Multiplex communications – Generalized orthogonal or special mathematical techniques
Reexamination Certificate
2001-10-31
2004-06-08
Qureshi, Afsar (Department: 2667)
Multiplex communications
Generalized orthogonal or special mathematical techniques
C370S210000, C370S481000, C375S260000, C375S265000
Reexamination Certificate
active
06747945
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an OFDM transmitting and receiving apparatus and its method for use in communication equipment of a digital radio communication system using OFDM.
BACKGROUND ART
In recent years, in digital radio communication system, the use of OFDM (Orthogonal Frequency Division Multiplexing), which is strong against noise and multipath interference, has been considered.
The following will explain signal processing of a conventional OFDM transmitting and receiving apparatus with reference to the drawings.
FIG. 1
is a block diagram showing the configuration of the conventional OFDM transmitting and receiving apparatus. It is assumed that the number of subcarriers is four in FIG.
1
.
First, in a transmitting side, transmitting signals that have been primary modulated (MOD-S) are parallel-converted to the number of subcarriers, that is, four subcarriers A to D by an S/P (Serial-Parallel) converter
11
.
Transmitting signals of the respective subcarries A to D are mapped by mapping circuits
12
to
15
, the mapped signals are subjected to inverse fast Fourier transform by an IFFT circuit
16
, and they are converted to analog signals by a D/A (Digital/Analog) converter
17
. Then, the resultant signals (TR-S) are amplified; thereafter they are radio transmitted from a transmission antenna (not shown).
In addition, in a receiving side, signals (RE-S) received by a reception antenna (not shown) are converted to digital signals by an A/D (Analog/Digital) converter
51
, and the converted digital signals are subjected to inverse fast Fourier transform by an FFT (Fast Fourier Transform) circuit
52
.
The received signals of subcarriers A to D output from FFT circuits
52
are subjected to detection processing by detectors
53
to
56
, respectively, and the resultant signals are demodulated by binary determination of determining units
57
to
60
, and the modulated signals are converted to signals (DEM-S) of one channel by a P/S (Parallel-Serial) converter
61
.
FIGS. 2A and 2B
are views showing a spectrum of the conventional OFDM transmitting and receiving apparatus.
FIG. 2A
shows a signal spectrum at a signal transmitting time of a base station, and
FIG. 2B
shows a signal spectrum at a signal receiving time of a partner station. As shown in
FIGS. 2A and 2B
, an error in reception power occurs by subcarriers under a multipath environment even if transmission power remains constant.
In the conventional OFDM transmitting and receiving apparatus, since reception power does not remain constant, errors concentrate on subcarries wherein reception power has dropped, and this causes a problem in which an error rate characteristic is deteriorated.
DISCLOSURE OF INVENTION
It is an object of the present invention is to provide an OFDM transmitting and receiving apparatus and OFDM transmitting and receiving method wherein power between subcarriers can be maintained substantially constant at a receiving time so as to improve an error rate characteristic.
The above object can be achieved by performing such a signal transmission wherein a weight is assigned to power every subcarrier so that power between subcarriers becomes constant at a receiving time and transmission power is differentiated in OFDM transmission.
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patent: 6009073 (1999-12-01), Kaneko
patent: 6118987 (2000-09-01), Hiramatsu et al.
patent: 6125103 (2000-09-01), Bauml et al.
patent: 6192066 (2001-02-01), Asanuma
patent: 6317470 (2001-11-01), Kroeger et al.
patent: 6345036 (2002-02-01), Sudo et al.
patent: 6456827 (2002-09-01), Kubo et al.
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PCT International Search Report dated Feb. 8, 2000.
Ishikawa Kimihiko
Sudo Hiroaki
Qureshi Afsar
Stevens Davis Miller & Mosher LLP
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