WLC46-3: Robust Optimal Cross Layer Designs for TDD-OFDMA Systems with Imperfect CSIT and Unknown Interference - State-Space Approach based on 1-bit ACK/NAK Feedbacks

Cross layer designs for OFDMA systems have been shown to offer significant gains of spectral efficiency by exploiting multiuser diversity over the temporal and frequency domains. However, in most existing designs, perfect knowledge of channel state information at the transmitter (CSIT) is assumed. When we have imperfect CSIT and unknown interference at the receiver, there may be packet transmission outage (error) and it is a tricky problem for cross layer design with imperfect CSIT and unknown interference. In this paper, we shall propose a robust optimal cross layer design for downlink TDD-OFDMA systems with imperfect channel state information (CSIT) and unknown interference in slow fading channels. Exploiting the ACK/NAK (1-bit) feedbacks from the mobiles, the proposed cross layer design does not require knowledge of the CSIT error nor interference statistics. Furthermore, for sufficiently large number of feedbacks, the system will converge to steady state (as if perfect CSIT were available). Simulation results illustrate that the performance of the proposed closed-loop cross layer design is very robust with respect to imperfect CSIT, unknown interference, model mismatch as well as channel variations due to Doppler.