JPH11275047A - Transmitter and receiver, and transmission method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an orthogonal frequency multiplexed modulated signal receiver, which has satisfactory reception characteristic, even when a propagation delay in excess of a guard period takes place and to provide a spatial division multiplexing method by which synthesized orthogonal frequency multiplexed modulated signals are transmitted by using this receiver. SOLUTION: An adaptive array antenna is used, a periodic autocorrelation function is estimated from a signal denoting a guard period of a signal received by a plurality of antennas 33, 34, 35, a period correlation function among a plurality of antennas is estimated, and an interference signal is removed from the signals to compensate for the received signal. Furthermore, a plurality of orthogonal frequency multiplexed modulated signals are synthesized and the synthesized signal is sent and received by an orthogonal frequency multiplexed modulated signal receiver, which receives the transmitted synthesized signal after demultiplexing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital radio transmission receiver and transmission method, and more particularly to a receiver in an orthogonal frequency multiplexing modulation method (hereinafter referred to as OFDM).
And a space division multiplexing transmission method using the receiver.

[0002]

2. Description of the Related Art In terrestrial digital broadcasting, high-speed digital mobile radio transmission, or subcarrier transmission,
OFDM resistant to multipath distortion is being studied.

[0003] OFDM is a method of frequency-division multiplexing transmission digital data using a plurality of carriers arranged at a reciprocal frequency interval of a symbol period. In this case, about 1000 to 8000 carriers are used.

[0004] Each carrier is modulated by multi-level QAM or the like, which is a method of high band use efficiency.

FIG. 11 shows a configuration of a conventional transmission method using OFDM.

In FIG. 11, in a transmitter (2), a binary digital signal input from an input terminal 1 is phase-modulated (hereinafter, PSK (Pha) by a digital modulator (3).
seShift Keying) signal or quadrature amplitude modulation (hereinafter referred to as QAM (Quadratur)
e Amplitude Modulation)).

[0007] The modulation symbol is input to a serial-to-parallel converter (4), and the transmission rate is one of the transmission rate of the input symbol sequence.
/ N is converted into N symbol sequences. This sequence is formed by an inverse discrete Fourier transformer (hereinafter, IDFT (Inve
rsed DiscreteFourier Tran
(sformer)) (5), the sub-carriers of the corresponding frequency are modulated, combined and output.

The output signal is a signal of the sum of a plurality of modulation signals arranged at a frequency interval that is the reciprocal of the symbol period.

A guard section having the same waveform as the end of the observation section of the orthogonal frequency multiplex modulation signal is inserted into the output signal of the IDFT (5) by the guard section insertion section (6) and transmitted.

On the other hand, the receiver (7) performs the reverse operation of the transmitter (2) to estimate the transmission data sequence.

First, a guard section signal is removed in a guard section remover (8), and a discrete Fourier transformer (hereinafter referred to as DFT (Discrete Fourier Tr) is used.
(informer) is input to (9). In the DFT (9), the received signal is separated into an equivalent low-band received signal corresponding to each sub-channel and output as parallel data composed of N symbols.

This symbol is converted into the original serial data by the parallel / serial converter (10), and the PSK signal or the QAM signal is demodulated by the digital demodulator (11). 12).

Here, the guard interval means that OFDM has a sufficiently low transmission rate for each sub-channel, so that it is hardly affected by multipath delay waves. In order to transmit high-quality information, an invalid symbol is added as a buffer data portion before an effective symbol originally intended to be transmitted.

At this time, the invalid symbol to be added uses a part of the valid symbol, and corresponds to a period of several tenths to several tenths of the whole.

Hereinafter, the guard section will be outlined with reference to FIG.

FIG. 12 is a diagram showing the outline of the OFDM modulated signal waveform. As shown in FIG. 12, the OFDM modulated signal waveform is composed of two sections, a guard section and an observation section. In the guard section, the same waveform as the end of the observation section signal is inserted.

By providing this guard section, it is possible to prevent interference due to a delay wave having a delay time within the guard section length, and to suppress deterioration of transmission characteristics.

[0018]

However, OFDM is
If there is a delayed wave with a delay time exceeding the guard section length,
Since the orthogonality between adjacent subchannels is lost and intersymbol interference occurs, transmission characteristics are significantly deteriorated.

Further, as with the conventional transmission method using a single carrier, it is impossible to eliminate the influence of interference by other transmission signals existing on the same frequency.

To solve such a problem, there has been proposed an adaptive array antenna technique for removing interference by combining signals received by a plurality of antennas.

However, in order to perform interference cancellation by an adaptive array, it is necessary to perform channel estimation for a long time using a known training sequence, which leads to an improvement in frequency use efficiency and an environment in which channel characteristics fluctuate at high speed. There was a problem that it was difficult to apply.

Also, a method called a CMA adaptive array antenna which does not use a training sequence has been proposed. However, this method requires that the amplitude of a modulated signal be constant, and is applied to OFDM where the amplitude fluctuates greatly. Had the problem of being difficult.

The present invention addresses this problem by focusing on the difference in the arrival direction and propagation loss between the desired received wave and the interference wave, and removes the interference signal component from the interference-based OFDM signal to improve the transmission characteristics. , OFDM receiver, and a space division multiplexing transmission method for separating and demodulating respective signals from a plurality of received signals obtained by combining the same OFDM signals. is there.

[0024]

According to a first aspect of the present invention, there is provided a receiver for receiving data wirelessly transmitted using OFDM, wherein the receiver receives the transmitted data with a plurality of antennas. Receiving means, from a plurality of received signals received by the receiving means, a weight estimating means to calculate a weight coefficient, a plurality of received signals received by the receiving means, multiplying means to multiply the weight coefficient, An object of the present invention is to provide a receiver having an adding means for obtaining a sum of products obtained by the multiplying means, and the weight estimation means sets a guard period to A periodic autocorrelation function estimating means for estimating a used cyclic autocorrelation function; a periodic crosscorrelation function estimating means for obtaining a periodic crosscorrelation function between the plurality of antennas; A covariance matrix estimating means for obtaining a covariance matrix of the received signal between the teners; an inverse matrix calculating means for obtaining an inverse matrix of the covariance matrix obtained by the covariance matrix estimating means; and the periodic autocorrelation function estimation Means for calculating a product of the autocorrelation function estimated by the means and the cross-correlation function calculated by the periodic cross-correlation number estimating means and the inverse matrix of the covariance matrix calculated by the inverse matrix calculating means. The invention of claim 3 provides a receiver according to claim 1 or claim 2 which comprises synchronization signal input means. According to a fourth aspect of the present invention, there is provided a transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplex modulated signals, wherein a plurality of identical orthogonal frequency multiplexes are provided by a symbol clock generator. A transmitter for synchronizing an output signal of a keying transmitter and a means for transmitting the output signals of the plurality of identical orthogonal frequency multiplex modulation transmitters with delays respectively different from each other by different delay times. The invention according to claim 5 is a transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplexed modulated signals, wherein a symbol clock generator generates a plurality of identical orthogonal frequencies. A transmitter having means for synchronizing the output signals of the multiplex modulation transmitters, and means for transmitting the output signals of the plurality of identical orthogonal frequency multiplex modulation transmitters with respective delay times different from each other; A receiver for receiving data wirelessly transmitted by using a multiplex modulation method, receiving means for receiving the transmitted data by a plurality of antennas, and receiving by the receiving means Weight estimating means for calculating a weight coefficient from the plurality of received signals obtained, a means for inputting a synchronization signal to the weight estimating means, and a multiplication of multiplying the plurality of received signals received by the receiving means by the weight coefficient Means, and a transmission method using a receiver comprising an addition means for obtaining a sum of products obtained by the multiplication means, wherein a step of transmitting a signal at the transmitter, receiving the transmitted signal From the received signal, detecting the synchronization of the output signals of the plurality of the same orthogonal frequency multiplexing modulation transmitter, and the detected synchronization,
A plurality of receivers are synchronized by the step of delaying by the respective different delay times and the detected synchronization delayed by the respective different delay times, and the plurality of the same orthogonal frequency multiplex modulation transmitters are synchronized. It is another object of the present invention to provide a transmission method which comprises a step of extracting each output signal from the plurality of receivers. A transmission method according to claim 5, wherein the transmission method is used.

According to the above means, a feature of OFDM is
Utilizing the fact that the same waveform is transmitted at the end of the guard interval and the observation interval, by comparing the waveforms of the two intervals, the propagation path characteristics can be estimated with high accuracy without using a training sequence. Can be used to remove interference.

Further, by performing interference removal a plurality of times,
A plurality of orthogonal frequency modulation signals transmitted at the same frequency are separated from each other to realize space division multiplex transmission.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an OFDM transmitter (31) according to a first embodiment of the present invention, and an OFDM transmitter (31) according to the present invention.
It is a system diagram which shows a receiver (36) and a propagation path environment.

In FIG. 1, a transmission signal transmitted from an OFDM transmitter (31) through a transmission antenna (32) receives K-1 interferences by a propagation path and is received by an OFDM receiver (36). .

In the OFDM receiver (36), the transmission signals are independently received by the L receiving antennas (33, 34, 35).

The desired transmission signal is x ₁ , and the interference signal is x _k (k =
2, 3,. . . , K), the received signals received by the L receiving antennas (33, 34, 35) are represented by vectors y = [y ₁ , y ₂ ,. . . , Y _L ] ^T
Can be written as

[0032]

(Equation 1)

Here, the vector C _k = [C _k1 ,
C _k2,. . . , C _kL ] ^T _represents the complex envelope variation vector of the interference signal x _k , and C _kl represents the complex envelope variation when the interference signal x _k is received in the l-th branch.

[0034] In OFDM receiver (36), the mean square error minimum estimate of the desired transmission signal x ₁ from the received signal vector y (hereinafter referred to as desired signal estimates) performs interference cancellation by determining demodulates .

FIG. 2 is a block diagram of the OFDM receiver (36), and an operation for obtaining the desired signal estimated value will be described.

In FIG. 2, input terminals (41, 42, 4)
3) are the signals received by the L receiving antennas (33, 34, 35) in FIG. 1, respectively, and the received signals input from the input terminals (41, 42, 43). Is a weight estimator (49) and a multiplier (44,
45, 46).

The received signals are respectively applied to the multipliers (44, 44).
45, 46), weighted by the value detected by the weight estimator (49), and added by an adder (47) to obtain the desired signal estimated value.

Hereinafter, the principle of obtaining the desired signal estimated value will be described.

The desired signal estimation value is expressed by the following equation.

[0040]

(Equation 2)

Here, the vector H = [h ₁ ,
h _2,. . . , H _L ] ^T is a weight vector and is given by the following equation.

[0042]

(Equation 3)

Where a is a constant,

[0044]

(Equation 4)

Is the cross-correlation matrix of x and vector y,

[0046]

(Equation 5)

Is the autocorrelation matrix of the vector y.

Therefore, if the weight vector H is obtained, the desired signal estimated value can be obtained.

The weight vector H is estimated by the weight estimator (49).

The operation of the weight estimator (49) will be described below.

First, a periodic autocorrelation function is obtained by the periodic autocorrelation estimator (50).

FIG. 3 shows the configuration of the periodic autocorrelation estimator (50).
Shown in

In FIG. 3, a received signal input from an input terminal (61) is observed by a delay unit (62) for an observation time t _s.
Only a delay. The output signal of the delay unit (62) is input to a complex conjugate operation unit (63), and a complex conjugate signal is obtained. The output signal of the complex conjugate operation unit (63) is input to the complex multiplier (64) together with the reception signal input from the input terminal (61).

The output signal of the complex multiplier (64) is input to a rectangular window filter (65) having a rectangular impulse response having a width of Delta. The rectangular window filter (65)
Is input to the distribution switch (67).

The sampling clock signal output from the sampling clock generator (66) is input to the distribution switch (67), and is supplied to the rectangular window filter (65).
The output is distributed to the N _T integrators (68, 69) in the clock timing.

In each of the integrators (68, 69, 70),
The input signal is integrated over M symbol intervals. Accordingly, the output of the n-th integrator is expressed by the following equation.

[0057]

(Equation 6)

[0058] In this case, t _samp is the sampling period, t _s
Is the observation section length of the orthogonal frequency multiplexed modulation signal, △ is the guard section length, and T _s = t _s + △ is the symbol length.

FIG. 4 shows an outline of the output amplitude of each integrator.

The peak value of the amplitude in the figure corresponds to the symbol timing. Each of the integrators (68, 69, 70)
The output is input to a peak detector (71) to detect which integrator output is the maximum.

The output of the peak detector (71) is output from a symbol timing signal output terminal (73).
Further, the output of the integrator having the maximum amplitude is selected from the outputs of the integrators (68, 69, 70) inputted to the selector switch (72), and the autocorrelation function output terminal (autocorrelation function output terminal) is selected. 74). here,
The autocorrelation function is represented by the following equation.

[0062]

(Equation 7)

Next, the input signal and the symbol timing signal output of the periodic autocorrelation estimator 50 are input to the periodic cross-correlation estimators (51, 52) shown in FIG.

In FIG. 5, a received signal # 1 is input from an input terminal (81), and a received signal # 2 is input as an input signal from an input terminal (82).

The reception signal # 2 input from the input terminal (82) is delayed by the observation time t _s in the delay unit (84), and the output signal of the delay unit (84) is converted into a complex conjugate operation unit. (85), and a complex conjugate signal is obtained.

The output signal of the complex conjugate operation unit (85) is
Along with the received signal # 1 input from the input terminal (81), the signal is input to the complex multiplier (86), and the complex arithmetic unit (8
6) The output signal is input to a rectangular window filter (87) having a rectangular impulse response with a width of Delta.

The signal level of the output of the rectangular window filter (87) is held at the cycle of the symbol timing signal by a sample and hold circuit (88) controlled by a symbol timing signal input from a symbol timing signal input terminal (83). Is done.

The output signal of the sample and hold circuit (88) is input to an integrator (89) and performs integration over M symbol intervals.

The periodic cross-correlation function calculated by the above process is output from the output terminal (90).

The periodic cross-correlation estimator (51,
At 52), a periodic cross-correlation function represented by the following equation is calculated and output.

[0071]

(Equation 8)

Here, t _max is the time when the output of the periodic autocorrelation function estimator is the maximum, t _s is the observation section length of the orthogonal frequency multiplex modulation signal, △ is the guard section length, and T = t _s + △ is the symbol. Long.

The vector composed of the periodic autocorrelation and periodic cross-correlation estimator output signals is an estimated value of R _xy represented by the following equation.

[0074]

(Equation 9)

R _yy is obtained by the following calculation.

[0076]

(Equation 10)

Here, r _ln is given by the following equation.

[0078]

[Equation 11]

[0079] In this case, t _samp is the sampling period, t _s
The observation interval length of OFDM, M is an integer, T _s = t _s + △ is the symbol length.

On the other hand, the covariance matrix estimator (53) in FIG. 2 estimates the elements of the covariance matrix of the received signal by the following equation.

[0081]

(Equation 12)

Here, T ₀ is a covariance matrix estimator (53)
, Ρ _nl is an n-row, l-column element of the estimated covariance matrix. The covariance matrix obtained by the covariance matrix estimator (53) is input to the inverse matrix calculator (54) of FIG.
An inverse matrix is obtained.

Therefore, the product of the vector obtained by Expressions (9) and (10) and the inverse matrix is calculated by the matrix multiplication unit (5
The weight vector H is obtained by performing the calculation in 5).

In this embodiment, the propagation delay of a signal to each antenna input is assumed to be the same, and estimation is performed only for l = 1. However, by estimating the timing separately for each antenna, the propagation delay Can be estimated even if is different.

Next, the space division multiplex transmission method will be described.

First, FIG. 6 shows the configuration of a transmitter when the space division multiplex transmission method is performed.

In FIG. 6, L input terminals (91, 9
2, 93), digital signals are separately input. Transmission signals are generated from these digital signals by L OFDM transmitters (95, 96, 97). The symbol timing of each of the OFDM transmitters (95, 96, 97) is matched by a synchronization signal generated by a symbol clock (94). Each OF
The output of the DM transmitter (95, 96, 97) is supplied to the delay unit (9).
8, 99) and given a predetermined delay.

Each of the OFDM transmitters (95, 96, 9)
FIG. 7 shows the relationship of the symbol timing of the output signal of 7).

Transmission signal 1 (110) is output to output terminal 1 (1
00) a signal having a symbol length T _s, which is transmitted from the transmission signal 2 (111) has a symbol length T _s, which is transmitted from the output terminal 2 (101), the transmission signal 1
(110) is from 1 / T _s delayed signal. The transmission signal L (113) has a symbol length T _s, which is transmitted from the output terminal L (102), the transmission signal 1
(110) from (L-1) is a signal delayed by / T _s.

These OFDM transmitters (95, 96, 9)
7) is output to each output terminal (100, 101,
102) and transmitted from L independent transmission antennas.

Next, FIG. 8 shows a configuration of a receiver when the space division multiplexing transmission method is performed.

In FIG. 8, signals received by L independent receiving antennas are input to input terminals (120, 121,
122). From the signal input from the input terminal (120), the periodic autocorrelation function of the received signal is obtained by the periodic autocorrelation estimator (123). The configuration of the periodic autocorrelation estimator used here is the same as the configuration of FIG.

In space division multiplexing transmission, the output of each integrator of the periodic autocorrelation estimator (123) is synchronized with the symbol timing obtained by delaying the output signal of each OFDM transmitter (95, 96, 97) by the transmitter. Then, K peaks are detected at intervals of T _s / K. One of these peaks is selected and output as symbol timing.

FIG. 10 shows the state of the symbol timing.

The symbol timing is determined by the delay unit (12
7, 128) and is applied to each OFDM receiver (124, 125, 126) with a delay of T _s / K.

FIG. 9 shows the configuration of the OFDM receiver in FIG.

In the OFDM receiver shown in FIG. 9, a periodic autocorrelation estimator (149) and a periodic cross-correlation estimator (150, 15)
2 except that the operation of 1) operates in synchronization with the synchronization signal from the synchronization signal input terminal (143).
Almost the same processing as that of the receiver is performed. As a result, the K multiplexed transmitted signals can be separated and received.

[0098]

As described above, according to the first, second, or third aspect of the present invention, the OFDM signal is transmitted to another modulated signal or guard signal transmitted at the same frequency. Even if interference is caused by a delayed wave having a long delay time exceeding the section length, the interference can be removed, and there is an effect of improving deterioration of transmission characteristics due to the interference.

Further, in OFDM, by utilizing the fact that the same waveform is transmitted at the end of the guard section and the observation section, the waveforms of the two sections are compared, so that even OFDM signals whose amplitude fluctuates can be used. There is no need to use a training sequence, which makes it possible to apply the present invention to an environment where transmission path characteristics fluctuate at high speed.

According to the fourth, fifth or sixth aspect of the present invention, a plurality of orthogonal frequency multiplex modulation signals can be simultaneously spatially multiplexed and transmitted using the same frequency, and the frequency utilization efficiency can be improved. There is an effect of dramatically improving, and accordingly, transmission costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a transmitter, a receiver, and a propagation path environment according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a receiver according to the embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a periodic autocorrelation function estimator of the present invention.

FIG. 4 is an integrator output waveform of the periodic autocorrelation function estimator of the present invention.

FIG. 5 is a block diagram showing a configuration of a periodic cross-correlation function estimator of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a transmitter according to the embodiment of the present invention.

FIG. 7 shows a transmission symbol timing of a transmitter in the transmission method of the present invention.

FIG. 8 is a block diagram showing an overall configuration of a receiver in the transmission method according to the present invention.

FIG. 9 is a block diagram showing an internal configuration of a receiver unit in the transmission method of the present invention.

FIG. 10 is a waveform of a periodic autocorrelation function of a received signal in the transmission method of the present invention.

FIG. 11 is a block diagram showing a configuration of a conventional orthogonal frequency division multiplexing modulation transmitter and receiver.

FIG. 12 is a signal waveform of an orthogonal frequency multiplex modulation signal.

[Explanation of symbols]

 Reference Signs List 1 signal input terminal 2 OFDM transmitter 3 modulator 4 serial-parallel converter 5 IDFT 6 guard section insertion unit 7 OFDM receiver 8 guard section deletion unit 9 DFT 10 parallel-serial converter 11 demodulator 30 signal input terminal 31 OFDM transmitter 32 transmitting antenna 33, 34, 35 receiving antenna 36 OFDM receiver 37 signal output terminal 41, 42, 43 signal input terminal 44, 45, 46 multiplier 47 adder 48 signal output terminal 49 weight estimator 50 period autocorrelation function estimation Devices 51, 52 periodic cross-correlation estimator 53 covariance matrix estimator 54 inverse matrix calculator 55 matrix multiplier 61 signal input terminal 62 delayer 63 complex conjugate calculator 64 complex multiplier 65 rectangular window filter 66 sampling clock generator 67 Distribution switch 68, 69, 70 Integrator 71 Peak detector 72 Selector switch 73 Symbol timing output terminal 74 Autocorrelation function output terminal 81, 82 Signal input terminal 83 Symbol timing input terminal 84 Delay unit 85 Complex conjugate operation unit 86 Complex multiplication unit 87 Rectangular window filter 88 Sample hold circuit 89 Integrator 90 Cross correlation Function output terminals 91, 92, 93 Signal input terminal 94 Symbol clock generator 95, 96, 97 OFDM transmitter 98, 99 Delay unit 100, 101, 102 Signal output terminal 120, 121, 122 Signal input terminal 123 Periodic autocorrelation function Estimators 124, 125, 126 OFDM receiver 127, 128 Delayer 129, 130, 131 Signal output terminal 140, 141, 142 Signal input terminal 143 Synchronization signal input terminal 144, 145, 146 Multiplier 147 Adder 148 Signal Output terminal 149 Periodic autocorrelation function estimator 150, 151 Periodic cross-correlation function estimator 152 Covariance matrix estimator 153 Inverse matrix calculator 154 Matrix multiplication unit 155 Weight estimation unit

Claims (6)

[Claims] 1. A receiver for receiving data wirelessly transmitted using an orthogonal frequency multiplexing modulation method, a receiving unit receiving the transmitted data with a plurality of antennas, and a plurality of receiving units receiving the data. Weight estimating means for calculating a weight coefficient from a received signal; multiplying means for multiplying a plurality of received signals received by the receiving means by the weight coefficient; and adding means for obtaining a sum of products obtained by the multiplying means. A receiver comprising: 2. The weighting estimator includes: a periodic autocorrelation function estimator that estimates a periodic autocorrelation function using a guard period; and a periodic crosscorrelation function estimator that obtains a periodic crosscorrelation function between the plurality of antennas. Means, find a covariance matrix of the received signal between the plurality of antennas, a covariance matrix estimating means, find the inverse matrix of the covariance matrix found by the covariance matrix estimating means, inverse matrix calculating means, The product of the autocorrelation function estimated by the periodic autocorrelation function estimating means and the cross-correlation function obtained by the periodic cross-correlation function estimating means and the inverse matrix of the covariance matrix obtained by the inverse matrix calculating means are obtained. The receiver according to claim 1, further comprising a matrix multiplication operation means. 3. The receiver according to claim 1, further comprising a synchronization signal input unit. 4. A transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplex modulated signals, wherein a symbol clock generator synchronizes output signals of the same plurality of orthogonal frequency multiplex modulated transmitters. And means for transmitting the output signals of the plurality of the same orthogonal frequency multiplex modulation transmitters with delays by different delay times, respectively. 5. A transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplex modulated signals, wherein a symbol clock generator synchronizes output signals of the same plurality of orthogonal frequency multiplex modulated transmitters. Means for transmitting the output signals of the plurality of identical orthogonal frequency multiplex modulation transmitters with different delay times, respectively, and data transmitted wirelessly using the orthogonal frequency multiplex modulation method. Receiving means for receiving the transmitted data by a plurality of antennas; weight estimating means for calculating a weight coefficient from a plurality of received signals received by the receiving means; Means for inputting a synchronization signal to the means, multiplying means for multiplying the plurality of received signals received by the receiving means by the weighting coefficient, A transmission method using a receiver including an adding means for obtaining a sum of the products, wherein: a step of transmitting a signal by the transmitter; receiving the transmitted signal; Detecting the synchronization of the output signals of the same orthogonal frequency multiplex modulation transmitter; delaying the detected synchronization by different delay times; and detecting the detected synchronization by delaying the respective different delay times. A method of synchronizing a plurality of said receivers with said plurality of receivers and extracting respective output signals of said plurality of identical orthogonal frequency multiplex modulation transmitters from said plurality of receivers. 6. The transmission method according to claim 5, wherein a periodic autocorrelation function is used as the synchronization detection method.