JPH0870264A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE: To reduce the deterioration in the speech quality by providing a sliding correlator to detect delayed wave information and using the correlator to detect the delay wave information and sending the detected delay wave information to a base station side. CONSTITUTION: This system is provided with a sliding correlator 8, a PN series signal generator 9 driven by a frequency signal whose frequency is slightly slower than a chip rate and an A/D converter 10. The sliding correlator 8 makes continuous sliding and starts sliding again while being reset in a timing of a correlation device 6 acquiring the synchronism at a proper time. Then a correlation peak with a level corresponding to a level of a delayed wave corresponding to a delay time of an arrival wave is provided. An output of the sliding correlator 8 is A/D converted by the A/D converter 10 and the result is received by a CPU of a receiver to provide information relating to selective fading in the current propagation state to a base station.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to frequency selective fading countermeasures when a spread spectrum communication system is applied to mobile communications, and particularly detects delayed wave information in addition to a correlator for synchronization supplement. The present invention proposes a mobile communication system in which a reception device having a sliding correlator for transmitting delay wave information to a base station in addition to reception signal length indication to maintain good communication quality.

[0002]

2. Description of the Related Art In mobile communication, application of spread spectrum communication is being studied as one of the effective means for increasing subscriber capacity. For example, according to William CYLee. Cellular C
Overview of DMA (Overvew of Celluar CDMA) ”, I
EEE Transaction on Vichycler Technology (vol.40, NO.2, pages 291-302, 1991 May 5
It is widely known by the moon). The CDMA system spreads a modulated carrier in a sequence having a sharp autocorrelation characteristic,
It is a communication method used by multiple users in one frequency band, and synchronization is supplemented by a correlator to avoid interference with other stations. That is, a signal spread in the same sequence as that of the own station is detected from radio waves of the same frequency, and communication with less interference is realized by synchronizing the signal with the reception timing of the own station. Is.

On the other hand, fading is one of the elements that characterize mobile communication. This is because the amplitude, phase, etc. of the received radio wave fluctuate sharply as the mobile station travels, making high-quality mobile communication difficult. Furthermore, in addition to the fluctuations in the amplitude and the phase, frequency-selective fading occurs in high-speed digital mobile communication. This is a phenomenon in which the arrival time difference of multiple waves, which causes fading with respect to the reciprocal of the data transmission rate, cannot be ignored, and the delayed wave causes interference with the desired wave.

[0004]

FIG. 4 schematically shows how a CDMA transmission wave arrives at a mobile station. That is, in addition to the desired wave A1, the radio wave is an interference wave of B, C, ... N diffused by the code sequence of another station and a propagation different from A1 by being reflected or scattered by buildings or mountains. A that arrives with a delay time to A1 due to the route
2, A3, ... An arrives as a composite wave of delayed waves. Selective fading occurs when there are incoming waves A2, A3, ...
In order to realize high-quality communication, it is necessary to select a transmission path in which not only the A1 level is high, but also the delayed wave levels of A2 and A3 are small.

On the receiver side, a correlator is provided to perform correlation calculation between the self sequence and the incoming wave. Interference waves B, C, ... N
Does not show a correlation output because is spread by a sequence different from its own sequence. Therefore, if the chip rate on the receiver side is slightly delayed for sliding, A1
A correlation peak is output at a timing corresponding to A2 .... The chip rate on the receiver side, which was slightly delayed at the time when these correlation peaks were detected and the sharpest correlation value was obtained, completely matched the chip rate of the system, and after that, it was tracked by a delay lock loop, etc. I will do it.

The above is the operation of the CDMA synchronization supplement-tracking. Usually, among the incoming waves A1, A2 ..., A1 which is the first incoming wave has the highest level, so the correlator is A
Synchronization is established at the arrival timing of 1. In the conventional method, the information about the propagation environment obtained in this state is at most only the level of A1 which is currently supplemented, that is, RSSI, and the information that determines selective fading is A.
No information about 2, A3, ...

A block diagram of a conventional receiver is shown in FIG. Reference numeral 1 is an antenna, 2 is an RF amplification unit, 3 is a frequency conversion unit, 4 is a synchronous complementary tracking unit, 5 is a PN generator, 6 is a synchronous complementary correlator, and 7 is an information demodulating unit.

The CDMA system is a communication system that is strong against interference because carriers of different sequences can be regarded as noise. However, there is a so-called near-far problem that another transmitting station exists closer to the communication base station. appear. That is, since there is no ideal sequence group having a sharp autocorrelation characteristic and no cross-correlation, it is affected by interference to some extent. Therefore, the CDMA system is essentially the same quality as the conventional mobile communication, and a system method for obtaining and utilizing information on the propagation environment such as reporting the RSSI (Received Signal Length Indication) level to the base station is desirable. However, in the current mobile communication, although the RSSI level is reported to the base station, the information on the frequency selective fading is not reported at all because it is very difficult to detect. It is expected that the data transmission rate will increase more and more in the future due to effective use of frequencies, and the countermeasure against frequency selective fading is very important, but the countermeasure is very difficult in the conventional communication system. In the conventional technology, an attempt is made to remove or combine delayed waves using, for example, an adaptive equalizer.
(Digital signal processor) It has not been adopted because it has other problems such as a significantly large circuit scale and the possibility of divergence due to insufficient convergence time for high-speed data.

[0009]

In order to solve the above problems, the present invention provides a high quality communication in a CDMA system by obtaining information about frequency selective fading such as delay time and amplitude of a delayed wave from a mobile station. It is an object of the present invention to provide a communication system that realizes the above and a receiving device that can detect delayed wave information simply and efficiently.

Therefore, in the present invention, the receiving device is provided with a sliding correlator for detecting delayed wave information in addition to the correlator provided for receiving the CDMA transmission wave.
The correlator detects the delayed wave information, and the detected delayed wave information can be transmitted to the base station side.

[0011]

Since the present invention is configured as described above, since the delayed wave information can be detected by the sliding correlator, the detected delayed wave information is transmitted to the base station side to improve the speech quality due to frequency selective fading. It is possible to make the deterioration very small.

[0012]

Embodiments of the present invention will be described below.

FIG. 1 is a block diagram showing the configuration of the present invention. In addition to the configuration of FIG. 3, a sliding correlator 8 and a PN driven at a frequency slightly slower than the chip rate
(Pseudo Noise) sequence signal generator 9, A / D converter 10
Has been added.

Here, the correlator 8 is constantly sliding, and is reset to the timing of the correlator 6 that is synchronously capturing at an appropriate time, and starts sliding again. FIG. 2 shows the output state of the sliding correlator 8 added to the conventional configuration. Immediately after the reset, the sliding correlator 8 has the same timing as the correlator that performs the synchronous supplement, and therefore the same correlation peak as the synchronous supplement correlator 6 corresponding to A1 is output. The timing of the sliding correlator shifts as time passes, and the correlation peak with A2 is output at the time corresponding to the arrival time of A2. Similarly, the delay is delayed at the timing corresponding to the delay time of each incoming wave. A correlation peak having a magnitude corresponding to the wave level is output. FIG. 2 shows the delay time and the amplitude level of each delayed wave called a delay profile, and is information that suggests the occurrence of selective fading. Therefore, the output of the sliding correlator 8 is A / D converted by the A / D converter 10 and taken into the CPU of the receiving device, so that the base station can be provided with information regarding the selective fading in the current propagation environment. , Higher quality communication can be realized.

[0015]

As described above, in the case of applying the CDMA system, the present invention can easily detect the delayed wave information by monitoring the series having a sharp autocorrelation characteristic used for spread spectrum. Therefore, when applying the CDMA system to mobile communication, it is possible to improve communication quality very efficiently by simply adding a correlator.

[Brief description of drawings]

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

FIG. 2 is a delay profile diagram showing a delay time and an amplitude level of each delayed wave.

FIG. 3 is a block diagram of a conventional receiving device.

FIG. 4 is a diagram schematically showing how a CDMA transmission wave arrives at a mobile station.

[Explanation of symbols]

 1 Antenna 2 RF Amplifying Unit 3 Frequency Converting Unit 4 Synchronous Supplement Tracking Unit 5 PN Generator 6 Synchronous Supplement Correlator 7 Information Demodulating Unit 8 Sliding Correlator 9 PN Generator 10 A / D Converter

Claims (1)

[Claims] 1. A sliding correlator is provided on the side of a receiving device having at least a synchronization supplementing correlator, information of a delayed wave is detected by the sliding correlator, and the detected delayed wave information can be transmitted to a base station side. A spread spectrum communication system characterized by being configured as described above.