JP2002353857A - RAKE receiver and RAKE receiving method - Google Patents

Abstract

(57) [Problem] To provide a RAKE receiver that can always obtain good reception quality by adapting to changes in a propagation environment. SOLUTION: A RAKE receiver is provided with each of correlation means 101 to 10.
k, a plurality of fading compensation means 121 to 12k for fading compensation of a plurality of outputs for a plurality of spreading codes obtained by k, and a selection means 13 for selectively outputting the outputs of the fading compensation means 121 to 12k.
0, a combining means 131 for performing a combining process for obtaining a demodulation result with respect to the output of the selecting means 130, and a receiving quality estimating means 132 for estimating the respective receiving quality based on the outputs of the fading compensation means 121 to 12k. And a selection control unit 135 for determining the output of the selection unit 130 from the estimation result of the reception quality estimation unit 132.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a RAKE receiver and a RAKE receiving method used in a DS-CDMA wireless access system.

[0002]

2. Description of the Related Art A DS-CDMA (Direct Spreading-Code Division Multiple Access) system has attracted attention as a promising candidate for a wireless access system for next-generation mobile communication. The DS-CDMA system is a system in which a plurality of users perform communication using the same frequency band, and users are identified by a spreading code.

A characteristic propagation in land mobile communication is that multiple propagation occurs due to reflection, scattering, and diffraction of surrounding buildings and trees. In multiplex propagation, incoming waves interfere with each other due to differences in propagation path length. Further, since each radio wave reaches a receiving point through a different propagation path, the amplitude and the phase vary depending on the location. This fluctuation distribution can be approximated to a Rayleigh distribution in places other than the line of sight.

In the DS-CDMA system, since information data is band-spread with a high-speed spreading code, it is possible to separate a path having a propagation delay time difference larger than the period of the spreading code. By adding a plurality of separated multipath signals while adjusting their phases, a diversity effect can be obtained, and reception characteristics can be improved.

However, the mobile station fluctuates with respect to the base station, so that the delay profile also fluctuates. Therefore, in the case of mobile communication, the receiver must have a function of absorbing the fluctuation for each path and synthesizing a plurality of multipath signals in phase. Since the speed of the fluctuation increases in accordance with the speed of the mobile station, in order to perform communication even in a high-speed moving environment, a highly accurate channel estimation capable of following the fading fluctuation is required.

In the DS-CDMA system, a RAKE receiver that performs channel estimation for each path, compensates for fading fluctuations, and combines phases to achieve maximum ratio combining has been proposed. Selection of a plurality of paths for performing maximum ratio combining is performed by selecting a fixed number of paths that appear in the delay profile in descending order of signal power.

On the other hand, in the channel estimation method, when a pilot symbol has a frame structure inserted between information symbols at a fixed period, channel estimation is performed during a known pilot symbol reception period, and unknown data reception is performed. Using the channel estimation value during the period, the channel estimation value during the pilot symbol reception period, performing a process such as interpolation to obtain fading compensation, and a method of constantly transmitting a known symbol separately from the data channel. When there is an existing pilot channel, there are two types: a method of constantly acquiring a channel estimation value using the pilot channel and performing fading compensation on the data channel.

Next, the configuration of a conventional RAKE receiver will be described with reference to FIGS. Figure 4 shows the conventional RA
FIG. 5 is a block diagram showing the configuration of the KE receiver, and FIG. 5 is a diagram showing an example of a delay profile obtained by the delay profile estimating means of the RAKE receiver in FIG. In this example, a delay profile estimating means and a RAKE receiver for obtaining a demodulated output are separately provided.

The delay profile estimating means includes a spreading code generating means 401 for generating a spreading code necessary for estimating a delay profile from a received spread spectrum signal (hereinafter, simply referred to as a received signal) S; A correlator (MF) 402 comprising a correlator or a matched filter for correlating with the received signal S;
After calculating the power of the output of No. 02, a profile estimating means 403 for estimating the delay profile by performing an averaging process.

FIG. 5 shows an example of a delay profile obtained by the delay profile estimating means. In the figure, the dotted arrow indicates the signal strength of each reception path. Where RAKE
Assuming that the total number of paths used for combining is 3, the signal strengths of the respective reception paths appearing in the delay profile are selected in descending order. In this figure, a certain number (3
Selected).

Next, the RAKE receiver will be described. The received signal S is correlated with the correlation means 402 for profile estimation.
, And a plurality of correlators 411, 41
, 41k. Here, for example, if the number of correlators provided for the reception path combining is 3, the above-mentioned suffix k = 3. Similarly, the subscript k = 3 for the spreading code generating means 431, 432,..., 43k for correlating with each reception path. Here, it is assumed that the code phases of the respective spread code generating means 431 to 43k are determined based on the respective times shown in the delay profile shown in FIG.
Assuming that the correlators 411, 412, and 413 are assigned as the correlators corresponding to the order of the signal path intensities, the spread code units 431, 432,... 43k (k =
From 3), a spreading code is generated in consideration of the code phases at times t1, t2, and t3, and a correlation operation is performed with each reception path. After the correlation operation is performed, the fading compensation means 421, 422,.
By 42k (k = 3), fading distortion generated in each multiplex propagation path is reduced. Fading compensation means 421-
Each output of 42k is RAKE-combined by the combining means 404.

[0012]

However, in the above-described method of fixedly setting the number of reception paths used for RAKE combining, the number of effective reception paths differs depending on the propagation environment, so that an environment with good visibility such as a suburb. In the case where only the direct wave appears in the delay profile as in the case of, the other reception paths to be RAKE-combined contain many noise components, and as a result, the RAKE-combined output Degrades the S / N ratio.

Also, Japanese Patent Application Laid-Open No. 2000-252954 proposes a configuration in which each reception path is determined using the reception quality of the correlator output. In this proposal, however, a configuration based on the correlator output is used. Since the reception quality is used, the estimation error of the reception quality becomes large.
Ratio degradation occurs.

The use environment of the DS-CDMA system is diverse in suburbs, urban areas, and indoors, and the propagation environment changes rapidly due to the change in the use environment. Accordingly, the reception quality of each reception path is also increased at high speed. Change. Therefore, it is required to select a plurality of reception paths to be used for RAKE combining optimally according to changes in the environment.

An object of the present invention is to provide a RAKE receiver and a RAKE receiving method that can always obtain good reception quality by adapting to changes in the propagation environment.

[0016]

According to the first aspect of the present invention,
Correlation means for despreading a spread spectrum signal received using a plurality of spreading codes, and a plurality of fading compensation means for fading compensation of a plurality of outputs for a plurality of spreading codes obtained by the correlation means, respectively. Selecting means for selectively outputting the outputs of the plurality of fading compensating means; synthesizing means for performing a synthesizing process on the output of the selecting means to obtain a demodulation result; and outputs of the plurality of fading compensating means. Receiving quality estimating means for estimating the respective receiving qualities on the basis of the above, and selection control means for determining the output by the selecting means from the estimation result of the receiving quality estimating means.

The invention according to claim 2 provides the RAK according to claim 1
In the E-receiver, the reception quality estimating means includes an estimating means for estimating a ratio between signal power and interference power of each fading-compensated reception path.

[0018] The invention according to claim 3 is the RA according to claim 1.
In the KE receiver, the reception quality estimating means is constituted by estimating means for estimating a bit error rate using a known pilot symbol included in each fading-compensated reception path.

According to a fourth aspect of the present invention, the received spread spectrum signal is despread using a plurality of spread codes, and a plurality of outputs for the plurality of spread codes obtained by the despread are respectively fading-compensated. Selecting a plurality of fading compensation results, performing a combining process on the selection results to obtain a demodulation result, estimating respective reception qualities based on the plurality of fading compensation results, in the selecting step, The method is characterized in that the plurality of fading compensation results are selected from quality estimation results.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a configuration of a RAKE receiver according to a first embodiment of the present invention.

The RAKE receiver includes a plurality of correlating means 101, 102,..., 10k and spreading code generating means 111, 112,. Each of the correlation means 101 to 10k performs a correlation operation between the received signal (received spread spectrum signal) S and the spread code generated from the spread code generation means 111 to 11k, and outputs the respective results as fading compensation means 121 and 122, respectively. ,…,
Input to 12k. Fading compensation means 121,1
, 12k apply fading compensation to the input outputs, and the reception paths subjected to fading compensation are input to the selection means 130 at the same time that the reception quality estimation means 132 estimates the reception quality. You.

The selecting means 130 performs a selecting operation for selecting a desired receiving path from the input receiving paths, and the selected receiving path is connected to the synthesizing means 131. The selection operation of the selection unit 130 is performed by a selection control unit 13 described later.
4. The combining means 131 combines the selected reception paths and outputs a demodulation result DO.

On the other hand, the reception quality estimating means 132 estimates the reception quality, and the received quality estimation value is compared with the comparing means 133.
Is input to The comparing means 133 compares the input received quality estimation value with the threshold value TH, and the result of the comparison is input to the selection control means 134 and simultaneously to the delay profile 134. In the delay profile 134, the delay profile data is updated. The updated delay profile data is input to the selection control means 135. .., Based on the comparison result of the comparing means 133 and the delay profile data of the delay profile 134.
At the same time as determining the code phase of each spreading code generated from 11k and the number of generated codes, the fading compensation means 1
.., 12k so as to determine which output is connected to the synthesizing means 131.
Operation control is performed on 30.

Next, a method will be described in which some of the receiving paths provided for RAKE combining need to be deleted.

Each of the reception quality estimation values estimated by the reception quality estimation means 132 for each output of the fading compensation means 121 to 12k of each reception path is compared with the comparison means 1
When the threshold value TH is smaller than the threshold value TH of 33, the comparison result is output to the selection control means 135, and the selection control means 135 stops the generation of spread codes by the corresponding spread code generation means 111 to 11k, and the corresponding fading compensation. The selecting means 130 is controlled so that the outputs of the means 121 to 12k are not connected to the combining means 131.

Then, in order to estimate the reception quality of a path other than the selected reception path, the spread code generation means 11
Spreading codes having different code phases are generated by 1 to 11k, and the result outputs of the correlating means 101 to 10k are input to the fading compensating means 121 to 12k. The outputs of the fading compensation means 121 to 12k are input to the reception quality estimation means 132, and the reception quality corresponding to the input new code phase is estimated. This received quality estimate is
The value of the delay profile 134 is updated.

Thus, even in a situation where the propagation environment changes, the fading compensation means 121 to 12
By performing accurate reception quality estimation based on the output of k, the reception path can be deleted with high reliability.

Next, a method in the case where it is necessary to add some of the receiving paths not used for RAKE combining will be described.

In the delay profile 134, the current R
When a reception path having a reception estimation value larger than the reception quality estimation value of each reception path used for AKE combining appears, the selection control unit 135 sets a spreading code corresponding to the reception path having the larger reception estimation value to The code phase is set for the spreading code generating means 111 to 11k, and at the same time as generating the spreading code, the corresponding correlation means 101 to 101k and the corresponding fading compensating means 121 to 12k are assigned to perform a correlation operation with a new reception path. . The output of the newly assigned fading compensation means is input to the reception quality estimation means 132, and the reception quality estimation means 132 estimates the reception quality of the new reception path. When the reception quality estimation value of the new reception path is larger than the threshold value of the comparing means 133, the comparison result is output to the selection control means 135, and the output of the corresponding fading compensation means is output to the combining means 131. It is controlled to be connected.

As described above, the reception quality estimation value of each fading-compensated receiving path is used to determine the receiving path to be RAKE-combined, so that the path can be deleted from each receiving path provided for RAKE combining, or Even when a path that has not been used for RAKE combining is added, the reception path can be added or deleted while ensuring good reception quality in response to a change in the propagation environment. That is, the reception path can be effectively used, and anti-fading and anti-AWGN effects can be expected.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration of the reception quality estimating means in the RAKE receiver according to the second embodiment of the present invention.

In the present embodiment, the reception quality estimating means
It is composed of estimating means for estimating the ratio between the signal power and the interference power of each reception path for which fading has been compensated. Specifically, as shown in FIG. 2, the reception quality estimating means in the present embodiment includes modulation effect removing means 201, and modulation effect removing means 201 includes a known effect included in each fading-compensated reception path. The modulation effect is removed by quadrant correction using the pilot symbols of The output of the modulation effect removing means 201 is input to the vector averaging means 202, and the vector averaging means 202 takes a complex average of the output of the modulation effect removing means 201. The output (complex average) of the vector averaging means 202 is input to the signal power calculating means 203 and simultaneously to the interference power calculating means 204 together with the output of the modulation effect removing means 201.

The signal power calculating means 203 calculates the signal power from the output (complex average) of the vector averaging means 202. The interference power calculating means 204 is provided with the modulation effect removing means 20.
1 and the output of vector averaging means 202 (complex averaging)
Then, the interference power is calculated from the difference. Signal power calculation means 2
03 and the interference power calculated by the interference power calculation means 204 are the SIR calculation means 20
5 is input. The SIR calculation means 205 calculates a ratio between the input signal power and the interference power, and outputs this ratio as an SIR estimate (signal power to interference power ratio). This SIR estimation value is used as the reception quality estimation value of the first embodiment described above.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of the reception quality estimating means of the RAKE receiver according to the third embodiment of the present invention.

In the present embodiment, the reception quality estimating means
A BER estimating means for estimating reception quality using known pilot symbols included in each fading-compensated reception path.

More specifically, as shown in FIG. 3, the reception quality estimating means according to the present embodiment uses the incorrect reception among the total number of bits in the known pilot symbols included in each fading-compensated reception path. It has a bit error counter 301 for counting the number of bits, and a bit counter 302 for counting the total number of received bits in known pilot symbols included in each fading-compensated reception path.

Output BE of bit error counter 301
The (incorrect number of received bits) and the output BC (total number of received bits) of the bit counter 302 are input to the instantaneous BER measuring means 303. The instantaneous BER measuring means 303 calculates the ratio between the output BE of the bit error counter 301 and the output BC of the bit counter 302. Here, the instantaneous measuring means 303
Is an instantaneous value of the bit error rate, the calculated value is input to the average BER measuring means 304 to perform averaging processing such as exponential weighted averaging. Averaging processing such as exponential weighted averaging is performed, and the result of this processing is output as a BER (bit error) estimation value. This BER estimation value is used as a reception quality estimation value.

[0039]

As described above, according to the RAKE receiver of the present invention, a correlation means for despreading a spread spectrum signal received using a plurality of spreading codes, and a signal obtained by the correlation means are provided. A plurality of fading compensation means for fading compensation of a plurality of outputs for a plurality of spreading codes, a selection means for selectively outputting the outputs of the plurality of fading compensation means, and demodulation of the output of the selection means. Combining means for performing combining processing for obtaining a result, reception quality estimating means for estimating respective reception qualities based on outputs of the plurality of fading compensating means, and output by the selecting means from the estimation result of the reception quality estimating means. And selection control means for deciding the transmission quality, it is possible to always obtain good reception quality by adapting to changes in the propagation environment. Further, anti-fading and anti-AWGN effects can be expected.

Further, according to the RAKE receiving method of the present invention, the same effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a RAKE receiver according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a reception quality estimation unit in a RAKE receiver according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a reception quality estimating unit of a RAKE receiver according to a third embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of a conventional RAKE receiver.

FIG. 5 is a diagram illustrating an example of a delay profile obtained by a delay profile estimating unit of the RAKE receiver in FIG. 4;

[Explanation of symbols]

 101, 102 to 10k Correlation means 111, 112 to 11k Spreading code generation means 121, 122 to 12k Fading compensation means 130 Selection means 131 Synthesis means 132 Reception quality estimation means 133 Comparison means 134 Delay profile 135 Selection control means 201 Modulation effect removal means 202 vector averaging means 203 signal power calculating means 204 interference power calculating means 205 SIR calculating means 301 bit error counter 302 bit counter 303 instantaneous BER measuring means 304 average BER measuring means

Claims (4)

[Claims] A correlation means for despreading a spread spectrum signal received using a plurality of spreading codes, and a plurality of fading compensation means for fading compensation of a plurality of outputs for a plurality of spreading codes obtained by the correlation means, respectively. A fading compensating means, a selecting means for selectively outputting outputs of the plurality of fading compensating means, a combining means for performing a combining process for obtaining a demodulation result on an output of the selecting means, A reception quality estimating unit for estimating each reception quality based on an output of the fading compensation unit; and a selection control unit for determining an output by the selection unit from an estimation result of the reception quality estimation unit. RAKE receiver. 2. The RAKE receiver according to claim 1, wherein said reception quality estimating means comprises estimating means for estimating a ratio between signal power and interference power of each of the fading-compensated reception paths. . 3. The reception quality estimating means comprises an estimating means for estimating a bit error rate using a known pilot symbol included in each fading-compensated reception path. RAKE receiver. 4. A spread spectrum signal received using a plurality of spreading codes is despread, a plurality of outputs for a plurality of spreading codes obtained by the despreading are respectively fading-compensated, and the plurality of fading compensation results are obtained. Selecting, performing a combining process for obtaining a demodulation result on the selection result, and estimating respective reception qualities based on the plurality of fading compensation results. A RAKE receiving method, wherein a fading compensation result is selected.