Performance Analysis Of MIMO Systems Based On Spatial Diversity And Multiuser Diversity

With the high-speed development of wireless multimedia communications network development and the rapid growth of the number of users, the demond for high-speed rate and high reliability of date transmission services in wireless communication system is increasing. MIMO systems at both the transmitter and receiver sites with multiple users seems to meet these demands by offering increased date rate and link reliability through spatial multiplexing gain and diversity gain, resperctively. STBC and SM are two dominate techniques in MIMO systems, which separately offers diversity gain and spatial multiplexing gain. Among the ways to improve deiversity gain, opportunistic scheduling could improve performance through multiuser diversity by allocating the channel to the user with maximum SNR and in the meantime delaying scheduling those in deep fading, while antenna subset selection could improve spatial diversity and reduce hardware cost induced by radio frequency chains by always selecting antenna subset with best channel condition. According to the limitations in current research of MIMO, through the direct way based on polynomial expansion and the asymptotic way based on Taylor series, three aspects are mainly analyzed as follows.First, we analyze the impact of opportunistic scheduling on STBC-MIMO systems based on spatial diversity and multiuser diversity. From the point of practical system, the closed-form and asymptotic expressions of the BER, the outage probability and ergodic capacity with imperfect channel estimation error in rayleigh channels are derived. Simulation results show that the diversity gain is improved in proportion to spatial diversity and multiuser diversity, whereas the SNR gain worsens as spatial diversity increases and in the meantime, imperfect channel state information limits finite-SNR diversity gain and brings the capacity loss.Second, we investigate the performance improvement of SM-MIMO systems with opportunistic scheduling based on multiuser diversity. Exact close-form expressions of the outage probability and error rate for the M-ary QAM and PSK modulations and the sum-rate capacity expression for arbitrary numbers of transmit and receive antennas are derived. The analytical results are verified through simulation results. It is indicated that the diversity gain of this scheme is in proportion to the number of users, which plays a great impact on performance. Since users can be treated as equivalent to"virtual"transmit antennas, therefore, multiuser diversity should be fully utilized to improve system performance in the design of multi-antenna systems.Finally, we investigate the impact of a joint scheme that combing antenna subset selection and opportunistic scheduling on MIMO systems based on spatial diversity and multiuser diversity. Error rate, outage probability and sum-rate capacity both under perfect channel estimation and imperfect channel estimation are presented. Analysis and simulation results show that the reliability is limited by channel estimation error but improved by multiuser diversity and antenna selection diversity, and in special SNR region, capacity can be improved by choosing the number of the best transmit antennas. Further, it is found that the number of antenna subset increases with the number of transmit antennas, which can improve system performance at no additional burden.