Cluster-Directed Acyclic Graph Formation for IEEE 802.15.4 in Multihop Topologies

IEEE 802.15.4 represents the future standard for multihop Wireless Sensor Networks. However, this protocol is based on a cluster-tree which performs poorly in multihop. In the same way, scheduling the superframes to avoid collisions represents a key challenge. We propose here a simple greedy scheduling algorithm, integrated with the IEEE 802.15.4 MAC mechanisms. This scheduling permits to modify the Cluster-Tree into a Directed Acyclic Graph which reduces the delay while improving robustness, removing the single point of failure problem of the original structure. Simulations proved that these mechanisms permit to obtain an efficient MAC layer for multihop topologies.