Research On Space-Time Coding In Keyhole Channel

In wireless channel, multipath-fading is one of the important factors to hander the augment of channel capacity and the improvement of the service quality. In order to reduce the effects of multipath-fading, space-diversity uses multi-transmitting antenna and multi-receiving antenna(multiple independent channel)to process signals separately. In recent years, MIMO(MIMO: Multi-Input- Multi-Output)effectively improves the service quality in multipath-fading channel and time-varying fading channel, so it develops rapidly and has been widely used in the base station. Besides, it has been adopted by the mainstream protocol of the new generation of wireless communication system. Space time coding is a channel coding scheme for MIMO system, which combines the merits of the spatial-diversity and time-diversity. It provides both diversity gain and coding gain, which can provide much higher data rate-to-bandwidth ratio than single-antenna system. Without sacrificing bandwidth, space-time coding technology in MIMO system can provide higher coding gain to increase the capacity of wireless communication systems, so it has become the key technology of B3G communication systems. Besides, it has been increasingly used to transfer high rate data(such as video conference) and broadband wireless mobile service.Research shows that MIMO can effectively enhance the spectral efficiency without additional bandwidth in multi-path fading environment of wireless communication systems. However, in the actual transmission environment, there will be lack of rank in keyhole, so it will reduce the MIMO system capacity and performance. Usually, the correlation between antennas can not effectively improve the spectrum utilization. In fact, in the actual channel, the deterioration of the transmission conditions(often named as keyhole effect)seriously reduce the MIMO channel capacity. At present, the research on keyhole channel is still in initial stage. In this paper, research of space time coding mainly bases on keyhole channel. Two effective techniques to improve the performance of keyhole channel are proposed by analysis. They are Dual Polarization Antenna and Cooperative Diversity. Simulation results show that both of these methods are effective.Researches of this paper are as following:(1)Channel capacity and performance of keyhole channel are analysised. The effects of keyhole on MIMO channel capacity are researched. Simulation results show that channel capacity and performance decreased significantly in keyhole channel, compared with Rayleigh channel.(2)Research on space-time block codes in keyhole channel includes orthogonal space-time block codes, quasi-orthogonal space-time block codes, rotating quasi-orthogonal space-time block codes. Channel model is established, then coding, decoding, simulation and error analysis are finished. The simulation results show that no matter what kinds of encoding, performance decreases significantly in keyhole channel compared with Rayleigh channel.(3)Research on Space time trellis codes in keyhole channel includes STTC coding, performance analysis, coding criterion and designing optimum codes. As can be seen from the simulation results, STTC performance decreases significantly in keyhole channel compared with Rayleigh channel.(4)Proposing two methods to improve the performance of keyhole channel. They are dual polarization antenna and cooperative diversity. Simulation results verify the validity of these two methods and both of them reduce the bit error ratio of the system.