Multiuser Diversity with Imperfect Channel Quality Feedback in MIMO Broadcast Networks

In this paper, we analyze the impact of imperfect channel quality feedback on the scheduling algorithms that exploit multi-user diversity. We consider a time-slotted MIMO broadcast network where the transmitter uses its multiple antennas for spatial multiplexing to communicate simultaneously to a subset of the receivers in each slot. The transmitter sends training symbols at the beginning of a slot so that each receiver can estimate the data rate it could potentially receive from each transmit antenna. For this purpose, we develop a maximum-likelihood estimator (MLE) of SINR. The receivers report the rate information, which is noisy due to estimation errors, to the transmitter to assist its scheduling decisions. Through numerical examples, we discuss some general issues regarding exploitation of multi-user diversity with imperfect channel state information. For example, the scheduler introduces a bias for positive SINR estimation errors, which is important to take into account when the receivers declare a potential data rate in each slot.