A cluster-based hybrid access protocol for wireless sensor networks

Wireless sensor networks (WSNs) are deployed for a wide range of applications that involve collecting information from the operational region in which they inhabit. Depending on the application, sensor nodes may have to transport a time-varying load of sensing data. However, medium access protocols used in WSNs are not generally designed to deal with time varying traffic and may be efficient only for one particular range of traffic load. In this work, assuming a clustering routing scheme, the objective is to improve the performance of wireless sensor networks using a hybrid access protocol. The main idea is to use a protocol which incorporates the characteristics of both random (e.g., CSMA) and contention-free (e.g., TDMA) medium access schemes and smoothly switches between the two depending on the level of traffic load of the sensor nodes. TDMA is used when the network is subject to high traffic or contention and CSMA is used during the clusters´ setup phase as well as low contention scenarios. The NS-2 simulations results show that our scheme, compared to TDMA stand-alone, improves the throughput and reduces the latency in variable traffic scenarios.