A low complexity limited feedback scheme in MIMO broadcast channels

Multiple-input multiple-output (MIMO) technologies have the advantage of improving system throughput and error performance by exploiting the spatial diversity, owing to the multiple independent transmit-receive paths. A lot of efforts have been put into MIMO broadcast channels research and it is expected to be a core technology for 3G and 4G wireless systems. Generally, channel state information (CSI) is required at the transmitter, to fully exploit the diversity. In the case that channel reciprocity does not apply, limited feedback is one effective solution to get CSI at the transmitter but it increases system complexity and degrades the performance. In this paper, we propose a low complexity limited feedback scheme for MIMO broadcast channels. Non-cooperative receivers without full CSI and a feedback link with a limited rate are considered. The proposed scheme is based on a novel Grassmannian-based two-layer codebook, each layer having a small dimension, and a vector selection algorithm, to maximize the effective channel gain. A simulation is presented for the proposed scheme, showing that the performance is very close to the best known conventional high dimensional codebook, while the search complexity and memory requirement are reduced by several orders of magnitude.