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To cope with the internal and external interference induced by other ambient signals, physical obstacles and the dynamic change of topology in wireless sensor networks, we propose an efficient and reliable MAC protocol combining TDMA and CSMA with channel hopping. The principle operation of the proposed protocol relies on the Big Slot Scheduling Algorithm that uses the tree routing and the notion of a sharable slot. A sharable slot of an appropriate size is allocated to each tree level and shared by all the nodes at the same level for data transmission. To adapt the dynamic change of topology, a node performs a slot scheduling in a distributed manner depending on its level. Data transmission is performed progressively, starting with the highest tree level. To mitigate external interference, the proposed protocol uses a blind channel hopping mechanism in which in channel switching, each node simply …