A hybrid contention/reservation medium access protocol for Wireless Sensor Networks

Most Wireless Sensor Networks (WSNs) applications require that a large number of low-complexity energy-constrained sensors forward the sensed information to a sink node, which gathers, processes and forwards the information to the end-user. Although, this approach is beneficial for the sensor nodes, since most of the complexity is delegated to the sink node, it is also the origin of severe bottleneck effects near to sink. Having a large number of sensors trying to forward their data to a single sink node leads to increased traffic intensity, congestion and increased packet loss probabilities. The key point in coping with this problem is the medium access control (MAC) protocols that handle the sensors´ traffic, with respect to specific performance optimization criteria. Following the general research trend, which focuses on hybrid contention/reservation MAC protocols, we present a novel hybrid protocol, which decides on the access mode to be used, based on the trade-off between the expected throughput and protocol complexity. The expected throughput can be predicted by exploiting an analytical framework grounded on the queueing theory, which evaluates the performance of both contention based and contention-free access schemes. Extensive system simulation results validate the theoretical derivations and the ability of the proposed hybrid MAC scheme to balance between performance and complexity.