Differential Space–Time Coded Switch and Stay Combining

The design and analysis of differential space-time coding is considered where the receiver, with a single radio frequency (RF) chain, uses switch and stay combining (SSC). Without channel knowledge at the receiver, a receive-power-based switching algorithm is proposed. By deriving the distribution of the received signal on the selected antenna, upper and lower bounds on the Chernoff bound on the pairwise error probability are derived. Using the upper bound, it is shown that even when the code satisfies the conditions to achieve full transmit diversity, if a fixed switching threshold with respect to the average SNR is used, receive diversity will not be attained. Following this, a switching threshold that offers full diversity is obtained and shown to be a logarithmic function of the average SNR at a high SNR. Furthermore, code design criteria for the proposed system are developed. For the special case of two transmit antennas, new codes for the proposed differentially modulated SSC scheme are designed and shown to perform better than existing codes. Simulation results are included to corroborate our analytical results.