Research On The Energy Efficient MAC Protocol And Cross Layer Optimization Of Wireless Sensor Network

Wireless Sensor Networks(WSNs)have become a leading solution in many important applications such as intrusion detection,target tracking,industrial automation,smart building and so on.The performance of a WSN is required to be more and more efficient.Typically,a WSN consists of a large number of low-cost sensor nodes powered by disposable batteries and wireless communication consumes most energy of a node.Therefore,in order to prolong the network lifetime,each node periodically alternates between active and sleep states to achieve lower power consumption.Sensor nodes should keep their radio transceivers off as long as possible and only wake up when they need to transmit or forward packets.With this duty cycle technique,WSNs face many challenges such as maintaining reliable packet transmission,reasonable wireless channel allocation and high energy efficiency under dynamic channel conditions.To address these challenges,this thesis focuses on low-power medium access protocol and corresponding cross layer optimization mechanism in wireless sensor networks,and aims to allocate the limited channel resources reasonably,improve the reliability of packet transmission,optimize route path and reduce packet delivery latency.The first part of this thesis presents a novel single channel asynchronous duty cycle MAC protocol,called PBA-MAC(Prediction-Based Asynchronous MAC protocol).PBA-MAC applies a simple pseudo random algorithm in an energy efficient predictive wake-up mechanism.It reduces communication cost by enabling senders to predict intended receiver's wakeup times,without introducing unnecessary idle listening or overhearing cost.In addition,it introduces an advanced wakeup mechanism to handle the prediction error caused by clock drift and hardware platform latency.More importantly,its backcast-based retransmission characteristic is capable of achieving high energy efficiency even when wireless collisions happen and packets must be retransmitted.The PBA-MAC is implemented in Contiki operating system.The comparisons are made between PBA-MAC and some existing energy-efficient MAC protocols.The results show that PBA-MAC significantly reduces the network energy consumption and packet delivery latency even under heavy traffic load.Then,this thesis proposes a new multi-channel MAC protocol PM-MAC(Predictive Multi-channel MAC)based on the predictive wakeup mechanism of PBA-MAC.In PM-MAC,each node chooses its wakeup times and wakeup channels independently according to the generated pseudo random numbers.The channel “blacklist” mechanism in PM-MAC can sense and perform statistic on channel conditions.Hence,PM-MAC is able to avoid using channels that are currently heavily loaded or currently with wireless interference.In addition,PM-MAC adopts the adaptive time compensation technique to accurately predict wakeup time between neighbor nodes.At the same time,PM-MAC uses the exponential increase algorithm to achieve precise and fast resynchronization,even under condition such as great prediction error between nodes.Since senders in PM-MAC can accurately predict the wakeup times and wakeup channels of intended receivers,PM-MAC has no problem of poor extensibility in static TDMA-based protocol and also avoid the severe control overhead in dynamic allocation mechanisms.PM-MAC not only reduces multihop packet delay and the energy consumption of communication between nodes,but also increases network capacity and throughput.Experimental results confirm the outstanding performance of PM-MAC in all testbeds.Finally,this thesis proposes an adaptive network coding mechanism based on cross-layer optimization,which can greatly reduce network traffic in data distribution.Considering the characteristics of asynchronous duty cycle MAC protocol,this thesis also proposes a cross-layer optimization mechanism which focuses on solving the suboptimal route discovery problem.Four kinds of route discovery optimization mechanisms have been presented to improve the quality of the routes discovered in asynchronous duty cycle networks.These four optimization mechanisms can be easily integrated with existing wireless on-demand route discovery protocols without introducing additional routing messages among the nodes.Furthermore,these optimizations are distributed and achieve significant performance without the need of global routing information when a node uses them to determine an optimal transmission route path.