Implementation and Performance Evaluation of nanoMAC: A Low-Power MAC Solution for High Density Wireless Sensor Networks Junaid Ansari, Janne Riihij¨ arvi and Petri M¨ ah¨ onen Department of Wireless Networks RWTH Aachen University Kackertstrasse 9, D-52072 Aachen, Germany Email: {jan, jar, pma}@mobnets.rwth-aachen.de Jussi Haapola Centre for Wireless Communications P.O. Box 4500 FIN-90014 University of Oulu, Finland Email: jhaapola@ee.oulu.fi Abstract— This paper describes the implementation architec- ture and performance analysis of nanoMAC, a CSMA/CA based medium access control protocol, which is specifically designed for high density wireless sensor networks. We empirically show that nanoMAC performs with high reliability in a variety of network traffic conditions in single and multihop scenarios. For energy efficient operation and minimizing idle-overhearing, nanoMAC uses a specialized sleep algorithm. We also show results from a comparative study of nanoMAC with B-MAC in terms of performance measures. Keywords–Wireless Sensor MAC, Multihop communication, Re- liability I. I NTRODUCTION Wireless Sensor Networks (WSNs for short) have poten- tially a wide range of applications. Each of these applica- tions has, of course, its own specific requirements and goals. However, some common requirements and constraints are encountered in practically every scenario. For example, the wireless sensor nodes typically have very limited memory, power resource and computational abilities. These constraints make reliable data transport over multiple hops very challeng- ing and this has become a key area of research in WSNs. With the advancements in radio design techniques, low power solutions are becoming a reality. However much is dependent on the way the medium access control (MAC) protocols behave. In WSN-MAC protocols, energy consump- tion and reliability with acceptable throughput is of primary concern. Wei Ye et al. [1] identified that the key sources of energy wastage are collisions, over-hearing, control-packet- overhead and idle listening to the wireless medium. We argue that reliable transmission and energy consumption are inter- linked with each other. The higher the number of collisions, the higher the number of retransmissions, resulting in more energy consumption and also an added overall latency. Most common causes of collisions are false channel sensing and hidden terminals in a multihop communication environment. NanoMAC [2,3] is a non-persistent carrier sense multiple access with collision avoidance (CSMA/CA) based MAC protocol explicitly designed for dense WSNs. It is intended to be highly scalable and it supports IEEE-addressing. The nanoMAC control frames: (RTS, CTS and ACK) are designed to achieve a high MPDU-to-packet ratio. The idle channel listening and over-hearing is reduced to a minimum by a sophisticated sleep algorithm employed in nanoMAC. The lightweight RTS/CTS handshake not only works to solve problems associated with hidden terminals, but it also an- nounces the sleep-durations and governs the synchronization mechanism among the nodes in a cluster. In this paper, we give the design and implementation details of nanoMAC on commercially available Telos motes [4] running TinyOS [5] in addition to extensive performance evaluation using measurements on these testbeds. We also conducted similar experiments on B-MAC using the same testbeds. The rest of the paper is organized as follows: In section II, we give the state-of-the-art overview of the existing WSN MAC solutions. Section III gives details on the design and implementation of nanoMAC protocol. In section IV, we describe our experimental set-up and the results. In section V, these results are discussed in depth. Finally in section VI, we conclude the paper. II. RELATED WORK Great deal of research has been going on in the field of power-aware MAC protocols for WSNs and several solutions have been proposed for minimizing battery usage. Determin- istic protocols based on TDMA [6,7] appear to be promising owing to negligible number of collisions and low-power oper- ation. However, such schemes suffer from scalability problems in large and dense WSNs and also the sub-optimal use of the channel. Simple CSMA-based MAC protocols, while offering good performance in terms of channel utilization are lacking any kind of energy conservation mechanisms and thus perform quite poorly with respect to the goals of the WSN MAC proto- col designs. We refer the reader to [8] for more details. Earlier schemes like PAMAS [14], which uses separate channel for sleep scheduling to packet overhearing are sub-optimal and inherently resource hungry. The reason is that it consumes