Space-Time Coding Technology For Downlink Transmission In Wireless Communications

The technique of space-time coding (STC) has been advancing drastically in recent years. This technique is mainly designed to combat channel fading in downlink transmission by combining the technique of channel coding and that of array diversity, hence increasing the capacity of wireless communications systems and giving diversity gain and coding gain to them. It can also improve the bandwidth efficiency of traditional single-antenna systems. This technique is intended to provide new solutions to the problem of limited bandwidth. In this paper, a detailed analysis is made of the structure and performance of some typical STC techniques, namely, Layered Space-Time Coding (LSTC), Space-Time Trellis Coding (STTC) and Space-Time Block Coding (STBC). An improved layered coding method is suggested and a classification is made of the transmit diversity technique which is closely associated with STC technique. Also studied are techniques used to counteract interference of all kinds as a result of the combination of STC and multi-user detection. In this paper, the author makes the following contributions: 1. An improved structure is suggested for LSTC which is based on the theory of multi-stage detection and cancellation. In the new structure, LSTC and STBC are combined in the transmitter and the technique of Group Interference Suppression is used in the receiver. The improved structure greatly simplifies decoding, and simulation demonstrates that the improved system is superior to LSTC in performance and the structure of the receiver is much simpler than that of the STBC. 2. The DS-CDMA open-loop transmit diversity technique is studied in a frequency selective fading environment. On this basis, a new method is suggested of combining linear multi-user detection and transmit diversity. This method enjoys the merit of combating channel fading while suppressing multi-user interference and inter-symbol-interference. For the two ways of spreading codes, algorithms for the blind and semi-blind receivers are provided. Simulations indicates that the algorithms suggested in the paper are superior, especially in a near-far situation, to that used in RAKE receiver which is based on STBC.