Capacity Analysis Of Ssk, GSSK And SM Modulated MIMO Systems

With the development of wireless communication services and people’s increasing demands, the limited spectrum resources will no longer meet the increasing demand for system capacity. MIMO wireless communication system combines both transmit diversity and receive diversity technologies, which greatly improved the anti-fading performance of wireless communication system. In MIMO system, the data transmission is more reliable and the bit error rate is reduced. The system can improve its capacity performance significantly without increasing the transmitter power or system bandwidth. Based on a number of advantages, MIMO has become an important technology in the next generation of wireless communication.Spatial modulation (SM)、space shift keying (SSK) and generalized spatial shift keying (GSSK) are special technologies of MIMO modulations. SM transmits information by transmit antenna indexes and carrier modulation symbols. SSK and GSSK transmit information by transmit antennas indexes and the combination of transmit antennas indexes separately. It do not need synchronization control of transmit antennas, so the system complexity is reduced, and there is no inter-channel interference. This paper gives a detailed analysis of the performance of MIMO system with SSK、GSSK and SM from the perspective of channel capacity.The results show that in Rayleigh fading channels, the capacity of MISO wireless system using SSK and GSSK will be restricted by two factors of SNR and the number of transmit antennas (combination). When the SNR is fixed, the upper-bounds of capacities of SSK and GSSK systems exist. When the number of transmit antennas goes to infinity, the maximum channel capacity equals to the capacity of the SISO system in AWGN channel; when the number of transmit antennas and the number of transmit antennas combination are fixed, the capacities of SSK and GSSK systems are no more than the logarithmic values of these two numbers separately. The upper-bound of MISO system with SM is the Shannon formula.Correlation between channels affects the capacity performance. In AWGN channels, the capacities of SSK and GSSK systems are both zero. Line-of-sight (LOS) may cause performance degradation for SSK and GSSK systems, but do not have a significant impact on SM system.