Energy-Efficient, Collision-Free Medium Access Control for Wireless Sensor Networks

The traffic-adaptive medium access protocol (TRAMA) is introduced for energy-efficient collision-free channel access in wireless sensor networks. TRAMA reduces energy consumption by ensuring that unicast and broadcast transmissions have no collisions, and by allowing nodes to assume a low-power, idle state whenever they are not transmitting or receiving. TRAMA assumes that time is slotted and uses a distributed election scheme based on information about the traffic at each node to determine which node can transmit at a particular time slot. Using traffic information, TRAMA avoids the assignment of time slots to nodes with no traffic to send, and also allows nodes to determine when they can become idle and not listen to the channel. TRAMA is shown to be correct, in that no idle node is an intended receiver and no receiver suffers collisions, and fair. The performance of TRAMA is evaluated through extensive simulations using both syntheticas well as sensor-network scenarios. The results indicate that TRAMA outperforms contention-based protocols (CSMA, 802.11 and S-MAC) and also static scheduling protocols (NAMA) with significant energy savings.