Time division duplex transmission of direct sequence spread spectrum signals in multipath channels

Abstract

The time division duplex (TDD) mode of transmission of direct sequence spread spectrum (DS-SS) signals is proposed for systems operating in multipath channels. It is shown that the TDD systems are simpler, can facilitate efficient power control, consume less power and can operate with simpler mobile unit receivers. In the proposed TDD method, both reverse and forward links use the same frequency band and thus have a highly correlated fading pattern. The reciprocity of fading patterns of forward and reverse links provides for a non-feedback power control technique to improve system performance under multipath fading. In systems where the multipaths are created artificially by using multiple antennas, such as indoor distributed antenna systems, the characteristic of the channel as seen by each antenna can be estimated at base station. The best situated antenna can then be selected and used for transmission, creating in effect a pre-selection diversity combining system at the base station. The function of power control is still carried out at mobile units. Computer simulation results show the performance of a power controlled two-path selection diversity to be within 4 dB of static channel performance at bit error rate (BER) of 10/sup -4/. >