On the Power of MIMO Broadcast Systems Under SNR Constraints With Limited Feedback

The power problem of joint zero-forcing beamforming and scheduling is addressed in a multiple-input-multiple-output (MIMO) broadcast channel under individual signal-to-noise ratio (SNR) constraints. Perfect channel knowledge is assumed to be available for each single antenna user, whereas the base station (BS) with multiple antennas is provided with partial channel-state information through limited-rate feedback channels. Each user can feed back its quantized channel direction information and needed power information. Only the user with the minimum power is selected to communicate with the BS. Expressions for the average minimum power used to transmit are derived, and tradeoffs between the number of feedback bits, the number of users, and the number of transmit antennas are observed.