A Random Beamforming technique in MIMO Broadcast Channels

In systems with a large number of transmit antennas M and a large number of users N, it is not always reasonable to assume that perfect channel knowledge can be made available to the transmitter. Since lack of channel knowledge does not lead to multi-user gains, it is therefore of interest to investigate transmission schemes that employ only partial channel state information (CSI). In this project, in order to exploit having multiple antennas in the transmitter without having full CSI in the transmitter, we propose a scheme that constructs M random beams and transmits to the users with the highest signal to interference plus noise ratio (SINR). We show that how the ricean factor K and SINR affect on the sum rate capacity. We also show that, when M is large enough, the system becomes interference-dominated.