Performance Evaluation of MAC protocols in Wireless Sensor Networks

Abstract: Wireless Sensor Networks have limited resources in terms of processing capability, battery power, and channel bandwidth, which makes them both lightweight and cheap. These limitations and also advantages come with some problems regarding network lifetime and fault tolerance, as the nodes share the same wireless media with WiFi, Bluetooth and microwaves. The protocol that affects this the most is the Medium Access Control (MAC) protocol running on the MAC layer. The traditional MAC layer in wireless networking is responsible for accessing the wireless medium and decides when and how data is sent. This is really important as the wireless media is shared between all nodes and collisions needs to be avoided. In a typical sensor network operating system (ContikiOS), the MAC layer design is split into three main parts; (I) MAC, (ii) framer, and (iii) RDC (Radio Duty Cycling). Each of these parts constitute a driver which is responsible for its tasks and it is the combination of these drivers that create the traditional MAC layer. The two drivers which are focused on in this work is the MAC driver and the RDC driver. The MAC driver is responsible for detecting collisions and retransmissions. The MAC drivers being evaluated in this thesis are CSMA and NullMAC. The RDC driver is responsible for the nodes’ wakeup and sleep mechanism. This makes it the most important one as it controls if the radio is on and thus greatly affects both the delay and the energy consumption of the node. The RDC drivers evaluated in this research are ContikiMAC, XMAC and NullRDC. Through extensive simulations with ContikiOS, six different topologies with different parameters are considered. The different MAC design were compared by evaluating them in terms of average delay, delivery rate and overhead. The resulting analysis concluded that the simulations running CSMA as the MAC driver improves the delivery rate by just adding a slightly more delay in comparison to the NullMAC driver. Simulations running ContikiMAC as the RDC driver has significantly higher delivery rate than the other RDC drivers, with the tradeoff of having a higher delay. The NullRDC RDC driver reveals the lowest average delay, while consuming more power than other RDC drivers by keeping the radio always on. Thus, based on the results from the simulations, it is possible to simply choose proper MAC and RDC drivers in ContikiOS in order to provide reliability and timeliness based on application requirements.