JP2882480B1 - RAKE receiver - Google Patents

Abstract

Kind Code: A1 RAKE for performing RAKE combining by selecting only a signal effective for RAKE combining according to characteristics of a received signal.
Provide a receiver. A level measuring section (3) measures the level of a despread received signal, and an adaptive threshold value determining section (8) changes the level of the despread received signal while changing the variable threshold. The frequency of occurrence exceeding the threshold is counted, and based on the change characteristics of the increment of the frequency of appearance, a determination threshold for discriminating between the preceding wave and the delayed wave and noise is set, and the despread reception signal is set. The timing at which the level exceeds the determination threshold is determined, and timing information is output. The path selection unit 6 selectively outputs the despread received signal, which has been phase-inphased and weighted by the multiplier 5, to the RAKE combining unit in accordance with the timing information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rake receiver used in a spread spectrum communication system.

[0002]

2. Description of the Related Art In a spread spectrum communication system used in the DS-CDMA system, a RAKE reception is performed on the receiving side, so that a signal power ratio to thermal noise can be improved. RAKE reception is a method of separating a leading wave and a delayed wave by despreading from a received signal on which a delay time differs and which has undergone independent fading fluctuation and a superimposed delayed wave in a multipath propagation path. ,
Align the delay time of the delayed wave, and make the phases in-phase and
A diversity effect is obtained by performing weighting according to the received signal level and performing RAKE combining (maximum ratio combining). In wideband DS-CDMA, since the chip rate can be increased, the received signal is separated into many multipaths, so that the effect of RAKE reception is large.

FIG. 7 is a block diagram of a conventional RAKE receiver using a two-step threshold multipath selection method. In the figure,
1 is a matched filter, 2 is a channel fluctuation estimating unit, 3 is a level measuring unit, 4 is a complex conjugate unit, 5 is a multiplier, 7 is RAK.
An E combining unit 101 is a two-stage multipath selecting unit, and 102 is a threshold setting unit. The two-step threshold multipath selection method is described in Akira Fukumoto et al., “IEICE Technical Report RCS97-119” (1997-10), p. 43-4
It is known as 8 mag. In RAKE reception,
It is necessary to separate a noise component and a multipath component from the correlation output obtained by despreading the received signal, and to perform diversity combining of only the multipath component. In the configuration shown in the figure, a threshold value is set in two stages to select a multipath input signal to be subjected to diversity combining.

[0004] The example shown in the figure is a configuration example in which a spectrum spread received signal is despread by a matched filter 1 to output a correlation waveform (delay profile), and a RAKE combining unit 7 performs RAKE reception. In the reception signal, the transmission data is QPSK-modulated,
It is spread modulated by SK.

[0005] The matched filter 1 is a circuit that matches the spread code of the received signal. The correlation output of the matched filter 1 is output to the propagation path fluctuation estimating unit 2, the level measuring unit 3, and the multiplier 5. In the propagation path fluctuation estimation unit 2,
PSA (Pilot symbol a) using pilot symbols
A channel fluctuation is estimated by channel estimation of a veraging coherent detection method, and a phase of each multipath for performing phase in-phase necessary at the time of RAKE combining and a value of a weight at the time of RAKE combining are obtained.

[0006] The level measuring section 3 measures the received signal level of each multipath from the correlation output. The complex conjugate unit 4 and the multiplier 5 take the complex conjugate of the estimation result by the propagation path fluctuation estimating unit 2 and multiply this by the correlation output for the above-mentioned phase in-phase and weighting. The two-stage multipath selection unit 101 receives the output of the multiplier 5, performs multipath selection using two-stage threshold values, and outputs the result to the RAKE combining unit 7. The threshold setting unit 102 is a block for inputting the output of the level measuring unit 3 and setting the two-step threshold.

FIG. 8 is a diagram showing a frame structure of a received signal. One frame is composed of a plurality of slots, and one slot has several pilot symbols at the beginning, followed by data symbols. Here, the pilot symbol is a symbol used for measuring the state of the propagation path, and is composed of data known between the transmitting side and the receiving side. The data symbol is a symbol for transmitting transmission information.

The received signal having the above-described frame structure is shown in FIG.
And the spectrum is despread. This despreading corresponds to correlating the reference signal preset in the matched filter 1 with the received signal. The reference sequence is a sequence that matches the spreading code of the received signal. During the correlation output output from the matched filter 1, each multipath of the propagation path of the received signal is output in a state where it is time-separated. At this time, the amplitude and phase of each multipath fluctuated for each multipath due to the fluctuation of the propagation path.
It is output in a form that includes the phase fluctuation.

The unit period in which the level measurement unit 3 measures the level is the pilot symbol section shown in FIG. 8 for efficiency, but may be the entire section including the data symbol section. This unit period can be, for example, one diffusion cycle. There are various methods for updating the threshold. For example, the threshold setting unit 102 determines the threshold from the level measurement of the first pilot symbol section of one slot, and determines the threshold value in the subsequent data symbol section. It is used to determine the despread data symbol, and the threshold is updated by measuring the level of the pilot symbol section of the next slot. The method of updating the threshold value is set to an appropriate value according to the changing speed of the radio wave propagation environment and the moving speed of the mobile communication terminal.

The propagation path fluctuation estimating section 2 separates each multipath of the propagation path from the correlation output,
, And using the fact that the information (amplitude, phase, etc.) of this pilot symbol is known to the receiving side, the amplitude and the phase variation of the fading variation in each multipath are measured, and the measurement is performed. The result is used to measure the fading variation of each multipath in the data symbol.

The complex conjugate unit 4 takes the complex conjugate of the fading fluctuation of each multipath obtained by the propagation path fluctuation estimating unit 2 and converts the result into a correlation output which is an output of the matched filter 1 in a multiplier 5. Multiply. In the correlation output of the matched filter 1, each multipath such as a preceding wave and a delayed wave by a multipath propagation path is separated and output by a delay time difference due to the property of spread spectrum communication, but each multipath is independent. The amplitude and phase fluctuate due to fading fluctuation. By multiplying each multipath by the complex conjugate of the estimated value of the amplitude and phase fluctuation of each multipath estimated by the propagation path fluctuation estimating unit 2, it is possible to remove the phase fluctuation and to multiply the multipath amplitude by the multiplication. it can. Removing the phase variation corresponds to making the phase variation of each multipath in phase. Further, the operation of multiplying the estimated value of the amplitude fluctuation by multiplication corresponds to performing weighting of each multipath at the time of RAKE combining.

The level measuring section 3 measures the received signal level of each multipath from the output of the matched filter 1. The two-stage multipath selecting section 101 uses the measurement result of the received signal level of each multipath and the threshold value set in the threshold value judging section 102 to convert the output of the multiplier 5 into a multilevel signal used for RAKE combining. Select a path. Next, details of the multipath selection will be described with reference to FIG.

FIG. 9 is a diagram showing the level of a received signal for explaining the operation of the threshold value selecting section and the two-stage multipath selecting section shown in FIG. In the figure, the vertical axis represents the received signal level, and the horizontal axis is the time axis representing the delay time of each multipath of the preceding wave and the delayed wave. Further, a to p are obtained by sampling the reception signal levels of the respective multipaths output from the level measurement unit 3, and hereinafter simply referred to as samples a to p.
It is called p. The level of each sample a to p indicates the level of multipath or noise. Here, sample a,
Sample b, sample d, and sample k are used as samples indicating the received signal levels of the preceding wave and the delayed wave due to multipath, and the other samples are used as noise sample values.

In order for communication to be established, the preceding wave and the delayed wave due to the multipath need to be higher than the noise level. Therefore, the two-stage multipath selecting unit 101 and the threshold setting unit 102 perform path selection in the following procedure. In the samples a to p in FIG. 9, when the number of samples is L, the minimum received power S _min and the maximum received power S _max are detected in the L samples. Then S
_{For min} , in order not to synthesize a sample with only noise,
Set the threshold value Δnoise (Δnoise ≧
0).

On the other hand, in order to select a sample having a signal effective for RAKE synthesis with respect to S _max , a threshold Δ
RAKE is set (ΔRAKE ≧ 0). Sample a ~
From p, only those samples whose level S (l) satisfies the following conditions are selected. S (l) ≧ max ｛S _min + Δnoise, S _max −Δ
RAKE｝ where max {A, B} means that A and B take the larger value.

As a result, assuming that .DELTA.RAKE and .DELTA.noise are correctly set, it is possible to select only the samples indicating the reception signal levels of the multipath preceding wave and the delayed wave from the samples a to p, Can be not selected. In the example of FIG. 12, since (S _min + Δnoise) <(S _max −ΔRAKE), a sample having a higher level than (S _max −ΔRAKE) is selected, and the multipath reception signal level is reduced. The sample a, sample b, sample d, and sample k shown are selected.

The two-stage multi-pass selector 106 selects a multi-pass sample by the above-described method, and outputs the output of the multiplier 5 at the same timing as the selected sample to R.
Output to the AKE combining unit 7. The RAKE combining unit 7 receives only the output of the multiplier 5 corresponding to the timing of the multipath sample selected by the two-stage multipath selecting unit 101, and combines the signals to obtain
It is possible to exclude only a signal consisting of noise and perform combining only with a signal effective for RAKE combining.

However, in an actual propagation path, the magnitude of the level fluctuation due to fading and the noise level differ depending on the propagation path. Therefore, if the propagation environment changes, these level fluctuations and noise fluctuations greatly differ. Therefore, the conventional RAKE receiving unit has the following problem if both of the above-mentioned parameters ΔRAKE and Δnoise are not properly selected.

(1) When ΔRAKE is smaller than the optimum value, S _max −ΔRAKE is smaller than the minimum value of the samples a to p indicating the multipath received signal level.
Becomes large, so that all of the samples that can be used for RAKE synthesis cannot be used for RAKE synthesis, and the characteristics deteriorate. (2) ΔRAKE is larger than the optimum value and Δnoise
Is smaller than the optimum value, the sample value of the noise level becomes larger than S _max -ΔRAKE, and a noise component that cannot be used for RAKE synthesis is synthesized, resulting in deterioration of characteristics. (3) When Δnoise is larger than the optimum value, S _min + Δnoise becomes larger than the minimum value of the levels of the samples a to p indicating the received signal level of the multipath, and all the samples that can be originally used for RAKE combining are raked.
It cannot be used for synthesis, and its properties deteriorate. This makes it difficult to exclude only noise signals and perform synthesis using only signals effective for RAKE synthesis.

[0020]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problem, and selects only a signal effective for RAKE combining by adapting to the characteristics of a received signal to perform RAKE combining. It is an object of the present invention to provide a RAKE receiver for performing the above.

[0021]

According to the first aspect of the present invention, an RA for despreading a received signal and performing RAKE combining is provided.
The KE receiver includes a level measuring unit, an adaptive threshold value determining unit, a path selecting unit, and a RAKE combining unit, wherein the level measuring unit measures a level of a despread received signal, The adaptive threshold determination unit receives the output of the level measurement unit, sets a variable threshold, and changes the variable threshold to change the level of the despread received signal while changing the variable threshold. Count the appearance frequency exceeding the value, based on the change characteristics of the increase of the appearance frequency,
A decision threshold for discriminating between a preceding wave and a delayed wave and noise is set, and timing information is outputted by discriminating a timing at which the level of the despread received signal exceeds the decision threshold. The path selection unit selectively outputs the despread received signal or a despread signal based on the despread received signal to the RAKE combining unit in accordance with the timing information. . Therefore, the decision threshold for distinguishing the preceding wave and the delayed wave from the noise can be set in accordance with the characteristics of the despread received signal, and only the signal effective for RAKE combining can be easily selected. To perform RAKE synthesis.

According to a second aspect of the present invention, in the RAKE receiver according to the first aspect, the adaptive threshold value judging section changes the variable threshold value in a direction of decreasing the variable threshold value, and the increment is a predetermined value. The determination threshold value is set based on a variable threshold value when the threshold value is exceeded. Therefore, a determination threshold for discriminating between a delayed wave and noise can be realized with a simple configuration.

According to a third aspect of the present invention, in the rake receiver according to the first or second aspect, the path selection unit has a multiplication unit, and the multiplication unit is configured to receive the despread reception signal or By multiplying the despread signal based on the despread received signal by the timing information, the despread received signal or a despread signal based on the despread received signal, corresponding to the timing information Selective output. Therefore, the path selection unit can be realized with a simple configuration.

According to a fourth aspect of the present invention, in the rake receiver according to the first or second aspect, the path selecting section has a multiplying section, and the multiplying section has a function of multiplying the despread received signal by the despread received signal. By multiplying the timing information by multiplying a phase in-phase signal for weighting and de-phasing the received signal generated based on the output of the propagation path estimating unit and performing phase in-phase, The received signals are weighted and phase-in-phase, and selectively output in accordance with the timing information. Therefore, the path selection unit can be realized with a simple configuration.

According to a fifth aspect of the present invention, in the rake receiver according to the first or second aspect, the path selecting section has a multiplying section and a switch, and the switch is provided in the propagation path estimating section. A phase in-phase signal for weighting and de-phasing the received signal that is generated based on the output and despread is selectively output in accordance with the timing information. Multiplying the despread received signal by the output of the switch to weight and dephase the despread received signal and selectively output the signal in response to the timing information It is. Therefore, the path selection unit can be realized with a simple configuration.

[0026]

FIG. 1 is a block diagram of a RAKE receiver according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of a specific example of the adaptive threshold value determination unit 8 of FIG. FIG.
FIG. 11 is a diagram showing the level of a received signal for explaining the operation of the adaptive threshold value determining section shown in FIG. 2, and the value and time of each sample are the same as in FIG.

In FIG. 1, the same parts as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. Reference numeral 6 denotes a path selection unit, and 8 denotes an adaptive threshold value judgment unit.
Is for obtaining a path to be selected by the path selection unit 6. Compared to the prior art, the two-stage multipath selection unit 101 in FIG. 7 is replaced by the path selection unit 6 and the threshold determination unit 102 is replaced by the adaptive threshold determination unit 8.
The frame configuration is the same as that shown in FIG.

The level measuring section 3 measures the level of the despread received signal, and the adaptive threshold value judging section 8 receives the output of the level measuring section 3 and despreads while changing the variable threshold. The frequency of occurrence of the level of the received signal exceeding the variable threshold is counted, and a determination threshold for discriminating the preceding wave and the delayed wave from noise is determined based on the change characteristic of the increase of the frequency of appearance. A timing at which the level of the set and despread received signal exceeds the determination threshold is determined, and timing information is output. In the path selection unit 6, the despread received signal, in this example, the despread received signal that has been phase in-phased and weighted by the multiplier 5,
The output is selectively output to the RAKE combiner 7 in accordance with the timing information. The RAKE combining unit 7 removes a noise signal by RAKE combining the output of the path selecting unit 6 and performs RAK combining.
Synthesis is performed using a signal effective for E synthesis.

Although omitted in FIG. 7 for the sake of simplicity, the matched filter 1 in the multiplier 5 is omitted.
, And the phase in-phase signal output from the complex conjugate unit 4 for timing matching between the output of the multiplying unit 5 in the two-stage multipath selecting unit 101 and the output of the threshold setting unit 102, etc. , A time delay unit or a buffer is appropriately provided. Alternatively, the output of the matched filter 1 can be temporarily stored in a memory, and the subsequent processing blocks can take out necessary sample data from this memory and process it. For example, the level measurement unit 3 performs processing by extracting sample data of a pilot symbol section from this memory.

In the adaptive threshold value judging section shown in FIG.
9 is a first threshold value judgment unit, 10 is a second threshold value judgment unit,
11 is a first sample counter, 12 is a second sample counter, 13 is a comparator, and 14 is a threshold reset controller. First threshold value judgment unit 9, second threshold value judgment unit 10
Inputs the output of the level measurement unit 3 in FIG. 1, compares it with a predetermined variable threshold value, and outputs timing information indicating whether the threshold value has been exceeded. The first sample counting unit 11 and the second sample counting unit 12 respectively
The timing information of the threshold value judging unit 9 and the second threshold value judging unit 10 is counted, and the comparator 13 outputs the first sample counting unit 1
The outputs of the first and second sample counters 12 are compared, and the difference obtained by subtracting the former count value from the latter count value is output to the threshold reset controller 14.

The threshold resetting control unit 14 compares the difference with a predetermined reference value, and when the difference does not exceed the predetermined reference value, the first threshold value judgment unit 9 and the second threshold value judgment unit 10
Change each variable threshold value. This series of operations is repeated until the above-described difference exceeds a predetermined reference value. At this time, the variable threshold value of the first threshold value determination unit 9 is set as a determination threshold value, and this determination threshold value is The timing information of the exceeded sample is output to the path selection unit 6 in FIG.

The operation of the adaptive threshold value judging unit 8 and the path selecting unit 6 shown in FIGS. 1 and 2 will be described with reference to FIG. FIG.
3 shows the measurement result of the reception level of each multipath in the level measurement unit 3 for one unit period. Here, similarly to FIG. 9, samples a, b, d, and k are samples by a multipath preceding wave and a delayed wave, and the other samples are noise samples.

In a normal case, a sufficiently large value is used for the spreading factor of spread spectrum, so that the number of preceding waves and delayed waves in a multipath is sufficiently small with respect to the total number of samples in one spreading period. In order to establish communication, the preceding wave and the delayed wave that can be used for signal demodulation are higher than the noise level. As described above, while changing the threshold value from a large value to a small value, the number of samples exceeding the threshold value is counted. Since this number is a number per unit period, it means an appearance frequency per unit period of a sample having a level exceeding a threshold value.

When the threshold value is relatively large, the value exceeding the threshold value is small because most of the preceding wave and the delayed wave that can be used for signal demodulation are used. On the other hand, when the threshold value is changed to a smaller value, noise samples in addition to the preceding wave and the delayed wave also exceed the threshold value. Here, since the number of noise samples is larger than the number of preceding waves and delayed waves in the multipath, the value of the above-described increment becomes larger. Therefore, if the value of the increment is compared with a predetermined reference value and a threshold for determination is set based on the threshold when the predetermined reference value is exceeded, the leading wave and the delayed wave in the multipath can be set. Samples and noise samples can be distinguished. According to an example of the simulation result, in a normal radio wave propagation situation, when the threshold value is lowered near 0.1 _{Smax to} 0.07 _Smax , the number of samples exceeding the threshold value increases.

As described above, the threshold value is changed from the maximum level to a lower value, and the determination threshold value is set based on the variable threshold value when the above-mentioned increment exceeds a predetermined reference value. You have set. However, conversely, the threshold may be changed from the minimum level to a higher level to obtain a variable threshold when the increment does not exceed a predetermined reference value.

In FIG. 2, in the initial state, the first threshold value determining section 9 and the second threshold value determining section 10 are set to the initial threshold values. The first threshold value judging unit 9
_Are determined by the ratio to the maximum received power _Smax in the despread received signal, and the threshold value of the first threshold value The threshold value is set to a value larger than the threshold value of the second threshold value determination unit 10. Here, assuming that the initial values of the threshold values set in the first threshold value judgment unit 9 and the second threshold value judgment unit 10 are S ₁ and S _{2 in} FIG. 3, respectively, S ₁ = nS _max , S ₂
= MS _max . However, m <n <1.

The first sample counting section 11 receives the timing information output from the first threshold value judging section 9 and
The number of samples exceeding the threshold set by the threshold determiner 9 is counted. Similarly, the second sample counting unit 12 receives the timing information output by the second threshold value judging unit 10 and calculates the number of samples exceeding the threshold value set by the second threshold value judging unit 10. Count.

In the example of FIG. 3, in this initial state, the output of the first sample counter 11 is 2 and the output of the second sample counter 12 is 3. Note that samples a, b, and d exceeding the thresholds S ₁ and S ₂ are preceded by multipath,
This is a sample using a delayed wave. In the comparator 13,
The output values of the first sample counter 11 and the second sample counter 12 are compared. The comparator 13 subtracts the output value of the first sample counter 11 from the output value of the second sample counter 12. Thus, the output of the comparator 13 is an increment of the number of samples where the despread received signal exceeds the threshold when the threshold is lowered. This increment is the number of samples that take a level between two threshold values S ₁ and S ₂ among the samples of the despread received signal.

In the initial state, the first sample counting section 1
Since the output of 1 is 2 and the output of the second sample counter 12 is 3, the output of the comparator 13 is +1. The threshold reset control unit 14 holds a predetermined reference value, and when the output of the comparator 13 is smaller than this reference value, the first threshold determination unit 9 and the second threshold determination unit The threshold value of 10 is reset to a smaller value.

Then, the first threshold value judging unit 9 and the second threshold value judging unit 10 similarly output whether or not these threshold values have been exceeded, using the reset threshold values. I do. The comparator 13 subtracts the output value of the first sample counting unit 11 from the output value of the second sample counting unit 12 to obtain the number of samples that take a level between two reset thresholds. The resetting of this threshold value, the counting of the number of samples exceeding the threshold value, and the comparison operation are performed by the comparator 13
Is repeated until the output exceeds the predetermined reference value.

The predetermined reference value of the threshold resetting unit 14 is set to +
If it is 3, the output of the comparator 13 in the initial state is +
Since it is 1, which is smaller than the reference value, the threshold values of the first threshold value judgment unit 9 and the second threshold value judgment unit 10 are reset to smaller values. The threshold values after resetting of the first threshold value judging unit 9 and the second threshold value judging unit 10 are denoted by S ₂ and S ₃ shown in FIG. 3, respectively.

The first sample counter 11, second sample counter 12, comparator 1
In 3, the number of samples exceeding the threshold value is counted and compared as in the initial state. The output of the first sample counter 11 is 3, the output of the second sample counter 12 is 4, and the output of the comparator 13 is +1. The samples a, b, d, and k exceeding the threshold values S ₂ and S ₃ at this time are also samples by multipath preceding waves and delayed waves.
The threshold resetting unit 14 compares the output of the comparator 13 with a reference value. Since the reference value is +3, +1 which is the output of the comparator 13 after resetting the threshold value is smaller than the reference value. Therefore, the threshold values of the first threshold value judgment unit 9 and the second threshold value judgment unit 10 are set again to smaller values. The threshold values of the first threshold value judgment unit 9 and the second threshold value judgment unit 10 after the resetting are set as S ₃ and S _{4 in} FIG. 3, respectively.
And

With respect to the threshold value after the resetting, the first
The output of the sample counting unit 11 is 4, the second sample counting unit 1
The output of 2 becomes 8, and the output of the comparator 13 becomes +4.
The threshold resetting unit 14 compares the output of the comparator 13 with a reference value. Here, since the reference value is 3, the output of the comparator 13 after resetting the threshold value is a value larger than the reference value. Therefore, the threshold is not reset.

As a result, the samples exceeding the threshold value S ₃ set in the first threshold value judging section 9 contain most of the samples of the preceding wave and the delayed wave which can be used for reception. contrast, samples above the threshold S _4, which is set to the second threshold determination unit 10, the preceding wave that can be used for reception, noise is included in the sample to the sample of the delay wave.
In this case, the first threshold determination unit 9, samples a the threshold is exceeded S _3, b, d, timing information k is obtained.

Accordingly, at this time, the threshold value S ₃ set in the first threshold value judgment section 9 is set as a judgment threshold value,
The timing information of the samples exceeding this is transmitted to the path selection unit 6 in FIG. The path selection unit 6 uses the current timing information indicating that the despread received signal is a sample that has exceeded the determination threshold value, and uses the samples a, b, d, and k as samples.
Are passed from the output of the multiplier 5 to the RAKE combining section 7, and the RAKE combining section 7 performs RAKE combining.

The adaptive threshold value judging section shown in FIG. 2 is one specific example and can be variously modified. As described above, if the operation is to gradually decrease the variable threshold value, the threshold value of the second threshold value determination unit 10 is set to the first value every time the variable threshold value is reset.
The threshold value of the threshold value judgment unit 9 is used. Therefore, the variable threshold values of the first threshold value judging section 9 are sequentially set to S ₁ , S ₂ ,.
The comparator 13 is different from the first sample counter 1 in each time.
The increment of the count value may be detected by comparing one count value.

In the above description, the determination threshold value is the first
Of the threshold value determination unit 9 of
It is not always necessary to match this threshold value, and the threshold value of the second threshold value judging unit 10 or the threshold value newly determined according to the output of the comparator 13 is changed to the first threshold value. The timing information may be output to the path selection unit of FIG. 1 by setting the threshold value of the determination unit 9.

FIG. 4 is a block diagram of a second embodiment of the RAKE receiver according to the present invention. In the figure, the same parts as those in FIG. 7 and FIG. Reference numeral 15 denotes a multipath selection multiplier, which is a specific example of the path selection unit 6 in FIG.

In this embodiment, the first threshold value judging unit 9 and the second threshold value judging unit 10 shown in FIG. "0" is output to the sample. The output of the adaptive threshold determination unit 8 is
First threshold value judging section 9 when judgment threshold value is set
Therefore, "1" is output to the multipath selecting multiplier 15 for a sample exceeding the determination threshold and "0" for a sample not exceeding the determination threshold. The multipath selecting multiplier 15 multiplies the output of the multiplier 5 with the despread reception signal on which the weighting and the phase in-phase are performed by the timing information. The RAKE combining section 7 performs RAKE combining by combining the outputs of the multipath selecting multipliers 15.

FIG. 5 is a block diagram of a RAKE receiver according to a third embodiment of the present invention. In the figure, the same parts as those in FIGS. 7, 1 and 4 are denoted by the same reference numerals, and description thereof will be omitted. The multipath selecting multiplier 15 is realized by inserting the same function as that of the multipath selecting multiplier 15 in FIG. 4 between the complex conjugate unit 4 and the multiplier 5. The output of the adaptive threshold determination unit 8 outputs to the multipath selection multiplier 15 “1” for a sample exceeding the determination threshold and “0” for a sample not exceeding the determination threshold. The multipath selecting multiplier 15 multiplies the output of the complex conjugate unit 4 of the output of the propagation path fluctuation estimating unit 2 by 1 or 0.

As a result, the output of the multipath selecting multiplier 15 is a complex conjugate signal of the propagation path fluctuation estimation result,
This signal has a value only at the timing of the preceding wave and the delayed wave of the multipath exceeding the determination threshold value, and becomes 0 at other timings. This multipath selection multiplier 1
5 is multiplied by the despread received signal output from the matched filter 1 by the multiplier 5 to select a path only at the timing of the multipath preceding wave and the delayed wave.
In addition, the weighting and the phase in-phase are performed simultaneously, and otherwise, the output value of the multiplier 5 is set to 0. The output of the multiplier 5 is RAKE-combined by the RAKE combiner 7 to form a RAKE receiver. Therefore, the multipliers 15 and 5 are integrated to perform path selection, weighting, and phase in-phase.

FIG. 6 is a block diagram of a RAKE receiver according to a fourth embodiment of the present invention. In the figure, the same parts as those in FIGS. Reference numeral 16 denotes a switch. The output of the adaptive threshold value judging unit 8 outputs to the switch 16 “1” for a sample exceeding the judgment threshold value and “0” for a sample not exceeding the judgment threshold value. The switch 16 selects the output of the complex conjugate unit 4 when the output of the adaptive threshold value judgment unit 8 is “1”, and outputs 0 when it is “0”. The output of the switch 16 is multiplied by the multiplier 5 with the despread received signal which is the output of the matched filter 1 by the multiplier 5, whereby a multipath preceding wave,
Only at the timing of the delayed wave, weighting and phase in-phase are performed. Otherwise, the output value of the multiplier 5 is set to 0. Note that the output of the adaptive threshold value determination unit 8 does not necessarily need to take the values of “1” and “0”, and the switch 16 may be controlled using another value.

In the above description, spread spectrum communication to which fading compensation using pilot symbols is applied has been described. However, even when such fading compensation is not performed, similar effects can be obtained. In the case of synchronous detection, it is necessary to match the phases because a phase reference is required. However, when delay detection is used, it is not always necessary. For this reason, in the first and second embodiments shown in FIGS. 1 and 4, the path selection unit 6 performs the case where the despread received signal is directly input or the weighting and the phase in-phase are performed. The received despread received signal may be input.

[0054]

As is clear from the above description, according to the RAKE receiver of the present invention, it is possible to easily select a multipath preceding wave and a delayed wave in accordance with the characteristics of a received signal. effective. Since RAKE synthesis is performed on the despread signal from which the noise component has been removed, the optimal RA
There is an effect that KE reception is performed.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a specific example of an adaptive threshold value determination unit 8 of FIG. 1;

FIG. 3 is a diagram illustrating a level of a received signal for describing an operation of an adaptive threshold value determination unit illustrated in FIG. 2;

FIG. 4 is a configuration diagram of a RAKE receiver according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a third embodiment of a RAKE receiver according to the present invention.

FIG. 6 is a configuration diagram of a RAKE receiver according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of a RAKE receiver using a conventional two-step threshold multipath selection method.

FIG. 8 is a diagram illustrating a frame configuration of a received signal.

FIG. 9 is a diagram showing levels of received signals for explaining operations of the threshold value selecting unit and the two-stage multipath selecting unit shown in FIG. 7;

[Explanation of symbols]

1 matched filter, 2 propagation path fluctuation estimation section, 3 level measurement section, 4 complex conjugate section, 5 multiplier, 6 path selection section, 7 RAKE synthesis section, 8 adaptive threshold value judgment section,
9 first threshold value judgment unit, 10 second threshold value judgment unit,
11 first sample counting section, 12 second sample counting section, 13 comparator, 14 threshold value resetting control section, 15
Multiplier, 16 switcher, 101 two-stage multipath selector, 102 threshold setting unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-231278 (JP, A) JP-A 8-181636 (JP, A) JP-A 10-190522 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04B 1/707 H04B 1/06

Claims (5)

(57) [Claims] An RAKE receiver for despreading a received signal and performing RAKE combining includes a level measuring unit, an adaptive threshold value judging unit, a path selecting unit, and a RAKE combining unit. Measuring the level of the spread received signal, wherein the adaptive threshold value determination unit receives the output of the level measurement unit, sets a variable threshold value, and changes the variable threshold value. While counting the frequency of occurrence where the level of the despread received signal exceeds the variable threshold, and determining the preceding wave, the delayed wave, and the noise based on the change characteristics of the increase in the frequency of appearance. Set the threshold,
Determining the timing at which the level of the despread received signal exceeds the determination threshold and outputting timing information, wherein the path selection unit is configured to output the despread received signal or the despread signal. A RAKE receiver, which selectively outputs a despread signal based on a received signal to the RAKE combining section in accordance with the timing information. 2. The adaptive threshold value judging section changes the variable threshold value in a lowering direction, and determines the judgment threshold value based on the variable threshold value when the increment exceeds a predetermined reference value. The RAKE receiver according to claim 1, wherein a value is set. 3. The path selection unit has a multiplication unit, and the multiplication unit multiplies the despread received signal or a despread signal based on the despread received signal by the timing information, 3. The apparatus according to claim 1, wherein the despread reception signal or a despread signal based on the despread reception signal is selectively output in accordance with the timing information. RAKE receiver. 4. The path selection section has a multiplication section, and the multiplication section weights the despread reception signal and the despread reception signal generated based on an output of a propagation path estimation section. A phase in-phase signal for phase in-phase
2. The multiplying unit according to claim 1, wherein the despread received signal is weighted and phase-in-phase by multiplying the received signal by the timing information, and selectively output in accordance with the timing information. Or RA described in 2 above
KE receiver. 5. The path selection unit includes a multiplication unit and a switching unit, and the switching unit weights the despread reception signal generated based on an output of a propagation path estimation unit and performs phase in-phase. A phase in-phase signal for selectively outputting in response to the timing information, wherein the multiplying unit multiplies the despread received signal by an output of the switch, The RAKE receiver according to claim 1 or 2, wherein the despread received signal is weighted, phase-in-phased, and selectively output in accordance with the timing information.