Tone-Based Contention Resolution for Multi-hop Wireless Sensor Networks

Medium access control protocols with common active period (AP MACs) are frequently used in wireless sensor networks (WSNs) with medium-load traffic requirements. In this class of low duty-cycle contention-based protocols, sensor nodes synchronously alternate between active periods (used for data exchange) and sleep periods (used for energy conservation). The key component of AP MAC protocols is the contention resolution mechanism (CRM), which should provide channel access to as many nodes as possible, while eliminating, or at least minimizing the chance of date message collisions. Current AP MAC protocols commonly employ CRMs based on the traditional CSMA scheme, possibly extended with RTS–CTS handshake mechanism, which are known to be energy inefficient under heavy traffic conditions, especially in dense multi-hop WSNs. In this paper, we propose a collision-free and energy-efficient CRM, specially designed for application in AP MACs. The proposed CRM, referred to as AP/TONE protocol, replaces RTS-CTS control packets with short RF tones for exchanging elementary status information among neighbouring nodes. At the top of the tone-based signalling mechanism, AP/TONE implements a distributed two-phase multi-round contention resolution procedure. In the first phase, the network is partitioned into non-interfering clusters by selectively blocking sending/receiving status of contending nodes. In the second phase, the existing intra-cluster tone-based CRM is used to make the final selection. The performance of the proposed approach was evaluated by simulation of a multi-hop WSN with varying traffic parameters and node density. The obtained results show that AP/TONE achieves significantly higher throughput with reduced energy consumption with respect to CSMA-based approaches.