of orthogonal demodulation of
converting the IF signal to the baseband signal but in
10 the stage of converting the RF signal to the IF signal.
[0150]
Fig. 25 is a diagram illustrating another example
of shifting the band of the received signal.
[0151]
15 As is the case with Fig. 10, a bandwidth of a
dependent static DS in Fig. 25 is 2 MHz and includes five
data slices DS0 to DS4. A desired data slice to be
received is the leftmost DS0. The left end of the
dependent static DS contacts a broadband notch and the
20 right end thereof contacts a band outside a C2 system.
The dependent static DS in Fig. 25 is a data slice set at
the end of the C2 system.
[0152]
In this case, the frequency setting unit 36
25 specifies a frequency f2 based on Ll information. The
frequency f2 is the center frequency in the band of the
desired OFDM signal. The frequency setting unit 36 sets,
as a center frequency in the band of the received signal,
a predetermined frequency distant from the broadband
30 notch based on the frequency f2. The frequency f2 is the
center frequency in the band of the desired OFDM signal.
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SP321720WO00
In the example in Fig. 25, a frequency £3 is set as the
center frequency in the band of the received signal. The
frequency f3 is closer to the band outside the C2 system
than the frequency f2. The frequency £3 is a center
5 frequency of DS3.
[0153]
A bandwidth of the notch included in the band of
the received signal may be narrowed by setting the center
frequency in the band of the received signal at the
10 frequency closer to the band outside the C2 system than
the center frequency in the band of the desired OFDM
signal. Consequently, in the case where some disturbance
exists in the band of the notch, influence from the
disturbance may be reduced.
15 [0154]
[Exemplary Structure of the Receiving System]
Fig. 2 6 is a block diagram illustrating an
exemplary structure of a receiving system to which the
receiving device 1 is applied.
20 [0155]
A receiving system 201 illustrated in Fig. 2 6
includes a tuner 211, a demodulation unit 212, a signal
processing unit 213, and an output unit 214.
[0156]
25 The tuner 211 receives a signal transmitted via a
channel, such as digital terrestrial broadcasting,
digital satellite broadcasting, CATV network, or the
Internet, and outputs the received signal to the
demodulation unit 212. The above-described RF tuner 11
30 is included in the tuner 211.
[0157]
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SP321720WO00
The demodulation unit 212 performs, for the signal
supplied from the tuner 211, channel decoding including
demodulation and error correction and then outputs the
data obtained from the channel decoding to the signal
5 processing unit 213. The above-described demodulation
unit 12 is included in the demodulation unit 212.
[0158]
The signal processing unit 213 performs signal
processing, such as decompression and descrambling, for
10 the data obtained from channel decoding as appropriate
and acquires data to be transmitted. The above-described
MPEG decoder 13 is included in the signal processing unit
213.
[0159]
15 The decompression by the signal processing unit 213
is performed in the case where data to be transmitted,
such as video or audio, has been compressed by the
transmitting side, using the MPEG or other predetermined
compression method. Further, the descrambling is
20 performed in the case where the data to be transmitted
has been scrambled by the transmitting side. The signal
processing unit 213 outputs, to the output unit 214, the
data to be transmitted which has been obtained by
suitably performing the signal processing.
25 [0160]
The output unit 214 performs a process, such as D/A
conversion, for the data supplied from the signal
processing unit 213 when displaying an image based on the
data supplied from the signal processing unit 213. The
30 output unit 214 outputs the image signal obtained from
the D/A conversion to a display provided in the receiving
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system 201 or a display outside the receiving system 201,
to display the image.
[0161]
Further, in the case of recording the data supplied
5 from the signal processing unit 213 on a recording medium,
the output unit 214 outputs the data supplied from the
signal processing unit 213 to the recording medium inside
the receiving system 201 or the recording medium outside
the receiving system 201 for recording. The recording
10 medium includes, for example, a hard-disk, a flash memory,
or an optical disk. The recording medium outside the
receiving system 201 may be not only a recording medium
external to the receiving system 201 but also the
recording medium connected via a network.
15 [0162]
The receiving system 201 having the above-described
structure may include hardware, such as an IC (Integrated
Circuit) chip. Alternatively, the receiving system 201
may include a component such as a board on which a
20 plurality of IC chips is arranged. Still alternatively,
the receiving system 2 01 may include an independent
device that includes the above-mentioned component.
[0163]
Each of the tuner 211, the demodulation unit 212,
25 the signal processing unit 213, and the output unit 214
may be configured as single independent hardware or
software module. Further, two or more of the tuner 211,
the demodulation unit 212, the signal processing unit 213,
and the output unit 214 may be combined as the single
30 independent hardware or the software module. For example,
the tuner 211 and the demodulation unit 212 may be
V. 46
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configured of a single piece of hardware, and the signal
processing unit 213 and the output unit 214 may be
configured of a single piece of hardware.
[0164]
5 The receiving system 2 01 is applicable, for example,
to a television set to receive digital television
broadcasting, a radio receiver to receive radio
broadcasting, and a recorder to record television
broadcasting.
10 [0165]
[Exemplary Structure of Computer]
The above-described series of processes may be
performed by either hardware or software. In a case
where the series of processes is performed by the
15 software, a program constituting the software is
installed from a program recording medium into a computer
incorporated into dedicated hardware, a general-purpose
personal computer, or the like.
[0166]
20 Fig. 27 is a block diagram illustrating an
exemplary structure of computer hardware which executes
the above-described series of processes by the program.
[0167]
A CPU (Central Processing Unit) 251, a ROM (Read
25 Only Memory) 252, and a RAM (Random Access Memory) 253
are mutually connected via a bus 254.
[0168]
The bus 254 is further connected to an input/output
interface 255. An input unit 256 and an output unit 257
30 are connected to the input/output interface 255. The
input unit 256 includes, for example, a keyboard and a
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mouse. The output unit 257 includes, for example, a
display and a speaker. Further, a storage unit 258, a
communication unit 259 and a drive 2 60 are also connected
to the input/output interface 255. The storage unit 258
5 includes, for example, a hard disk or a non-volatile
memory. The communication unit 259 includes, for example,
a network interface. The drive 2 60 drives a removable
medium 2 61.
[0169]
10 In the computer having the above-described
structure, the above-described series of processes is
performed by the CPU 251 loading a program, stored in the
storage unit 258, into the RAM 253 via the input/output
interface 255 and the bus 254 for execution.
15 [0170]
The program executed by the CPU 251 is recorded,
for example, on the removable medium 2 61, or provided via
a wired or wireless transmission medium such as a local
area network, the Internet or digital broadcasting, and
20 is installed on the storage unit 258.
[0171]
Meanwhile, a program to be executed by the computer
may be a program for performing operations in
chronological order in accordance with the sequence
25 described in this specification, or may be a program for
performing operations in parallel or performing
operations when necessary, such as when a call is made.
[0172]
The embodiments of the present technology are not
30 limited to those described above, but may be modified in
various manners without departing from the scope of the
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present technology.
[0173]
[Modified Examples]
The present technology may also include the
5 following configurations.
[0174]
(1)
A receiving device including:
a demodulation unit configured to convert a
10 received signal to a baseband signal in the case where a
first frequency differs from a second frequency,
wherein the first frequency is a center frequency
in a band of the received signal, the second frequency is
a center frequency in a band of a desired signal included
15 in a part of the band of the received signal, and a DC
component of the baseband signal is to be a frequency in
the vicinity of the second frequency.
[0175]
(2)
20 The receiving device according to (1), wherein a
band of a signal to be received and a band of an adjacent
signal adjacent to the band of the signal to be received
are included in the band of the desired signal.
[0176]
25 (3)
The receiving device according to (2), wherein in
the case where the first frequency differs from the
second frequency, the demodulating unit converts the
received signal to the baseband signal when either of
30 both ends of the signal to be received is adjacent to the
adjacent signal.
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[0177]
(4)
The receiving device according to any one of (1) to
(3), further including
5 a setting unit configured to specify the first
frequency and the second frequency based on transmission
control information contained in the received signal and
set a frequency which is to be the DC component of the
baseband signal,
10 wherein the demodulation unit converts the received
signal in accordance with the frequency set by the
setting unit.
[0178]
(5)
15 The receiving device according to (4), further
including
a receiving unit configured to receive a signal
with a fixed bandwidth in a predetermined frequency band
including the bandwidth of a signal used for transmitting
20 the transmission control information,
wherein the demodulation unit converts the received
signal received by the receiving unit to the baseband
signal.
[0179]
25 (6)
The receiving device according to any one of (1) to
(5), further including
a processing unit configured to suppress a signal
in a band other than the band of the desired signal,
30 wherein the demodulation unit converts the received
signal, for which the signal has been suppressed by the
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processing unit, to the baseband signal.
[0180]
(7)
The receiving device according to any one of (1) to
5 (6), wherein a band whose center frequency is the first
frequency is a band of a DVB-C2 tuning window, and the
band of the desired signal is a band of an OFDM signal
which includes, at least in part, an OFDM signal of a
data slice to be received.
10 [0181]
(8)
The receiving device according to (7), wherein in
the case where the band of the desired signal is
interposed between a band outside C2 system and a band of
15 a notch, the demodulation unit converts the received
signal to the baseband signal, and a DC component of the
baseband signal is to be a frequency closer to the band
outside C2 system than the center frequency in the band
of the desired signal.
20 [0182]
(9)
A receiving method including:
a step of converting a received signal to a
baseband signal in the case where a first frequency
25 differs from a second frequency,
wherein the first frequency is a center frequency
in a band of the received signal, the second frequency is
a center frequency in a band of a desired signal
contained in a part of the band of the received signal,
30 and a DC component of the baseband signal is to be a
frequency in the vicinity of the second frequency.
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[0183]
(10)
A program for causing a computer to perform a
process including:
5 a step of converting a received signal to a
baseband signal in the case where a first frequency
differs from a second frequency,
wherein the first frequency is a center frequency
in a band of the received signal, the second frequency is
10 a center frequency-in a band of a desired signal
contained in a part of the band of the received signal,
and a DC component of the baseband signal is to be a
frequency in the vicinity of the second frequency.
[0184]
15 (11)
A receiving system including:
a receiving unit configured to receive a signal
transmitted via a channel so that the signal has a fixed
bandwidth in a predetermined frequency band;
20 a demodulation unit configured to demodulate the
received signal received by the receiving unit;
a signal processing unit configured to perform
signal processing for data demodulated by the
demodulation unit to obtain data to be transmitted; and
25 an output unit configured to output the data to be
transmitted obtained by the signal processing unit,
wherein the demodulation unit includes a conversion
unit configured to convert the received signal to a
baseband signal in the case where a first frequency
30 differs from a second frequency, the first frequency is a
center frequency in a band of the received signal, the
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second frequency is a center frequency in a band of a
desired signal included in a part of the band of the
received signal, and a DC component of the baseband
signal is to be a frequency in the vicinity of the second
5 frequency.
REFERENCE SIGNS LIST
[0185]
1 Receiving device, 11 RF tuner, 12 Demodulation
0 unit, 13 MPEG decoder, 21 Frequency conversion unit, 22
Oscillator, 31 Orthogonal demodulation unit, 32
Oscillator, 33 FFT calculation unit, 34 Equalization unit,
35 ECC processing unit, 36 Frequency setting unit, 101
Filter processing unit

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CLAIMS
1. A receiving device comprising:
a demodulation unit configured to convert a
5 received signal to a baseband signal in the case where a
first frequency differs from a second frequency,
wherein the first frequency is a center frequency
in a band of the received signal, the second frequency is
a center frequency in a band of a desired signal
10 contained in a part of the band of the received signal,
and a DC component of the baseband signal is to be a
frequency in the vicinity of the second frequency.
2. The receiving device according to claim 1, wherein
15 a band of a signal to be received and a band of an
adjacent signal adjacent to the band of the signal to be
received are included in the band of the desired signal.
3. The receiving device according to claim 2, wherein
20 in the case where the first frequency differs from the
second frequency, the demodulation unit converts the
received signal to the baseband signal when either of
both ends of the signal to be received is adjacent to the
adjacent signal.
25
4. The receiving device according to claim 1, further
comprising
a setting unit configured to specify the first
frequency and the second frequency based on transmission
30 control information contained in the received signal and
set a frequency which is to be the DC component of the
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SP321720WO00
baseband signal,
wherein the demodulation unit converts the received
signal in accordance with the frequency set by the
setting unit.
5
5. The receiving device according to claim 4, further
comprising
a receiving unit configured to receive a signal
with a fixed bandwidth in a predetermined frequency band
10 including a bandwidth of a signal used for transmitting
the transmission control information,
wherein the demodulation unit converts the received
signal received by the receiving unit to the baseband
signal.
15
6. The receiving device according to claim 1, further
comprising
a processing unit configured to suppress a signal
in a band other than the band of the desired signal,
20 wherein the demodulation unit converts the received
signal, for which the signal has been suppressed by the
processing unit, to the baseband signal.
7. The receiving device according to claim 1, wherein
25 the band whose center frequency is the first frequency is
a band of a DVB-C2 tuning window, and the band of the
desired signal is a band of an OFDM signal that includes,
at least in part, an OFDM signal of a data slice to be
received.
30
8. The receiving device according to claim 7, wherein
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in the case where the band of the desired signal is
interposed between a band outside a C2 system and a band
of a notch, the demodulation unit converts the received
signal to the baseband signal, and a DC component of the
5 baseband signal is to be a frequency closer to the band
outside the C2 system than the center frequency in the
band of the desired signal.
9. A receiving method comprising:
10 a step of converting a received signal to a
baseband signal in the case where a first frequency
differs from a second frequency,
wherein the first frequency is a center frequency
in a band of the received signal, the second frequency is
15 a center frequency in a band of a desired signal
contained in a part of the band of the received signal,
and a DC component of the baseband signal is to be a
frequency in the vicinity of the second frequency.
20 10. A program for causing a computer to perform a
process comprising:
a step of converting a received signal to a
baseband signal in the case where a first frequency
differs from a second frequency,
25 wherein the first frequency is a center frequency
in a band of the received signal, the second frequency is
a center frequency in a band of a desired signal
contained in a part of the band of the received signal,
and a DC component of the baseband signal is to be a
30 frequency in the vicinity of the second frequency.
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11. A receiving system comprising:
a receiving unit configured to receive a signal
transmitted via a channel so that the signal has a fixed
bandwidth in a predetermined frequency band;
5 a demodulation unit configured to demodulate the
received signal received by the receiving unit;
a signal processing unit configured to perform
signal processing for data demodulated by the
demodulation unit to obtain data to be transmitted; and
10 an output unit configured to output the-data to be
transmitted obtained by the signal processing unit,
wherein the demodulation unit includes a conversion
unit configured to convert the received signal to a
baseband signal in the case where a first frequency
15 differs from a second frequency, the first frequency is a
center frequency in a band of the received signal, the
second frequency is a center frequency 'in a band of a
desired signal included in a part of the band of the
received signal, and a DC component of the baseband
2 0 signal is to be a frequency in the vicinity of the second
frequency.