Improved Switched Combining with cooperative diversity for wireless body area networks: Empirical analysis and theory

An improved form for Switched Combining (SwC) with on-body cooperative communications is presented, particularly suited to the `everyday´ wireless body area network (BAN) wireless channel. Two and three-branch cooperative coherent SwC is analyzed theoretically and empirically and compared with cooperative coherent selection combining (SC), and a previous switched combining implementation. New expressions for outage probability and approximate switching rate are derived for the proposed SwC. Three locations for relays/hubs are considered, along with seven sensor locations, all using extensive on-body “open-access” channel measurements. The outage performance of SwC is not considerably degraded with respect to SC with large improvement over single-link communications, and significant improvement over the previous SwC. The benefit of the proposed SwC is shown as the two and three-branch switching rate for this SwC, is typically between 10% and 15% of that of SC. Further, compared to the previous switched combining method, there is only a small increase in switching rate at the same time as improved outage performance. The low switching rate here may allow for easier implementation in practical IEEE 802.15.6 BAN.