Chinese Journal of Computers   Full Text
Title	A MAC Layer Optimization Algorithm in Wireless Sensor Networks
Authors	LIU Yun-Lu1) PU Ju-Hua1) FANG Wei-Wei2) XIONG Zhang1)
Address	1)(School of Computer Science and Engineering, Beihang University, Beijing 100191) 2)(School of Computer and Information Technology, Beijing Jiaotong University, Beijing 100044)
Year	2012
Issue	No.3(529—539)
Abstract &   Background	Abstract In wireless sensor networks (WSNs), data converges to sinks via multi-hop transmission, which can be described by a transmission tree. In this paper, we analyzed the conflict between Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based MAC protocols and the tree structured transmission in WSNs. Based on the address of the transmission feature of WSNs, we proposed a MAC layer optimization algorithm based on the CSMA/CA. The optimization algorithm improves the equal channel access strategy in CSMA/CA and adjusts the channel access strategy based on the location of the nodes in the transmission tree to fit the transmission feature of WSNs, which enhances the network fairness. The objective of the algorithm is to improve MAC efficiency, including loss ratio, throughput and energy consumption. The performances on data loss, throughput and energy consumption of the algorithm are verified via the simulation results. Keywords Internet of Things; wireless sensor networks; transmission tree; MAC protocol Background Wireless sensor networks (WSNs) have been widely used in many applications, such as region detection, medical services, traffic control and etc. Node-to-Sink is one of the most common data transmission manners in WSNs. In a WSN, the traffic of the whole network converges to the Sink. Generally, nodes which are closer to the Sink and have more children may have more traffic loads. That means nodes take unequal responsibilities for the traffic transmission. In CSMA/CA based MAC protocol, such as IEEE 802.11, SMAC etc., the access mechanism is designed based on equal channel access mechanism. However, it does not coincide with the features of WSNs. In a WSN, smooth data stream from nodes with less traffic load will converge on their parents, and may incur congestions there. That is caused by the conflict between channel access strategies of IEEE802.11 based MAC protocols and the tree structured transmission of WSNs. To the best of our knowledge, the problem is seldom considered in the previous work on WSNs. This paper focuses on the problem and proposes a novel MAC layer optimization protocol to solve it. The contributions of this paper are as follows. First, the conflict between channel access strategy of IEEE 802.11 based MAC protocols and the tree structured transmission of WSNs is proposed as a problem in WSNs. Second, we give a MAC optimization algorithm based on the introduction of transmission condition in WSNs. Finally, we design and implement the algorithm. The optimization algorithm is lightweight, energy saving and flexible, i.e., easy to be either applied solely or combined with other CSMA/CA based MAC protocols to improve the efficiency. The performance of the proposed method is evaluated via simulation experiments. This work is supported by the National Natural Science Foundation of China (grant No.60803120), Doctoral Fund of Ministry of Education of China (grant No.20091102110017), and National High-Tech Research and Development Program of China (grant No.2011AA010500).