MIMO-OFDMA opportunistic beamforming with partial channel state information

Over the past few years, a lot of interest has focused on Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple Input Multiple Output (MIMO) systems thanks to the tremendous gain on system capacity they offer. Transmit beamforming is a low complexity technique that helps in achieving the full diversity afforded by the multiple antenna environment. MIMO-OFDMA systems using opportunistic beamforming are a promising solution to satisfy the growing demand in terms of data rate and Quality of Service (QoS). An important practical issue in MIMO-OFDMA systems is the feedback load. As a large number of carriers (e.g. 2048 for WiMax) is usually used in such systems, feeding back full Channel State Information at the transmitter (CSIT) for each carrier is prohibitive. In this paper, the problem of feedback reduction in MIMO-OFDMA opportunistic beamforming is addressed. We present different partial CSIT schemes that reduce significantly the feedback overload at little expense of system throughput.