Research Of MAC Protocol For Energy Harvesting-Wireless Sensor Networks

Wireless sensor networks(WSNs)have been widely used in recent years.However,there is a serious problem in traditional WSNs,i.e.,energy limitation.The sensor nodes are usually small,simple,and equipped with energy-limited batteries,resulting in limited lifetime of the sensor nodes,which leads to limited lifetime of the entire network.Therefore,in the past decades,a lot of methods and protocols were proposed to minimize the energy consumption.But such networks always trade off the performance for lifetime extensions,so WSNs cannot provide appropriate services.In addition,disposable batteries used in the sensor may cause pollution.In recent years,the proposed energy harvesting technology for sensor network,i.e.,energy harvesting wireless sensor networks(EH-WSNs),can solve all the problems as mentioned above.EH can solve the problem of energy shortage,thus reducing the need for minimizing energy consumption.And there is no need to sacrifice Qo S for lifetime extensions,thus improve the performance of the network.Furthermore,rechargeable batteries and super-capacitors employed for energy storage in EH-WSNs are more environmentally-friendly than disposable batteries.In WSNs,media access control(MAC)protocol is so important to determine the network performance.The MAC protocol in traditional WSNs is no longer applicable to EH-WSNs because the goal of EH-WSNs is to take advantage of the available energy to enhance the performance of the network rather than minimize the energy consumption.And when the energy source is RF,the transmission of data and energy content the channel and rely on each other.In the background,this thesis launched the research of MAC protocol for energy harvesting-wireless sensor networks.The contents are divided into three parts shown as follows.Firstly,reviews the classic MAC protocol,and then summarizes the MAC protocol design of EH-WSNs,including the scenarios involved in these protocols,the technology used and the advantages and disadvantages of the scheme.Secondly,when the energy comes from natural environment,the improved EHALOHA protocol is proposed according to the shortcomings in the existing research.In this scenario,the energy arrival process is not man-made and difficult to predict,and the goal is no longer to minimizing energy consumption,but to take advantage of the available energy to improve the performance of the network.Considering these characteristics,this thesis use Bayesian formula to improve the contention probability of existing protocol which called probabilistic polling.Then compare it with the traditional MAC protocol and probabilistic polling protocol based on the environmental energy harvesting.The simulation results show that this method can effectively improve the throughput and fairness of the network and reduce the delay.Finally,when the energy source is RF,energy and data share resources such as frequency and time,the transmission of data and energy content the channel and rely on each other,and the energy harvesting rate of sensors can be controlled by adjusting the power of RF signal.Considering these factors,this thesis proposed RF-CSMA/CA protocol based on CSMA/CA,including initial phase of RF energy adjustment,charging time based on importance index,transmission priority.