JP2002094413A - Rake receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a RAKE receiver which exhibits superior reception characteristic by finding an appropriate weighting factor to each path, through simple calculation without significantly increasing the scale of hardware or power consumption. SOLUTION: Matched filters 11 and 12 input signals received through antennas 1 and 2, after the signals are converted into digital signals, respectively, and find the correlations between an already known signal contained in a pilot signal and the received signals, based on the digital signals. A channel estimator 20 detects the paths assigned to fingers 401-412, based on the outputs of the filers 11 and 12 and a RAKE combiner 50 finds the weighing factors given to the despreading results of the fingers 401-412, from the ratio of the power level of the interference amount to a path for which a weighing factor is to be calculated to the sum total of the power levels of the interference amounts to the other paths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CDM (Code Division Mu
It relates to a rake receiver of the ltiplex type.

[0002]

2. Description of the Related Art As is well known, a mobile radio system is operated in a radio wave environment in which multipath and fading have occurred due to movement of a receiving side and reflection from surrounding buildings.

On the other hand, in a mobile radio system using the CDM system, a receiver called a RAKE receiver is used as a receiver on the mobile terminal side to increase resistance to multipath and fading and to reduce reception quality. Restrained.

A RAKE receiver includes a plurality of receivers called fingers, separates a plurality of paths in a multipath environment, allocates one to each finger and receives them, and RAKE combines these reception results. Things.

[0005] By the way, it is known that, when the RAKE combining is performed, reception quality is improved by appropriately weighting the reception result of each finger. Combining by weighting such that the result of RAKE combining has the maximum gain is called maximum ratio combining. For example, the number of multipaths is m, and the S / N ratio of each path is σi (i = 1,
2,..., M), the S / N ratio when the maximum ratio is combined is σ1 + σ2 +.

In general, the calculation of a weighting coefficient for each path uses a known signal periodically included in a pilot signal in a received signal. In this calculation, in a matched filter provided in the receiver, the correlation between the known signal and the received signal is obtained for each path, and the ratio of the power level (transmission path response value) of the correlation is weighted for each path. Used as a coefficient.

However, such a transmission path response value,
Even if RAKE combining is performed with weighting based on the ratio of itself, the maximum S / N ratio cannot be obtained. In addition, in order to accurately calculate the weighting coefficient of each path so that the maximum ratio combining is performed, not only the amount of calculation is large and the hardware scale is large, but also the transmission line response value is frequently calculated. There is a problem of increasing.

[0008]

In the conventional RAKE receiver, the weighting factor of each path is calculated accurately and frequently in order to improve the S / N ratio, so that the hardware scale is increased or the power consumption is increased. Has to be increased.

The present invention has been made in order to solve the above-mentioned problem, and it is possible to obtain an appropriate weighting coefficient for each path by a simple calculation without greatly increasing the hardware scale and power consumption, thereby obtaining excellent reception characteristics. It is an object of the present invention to provide a RAKE receiver exhibiting the following.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for demodulating a received signal modulated by code spreading by despreading the received signal with a plurality of despreading means. Path allocating means for despreading a received signal, detecting a plurality of paths suitable for reception from the despread result, and allocating these paths to despreading means for reception. Combining means for performing rake combining by weighting the demodulation results of the plurality of despreading means, transmission path response value detecting means for obtaining a transmission path response value of each path assigned to the despreading means, A weighting coefficient used in rake combining is obtained based on the transmission path response value of each path obtained by the path response value detection means, and the transmission path response value of the path for which the weighting coefficient is to be calculated, and the like. The ratio of those combined channel response values of the path and comprises a weighting coefficient determination means for calculating a weighting factor for the calculation target path so as to constitute.

In the RAKE receiver having the above-described configuration, the weighting coefficient used for rake combining the results of demodulation by the plurality of despreading means is determined by the transmission path response value of the path for which the weighting coefficient is to be calculated and the other path. Of the transmission line response values.

Therefore, according to the RAKE receiver having the above configuration, the weighting coefficient can be calculated by a relatively simple calculation, so that a large-scale increase in hardware is not required, and the maximum ratio is higher than in the past. RAKE reception exhibiting excellent reception characteristics close to combining can be performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a RAKE receiver according to an embodiment of the present invention. The RAKE receiver has a matched filter (MF) 1
1 and 12, a channel estimator 20, a delay unit 30, fingers 401 to 412, and a RAKE combiner 50.

A matched filter 11 is input after a received signal received by the antenna 1 is converted into a digital signal, and based on the digital signal, a correlation between a known signal included in a pilot signal and the received signal is received. Ask for.

Similarly, the matched filter 12 is input after the received signal received by the antenna 2 is converted into a digital signal, and based on the digital signal, a known signal included in a pilot signal and a received signal are received. Find the correlation with

The correlation determined by the matched filters 11, 12, ie, the outputs of the matched filters 11, 12, are:
In a multipath delay profile as shown in FIG. 2, the level of correlation with each path is represented by a power level.

The channel estimator 20 has one slot period T
With 1 as one cycle, paths to be assigned to fingers 401 to 412 described later are detected based on the outputs of the matched filters 11 and 12. The detected paths are assigned to the fingers 401 to 412, respectively.

The channel estimator 20 controls the delay time of the delay unit 30 in accordance with the reception timing of each path assigned to the fingers 401 to 412 so that the combining timing in the RAKE combining unit 50 described later is appropriate. I do.

The channel estimator 20 determines each weighting coefficient when RAKE combining the results received by the fingers 401 to 412 with one slot period T1 as one period. The obtained weighting coefficient is
The RAKE combiner 50 is notified in association with the identification information 1 to 412.

The delay unit 30 converts the received signals received by the antennas 1 and 2 into digital signals and inputs the digital signals.
412 is input. Note that the delay unit 30 is
The digital signal is delayed by the time specified by the channel estimator 20 every 1 to 412.

The fingers 401 to 412 despread the digital signal input through the delay unit 30 based on the reception signal of the antenna 1 or 2 and receive the path allocated by the channel estimator 20. is there.

The RAKE combiner 50 includes fingers 401 to
After multiplying each despread result of 412 by a weighting coefficient for each of the fingers 401 to 412 notified from the channel estimator 20, RAKE combining is performed.

Next, the operation of the RAKE receiver having the above configuration will be described. The received signal received by the antenna 1 is converted into a digital signal and then input to the matched filter 11. Similarly, a received signal received by the antenna 2 is converted into a digital signal and then input to the matched filter 12.

The matched filters 11 and 12 calculate the correlation between the known signal and the received signal included in the pilot signal based on the digital signal, and output the correlation to the channel estimator 20.

The channel estimator 20 converts the delay profiles obtained by the matched filters 11 and 12 into power values for each slot period T1, and obtains their envelopes.

Then, as shown in FIG. 3, the maximum value of each envelope is obtained. Then, among these local maxima, as shown in FIG. 4, paths corresponding to the top 16 are detected.

Then, the interference amounts of the 16 paths obtained from the delay profile of the matched filter 11 are obtained, and based on the interference amounts, the weighting coefficients used in the RAKE combiner 50 of each path are obtained.

As a calculation method, as shown in FIG. 5, the ratio of the power level of the interference amount of the path whose weighting coefficient is to be calculated to the sum of the power levels of the interference amounts of the remaining 15 paths is calculated. Ask for. Such calculation is performed for each of the 16 paths, and the desired path power to interference power ratio Si
/ Ii (i = 1, 2,..., 16).

The channel estimator 20 also performs such calculations for 16 paths obtained from the delay profile of the matched filter 12, and a total of 32 desired filters including the matched filter 11 and the matched filter 12. A path power to interference power ratio Si / Ii is determined.

In the channel estimator 20, the process of assigning paths to the fingers 401 to 412 is performed as shown in FIG.
Is performed according to the flowchart shown in FIG. That is, in step 6a, the upper 12 paths are obtained from the total of 32 desired path power to interference power ratios Si / Ii. Then, from the maximum desired path power to interference power ratio, a path having a desired path power to interference power ratio that is included within a predetermined threshold is determined, and the process proceeds to step 6b.

In step 6b, the maximum of 12 paths obtained in step 6a are already
It is determined whether or not it is assigned to 1 to 412. Here, when all the fingers are assigned to the fingers 401 to 412, the process ends, and a preparation is made for the path assignment process based on the received signal of the next slot.

On the other hand, at most 1 obtained in step 6a
If any of the two paths is unassigned, the process proceeds to step 6c, where the value of the backward protection number BN is incremented by 1 for that path, and step 6d is performed.
Move to

In step 6d, the backward protection number BN of the path to which the backward protection number BN is added in step 6c.
Is greater than a threshold value BTHR. here,
If the threshold value BTHR has been exceeded, the process proceeds to step 6e. If not, the process ends.
Prepare for path allocation processing based on the received signal of the next slot.

In step 6e, the fingers 401 to 41
Among the two, an empty finger to which no path is assigned is detected. Here, if a vacant one can be detected, the process proceeds to step 6f. If no vacant one can be detected, the process ends, and a preparation is made for a path assignment process based on the received signal of the next slot.

In step 6f, the number of times of back protection BN is set to the threshold value B for the empty finger detected in step 6e.
A path exceeding the THR is allocated, the processing is terminated, and preparations are made for path allocation processing based on the received signal of the next slot.

In parallel with such a path assignment process, the channel estimator 20 sets the fingers 401 to 412
Is performed according to a flowchart as shown in FIG.

That is, in step 7a, the finger 4
The desired path power to interference power ratio of each path being allocated to 01 to 412 is obtained, and the process proceeds to step 7a. Step 7
In b, the fingers 401 to 41 obtained in step 7a
It is determined whether or not the desired path power to interference power ratio of each path currently assigned to No. 2 is included in the upper 12 desired path power to interference power ratios Si / Ii obtained in step 6a.

If all of the paths are included in the upper 12 paths, the processing is terminated to prepare for the path release processing at the timing of the next slot. In step 7c, the value of the forward protection frequency FN for the path is incremented by 1, and the process proceeds to step 7d.

In step 7d, the forward protection count FN of the path to which the forward protection count FN has been added in step 7c.
Is greater than a threshold value FTHR. here,
If the threshold value FTHR is exceeded, the process proceeds to step 7e. If the threshold value FTHR is not exceeded, on the other hand, the process is terminated to prepare for the path release process at the next slot timing.

In step 7e, the path allocation is released to the finger to which the path whose forward protection frequency FN has exceeded the threshold value FTHR in step 7d has been allocated,
This processing is completed, and the path release processing at the timing of the next slot is prepared.

Thus, the fingers 401 to 412
Is assigned and released, the channel estimator 20 adjusts the delay according to the reception timing of each path assigned to the fingers 401 to 412 so that the combining timing in the RAKE combiner 50 described later becomes appropriate. The delay time of the device 30 is controlled.

Further, as described above, the channel estimator 20 notifies the RAKE combiner 50 of the determined weighting coefficients corresponding to the paths assigned to the fingers 401 to 412.

On the other hand, the RAKE combiner 50 multiplies each despread result of the fingers 401 to 412 by a weighting coefficient for each of the fingers 401 to 412 notified from the channel estimator 20, and then performs the RAKE combining. I do.

As described above, in the RAKE receiver having the above-described configuration, the weighting coefficient to be given to each despread result of the fingers 401 to 412 is determined by the power level of the interference amount of the path for which the weighting coefficient is to be calculated and the remaining 15 Is set to the ratio of the total power level of the interference amount of the path.

Therefore, according to the RAKE receiver having the above configuration, the weighting coefficient can be calculated by a relatively simple calculation, so that a large-scale increase in hardware is not required, and the maximum ratio is larger than in the conventional case. RAKE reception exhibiting excellent reception characteristics close to combining can be performed.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the channel estimator 20 sets one slot period T1 as one period.
Detection of a path suitable for reception and RA
Weighting coefficients for KE combining are calculated.

Alternatively, for example, among the paths determined in step 6a, the maximum desired path power to interference power ratio is:
In the case where the threshold value TH exceeds a preset threshold value TH, the period of the processing relating to the path detection and the calculation of the weighting coefficient of the channel estimator 20 as described above may be set to T2 (> T1).

In this way, if a path having a desired path power-to-interference power ratio exceeding the threshold value TH can be received and good reception can be performed, unnecessary calculation is not performed. The power consumption of the RAKE receiver can be reduced.

As shown in FIG. 8, a speed detector 60 for detecting the moving speed of the RAKE receiver is provided. When the RAKE receiver is mounted on an automobile or the like, the speed detector 60 detects a moving speed based on the vehicle speed pulse.

If the moving speed detected by the speed detector 60 is smaller than a predetermined speed threshold value STH, the above-described processing related to path detection and calculation of weighting coefficients of the channel estimator 20 is performed. The cycle of T2 (>
T1).

In this way, when good reception can be performed by low-speed movement, unnecessary calculations are not performed, so that the power consumption of the RAKE receiver can be reduced.

Further, it is also possible to reduce the power consumption of the matched filters 11 and 12 by operating the matched filters 11 and 12 intermittently in accordance with the prolongation of the processing cycle of the channel estimator 20. It goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0053]

As described above, according to the present invention, the weighting coefficient used for rake combining the results of demodulation by the plurality of despreading means is determined by the transmission path response value of the path for which the weighting coefficient is to be calculated. , And the ratio to the sum of the transmission path response values of the other paths.

Therefore, according to the present invention, the weighting coefficient can be calculated by a relatively simple calculation, so that a large-scale increase in hardware is not required, and the present invention is superior to the conventional one in the maximum ratio combination. A RAKE receiver capable of performing RAKE reception exhibiting improved reception characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a configuration of an embodiment of a RAKE receiver according to the present invention.

FIG. 2 is a view showing a delay profile obtained by a matched filter of the RAKE receiver shown in FIG. 1;

FIG. 3 is a view for explaining a state in which a transmission path response value of a path showing a local maximum value is extracted from the delay profiles shown in FIG. 2;

FIG. 4 is a view for explaining a state in which, from among the transmission path response values shown in FIG. 3, upper 16 power supply levels are extracted.

FIG. 5 is a view for explaining a calculation method for obtaining weighting coefficients for 16 extracted paths;

FIG. 6 is a flowchart illustrating a process of assigning paths to fingers by the channel estimator illustrated in FIG. 1;

FIG. 7 is a flowchart illustrating a process of releasing a path allocated to a finger by the channel estimator illustrated in FIG. 1;

FIG. 8 is a circuit block diagram showing a configuration of a modified example of the RAKE receiver according to the present invention.

[Explanation of symbols]

 1, 2, antenna 11, 12, matched filter (MF) 20, channel estimator 30, delay unit 401-412, finger 50, RAKE combiner 60, velocity detector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K022 EE01 EE33 5K059 CC03 CC07 DD32 DD35 EE02 5K067 AA42 BB02 CC10 CC24 DD25 EE02 GG11

Claims (3)

[Claims] 1. A receiving signal modulated by code spreading is demodulated by despreading by a plurality of despreading means, respectively.
In a RAKE receiver for rake combining these demodulated signals, the received signal is despread, a plurality of paths suitable for reception are detected from the result of the despreading, and these paths are assigned to the despreading means. Allocating means for performing rake combining by weighting demodulation results of the plurality of despreading means, respectively, and a transmission path for obtaining a transmission path response value of each path allocated to the despreading means. A response value detecting means for obtaining a weighting coefficient used in the rake combining based on the transmission path response value of each path obtained by the transmission path response value detecting means; Weighting coefficient determining means for calculating a ratio between the transmission path response value of the path and the sum of the transmission path response values of the other paths as a weighting coefficient of the path to be calculated. A RAKE receiver, characterized in that: 2. The transmission line response value detection means according to claim 2, wherein when the maximum value among the transmission line response values of each path obtained by said transmission line response value detection means exceeds a preset threshold value. 2. The RAKE receiver according to claim 1, further comprising a detection cycle control unit that extends a detection cycle to a preset cycle. 3. A moving speed detecting means for detecting a moving speed, and a detecting period of the transmission path response value detecting means when the moving speed detected by the moving speed detecting means is less than a predetermined threshold value. 2. The RAKE receiver according to claim 1, further comprising a detection period control unit that extends the period to a preset period.