Multiuser diversity and beamforming gain in a fast fading MU-MISO downlink with many users

Multiuser diversity is an inherent form of diversity present in time-varying systems with several users, like for instance the broadcast channel. An opportunistic scheduler has to be used in order to exploit this type of diversity. Besides the number of users and speed of the channel fluctuations, the degree of multiuser diversity depends on the dynamic range of the channel. A scheme that increases the effective dynamic range of the channel by deploying multiple antennas at the transmitter is called opportunistic beamforming It has been shown that the deployment of multiple transmit antennas with opportunistic beamforming increases the degree of multiuser diversity in several scenarios, including in slow fading and correlated fading scenarios. However, in this work we show that even in a fast fading scenario the deployment of multiple transmit antennas with opportunistic beamforming also results in having beamforming gain when the number of users is large. In the present work, we have considered a multiuser multiple-output single-output (MU-MISO) downlink channel in a single cell scenario.