Quantized maximum ratio transmission for multiple-input multiple-output wireless systems

Multiple-input multiple-output wireless systems can provide substantial gains in capacity and quality compared to single-input single-output (SISO) wireless systems. Maximum ratio transmission has been shown to be a low complexity solution to improving average signal-to-noise ratio (SNR), however, it requires feedback. Since in practice full channel knowledge at the transmitter is difficult to realize, we propose a technique where the receiver sends channel state information in the form of a codebook label. A codebook design method is based on a quantized version of traditional maximum ratio transmission with maximum ratio combining at the receiver. The codebook design criterion exploits the quantization problem's relationship with Grassmannian line packaging. Systems using the transmit diversity codebooks are shown to have a diversity order of the product of the number of transmit and the number of receive antennas. Monte Carlo simulations compare the performance of systems using this new codebook method with previously proposed systems.