A cyclic MAC scheduler for collecting data from heterogeneous sensors

Many wireless sensor networks applications, e.g., structural health monitoring (SHM), require the sensors to construct a multihop network to collect the environmental data in real-time. These sensors generally generate sensing data in fixed rates, so their transmission schedules can be deterministically listed. Time division multiple access (TDMA) is especially appropriate for these applications because it can prevent radio interference, thereby reducing the transmission power and maximizing wireless spectrum reuse. However, to reserve sufficient bandwidths on distinct links of a heterogeneous WSN, a complex TDMA schedule is necessary, and a sensor node might need to keep a large TDMA schedule table in its tiny memory. To prevent a large size TDMA schedule table, this paper proposes a CyclicMAC scheduler that assigns each node a temporal transmission pattern which is merely parameterized by period and phase. The CyclicMAC scheduler determines the period to satisfy the bandwidth requirement of the node, and adjusts the phase to achieve collision-freeness and reduce the end-to-end latency as well. The end-to-end latency of the resulting schedule is proven to be optimal if the wireless links only interfere with their parent link and sibling links. As far as we know, CyclicMAC is the first that simultaneously addresses the three design issues of TDMA scheduling, which satisfies heterogeneous bandwidth requirements, minimizing schedule table size, and reducing end-to-end latency, for multihop wireless sensor networks.