JPH10336072A - Rake receiver for direct diffusion cdma transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a RAKE receiver which makes RAKE reception by selecting many signals having sufficient receiving power as much as possible by rejecting signals only containing noise, etc. SOLUTION: Diffusion-modulated signals in a base band are inputted to a matched filter 150 and reversely diffused by using the output of a diffused code replica generating section 151. The reversely diffused signals at L different timing are demodulated by means of a demodulating section 152. An average receiving power measuring section 153 measures the average receiving power at the L different timing. A minimum power detecting section 201 and a maximum power detecting section 203 detect the minimum signal power and maximum signal power at the L different timing. Two thresholds can be found by respectively multiplying the minimum and maximum signal power by constants GA and GB. A path selecting timing detecting section 205 detects the timing of a multipath having large signal power from the timing at which the average signal power is larger than the thresholds A and B.

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 direct spread CDMA (DS-CDMA) transmission for performing multiple access using spread spectrum in mobile communication.

[0002]

2. Description of the Related Art The DS-CDMA transmission system is a system in which an information data modulated signal is spread by a spreading code of a spreading factor (= number of chips / symbol) pg into a wideband signal and transmitted. , A plurality of communicators communicate using the same frequency band.

FIG. 5 shows a configuration of a receiver using a sliding correlator in the conventional DS-CDMA transmission system. In the receiver, after the spread-modulated signal received by the antenna 101 is amplified by the low-noise amplifier 103, the oscillator 105,
A frequency mixer 104 and a band pass filter (BP
F) The frequency is converted into an intermediate frequency (IF frequency) signal using 106, and an automatic gain control amplifier (AGC amplifier) 1
At 07, linear amplification is performed. In the AGC amplifier 107,
The amplitude envelope of the received signal is detected by the envelope detector 108, and the amplitude fluctuation is negatively fed back to the AGC amplifier 107, thereby compensating for the amplitude fluctuation caused by fading.

The signal linearly amplified by the AGC amplifier 107 is orthogonally detected by a quadrature detector 109 into a baseband signal. Then, the baseband in-phase (I) and quadrature (Q) components are converted to A / D converters 112 and 113, respectively.
To a digital value. Spreading code generator (1)
To (N) 118 using a spreading code replica synchronized with the delay time of each multipath signal,
The despreading process is performed by the sliding correlator 131 in the AKE combining path finger 114. The despread signal is subjected to delay detection or synchronous detection to perform data demodulation.

[0005] Here, a description will be given of a system in which pilot symbols are inserted at regular intervals between information symbols in a received transmission frame, and absolute synchronous detection and demodulation is performed using the pilot symbols. In land mobile communication, amplitude and phase fluctuations of a received signal, called fading, occur due to movement of the relative positions of a base station and a mobile station. In order to perform synchronous detection demodulation, it is necessary for a receiver to estimate a complex envelope due to the fading, that is, amplitude and phase fluctuations (also referred to as channels). A reception fading complex envelope at a pilot symbol inserted into a transmission information symbol at a fixed period is obtained, and a fading complex envelope at an information symbol position between pilot symbols can be obtained using this value. The fading complex envelope variation (channel variation) of each information symbol is compensated using the value used for this pilot symbol. This is because channel estimator 132 and multiplier 13 in RAKE combining path finger 114
Going at 3.

The plurality of multipath signals having been subjected to the channel fluctuation compensation are combined in phase by a RAKE combiner 119 (RAK combiner).
E combining) can improve the signal power ratio with respect to an interference signal or thermal noise. Selection of a multipath signal to be RAKE-combined is performed by a sliding correlator 115 called a search finger. In the search finger, the average received signal power measuring section 116 measures the average received signal power of the despread signals at L timings within the multipath search range, and a multipath having a large received signal power on average is selected as a path selection timing detecting section. At 117, a selection is made. For example, as shown in FIG. 5, when one sliding correlator 115 is used, a correlation value (despread value) at one timing is obtained for each symbol, and the signal of the despread signal at this timing is obtained. The received signal power can be measured. Then, the timing of the spread code is shifted one by one, and power measurement is performed for all L timings.

Now, in selecting a RAKE combining path, it is necessary to select a multipath signal having a large average signal power (after receiving a variation caused by a distance variation between a base station and a mobile station and a shadowing). . This is subject to instantaneous fluctuations due to Rayleigh fading in a land mobile communication environment. Therefore, in the estimation of the received signal power at one time,
Since the received signal power drops by chance due to this Rayleigh fading fluctuation for a certain multipath signal, the signal power is low, and the signal may be omitted from the selection of the RAKE combining path. Therefore, in order to remove the influence of the instantaneous fluctuation of the received power, it is necessary to measure the received signal power for a signal obtained by averaging the Rayleigh fading fluctuation.

More specifically, L within the multipath search range
The signal power measurement is repeated X times for the despread signal at the number of timings, a delay profile is generated based on the average signal power, and the top N RAKE combining multipaths are selected. As shown in FIG. 5, when one sliding correlator 115 is used, it takes L × X symbol times to generate one delay profile. When f sliding correlators (search fingers) are used, (L
× X) / f symbol time is required. The timing of the spreading code replica used in the RAKE combining finger is updated every time the delay profile is generated. When the mobile station moves at a high speed with respect to the base station, the variation of the delay profile becomes faster. Therefore, in the multipath search using the sliding correlator, it takes time, and it may not be possible to follow the variation of the delay profile. is there.

To perform a high-speed multipath search,
The multipath search range and the number of times of averaging may be reduced. However, if the search range is narrowed, the time diversity effect of RAKE combining is reduced, and if the number of times of averaging of signal power is reduced, RAK by the search finger is reduced.
E-synthesis multipath selection cannot be performed accurately.

FIG. 6 shows a configuration of a receiver using a matched filter in a conventional DS-CDMA transmission system. In FIG. 6, the same components as those of the receiver in FIG. 5 are denoted by the same reference numerals.

In FIG. 6, a received spread modulation signal is amplified by a low noise amplifier 103 and then frequency-converted to an IF frequency. Then, the AGC amplifier 107 compensates for amplitude fluctuation due to fading, and performs quadrature detection. The output baseband signal of the quadrature detector 109 is A / D
The signals are converted into digital signals by converters 112 and 113. The spread modulated signal converted into the digital value is despread by the matched filter 150 having pg taps using the output of the spread code replica generation unit 151, and is separated into L timing signals. Here, if s is the number of oversamplings per chip, L = pg × s. L
The N multipaths are selected from these timings, and delay detection or synchronous detection is performed to perform data demodulation.

In this receiver, a scheme is used in which a pilot symbol is inserted at a fixed period between information symbols in a transmission frame, and absolute synchronous detection and demodulation is performed using the pilot symbol. The channel of each despread signal at L timings is estimated by a channel estimator 132 using pilot symbols, and the estimated value is used to compensate for channel fluctuation of each information symbol. On the other hand, the average received signal power at each of the L timings is measured by the average signal power measurement unit 153 to generate a delay profile, and the top N RAKEs are generated.
The combined multipath is selected using the path selection timing detection unit 154. At this time, the multipath is selected from the timing at which the received power is large, but the next multipath is selected excluding the same multipath detected by oversampling. In a configuration using a matched filter, despread signals at L timings are output every symbol period. Therefore, the power measurement by the search finger using the sliding correlator as in the configuration of FIG. 5 is unnecessary. Further, multipath updating for RAKE combining can be performed at high speed.

As described above, when the mobile station moves at a high speed with respect to the base station, the shape of the delay profile changes, and the number of multipaths also changes. However, since the receiver having the above configuration is configured to combine the upper N multipaths having large received signal powers, when the number of multipaths is larger than N, all of them are combined to reduce interference components and thermal noise. The signal power ratio cannot be improved. When the number of multipaths is smaller than N, the characteristic is degraded by synthesizing a signal including only a noise component and a mutual interference component and a multipath having a very small reception power.

[0014]

As described above, when the mobile station moves at a high speed with respect to the base station, the delay profile changes at a high speed and the shape changes. Therefore, when the number of multipaths to be combined is fixed as in a conventional RAKE receiver, all multipaths having sufficient reception power cannot be combined. Alternatively, a signal composed of only the interference component and the noise component may be combined. As a result, the signal power ratio with respect to the interference component and the thermal noise cannot be improved, and the characteristics deteriorate.

An object of the present invention is to provide a RAKE receiver which removes only noise components and mutual interference components in RAKE reception based on a matched filter and synthesizes as many multipaths as possible. Is to do.

[0016]

SUMMARY OF THE INVENTION In order to achieve the above object of the present invention, RAKE in a direct spread CDMA transmission system is used.
A matched filter for outputting a signal despread at an integer multiple of the number of chips in one symbol, a demodulation unit for demodulating the despread signal at each timing from the matched filter, Signal power measurement unit that measures the respective average signal powers of the despread signals at each timing from the filter, and a threshold for preventing the synthesis of noise and interference components from the output of the average signal power measurement unit. A and a threshold calculator for determining a threshold B for selecting a signal having sufficient signal power, and an average power from an average signal power measuring unit,
A path selection timing detection unit for detecting a signal having an average power greater than threshold value A and threshold value B from a threshold value control unit and determining the timing of a multipath to be combined, and an output of the path selection timing detection unit , A RAKE combining path selector for selecting a signal to be RAKE-combined from the signal demodulated from the demodulator, and a RAKE for RAKE-combining the demodulated signal selected by the RAKE combining path selector.
And a synthesizer.

Further, the threshold value calculating section includes a minimum power detecting section for detecting a minimum power value from an average power at all timings from the average signal power measuring section, and a minimum power detecting section at all timings from the average signal power measuring section. From the maximum power detection unit that detects the maximum power value from the average power, the minimum power value from the minimum power detection detection unit, and the maximum power value from the maximum power detection unit, the two threshold values A,
And a threshold control unit for obtaining B.

[0018] Then, the threshold value control unit multiplies the constant G _A (G _A ≧ 1) in the minimum power value is multiplied by a constant _{G B (0 <G B ≦} 1) to the maximum power value 2 One threshold can be determined.

In addition, the matched filter performs oversampling (the number of oversamplings per chip s), and the path selection timing detecting section includes:
When detecting multipath timings in descending order of received signal power from all timings, signals at ± k (k is a natural number) timings from the already detected path timings are excluded, and the next multipath timing is excluded. Timing can also be detected sequentially.

As described above, the RAKE receiver of the present invention measures the average received power of the signal at all timings despread by the matched filter and determines two thresholds. Then, a multipath is selected from the despread signals satisfying the two threshold values and RAKE-combined.

[0021] By using this configuration, it is possible to exclude signals including only noise and interference components, and to RAKE combine all multipath signals having a sufficient received power.
Therefore, even when the number of multipaths changes due to a change in the delay profile, only valid paths can be combined.

In the configuration of the present invention, the RAK is particularly high for the chip rate, that is, for wideband DS-CDMA.
It is possible to improve the characteristics of the reception quality by the time diversity effect by E.

[0023]

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

FIG. 1 is a block diagram showing the principle configuration of the present invention. In this figure, the same components as those in FIG. 6 are denoted by the same reference numerals.

The baseband spread modulated signal subjected to quadrature detection and A / D conversion is input to a matched filter 150 having pg taps. Matched filter 150
Despreads the spread modulation signal using the output of the spreading code replica generator 151. If s is the number of oversamplings per chip, L (= p
Despread signals at (g × s) timings are output. Each of the despread signals at the L timings is demodulated by the demodulation unit 152.

The average received power measurement section 153 measures the average received power at each of the L timings. The minimum power detection unit 201 and the maximum power detection unit 203 detect the minimum signal power and the maximum signal power at L timings. Threshold control unit A20
In step 2, the threshold value A is obtained using the detected minimum signal power. Further, threshold value control section B204 calculates threshold value B using the detected maximum signal power. The threshold value A is set to prevent synthesis of a signal including only noise and interference components, and the threshold value B is set to synthesize a signal having sufficient signal power. The reason for determining the two thresholds is to combine all multipaths having sufficient signal power and not to combine the thermal noise component and the cross-correlation of the received signal of another user. This is for improving the characteristics. These thresholds are, for example, the minimum signal power detected by the minimum power detection unit 201 and the maximum power detection unit 20.
3 can be obtained by multiplying the maximum signal power detected in step 3 by a threshold gain. The path selection timing detection unit 205 compares the output of the average signal power measurement unit at L timings with the thresholds A and B, and determines that the average signal power is equal to or higher than the threshold A and equal to or higher than the threshold B. Out of the timings, a multipath timing having a large signal power is detected. At this time, signals at ± k (k is a natural number) timings from the already selected multipath timing are excluded, and the next multipath timing is sequentially detected. The output of demodulation section 152 at the detected multipath timing is RAK
The signal selected by the E synthesis path selection unit 155 and the selected signal is synthesized by the RAKE synthesis unit 119.

The operation of determining a threshold and selecting a RAKE combining path in the present invention shown in FIG. 1 will be described. First,

[0028]

[Outside 1]

On the other hand, the threshold value A and the threshold value B are determined as follows.

[0030]

(Equation 1)

Here, G _A (G _A ≧ 1), G _B (0 <G
_B ≦ 1) are threshold value determination gains. next

[0032]

[Outside 2]

The P timings that satisfy the conditions are detected as multipath candidates.

From the signals at these timings, RAK
E Select the multipath to be combined. First, a signal having the largest timing of the received signal power is selected by the first multipath. Then, a multipath having a large received power is sequentially selected from the remaining candidates. At this time, the multipath with the next highest received power is selected excluding ± k timings from the already selected multipath timing. For example, if the timing of the q-th selected multipath is u _q , the candidates included in the timing of (u _q −k) ≦ l ≦ (u _q + k) are excluded from the target of the next multi-path selection. The reason for excluding the signals at the timings before and after the multipath selected in this way is to prevent the same multipath from being selected by oversampling. k is, for example, the oversampling number as s,
Set as k = s / 2. In this way, the multipath selection is repeated, all the multipaths are selected, and the RAK
Perform E synthesis.

FIG. 2 shows an example of multipath timing detection. The timing detection in the case where the timings of the multipath candidates having the reception power satisfying the threshold as shown in the drawing are continuous will be described. At this time, the oversampling number s = 4, and the number of timings k = s / 2 = 2 for excluding candidates from the multipath that has been selected.
Assume that the signal at the timing at point p in FIG. 2 is selected as a multipath. At this time, the next timing at which the received power is the largest is p + 1. However, ±
The four points p-2, p-1, p + 1, p + 2 in the range of s are excluded from the multipath candidates to be selected next, and p + 4
The signal at the point is selected as the next multipath. Then, among the four points in the range of ± s with respect to the point p + 4, p
The three points +3, p + 5, and p + 6 are newly excluded from the candidates. In this way, signals at timings before and after the selected multipath are not selected.

FIG. 3 shows an example of a frame structure of a received signal received by the receiver of the present invention. The N _p pilot symbols is a frame configuration to be inserted for each N _s information symbols. It is assumed that one slot is composed of N _p pilot symbols and N _s information symbols.

FIG. 4 shows an embodiment of the receiver configuration of the present invention. 4, the same components as those in FIGS. 1 and 6 are denoted by the same reference numerals.

The received spread modulated signal is transmitted to the low noise amplifier 10
3, the oscillator 105 and the frequency mixer 1
04 is converted to an IF frequency. And AG
Amplitude fluctuations due to fading are compensated by the C amplifier 107 and the envelope detector 108, and quadrature detection is performed. The output baseband signal of the quadrature detector 109 is A /
The signals are converted into digital signals by D converters 112 and 113. The signal converted to the digital value is despread by the tap number pg matched filter 150. When s is the number of oversamplings per chip, L (= pg × s)
A despread signal at this timing is output. Each of the despread signals at the L timings is demodulated by the demodulation unit 152.

In this embodiment, for example, a method of performing absolute synchronous detection and demodulation using pilot symbols in the frame configuration of FIG. 3 is used. Estimation and compensation of channel fluctuation due to fading are performed in the channel estimation / compensation unit as follows. The matched filter output signal of the n-th slot at the l (1 ≦ l ≦ L) timing is averaged, and

[0040]

[Outside 3]

Is obtained as follows.

[0042]

(Equation 2)

Where

[0044]

[Outside 4]

Is obtained by the following equation.

[0046]

(Equation 3)

In a two-slot pitot symbol

[0048]

[Outside 5]

Is estimated as follows:

[0050]

(Equation 4)

This estimated

[0052]

[Outside 6]

Is compensated for.

[0054]

(Equation 5)

Here, ^* indicates a complex conjugate. Also, the average signal power measurement unit 153 measures the received signal power at all timings and generates a delay profile. The average signal power measurement in each average signal power measurement unit 153 is performed, for example, as follows. By averaging the matched filter output signal at the l-th timing in the n-th slot,

[0056]

[Outside 7]

Is obtained as follows.

[0058]

(Equation 6)

Where

[0060]

[Outside 8]

[0061]

[0062]

(Equation 7)

Is as follows. Furthermore, the power of the instantaneous received power is averaged over a plurality of immediately preceding slots in order to average the fluctuation due to fading,

[0064]

[Outside 9]

For example, it is obtained by the following two methods.

(1) Method of averaging the instantaneous received power of a plurality of slots

[0067]

(Equation 8)

Here, R is the number of slots to be averaged.

(2) A method of successively averaging the instantaneous received power of a plurality of slots

[0070]

(Equation 9)

Here, α is a forgetting factor. At this time, R =
1 / (1−α).

The minimum signal power and the maximum signal power are detected by the minimum power detection unit 201 and the maximum power detection unit 203, respectively, from the average reception powers of the L timings obtained as described above. The threshold control unit A202 obtains a threshold A using the detected minimum signal power. Further, threshold value control section B204 calculates threshold value B using the detected maximum signal power. The path selection timing detection section 205 compares the output of the average signal power measurement section 153 at L timings with the threshold A and the threshold B, and determines that the average signal power is equal to or larger than the threshold A and equal to the threshold. The timing of B or more is detected. Then, the timing of the multipath is detected from the timing at which the signal power is large. At this time, signals at ± k (k is a natural number) timings from the already selected multipath timing are excluded, and the next multipath timing is sequentially detected. The output of the demodulation unit 152 at the detected multipath timing is the RAKE combining path selection unit 155.
And the selected signal is combined by the RAKE combining unit 119. The RAKE-combined signal is randomized in error by a deinterleave circuit 120 and decoded by a Viterbi decoder 121. Then, the data decision unit 12
2 makes the received data.

[0073]

As described above, in the RAKE receiver of the present invention, the average received power of a signal at all timings despread using a matched filter is measured, and two threshold values are determined from the minimum and maximum values. To determine. Then, a multipath is selected from despread signals having received signal powers equal to or greater than two thresholds and RAKE-combined. By using this configuration, signals with only noise and interference components are excluded, and
RAKE combining can be performed on all multipath signals having a sufficient reception power. Therefore, even when the number of multipaths changes due to a change in the delay profile, only valid paths can be combined. This configuration can realize an improvement in reception quality characteristics due to a time diversity effect by RAKE especially for a high chip rate, that is, for wideband DS-CDMA.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is an explanatory diagram of path selection timing detection in the present invention.

FIG. 3 is a diagram illustrating an example of a frame configuration of a received signal.

FIG. 4 is a block diagram showing an embodiment of a receiver according to the present invention.

FIG. 5 shows a DS-C using a conventional sliding correlator.
FIG. 3 is a block diagram illustrating a configuration of a DMA receiver.

FIG. 6 shows a DS-CDM using a conventional matched filter.
It is a block diagram which shows the structure of A receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Antenna 102 Band pass filter (BPF) 103 Low noise amplifier 104 Frequency mixer 105 Oscillator 106 Band pass filter (BPF) 107 Automatic gain control amplifier (AGC amplifier) 108 Envelope detector 109 Quadrature detector 110, 111 Low pass filter 112, 113 A / D converter 114 RAKE combining path finger 115 Sliding correlator 116 Average signal measuring unit 117 Path selection timing detecting unit 118 Spreading code generating unit 119 RAKE combiner 120 Deinterleaver 121 Viterbi decoder 122 Data decision unit 131 Sliding correlator 132 channel estimator 133 multiplier 150 matched filter 151 spreading code replica generation unit 152 demodulation unit 153 average signal power measurement unit 155 RAKE combining unit Selection unit 201 minimum power detection unit 202 threshold control unit A 203 maximum power detection unit 204 threshold control unit B 205 path selection timing detection unit

Claims (4)

[Claims] 1. An RA in a direct spread CDMA transmission system.
In the KE receiver, a matched filter that outputs a signal whose path is despread at an integer multiple of the number of chips in one symbol, and a demodulation that demodulates the despread signal at each timing from the matched filter. Unit, an average signal power measurement unit that measures the respective average signal power for the despread signal at each timing from the matched filter, and synthesizes noise and interference components from the output of the average signal power measurement unit. A threshold calculator for determining a threshold A for preventing and a threshold B for selecting a signal having a sufficient signal power; and the threshold from the average power from the average signal power measuring unit. Path selection for detecting a signal having an average power greater than threshold value A and threshold value B from control unit and determining timing of multipath to be combined An imaging detector, a RAKE combining path selector for selecting a signal to be RAKE combined from the signal demodulated from the demodulator, and a demodulated signal selected by the RAKE combining path selector, based on an output of the path selection timing detector. R for RAKE combining signals
A RAKE receiver comprising an AKE combiner. 2. The RAKE receiver according to claim 1, wherein the threshold value calculation unit detects a minimum power value from an average power at all timings from the average signal power measurement unit; A maximum power detection unit that detects a maximum power value from an average power at all timings from an average signal power measurement unit, a minimum power value from the minimum power detection detection unit, and a maximum power value from the maximum power detection unit. And a threshold control unit for obtaining the two thresholds A and B, respectively. 3. The RAKE receiver according to claim 2, wherein the threshold value control unit sets the minimum power value to a constant G _A (G _A ≧
1) multiplied by, the maximum power value constant _{G B (0 <G B ≦} 1)
R to obtain two thresholds.
AKE receiver. 4. The RAK according to claim 1, wherein:
In the E receiver, the matched filter performs oversampling (the number of oversamplings per chip s), and the path selection timing detection unit determines a multipath timing from all timings in descending order of received signal power. A RAKE receiver which detects signals at ± k (k is a natural number) timings of a path already detected, and sequentially detects the timing of the next multipath, upon detection.