JPH05292063A - Spread spectrum receiver - Google Patents

Abstract

PURPOSE:To simplify the constitution and minimize an error of a signal after detection at all times by weighting components corresponding to respective delayed waves obtained through a matching filter with a coefficient calculated by using adaptive algorithm and adding them. CONSTITUTION:The respective delayed waves received are inputted to the matching filter 61 which matches a diffusion code and reversely diffused, and also separated into the components corresponding to the respective delayed waves and inputted to a detector 62, so that they are detected at spreading code timing corresponding to the respective delayed waves. The output of the detector 62 is inputted to a multistage delay element 63 and detected components corresponding to the respective delayed waves are led out of respective delay elements. In this case, a reference signal is supplied from a reference signal generator 13 to a coefficient setter 14 in the training section of a transmitted signal to estimate the state of the transmission line, a multiplier 11 weights the components corresponding to the respective delayed waves obtained through the multistage delay element 63 by using the obtained coefficient, and an adder 12 adds them. Then control is so performed that the error of the reference signal becomes minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum receiver whose transmission characteristics are improved by diversity reception.

[0002]

2. Description of the Related Art In spread spectrum communication, a transmitting side modulates an information code with a high-speed spreading code (pseudo random code) to perform wide band spreading to spread the spectrum of a modulated wave in a wide frequency band, and the receiving side uses the same spreading. By demodulating (despreading) the received wave with a code and extracting the information code,
It is a communication method for transmitting information codes.

In the direct spread system in which the information code is multiplied by the high speed spread code to expand the band, if the delay time dispersion of the transmission path becomes larger than one code time of the spread code, the spread code time interval at the receiving side. The delayed waves extracted in step 1 can be treated as uncorrelated. That is, the amplitude and phase of each such delayed wave exhibit independent fluctuations. Therefore, by selecting one having a large amplitude from a plurality of delayed waves or combining the phases by combining them, a diversity reception effect capable of increasing the average reception level can be obtained, and the transmission error rate can be greatly improved.

FIG. 5 is a block diagram showing an example of the configuration of a conventional spread spectrum receiver for performing diversity reception. In the figure, the respective delayed waves received are subjected to despreading processing by the corresponding despreaders 51 _{1 to} 51 _n , their respective outputs are input to the combiner 52, and predetermined diversity combining processing is carried out. The combined output is detected by the detector 53.

In the combiner 52, a selective combining method of selecting the output having the largest amplitude among the respective despreaders, a pre-detection equal gain combining method of adding the phases of the respective outputs together, and other combining methods. However, the diversity reception effect can be obtained by any of the combining methods.

However, in the case where independent despreaders 51 _{1 to} 51 _n are configured for such a plurality of delayed waves, respectively, spreading codes synchronized with the timing corresponding to the delay time of each delayed wave are provided. It is necessary to generate by the despreader, multiply this by the received wave, and execute the despreading process. That is, a plurality of despreaders are required according to the number of delayed waves, which inevitably increases the circuit scale.

To overcome this drawback, there is a configuration using a matched filter as shown in FIG. In FIG. 6, each delayed wave received is input to a matched filter 61 matched to a spread code for despreading, separated into components corresponding to each delayed wave, and input to a detector 62. Each is detected at the spreading code timing corresponding to the delayed wave. The output of the detector 62 is input to the multi-stage delay element 63, the detection component corresponding to each delay wave is extracted from each delay element, and input to the combiner 64 to perform a predetermined diversity combining process.

The synthesizer 64 detects a component having a large level and selects the largest component among them, or synthesizes components having a level equal to or higher than a predetermined value. ..

[0009]

As described above, in the configuration using the matched filter 61, a plurality of despreaders can be eliminated. However, in the components corresponding to the respective delayed waves obtained as the output of the matched filter 61, as shown in the delay time dispersion diagram shown in FIG. And that only noise components are received. Note that in FIG. 7, the horizontal axis represents time and the vertical axis represents level. Components A, B, C,
Although D exceeds a predetermined level, a large interference wave or noise is superimposed on the desired wave in the component B, and the component C is only the interference wave component or the noise component.

Here, if the combiner 64 simply selects one with a large level of each component, first the components A, B, C, D
Is extracted. In this way, the combiner 64 cannot determine whether each component is a desired wave or an unnecessary component. Therefore, when selecting or combining only the level of each component, the unnecessary components are combined together. As a result, the transmission characteristics deteriorate.

Furthermore, in the case of equal gain combining by the combiner 64, it is necessary to measure the delay time and phase of each delayed wave and to combine the components in-phase based on the measured delay time and phase. To this end, it is necessary to newly provide a device for measuring the delay time and the phase of each delayed wave. Literature (A. Salmasi and K.
S. Gilhousen, "On the system desine aspects of coded
ivision multiple access (CDMA) applied to digital
cellular and personal communications networks ", 41th
(IEEE VCT pp.57-62, 1991), the transmitter side is equipped with a transmitter that separately transmits a pilot signal for measuring the delay time and phase of each delayed wave, and the receiver side receives the pilot signal. A configuration for arranging the receiver is shown. In this case, it is necessary to further allocate signal power to the pilot signal, which is uneconomical.

The present invention provides a spread spectrum receiver capable of maximizing the diversity reception effect by reducing the characteristic deterioration due to the interference component and the noise component at the time of diversity combining of the components in the configuration using the matched filter. The purpose is to do.

[0013]

According to the present invention, in a spread spectrum receiver using a matched filter, as a diversity reception processing means, a detection component corresponding to each delayed wave is weighted with a predetermined weight and added, and diversity combining is performed. The weighted addition means that outputs the result, the detection component corresponding to each delayed wave, the weighted addition output, and the predetermined reference signal are used to estimate the transmission path state using an adaptive algorithm, and a weighting coefficient that reduces the error after the weighted addition is set. And a weighting control means for setting.

[0014]

The present invention reduces the error after weighted addition by weighting and adding the components corresponding to each delayed wave obtained through the matched filter with the coefficient calculated using the adaptive algorithm. can do. As the reference signal, a known training signal is used in the training section of the transmission signal, and the weighted addition output code is used in the data section, so that the influence of the interference component and the noise component in each delayed wave can be reduced, and the diversity signal can be reduced. The reception effect can be effectively brought out.

In the configuration of the present invention, since a matched filter is used, a plurality of despreaders corresponding to each delayed wave are unnecessary, and the delay time and phase of each delayed wave are measured by diversity combining after detection. There is no need to provide a special device therefor.

[0016]

1 is a block diagram showing the configuration of an embodiment of a spread spectrum receiver according to the present invention.

In the figure, each delay wave received is input to a matched filter 61 matched to a spread code for despreading, separated into components corresponding to each delay wave, and input to a detector 62. , Are detected at the spreading code timings corresponding to the respective delayed waves. The output of the detector 62 is input to the multistage delay element 63, and the detection component corresponding to each delayed wave is extracted from each delay element.

Here, the feature of this embodiment is that
A multiplier 11 that multiplies the components extracted from each stage of the multi-stage delay element 63 by a predetermined coefficient, and an adder 1 that adds the outputs of the multipliers and outputs the result as a diversity combining result.
2, a known training signal in the training section of the transmission signal, a reference signal generator 13 that outputs the sign of the adder output as the reference signal in the data section, and the reference signal,
The multi-stage delay element 63 is provided with a coefficient setter 14 for inputting the components extracted from each stage and the adder output and setting a predetermined coefficient in the multiplier 11.

That is, one matched filter 61 despreads and separates a plurality of delayed wave components, and a detector 62
The component corresponding to each delayed wave is detected by and the multistage delay element 63
The configuration in which each component is separated and taken out is the same as the conventional one. In the present invention, the reference signal is supplied from the reference signal generator 13 to the coefficient setter 14 in the training section of the transmission signal to estimate the state of the transmission path, and the multiplier 1 is used using the obtained coefficient.
At 1, the components corresponding to the respective delayed waves obtained via the multi-stage delay element 63 are weighted, and the adder 12 adds them. Then, in this weighting, by controlling so that the error between the reference signal and the adder output is minimized, compared to the conventional case where the magnitude of the level of the component corresponding to each delayed wave is simply observed, The influence of the interference component and the noise component can be reduced. As described above, the present invention is characterized in that the diversity reception effect is realized by a new method using the multiplier 11, the adder 12, the reference signal generator 13, and the coefficient setting device 14.

Here, a method of estimating the transmission line state will be described. FIG. 2 shows a frame configuration example of a transmission signal. In the training section in which the training signal 21 is transmitted, the reference signal generator 13 generates a known training signal as a reference signal. Therefore, the coefficient setter 14 uses an adaptive algorithm (for example, S. Haykin, "Adaptive Filter") according to each output of the multistage delay element 63 and the output of the adder 12.
(Detailed in "Theory") can be used to estimate the state of the transmission line. First, by comparing each output of the multistage delay element 63 with the reference signal, each output is affected by interference and noise. The coefficient setting unit 14 sets a small multiplication coefficient for the delay element output containing a lot of interference or noise, and contains a large number of desired wave components. A large multiplication coefficient is first determined for the delay element output, and then the coefficient setter 14 squares the difference between the reference signal and the output of the adder 12 using, for example, an algorithm based on the least square method. If the multiplication coefficient of each delay element output is controlled so that the error is minimized, the adder 12 can obtain an output with the least influence of interference and noise.

In the data section in which the data signal 22 is transmitted, there is no known signal on the receiving side, so the reference signal generator 13 determines the sign of the output of the adder 12 and outputs the sign as the reference signal. To do. The coefficient setter 14
Using the adaptive algorithm described above, each multiplication coefficient is changed so that the error is minimized.

As a result, even if the state of the transmission line fluctuates with time and the amount of the interference wave component and the noise component overlapping each delayed wave fluctuates, the optimum reception with the least influence of the interference and noise at that time is obtained. It can be tracked to get the signal. That is, it is possible to avoid the deterioration of the diversity reception effect by directly combining the interference component and the noise component, which are the drawbacks of the conventional technique.

Here, the results of computer simulation performed to confirm the effectiveness of the present invention will be shown. In the simulation model, as shown in FIG. 3, an interference wave is generated at a temporally different position with respect to the desired wave, the desired wave is combined with the interference wave, and noise that fluctuates randomly is added. Figure 4
Is the result, and the horizontal axis is the signal-to-interference power ratio (SI
R), the vertical axis is the average bit error rate (BER). The signal-to-noise power ratio was 2 dB.

For reference, the characteristic by the conventional equal gain combining method is shown, but the BER increases as the SIR decreases. On the other hand, in the configuration according to the present invention, the BER is kept at a constant value even if the SIR is lowered, and it can be seen that the diversity reception effect is effectively brought out.

[0025]

As described above, according to the present invention, the diversity reception effect can be obtained with one matched filter and one detector, and the structure of the spread spectrum receiver can be simplified. In addition, since the error of the signal after detection can always be minimized by the transmission path state estimation function, it is possible to avoid deterioration of the diversity reception effect due to the influence of interference power and noise power, and further improve transmission characteristics. Can be made

In the description of the embodiments, the algorithm for minimizing the error of the weighted addition output with respect to the reference signal has been described, but the adaptation algorithm is simplified by relaxing the condition of "minimizing the error". Can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a spread spectrum receiver according to the present invention.

FIG. 2 is a frame configuration example of a transmission signal.

FIG. 3 is a simulation model for confirming the effectiveness of the present invention.

FIG. 4 is a simulation result confirming the effectiveness of the present invention.

FIG. 5 is a configuration example of a conventional spread spectrum receiver that performs diversity reception.

FIG. 6 is a configuration example of a conventional spread spectrum receiver using a matched filter.

FIG. 7 is a delay time dispersion of a transmission line.

[Explanation of symbols]

 11 multiplier 12 adder 13 reference signal generator 14 coefficient setter 51 despreader 52 synthesizer 53 detector 61 matched filter 62 detector 63 multi-stage delay element 64 synthesizer

Claims (1)

[Claims] 1. A matched filter that takes in a spread spectrum received wave, performs despreading matching the spread code, separates into a component corresponding to each delayed wave, and outputs each matched wave. A detector that detects each of the components at each spread code timing, a multistage delay element that separates and extracts the detection component corresponding to each delayed wave, and captures each detection component that is separated by the multistage delay element,
In a spread spectrum receiver equipped with a diversity reception processing means for performing a predetermined diversity reception processing and outputting, the diversity reception processing means adds a predetermined weight to the detection component corresponding to each of the delayed waves, A weighted addition means for outputting as a diversity combining result, a detection component corresponding to each delayed wave, the weighted addition output, and a predetermined reference signal are used to estimate the transmission path state using an adaptive algorithm, and the error after weighted addition is reduced. And a weighting control means for setting a weighting coefficient for the spread spectrum receiver.