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Abstract-A hybrid TDMA/CDMA MAC protocol for WSN is proposed that combines the strengths of TDMA and CDMA while offsetting their weaknesses. The proposed scheme allows the network to operate in a collision-free manner, and takes advantage of broadband property provided by CDMA. The main features of this hybrid protocol are high throughput and low latency. Performance of this new protocol is compared with Zigbee, SMAC, TDMA and CDMA uses both OPNET simulation and real wireless sensor network experiments based on Crossbow's IRIS node.
Index Terms-WSN; MAC; TDMA; CDMA; TinyOS
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I. INTRODUCTION
A Wireless Sensor Networks (WSN) is a network made of tiny embedded systems each of which composed of sensors (for light, temperature, etc.), a low-power communication device (radio transceiver), and small amount of memory and processing capability as well as limited battery power supply [1]. WSNs become popular recently [2] due to their applications in unattended tracking [3] and detection [4] of undesirable objects, hazard detection, data gathering, environment monitoring [5], and so on. In addition, due to their low cost and small size, it is easy to deploy them in large numbers.
A Medium Access Control (MAC) protocol is required in WSN to coordinate the sensor nodes' access to the shared medium. The objectives of MAC protocol for WSN are establishing the communication links between sensor nodes and sharing the communication medium fairly and efficiently [6]. Attributes of a good MAC protocol are high energy efficiency [7], low latency [8], high throughput [9] and fairness between nodes [10].
Two important problems in MAC layer for WSN is message collision [11] and idle listening. To deal with the problems above, many MAC protocols have been proposed [12-14]. The MAC protocols for WSN can be classified broadly into two categories: contention based [15] and schedule based [16].
The contention based protocol relax time synchronization requirements and can easily adjust to the topology changes as some new nodes may join and others may die few years after deployment.These protocols are based on Carrier Sense Multiple Access (CSMA) technique and have higher costs for message collisions, overhearing and idle listening. SMAC [17], WiseMAC [18], TMAC [19], Zigbee [20] and XMAC [21] are some typical protocols of this category.
In SMAC, neighboring...