The Study Of Turbo Joint Detection Technology In TD-SCDMA

TD-SCDMA has become one of the third-generation mobile telecommunication international standards, in which the intersymbol interference (ISI) and multi-access interference (MAI) are eliminated through joint detection (JD), and the system capacity and communication quality are thus greatly improved. Based on the conventional JD technology, Turbo JD comes into being by introducing the iteration in Turbo decoding to JD. In this way, the JD and channel decoding are combined by exchanging the soft information between the two, and yield much better performance after several iterations. So in this paper the Turbo JD principle and its application in TD-SCDMA system are deeply discussed. First, the optimal maximum a posteriori probability (MAP) Turbo JD is analyzed, to which a simple scheme is then proposed. Then, for the sake of reducing computational complexity of Turbo JD algorithms, two kinds of low-complexity Turbo JD—Instantaneous MMSE+Soft Interference Cancellation (IMMSE+SIC) Turbo JD and Parallel Interference Cancellation (PIC) Turbo JD are developed. For the IMMSE+SIC Turbo JD, an improved scheme is described, which can remedy effectively the shortcoming in the original scheme; by modifying the PIC Turbo JD, we successfully apply it to TD-SCDMA. The ping-pong effects in PIC Turbo JD are deeply analyzed and the corresponding compensation approach is derived in this paper too. Furthermore, the Turbo JD simulation approach in TD-SCDMA is presented. The performance of each Turbo JD is evaluated for the TD-SCDMA uplink transmission. Finally the computational complexity for each JD algorithm is discussed and the conclusions are made by considering the two aspects--performance and complexity.