Research On Relay Selection And Power Allocation Algorithms In Distributed Space Time Coding System

The main drawback of the multi-node DF protocol and the multi-node AF protocol is the loss in the data rate as the number of relay nodes increases. The use of orthogonal sub-channels for the relay node transmissions, results in a high loss of the system spectral efficiency. This leads to the use of what is known as DSTC,Recently there are many researches on relay selection and power allocation algorithms of multi-relay AF protocol, but rarely combined with DSTC. On the basis of the research on multi-relay AF protocol, this thesis focus on the relay selection and power allocation algorithms of DSTC system.Firstly, diversity technique, cooperative communication and space-time coding are introduced. A DSTC system based on QOSTC is analyzed.Secondly, In order to reduce the high compute complexity of ML detection for DSTC, a ZF detection algorithm using the linear property of the LD code is introduced. Simulation results show that, the ZF detection algorithm can reduce computation complexity while preserving the BER performance.Thirdly, based on the research of the relay selection algorithms in multi-relay AF protocol, relay selection in DSTC system is analyzed. The SNR expression of the sink node is given and a relay selection algorithm based on the SNR criterion is introduced. A sub-optimal algorithm is used to reduce the computation complexity of the algorithm. Simulation comparisons of the algorithm and existing relay selection algorithms are given.Finally, based on the research of existing power allocation algorithms, the power allocation of DSTC system is analyzed. A SNR-based power allocation algorithm is introduced. The harmonic mean function of channel coefficients is used in relay power allocation, so that the power allocation problem becomes a one dimension numerical search. This power allocation algorithm can adjust node power according to channel condition. Simulation comparison of two joint schemes of relay selection and power allocation is given at last:power allocation after relay selection, and simultaneous power allocation and relay selection. It can be seen that these two schemes have similar BER performance, but the latter has larger compute complexity.