Optimal Switch and Stay Combining (SSC) under Switching Rate Constraints

Switch-and-stay combining (SSC) is a low-complexity alternative of selection combining in diversity schemes with two receiving antennas. Its operation is based upon activating a single diversity branch and maintaining it active for as long as the corresponding channel is sufficiently strong, regardless of the quality of the remaining branch. In this respect, we optimize here the switching threshold of SSC applications in terms of the achievable bit error rate (BER), under certain constraints on the switching rate, defined as the number of times per second a branch-switching takes place. Specifically, an approximate closed-form solution of the optimization problem is presented, which, however, matches closely to the optimal solution obtained via numerical optimization methods. The results apply to practical scenarios where the BER performance is of high importance, yet hardware constraints limit the maximum switching rate between the receiving antennas that the system can tolerate.