JP2004201338A - Transmitter and transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an orthogonal frequency multi-modulation signal receiver which provides good reception characteristic even when transmission delay exceeding a guard zone length occurs, and to provide a space-division multiplexing method which combines multiple orthogonal frequency multi-modulation signals and transmits it by using the receiver. <P>SOLUTION: Using adaptive array antennas, a periodic auto-correlation function is estimated from a signal in the guard zone of a signal which multiple antenna received, a periodic cross-correlation function between multiple antennas is also estimated, and an interference signal is removed from those signals to compensate the received signal. Furthermore, by combining multiple orthogonal frequency multi-modulation signals and transmitting it, and by receiving it with the orthogonal frequency multi-modulation signal receiver, the combined and transmitted signal can be separated and received. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a receiver and a transmission method for digital wireless transmission, and more particularly to a receiver in an orthogonal frequency multiplex modulation method (hereinafter, referred to as OFDM) and a space division multiplex transmission method using the receiver.

  In terrestrial digital broadcasting, high-speed digital mobile radio transmission, or subcarrier transmission, OFDM resistant to multipath distortion is being studied.

  OFDM is a method of frequency-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.

  In addition, each carrier is modulated by multi-level QAM or the like, which is a method with 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 converted into a phase-modulated (hereinafter, referred to as PSK (Phase Shift Keying)) signal or a quadrature amplitude modulated signal by a digital modulator (3). (Hereinafter referred to as QAM (Quadrature Amplitude Modulation)) signal.

  The modulation symbol is input to the serial-to-parallel converter (4), and is converted into N symbol sequences whose transmission rate is 1 / N of the transmission speed of the input symbol sequence. This series is modulated by a subcarrier of a corresponding frequency by an inverse discrete Fourier transformer (hereinafter referred to as IDFT (Inverted Discrete Fourier Transformer)) (5), synthesized, 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 by the guard section insertion section (6) into the output signal of the IDFT (5) and transmitted.

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

  First, the guard section signal is removed in the guard section removing section (8) and input to a discrete Fourier transformer (hereinafter referred to as DFT (Discrete Fourier Transformer)) (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 to the original serial data by the parallel / serial converter (10), the PSK signal or the QAM signal is demodulated by the digital demodulator (11), and the received data is output from the reception data output terminal (12). Is output.

  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. However, it further completely eliminates intersymbol interference due to delay waves and improves quality in digital transmission. This is provided so that high information can be transmitted, and takes a form in which 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.

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

  FIG. 12 is a diagram showing an 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. , 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.

  However, in OFDM, when a delay wave having a delay time exceeding the guard section length is present, orthogonality between adjacent subchannels is lost and intersymbol interference occurs, so that transmission characteristics are significantly deteriorated.

  In addition, as with the conventional transmission method using a single carrier, it is impossible to eliminate the influence of interference by another transmission signal existing on the same frequency.

  In order to solve such a problem, an adaptive array antenna technology for removing interference by combining signals received by a plurality of antennas has been proposed.

  However, in order to perform interference cancellation using an adaptive array, it is necessary to perform channel estimation for a long time using a known training sequence. There was a problem that it was difficult.

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

  In order to solve the above problem, the present invention focuses on the difference in the arrival direction and propagation loss between a desired reception wave and an interference wave, removes an interference signal component from a signal by the OFDM which has received interference, and improves transmission characteristics. Another object of the present invention is to provide 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.

  According to a first aspect of the present invention, in a transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplex modulated signals, a symbol clock generator synchronizes output signals of a plurality of the same 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 respectively different from each other by different delay times.

  A second invention of the present application is a transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplexed modulated signals, wherein a symbol clock generator outputs a plurality of identical output signals of the same orthogonal frequency multiplexed modulated transmitter. Synchronizing means, a transmitter having means for transmitting the output signals of the plurality of identical orthogonal frequency multiplex modulation transmitters with different delay times respectively, and radio transmission using an orthogonal frequency multiplex modulation method A receiver for receiving the transmitted data, receiving means for receiving the transmitted data by a plurality of antennas, from a plurality of received signals received by the receiving means, a weight estimating means for calculating a weight coefficient, Means for inputting a synchronization signal to the weight estimating means, multiplying means for multiplying the plurality of received signals received by the receiving means by the weight coefficient, and A transmission method using a receiver including an adding means for obtaining the sum of the obtained products, wherein a step of transmitting a signal with the transmitter, receiving the transmitted signal, and, based on the received signal, Detecting the synchronization of the output signals of a plurality of identical orthogonal frequency multiplex modulation transmitters, delaying the detected synchronization by different delay times, respectively, and delaying the detected synchronization by the different delay times. Synchronizing the plurality of receivers with the detected synchronization, and extracting output signals of the plurality of identical orthogonal frequency multiplex modulation transmitters from the plurality of receivers.

  The third invention of the present application is characterized in that a periodic autocorrelation function is used as the synchronization detection method.

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

  Also, in OFDM, the same waveform is transmitted at the end of the guard interval and the observation interval, and by comparing the waveforms of the two intervals, a training sequence can be generated even for a signal by OFDM whose amplitude fluctuates. This eliminates the need to use it, thereby making it possible to apply the present invention to an environment where transmission path characteristics fluctuate at high speed.

  In addition, it is possible to simultaneously spatially multiplex a plurality of orthogonal frequency division multiplexed modulation signals at the same frequency for transmission, which has the effect of dramatically improving the frequency use efficiency, thereby reducing transmission costs. Can be.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment of the present invention, and is a system diagram showing an OFDM transmitter (31), an OFDM receiver (36) according to the present invention, 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 interference via 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).

  Assuming that the desired transmission signal is x1 and the interference signal is xk (k = 2, 3,..., K), the reception signals received by the L receiving antennas (33, 34, 35) are expressed in vector form. The vector y = [y1, y2,. . . , YL] T by the following equation.

ここで、ベクトルＣk＝［Ｃk1、Ｃk2、．．．、ＣkL］Tは、干渉信号ｘkの複素包絡線変動ベクトル、Ｃklは干渉信号ｘkがｌ番目のブランチで受信された時の複素包絡線変動を表す。

Here, the vector Ck = [Ck1, Ck2,. . . , CkL] T represents the complex envelope variation vector of the interference signal xk, and Ckl represents the complex envelope variation when the interference signal xk is received on the l-th branch.

  The OFDM receiver (36) performs interference cancellation by obtaining a minimum mean square error estimated value (hereinafter, referred to as a desired signal estimated value) of the desired transmission signal x1 from the received signal vector y, and performs demodulation.

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

  In FIG. 2, signals input from the input terminals (41, 42, 43) are signals received by the L receiving antennas (33, 34, 35) of FIG. , 42, 43) are input to the weight estimator (49) and the multipliers (44, 45, 46).

  The received signals are weighted by the multipliers (44, 45, 46) according to the values detected by the weight estimating unit (49), and then added by an adder (47), thereby obtaining the desired signal A value is required.

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

  The desired signal estimate is represented by the following equation.

ここで、ベクトルＨ＝［ｈ1、ｈ2、．．．、ｈL］Tは重みベクトルであり、次式で与えられる。

Here, the vector H = [h1, h2,. . . , HL] T is a weight vector and is given by the following equation.

ここで、ａは定数であり、

Where a is a constant,

は、ｘとベクトルｙの相互相関行列であり、

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

は、ベクトルｙの自己相関行列である。

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 estimating unit (49).

  Hereinafter, the operation of the weight estimating unit (49) will be described.

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

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

  In FIG. 3, a reception signal input from an input terminal (61) is delayed by an observation time ts by a delay unit (62). 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 output of the rectangular window filter (65) is input to a distribution switch (67).

  The sampling clock signal output from the sampling clock generator (66) is input to the distribution switch (67), and the output of the rectangular window filter (65) is divided into NT integrators (68, 69) at this clock timing. , 70).

  Each of the integrators (68, 69, 70) integrates the input signal over M symbol intervals. Accordingly, the output of the n-th integrator is represented by the following equation.

ここで、ｔsampはサンプリング周期、ｔsは直交周波数多重変調信号の観測区間長、△はガード区間長、Ｔs＝ｔs＋△はシンボル長である。

Here, tsamp is the sampling period, ts is the observation section length of the orthogonal frequency multiplexed modulation signal, △ is the guard section length, and Ts = ts + △ is the symbol length.

  FIG. 4 schematically shows the output amplitude of each integrator.

  The peak value of the amplitude in the figure corresponds to the symbol timing. The output of each of the integrators (68, 69, 70) 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 ( 74). Here, the autocorrelation function is represented by the following equation.

次に、入力信号および周期自己相関推定器５０のシンボルタイミング信号出力は、図５に示される周期相互相関推定器（５１、５２）に入力される。

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 received signal # 2 input from the input terminal (82) is delayed by the observation time ts in the delay unit (84), and the output signal of the delay unit (84) is sent to the complex conjugate operation unit (85). It is input and a complex conjugate signal is obtained.

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

  The signal level of the output of the rectangular window filter (87) is held at a period 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).

  The output signal of the sample and hold circuit (88) is input to the 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).

  In the periodic cross-correlation estimators (51, 52) as described above, a periodic cross-correlation function represented by the following equation is calculated and output.

ここで、ｔmaxは上記周期自己相関関数推定器出力が最大となる時間、ｔsは直交周波数多重変調信号の観測区間長、△はガード区間長、Ｔ＝ｔs＋△はシンボル長である。

Here, tmax is the time when the output of the periodic autocorrelation function estimator is maximum, ts is the observation section length of the orthogonal frequency multiplexed modulation signal, △ is the guard section length, and T = ts + △ is the symbol length.

  The vector consisting of the periodic autocorrelation and periodic crosscorrelation estimator output signals is an estimated value of Rxy expressed by the following equation.

また、Ｒyyは、以下の計算より求められる。

Ryy is obtained by the following calculation.

ここで、ｒlnは、次式で与えられる。

Here, rln is given by the following equation.

ここで、ｔsampはサンプリング周期、ｔsはＯＦＤＭの観測区間長、Ｍは整数、Ｔs＝ｔs＋△はシンボル長である。

Here, tsamp is a sampling period, ts is an observation section length of OFDM, M is an integer, and Ts = ts + △ is a 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.

ここで、Ｔ0は共分散行列推定器（５３）の観測区間、ρnlは推定した共分散行列のｎ行ｌ列要素である。共分散行列推定器（５３）により求められた共分散行列は、図２の逆行列演算部（５４）に入力され、逆行列が求められる。

Here, T0 is an observation section of the covariance matrix estimator (53), and ρnl 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) in FIG. 2, and the inverse matrix is obtained.

  Accordingly, the weight vector H is obtained by calculating the product of the vector obtained by Expressions (9) and (10) and the inverse matrix by the matrix multiplication unit (55).

  In this embodiment, the propagation delay of the 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 differs. However, estimation is possible.

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

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

  In FIG. 6, digital signals are separately input from L input terminals (91, 92, 93). 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) coincides with the synchronization signal generated by the symbol clock (94). The outputs of the OFDM transmitters (95, 96, 97) are input to delay units (98, 99) and given a predetermined delay.

  FIG. 7 shows the relationship between the symbol timings of the output signals of the OFDM transmitters (95, 96, 97).

  The transmission signal 1 (110) has a symbol length Ts transmitted from the output terminal 1 (100), and the transmission signal 2 (111) has a symbol length Ts transmitted from the output terminal 2 (101). It is a signal delayed by 1 / Ts from the transmission signal 1 (110). The transmission signal L (113) has a symbol length Ts transmitted from the output terminal L (102), and is a signal delayed by (L-1) / Ts from the transmission signal 1 (110).

  Output signals of these OFDM transmitters (95, 96, 97) are output from respective output terminals (100, 101, 102) and transmitted from L independent transmission antennas.

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

  In FIG. 8, signals received by L independent receiving antennas are input from 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 in FIG.

  In the space division multiplex 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, and Ts / K peaks are detected at intervals of / K. One of the peaks is selected and output as a symbol timing.

  The state of the symbol timing is shown in FIG.

  This symbol timing is delayed by Ts / K by delay units (127, 128) and added to each OFDM receiver (124, 125, 126).

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

  In the OFDM receiver shown in FIG. 9, the operation of the periodic autocorrelation estimator (149) and the operation of the periodic cross-correlation estimator (150, 151) operate in synchronization with the synchronization signal from the synchronization signal input terminal (143). Except for this, almost the same processing as that of the OFDM receiver in FIG. 2 is performed. As a result, the K transmission signals multiplexed and transmitted can be separated and received.

  It is applicable to digital terrestrial broadcasting and high-speed digital mobile radio transmission.

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 illustrating a configuration of a periodic autocorrelation function estimator of the present invention. 5 is an integrator output waveform of the periodic autocorrelation function estimator of the present invention. FIG. 3 is a block diagram illustrating a configuration of a periodic cross-correlation function estimator of the present invention. FIG. 2 is a block diagram illustrating a configuration of a transmitter according to the embodiment of the present invention. 5 is a transmission symbol timing of a transmitter in the transmission method of the present invention. FIG. 2 is a block diagram illustrating an overall configuration of a receiver in the transmission method according to the present invention. FIG. 3 is a block diagram illustrating an internal configuration of a receiver unit in the transmission method according to the present invention. 6 is a waveform of a periodic autocorrelation function of a received signal in the transmission method of the present invention. FIG. 9 is a block diagram showing a configuration of a conventional orthogonal frequency multiplex modulation transmitter and receiver. 3 is a signal waveform of an orthogonal frequency multiplex modulation signal.

Explanation of reference numerals

Reference Signs List 1 signal input terminal 2 OFDM transmitter 3 modulator 4 serial-parallel converter 5 IDFT
6 guard section insertion section 7 OFDM receiver 8 guard section deletion section 9 DFT
Reference Signs List 10 parallel-serial converter 11 demodulator 30 signal input terminal 31 OFDM transmitter 32 transmission antennas 33, 34, 35 reception antenna 36 OFDM receiver 37 signal output terminals 41, 42, 43 signal input terminals 44, 45, 46 multiplier 47 Adder 48 Signal output terminal 49 Weight estimator 50 Periodic autocorrelation function estimator 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 Arithmetic unit 64 Complex multiplier 65 Rectangular window filter 66 Sampling clock generator 67 Distribution switches 68, 69, 70 Integrator 71 Peak detector 72 Selector switch 73 Symbol timing output terminal 74 Autocorrelation function output terminals 81, 82 Signal input terminal 83 Symbol timing input terminal 84 Delay unit 85 Complex conjugate operation Unit 86 complex multiplying 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 generators 95, 96, 97 OFDM transmitters 98, 99 delay unit 100, 101, 102 Signal output terminals 120, 121, 122 Signal input terminal 123 Periodic autocorrelation function estimator 124, 125, 126 OFDM receiver 127, 128 Delayer 129, 130, 131 Signal output terminal 140, 141, 142 Signal input terminal 143 Synchronous signal input terminals 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 (3)

In a transmitter that wirelessly transmits data using a plurality of orthogonal frequency multiplex modulated signals,
Means for synchronizing the output signals of a plurality of identical quadrature frequency multiplex modulation transmitters with a symbol clock generator;
A transmitter comprising means for transmitting output signals of the plurality of identical orthogonal frequency division multiplexing modulation transmitters with different delay times respectively. A transmitter for wirelessly transmitting data using a plurality of orthogonal frequency multiplex modulation signals, means for synchronizing output signals of a plurality of the same orthogonal frequency multiplex modulation transmitters with a symbol clock generator, A transmitter comprising means for transmitting the output signal of the same orthogonal frequency multiplex modulation transmitter with a delay time different from each other,
A receiver for receiving data wirelessly transmitted using an orthogonal frequency multiplexing modulation method, receiving means for receiving the transmitted data with a plurality of antennas, and a plurality of received signals received by the receiving means, Weight estimating means for calculating a weighting coefficient, means for inputting a synchronization signal to the weight estimating means, multiplying means for multiplying a 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 the sum of the products,
Transmitting a signal with 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,
Delaying the detected synchronization by different delay times,
The plurality of receivers are synchronized by the detected synchronization delayed by the respectively different delay times, and the output signals of the plurality of the same orthogonal frequency multiplex modulation transmitters are output to the plurality of receivers. A transmission method characterized by comprising a step of taking out. 3. The transmission method according to claim 2, wherein a periodic autocorrelation function is used as the synchronization detection method.

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