Abstract: In order to utilize the multiuser diversity efficiently in multiuser MIMO systems，employing opportunistic scheduling(OS) and in the meantime, to utilize the spatial diversity gain and coding gain effectively, the theory of spacetime block codes(STBC) was applied, which could resist the multipath fading and improve the performance of systems. Thus, a novel scheme that combining STBC and OS was presented and its capacity was analyzed under Rayleigh channels. Through the direct way based on polynomial expansion, ergodic capacity expressions over MIMO Rayleigh channels under perfect and imperfect channel estimation were derived for several cases: the exact closedform, asymptotic expressions for high and low SNR regions, and moreover, the capacity ratio between perfect and imperfect CSI was analyzed. Besides, capacity improvements based on MUD and SD were analyzed. The correctness of theoretical analysis was verified by the corresponding numerical and MontaCarlo simulation results which indicate that the capacity of this scheme is improved by MUD and the capacity loss is caused by channel estimation error, the ergodic capacity can be approximated by corresponding asymptotic expressions in different SNR regions.

Key words: multiinput multioutput(MIMO), spacetime block codes(STBC), opportunistic scheduling(OS), ergodic capacity, multiuser diversity