Multi-user MIMO systems with Imperfect CSIT and ARQ

Abstract

A robust closed-loop cross-layer design provides for the downlink multi-user multi-antenna systems with imperfect Channel State Information at the transmitter (CSIT) for slow fading channels. Using ACK/NAK feedbacks from mobiles, a closed-loop cross-layer scheduler does not require any knowledge of the CSIT error statistics. To take into account of the potential packet outage (due to imperfect CSIT), we define system goodput, which measures the average bits per second per Hertz (b/s/Hz) successfully delivered to the mobiles, as the optimization objectives. We formulate the cross-layer design as a mixed combinatorial search and Markov decision problem. Based on dynamic programming approach, the optimal power and rate allocation is determined using backward recursion and forward recursion algorithms. Simulations illustrate that the proposed closed-loop cross-layer scheduler has very robust goodput performance at moderate to high CSIT errors and pedestrian mobility.

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