Improving latency in Crankshaft - An energy-aware MAC protocol for Wireless Sensor Networks

Pratapa, Suvesh

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Improving latency in Crankshaft - An energy-aware MAC protocol for Wireless Sensor Networks

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Due to the dramatic growth in the use of Wireless Sensor Network (WSN) applications â€“ ranging from environment and habitat monitoring to tracking and surveillance, network research in WSN protocols has been very active in the last decade. With battery-powered sensors operating in unattended environments, energy conservation becomes the key technique for improving WSN lifetimes. WSN Medium Access Control (MAC) protocols address energy awareness and reduced duty cycles since the radio is the component that consumes most of the energy. This thesis investigates the performance of two recently published energy-aware MAC protocols, Crankshaft and SCP-MAC. Crankshaft has been shown to be one of the best protocols in terms of energy consumption in dense WSNs while SCP-MAC has a dedicated low duty cycle and low average latencies. The focus of this investigation is to discover techniques for reducing the latency of Crankshaft. Using OMNeT++, an open source and component-based simulation framework, this study investigates possible modifications to Crankshaft to improve its latency. The potential improvements considered include modifications to Crankshaftâ€™s retransmission contention scheme (Sift), adjustments to its inherent settings, and investigating the impact of ACKs. Since OMNeT++ readily provided only a variant of SCP-MAC identified as SCP-MAC*, the simulations results presented involve comparing variants of both protocols (Crankshaft and SCP-MAC*). The performance of these protocols is also analyzed using distinct sensor node communication patterns. It was determined that Crankshaftâ€™s latency depends on its ACK/Retransmission settings. Specifically, Crankshaft has the best latency with No ACKs, without much loss in energy consumption. But the latency can also be improved when ACKs are enabled by reducing the number of retries. Furthermore, the latency and delivery ratio are also directly governed by the WSN traffic pattern and the congestion in the network, as there was a noticeable improvement for both parameters in one-hop traffic, compared to multi-hop convergecast traffic to the sink. Finally, it was observed that Crankshaftâ€™s broadcast performance in flooding traffic can be improved by increasing the number of broadcast slots used, though this is detrimental to its performance in unicast traffic.

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