Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-01-20
2004-04-27
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C370S210000
Reexamination Certificate
active
06726297
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an OFDMA (Orthogonal Frequency Division Multiple Access) signal transmission apparatus and its method.
BACKGROUND ART
In mobile communications, overcoming multipath fading and improving transmission quality have been conventionally present as problems to be solved. In connection with the multipath fading, there is a ii multi-carrier transmission as one of measures to transmit data with a good quality without lowering a symbol rate.
OFDM (Orthogonal Frequency Division Multiplexing) is one of multi-carrier transmission systems, that is, one that sets a distance between adjacent sub-carriers to 1/symbol rate to allow the distance between the sub-carriers to be narrowed at the maximum.
Also, OFDMA is a system in which a plurality of users performs multiple access using OFDM. In the conventional OFDMA data transmission apparatus, there is proposed a method in which frequency division and time division are carried out when multiple access is performed. Also, it has been considered that diversity is carried out in a frequency direction and a time direction to make it possible to improve an error correction capability.
FIG. 1
is a block diagram showing the configuration of a transmission section in the conventional OFDMA signal transmission apparatus.
FIG. 2
is a block diagram showing the configuration of a reception section in the conventional OFDMA signal transmission apparatus.
A transmission section
10
shown in
FIG. 1
mainly comprises S/P (Serial/Parallel) converter
11
, IFFT (Inverse Fast Fourier Transform) apparatus
12
, P/S (Parallel/Serial) converter
13
, a D/A (Digital/Analog) converter and orthogonal modulator
14
, a transmission amplifier
15
, and a transmission antenna
16
.
A reception section
60
shown in
FIG. 2
mainly comprises reception antenna
61
, quasi-coherent detector and A/D (Analog/Digital) converter
62
, S/P converter
63
, FFT (Fast Fourier Transform) apparatus
64
, and P/S converter
65
.
An explanation will be given of the operation of the conventional OFDM transmission and reception in the OFDMA signal transmission apparatus having the above-configured transmission section
10
and reception section
60
. In this case, it is assumed that transmission section
10
and reception section
60
are provided in the base station of the mobile communication system (not shown) and the mobile station.
First, an explanation will be given of the operation, which is performed when forward signals are transmitted to the mobile station from the base station. In the case of the forward OFDMA, the base station performs the same operation as the case in which the sub-carriers are present in all bands of OFDM no matter how the sub-carrier is assigned to each mobile station.
Transmission data shown in
FIG. 1
is data with respect to each mobile station, and transmission data is input to S/P converter
11
simultaneously, and converted in parallel. If the number of sub-carriers is N, N complex number values are set after conversion.
Here, 0 is placed at extra sub-carriers. The result is changed to time-waveform by performing Fourier transform of sub-carriers N by IFFT apparatus
12
. Then, time series of sub-carriers N are arranged in order of time by P/S converter
13
. Then, the result is converted to analog waveform, and orthogonally modulated by D/A converter and orthogonal modulator
14
, thereafter converting the analog waveform to high frequency. Then, the resultant signals are amplified by transmission amplifier
15
, and the amplified signals are emitted from transmission antenna
16
.
On the other hand, in the mobile station, the emitted signals are received by the reception antenna
61
shown in FIG.
2
and the received signals are demodulated by quasi-coherent detector and A/D converter
62
, thereafter converting the demodulated signals to digital values by S/P converter
63
. Then, the converted signals are converted to parallel signals every N sample, thereafter the parallel signals are Fourier transformed to signals on a frequency axis by FFT apparatus
64
. Moreover, the converted signals are converted to serial signals by P/S converter
65
so as to obtain received data.
Thus, since all sub-carriers are completely orthogonal to the forward signals, signals can be transmitted in a state that interference between the respective signals little occurs.
Next, an explanation will be given of the operation, which is performed when reverse signals are transmitted to the base station from the mobile station. In the case of the reverse OFDMA, as a method of multiple access, there are a method in which the sub-carriers are divided and a method in which time division is carried out using sub-carriers, or a method, which mixes the above two methods.
In the case of the method in which time division is carried out using all sub-carriers, the same operation as that of the case of forward signals is used, and only ON/OFF of transmission is added thereto.
The method in which the sub-carriers are divided will be explained. A certain mobile station is assumed. The mobile station converts transmission data to parallel data using S/P converter
11
. If the number of sub-carriers assigned to the mobile station is N, N complex number values are set after conversion.
Data is changed to time-waveform by performing Fourier transform of sub-carriers N by IFFT apparatus
12
. Then, time series of sub-carriers N are arranged in order of time by P/S converter
13
. Then, data is converted to analog waveform, and orthogonally modulated by D/A converter and orthogonal modulator
14
, thereafter converting the analog waveform to high frequency. Then, the resultant signals are amplified by transmission amplifier
15
, and the amplified signals are emitted from transmission antenna
16
.
The base station receives signals each having a different sub-carrier from a plurality of mobile stations. Synthetic signals of signals emitted from the plurality of mobile stations are received through the reception antenna
61
, and the received signals are demodulated by quasi-coherent detector and A/D converter
62
, thereafter converting the demodulated signals to digital values. Then, the converted signals are converted to parallel signals every N sample by S/P converter
63
, thereafter the parallel signals are Fourier transformed to signals on a frequency axis by FFT apparatus
64
. Moreover, the converted signals are converted to serial signals by P/S converter
65
so as to obtain received data.
In the reverse signals, if frequency offset is present every mobile station and maximum Doppler frequency is different, all sub-carriers are not completely orthogonal to the reverse signals. However, if these influences, which are exerted upon the symbol rate, are small, signals can be transmitted in a state that interference between the respective signals little occurs.
However, in the conventional OFDMA signal transmission apparatus, the following problems are present.
First, in the case of receiving the forward signals, since the sub-carriers can be separated only after FFT has been carried out, not only the sub-carriers assigned to the station but also the sub-carriers of all OFDM bands must be demodulated in the mobile station. For this reason, even if a traffic volume is low, the number of A/D converters and that of FFT apparatuses, which are the same as that of sub-carriers, must be provided. This increases in the circuit scale and power consumption.
Also, since the signals of all OFDM users (all mobile stations) are synthesized and the synthesized signals are amplified by the transmission amplifier in the base station, the dynamic range is large and it is difficult to restrain nonlinear distortion.
Moreover, since AFC (Automatic Frequency Control) is provided to only all OFDMA bands in the base station, deterioration in the quality of signals increases when the frequency offset differs depending on each mobile station or the maximum Doppler frequency is large.
DISCLOSURE OF INVENTION
A first object of the present invention is to provi
Burd Kevin M
Ghebretinsae Temesghen
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
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