JPH11239080A - Spread spectrum receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable rake composition with a signal requiring no training signal and to reduce the redundancy of signals by using a constant modulus algorithm as a rake composition algorithm. SOLUTION: A signal inputted from an antenna 10 is converted by a receiver 11 from a radio frequency band to a base band, The converted signal is reversely spread by a reverse spreader 12 with the same spread code (replica) as a spread code used for spreading and separated into a precedent signal and a delayed signal by a delay line 13. The separated precedent signal and delayed signal are weighted by being multiplied through a multiplier 14 by a tap coefficient under the control of a constant modulus algorithm(CMA) control part 17 and the weighting results are added by an adder 15 to enable rake composition so that the signal-to-noise power ratio becomes maximum. Consequently, the same result as with maximum ratio diversity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for use in a spread spectrum communication system using a spread transmission signal spread over a wide band by multiplying an information signal of a transmission signal by a spreading code having a high signal speed. . The present invention particularly relates to a receiving apparatus that performs rake combining (RAKE combining) for performing in-phase combining of a leading signal and a delayed signal of a received signal.

[0002]

2. Description of the Related Art FIG. 2 shows an example of the configuration of a conventional spread spectrum receiver for realizing rake combining. This receiving device
RLS algorithm (R
ecursive leastsquares Algorithm). The received signal input from the antenna 20 is
Is converted from the radio frequency band to the baseband. The converted signal is despread by the despreader 22 using the same spreading code as the spread signal used for transmission, and separated by the delay line 23 into a leading signal and a delayed signal. A rake combining is realized by multiplying the preceding signal and the delayed signal, which are the outputs of the delay line 23, by a tap coefficient in a multiplier 24 and weighting them, and adding them in an adder 25. The tap coefficients in the multiplier 24 are sequentially updated, and the update algorithm uses the RLS algorithm. That is, an RLS algorithm control unit 27 is provided, and the weighting of the tap coefficients of the multiplier 24 is controlled based on the training signal from the training signal generator 28.

References: Higashi and Matsumoto: "Experimental study of RAKE reception after adaptive detection for mobile radio," 1992 Shushingaku Zendai A-132 RLS algorithm automatically adjusts tap coefficients using least squares method. It is a recursive algorithm, also called a recursive least squares algorithm. Hereinafter, the operation when the RLS algorithm is applied to rake combining will be described in detail.

First, the symbols are defined as follows: input signal vector [1], tap coefficient vector [2], output signal y (n), training signal d (n), forgetting coefficient λ, input signal It is assumed that the inverse matrix of the signal correlation matrix is [outside 3], the gain vector is [outside 4], and the estimation error is α (n). The input signal vector represents a plurality of outputs of the delay line as a vector, and when the i-th output of the delay line is u (i, n), it is expressed by the following equation.

[0005]

[Outside 1]

[0006]

[Outside 2]

[0007]

[Outside 3]

[0008]

[Outside 4]

[0009]

[Outside 5] Here, each output u (i, n) is a complex number and represents an in-phase component and a quadrature component of the signal. A signal y (n) is obtained by multiplying the input signal vector [1] by the tap coefficient vector [2], and is represented by the following equation.

[0010]

[Outside 6] Further, the training signal d (n) is externally used in the RLS algorithm (in FIG. 2, the training signal generator 2).
8), and it is necessary to refer to this signal when updating the tap coefficient. The forgetting factor λ is a parameter used to forget the distant past data in order to follow the statistical fluctuation of the incoming data. The operation of the RLS algorithm based on the above preparation is as follows (reference: S. Heikin: "Introduction to Adaptive Filters", Hyundai Kogyosha).

The following initial conditions

[0012]

[Outside 7] Start at and proceed as follows. (1) It is assumed that n = 1. (2) Calculate the gain vector.

[0013]

[Outside 8] (3) Calculate the true estimation error.

[0014]

[Outside 9] (4) Calculate the estimation error of the coefficient vector.

[0015]

[Outside 10] (5) Update the inverse matrix of the correlation matrix of the input signal.

[0016]

[Outside 11] (6) Return to step (2) with n = n + 1, and repeat the procedure.

As can be seen from these procedures, RLS
The algorithm needs a known training signal d (n) during the training process, and updates the tap coefficients with reference to the training signal from the training signal generator.

FIG. 3 shows a frame format of a signal when the RLS algorithm is used. As shown in FIG. 3, since the transmission signal includes the information signal and the training signal, the redundancy of the signal increases.

[0019]

As described above, the conventional R
With the method of performing rake combining using the LS algorithm, there is a problem that a signal requires a training signal, thereby increasing signal redundancy, and a problem that requires a training signal generator in a receiving device. Was.

The present invention solves such a problem, and does not require a training signal for the signal, reduces signal redundancy, and does not require a training signal generator in the receiving apparatus. An object is to provide a receiving device.

[0021]

SUMMARY OF THE INVENTION The present invention provides a MOD synthesis algorithm for a spread spectrum receiver.
thm, hereinafter also referred to as CMA). By using this CMA, the present invention can realize rake combining with a signal that does not require a training signal, and can reduce signal redundancy. Also, no training signal generator is required for the receiving device.

That is, a first aspect of the present invention is a direct spread spectrum communication using a transmission signal whose spectrum is spread over a wide band by multiplying an information signal by a spreading code having a higher signal speed than the information signal. An antenna, a receiver that converts a frequency band of a received signal received by the antenna from a radio frequency band to a baseband, and a despreader that performs despreading with the same spreading code as that used for spread spectrum. In a spread spectrum receiving apparatus including a spreader, a combiner that combines a delay line corresponding to a delay time of a preceding wave and a delayed wave generated in a radio section and a leading signal and a delayed signal after despreading using a CMA And characterized in that:

The despread signal is input to a delay line, and is delayed so as to correspond to the delay time of the preceding wave and the delayed wave generated in the radio section. The in-phase component and the quadrature component delayed by the delay line are sequentially converted by the CMA. Are weighted by a tap coefficient that is dynamically updated, the weighted result is added by an adder, and rake combining is performed. By performing rake combining using this CMA, rake combining can be performed without the need for a training signal. Further, after a delay is given by a delay line, despreading can be performed.

A second aspect is a spread spectrum receiving apparatus having a plurality of antennas to simultaneously realize spatial diversity and rake combining, and has a higher signal speed for an information signal than an information signal. It is used in a direct spread spectrum communication system using a transmission signal in which a spectrum is spread over a wide band by multiplying by a spreading code. In a spread spectrum receiving apparatus comprising a plurality of receivers for converting to a spread code and a plurality of despreaders for performing despreading with the same spreading code as that used for spread spectrum, a leading wave and a delayed wave generated in a radio section are generated. A plurality of delay lines corresponding to the delay time and a despread preceding signal and a delayed signal corresponding to each antenna are represented by C Characterized by comprising a combiner for combining with the A. In the invention of the second aspect, the rake combining and the spatial diversity can be simultaneously realized at the same time, and the influence on fading can be reduced.
Fading resistance can be improved.

A third aspect of the present invention is to select a signal having the largest signal-to-noise power ratio among a preceding signal and a delayed signal after despreading of a plurality of antennas, and then perform rake combining. A plurality of delay lines corresponding to the delay time of the preceding wave and the delayed wave generated in the section, and the signal having the largest signal-to-noise power ratio among the leading signal and the delayed signal after despreading of the individual antennas are selected, And a combiner for combining the selected signals for all antennas using CMA. According to the invention of the third aspect, it is possible to perform rake combining after performing diversity selection, and to provide a receiving apparatus in which the effect of fading is reduced and fading resistance is enhanced.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 illustrates an embodiment of the present invention. This spread spectrum receiving apparatus is used for a direct spread spectrum communication system using a transmission signal whose spectrum is spread over a wide band by multiplying an information signal by a spreading code having a higher signal rate than the information signal, An antenna 10, a receiver 11 for converting a frequency band of a received signal received by the antenna 10 from a radio frequency band to a baseband, and a despreader for performing despreading using the same spreading code as that used for spread spectrum. And a delay line 13 corresponding to a delay time of a preceding wave and a delay wave generated in a radio section.
, A multiplier 14 and an adder 15, and a tap coefficient of the multiplier 14 is a constant modulus Algori.
and a CMA control unit 17 which controls by thm. Note that a discriminator 16 is provided at a stage subsequent to the adder 15, and the rake combined output of the adder 15 is decoded and output as data.

The operation of FIG. 1 will be described. Antenna 10
Is converted from a radio frequency band to a baseband by the receiver 11. The converted signal is despreader 1
2, the signal is despread by the same spreading code (replica) as the spreading code used for spreading, and is separated by the delay line 13 into a leading signal and a delayed signal. The separated leading signal and delayed signal are weighted by the multiplier 14 by multiplying the tap coefficient under the control of the CMA control unit 17, and the weighted result is added by the adder 15, thereby dividing the leading signal and the delayed signal. Rake combining can be performed so that the signal-to-noise power ratio is maximized. Thereby, a result equivalent to the maximum ratio combining diversity is obtained. In the present invention shown in FIG. 1, CMA is used as an algorithm for updating tap coefficients. CMA is an algorithm that uses the constant envelope of a signal as prior knowledge, and does not require a training signal in the signal format. Therefore, there is an advantage that signal redundancy is reduced as compared with a method using a conventional RLS algorithm. . It is not necessary to provide a training signal generator in the receiving device. Also, if the number of tap coefficients is M in the RLS algorithm, the required number of multiplications is proportional to M ² because of the M × M matrix operation. There is the advantage of a small amount. This means that the CMA is also effective in that the arithmetic unit of the receiving device can be simplified.

[0029]

FIG. 4 shows the configuration of a receiving apparatus according to a first embodiment of the present invention. The configuration shown in FIG. 4 is an example in which a matched filter is used as a despreader and a delay detector is applied. In FIG. 4, the antenna 40, the receiver 4
1, the delay line 43, the multiplier 44, the adder 45, the CMA control unit 47, and the discriminator 46 are the antenna 10 and the receiver 1 shown in FIG.
1, a delay line 13, a multiplier 14, an adder 15, a CMA control unit 17, and a discriminator 16. The matched filter 42 corresponds to the despreader 12 in FIG. 1 and has a configuration in which a delay detector 48 is inserted between the adder 45 and the discriminator 46.

The operation of the receiver shown in FIG. 4 will be described. The radio frequency signal input from the antenna 40 is converted by the receiver 41 into a baseband in-phase component and a quadrature component. Next, the output of the receiver 41 is subjected to despreading by a matched filter 42 using a spreading code, and is input to a delay line 43. Each of the in-phase component and the quadrature component delayed by the delay line 43 is weighted by a multiplier 44 to a tap coefficient sequentially updated by a CMA, and the weighted result is added by an adder 45. Then, the delay detector 48 provided at the subsequent stage of the adder 45 removes an error caused by the carrier frequency shift occurring between the transmitting and receiving devices. The data is decoded and output by the discriminator 46 at the subsequent stage of the delay detector 48.

In the first embodiment, an example is shown in which the despreader is applied in the baseband. However, the despreader can be applied in the intermediate frequency band or the radio frequency band. Although an example using a matched filter as the despreader has been described, a method of multiplying by a spreading code and integrating by a low-pass filter or the like or a convolver may be used as the despreader. Further, when the above-described method of multiplying and integrating the spreading code is applied, the delay line can be arranged before the despreader. Furthermore, synchronous detection can be used instead of delay detection as the detection method.

Next, the rake combining operation will be described in detail. First, for ease of explanation, the in-phase component of the i-th output signal of a delay line having a different delay time is expressed as I _i and the quadrature component Q _i . Each I _i , Q _i is multiplied by a tap coefficient,
This operation is shown in equation (1).

[0033]

[Outside 12] In this equation (1), WC _i (m) and WS _i (m) are calculated at time m
Represents the tap coefficient at the time of I _i ′ and Q _i ′
4 shows an in-phase component and a quadrature component after being weighted by tap coefficients. Here, since the tap coefficient is sequentially updated, the time m is used. Weighted I _i ′,
Q _i ′ are added over all i to obtain an in-phase component I and a quadrature component Q after the addition. This relationship is represented by equation (2).

[0034]

[Outside 13] The outputs I and Q are obtained as a result of rake combining. By controlling the tap coefficients so that the signal power to noise power ratio is maximized, rake combining having characteristics equivalent to the maximum ratio combining diversity is realized. it can.

Next, a description will be given of a tap coefficient formula by CMA. (Reference: JR Treichler and M.G. Larimore: "Ne
w processing techneques based on the constant adap
tivealgorithm, "IEEE Trans. Acoust., Speech & Sign
al processing, ASSP-33, pp.420-431, 1985) The evaluation function used in CMA is

[0036]

[Outside 14] It is. Here, σ represents a desired amplitude. This evaluation function uses prior knowledge that the amplitude of the desired signal is constant, and does not include a training signal.
The CMA operates to minimize the evaluation function J and updates the tap coefficients. By minimizing the evaluation function, the signal-to-noise power ratio can be maximized. An update equation using the steepest descent method is shown by equation (3).

[0037]

[Outside 15] In the equation (3), the in-phase component I _i and the quadrature component Q _i which are outputs of the delay line, and I and Q obtained by adding the result obtained by multiplying them by a tap coefficient are added. Not included.

(Second Embodiment) FIG. 5 shows an embodiment of the second aspect of the present invention. The embodiment shown in FIG. 5 is an example applied to space diversity having a plurality of antennas. Compared with the example of FIG. 1, the embodiment has a plurality of antennas 50 and a receiver 51,
The difference is that there are a plurality of despreaders 52 and delay lines 53.
In the receiving apparatus shown in FIG. 5, one set of a preceding signal and a delayed signal exists for one antenna, but a plurality of such sets exist due to a plurality of antennas. This receiving apparatus can simultaneously realize rake combining and spatial diversity by combining all sets of outputs collectively by CMA.

(Third Embodiment) FIG. 6 shows an embodiment of the third aspect of the present invention. In the embodiment shown in FIG. 6, the selector 68 selects a signal having the largest signal-to-noise power ratio among the despread leading signal and the delayed signal of the signals received by the individual antennas using a plurality of antennas. And combine the result into C
Rake synthesis by MA. That is, a plurality of antennas 60a to 60c, receivers 61a to 61c, despreaders 62a to 62c, and delay lines 63a to 63c are provided.
For each of the delay lines 63a to 63c, the selector 68a selects the signal having the largest signal-to-noise power ratio among the despread preceding signal and the delayed signal for each individual antenna.
６８68c, weighting is performed by the tap coefficients under the control of the CMA control unit 67 in the multipliers 64a〜64c,
Rake combining is performed by adding in the adder 65. The output after the rake combination is decoded by the discriminator 66 and output as data. In the third embodiment, a diversity effect cannot be expected because a selective combining method which is partially inferior to the maximum ratio combining method is used as compared with the second embodiment, but the number of tap coefficients controlled by the CMA is reduced. Because you can
Since the convergence time of the CMA is reduced, fading tracking is good, and reception with high fading resistance can be performed.

[0040]

As described above, in the present invention, since CMA is used as an algorithm for synthesizing a preceding signal and a delayed signal in rake synthesis, a known training signal is not required, signal redundancy is reduced, and transmission is performed. Road efficiency can be improved. Further, since it is not necessary to provide a training signal generator in the receiving device, the receiving device can be simplified. Furthermore, since the amount of calculation of the CMA is smaller than that of the RLS algorithm, the receiving apparatus can be simplified. Further, by adopting the space diversity configuration, it is possible to follow the change even in a radio section where fading is large, and it is possible to provide a receiving apparatus with high anti-fading property.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a receiving apparatus according to a first aspect of the present invention.

FIG. 2 is a block diagram showing a conventional receiver for performing rake combining.

FIG. 3 is a diagram showing a signal format of a conventional system.

FIG. 4 is a block diagram showing a receiving apparatus according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing a receiving apparatus according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a receiving apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 10, 20, 40, 50, 60 Antennas 11, 21, 41, 51, 61 Receivers 12, 22, 52, 62 Despreaders 42 Matched Filters 13, 23, 43, 53, 63 Delay Lines 14, 24, 44, 54, 64 Multipliers 15, 25, 45, 55, 65 Adders 16, 26, 46, 56, 66 Classifiers 17, 47, 57, 67 CMA control unit 27 RLS algorithm control unit 28 Training signal generator 48 Delay detector 68 selector

Claims (3)

[Claims] 1. A direct spread spectrum communication system using a transmission signal whose spectrum is spread over a wide band by multiplying an information signal by a spreading code having a signal speed higher than that of the information signal. A spread spectrum receiver comprising a receiver for converting a frequency band of a received signal received by an antenna from a radio frequency band to a base band, and a despreader for performing despreading using the same spreading code as that used for spread spectrum. In the device, a delay line that gives a delay corresponding to the delay time of the leading wave and the delayed wave generated in the radio section and separates the leading signal and the delayed signal, and the leading signal and the delayed signal after despreading are used as a constant modulus algorithm. And a combiner for performing rake combining using the algorithm. Place. 2. A direct spread spectrum communication system using a transmission signal whose spectrum is spread over a wide band by multiplying an information signal by a spreading code having a higher signal speed than the information signal. A plurality of receivers for converting the frequency band of the received signal received by this antenna from a radio frequency band to a baseband, and a plurality of despreaders for performing despreading using the same spreading code as that used for spread spectrum. A plurality of delay lines for providing a delay corresponding to the delay time of the preceding wave and the delayed wave occurring in the radio section and separating the leading signal and the delayed signal, and a despreading corresponding to each antenna. The leading signal and the delayed signal of the constant modulus algorithm (Constant Mo
and a synthesizer for synthesizing the spread spectrum using a dulus algorithm. 3. A direct spread spectrum communication system using a transmission signal whose spectrum is spread over a wide band by multiplying an information signal by a spreading code having a higher signal rate than that of the information signal. A plurality of receivers for converting the frequency band of the received signal received by this antenna from a radio frequency band to a baseband, and a plurality of despreaders for performing despreading using the same spreading code as that used for spread spectrum. A plurality of delay lines for providing a delay corresponding to the delay time of the preceding wave and the delayed wave generated in the radio section and separating the leading signal and the delayed signal, Select the signal with the largest signal-to-noise power ratio from the signal and the delayed signal, and connect the selected signal to all antennas. Constant Te-modulus algorithm (Constant Modulus Algorithm)
A spread spectrum receiving apparatus comprising: