JP2004096230A - Spectrum diffused signal receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize the circuit scale of a spectrum diffusion signal receiver without deteriorating the time accuracy for acquiring inverse diffusion timings. <P>SOLUTION: A thinning processor 26 thins received digital signals I(i), Q(i) at a first sampling rate (m) to obtain thinned signals I(j), Q(j) at a second lower sampling rate (n). A complex correlator 28 inversely diffuses the thinned signals I(j), Q(j) at timings (j) of the second sampling rate (n) one after another to obtain correlation values Ci(j), Cq(j), using corresponding diffusion code strings thereto. Based on a correlation value C(jp(np)) at a timing jp(np) at which a correlation value C(j) being the square root of a squares sum peaks, and correlation values C(jp(np)-1), C(jp(np)+1) at one timing just before and one time just after that timing for peaking the correlation value C(j), an inverse diffusion timing determiner 36 determines the inverse diffusion timing ir(np) as a timing (i) of the first sampling rate (m) after the one timing just before and the one timing just after the timing jp(np). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spread spectrum signal receiving apparatus for receiving a spread spectrum signal.
[0002]
[Prior art]
In a direct spread spectrum spread communication system, a transmission device generates a transmission signal by modulating a baseband signal by a predetermined modulation method and performing spread spectrum processing using a spreading code such as a PN code. On the other hand, the receiving device despreads the received signal with the spreading code used in the spreading process in the transmitting device, and obtains a demodulated signal by demodulating it.
[0003]
Here, an outline of the configuration and operation of the conventional receiving apparatus will be described with reference to FIG. The conventional receiving apparatus 40 shown in FIG. 6 roughly includes a signal processing unit 12 and a searcher 42. Among them, the signal processing unit 12 converts the received signals I (t) and Q (t) separated into the I channel (Ich) and the Q channel (Qch) into digital signals, respectively, by A / D converters 14i and 14q. A despreading processing section 16a, 16b, 16c, 16d for despreading the digital reception signal, a demodulation processing section 18a, 18b, 18c, 18d for demodulating the despread signal, and a RAKE synthesis section for synthesizing the demodulated signal. 22. One of the plurality of despreading processing units 16a, 16b, 16c, 16d and one of the plurality of demodulation processing units 18a, 18b, 18c, 18d are connected in series, and the fingers 20a, 20b, 20c, 20d are respectively connected. Constitute. Signals despread and demodulated by a plurality of (four in the example of FIG. 6) parallel fingers 20a, 20b, 20c, and 20d are combined by RAKE combining section 22, and a demodulated signal is obtained.
[0004]
The fingers 20a, 20b, 20c, and 20d are used to demodulate received signals having different delay times received through a plurality of transmission paths (multipaths). That is, the despreading timing (phase) differs for each of the plurality of fingers 20a, 20b, 20c, and 20d.
[0005]
The despreading timing is determined by the searcher 42 based on the digitized received signal. The searcher 42 performs complex despreading on the digital reception signal at each timing of the sampling rate of the A / D converters 14i and 14q to obtain a correlation value, and a complex correlator 44 for each of the timings. A power detection unit 46 that detects the output level of the power detection unit, a threshold determination unit 48 that determines the magnitude of the output level of the power detection unit 46 with respect to a predetermined threshold, and a timing determination unit 50 that determines the despread timing based on the magnitude determination result. Have. The timing determination unit 50 acquires one or more timings at which the correlation value changes over time, among the timings at which the output level (that is, the correlation value) of the power detection unit 46 becomes higher than the threshold value. When there are a plurality of peak timings, a predetermined number (four in this case) from the one with the highest correlation value is set as the despread timing of each finger 20a, 20b, 20c, 20d.
[0006]
[Problems to be solved by the invention]
The despreading timing determined by the conventional receiving apparatus as described above is determined as one of the timings of the sampling rate of the A / D converter, and the true despreading timing (that is, the correlation value due to the despreading is (The highest timing). The larger the deviation is, the lower the output level due to the despreading is, and as a result, the demodulation accuracy is reduced and the code error rate is increased. For this reason, the sampling frequency of the A / D converter is often set higher than the chip frequency in order to secure the temporal accuracy of the despreading timing. However, the higher the sampling frequency of the A / D converter, the larger the circuit size, especially in searchers.
[0007]
Demands for smaller and lighter spread spectrum receivers, such as mobile phones, are increasing, and a reduction in circuit size is desired. However, as described above, it is not preferable to lower the sampling frequency of the A / D converter from the viewpoint of demodulation performance.
[0008]
[Means for Solving the Problems]
The spread spectrum signal receiving apparatus according to the present invention is a spread spectrum signal receiving apparatus having a despread processing unit for despreading a digital received signal at a first sampling rate at a predetermined despread timing using a spread code sequence. A thinning-out processing unit that thins out a received signal to obtain a thinned-out signal having a second sampling rate lower than the first sampling rate, and performs second sampling using the spreading code sequence corresponding to the thinned-out signal. A correlation value acquiring unit for sequentially despreading at each timing of the rate to acquire a correlation value, a correlation value at a timing at which the correlation value reaches a peak, and a timing at one timing before and one timing after the timing at which the peak becomes Based on the correlation value, the first sample after the immediately preceding timing and before the immediately following timing. A despreading timing decision unit for determining a despreading timing as the timing of the ring rate, a. According to this spread spectrum signal receiving apparatus, by processing a signal whose sampling rate has been reduced by thinning out in a searcher, the circuit scale can be reduced, and the despreading timing can be set as the timing of the first sampling rate. By determining, it is possible to suppress a decrease in the time accuracy of the despreading timing.
[0009]
In the spread spectrum signal receiving apparatus according to the present invention, the despreading timing determining unit determines the peak value as a difference between the timing immediately before the correlation value reaches the peak and the timing at which the correlation value reaches the peak. A despreading timing is determined based on a ratio of a difference and a peak difference as a difference between a timing at which the correlation value reaches a peak and a timing immediately after the correlation value reaches a peak. Is preferred. By doing so, the despreading timing can be determined more simply and more accurately.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a spread spectrum signal receiving apparatus (hereinafter, referred to as a receiving apparatus) according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a main part of a receiving apparatus 10 according to the present embodiment, FIG. 2 is an explanatory diagram showing an example of a thinning process in a thinning processing unit 26, and FIG. FIG. 4 is an explanatory diagram showing an example, and FIG. 4 is an explanatory diagram showing an example of a timing determination process in the timing determination section 36.
[0011]
The receiving device 10 includes a signal processing unit 12 and a searcher 24 roughly. Among them, the signal processing unit 12 has the same configuration as that of the conventional receiving device 40 shown in FIG. As shown in FIG. 1, the A / D converters 14i and 14q sample the received signals I (t) and Q (t) (t: time) at a first sampling rate (m samples per chip). The digital received signals I (i) and Q (i) (where i is a parameter indicating each timing (phase) of the first sampling rate m) are generated.
[0012]
The searcher 24 includes a thinning processing unit 26, a complex correlator (correlation value acquisition unit) 28, a power detection unit 30, a threshold determination unit 32, a storage unit 34, and a timing determination unit 36.
[0013]
As shown in FIG. 2, the decimation processing unit 26 performs decimation processing on the digital reception signals I (i) and Q (i) at the first sampling rate m, and performs the second decimation processing at a lower rate than the first sampling rate m. Of the sampling rate n (where j is a parameter indicating each timing (phase) of the second sampling rate n (n samples per chip)). The formula: m = αn (here, α: an integer of 2 or more) holds between the first sampling rate m and the second sampling rate n. For example, the received signals I (i) and Q (i) at the first sampling rate are decimated every other timing to generate decimated signals I (j) and Q (j) with m / 2 samples per chip. Then, α = 2 and m = 2n.
[0014]
As shown in FIG. 3, the complex correlator 28 generates a spread code sequence Bi (k), Bq corresponding to each of the timings j of the second sampling rate n with respect to the decimated signals I (j), Q (j). (K) Perform complex despreading using (k = 1, 2,..., K) to obtain correlation values Ci (j) and Cq (j). In the example of FIG. 3, the correlation value when the parameter j of the decimated signals I (j) and Q (j) corresponds to the parameter k = 1 of the spread code strings Bi (k) and Bq (k) is Ci. (J) and Cq (j), but are not limited thereto. FIG. 3 shows a case where j = 3.
[0015]
In addition, the power detection unit 30 calculates the square root C (j) of the sum of squares of the correlation values Ci (j) and Cq (j) (or the sum of squares, hereinafter simply referred to as the correlation value C (j)) for each timing j. The power (amplitude level) is detected, and the threshold determination unit 32 compares the correlation value C (j) with the corresponding threshold Th, and stores the correlation value C (j) higher than the threshold Th and the timing j thereof. It is stored in the unit 34. The threshold value Th is set to a level at which the correlation value C (j) for the peak and several points before and after the peak is equal to or greater than the threshold value Th.
[0016]
Next, the operation of the timing determination unit 36 will be described with reference to FIGS. FIG. 5 is a flowchart relating to the timing determination process. First, the timing determination unit 36 changes the correlation value C (j) over time corresponding to several timings (that is, the change accompanying the increase (or decrease) of j) among the correlation values C (j) stored in the storage unit 34. Based on the peak correlation value C (jp (np)) (here, jp (np): a peak timing j among a plurality of cascaded correlation values C (j), np: a peak (that is, a path). The parameters (np = 1, 2,..., NP) and NP: the number of multipaths for performing RAKE combining are acquired (step S10). It should be noted that the number of peak correlation values C (jp (np)) to be acquired does not exceed at most NP, that is, the number of fingers (4 in the example of FIG. 1). Specifically, for example, each time the peak correlation value C (jp (np)) is detected, the parameter np is incremented (starting from np = 0) (step S12), and the np-th peak equal to the number of fingers NP is obtained. When the process of determining the despread timing (Step S20; described later) is completed, the subsequent processes for the thinned-out signals of the same origin (that is, received signals having the same transmission signal) I (j) and Q (j) are completed. (Step S14).
[0017]
Next, for each peak timing jp (np), the timing determination unit 36 calculates the peak correlation value C (jp (np)), the immediately preceding correlation value C (jp (np) −1), and the next one. Using the correlation values C (jp (np) +1) and their corresponding timings jp (np), jp (np) -1, jp (np) +1 (all at the timing j of the second sampling rate n) The despread timing ir (np) is determined as the timing i at the first sampling rate m (step S20).
[0018]
Specifically, first, the timing determination unit 36 determines, for each peak correlation value C (jp (np)), the peak correlation value C (jp (np)) and the immediately preceding correlation value C (jp (np) −). 1), and a post-peak difference D2 between the peak correlation value C (jp (np)) and the next correlation value C (jp (np) +1) is obtained (step S21).
[0019]
Then, the timing determination unit 36 compares the difference before peak D1 and the difference after peak D2 (step S22), and when the ratio thereof is equal to or more than a predetermined threshold Thd1 and equal to or less than a predetermined threshold Thd2 (that is, Thd1 ≦ D2 / In the case of D1 ≦ Thd2; for example, Thd2 = 1 / Thd1, where Thd1 ≦ 1, the peak timing jp (np) (that is, ib) is set as the despread timing ir (np) (step S23, FIG. 4 (b)). . Note that these thresholds Thd1 and Thd2 can be appropriately set according to a temporal change pattern (temporal degree of change) of the correlation value due to despreading.
[0020]
When the ratio between the difference before peak D1 and the difference after peak D2 is smaller than the threshold value Thd1 (that is, when D2 / D1 <Thd1), the timing jp (np) is one timing later than the peak timing jp (np). In the period ΔT2 before (np) +1 and after the peak timing jp (np), the despread timing ir (np) is selected as the timing i of the first sampling rate m (step S24, FIG. 4A). ). Conversely, when the ratio between the difference after peak D2 and the difference before peak D1 is larger than the threshold Thd2 (that is, when D2 / D1> Thd1), the timing jp which is one time earlier than the peak timing jp (np). In the period ΔT1 after (np) −1 and before the peak timing jp (np), the despread timing ir (np) is selected as the timing i of the first sampling rate m (step S25, FIG. 4 ( c)). As can be seen from FIGS. 4A to 4C, in steps 23 to 25, the true despread timing Rir and the peak timing jp (np) are determined according to the magnitude relationship between the pre-peak difference D1 and the post-peak difference D2. ), The despread timing ir (np) closer to the true despread timing Rir is selected.
[0021]
The selection of the despread timing ir (np) in steps 24 and 25 depends on the thinning rate in the thinning processing unit 26. Here, as an example, the received signals I (i) and Q (i) at the first sampling rate are used. ) Is thinned out every other timing to generate thinned-out signals I (j) and Q (j) of m / 2 samples per chip, that is, a case where α = 2 and m = 2n. . In this case, the timing i of the first sampling rate m during the periods ΔT1 and ΔT2 is the peak timing jp (np) (ie, ib in FIG. 4) and the timings jp (np) −1, jp (np) +1 before and after it. 4 (i.e., ia, ic in FIG. 4), and thus, as the despread timing ir (np), in step S24, the timing immediately after the peak timing jp (np) (ic in FIG. 4). In step S25, the timing immediately before the peak timing jp (np) (ia in FIG. 4) is selected, so that the despread timing ir () closest to the true despread timing Rir in each case is selected. np) can be obtained.
[0022]
Even when the number of thinning points is increased, the despread timing ir (np) can be determined as the timing i of the first sampling rate m by the same method as described above. However, as the number of thinning points increases, the number of cases (conditional branches) based on the ratio between the difference before peak D1 and the difference after peak D2 increases. For example, when three points are thinned out for four points at the timing i of the first sampling rate m (that is, when α = 4 and m = 4n), the predetermined threshold values Thd11, Thd12, Thd13, Thd14, Thd15 are set. (Thd11 <Thd12 <Thd13 <Thd14 <Thd15) is compared with D2 / D1. 1) When D2 / D1 <Thd11, ir (np) = ie1, 2) When Thd11 ≦ D2 / D1 <Thd12, ir (Np) = id1, 3) when Thd12 ≦ D2 / D1 <Thd13, ir (np) = ic1, 4) when Thd13 ≦ D2 / D1 <Thd14, ir (np) = ib1, and 5) D2 / D1 If Thd15, ir (np) = ia1 for a total of five. Here, ia1, ib1, ic1, id1, ie1 (ia1 <ib1 <ic1 <id1 <ie1; ic1 and jp (np) have the same timing) are all timings of the first sampling rate m. Regardless of the number of thinning points, as the difference ratio D2 / D1 is smaller than 1, the despreading timing ir (np) becomes a timing later than the peak timing jp (np), and conversely, the difference ratio D2 / D1. Is larger than 1, the despread timing ir (np) is a timing earlier than the peak timing jp (np).
[0023]
In the searcher, when the despreading timing is determined as the timing j of the decimated second sampling rate n, the time accuracy deteriorates by the decimation, and the error of the determined despreading timing with respect to the true despreading timing Rir is reduced. growing. In contrast, in the present embodiment, the searcher 24 uses the timing jp (np) close to the true despread timing Rir as the timing j of the second sampling rate n, the true despread timing Rir, and the timing jp (np ) Is obtained, and the despreading timing ir (np) is determined as the timing i of the first sampling rate m having a high sampling rate. It can be said that the time accuracy in the determination of is high.
[0024]
Then, the despreading processing units 16a, 16b, 16c, and 16d (FIG. 1) apply the obtained multipath components of the digital reception signals I (i) and Q (i) at the despread timing ir (np). To perform despreading.
[0025]
【The invention's effect】
As described above, according to the present invention, the circuit size of the searcher can be made smaller than before while ensuring the time accuracy of the despreading timing, and the receiving device can be downsized without lowering the performance. The weight can be reduced.
[Brief description of the drawings]
FIG. 1 is a main part configuration diagram of a spread spectrum signal receiving apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing an example of a thinning-out process in a thinning-out processing section of the spread spectrum signal receiving apparatus according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram showing an example of processing in a complex correlator and a power detection unit of the spread spectrum signal receiving apparatus according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram illustrating an example of a timing determination process in a timing determination unit of the spread spectrum signal receiving apparatus according to the embodiment of the present invention.
FIG. 5 is a flowchart of a timing determination process in the spread spectrum signal receiving apparatus according to the embodiment of the present invention.
FIG. 6 is a configuration diagram of a main part of a conventional spread spectrum signal receiving apparatus.
[Explanation of symbols]
10 (spread spectrum) receiving apparatus, 12 signal processing section, 14i, 14q A / D converter, 16a, 16b, 16c, 16d despreading processing section, 18a, 18b, 18c, 18d demodulation processing section, 20a, 20b, 20c , 20d finger, 22 RAKE combiner, 24 searcher, 26 thinning processor, 28 complex correlator, 30 power detector, 32 threshold determiner, 34 storage, 36 timing determiner.

Claims (3)

In a spread spectrum signal receiving apparatus having a despreading processing unit for despreading a digital reception signal of a first sampling rate at a predetermined despreading timing using a spreading code sequence,
A thinning-out processing unit that thins out the received signal to obtain a thinned-out signal of a second sampling rate lower than the first sampling rate,
A correlation value acquisition unit that sequentially despreads the decimated signal using a corresponding spreading code sequence at each timing of the second sampling rate to acquire a correlation value,
The correlation value at the timing at which the correlation value becomes a peak, and the correlation value at the timing before and after the timing at which the peak becomes the peak, based on the correlation value at the timing before and after the previous timing. A despreading timing determining unit that determines the despreading timing as the timing of the earlier first sampling rate,
Spread spectrum signal receiving apparatus having The despreading timing determination unit, a difference before the peak as a difference between the correlation value between the timing immediately before the correlation value becomes a peak and the timing at which the correlation value becomes a peak, and the timing at which the correlation value becomes a peak. 2. The despreading timing is determined based on a ratio of a post-peak difference as a difference between the correlation value and a timing immediately after the correlation value becomes a peak. Spread spectrum signal receiver. A method for determining the despread timing in a spread spectrum signal receiving apparatus having a despread processing unit for despreading a digital reception signal of a first sampling rate at a predetermined despread timing using a spread code sequence,
A step of decimating the received signal to obtain a decimated signal of a second sampling rate lower than the first sampling rate,
A step of sequentially despreading the decimated signal using the corresponding spreading code sequence at each timing of the second sampling rate to obtain a correlation value,
The correlation value at the timing at which the correlation value becomes a peak, and the correlation value at the timing before and after the timing at which the peak becomes the peak, based on the correlation value at the timing before and after the previous timing. Determining the despread timing as the timing of the earlier first sampling rate,
Having a method.

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