This work outlines challenges and requirements of designing a Medium Access Control (MAC) protocol for Body Area Networks, where sensor nodes send their measurement data to a central gateway device (also known as sink or hub) regularly on TDMA basis. While a number of protocols has already been proposed specifically for BAN's, they fail to account for unique characteristics of wireless channel around the human body, namely the deep and long fades that hinder communication. As such, they can not provide reliability and latency guarantees that are essential for many BAN applications. This work proposes to employ variable TDMA scheduling that allows the order of transmissions within each TDMA round to be decided dynamically, rather than be fixed in advance. Accordingly, the hub is able to account for variations of the wireless channel when allocating TDMA slots, thus increasing the probability of successful transmissions. Initial evaluations based on extensive experimental measurements have shown that, under strict latency constraints, variable scheduling approach allows to reduce transmission losses by up to 15% without accounting for retransmissions, and achieve over 99.5% reliability when retransmissions are enabled.
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