Performance of adaptive Multi-user MIMO system with imperfect feedback

Cross-layer breaks away from traditional network design, which can adapt to the dynamically variable wireless channel characters to improve the wireless communication system performance. In this paper, an adaptive cross-layer scheme (Beamforming-MIMO) for multi-user system is proposed, which combine multilevel adaptive modulation (AM) at physical layer with truncated automatic repeat request (ARQ) and multi-user diversity at data link layer, and feed backing modulation mode, ARQ request and transmit weight vector from receiver. This paper derives close-form expressions of the system spectral efficiency under outdated feedback. It shows by simulation that for single-user system, compared to other cross-layer schemes, the proposed cross-layer scheme can achieve better performance. And under outdated feedback, we also analyze the impact of delay-time; transmit antenna and number of mobile user on the performance of the multi-user system.