DESCRIPTION
Technical Field
The present invention relates to a radio base station
apparatus and communication terminal apparatus used in
a. digital radio communication system.
Background Art
In recent years, attention has been drawn to an OFDM
(Orthogonal Frequency Division Multiplexing)
transmission system high in resistance to multipath
interference that is a main factor in deterioration of
transmission performance on transmission paths. OFDM
is such a system that multiplexes a large number of (a
few tens to hundreds) digital modulated signals with
frequencies orthogonal to each other at a signal interval.
One of communication methods using OFDM
transmission is disclosed in "Coded OFDM System using
Guard Interval Length Control" IEICE, General Conference,
B-5-92, 2001.
In this communication method, a base station
(described as an access point in the above document)
receives a known signal (preamble) transmitted from a
mobile apparatus (described as a mobile terminal in the
above document) and using the known signal, generates
a delay profile, while measuring Carrier to Noise ratio
(C/N ratio) . Using the delay profile and C/N ratio, the
base station determines an optimal guard interval, the
modulation level of M-ary modulation and coding rate of
FEC (Forward Error Correction) to transmit over the
downlink.
Since the communication method employs a TDMA/TDD
(Time Division Multiple Access/Time Division Duplex)
system as an access scheme, the reversibility is used
of transmission paths over the uplink (communication
terminal to base station) and downlink (base station to
communication terminal).
The communication method employs OFDM over both the
uplink and downlink . In OFDM, by increasing the duration
of a symbol, effects of delayed versions are decreased.
Accordingly, since the duration of a symbol is increased,
time resolution is insufficient, and it is thereby
impossible to measure a delay profile accurately. When
a guard interval is determined based on a delay profile
generated under such a condition that the time resolution
is insufficient, there is a risk that an unnecessary time
is also set as a guard interval and the spectral efficiency
deteriorates.
Disclosure of Invention
The present invention is carried out in view of the
foregoing, and it is an object of the present invention
to provide a radio base station apparatus and
communication terminal apparatus that generate delay
profiles with high accuracy to determine guard intervals
so as to ensure the transmission quality while improving
the spectral efficiency.
The inventor of the present invention focused on
that it is difficult to measure the delay profile using
OFDM signals, found out by using the fact that delay
profiles are not different between the uplink and downlink,
the delay profile is generated with high accuracy using
uplink DS/CDMA (Direct Sequence/Code Division Multiple
Access) signals, and determining a guard interval using
such a delay profile makes it possible to ensure the
transmission quality and to improve the spectral
efficiency, and reached the present invention.
In other words, the object of the present invention
is achieved by using OFDM signals or OFDM/CDMA signals
over the downlink and CDMA signals over the uplink,
generating delay profiles using the CDMA signals, and
determining guard intervals using the delay profiles.
Brief Description of the accompaying Drawings
FIG.1 is a diagram to explain communications between
a radio base station apparatus and communication terminal
apparatus of the present invention;
FIG.2 is a block diagram illustrating a
configuration of a radio base station apparatus according
to a first embodiment of the present invention;
FIG.3 is a block diagram illustrating a
configuration of a communication terminal apparatus
according to the first embodiment of the present
invention;
FIG.4 is a diagram showing frame formats of a
downlink signal and uplink signal;
FIG.5 is a diagram to explain a delay profile used
in selecting a guard interval;
FIG.6 is a block diagram illustrating a
configuration of a radio base station apparatus according
to a second embodiment of the present invention;
FIG.7 is a block diagram illustrating a
configuration of a communication terminal apparatus
according to the second embodiment of the present
invention;
FIG. 8 is a diagram illustrating a configuration of
a multiplexing section (time multiplexing) in the radio
base station apparatus illustrated in FIG.6;
FIG.9 is a diagram illustrating a configuration of
a multiplexing section (code multiplexing) in the radio
base station apparatus illustrated in FIG.6;
FIG.10 is a block diagram illustrating a
configuration of a radio base station apparatus according
to a third embodiment of the present invention; and
FIG.11 is a block diagram illustrating a
configuration of a communication terminal apparatus
according to the third embodiment of the present
invention.
Best Mode for Carrying Out the Invention
The present invention aims to ensure the
transmission quality while improving the spectral
efficiency, by using OFDM signals or OFDM/CDMA signals
over the downlink and CDMA signals over the uplink as
shown in FIG.l, generating delay profiles using the CDMA
signals, and determining guard intervals using the delay
profiles.
Embodiments of the present invention will be
described below with reference to accompanying drawings.
(First embodiment)
This embodiment explains a case that CDMA is used
as an access system over the uplink, and that a base station
generates delay profiles accurately to determine guard
intervals.
FIG.2 is a block diagram illustrating a
configuration of a radio base station apparatus
(hereinafter abbreviated as BS when necessary) according
to the first embodiment of the present invention.
An uplink signal transmitted from a communication
terminal apparatus (hereinafter referred to as MS when
necessary) is received in radio reception section 202
through antenna 201. Radio reception section 202
performs predetermined reception processing (such as,
for example, downconverting and A/D conversion) on the
uplink signal, and outputs the
radio-reception-processing processed signal to
despreading section 203.
Despreading section 203 performs despreading on the
radio-reception-processing processed signal with the
same spreading code as used inMS, and outputs the despread
signal to demodulation section 204 and delay profile
generating section 205. Demodulation section 204
demodulates the despread signal and outputs received
data .
Delay profile generating section 205 generates a
delay profile using the despread signal. The delay
profile is output to guard interval determining section
206. Using the delay profile , guard interval determining
section 206 determines a guard interval. Information
of the determined guard interval is output to Inverse
Fourier Transform section 208.
Transmission parameters such as the guard interval,
subcarrier frequency interval and the number of
subcarriers are inserted into a preamble portion of
transmission data. Accordingly, a frame of downlink
signal has a format as shown in FIG.4, and includes a
preamble portion and data portion. Transmission data
including the preamble is modulated in modulation section
207, and the modulated signal is output to Inverse Fourier
Transform section 208.
Inverse Fourier Transform section 208 performs on
the modulated signal OFDM processing (modulation) and
Inverse Fourier Trans form processing, for example, IDFT
(Inverse Discrete Fourier Transform) and IFFT (Inverse
Fast Fourier Transform), and outputs the I FT processed
signal to radio transmission section 209. Radio
transmission section 209 performs predetermined radio
transmission processing (such as, for example, D/A
conversion and upconverting) on the OFDM signal, and
transmits the resultant radio signal to MS as a downlink
signal through antenna 201.
FIG.3 is a block diagram illustrating a
configuration of MS according to the first embodiment
of the present invention.
A downlink signal transmitted from BS is received
in radio reception section 302 through antenna 301.
Radio reception section 302 performs predetermined
reception processing (such as, for example,
downconverting and A/D conversion) on the downlink signal,
and outputs the radio-reception-processing processed
signal to Fourier Transform section 303.
Fourier Transform section 303 performs on the
radio-reception-processing processed signal OFDM
processing (demodulation) and Fourier Transform
processing, for example, DFT (Discrete Fourier Transform)
and FFT (Fast Fourier Transform), and outputs the FT
processed signal to demodulation section 304.
Demodulation section 304 demodulates the FT processed
signal and outputs received data.
The demodulated signal is output to transmission
parameter extracting section 305. Transmission
parameter extracting section 305 extracts a preamble
portion from the demodulated signal, and recognizes
transmission parameters from the preamble portion. The
transmission parameters are output to Fourier Transform
section 303. Fourier Transform section 303 performs
Fourier Transform based on the transmission parameters
transmitted from BS.
Transmission data is modulated in modulation
section 306, and the modulated signal is output to
spreading section 307. Spreading section 307 performs
spreading on the modulated signal with a predetermined
spreading code, and outputs the spread signal to radio
transmission section 308. Radio transmission section
308 performs predetermined radio transmission processing
(such as, for example, D/A conversion and upconverting)
on the spread signal, and transmits the resultant radio
signal to BS as an uplink signal through antenna 301.
A case will be described below where BS and MS with
the above-mentioned configurations perform radio
communications according to the present invention.
MS as illustrated in FIG.3 modulates transmission
data, spreads the data in spreading section 307, and
transmits the spread signal (CDMA signal) to BS as an
uplink signal.
When receiving the uplink signal (CDMA signal), BS
despreads the CDMA signal in despreading section 203,
and generates a delay profile using the despread signal
in delay profile generating section 205.
At this point, since CDMA signals have higher time
resolution than OFDM signals, it is possible to generate
a delay profile with high accuracy. In other words, as
described above, in OFDM, the duration of a symbol is
increased to decrease effects of delayed version, which
becomes a factor in degrading the accuracy of delay profile
generation. Meanwhile, in CDMA, since processing is
performed for accurately detecting delayed versions to
combine, it is necessary to generate delay profiles with
accuracy for the processing. Further, since delayed
versions are combined instead of decreasing effects of
delayed versions, it is not necessary to increase the
duration of a symbol to decrease effects of delayed
versions, unlike OFDM. Therefore, CDMA signals have
higher time resolution than OFDM signals. As a result,
using CDMA signals is capable of generating delay profiles
with higher accuracy than using OFDM signals.
The delay profile generated in delay profile
generating section 205 is output to guard interval
determining section 206 and is used to determine a guard
interval. Specifically, the guard interval in OFDM is
set at a time interval to include delayed versions so
as to prevent the reception quality from deteriorating
due to the delayed versions. For example, as shown in
FIG. 5, a guard interval is set at a time interval including
a desired signal and a delayed signal.
Thus determined guard interval is output to Inverse
Fourier Transform section 208 as transmission parameter
information of OFDM. Information of subcarrier
frequency interval and of the number of subcarriers that
are of other transmission parameters is also output to
Inverse Fourier Transform section 208. These
transmission parameters (guard interval, subcarrier
frequency interval and the number of subcarriers) are
inserted into a preamble portion of transmission data
to broadcast MS.
As illustrated in FIG.4, the preamble portion
containing the transmission parameters is modulated as
transmission data as well as a data portion, and
subsequently undergoes Inverse Fourier Transform
processing to be an OFDM signal. At this point, the
Inverse Fourier Transform processing is performed based
on the transmission parameters (guard interval,
subcarrier frequency interval and the number of
subcarriers) in which the guard interval determined as
described above is reflected. The IFT processed OFDM
signal is transmitted to MS as a downlink signal.
When receiving the downlink signal, MS performs
Fourier Transform processing on the preamble portion of
the downlink signal to demodulate, and thus extracts
transmission parameters inserted into the preamble
portion. The transmission parameters (guard interval,
subcarrier frequency interval and the number of
sub carriers) are output to Fourier Transform section 3 03.
Fourier Transform section 303 performs Fourier
Transform processing on the data portion based on the
extracted transmission parameters. The FT processed
signal is demodulated in demodulation section 304, and
output as received data.
In this way, according to this embodiment, a CDMA
signal is used to generate an accurate delay profile,
and based on the delay profile a guard interval is
determined, whereby the need is eliminated of setting
a guard interval using an OFDM signal with insufficient
time resolution and it is thereby possible to set guard
intervals with high accuracy. It is thus possible to
ensure the transmission quality while preventing a
useless guard interval from being set and to improve the
spectral efficiency.
(Second embodiment)
This embodiment explains a case where a preamble
portion for delay profile generation is of a CDMA signal,
a data portion is of an OFDM signal, and both signals
are multiplexed to be transmitted.
FIG.6 is a block diagram illustrating a
configuration of BS according to the second embodiment
of the present invention.
An uplink signal transmitted from MS is received
in radio reception section 602 through antenna 601.
Radio reception section 602 performs predetermined
reception processing (such as, for example,
downconverting and A/D conversion) on the uplink signal,
and outputs the radio-reception-processing processed
signal to despreading section 603.
Despreading section 603 performs despreading on the
radio-reception-processing processed signal with the
same spreading code as used in MS, and outputs the despread
signal to demodulation section 604. Demodulation
section 604 demodulates the despread signal and outputs
received data.
The demodulated received data is output to guard
interval determining section 605. Guard interval
determining section 605 determines a guard interval using
information of delay profile transmitted in the uplink
signal. The determined guard interval information is
output to Inverse Fourier Transform section 607.
Transmission parameters such as the guard interval,
subcarrier frequency interval and the number of
subcarriers are inserted into a preamble portion of
transmission data. The preamble is modulated in
modulation section 606, and the modulated signal
(preamble portion) is output to spreading section 609.
Spreading section 60 9 performs spreading on the modulated
signal (preamble portion) , and outputs the spread signal
(CDMA signal) to multiplexing section 610.
Transmission data is modulated in modulation
section 606, and the modulated signal (data portion) is
output to Inverse Fourier Transform section 6 07. Inverse
Fourier Transform section 607 performs Inverse Fourier
Transform processing on the modulated signal (data
portion), and outputs the I FT processed signal (OFDM
signal) to multiplexing section 610.
Multiplexing section 610 multiplexes (time
multiplexing or code multiplexing) the OFDM signal from
Inverse Fourier Transform section 607 and the CDMA signal
from spreading section 609. Thus, multiplexing section
610 has either configuration for time multiplexing or
code multiplexing.
FIG.8 illustrates a configuration of multiplexing
section 610 for performing time multiplexing on the OFDM
signal and CDMA signal. Multiplexing section 610 as
illustrated in FIG. 8 has switch 6101 for switching between
outputs from Inverse Fourier Transform section 607 and
from spreading section 609 to output to radio transmission
section 611.
FIG.9 illustrates a configuration of multiplexing
section 610 for performing code multiplexing on the CFDM
signal and CDMA signal. In the case of performing code
multiplexing on OFDM and CDMA signals, an OFDM signal
needs to be an OFDM-CDMA signal. When chips of a spread
signal are mapped onto OFDM to obtain the OFDM-CDMA signal,
there is used a time-axis spreading method,
frequency-axis spreading method or two-dimensional
spreading method including time axis and frequency axis .
In FIG.9, the modulated signal is subjected to
spreading and subsequently to Inverse Fourier Transform,
and is output to multiplexing section 610. Inother words,
in FIG.9, spreading section 6102 is provided before
Inverse Fourier Transform section 607, and multiplexing
section 610 has adder 6103 that adds an output from Inverse
Fourier Transform section 607 and an output from spreading
section 60 9.
The multiplexed signal is output to radio
transmission section 611. Radio transmission section
611 performs predetermined radio transmission processing
(such as, for example, D/A conversion and upconverting)
on the multiplexed signal, and transmits the resultant
radio signal to MS as a downlink signal through antenna
601 .
FIG.7 is a block diagram illustrating a
configuration of MS according to the second embodiment
of the present invention.
A downlink signal transmitted from BS is received
in radio reception section 702 through antenna 701.
Radio reception section 702 performs predetermined
reception processing (such as, for example,
downconverting and A/D conversion) on the downlink signal,
and outputs the radio-reception-processing processed
signal to Fourier Transform section 703 and despreading
section 706.
Fourier Transform section 703 performs Fourier
Transform processing on the radio-reception-processing
processed signal, and outputs the FT processed signal
to demodulation section 704. Demodulation section 704
demodulates the FT processed signal and outputs received
data .
Despreading section 706 performs despreading on the
radio-reception-processing processed signal with the
same spreading code as used in BS, and outputs the despread
signal to demodulation section 704 and delay profile
generating section 707. Demodulation section 704
demodulates the despread signal, and outputs the
demodulated signal to transmission parameter extracting
section 7 05.
Transmission parameter extracting section 705
extracts a preamble portion from the demodulated signal,
and recognizes transmission parameters from the preamble
portion. The transmission parameters are output to
Fourier Transform section 703. Fourier Transform
section 703 performs Fourier Transform based on the
transmission parameters transmitted from BS .
Delay profile generating section 707 generates a
delay profile using the despread signal. The delay
profile is output to modulation section 708.
Transmission data and the delay profile are modulated
in modulation section 708, and the modulated signal is
output to spreading section 709. Spreading section 709
performs spreading on the modulated signal with a
predetermined spreading code, and outputs the spread
signal to radio transmission section 710. Radio
transmission section 710 performs predetermined radio
transmission processing (such as, for example, D/A
conversion and upconverting) on the spread signal, and
transmits the resultant radio signal to BS as an uplink
signal through antenna 701.
A case will be described below where BS and MS with
the above-mentioned configurations perform radio
communications according to the present invention.
BS as illustrated in FIG.6 modulates the preamble,
spreads the resultant in spreading section 609, and
outputs the spread signal (CDMA signal) to multiplexing
section 610. Multiplexing section 610 multiplexes the
CDMA signal and OFDM signal, and transmits the multiplexed
signal to MS as a downlink signal. The multiplexing of
OFDM and CDMA signals will be described later.
When receiving the downlink signal (multiplexed
signal), MS as illustrated in FIG.7 despreads the CDMA
signal of the preamble portion in despreading section
706, and generates a delay profile using the despread
signal in delay profile generating section 707. The
delay profile is generated using the CDMA signal with
high time resolution, and, therefore, is generated with
high accuracy. The information of the delay profile is
output to modulation section 708.
MS modulates transmission data and the information
of delay profile in modulation section 708, spreads the
resultant in spreading section 709, and transmits the
spread signal (CDMA signal) to BS as an uplink signal.
When receiving the uplink signal (CDMA signal), BS
despreads the CDMA signal in despreading section 603,
and demodulates the despread signal in demodulation
section 60 4.
The information of delay profile, contained in the
uplink signal, obtained by demodulation is output to guard
interval determining section 605.
As in the first embodiment, guard interval
determining section 605 determines a guard interval using
the delay profile. Thus determined guard interval is
output to Inverse Fourier Transform section 607 as
transmission parameter information of OFDM.
Information of subcarrier frequency interval and of the
number of subcarriers that are of other transmission
parameters is also output to Inverse Fourier Transform
section 607. These transmission parameters (guard
interval, subcarrier frequency interval and the number
of subcarriers) are inserted into a preamble portion of
transmission data to broadcast MS.
A data portion is modulated in modulation section
608, and subsequently is subjected to Inverse Fourier
Transform to be an OFDM signal . At thispoint, the Inverse
Fourier Transform processing is performed based on the
transmission parameters (guard interval, subcarrier
frequency interval and the number of subcarr ier s ) in which
the guard interval determined as described above is
reflected. The IFT processed OFDM signal is output to
multiplexing section 610. The preamble portion is
modulated in modulation section 608, subsequently
subjected to spreading in spreading section 609, and
output to multiplexing section 610 as a CDMA signal.
As illustrated in FIG.8, multiplexing section 610
switches between an output (OFDM signal) from Inverse
Fourier Transform section 607 and an output (CDMA signal)
from spreading section 609 by switch 6101 to output to
radio transmission section 611. In this way, the OFDM
signal (data portion) and CDMA signal (preamble portion)
are subjected to time multiplexing and output to radio
transmission section 611.
Meanwhile, in the case of performing code
multiplexing on the OFDM signal and CDMA signal, as
illustrated in FIG.9, the data portion is modulated in
modulation section 608, spread in spreading section 6102,
and undergoes Inverse Fourier Transform processing in
Inverse Fourier Transform section 607 tobean OFDM signal.
At this point, the Inverse Fourier Transform processing
is performed based on the transmission parameters (guard
interval, subcarrier frequency interval and the number
of subcarriers) in which the guard interval determined
as described above is reflected. The IFT processed OFDM
signal is output to multiplexing section 610. The
preamble portion is modulated in modulation section 608,
subsequently subjected to spreading in spreading section
609, and output to multiplexing section 610 as a CDMA
signal.
Multiplexing section 610 adds an output (OFDM/CDMA
signal) from Inverse Fourier Transform section 607 and
an output (CDMA signal) from spreading section 609 in
adder 6103 to output to radio transmission section 611.
Inthisway, the OFDM signal (data port ion) and CDMA signal
(preamble portion) are subjected to code multiplexing
and output to radio transmission section 611. In
addition, in this case, a spreading code used in spreading
section 6102 needs to differ from a spreading code used
in spreading section 609.
The signal multiplexed in multiplexing section 610,
i.e., OFDM signal or OFDM/CDMA signal (data portion) and
CDMA signal (Preamble portion) is transmitted to MS as
a downlink signal.
When receiving the downlink signal, MS performs
despreading on the preamble portion of the downlink signal
to demodulate, and thus extracts transmission parameters
inserted into the preamble portion. The transmission
parameters (guard interval, subcarrier frequency
interval and the number of subcarriers) are output to
Fourier Transform section 703.
Fourier Transform section 703 performs Fourier
Transform processing on the data portion based on the
extracted transmission parameters. The FT processed
signal is demodulated in demodulation section 704, and
output as received data. In addition, in the case of
OFDM/CDMA signal subjected to code multiplexing, the
signal is subjected to Fourier Trans form processing, then
to despreading, and is obtained as received data.
Thus, according to this embodiment, a data portion
is transformed into an OFDM signal, a preamble portion
is transformed into a CDMA signal, both signals are
multiplexed (time multiplexing and code multiplexing)
and transmitted over the downlink signal, MS generates
a delay profile and transmits the delay profile over the
uplink, and BS determines a guard interval using the delay
profile.
Also in such a case, the need is eliminated of setting
a guard interval using an OFDM signal with insufficient
time resolution and it is thereby possible to set guard
intervals with high accuracy. It is thus possible to
ensure the transmission quality while preventing a
useless guard interval from being set and to improve the
spectral efficiency.
(Third embodiment)
This embodiment explains a case of determining OFDM
transmission parameters (guard interval, subcarrier
frequency interval and the number of subcarriers),
modulation scheme and coding rate of FEC using information
such as received quality, Doppler shift and delay profile
in MS .
FIG.10 is a block diagram illustrating a
configuration of BS according to the third embodiment
of the present invention.
An uplink signal transmitted from MS is received
in radio reception section 1002 through antenna 1001.
Radio reception section 1002 performs predetermined
reception processing (such as, for example,
downconverting and A/D conversion) on the uplink signal,
and outputs the radio-reception-processing processed
signal to despreading section 1003.
Despreading section 1003 performs despreading on
the radio-reception-processing processed signal with the
same spreading code as used inMS, and outputs the despread
signal to demodulation section 1004, delay profile
generating section 1005 and Doppler frequency measuring
section 1007 . Demodulation section 1004 demodulates the
despread signal and outputs received data. The received
quality information of the downlink of the demodulated
signal is output to modulation scheme/coding rate
selecting section 1009.
Delay profile generating section 1005 generates a
delay profile using the despread signal. The delay
profile is output to guard interval determining section
1006. Using the delay profile, guard interval
determining section 1006 determines a guard interval.
Information of the determined guard interval is output
to Inverse Fourier Transform section 1012 and modulation
scheme/coding rate selecting section 1009.
Doppler frequency measuring section 1007 measures
the Doppler frequency using the despread signal, and
outputs the measurement result (Doppler shift) to carrier
interval selecting section 1008. Carrier interval
selecting section 1008 selects the carrier interval based
on the measurement result of Doppler frequency. The
selected carrier interval is output to Inverse Fourier
Transform section 1008 and modulation scheme/coding rate
selecting section 1009.
Modulation scheme/coding rate selecting section
1009 selects a modulation scheme (for example, the
modulation level of M-ary modulation) based on the
transmission parameters such as the guard interval and
carrier interval. The information of the selected
modulation scheme is output to modulation section 1011.
The selected coding rate is output to coding section 1010.
Transmission parameters such as the guard interval,
subcarrier frequency interval and the number of
subcarriers are inserted into a preamble portion of
transmission data . The information of modulation scheme
and coding rate is also inserted into the preamble. The
transmission data containing the preamble is coded in
coding section 1010 with the coding rate selected as
described above, and is output to modulation section 1011 .
Modulation section 1011 modulates the coded transmission
data, and outputs the modulated signal to Inverse Fourier
Transform section 1012.
Inverse Fourier Transform section 1012 performs
Inverse Fourier Transform processing on the modulated
signal, and outputs the IFT processed signal (OFDM signal)
to radio transmission section 1013. Radio transmission
section 1013 performs predetermined radio transmission
processing (such as, for example, D/A conversion and
upconverting) on the OFDM signal, and transmits the
resultant radio signal to MS as a downlink signal through
antenna 1001.
FIG.11 is a block diagram illustrating a
configuration of MS according to the third embodiment
of the present invention.
A downlink signal transmitted from BS is received
in radio reception section 1102 through antenna 1101.
Radio reception section 1102 performs predetermined
reception processing (such as, for example,
downconverting and A/D conversion) on the downlink signal,
and outputs the radio-reception-processing processed
signal to Fourier Transform section 1103.
Fourier Transform section 1103 performs Fourier
Transform processing on the radio-reception-processing
processed signal, and outputs the FT processed signal
to demodulation section 1104 and received quality
measuring section 1111. Demodulation section 11C4
demodulates the FT processed signal and outputs the
demodulated signal to decoding section 1107. Decoding
section 1107 decodes the demodulated signal and outputs
received data.
The demodulated signal is output to transmission
parameter extracting section 1105 and modulation
scheme/coding rate extracting section 1106.
Transmission parameter extracting section 1105 extracts
a preamble portion from the demodulated signal, and
recognizes transmission parameters from the preamble
portion. The transmission parameters are output: to
Fourier Transform section 1103. Fourier Transform
section 1103 performs Fourier Transform based on the
transmission parameters transmitted from BS .
Modulation scheme/coding rate extracting section
1106 recognizes information of the modulation scheme and
coding rate from the preamble portion. The information
of the modulation scheme is output to demodulation section
1104, while the information of the coding rate is output
to decoding section 1107. Demodulation section 1104
performs demodulation based on the information of the
modulation scheme transmitted from BS . Decoding section
1107 performs decoding based on the information of the
coding rate transmitted from BS .
Received quality measuring section 1111 measures
C/I that is the received quality using the FT processed
signal, and outputs the measurement result to modulation
section 1108. The measurement result and transmission
data is modulated in modulation section 1108, and the
modulated signal is output to spreading section 1109.
Spreading section 1109 performs spreading on the
modulated signal with a predetermined spreading code,
and outputs the spread signal to radio transmission
section 1110. Radio transmission section 1110 performs
predetermined radio transmission processing (such as,
for example, D/A conversion and upconverting) on the
spread signal, and transmits the resultant radio signal
to BS as an uplink signal through antenna 1101.
A case will be described below where BS and MS with
the above-mentioned configurations perform radio
communications according to the present invention.
MS as illustrated in FIG.11 measures the received
quality of a preamble portion of a downlink signal in
received quality measuring section 1111. Then, MS
modulates the measurement result of the received quality
and transmission data, spreads the modulated signal in
spreading section 1108, and transmits the spread signal
(CDMA signal) to BS as an uplink signal.
When receiving the uplink signal (CDMA signal), BS
despreads the CDMA signal in despreading section 1003,
and generates a delay profile using the despread signal
in delay profile generating section 1005. The delay
profile is generated using the CDMA signal with high time
resolution, and, therefore, is generated with high
accuracy. Further, using the despread signal, Doppler
frequency measuring section 1007 measures the Doppler
frequency.
The delay profile generated in delay profile
generating section 1005 is output to guard interval
determining section 1006. Guard interval determining
section 1006 determines a guard interval as in the first
embodiment. The guard interval is output to Inverse
Fourier Transform section 1012 as the transmission
parameter information of OFDM, and also to modulation
scheme/coding rate selecting section 1009.
The Doppler frequency (Doppler shift) measured in
Doppler frequency measuring section 1007 is output to
carrier interval selecting section 1008. Carrier
interval selecting section 1008 selects the subcarrier
interval based on the Doppler frequency. Further,
carrier interval selecting section 1008 determines the
number of subcarriers from a bandwidth used in radio
communications and the subcarrier interval. The
subcarrier interval and the number of subcarriers are
output to Inverse Fourier Transform section 1012 as the
transmission parameter information of OFDM, and also to
modulation scheme/coding rate selecting section 1009.
Modulation scheme/coding rate selecting section
1009 obtains the modulation scheme and coding rate from
the guard interval, subcarrier interval, the number of
subcarriers, and further the Doppler frequency and
received quality of downlink. Specifically, the section
1009 determines the number of symbols transmitted in a
single burst from the subcarrier interval, the number
of subcarriers (subcarrierparameter) and guard interval,
and based on the number of symbols and the Doppler
frequency, further determines the optimal coding rate.
For example, since the higher Doppler frequency better
randomizes portions with poor quality of the received
data at a single burst and thus provides higher error
correcting capability, the coding rate is set to
relatively high when the Doppler frequency is high.
Meanwhile, when the Doppler frequency is low, the received
signal strength sometimes decreases over the entire
received burst, resulting in low error correcting
capability, and therefore, the coding rate is set to
relatively low. In addition, the optimal coding rate
is predetermined by simulation. Further, the section
1109 determines the modulation scheme (the modulation
level of M-ary modulation) from the received quality of
the downlink measured in MS and the coding rate.
The information of the guard interval, subcarrier
frequency interval and the number of subcarriers that
are of transmission parameters and also the information
of the modulation scheme and coding rate is inserted into
a preamble portion of transmission data to broadcast MS.
As illustrated in FIG.4, the preamble portion
containing the transmission parameters is coded as
transmission data as well as a data portion, modulated
and subsequently undergoes Inverse Fourier Transform
processing to be an OFDM signal . At this point, the coding
is performed with the coding rate selected as described
above, and the modulation is performed with the modulation
scheme selected as described above . Further, the Inverse
Fourier Transform processing is performed based on the
transmission parameters (guard interval, subcarrier
frequency interval and the number of subcarriers) in which
the guard interval determined as described above is
reflected. The IFT processed OFDM signal is transmitted
to MS as a downlink signal.
When receiving the downlink signal, MS performs
Fourier Transform processing on the preamble portion of
the downlink signal to demodulate, and thus extracts
transmission parameters and the information of the
modulation scheme and coding rate inserted into the
preamble portion. The transmission parameters (guard
interval, subcarrier frequency interval and the number
of subcarriers) are output to Fourier Transform section
1103 . The information of the modulation scheme is output
to demodulation section 1104, while the information of
the coding rate is output to decoding section 1107.
Fourier Transform section 1103 performs Fourier
Transform processing on the data portion based on the
extracted transmission parameters. The FT processed
signal is output to demodulation section 1104, and therein
demodulated based on the information of the extracted
modulation scheme. The demodulated signal is output to
decoding section 1107 and therein decoded based on the
information of the extracted coding rate, and thus the
received data is output.
In this way, according to this embodiment, a CDMA
signal is used to generate an accurate delay profile,
and based on the delay profile a guard interval is
determined, whereby the need is eliminated of setting
a guard interval using an OFDM signal with insufficient
time resolution and it is thereby possible to set guard
intervals with high accuracy. It is thus possible to
ensure the transmission quality while preventing a
useless guard interval from being set and to improve the
spectral efficiency.
Further, according to this embodiment, it is
possible to vary the modulation scheme and coding rate
adaptively corresponding to the propagation path
condition, and to flexibly response to the propagation
environment to perform radio communications.
In addition, while this embodiment describes using
C/I as the received quality, the present invention is
applicable to cases of using received quality parameters
(such as SIR (Signal to Interference Ratio) and received
power) besides C/I as the received quality.
Further, while this embodiment describes the case
where BS generates a delay pro file and measures the Doppler
frequency, the present invention allows MS to generate
a delay profile, measure the Doppler frequency, and report
the delay profile and Doppler frequency to BS.
(Fourth embodiment)
The third embodiment explains determining the
optimal guard interval, carrier frequency interval and
the number of carriers for each user, in consideration
of the fact that the delay profile and Doppler frequency
are different for each user.
Over the downlink, signals for each user can be
subjected to code multiplexing using OFDM/CDMA signals.
In other words, over the downlink, it is possible to
perform code multiplexing on information to users having
the same transmission parameters (guard interval, the
number of subcarriers and subcarrier interval) to
transmit. However, it is not possible to perform code
multiplexing on information with different transmission
parameters.
In this embodiment, transmission parameters (guard
interval, the number of subcarriers and subcarrier
interval) are set for each user. Then, in performing
code multiplexing on signals for each user to transmit
in a time slot, when there is a remaining code resource,
different transmission parameters are adapted to
transmission parameters being transmitted currently to
perform transmission.
Specifically, in a time slot for multiplexing data
to users (a, b and c) with a delay time of a delayed signal
of X, data of user d with a delay time of y (x>y) can
be multiplexed . In this case, data of user d has a shorter
guard interval than that of users a, b and c and therefore,
can be transmitted at a high data rate, but is multiplexed
and transmitted even though the transmission parameters
are not optimal, in other words, the guard interval of
user d is changed to the guard interval of users a to
c to transmit the data of user d.
In this way, it is possible to improve the using
rate of code resource per one slot and to improve the
system throughput.
The present invention is not limited to the
above-mentioned first to fourth embodiments, and is
capable of being carried into practice with various
modifications thereof. For example, the
above-mentioned first to fourth embodiments are capable
of being carried out in a combination thereof as
appropriate.
As described above, according to the present
invention, OFDM signals or OFDM/CDMA signals are used
over the downlink, CDMA signals are used over the uplink,
delay profiles are generated using the CDMA signals, and
guard intervals are determined using the delay profiles
with high time resolution, whereby it is possible to ensure
the transmission quality while improving the spectral
efficiency.
This application is based on the Japanese Patent
Application No.2001-146576 filed on May 16, 2001, entire
content of which is expressly incorporated by reference
herein.
Industrial Applicability
The present invention is suitable for use in digital
radio communication systems.
WE CLAIM
1. A radio base station apparatus comprising:
a despreading section (203) that performs despreading on a spread
uplink signal to output a despread signal;
a delay profile generating section (205) that generates a delay profile
using the despread signal;
a guard interval determining section (206) that determines a guard
interval length in OFDM using the delay profile; and
an OFDM section (303,304) that performs OFDM processing on a known
signal and transmission data, using OFDM transmission parameters which
comprises the guard interval of the guard interval length and which is
inserted into the known signal.
2. A radio base station apparatus comprising:
a guard interval determining section that determines a guard interval
length in OFDM using information of delay profile contained in a spread
uplink signal;
an OFDM section that performs OFDM processing on transmission data
using the guard interval of the guard interval length;
a spreading section that performs spreading on a known signal for use by
a communication terminal apparatus to generate the delay profile; and
a multiplexing section that multiplexes the transmission data subjected to
the OFDM processing and the known signal subjected to the spreading.
3. The radio base station apparatus as claimed in claim 2, wherein the
multiplexing section performs time multiplexing on the transmission data
subjected to the OFDM processing and the known signal subjected to the
spreading.
4. The radio base station apparatus as claimed in claim 2, comprising:
a spreading section that performs spreading on the transmission data
prior to the OFDM processing,
wherein the multiplexing section performs code multiplexing on the
transmission data subjected to the OFDM processing and the known signal
subjected to the spreading.
5. A base station apparatus comprising:
a despreading section that performs despreading on a spread uplink signal
to output a despread signal;
a delay profile generating section that generates a delay profile using the
despread signal;
a guard interval determining section that determines a guard interval
length in OFDM using the delay profile;
a Doppler frequency measuring section that measures a Doppler
frequency using the despread signal;
a transmission parameter determining section that determines a
subcarrier parameter using a measurement result of the Doppler
frequency;
a modulation scheme/coding rate determining section that determines a
modulation scheme and a coding rate using OFDM transmission
parameters comprising the guard interval of the guard interval length and
the subcarrier parameter, the delay profile, the Doppler frequency and
downlink received quality contained in the uplink signal; and
an OFDM section that performs OFDM processing on transmission data
and a known signal into which the OFDM transmission parameters, the
modulation scheme and the coding rate are inserted.
6. A communication terminal apparatus comprising :
a transmission parameter extracting section that extracts the OFDM
transmission parameters from the known signal transmitted from the radio
base station apparatus as claimed in claim 1;
an OFDM section that performs OFDM processing on a received signal
using the OFDM transmission parameters; and
a spreading section that performs spreading transmission data.
7. A communication terminal apparatus comprising:
a despreading section that performs despreading on the known signal of a
spread downlink signal transmitted from the radio base station apparatus
as claimed in claim 2 to output a despread signal;
a delay profile generating section that generates a delay profile using the
despread signal;
a transmission parameter extracting section that extracts OFDM
transmission parameters from the despread signal;
an OFDM section that performs OFDM processing on a received signal
using the OFDM transmission parameters; and
a spreading section that performs spreading on information of the delay
profile and transmission data.
8. A communication terminal apparatus comprising:
a transmission parameter extracting section that extracts OFDM
transmission parameters from the known signal transmitted from the radio
base station apparatus as claimed in claim 3;
a modulation scheme/coding rate extracting section that extracts a
modulation scheme and a coding rate from the known signal;
an OFDM section that perform OFDM processing on a received signal
using the OFDM transmission parameters;
a demodulation section that demodulates a received signal based on the
modulation scheme;
a decosing section that decodes the demodulated signal based on the
coding rate;
a receiving quality measuring section that measures received quality using
the received signal; and
a spreading section that performs spreading on a measurement result of
the received quality and transmission data.
9. A radio communication method comprising :
in a radio base station apparatus,
a despreading step of performing despreading on a spread uplink signal to
output a despread signal;
a delay profile generating step of generating a delay profile using the
despread sigtnal;
a guard interval determining step of determining a guard interval length in
OFDM using the delay profile;
a first OFDM processing step of performing OFDM processing on a known
signal and transmission data, using OFDM transmission parameters which
comprises the guard interval of the guard interval of the guard interval
length and which is inserted into the known signal; and
a transmitting step of transmitting a signal subjected to the OFDM
processing to a communication terminal apparatus as a downlink signal,
and
in the communication terminal apparatus,
a transmission parameter extracting step of extracting the OFDM
transmission parameters from the known signal; and
a second OFDM processing step of performing OFDM processing on a
received signal using the OFDM transmission parameters.
10.A radio communication method comprising:
in a communication terminal apparatus,
a despreading step of performing despreading on a known signal of
a spread downlink signal to output a despread signal;
a delay profile generating step of generating a delay profile using the
despread signal; and
a first transmitting step of performing spreading on information of the
delay profile and transmitting the information in an uplink signal to a radio
base station apparatus, and
in the base station apparatus,
a guard interval determining step of determining a guard interval length in
OFDM using the information of the delay profile;
a multiplexing step of performing OFDM processing on transmission data
using OFDM transmission parameters comprising the guard interval of the
guard interval length, further performing spreading on the known signal
comprising the OFDM transmission parameters, and multiplexing an OFDM
signal subjected to the OFDM processing and a CDMA signal subjected to
the spreading;
a second transmitting step of transmitting the multiplexed signal to the
communication terminal apparatus as a downlink signal;
a transmission parameter extracting step of extracting the OFDM
transmission parameters from the multiplexed signal of the downlink
signal; and
an OFDM processing step of performing OFDM processing on a received
signal using the OFDM transmission parameters.
11. A radio communication method comprising :
in a base station apparatus,
a despreading step of performing despreading on a spread uplink signal to
output a despread signal;
a delay profile generating step of generating a delay profile using the
despread signal;
a guard interval determining step of determining a guard interval length in
OFDM using the delay profile;
a Doppler frequency measuring step of measuring a Doppler frequency
using the despread signal;
a transmission parameter determining step of determining a subcarrier
parameter using a measuring result of the Doppler frequency;
a modulation scheme/coding rate determining step of determining a
modulation scheme and coding rate using OFDM transmission parameters
comprising the guard interval of the guard interval length and the
subcarrier parameter, the delay profile, the Doppler frequency and
downlink received quality contained in the uplink signal;
a first OFDM processing step of performing OFDM processing on
transmission data and a known signal into which the OFDM transmission
parameters, the modulation scheme and the coding rate are inserted; and
a transmitting step of transmitting a signal subjected to the OFDM
processing to a communication terminal apparatus as a downlink signal,
and
in the communication terminal apparatus,
a transmission parameter extracting step of extracting the OFDM
transmission parameters from the known signal;
a modulation scheme/coding rate extracting step of extracting the
modulation scheme and the coding rate from the known signal;
a second OFDM processing step of performing OFDM processing on a
received signal using the OFDM transmission parameters;
a demodulation step of demodulating a received signal based on the
modulation scheme;
a decoding step of decoding the demodulated signal based on the coding
rate; and
a received quality measuring step of measuring received quality using the
received signal.
12. A radio communication method as claimed in any one of claims 9 to 11,
wherein when there is an available code resource in transmission path
parameter of downlink, the base station apparatus performs code
multiplexing on respective signals to communication terminal apparatus
while adapting the OFDM transmission parameters to transmit as a
downlink signal.

This invention relates to a radio base station apparatus comprising; a dispreading
section (203) that performs dispreading on a spread uplink signal to output a
despread signal; a delay profile generating section (205) that generates a delay
profile using the despread signal; a guard interval determining section (206) that
determines a guard interval length in OFDM using the delay profile; and an
OFDM section (303,304) that performs OFDM processing on a known signal and
transmission data, using OFDM transmission parameters which comprises the
guard interval of the guard interval length and which is inserted into the known
signal.