Transmission diversity for a CDMA/TDD mobile telecommunication system

Abstract

In a base station which has a plurality of antennas, each of a plurality of comparison circuits operates to compare correlation levels, which are obtained by despreading received signals for a plurality of channels, with each other with respect to the antennas. Each of a plurality of transmission antenna selecting circuits operates to determine from which antenna a transmission signal is to be transmitted for every channel. Each of a plurality of multiplexing circuits operates to multiplex the transmission signals of the individual channels, which are spread, for every antenna. As a result, on the basis of the result of the comparison of the correlation levels with respect to the antennas, a transmission antenna is selected for every channel, and the signals of the channels that are to be transmitted by a given antenna are multiplexed, whereby the base station achieves transmission diversity.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a mobile telecommunication system which is adapted to secure a communication link for a mobile unit moving in a wide area by utilizing wireless communications, and more particularly to a mobile telecommunication system which is adapted to perform communication by utilizing a CDMA / TDD system adopting the direct sequence spread spectrum (DS-SS) system.2. Description of the Related ArtA system in which communication is established among a plurality of stations in the same frequency band is called a multiple access system. CDMA (Code Division Multiple Access) is a technology in which the multiple access is performed on the basis of spread spectrum communication, in which an information signal is transmitted with the spectrum thereof spread into a sufficiently wider band than the band width of the information signal of the unit. A DS-SS system is a system wherein in the spreading, the information signal ...

AI Technical Summary

Benefits of technology

Therefore, according to the present invention, in the reverse link, an antenna by which an electric field having a good level is received is selected, whereby it is possible to maintain always a communication link in a good state. In addition, by increasing the number of antennas, even the request for the high communication quality can be satisfied. Further, since the correlation of the transmission path of the reverse link and that of the forward link is high, in the forward link as well, the same effects can be obtained.

In addition, since the transmission path or link states are different among the mobile stations, a transmission / reception antenna is selected for every link leading to the associated mobile station, whereby the interference due to the communication radio waves of other mobile stations is relatively reduced. As a result, since the communication quality is improved, and also the transmission power can be reduced, the mobile station can be miniaturized and lightened.

Problems solved by technology

This becomes a degradation factor of the transmission system.

(1) Since the correlation between the fading of the forward link and that of the reverse link is small, the space diversity technique in the base station can be applied to only the reverse link.

(2) In the case where the received power is reduced due to frequency selective fading, the communication quality is degraded and hence it is difficult to perform high quality communication.

(3) In the case where the communication capacity has greatly increased, since the interference of the communication radio waves of other stations with the communication radio wave of the local station becomes large, the communication quality is degraded, and hence it is difficult to perform high quality communication.

(4) In the case where the communication capacity has greatly increased, the requirements on the quadrature modulator and the linear amplifier of the base station become severe.

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