MBStar: A Real-time Communication Protocol for Wireless Body Area Networks

In this paper, we report on the design and implementation of MBStar, a higher-frequency, real-time, reliable, secure protocol for wireless body area networks (WBAN). As in most proposals for body sensor networks, MBStar adopts the star topology for communication, and is designed to support a message rate as high as 400 Hz, which to the best of our knowledge, is the highest among low-power wireless communication protocols implemented at the present time. The physical layer of MBStar utilizes 802.15.4 DSSS compatible radio for which a higher-frequency, reliable, TDMA MAC layer is built. There is a simple application layer designed for security on top of it. MBStar utilizes public/private key encryption for provisioning devices and does not involve any human configuration before device join. Considering the resource limit of most embedded systems, the TDMA requirement of computing a shared global communication schedule presents a practical problem since it may not be feasible for all the devices to communicate in a long hyper-period while the communication schedule between devices is being created or modified as devices depart and rejoin. We solve this problem by keeping only the global hyper-period schedule on the gateway side, with each device being configured with a shorter, local period. Then, retransmission is employed to resolve any conflicts between the devices. Our strategy has the property that, given any fixed task set, the minimal average number of retransmissions is independent of any communication scheduling algorithm, and the EDF (Earliest Deadline First) is optimal for our communication architecture. Finally, we present experimental results that demonstrate that MBStar is an effective protocol for wireless body area networks.