Research On Technologies Of Differential Space Time Coding In MIMO Systems

There are two the toughest challenges in wireless communication system: spectrum efficiency and power efficiency.Multiple input multiple output(MIMO)technology can obviously improve capacity and spectrum efficiency without additional bandwidth and transmit power.Differential space-time coding(DSTC)technology is an effective measure to avoid channel estimation and decrease detection complexity under the circumstances where channel changes rapidly.MIMO system combined with differential space-time coding technology is the trend of space resource utilization technology in the future.However,most studies are based on the assumption that channel fading coefficient is identically distributed.In the actual MIMO mobile communication system,MIMO channel exhibits strong correlation,which makes desired capacity and maximum diversity gain not be achieved.In this paper,the system structure,orthogonal design and realization principles are firstly summarized and analyzed.Subsequently,the space correlation is derived,and the effect of channel correlation on the system performance is also analyzed in terms of channel capacity and space diversity.Theoretical analysis and computer simulation are done in the MIMO wireless communication environment.A integrated differential space-time coding system including the design of the transmitted signal,the channel model and the signal detection is constructed through Matlab platform,and the performance of existent differential spacetime coding scheme is also analyzed in the system.In order to overcome the space correlation,this paper proposes a new differential space-time coding scheme,pre-weighted differential space-time coding,which is suitable for MIMO system with channel correlation.In this scheme,a factor is selected randomly from a predefined set to weight the signal before each transmit antenna sending it.In fact,the weighting factor can be equivalent to the channel,which may destroy the channel spatial correlation.Applying the weighting scheme to the differential space-time coding not only does not affect detection at the receiver,but also guarantee diversity gain and desired channel capacity,and this advantage becomes more obvious with the SNR.In addition,in order to make up the3 d B loss compared with coherent detection,multiple symbol differential detection is adopted at the receiver,which narrows the performance gap by extending the observation interval for differential decoding.