Research On Energy-efficient And Low-latency Goals-driven MAC Protocol Of Wireless Sensor Networks

Wireless sensor networks(WSNs) is a distributed, self-organizing and intelligentinformation systems, which has the functions of data gathering, data processing andwireless transmission. Wireless sensor networks is being widely applied in the fields ofthe military, the environment, the health-care, the transportation and the agriculture.Because of limited resources, dynamic and large-scale, researching on MAC protocolhas been become the focus currently. Based on the SMAC protocol, this paperresearches on the energy-saving algorithms for wireless sensor networks, and proposesa low-latency hybrid MAC protocol, LH-MAC.SMAC is one of the classic MAC protocol based on the competition for wirelesssensor networks, which first proposes the mechanism of periodical sleeping thatreduces the energy consumption greatly. But the Adaptive Listening mechanism, whichis used to reduce sleeping latency, causes a lot of nodes in idle listening andoverhearing, and results in a serious waste of energy. In this paper, to reduce the energyconsumption, we propose an energy-efficient protocol, E2SMAC. It only makes a smallportion of nodes involve in the adaptive listening. The theoretical analysis shows that,under the premise of implementing the adaptive listening function, theE2SMACdecreasesthe awakening nodes about60%and extends the life of networkseffectively.Although the adaptive listening reduces the sleeping latency effectively, it cannotmeet the requirements of real-time applications, such as disaster warning and medicalmonitoring. In order to satisfy the demands on real time, this paper proposes alow-latency hybrid LH-MAC protocol, which is based on CSMA/CA and TDMA. InLH-MAC protocol, the time is divided into successive super-frames, one of which isconsisted of competition period, non-competition period and update period. Thecompetition period completes the reservation of slots during the non-competition periodwith the competitive manner, and the non-competition period transfers the data packetswith the TDMA manner. This mode of operation makes data been forwarded continuously,and the cumulative sleeping latency been reduced greatly. In addition, to improve theeffectiveness of data with different distance from the Sink, the LH-MAC uses two differentmeasures of priority queue and unequal contention window，which improve the ability ofaccessing to the channel. Finally, we use the NS2to simulate the protocol. Compared with the SMAC, the LH-MAC reduces the end-to-end latency greatly.