Grassmannian Packings for Efficient Quantization in MIMO Broadcast Systems

It is well known that availability of the channel state information (CSI) at the transmitter significantly increases the throughput of MIMO broadcast systems. For even larger increase of the throughput it is important to identify and to transmit to receivers whose channel vectors are almost orthogonal to each other. Since typically the feedback link from the receivers to the transmitter is low-rate, only a quantized version of the CSI can be sent back to the transmitter. In this paper we consider the problem of designing Grassmannian packings that can serve as good quantization codebooks, have low maximum likelihood decoding complexity, and allow to identify receivers with orthogonal, and/or almost orthogonal, channel vectors in a very efficient way.