MERLIN: cross-layer integration of MAC and routing for low duty-cycle sensor networks

Sensor network MAC protocols typically sacrifice packet latency to achieve energy efficiency. Such delays may well increase due to routing protocol operation. For this reason it is imperative that we attempt to quantify the end-to-end delay and energy consumption when jointly using low duty cycle MAC and routing protocols. In this paper, we present a comprehensive evaluation of MERLIN (MAC and efficient routing integrated with support for localization), a cross-layer protocol that integrates both MAC and routing features. In contrast to many sensor network protocols, it employs a multicast upstream and multicast downstream approach to relaying packets to and from the gateway. Simultaneous reception and transmission errors are notified by asynchronous burst ACK and negative burst ACK messages. A division of the network into timezones, together with an appropriate scheduling policy, enables the routing of packets to the closest gateway. An evaluation of MERLIN has been conducted through simulation, against both the SMAC and the ESR routing protocols (an improved version of the DSR algorithm). The results illustrate that the joint usage of both SMAC and ESR, in low duty cycle scenarios, causes extremely high end-to-end delays and prevents acceptable data delivery rate. MERLIN, as an integrated approach, notably reduces latency, resulting in nodes that can deliver data in a very low duty cycle, yielding a significant extension to network lifetime.