Scan and wait combining (SWC): a switch and examine strategy with a performance-delay tradeoff

This paper proposes and analyzes an alternative form of switch and examine combining, namely one that waits for a channel coherence time if all the available diversity paths fail to meet a predetermined minimum quality requirement. This scanning through the available diversity paths followed by waiting is repeated indefinitely until a path with an acceptable quality is found. The performance of the resulting "scan and wait" combining (SWC) scheme is studied in terms of its average probability of error and ergodic capacity. The paper looks also into (i) the delay associated with SWC by deriving the statistics of the waiting time needed before satisfactory transmission occurs and (ii) the underlying complexity by studying the statistics of the number of diversity paths estimated per channel access. Selected numerical examples show that, for a fixed average number of channel estimates per channel access, SWC outperforms traditional diversity combining schemes at the expense of a negligible time delay.