JP2004172650A - Communication apparatus for code division multiple access - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a communication apparatus for code division multiple access, which can reduce a circuit scale when compared with the prior art, irrespective of an increase or decrease in code multiplexing number. <P>SOLUTION: The communication apparatus for code division multiple access is arranged to receive a mutiplexed signal (received signal) obtained by multiplexing a plurality of signals spread by different spreading codes in a multi-path environment. The apparatus further comprises an RAKE composer 22 and a despreader/decider 23. The composer 22 applies delay adjustment, phase compensation and RAKE-composing weighting to each received signal, using path detection timing and a channel characteristic estimate per path, and outputs a composition result of the signals after the weighting process as a RAKE composite signal. The despreader/decider 23 despreads the RAKE composite signal according to the different spreading codes and decides a resultant received symbol. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication device for code division multiple access (CDMA) in a radio communication field such as a mobile phone and a mobile phone.
[0002]
[Prior art]
Hereinafter, a conventional communication system that employs the CDMA method as a communication method (hereinafter, referred to as a CDMA communication system) will be described.
[0003]
In a CDMA communication system, a transmitting communication apparatus spreads a plurality of signals with mutually different spreading codes, multiplexes and transmits a plurality of spread signals to the same frequency and at the same time, and transmits the multiplexed signals to a receiving communication apparatus. To separate the multiplexed received signal. Hereinafter, the operation of the communication device on the transmitting side and the receiving side will be specifically described (see Non-Patent Document 1).
[0004]
The communication device on the transmitting side first converts the coded serial signal into a parallel signal, and performs a modulation process and a spreading process in a processing unit corresponding to each spreading code. Thereafter, the plurality of signals subjected to the spreading process are transmitted in a multiplexed state. Further, the communication device on the transmitting side spreads pilot symbols necessary for performing path detection and transmission path characteristic estimation on the receiving side with another spreading code, and transmits the multiplexed symbols. The pilot symbol is a signal sequence known on the receiving side.
[0005]
On the other hand, the communication device on the receiving side despreads the pilot symbols and estimates the channel characteristics based on the obtained received symbols. A signal spread by another spreading code is despread by a finger corresponding to a multipath for each spreading code, and as a result, a received symbol is obtained. Further, the communication device on the receiving side performs phase compensation of the received symbols output from each finger based on the estimated value of the transmission path characteristic, and further performs RAKE combining on the received symbols after the phase compensation. Then, the RAKE-combined symbols are converted from parallel to serial and output.
[0006]
[Non-patent document 1]
Okawa et al., "2 Mbps Multicode Transmission Characteristics in DS-CDMA" (IEICE Communications Society Conference B-345, 1998)
[0007]
[Problems to be solved by the invention]
However, in the above-described conventional communication system, for each spreading code, despreading and phase compensation are performed by fingers corresponding to multipaths, and RAKE combining is performed. There is a problem that the circuit scale increases in proportion.
[0008]
The present invention has been made in view of the above, and it is an object of the present invention to provide a CDMA communication device capable of reducing the circuit size as compared with the related art regardless of the increase or decrease in the number of code multiplexes.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, a code division multiple access communication apparatus according to the present invention provides a signal which is obtained by multiplexing a plurality of signals spread by different spreading codes in a multipath environment. (Received signal), and further, using the detection timing of each path (path detection timing) and the estimated value of the transmission path characteristic for each path obtained by predetermined processing, RAKE combining means for performing delay adjustment, phase compensation, and weighting for RAKE combining, and outputting a combined result of the weighted signals as a RAKE combined signal, and despreading the RAKE combined signal with the different spreading codes And a despreading / judging means for judging a received symbol obtained as a result.
[0010]
According to the present invention, RAKE combining is performed before despreading. That is, the number of fingers for performing delay adjustment and phase compensation of a received signal for each path becomes equal to the number of paths to be RAKE-combined, regardless of the number of multiplexed signals. This is performed only for the signal of
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a communication apparatus for code division multiple access (CDMA) according to the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited by the embodiment.
[0012]
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a CDMA communication device (receiving side) according to the present invention. The analog reception processing unit 2 that has received the high-frequency reception signal via the antenna 1 performs processing such as down-conversion to a baseband signal and gain control. The analog / digital converter (A / D) 3 converts a received baseband signal from an analog signal to a digital signal (A / D conversion). The digital reception processing unit 4 demodulates a digital reception signal.
[0013]
FIG. 2 is a diagram showing a configuration example of the digital reception processing unit 4. In the communication device on the transmitting side, a pilot symbol (spread signal) known on the receiving side is multiplexed, as in the related art.
[0014]
The path detecting unit 20 detects the timing of the received signal corresponding to each path of the multipath generated in the propagation path using the pilot symbols multiplexed on the received signal, and outputs the result as the path detection timing. (For example, refer to the technology described in “Path Search LSI Compatible with W-CDMA System” by Ishioka et al. (1999 IEICE General Conference B-5-121)).
[0015]
The transmission path characteristic estimating unit 21 calculates a transmission path characteristic estimation value by using pilot symbols multiplexed on the received signal (for example, "Effects of Eiji et al.," Frequency offset correction method in DS-CDMA receiver "). (Refer to the technology described in the 1999 IEICE General Conference B-5-123). Here, the transmission path characteristic estimation value corresponding to each path detected by the path detection unit 20 is calculated.
[0016]
The RAKE combining unit 22 receives the path detection timing output from the path detecting unit 20 and the transmission path characteristic estimation value corresponding thereto, and performs RAKE combining of the received signal.
[0017]
The despreading / determining unit 23 despreads the RAKE combined signal output from the RAKE combining unit 22 with a spreading code corresponding to each multiplexed signal, and determines the obtained received symbol.
[0018]
Next, the configuration and operation of the RAKE combining unit 22 will be described in detail. The RAKE combining unit 22 performs finger compensation on the phase of the received signal corresponding to each path, and finger units 24-1, 24-2,..., 24-P which perform phase compensation on the received signal corresponding to each path. , And a synthesizing unit 25 for synthesizing. Each of the finger units 24-1, 24-2,..., 24-P has a delay unit 28 that adjusts a received signal to the timing of a corresponding path, and a transmission unit based on a corresponding estimated channel characteristic value. A phase compensator 29 that compensates for the added phase rotation and performs weighting for RAKE combining.
[0019]
The processing of the RAKE combining unit 22 can be represented, for example, by the following equation (1).
X (n) = Σ ((r (n + T (i))) × CONJG (H (n, i))) (1)
[0020]
The sum by the combining unit 25 is calculated with i = 1, 2,..., P, where P corresponds to the number of finger parts. If the number of detected paths is smaller than the number of finger parts, the sum of only the outputs of the finger parts corresponding to the detected paths is calculated. CONJG (a) represents the complex conjugate of the complex number a. R (n) represents the n-th received signal input to the RAKE combiner 22, T (i) represents the timing of the path input from the path detector 20 to the i-th finger, and H ( (n, i) represents the estimated value of the transmission path characteristic input to the i-th finger unit from the transmission path characteristic estimating unit 21, and X (n) represents the RAKE combined signal output from the RAKE combining unit 22.
[0021]
Next, the configuration and operation of the despreading / determining unit 23 will be described in detail. The despreading / determining section 23 is composed of K despreading sections 26-1, 26-2,..., 26-K corresponding to the number of multiplexed signals, and a determining section 27.
[0022]
The despreading units 26-1, 26-2,..., 26-K perform despreading processing using the corresponding spreading codes and calculate received symbols. For example, when the spreading factor is 16, processing is performed as in the following equation (2).
S (k, m) = Σ (X (16 × m + i) × C (k, i)) (2)
[0023]
The sum in the expression (2) is calculated with i = 1, 2,..., 16. X (n) represents a RAKE combined signal output from the RAKE combining unit 22, C (k, i) represents a spreading code corresponding to a signal to be despread in the k-th despreading unit, and S ( (k, m) represents a received symbol output from the k-th despreading unit.
[0024]
The determination unit 27 performs a parallel / serial conversion process on the received symbols output by the despreading units 26-1, 26-2,..., 26-K, performs a determination process, and outputs the determination result. . The determination result of the m-th symbol, for example, when determining a signal of QPSK modulation, can be expressed as the following equation (3).
Re [S (1, m)], Im [S (1, m)], Re [S (2, m)], Im [S (2, m)], ..., Re [S (K-1, m)], Im [S (K-1, m)], Re [S (K, m)], Im [S (K, m)] (3)
[0025]
Note that Re [a] represents the real part of the complex number a, and Im [a] represents the imaginary part of the complex number a. Also, in the case of multi-level modulation such as modulation scheme 16QAM (Quadrature Amplitude Modulation), a soft decision value for each bit is calculated, and the result is output.
[0026]
As described above, in the present embodiment, since the RAKE combining is performed before the despreading, even if the number of multiplexed codes is large, the circuit scale can be reduced as compared with the related art. For example, the number of finger portions in the related art is the product of the number P of paths to be RAKE-combined and the number K of multiplexed signals, and further requires despreading processing at each finger portion. On the other hand, the number of finger portions in the present embodiment is equal to the number of paths P to be RAKE-combined, regardless of the number K of multiplexed signals. Only to do.
[0027]
Embodiment 2 FIG.
FIG. 3 is a diagram illustrating a configuration example of a RAKE combining unit according to the second embodiment. The RAKE combining unit 31 of the present embodiment is different from the RAKE combining unit 22 of FIG. 2 in that a path selecting unit 32 is added. The configuration of the communication device and the configuration of the digital reception processing unit 4 other than the RAKE combining unit 22 are the same as those of the first embodiment described above with reference to FIGS. Here, only operations different from those in the first embodiment will be described.
[0028]
The path selection unit 32 receives the path detection timing output from the path detection unit 20 and the transmission path characteristic estimation value output from the transmission path characteristic estimation unit 21, and determines a path to be RAKE-combined based on the transmission path characteristic estimation value. select. .., 24-P corresponding to the selected path, and outputs the path detection timing and the transmission path characteristic estimation value. As a criterion for selecting a path, for example, when the amplitude of the transmission path characteristic estimation value is equal to or larger than a predetermined threshold value, the path is selected as an effective path, and the amplitude of the transmission path characteristic estimation value is smaller than the threshold value. If not, do not select it as a valid path.
[0029]
As described above, in the present embodiment, by selecting an effective path based on a preset criterion, a path with poor quality is not synthesized. Accordingly, in addition to the same effects as in the first embodiment, the quality of the signal after RAKE combining can be significantly improved.
[0030]
Embodiment 3 FIG.
FIG. 4 is a diagram illustrating a configuration example of a RAKE combining unit according to the third embodiment. The configuration of the communication device and the configuration of the digital reception processing unit 4 other than the RAKE combining unit 22 are the same as those of the first embodiment described above with reference to FIGS. Here, only operations different from those in the first embodiment will be described.
[0031]
The path allocating section 42 receives the path detection timing output from the path detecting section 20 and the transmission path characteristic estimation value output from the transmission path characteristic estimating section 21, and the storage section 43 and the phase compensation section 44 perform time division processing. The path detection timing and the transmission path characteristic estimation value are output to the storage unit 43 and the phase compensation unit 44, respectively, so that the phase of the received signal corresponding to each path can be compensated. That is, the output corresponding to each pass is performed in the following order within the time to complete the RAKE combining for one chip.
[0032]
First time: path detection timing → T (1), transmission path characteristic estimated value → H (n, 1)
Second time: path detection timing → T (2), transmission path characteristic estimated value → H (n, 2)
Third time: path detection timing → T (3), transmission path characteristic estimated value → H (n, 3)
:
Time P: path detection timing → T (P), transmission path characteristic estimated value → H (n, P)
[0033]
The storage unit 43 stores a fixed amount of the received signal and outputs the received signal according to the path detection timing output from the path allocating unit 42. That is, at the i-th time, a received signal r (n + T (i)) is output.
[0034]
The phase compensator 44 compensates for the phase rotation of the received signal output from the storage 43, which is added in the transmission path, based on the transmission path characteristic estimated value output from the path allocator 42, and weights the signal for RAKE combining. I do. That is, at the i-th time, the received signal r (n + T (i)) and the transmission path characteristic estimation value H (n, i) are received, and the result of the following equation (4) is output.
Y (n, i) = r (n + T (i)) × CONJG (H (n, i)) (4)
[0035]
The combining unit 45 outputs the phase-compensated received signals Y (n, 1), Y (n, 2),..., Y (n, n) sequentially output by the phase compensating unit 44 until the RAKE combining for one chip is completed. P) is cumulatively added, and after all the additions are completed, a RAKE composite signal X (n) of the following equation (5) is output.
X (n) = Σ (Y (n, i)) (5)
[0036]
As described above, in the present embodiment, RAKE combining is performed in a time-division manner. Thus, in addition to the same effects as in the first embodiment, the circuit can be further downsized.
[0037]
Embodiment 4 FIG.
FIG. 5 is a diagram illustrating a configuration example of a despreading / determining unit according to the fourth embodiment. Despreading / determining section 51 of the present embodiment is different from despreading / determining section 23 of FIG. 2 in that scramble removing section 52 is added. The configuration of the communication device and the configuration other than the despreading / determining unit 23 in the digital reception processing unit 4 are the same as those of the first embodiment described above with reference to FIGS. Here, only operations different from those in the first embodiment will be described.
[0038]
For example, when the transmitting communication apparatus scrambles the spread signal, it is necessary to remove the scramble before despreading. If this is applied to the configuration of the prior art described above, since RAKE combining is performed after despreading, a configuration for removing scrambling for each finger is required.
[0039]
On the other hand, in the present embodiment, the scramble removing unit 52 arranged at the subsequent stage of the RAKE combining unit 22 removes the scramble and outputs the removal result to each despreading unit.
[0040]
As described above, in the present embodiment, scramble is removed after RAKE combining, and then despreading is performed. Thus, in addition to the same effect as in the first embodiment, the scramble can be removed by adding a small-scale circuit as compared with the related art which requires a configuration for removing scramble for each finger.
[0041]
In the present embodiment, scrambling may be removed before or after phase compensation, not only after RAKE combining. Further, in the present embodiment, despreading / determining section 51 is applied to the configuration of the first embodiment described above, but is not limited to this, and may be applied to the configuration of the second or third embodiment. It may be.
[0042]
Embodiment 5 FIG.
FIG. 6 is a diagram illustrating a configuration example of a despreading / determining unit according to the fifth embodiment. The despreading / determining unit 61 of the present embodiment includes a high-speed Hadamard transforming unit 62 and a selection / rearrangement processing unit instead of the above-described despreading units 26-1, 26-2,..., 26-K of FIG. 63. The configuration other than the high-speed Hadamard conversion unit 62 and the selection / rearrangement processing unit 63 is the same as that of the fourth embodiment described above. Here, only operations different from those in the fourth embodiment will be described.
[0043]
The high-speed Hadamard transform unit 62 performs despreading corresponding to each spreading code collectively from the RAKE composite signal for one symbol by a known high-speed Hadamard transform (for example, refer to the technology described in Japanese Patent Application Laid-Open No. 06-301711). Calculate the symbol of Then, the selection / rearrangement processing section 63 selects necessary symbols, performs rearrangement as necessary, and outputs the result.
[0044]
As described above, in the present embodiment, received symbols are obtained by performing collective processing by high-speed Hadamard transform instead of individually performing despreading processing corresponding to each spreading code. Thus, even if the number of multiplexed codes is large, received symbols can be efficiently generated, and further downsizing of the circuit can be realized.
[0045]
【The invention's effect】
As described above, according to the present invention, RAKE combining is performed before despreading. That is, the number of fingers for performing delay adjustment and phase compensation of a received signal for each path becomes equal to the number of paths to be RAKE-combined, regardless of the number of multiplexed signals. , Only the signal of As a result, even when the number of multiplexed codes is large, the circuit scale can be reduced as compared with the related art.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of a CDMA communication device (receiving side) according to the present invention.
FIG. 2 is a diagram illustrating a configuration example of a digital reception processing unit according to the first embodiment.
FIG. 3 is a diagram illustrating a configuration example of a RAKE combining unit according to a second embodiment;
FIG. 4 is a diagram illustrating a configuration example of a RAKE combining unit according to a third embodiment;
FIG. 5 is a diagram illustrating a configuration example of a despreading / determining unit according to a fourth embodiment.
FIG. 6 is a diagram illustrating a configuration example of a despreading / determining unit according to a fifth embodiment.
[Explanation of symbols]
Reference Signs List 1 antenna, 2 analog reception processing unit, 3 analog / digital converter (A / D), 4 digital reception processing unit, 20 path detection unit, 21 transmission path characteristic estimation unit, 22, 31, 41 RAKE combining unit, 23, 51, 61 despreading / determining section, 24-1, 24-2, 24-P finger section, 25 combining section, 26-1, 26-2, 26-K despreading section, 27 determining section, 32 path selecting section , 42 path allocation unit, 43 storage unit, 44 phase compensation unit, 45 synthesis unit, 52 scramble elimination unit, 62 high-speed Hadamard conversion unit, 63 selection / reordering processing unit.

Claims (6)

In a code division multiple access communication device for receiving a signal (received signal) obtained by multiplexing a plurality of signals spread by different spreading codes in a multipath environment,
Using the detection timing (path detection timing) of each path and the estimated value of the transmission path characteristic for each path obtained by predetermined processing, delay adjustment, phase compensation, and weighting for RAKE combining for each received signal And RAKE combining means for outputting the combined result of each signal after the weighting process as a RAKE combined signal;
Despreading / determining means for despreading the RAKE combined signal with the different spreading codes and determining a resulting received symbol;
A communication device for code division multiple access, comprising: The RAKE combining means includes:
Path selection means for selecting a valid path based on the transmission path characteristic estimation value,
With
2. The communication apparatus for code division multiple access according to claim 1, wherein a reception signal corresponding to the selected path is a target of RAKE combining. The path selection means,
When the amplitude of the transmission path characteristic estimation value is equal to or larger than a predetermined threshold, the path is selected as a valid path, and when the amplitude of the transmission path characteristic estimation value is smaller than a predetermined threshold, the path is enabled. 3. The communication apparatus for code division multiple access according to claim 2, wherein the communication apparatus is not selected as a simple path. The RAKE combining means includes:
Timing adjustment means for adjusting the path detection timing and sequentially outputting the path detection timing so that the phase compensation and weighting for RAKE combining can be performed in a time-division manner;
Reception signal holding / output means for holding a predetermined amount of reception signals and sequentially outputting corresponding reception signals in accordance with the path detection timing;
Phase compensating means for performing phase compensation of a received signal and weighting for RAKE combining in the order of reception based on the transmission path characteristic estimation value for each path;
Synthesizing means for accumulatively adding the signals output from the phase compensating means and outputting the sum as a RAKE synthesized signal;
The communication device for code division multiple access according to claim 1, further comprising: If the transmitting communication device is scrambling the spread signal,
The despreading / judging means comprises:
A scramble removing unit for removing the scramble from the RAKE combined signal,
The communication device for code division multiple access according to any one of claims 1 to 4, wherein the signal after descrambling is despread. If the transmitting communication device is scrambling the spread signal,
The despreading / judging means comprises:
A scramble removing unit for removing the scramble from the RAKE combined signal,
5. The communication device for code division multiple access according to claim 1, wherein a received symbol after despreading corresponding to each spreading code is obtained from the signal after scrambling by fast Hadamard transform. .

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