JP2004328418A - Spread spectrum signal receiving system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance reception characteristics in a receiver of a spread spectrum signal. <P>SOLUTION: In the receiver 10 which despreads and demodulates received signals of a plurality of antennas, a despread processing part 18 is constituted so that a received signal of one antenna branch can be inverse-spread in despread timing (delay) acquired from the received signal of the antenna branch or other antenna branch. By such configuration, the reception characteristics are enhanced since the despread and demodulation of a message part whose receiving strength is restored can be executed by despread timing acquired from receiving signals of other antenna branches even when receiving strength of a preamble is weak and the despread timing can not be acquired. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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 device 40 shown in FIG. 7 roughly includes a signal processing unit 12 and a searcher 42.
[0004]
The signal processing unit 12 includes an A / D converter 16, a despreading processing unit 18, a demodulation processing unit 20, and a RAKE combining unit 24. The A / D converter 16 converts the received signals I (t) and Q (t) separated into the I channel (Ich) and the Q channel (Qch) into digital signals. The digitally converted signal is despread by the despreading unit 18 and demodulated by the demodulation unit 20. Then, the plurality of signals demodulated by the demodulation processing unit 20 are combined by the RAKE combining unit 24 to generate a demodulated signal. Here, the part where the despreading processing unit 18 and the demodulation processing unit 20 are connected in series is called a finger 22. A plurality of fingers 22 are provided in parallel, each of which is used to demodulate a signal received via a different transmission path (multipath). Therefore, the despreading timing (phase) of the finger 22 is set to be different from each other so as to correspond to each path. Then, the signals despread and demodulated by each finger 22 are combined by a RAKE combining unit 24 to obtain a demodulated signal. The finger 22 performs despreading and demodulation on the message part of the received signal.
[0005]
The searcher 42 determines the despread timing of each finger 22 (despread processing unit 18) based on the digitized received signal. The searcher 42 has a complex correlator 28, a power detection unit 30, a threshold determination unit 32, and a timing determination unit 34. Among them, the complex correlator 28 sequentially performs complex despreading on the preamble of the digital reception signal at each timing of the sampling rate of the A / D converter 16 to obtain a correlation value. The power detector 30 detects the output level of the complex correlator 28 (ie, the magnitude of the correlation value) for each timing. The threshold determination unit 32 determines the magnitude of the output level of the power detection unit 30 with respect to a predetermined threshold. The timing determination unit 34 determines the despread timing based on the magnitude determination result. Specifically, among the timings at which the output level (that is, the correlation value) of the power detection unit 30 becomes higher than the threshold value, one or more timings at which the correlation value peaks over time are obtained. Here, when there are a plurality of peak timings, the timing is adopted as the despreading timing of the finger 22 in ascending order of the correlation value. As this type of receiving apparatus, for example, the one disclosed in Patent Document 1 is known.
[0006]
[Patent Document 1]
JP-A-2002-290277
[Problems to be solved by the invention]
As described above, in the conventional receiving apparatus, the despread timing is obtained from the preamble of the received signal, and the demodulated signal is obtained from the message part of the received signal. Usually, there is a time lag (for example, 3.99 ms) between the preamble and the message part. For this reason, in the conventional receiving apparatus, the message part of the signal arriving on a certain transmission path is received at a level that can be demodulated, and if the despreading is executed at the corresponding despreading timing, the components can be added and combined. Despite this, if the preamble is temporarily deteriorated due to, for example, fading and the despread timing cannot be obtained, the components cannot be added and synthesized. That is, in that case, there is a problem that the reception characteristic is reduced by the component corresponding to the despread timing that could not be obtained.
[0008]
[Means for Solving the Problems]
A spread spectrum signal receiving apparatus according to the present invention is a spread spectrum signal receiving apparatus for despreading and demodulating received signals of a plurality of antenna branches, and based on a correlation value with a known spread code sequence, A despreading timing obtaining unit that obtains despreading timing for the received signal; and a plurality of despreading units that despread any one of the plurality of antenna branches with the despreading timing obtained by the despreading timing obtaining unit. A spreading processing unit, wherein the despreading processing unit can despread the received signal of one antenna branch at the despread timing acquired from the received signal of the antenna branch or the other antenna branch. Is configured.
[0009]
Further, in the spread spectrum signal receiving apparatus according to the present invention, for each of the plurality of despreading processing units, an assignment processing unit that assigns a combination of an antenna branch of a reception signal to be processed and a despreading timing for performing processing is provided. The allocation processing unit is provided, wherein the correlation value is assigned to the despreading processing unit with priority given to the combination of the despread timing exceeding the predetermined threshold and the antenna branch of the received signal obtained at the despread timing. When the unassigned despreading processing unit remains, it is preferable to assign a combination of a despreading timing whose correlation value exceeds a predetermined threshold and an antenna branch different from the antenna branch of the received signal obtained at the despreading timing. It is suitable.
[0010]
In the spread spectrum signal receiving apparatus according to the present invention, the assignment processing unit assigns a combination of a despread timing whose correlation value exceeds a predetermined threshold and an antenna branch different from the antenna branch of the received signal that has obtained the despread timing. Is preferably performed in a priority order based on the magnitude of the correlation value.
[0011]
Further, in the spread spectrum signal receiving apparatus according to the present invention, it is preferable that the allocation processing unit performs the allocation such that the combination of the antenna branch and the despreading timing does not overlap among a plurality of despreading processing units.
[0012]
Further, in the spread spectrum signal receiving apparatus according to the present invention, for each of the plurality of despreading processing units, an assignment processing unit that assigns a combination of an antenna branch of a reception signal to be processed and a despreading timing for performing processing. It is preferable to include an assignment processing unit that assigns a combination of the despread timing and each antenna branch in order from the despread timing having the largest correlation value.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is a block diagram illustrating a schematic configuration of a main part of a receiving device 10 according to the embodiment of the present invention. The receiving device 10 includes the same components as the above-described conventional receiving device 40. Therefore, here, the same components are denoted by the same reference numerals, and redundant description will be omitted.
[0015]
The receiving device 10 has a so-called diversity configuration in which a signal is received by a plurality (for example, two) of antennas 14A and 14B that are spatially separated. The signals received by the antennas 14A and 14B are transmitted by separate paths (circuits) before the despreading processing unit 18, that is, up to the A / D converters 16A and 16B. In this specification, such a signal path for each of the antennas 14A and 14B is referred to as an antenna branch.
[0016]
The despreading processing unit 18 performs a despreading process on a digital reception signal from any one of the plurality of antenna branches. Here, the despreading processing unit 18 may be configured to be able to despread the received signal of any antenna branch, or may be configured to be dedicated to any one of the antenna branches. In the former case, the instruction of the assignment processing unit 35 of the searcher 26 is determined according to which antenna branch the reception signal is to be subjected to the despreading process. The configurations and basic operations of the despreading processing unit 18, demodulation processing unit 20, finger 22, and RAKE combining unit 24 are the same as those of the above-described receiving device 40.
[0017]
The searcher 26 includes complex correlators 28A and 28B, power detection units 30A and 30B, threshold determination units 32A and 32B, and timing determination units 34A and 34B for each antenna branch. The configuration and basic operation of these components are the same as those of the above-described receiving apparatus 40. Here, the peak of the timing at which the correlation value exceeds the threshold value is obtained as the despread timing for each antenna branch. That is, the timing determination unit 34 corresponds to the despread timing acquisition unit of the present invention.
[0018]
The assignment processing unit 35 determines the condition of the despreading process in each despreading processing unit 18, that is, the combination of the antenna branch of the received signal to be processed and the despreading timing at which the process is performed. Here, the operation of the allocation processing unit 35 according to the present embodiment will be described with reference to FIGS. FIG. 2 is a diagram illustrating an example of the despread timing acquired from the received signal of each antenna branch and a correlation value at the despread timing. FIG. 3 is a diagram illustrating the antenna branches assigned to each despread processing unit 18. It is a figure showing an example of combination with despread timing. The horizontal axis in FIG. 2 is time, and the vertical axis is a correlation value. Also, here, an example in which the number of fingers 22 is 8, that is, a case where the processing conditions of a total of eight despreading processing units 18 are determined will be described.
[0019]
In the example of FIG. 2, in the antenna branch A, the correlation values a1 and a2 that peak above the threshold Cth (or above the threshold Cth) are detected at timings (phases) t1 and t2, and these timings t1 and t2 Is obtained as the despread timing. In the antenna branch B, correlation values b1 and b3 that exceed the threshold value Cth and peak are detected at timings t1 and t3, and these timings t1 and t3 are acquired as despread timings. Note that the magnitude of the correlation value is a1>b1>a2> b3.
[0020]
As illustrated in FIG. 3, the allocation processing unit 35 first allocates the combination of the despread timing and the antenna branch of the received signal whose despread timing has been acquired to the despread processing unit 18. That is, the first (No. 1) despreading processing unit 18 receives the antenna branch A and the despreading timing t1, and the second (No. 2) despreading processing unit 18 receives the antenna branch B and the antenna branch B. The despreading timing t1 is given to the third (No. 3) despreading processing unit 18 by the antenna branch A and the despreading timing t2, and the fourth (No. 4) despreading processing unit 18 is given by: , Antenna branch B and despread timing t3. Note that it is preferable that the assignment is performed in the order of the correlation values as described above.
[0021]
In this example, the number of the despreading processing units 18 is eight in total, and the number of combinations of the despreading timing and the antenna branch of the received signal whose despreading timing is acquired is four in total. Even if assigned to each despreading processing unit 18, four unspread despreading processing units 18 still remain. In such a case, the allocation processing unit 35 according to the present embodiment, the combination of the despread timing and the antenna branch different from the antenna branch of the received signal whose despread timing is acquired, specifically, 1 to No. The combination obtained by changing the antenna branch to the other antenna branch in combination 4 is assigned to the despreading processing unit 18. That is, the fifth (No. 5) despreading processing section 18 receives the antenna branch B and the despreading timing t1, and the sixth (No. 6) despreading processing section 18 receives the antenna branch A and the antenna branch A. The despreading timing t1 is given to the seventh (No. 7) despreading processing section 18 by the antenna branch B and the despreading timing t2, and the eighth (No. 8) despreading processing section 18 is given by: , Antenna branch A and despread timing t3. Here, the assignment is also performed in the order of the correlation value.
[0022]
When the plurality of antennas 14A and 14B are arranged at an appropriate interval, signals of almost the same path may be received by both of the plurality of antennas 14A and 14B. In such a case, the despreading timings of the plurality of antenna branches A and B are aligned (or close to each other). In the example of FIG. 2, the despread timing t1 is detected in both the antenna branches A and B.
[0023]
However, in the example of FIG. 2, the despread timing t2 detected in the antenna branch A is not detected in the antenna branch B, and the despread timing t3 detected in the antenna branch B is detected in the antenna branch A. Not. If such a phenomenon occurs in a situation where other despreading timings (t1 in the example of FIG. 2) are aligned in a plurality of antenna branches, the reception strength of the preamble temporarily decreases due to the effects of fading and the like, and There may be a case where the spreading timing (t2, t3 in the example of FIG. 2) is not detected. In such a case, when the message part is received, there is a possibility that the reception strength may be restored.
[0024]
Therefore, as described above, the allocation processing unit 35 according to the present embodiment combines the combination of the despread timing and the antenna branch different from the antenna branch of the received signal whose despread timing is acquired with the despread processing unit 18. Assign to Accordingly, in the example of FIG. 3, the seventh (No. 7) despreading processing unit 18 does not detect the received signal of the antenna branch B but detects the received signal of the antenna branch B in the received signal of the antenna branch B. The received signal of the antenna branch A is not detected from the received signal by the eighth (No. 8) despreading processing unit 18 and the received signal of the antenna branch B is despread at the despread timing t2. Will be despread at the despread timing t3 detected in step (1). As described above, even when the reception strength of a signal received on a certain path is low at the time of reception of the preamble and thereafter the reception strength of the signal received at the message part is high, The signal components can be despread and RAKE combined. That is, the receiving characteristics are improved as compared with the conventional receiving apparatus which cannot despread such components.
[0025]
FIG. 4 is a diagram illustrating a comparison of reception characteristics between the receiving device 10 according to the present embodiment and the above-described conventional receiving device 40. In FIG. 4, the horizontal axis represents Eb / N0 (signal-to-noise power ratio per bit: dB), and the vertical axis represents BLER (BLOCK Error Rate: block error rate). From this figure, it can be seen that the block error rate is significantly reduced by the above-described assignment. It has been found that this effect is particularly remarkable when the number of symbols in an area from which the despread timing is acquired in the received signal is small.
[0026]
In the above-described example, when a combination of the despread timing and an antenna branch different from the antenna branch of the received signal whose despread timing is acquired is assigned to the despread processing unit 18, the assignment is performed in descending order of the correlation value. However, instead of this, the allocation may be performed in ascending order of the correlation value. In particular, in a relatively favorable communication environment, as shown in the example of FIG. 2, the probability that a despread timing having a large correlation value is acquired by a plurality of antenna branches A and B increases. In such a case, if assignment is performed in the order of smaller correlation values within the range exceeding the threshold value Cth, assignment of overlapping combinations (that is, combinations set to No. 5 and No. 6 in FIG. 3) will be postponed. When the reception strength is restored at the time of reception of the message part, the combination for despreading and demodulating it (combinations set in No. 7 and No. 8) is assigned preferentially first. Become.
[0027]
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a diagram illustrating an example of a combination of the antenna branch assigned to each despreading processing unit 18 and the despreading timing in the present embodiment. This embodiment is the same as the first embodiment except that the operation of the assignment processing unit 35 is different. Therefore, only the operation of the assignment processing unit 35 will be described here. It should be noted that also in this case, when the number of the fingers 22 is 8, that is, when the processing conditions of the total of eight despreading processing units 18 are determined, the case where the despread timing of FIG. Show.
[0028]
Here, referring to FIG. 1 and No. No. 6, and no. 2 and No. In No. 5, it can be seen that the combinations of the antenna branch and the despread timing overlap (are the same). Originally, it is not necessary for a plurality of despreading processing units 18 to despread signals on a common path. Therefore, when the combination to be determined is the same as the already determined combination, the allocation processing unit 35 according to the present embodiment does not allocate the combination. Specifically, a memory (not shown) for storing a combination that has already been determined to be allocated is provided, and the allocation processing unit 35 refers to the combination stored in the memory when determining the combination, and stores the combination in the memory. When information indicating the same combination as a candidate combination is stored, it is sufficient not to adopt it. In the present embodiment, since the assignment processing unit 35 refers to information stored in the memory in order to suppress duplication of combinations, the time required for the assignment process is shorter in the first embodiment. That is, when the assignment processing unit 35 is configured using a DSP or a CPU, the processing load of the first embodiment is lighter.
[0029]
Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a diagram illustrating an example of a combination of the antenna branch and the despread timing assigned to each despread processing unit 18 in the present embodiment. This embodiment is the same as the first embodiment except that the operation of the assignment processing unit 35 is different. Therefore, only the operation of the assignment processing unit 35 will be described here. It should be noted that also in this case, when the number of fingers 22 is 8, that is, when the processing conditions of the total of eight despreading processing units 18 are determined, the case where the despreading timing of FIG. 2 is obtained is shown as an example. .
[0030]
As shown in FIG. 6, in the present embodiment, the allocation processing unit 35 has the largest correlation value among the despread timings acquired at a plurality of antenna branches (that is, the timing t1 at which the correlation value a1 is acquired). , And a combination of the despreading timing t1 and each antenna branch (individually all antenna branches) A and B is assigned (No. 1 and No. 2 in FIG. 6). After that, the same assignment processing is performed in ascending order of the correlation value. That is, as shown in FIG. 3 and No. 3 No. 4 is a combination of the timing t1 at which the next largest correlation value b1 is obtained and each of the antenna branches B and A. 5 and No. 5 6 is a combination of the timing t2 at which the next largest correlation value b2 is obtained and each of the antenna branches A and B. With such an assignment, the same effect as in the above embodiment can be obtained. Note that, in the present embodiment, as in the second embodiment, the assignment may be made so that the combinations do not overlap.
[0031]
【The invention's effect】
As described above, according to the present invention, even for a path whose reception intensity is weak at the time of detecting the despreading timing and which cannot be detected, if the reception intensity is restored at the time of message reception, despreading and demodulation can be performed. Therefore, reception characteristics are improved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a main configuration of a receiving apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of a despreading timing acquired by a receiving apparatus according to an embodiment of the present invention and a correlation value at the timing.
FIG. 3 is a diagram showing an example of a combination of an antenna branch assigned to each despreading processing unit and a despreading timing in the receiving device according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of an effect of improving reception characteristics by the receiving device according to the first embodiment of the present invention.
FIG. 5 is a diagram illustrating an example of a combination of an antenna branch assigned to each despreading processing unit and a despreading timing in the receiving apparatus according to the second embodiment of the present invention.
FIG. 6 is a diagram illustrating an example of a combination of an antenna branch assigned to each despread processing unit and a despread timing in the receiving device according to the third embodiment of the present invention.
FIG. 7 is a block diagram of a conventional receiving device.
[Explanation of symbols]
Reference Signs List 10 receiving device, 12 signal processing unit, 14A, 14B antenna, 16A, 16B A / D converter, 18 despreading processing unit, 20 demodulation processing unit, 22 finger, 24 RAKE combining unit, 26 searcher, 28A, 28B complex correlation Detectors, 30A and 30B power detection units, 32A and 32B threshold value determination units, 34A and 34B timing determination units, and 35 allocation processing units.

Claims (5)

A spread spectrum signal receiving apparatus for despreading and demodulating received signals of a plurality of antenna branches,
A despread timing acquisition unit that acquires despread timing for a received signal of each antenna branch based on a correlation value with a known spread code sequence,
Any one of the plurality of antenna branches, a plurality of despread processing units that despread at the despread timing acquired by the despread timing acquisition unit,
With
The despreading processing unit is configured to be capable of despreading a received signal of one antenna branch at a despread timing obtained from a received signal of the antenna branch or another antenna branch. Spread spectrum signal receiving device. For each of the plurality of despread processing units, comprising an allocation processing unit that assigns a combination of the antenna branch of the received signal to be processed and the despread timing to perform the processing,
The assignment processing unit assigns the combination of the despread timing whose correlation value exceeds a predetermined threshold value and the antenna branch of the received signal whose despread timing has been acquired to the despread processing unit with priority, and the unassigned by the assignment. When the despread processing unit remains, the correlation value is assigned a combination of a despread timing that exceeds a predetermined threshold and a different antenna branch from the antenna branch of the received signal obtained at the despread timing. The spread spectrum signal receiving apparatus according to claim 1. The assignment processing unit assigns a combination of a despread timing whose correlation value exceeds a predetermined threshold value and an antenna branch different from the antenna branch of the received signal that has obtained the despread timing, in a priority order based on the magnitude of the correlation value. The spread spectrum signal receiving apparatus according to claim 2, wherein the reception is performed. 4. The spread spectrum signal receiving apparatus according to claim 2, wherein the allocation processing unit performs the allocation such that a combination of the antenna branch and the despread timing does not overlap in a plurality of despread processing units. 5. For each of the plurality of despreading processing units, an allocation processing unit that assigns a combination of the antenna branch of the received signal to be processed and the despreading timing to perform the processing, in order from the large despreading timing of the correlation value, The spread spectrum signal receiving apparatus according to claim 1, further comprising an assignment processing unit that assigns a combination of the despread timing and each antenna branch.

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