Design Of New MAC Protocol In Wireless Network

In recent years, the wireless sensor network(WSN) with low-cost, self-organization, dynamic topology, multi-hop routing and other features, has become a leading solution in many important applications such as: intrusion detection, target tracking, industrial automation and so on. The communication way of sensor nodes affects the performance of a wireless sensor network. Energy efficiency is a major factor considered in the communication process, since sensor nodes cannot be recharged in many cases. In addition other factors such as delay, packet loss, conflict collision and interference can also affect the performance of the entire network. While MAC layer is responsible for coordinating nodes to access the shared wireless medium, therefore, it is important to design very efficient MAC protocols for high throughput loads.In order to reduce the energy that consumed by idle listening, the majority of existing MAC protocols adopt the low duty-cycle mechanism to conserve energy. However, a sender in the asynchronous MAC protocol needs to wait until the receiver wakes up when it wants to send data. Thus periodically sleep-wake mechanism will cause the end-to-end transmission delay. Though, there has been a tremendous amount of research on the design and implementation of MAC protocols to reduce end-to-end delay, which are mainly considered for the light traffic loads ignoring the dynamic changes of the links. Moreover, to avoid conflicts, most wireless sensor networks adopt Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) mechanism, which brings the hidden terminal and exposed terminal problems. Note that, the hidden terminal problem brings collision of data transmission, increasing the latency of the network. The exposed terminal problem reduces the chance of data transmitted in parallel, reducing the channel utilization. Most of the studies are often based on request to send/ clear to send(RTS / CTS) handshake mechanism or a power control mechanism to solve a single problem, rather than solve the both problems together.To solve these problems, we focus our study on the MAC protocols of wireless sensor networks. This thesis consists of five chapters. The first chapter introduces the background, status and the value of our research. The second chapter classifies and summarizes the current MAC protocols. Moreover, it compares and analyzes the classical MAC protocols. In the third chapter, we propose a new asynchronous MAC protocol DS-MAC, nodes in the protocol can sleep adaptively according to the amount of data packets received. Thus nodes are able to timely receive or transmit data, whether the traffic load is high or low, which reduces the waiting delay and packet loss rate. DS-MAC adds the predicted sleep time into ACK package, which has the same effect with synchronous MAC protocol. With the prediction mechanism, a node only needs to wake up slightly before the receiver when it has data to transmit. Therefore, DS-MAC improves the energy efficiency and increases the lifetime of the network greatly. In the fourth chapter, we introduce a MAC protocol with rate adaptive, power adaptive mechanism and dual busy tone signal mechanism to solve the hidden terminal problem and the exposed terminal problem. It adopts the dual-channel communication model and sends busy tone signal before sending RTS and CTS data packets, which avoids the collision of RTS and CTS packets. That improves the communication stability and ability of parallel transmission, solving the hidden terminal problem and the exposed terminal problem, thereby improving overall network performance. We summarize this thesis in fifth chapter and point out the future research work of the MAC protocol.