SSMAB: A Slotted Sense Multiple Access Broadcasting Protocol for Dynamic Wireless Sensor Networks

In industrial monitoring and control sensor networks, a control server or a sink needs to send a message or command to a group of nodes, or all nodes in a reliable manner to control their operations. This is done by means of a repeated rebroadcasting. This suffers from message collision and high energy consumption due to all nodes that have to remain active. In the tree-based TDMA approach, every node is assigned a unique broadcast slot within which it rebroadcasts a message toward its children in order to prevent collision. This limits the active time of a node to its sending and receiving slot. However, this approach does not respond effectively to the dynamic change of topology and signal interference, requiring frequent tree reconstruction and slot rescheduling. The worse thing is that the failure of a node to receive a message affects all its descendants. To overcome this problem, one sharable slot is assigned to the nodes in each tree level so that the nodes at the same level compete for broadcasting. This approach allows a node to move to another level without causing a global slot rescheduling. Simulation results prove that this approach not only improves the reliability of message broadcasting, but also allows energy saving significantly.