Allocation Slot Arrangement for Flexible Polling-based TDMA in Wireless Body Area Networks

TDMA-based MAC schemes suit WBANs due to such networks' simple star topology and power limitations. In conventional ad hoc wireless networks, the specific arrangement of reservations within a TDMA frame is of minor importance as long as all nodes asking for a reservation are granted one within a frame interval. Yet emergency event preemptions or possible sensor-initiated and uncoordinated extensions of granted schedules, which seem inevitable for WBAN applications, make reservation arrangement an important problem. Here, such events could transgress an already scheduled reservation of maybe another node, jeopardizing the latter's transmission opportunity. This is more of an issue if we consider the power-limited nature of WBAN nodes, limiting the time they can keep awake looking forward for a maybe delayed transmission opportunity. In this paper we study the optimal arrangement of slave nodes' reservations which seeks to best fulfill the traffics' QoS requirements subject to a power consumption constraint. In that we account for nodes' reservation lengths, traffic QoS requirements, and the corresponding statistical characteristics of reservation extensions and emergencies. Our strategy protects the reservations of the more QoS-constrained of slaves' applications against the possible preemptions of others and also provides them with adequate bandwidth if they ever needed to extend their reservation on the fly.