Implementation of Enhanced Lightweight Medium Access (eL-MAC) Protocol for Wireless Sensor Network L.A.Latiff UTM Razak School of Engineering and Advance Technology UTM IC,Kuala Lumpur, Malaysia liza@ic.utm.my R A. Rashid, S.H.Syed Ariffin,W.M.A Wan Embong, N.Fisal, Faculty of Electrical Engineering Universiti Teknologi Malaysia, Malaysia Anthony Lo Wireless & Mobile Communications Group Delft University of Technology Netherlands. A.C.C.Lo@tudelft.nl Abstract— Wireless sensor network (WSN) is increasingly being used in a variety of applications which include habitat monitoring, smart health care system, building automation, to name a few. Many approaches were developed for all protocol layers, but an energy-efficient Medium Access Control (MAC) layer remains a key design challenge. MAC with scheduled based architecture provides greater advantage over other designs, such as contention-based and frequency division multiple access (FDMA), in terms of minimizing packet collision, overhearing, idle listening, and over emitting. Reliable and energy efficient data transmission are required to prolong the network lifetime. This paper presents the testbed development of an enhanced lightweight medium access (eL-MAC) protocol which introduces distributed time slot assignment and slotting communication mechanism. Therefore, with eL-MAC, idle listening, overhearing and hidden terminal will be eliminated where nodes transmit in its own time slot and sleep in other time slot if there is no activity. This will reduce energy consumption as nodes are active when transmitting and receiving and idle only in the beacon session. The testbed is developed using TelosB sensor nodes programmed with TinyOS. NesC programming language was used to implement the protocols in the WSN module. Experimental results were compared to the results obtained from simulation. As expected, there is a slight degradation in throughput and packet received ratio in the experiment but is consistent for all values. This concludes that the developed testbed reflects the eL-MAC protocol and has been successfully implemented. Keywords-component; Medium Access Layer (MAC), Time Division Multiple Access (TDMA), Contention-based MAC, Wireless Sensor Network (WSN), Distributed time slot assignment. I. INTRODUCTION Wireless sensor network (WSN) is composed of a collection of sensor nodes that interact with each other intentionally to gather information from the surveillance area. Sensor nodes such as TelosB, MicaZ and Sensinode are normally assembled from a low cost microcontroller, low power radio transceiver, data logger and a number of sensors. They are designed to support unattended operation for long duration, usually in remote areas, in smart building or even in hostile environments. WSN applications such as environmental monitoring [1], object tracking [2] and intelligent buildings [3] require a reliable data transmission and can endure long periods of operation. However, there are limited features in sensor node architecture which include low processing capabilities and low memory capacities. These constraints have motivated extensive research to design mechanisms that can lengthen the sensor nodes operating time and relatively prolongs the network lifetime. Medium access control (MAC) layer is responsible to managing the medium accessibility in order to minimize collision among transmitting packets [4]. Packet collision requires node to retransmit the packet, hence consuming additional energy. Since this layer controls the physical (radio transceiver) layer, it has a large impact on the overall energy consumption and hence, the lifetime of a node. There are several location-dependent carrier sensing issues that need to be addressed in designing MAC protocol. First is the hidden nodes problem where nodes falsely assumed that the channel is in idle condition and start transmiting. Hence, it will result in high probability of data collision. Meanwhile the exposed nodes problem occur when nodes are in transmitter range but out of receiver range. Lastly is the capture effect problem where nodes can receive one of two simultaneous transmissions. The hidden nodes problem causes retransmission of the collided data. Therefore, more energy is required, hence, inefficiency of energy usage. Exposed nodes problem results in packet overhearing, where node is forced to receive data that is not destined to it. The biggest source of energy consumption is idle listening. It occurs when a node is required to continuously listen to the channel in order to receive a potential packet from its neighboring nodes. Energy inefficiency caused by the idle-listening problem and high collision probability can be avoided in 2010 16th Asia-Pacific Conference on Communications (APCC) 978-1-4244-8129-3/10/$26.00 ©2010 IEEE 267