JPH1141139A - Synchronization timing detector for rake receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synchronous timing detector that realizes a RAKE receiver which accurately performs path search even in a low SNR(signal-to-noise ratio) environment. SOLUTION: This device performs path search by detecting synchronous timing of a diffusion code about plural respective delay waves that have different reach timings. In such cases, only a correlation level that shows a correlation value between a receiving signal and the spreading code which corresponds to a period when a sending source of the receiving signal transmits by providing a gate switch 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CDMA (Code D)
ivision Multiple Access, code division multiple access)
The present invention relates to a synchronization timing detection device used in a RAKE receiver applied to a mobile communication system of a system.

[0002]

2. Description of the Related Art A CDMA mobile communication system is effective for effectively utilizing a radio spectrum. Reference 1 (TI
A / EIA / IS-95; Telecommunications Indus
Issue of try Association Interim Standard95 Mobile St
ation-Base Station compatibility Standard for Dual
-Mode Wideband Spread Spectrum Cellular System) standardizes a CDMA mobile communication system.

[0003] In the IS-95 system, when communication is performed between a base station and a mobile station, a communication channel uses 20 channels.
Transmission is performed for each frame of m seconds long. The transmitting side makes an autonomous decision based on the amount of transmission information for each frame, and determines 9.6 kb.
ps, 4.8 kbps, 2.4 kbps, and 1.2
One of four transmission bit rates of kbps is selected and transmitted. The receiving side is not notified which transmission rate has been selected and transmitted.

[0004] One frame of 20 ms is subdivided temporally into a plurality of time slots. In case of IS-95, 2
One frame of 0 ms is composed of 16 time slots called power control groups (PCG). Therefore, one PCG length is 1.25 ms. Now, a radio channel in a direction in which a mobile station transmits and a base station receives is called a reverse channel. When the transmission rate is low in the reverse channel, intermittent transmission (burst transmission) is performed within one frame. For example, when one frame is transmitted at 4.8 kbps, the transmission rate is half of the maximum rate of 9.6 kbps. Therefore, transmission is performed only for half the time of 20 ms, and transmission is stopped for the other half. . Also, for example, 4.8 kb
When selecting ps, 8 out of 16 PCGs
PCGs are selected and transmitted. 8 PCGs to send
Is selected according to a predetermined algorithm. The above is described in detail in Chapter 6 of Document 1.

In general, in the CDMA system, the transmitting side transmits a signal spread with a spreading code sufficiently faster than the information signal, and the receiving side despreads the received signal with the same spreading code used on the transmitting side. To reproduce the original information signal. Such a C
In a communication system of the DMA system, in order for a receiving side to reproduce an information signal, it is necessary to accurately synchronize a spreading code generated on the receiving side with a transmitting side. As a method of determining the synchronization timing of the spread code on the receiving side, there is a method of determining the synchronization timing by relatively shifting the phase of the spread code on the receiving side and examining the phase at which the despread signal is maximized. . In a mobile communication environment, there is a RAKE reception method as a method for efficiently receiving a plurality of delay waves due to multipath. The RAKE reception method is described in Chapter 2, section 4.3 of Document 2 (CDMA system published by Trikeps and next-generation mobile communication system supervised by Osamu Ogawa, June 1996). In the RAKE reception method, it is necessary to detect the synchronization timing of the spreading code for each of a plurality of delayed waves having different arrival timings. The operation for obtaining multiple synchronization timings
Except for a part, it is called a path search. The present invention relates to an improvement in a synchronous timing detection device that performs a path search in a RAKE receiver.

A conventional synchronous timing detecting device for a RAKE receiver will be described with reference to FIGS.
Note that the synchronization method by this device is described in detail in Chapter 2, Section 3 of Document 2. Referring to FIG.
The synchronization timing detecting device for an AKE receiver includes a timing controller 34 for outputting a control signal, a correlator 32 for obtaining a correlation level of a received signal input to the input terminal 31 according to the control signal from the timing controller 34,
A maximum value detector 33 that detects a path search result based on the correlation level from the correlator 32 and outputs the result from an output terminal 35. Note that the correlation level is equivalent to the level of the despread signal.

Referring to FIG. 4, correlator 32 includes a spread code generator 322 for generating a spread code having a phase based on a control signal from timing controller 34, a received signal from input terminal 31, and a spread code. A multiplier 321 for obtaining the product of the signals of the spreading codes from the generator 322, and a multiplier 321
And an integrator 324 that integrates a detection signal from the envelope detector 323 for a predetermined period to calculate a correlation level and outputs the correlation level to the maximum value detector 33. ing. The correlator 32 completes calculation of the correlation level corresponding to a certain phase by one cycle operation, and shifts to the next cycle. At this time, the value of the integrator 324 is cleared, and the phase of the spreading code generator 322 is shifted by the control signal of the timing controller 34 to perform the same operation as in the previous cycle. Thereafter, this cycle is repeated.

Referring to FIG. 3 again, obtaining a phase having a large correlation level means obtaining a synchronization timing. The maximum value detector 33 obtains a synchronization timing by obtaining a phase at which the correlation level exhibits a peak.

[0009]

The conventional synchronous timing detection method, including the examples shown in FIGS.
When the present invention is applied to a system in which transmission from a transmission side is performed intermittently as in a −95 system, it is not known whether the transmission side is performing transmission or stopping. For this reason, a RAKE receiver having a conventional synchronization timing detection device may perform despreading even at a timing when a received signal does not exist, and may erroneously recognize a noise signal as a target signal. In particular, when searching for a path having a low signal-to-noise ratio (SNR), the false recognition rate is very high.

An object of the present invention is to provide a synchronous timing detecting device for a RAKE receiver that can realize a RAKE receiver that can accurately perform a path search even in a low SNR environment.

[0011]

According to the present invention, a path search is performed by detecting a synchronization timing of a spreading code for each of a plurality of delayed waves having different arrival timings.
The synchronization timing detection device for an E receiver, comprising a gate switch that outputs only a correlation level indicating a correlation value between a received signal and a spreading code, which corresponds to a period during which the source of the received signal is transmitting. A synchronous timing detection device for a RAKE receiver is obtained.

According to the present invention, there is also provided a synchronous timing detecting apparatus for a rake receiver for detecting a synchronization timing of a spreading code for each of a plurality of delayed waves having different arrival timings and performing a path search. A transmission rate discriminator for estimating a transmission rate based on a transmission rate discriminator, and selectively selecting an effective correlation level among correlation levels indicating correlation values between a received signal and a spreading code based on the estimated transmission rate obtained from the transmission rate discriminator. And a gate switch for outputting the signal. A synchronous timing detection device for a rake receiver is provided.

According to the present invention, further, a correlator for detecting a correlation value between a received signal and a spreading code while sequentially shifting the phase of the spreading code and outputting a correlation level indicating the correlation value, and the gate switch outputs the correlation level. A synchronous timing detector for a RAKE receiver, comprising: a maximum value detector for detecting a maximum value of a correlation level.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a synchronous timing detecting device for a rake receiver according to an embodiment of the present invention; This apparatus is used for a base station RA in a CDMA mobile communication system, particularly in an IS-95 system.
This is an example applied to a KE receiver.

FIG. 1 is a block diagram showing the configuration of the present apparatus. 1. Referring to FIG. 1, the present apparatus is similar to the conventional example shown in FIG.
A correlator 12 for obtaining a correlation level for a received signal input to the input terminal 11 in accordance with a control signal from the timing controller 14, and detecting a path search result based on the input correlation level to output a signal from the output terminal 15. And a maximum value detector 13 for outputting.

Further, the present apparatus comprises: a transmission rate discriminator 17 for estimating a transmission rate based on a reception signal inputted to the input terminal 11 and a path search result outputted from the maximum value detector 13; Gate switch 16 for selectively outputting an effective correlation level among the correlation levels from correlator 12 based on the estimated transmission rate obtained from
And

More specifically, the transmission rate discriminator 17 processes the received signal input to the input terminal 11 based on the path search result output from the maximum value detector 13 and selects from a plurality of transmission rate candidates. One transmission rate is estimated, and the estimated transmission rate as an estimation result is output to the gate switch 16. For example, in an IS-95 system, 9.6
It is estimated which of the four transmission rates of kbps, 4.8 kbps, 2.4 kbps, and 1.2 kbps was transmitted from the mobile station. Since a specific transmission rate estimating method is known, it will not be described in detail here.

The gate switch 16 specifies a transmission time slot of a mobile station by a predetermined algorithm (for example, described in the above-mentioned document 1) based on the estimated transmission rate, and obtains information on the transmission time slot. , The validity / invalidity of the correlation level output from the correlator 12 is discriminated, and only the valid correlation level is output to the maximum value detector 13. That is, the correlator 12 validates the correlation level processed using the received data of the time slot transmitted by the mobile station, and invalidates the received data of the time slot stopped by the mobile station. I do.

The maximum value detector 13 detects a predetermined number of relative delay times in descending order of correlation level,
This is output as a path search result.

Next, the essential points of the operation of the present synchronous timing detecting device for a RAKE receiver are shown in FIG. 2 (a) and FIG.
Description will be made with reference to FIG.

The correlator 12 obtains a correlation value between a spread code sequence generated with a relative delay time τ shifted from a reference timing and a received signal. In the case of this example, the relative delay time τ for obtaining the correlation value is within a predetermined range 0 <τ <τmax (τma
x is within a constant).

In FIG. 2A, the output level of the correlator 12 has a peak shape at the relative delay times τ1, τ3, τ5. That is, it indicates that a delayed wave exists. The maximum value detector 13 calculates the relative delay times τ1, τ3, τ
By detecting 5, a delayed wave is obtained.

However, even when an interference wave from another mobile station or a thermal noise on the receiver side accidentally has a waveform similar to the transmission signal, the output level of the correlator 12 exhibits a peak shape. It malfunctions. The gate switch 16 invalidates the output signal (correlation level) of the correlator 12 during the period when the mobile station stops transmitting, among the received signals used during the range of the relative delay time for obtaining the correlation value. For example, the period during which the mobile station stops transmitting is in the range of the relative delay time τ2 to τ.
If it is 4, the peak at τ3 is not a delayed wave but a malfunction due to noise, so that the correlation level corresponding to τ2 to τ4 is invalidated. Therefore, the output of the gate switch 16 is as shown in FIG.

[0024]

According to the present invention, there is provided a synchronous timing detecting apparatus for a RAKE receiver, which detects a synchronous timing of a spreading code for each of a plurality of delayed waves having different arrival timings and performs a path search. Has a gate switch that outputs only the correlation level indicating the correlation value between the received signal and the spreading code corresponding to the period during which the source of the received signal is transmitting, so that the path search can be performed even in a low SNR environment. Can be realized accurately.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a synchronization timing detection device for a RAKE receiver according to an embodiment of the present invention.

FIGS. 2A and 2B are diagrams for explaining the operation of the detection device shown in FIG. 1;

FIG. 3 is a block diagram illustrating a configuration of a conventional synchronous timing detection device for a RAKE receiver.

4 is a block diagram showing a configuration of a correlator in the detection device shown in FIG.

[Explanation of symbols]

 11, 31 Input terminal 12, 32 Correlator 13, 33 Maximum value detector 14, 34 Timing controller 15, 35 Output terminal 16 Gate switch 17 Transmission rate discriminator 321 Multiplier 322 Spread code generator 323 Envelope detector 324 Integrator

Claims (3)

[Claims] 1. A period in which a transmission source of a received signal is transmitting in a synchronous timing detection device for a rake receiver that detects a synchronization timing of a spreading code for each of a plurality of delayed waves having different arrival timings and performs a path search. And a gate switch for outputting only a correlation level indicating a correlation value between a received signal and a spread code, the synchronous timing detection device for a RAKE receiver. 2. A synchronous timing detecting device for a rake receiver for detecting a synchronization timing of a spreading code for each of a plurality of delayed waves having different arrival timings and performing a path search, based on a received signal and a path search result. And a gate switch for selectively outputting a valid correlation level among correlation levels indicating a correlation value between the received signal and the spreading code based on the estimated transmission rate obtained from the transmission rate discriminator. A synchronous timing detection device for a rake receiver, comprising: 3. A correlator for detecting a correlation value between a received signal and a spreading code while sequentially shifting the phase of the spreading code and outputting a correlation level indicating the correlation value, and a maximum value of the correlation level output by the gate switch. 3. The synchronous timing detecting device for a RAKE receiver according to claim 1, further comprising a maximum value detector for detecting the synchronous timing.