Research On Space-Time Coding Technique In Time-varying Channel

As the wireless telecommunication is developing rapidly, the demand of channel capacity in all kinds of services is becoming higher. The technique of MIMO (Multiple-Input Multiple-Output) can increase the channel capacity greatly without additional frequency sources and transmit power. When the channel changes rapidly, it is hardly to estimate CSI correctly. In this case, unitary space-time code which can decode without CSI has a great advantage. Therefore, the research on unitary space-time code in time-varying channel has important theoretic sense and practical value.Firstly, space-time block codes are introduced in this paper. The method of matched filter is extended into the multi-dimensional space-time block code system. The construction method of matched filter is also given. Secondly, in terms of the time-varying problem in the practical wireless channel, studies are mainly conducted on unitary space-time code. On the basis of studies on present unitary space-time code schemes, an improved encoding and decoding scheme for unitary space-time code is proposed. By designing the transmit signal matrix, maximum likelihood decoding at the receiver can be simplified to maximum Euclidean distance decoding so that complexity for decoding is reduced greatly. The lower bound of the capacity for the proposed scheme in Rayleigh channel is also deduced. Finally, in order to apply the presented unitary space-time encoding and decoding scheme to practical wireless communication system, the spatial channel model put forward by 3GPP is constructed. The encoding and decoding method of space-time block code (STBC-OFDM) and unitary space-time code (USTC-OFDM) in MIMO-OFDM is proposed. The validity of the two kinds of system, STBC-OFDM and USTC-OFDM, is also verified by simulation. The impact of different channel parameters, such as angle spread, antenna element spacing and the speed of terminal on USTC-OFDM system performance is also analyzed.