Research On Turbo Codes And Space-Time Codes In The Wireless Communication Link

Driven by cellular mobile, Internet and multimedia services, demands for capacity in wireless communications have been rapidly increasing worldwide. While the available radio spectrum is limited, the communication capacity needs can only be met by efficient coding corresponding to variant channels. In the past years, the advanced codes such as Turbo codes in system with a single antenna link and space-time codes in systems with multi-antenna link have been rapidly devoleped for which made it feasible to approach to the Shannon capacity limit and perform well in fading channels. In this paper, some aspects of Turbo codes and differential unitary space-time modulation (DUSTM) are studied including the stop criteria of Turbo codes, the design and the search of constellations for DUSTM and the simple trellis Viterbi decoding for uncoded DUSTM. Such works are detailed and summaried as below:1. Proposed a simple and powerful algorithm for adaptively stopping the Turbo iterations in accordance with the dynamic chaos course of Turbo decoding. In the course of decoding, it is useful to decrease the abstract values of extrinsic informations which are input as apriority so that it can accelerate the convergence and lower the error probability. Then consider the extrinsic informations as the multi-dimension vector and take the variance of Euclid distance between extrinsic informations of the two component decoders. The Trubo iterations will be stiopped at the condition that the variance of distance is less than a setted threshold for some consecutive times. The simulation results show that it is effective and can decrease by almost a half iteration at high SNR but meet the demands of decoding correctness.2. Deduced some more arguments, diversity sum, diversity average with order MN and diversity average with order N, which is somewhat important to the performance of DUSTM (Differential Unitary Space-Time Modulation) from the Chernoff upper bound of pairwise error probability, such that not only the performance at high SNR is regarded but also the performance at low SNR and average error probability are taken into account. Furthermore, a new rotation constellation is presented by left multiplying a rotation matrix with the diagonal matrix. It is shown that the diversity product and diversity sum of the new constellation are both greater than that of diagonal constellation. Simulation results show that almost 2dB gain can be obtained against the diagonal constellation.3. Proposed the equivalent partition search algorithm for the search of optimum diagonal constellation. It is presented that the constellations with the same singular values are...