Multiuser Opportunistic Beamforming Systems With Multiple Receive Antennas in Nakagami-$m$ Fading Channels

Opportunistic beamforming (OBF) is an appealing technique in wireless communications, since it can achieve multiuser diversity gains with low complexity. However, when the number of the waiting users is small, the system performances decline rapidly. In order to deal with the performance loss with a small number of waiting users scenario, this article presents a downlink multiuser OBF system, where each user equips multiple receive antennas. Three kinds of combining criteria are taken into consideration, which are selection combining (SC), equal gain combining (EGC), and maximum ratio combining (MRC) criteria. The statistical characteristics of equivalent channels are discussed in Nakagami-
$m$
fading channels. Then, we derive the closed-form expressions of the ergodic capacities. And the influences of channel quality indication (CQI) quantization are also deduced. Numerical results show that the proposed system can achieve better ergodic capacity than the conventional beamforming schemes with the limited feedback, regardless of the number of waiting users.