Nihar Jindal

Multiple Antenna Downlink Channels with Finite Rate Feedback

Multiple transmit antennas in a downlink channel can provide tremendous capacity (i.e. multiplexing) gains, even when receivers have only single antennas. In order to realize these gains, however, accurate channel state information is required at the transmitter. We consider a block fading channel with finite rate feedback from each receiver. Each receiver is assumed to obtain perfect knowledge of its channel at the beginning of each block (presumably via training), which is then quantized to a finite number of bits and fed back to the transmitter. The capacity degradation due to imperfection in channel knowledge at the transmitter is quantified, and the required feedback as a function of the number of transmit antennas and receivers is investigated. Additionally, it is shown that the full multiplexing gain is achievable in this system if the number of feedback bits per receiver is increased linearly with the SNR (in dB).