JP3236738B2 - Spread spectrum communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a countermeasure against frequency-selective fading when a spread spectrum communication system is applied to mobile communication, and in particular, detects delayed wave information in addition to a correlator for synchronization supplementation. The present invention proposes a mobile communication system that maintains a good communication quality by transmitting delayed wave information to a base station in addition to indicating a received signal length by a receiving apparatus having a sliding correlator for the purpose.

[0002]

2. Description of the Related Art In mobile communications, spread spectrum communication systems are being studied as one of the most effective means for increasing subscriber capacity. For example, William CYLee has proposed the use of spread spectrum communication systems. Cellular C
Overview of DMA (Overvew of Celluar CDMA) ", I
EEE Transactions on Viehler Technology (vol.40, No.2, pp.291-302, May 1991)
Monday) and others. The CDMA method spreads a modulated carrier with a sequence having a sharp autocorrelation characteristic,
This is a communication method used by a plurality of users in one frequency band, and synchronization is supplemented by a correlator in order to avoid interference with other stations. In other words, it detects a signal spread in the same sequence as that of its own station from radio waves of the same frequency, and realizes communication with less interference by synchronizing the signal with the reception timing of its own station. It is.

On the other hand, fading is one of the elements that characterize mobile communication. This is because the amplitude, phase and the like of the received radio wave fluctuate sharply as the mobile station travels, which makes high quality mobile communication difficult. Furthermore, in addition to the above-described fluctuations in amplitude, phase, and the like, frequency selective (selective) fading occurs in high-speed digital mobile communication. This is a phenomenon in which the arrival time difference of a multiplex wave that causes fading with respect to the reciprocal of the data transmission rate cannot be ignored, and a delayed wave causes interference with a 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 spread by a code sequence of another station, and a propagation that is different from A1 due to reflection, scattering, etc. on buildings and mountains. A that arrives with a delay time with respect to A1
2, A3,... An arrive as a composite wave of delayed waves. Selective fading occurs when arriving 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 levels of the delayed waves of A2 and A3 are small.

[0005] On the receiver side, a correlator is provided to perform a correlation operation between its own sequence and an incoming wave. Interference waves B, C, ... N
Has no correlation output because it is spread by a sequence different from its own sequence. Therefore, if the chip rate on the receiver side is slightly delayed and the sliding is performed, A1,
A correlation peak is output at a timing corresponding to A2. When the correlation peak is detected and the sharpest correlation value is obtained, the chip rate on the receiver side, which was slightly delayed at the time when it is the same as the chip rate of the system, is completely matched with that of the system. I will do it.

The above is the operation of the CDMA synchronous capture and tracking. Normally, among the arriving waves of A1, A2,..., A1 which is the first arriving wave has the highest level.
Synchronization is established at the arrival timing of 1. In the conventional method, the information on the propagation environment obtained in this state is at most the level of A1 currently supplemented, that is, only the RSSI, and the information that determines the selective fading is A
Information on 2, A3,... Cannot be obtained.

FIG. 3 shows a block diagram of a conventional receiving apparatus. 1 is an antenna, 2 is an RF amplification unit, 3 is a frequency conversion unit, 4 is a synchronous supplementary tracking unit, 5 is a PN generator, 6 is a synchronous supplementary correlator, and 7 is an information demodulation unit.

In the CDMA system, since carriers having different sequences can be regarded as noise, the communication system is resistant to interference. However, the so-called near-far problem, in which another transmitting station exists closer to the communication base station than that of the base station. appear. That is, since there is no ideal sequence group having a sharp autocorrelation characteristic and having no cross-correlation, there is considerable influence of interference. Therefore, the CDMA system is also essentially the same as the conventional mobile communication, and a system method for acquiring and utilizing information about the propagation environment, such as reporting the level of RSSI (Received Signal Length Indication) to the base station, is desirable. However, in the current mobile communication, although the RSSI level is reported to the base station, the above 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 be further increased in the future due to the effective use of the frequency, and the countermeasure against frequency selective fading is very important, but the countermeasure is very difficult in the conventional communication system. In the prior art, for example, an attempt is made to remove or combine a delayed wave using an adaptive equalizer.
(Digital signal processor) It has not been adopted because there are problems that the size of other circuits becomes extremely large, and convergence time for high-speed data becomes insufficient and divergence occurs.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a high-quality communication in a CDMA system by obtaining information on 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 method for realizing the above-mentioned method, and a receiving apparatus capable of detecting delayed wave information simply and efficiently.

For this reason, the present invention provides a receiving apparatus with a sliding correlator for detecting delayed wave information, in addition to a correlator provided for receiving a CDMA transmission wave,
The information of the delay wave is detected by the correlator, and the detected delay wave information can be transmitted to the base station.

[0011]

According to the present invention, since the delay wave information can be detected by the sliding correlator as described above, the detected delay wave information is transmitted to the base station side to improve the communication quality by frequency selective fading. Deterioration can be made 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 which is synchronizing and capturing at an appropriate time and starts sliding again. FIG. 2 shows an 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 correlating with the synchronization, so that the same correlation peak corresponding to A1 as that of the correlator 6 is output. As the time elapses, the timing of the sliding correlator shifts, and a correlation peak with A2 is output at a time corresponding to the arrival time of A2, and similarly at a 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 a delay time and an amplitude level of each delay wave called a delay profile, and is information indicating 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, whereby the base station can be provided with information on selective fading in the current propagation environment. , Higher quality communication can be realized.

[0015]

As described above, according to the present invention, when the CDMA system is applied, delayed wave information can be easily detected by monitoring a sequence having a sharp autocorrelation characteristic used for spread spectrum. Therefore, when the CDMA system is applied to mobile communication, communication quality can be improved very efficiently only by adding a correlator.

[Brief description of the 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 delay wave.

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

FIG. 4 is a diagram schematically illustrating a state in which a CDMA transmission wave arrives at a mobile station.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 RF amplification part 3 Frequency conversion part 4 Synchronous supplement tracking part 5 PN generator 6 Synchronous supplement correlator 7 Information demodulation part 8 Sliding correlator 9 PN generator 10 A / D converter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/69-1/713 H04J 13/00-13/06 H04Q 7/38

Claims (1)

(57) [Claims] A mobile device having at least a correlator for synchronous capture.
The sliding correlator is provided to the receiving apparatus side of the station, the same
The incoming arriving wave input to the period acquisition correlator is
Input to the sliding correlator.
The delay wave information detected by the correlator is transmitted to the base station.
A spread spectrum communication system characterized by having a configuration as described above .