JP2008042728A - Diversity receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a diversity receiver which outputs a high-quality signal that enables it to recover from a shut-off state of a receiving signal. <P>SOLUTION: The diversity receiver receives signals with a plurality of antennas and performs distortion removal, after weighting and superimposing the signals received, comprising a CIR detector 102 for calculating CIR (desired wave power-to-interference wave power ratio) that is the power level ratio between the main waves of each of the signals, received by the antennas and a maximum interference wave for the relevant main wave and calculates the weighting coefficient (CIR weighting coefficient) corresponding to each of the received signals, by using the CIR and complex multipliers 103-1 to 103-N for individually weighting the signals received by the antennas by using each of CIR weighting coefficients, wherein each of the weighted signals is defined as a weighted composited input. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diversity receiver that receives a plurality of spatially separated antennas.

  In wireless communication, deterioration of signal transmission characteristics due to fading is inevitable. Therefore, a diversity receiver is used that receives signals using a plurality of spatially separated antennas, combines the received signals, removes waveform distortion by an equalizer, and performs data demodulation. As this composite reception method, for example, as disclosed in (Patent Document 1), there are a determination data correlation method and an MRC (Maximum Ratio Combiner) method, and among these, the MRC method has a simple configuration and operates reliably. Have been widely used. This MRC method will be described below.

  The MRC method is a method (maximum ratio combining) in which a signal-to-noise ratio (SNR) is maximized. FIG. 5 shows a configuration example of a diversity receiver using the MRC method. As shown in FIG. 5, in this configuration example, signals are received by a plurality of diversity antennas 501-1 to 501-N, respectively, and complex multipliers 504-1 to 504-N and correlators 505-1 to 505-N are used. A weighting coefficient for combining is controlled, and diversity combining is performed in the combiner 506. The combined output is amplified by an AGC (Automatic Gain Control) 508, and the number of taps of the correlators 505-1 to 505-N is controlled using this amplified signal. A DFE (Decision Feedback Equalizer) 507 removes distortion due to multipath fading using this synthesized output.

Hereinafter, in order to simplify the description, a case where the number of diversity branches is two routes will be described. Usually, in a wireless communication path, multipath fading occurs due to the influence of an obstacle or the like, so that a preceding wave and a delayed wave are dispersed on the time axis. Considering that the received radio wave is a superposition of the preceding wave and the delayed wave, the received signals r _n ¹ and r _n ² of each route received by the diversity antennas 501-1 and 501-2 are expressed by , (Equation 2).

Here, n and i are discretized values representing time, h _i ¹ and h _i ² are impulse responses at time i, and a _ni is transmission data at time (n−i). a _n represents a main wave, and a _ni : when i ≠ 0, represents a radio wave received before or after the main wave. The received signals r _n ¹ and r _n ² are uncorrelated with each other, and after passing through different routes, specific weights are added by the complex multipliers 504-1 and 504-2, respectively. If the tap coefficients (weighting coefficients) of each route are w ₁ and w ₂ , the combined signal y _n can be expressed as (Equation 3).

Here, for simplification, it is assumed that w ₁ · h _i ¹ + w ₂ · h _i ² = 1. In the MRC method, since the tap coefficient is determined by correlating the received signal with the composite signal whose amplitude is controlled to 1 by the AGC 508, the value of the tap coefficient is as shown in (Expression 4). The same applies to the other route, except that the subscript changes.

As can be seen from this equation, in the MRC method, the tap coefficient does not take only the complex conjugate of the impulse response (h ₀ ¹ ) at the same time as the main wave, but the preceding wave that has passed through a communication path different from the main wave, It is the result of integrating the complex conjugate of the impulse response including the delayed wave. That is, at the time of convolution by the complex multipliers 504-1 and 504-2, a signal of only one route (main wave) having a high signal level is not used as in the determination data correlation method, but radio waves of all routes are used. Synchronous synthesis is performed by considering it as a signal. Therefore, under the multipath route environment, the maximum ratio is synthesized even for the leading wave and the lagging wave that can be the interference wave for the main wave, so that when the interference wave is large, distortion cannot be removed in the DFE and the signal quality is deteriorated. There's a problem.

  On the other hand, the above-described data correlation method is a combining method for obtaining a signal with good signal quality. However, when the received signal is subjected to severe fading in the propagation line and becomes a momentary interruption state, the signal level is lowered and the DFE divergence A phenomenon will occur. That is, since a forward equalizer (FE), which is a component of DFE, is a linear filter using a correlation value between an input signal to itself and a determination data signal as a tap coefficient, the level of the input signal is extremely high. When the value is lower, the coefficient becomes a numerical value of a meaningless random pattern.

  Since this input signal follows a Gaussian distribution, the tap coefficient becomes 0 on average and FE does not pass the signal to the subsequent stage. Therefore, a backward equalizer (BE), which is another component of the DFE, also cannot operate normally and converges to 0 like the FE. For this reason, since these FE and BE block the signal, even if the line is restored and the signal level rises, the determination data signal remains permanently 0. Strictly speaking, a voltage is always applied to one tap serving as a reference for FE, and when the signal is restored, FE is restored, but BE is preventing this.

  On the other hand, in the MRC method, since the signal immediately after the synthesis before the DFE input is used as the correlation value for determining the tap coefficient, when the line is restored, the tap coefficient can be recovered from the situation of “converging to 0”.

As described above, the data correlation method and the MRC method have different problems. In order to solve these problems, the following (Patent Document 1) discloses a diversity receiver which is usually combined by a data correlation method with good data quality and switched to the MRC method when the received signal is momentarily interrupted.
Japanese Patent Laid-Open No. 9-8718

  However, according to the above-described conventional technique, there is a problem that the circuit of the two kinds of synthesis methods, that is, the data correlation method and the MRC method, and the switching control of the synthesis method are required, and the configuration of the receiver becomes complicated. In addition, there is a problem that the operation may become unstable unless the composition method is switched appropriately.

  The present invention has been made in view of the above, and is capable of outputting a high-quality signal, recovering normally from an instantaneous interruption state of a received signal, and performing diversity with a simple configuration. The purpose is to obtain a receiver.

  In order to solve the above-described problems, the present invention provides a diversity receiver that receives a signal from a plurality of antennas, performs weighting synthesis on the received signals, and then performs distortion removal, and each of the main signals received by the antennas. CIR (Carrier to Interference Ratio), which is a power level ratio between the wave and the maximum interference wave with respect to the main wave, is calculated using the CIR and a weighting coefficient corresponding to each received signal CIR weighting coefficient calculating means for calculating (CIR weighting coefficient), and weighting means for individually weighting signals received by the respective antennas using the respective CIR weighting coefficients. Each weighted signal is used as an input for weighting synthesis.

  ADVANTAGE OF THE INVENTION According to this invention, the diversity receiver which can output a high quality signal and can operate | move reliably with a simple structure which can be recovered normally from the momentary interruption of a received signal is obtained.

  A diversity receiver according to a first aspect of the present invention is a diversity receiver that receives a signal by a plurality of antennas, performs weight removal synthesis on the received signal, and performs distortion removal, and the main wave of each signal received by the antenna A CIR (Carrier to Interference Ratio) that is a power level ratio of the main wave to the maximum interference wave is calculated, and a weighting coefficient (CIR weighting) corresponding to each received signal is calculated using the CIR. Each of the signals weighted by the weighting means, and a weighting means for individually weighting the signals received by the respective antennas using each CIR weighting coefficient. Is used as an input for weighted synthesis, and is of high quality Signal can be output, and such an action can successfully recovering from an interruption of the received signal.

  The diversity receiver according to the second invention is characterized in that the weighting synthesis is a synthesis by the MRC (Maximal Ratio Combiner) method, and can output a high quality signal, and when the received signal is momentarily interrupted. Has the effect of being able to recover normally.

  A diversity receiver according to a third aspect of the invention is characterized in that the CIR weighting coefficient calculating means normalizes the CIR weighting coefficient, and can output a high quality signal, and from the moment when the received signal is momentarily interrupted. It has the effect of being able to recover normally.

  In the diversity receiver according to the fourth aspect of the invention, the CIR weighting coefficient calculating means does not perform the CIR coefficient calculating process when the CIRs of all the received signals are equal to or less than a predetermined value defined according to the reception status. This is characterized in that all CIR weighting coefficients are output as equal values, and has the effect of being able to output a high quality signal and recovering normally from a momentary interruption of the received signal.

  A diversity receiver according to a fifth aspect of the invention is characterized in that the CIR weighting coefficient calculating means sets the weighting coefficient to 0 for a received signal in which the CIR is equal to or greater than a predetermined value defined according to the reception status. Therefore, it can output a high-quality signal and can normally recover from the momentary interruption of the received signal.

  Embodiments of the present invention will be described below.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a functional configuration example of a first embodiment of a diversity receiver according to the present invention.

  As shown in FIG. 1, the diversity receiver according to the present embodiment includes N (N ≧ 2) diversity antennas 101-1 to 101-N, CIR (Carrier to Carrier Power Ratio: Carrier to (Interference Ratio) detector 102, N complex multipliers 103-1 to 103-N, N complex multipliers 104-1 to 104-N, N correlators 105-1 to 105-N, and combiners 106, DFE (Decision Feedback Equalizer) 107, and AGC (Automatic Gain Control) 108.

  In the present embodiment, each input signal input from diversity antennas 101-1 to 101-N is weighted using CIR by CIR detector 102 and complex multipliers 103-1 to 103-N (hereinafter referred to as a weighting coefficient). The weighted signal is synthesized by a known MRC method.

  Since the MRC method synthesizes the maximum ratio of a leading wave and a lagging wave that can be an interference wave for the main wave, if the influence of the interference wave is large, the DFE cannot completely remove the distortion and the signal quality is deteriorated. Therefore, in the present embodiment, weighting using the CIR is performed before the synthesis by the MRC method in order to reduce the influence of the forward wave and the delayed wave that can be an interference wave for the main wave of the MRC method, and the output signal is Improve quality.

  Next, functions of each unit of the diversity receiver according to the present embodiment will be described. Diversity antennas 101-1 to 101-N receive signals, and output the received signals to corresponding complex multipliers 103-1 to 103-N and CIR detector 102, respectively. The CIR detector 102 calculates the CIR for each input signal using the input signals input from the diversity antennas 101-1 to 101 -N, and calculates the CIR weighting coefficient for each input signal using the calculated CIR. Then, the CIR weight coefficient is output to the corresponding complex multipliers 103-1 to 103 -N. The complex multipliers 103-1 to 103-N weight the signals input from the diversity antennas 101-1 to 101-N using the weighting coefficients input from the CIR detector 102, and the weighted signals are complex. The data is output to multipliers 104-1 to 104-N and correlators 105-1 to 105-N.

  Next, the complex multipliers 104-1 to 104-N apply the signals input from the complex multipliers 103-1 to 103-N to the MRC methods respectively input from the correlators 105-1 to 105-N. Weighting is performed using the tap coefficient (weight coefficient) based on the result, and the result is output to the combiner 106. Correlators 105-1 to 105-N calculate tap coefficients using the signals input from 103-1 to 103-N and the amplified signals input from AGC 108, respectively. The combiner 106 performs diversity combining using the signals input from the complex multipliers 104-1 to 104-N, and outputs the combined output to the DFE 107 and the AGC 108. The AGC 108 amplifies the input combined signal and outputs the amplified signal to the correlators 105-1 to 105-N. The DFE 107 removes multipath distortion from the combined output input from the combiner 106.

  Subsequently, a CIR weighting coefficient and a calculation method thereof will be described.

  FIG. 2 is a diagram illustrating a configuration example of the CIR detector 102 of the diversity receiver illustrated in FIG. As shown in FIG. 2, the CIR detector 102 includes DMFs (Digital Matched Filters) 201-1 to 201-N, correlation detectors 202-1 to 202-N, and a weighted tap coefficient control circuit 203.

  Each of the DMFs 201-1 to 201-N performs despreading processing using the same spreading code as that on the transmission side, and then calculates the autocorrelation coefficient for each time difference by sequentially shifting the time (calculation of autocorrelation function). , Output to the corresponding correlation detectors 202-1 to 202-N, respectively. FIG. 3 is an example of an autocorrelation coefficient sequence input to one of the correlation detectors 202-1 to 202-N, where the horizontal axis represents the time difference and the vertical axis represents the autocorrelation coefficient. In the example of FIG. 3, there are three peaks of A, B, and C. Among these, the maximum peak value A can be estimated to be due to the main wave, and the second peak value B can be estimated to have the maximum power among the interference waves. Accordingly, the correlation detectors 202-1 to 202-N respectively receive the maximum peak value (A in the example of FIG. 3) and the second peak value (B in the example of FIG. 3) of the input autocorrelation coefficient. And the CIR value as the main wave and the maximum interference wave, respectively. For example, in the example of FIG. 3, when the autocorrelation coefficient is expressed in dB, it is calculated as CIR value = A−B.

The weighting tap coefficient control circuit 203 uses the CIR values calculated by the correlation detectors 202-1 to 202-N to calculate a normalized CIR weighting coefficient α _n according to the following (Equation 5). The reason for performing normalization is to prevent a change in received power at the time of synthesis due to the addition of the CIR weighting control function.

Here, n is an integer of 1 ≦ n ≦ N and represents the number of each received signal received by the N diversity antennas 101-1 to 101 -N. CIR _n is a CIR value obtained by the correlation detector 202-n.

Then, the weighting tap coefficient control circuit 203 outputs α _n calculated by (Equation 5) to the complex multiplier 103-n. The complex multiplier 103-n performs weighting control on the input from the diversity antenna 101-n using the input α _n .

  On the other hand, when the reception state is good, the CIR values of the respective reception signals may be all below a certain value. In this case, weighting results in a decrease in the signal quality after synthesis. Therefore, when the CIR level is smaller than a certain value, the CIR is set so as not to be weighted.

  FIG. 4 shows an example of a result obtained by numerical simulation of a bit error rate (BER) with respect to a carrier / noise power ratio (CNR). In this simulation, the transmission signal is a CCK signal of a wireless LAN system (802.11b), which is an example of a spread spectrum communication system, and the diversity branch has two routes (when N = 2 in this embodiment). When each received signal is input # 1, input # 2, CIR value of input # 1 is CIR # 1, and CIR value of input 2 is CIR # 2, CIR # 1 = 9 dB (maximum with respect to the main wave) The simulation was performed under the condition of the interference wave power level AB = 9 dB) and CIR # 2 = 3 dB.

  A curve 401 in FIG. 4 shows a simulation result when only the received signal of the input # 1 is input to the DFE without performing any weighting, and a curve 402 similarly shows only the received signal of the input # 2 and is weighted. The simulation result when it inputs into DFE without performing at all is shown. A curve 403 shows a simulation result when only the weighting of the conventional MRC method is performed, and a curve 404 shows a simulation result when the diversity receiver according to the present embodiment is used. In the present embodiment (curve 404), the BER characteristic is improved (BER is low in the case of the same CNR) and the output signal quality is improved as compared with the conventional MRC method (curve 403). I understand.

  In addition, since the propagation path response of each received signal can be estimated using the CIR detector 102, a constraint condition can be imposed on the synthesis of the received signal using this. For example, if the CIR deteriorates (becomes larger) than a certain value, the overall reception quality may improve if the signals are not synthesized. Therefore, when the CIR is equal to or greater than a certain value, it is possible to improve the reception performance by cutting off the line by setting the weighting coefficient of the received signal to 0 and combining using only other good received signals. .

  As described above, in this embodiment, weighting using the CIR value is performed before synthesis by the MRC method. This makes it possible to improve the quality of the signal after diversity combining as compared with the conventional MRC method, while taking advantage of the MRC method that has a simple configuration and operates reliably.

  As described above, the diversity receiver according to the present invention is useful for wireless communication, and is particularly suitable as a reception technique when there is a possibility that signal transmission characteristics may be deteriorated due to fading.

Block diagram in an embodiment of the present invention Detailed block diagram of CIR detector in an embodiment of the present invention The figure which shows an example of the correlation output in embodiment of this invention The figure which shows the simulation result of the bit error rate with respect to CNR Block diagram of a receiver employing a conventional MRC method

Explanation of symbols

101-1 to 101-N, 501-1 to 501-N Diversity antenna 102 CIR detector 103-1 to 103-N, 104-1 to 104-N, 504-1 to 504-N Complex multiplier 105-1 -105-N, 505-1-505-N Correlator 106,506 Synthesizer 107,507 DFE
108,508 AGC
201-1 to 201-N DMF
202-1 to 202 -N Correlation detector 203 Weighted tap coefficient control circuit

Claims (5)

A diversity receiver that receives signals by a plurality of antennas and performs distortion removal after weighted synthesis of the received signals,
A CIR (Carrier to Interference Ratio) is calculated as a power level ratio between the main wave of each signal received by the antenna and the maximum interference wave with respect to the main wave, and the CIR is used. CIR weighting coefficient calculating means for calculating a weighting coefficient (CIR weighting coefficient) corresponding to each received signal,
Weighting means for individually weighting signals received by the respective antennas using the respective CIR weighting coefficients;
With
A diversity receiver characterized in that each signal weighted by the weighting means is used as an input for weighting synthesis. The diversity receiver according to claim 1, wherein the weighting combining is combining by an MRC (Maximum Ratio Combiner) method. The diversity receiver according to claim 1, wherein the CIR weighting coefficient calculating unit normalizes the CIR weighting coefficient. The CIR weighting coefficient calculation means does not perform the CIR coefficient calculation processing when all the received signals have CIRs equal to or less than a predetermined value defined according to the reception status, and sets all the CIR weighting coefficients to the same value. The diversity receiver according to claim 1, wherein the diversity receiver outputs the diversity receiver. 5. The CIR weighting coefficient calculating means sets a weighting coefficient to 0 for a received signal whose CIR is equal to or greater than a predetermined value defined according to reception conditions. Diversity receiver described in 1.

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