Research On Communication Protocols Of Dynamic Sleep For Wireless Sensor Networks

Wireless sensor networks(WSN) is a novel technology about acquiring and processing information, with the fast development of embedded system,wireless communication,network and micro-electro-mechanical system. A mass of sense nodes with the capacity of sensing, computation and wireless communication compose self-organized networks, they can be used for sensing, collecting and processing information of monitored objects,which promises wide application area, has attached military branches, industrial world and academic circles in many countries. Compares with the traditional wireless network, the power energy of sense node is extremely limited, and is often unable to obtain the supplement because of severe working conditions, the network life shows a strong dependence on battery energy. How uses the limited energy to maximize network life is an essential topic which WSN needs to solve at present. Under the funding of the natural science foundation of Chongqing Municipality of China (Grant No.CSTC 2005BB2198), the thesis researchs the energy-efficient mechanism based on node sleep for WSN, and proposes LD3-MAC, a dynamic sleep Medium Access Control protocol with low dissipation, low delay and low duty cycle for wireless sensor networks, which realizes nodes synchronization on sleep schedule; The medium access control mechanism of LD3-MAC is designed; and an efficient cross-layer route mechanism based on LD3-MAC is proposed. The main works include the following content.Firstly, the power dissipation characteristics of basic components of a sensor node are analyzed; the results show sleep is an important method of reducing energy cost of node. The existing energy conservation mechanism is elaborated, and the characteristic of each mechanism is analyzed. The energy conservation theory based on sleep and the characteristic of typical sleep protocol are researched, the research shows the sleep protocol can prolong the life of wireless sensor networks, but sleep cause significant multi-hop latency and low throughput under heavy load.The thesis proposes a synchronization mechanism designed for the LD3-MAC protocol which realized nodes synchronization on sleep schedule. Sleep reduce not only energy cost of idle listening and overhear, but also avoid collision and interference of neighboring nodes. If a node turns off radio, it will not realize surrounding communication; therefore nodes must coordinate on their sleep schedules. The thesis describes synchronization principle and algorism; analyze the characteristic of existing synchronization mechanism for the low duty cycle MAC, proposed a synchronization mechanism for the LD3-MAC. The synchronization mechanism uses the unidirectional synchronization and global schedule to reduce computation complexity and the network dataflow, enhance the whole energy conservation effect; Uses the cascade diffuseness and the relative synchronization to guarantee the synchronized precision, enhance the synchronized extendibility, and accelerate synchronized process convergence; Uses staggered sleep schedule and the cyclical synchronization to reduce the forward latency, enable the synchronization mechanism to be flexible and adaptive. Simulation results show that the synchronization mechanism for the LD3-MAC realizes nodes synchronization on sleep schedule, and reduces energy cost for idle listening, forward delay and collision probability, enhances the success ratio of data transmission.The thesis analyzes the key issue that MAC needs to solve, determines the medium access mechanism for LD3-MAC according to sleep MAC characteristic. Compares RTS/CTS with the virtual carrier sense on effect to avoid collision, definites the handshake mechanism for LD3-MAC; analyzes retransmission mechanism in data link layer, and definites the retransmission mechanism for LD3-MAC and the optimal frame length; make a deep study of the Binary Exponential Backoff algorism and redinement algorism, definites the backoff mechanism for LD3-MAC; deduces the relationship between throughput and contention window based on Markov model, and definites contention window for LD3-MAC.Aim at the poor performance of sleep MAC under heavy load, the thesis proposes a dynamic sleep mechanism. For different application, dataflow difference is very big; moreover traffic in the network can be extremely bursty. If MAC uses the fixed sleep schedule, when the data load increases suddenly, mass data package will lead to jam at nodes near the base station because of the sleep delay. If the network cannot process the jam effectively, the succeeding data will cause the jam to be more serious and finally cause the buffer overflow, the mass datas are lost, in turn the retransmission by reason of lost lead to rapid rise of end to end delay, and lower throughput. To solve the problem, the thesis proposes the dynamic listening and dynamic duty cycle mechanism. The dynamic listening mechanism adopts the finite competition and the fast transmission, reduces forward latency and the conflict when the traffic in the network arises suddenly; The dynamic duty cycle mechanism adjusts the regular listening period according to the traffic load, raises spatial use factor of wireless channel. The thesis implements LD3-MAC on NS2 and evaluates its performance; the result show LD3-MAC with dynamic sleep mechanism has outstanding energy-saving effect, effectively solves the prominent delay and low throughput problem of the sleep MAC under heavy load.The high latency associated with sleep MAC also set the special request to the high-level route protocol. Many energy effient route protocols assume the MAC keep listening the channel; the transmission timers for route information collection and route establishment are designed based on low latency. Using sleep MAC, the high latency enable the timer triggering disorder to cause the route agreement expiration when the load is heavy. Moreover, the existing energy efficient route protocols are very little considered integrating with energy efficient MAC protocols, and the route overhead is significant. The thesis analyzes energy-costing route strategies of wireless sensor network,proposes a cross layer route protocol based on LD3-MAC. Does not need to transmit the special route package, the routing protocol uses the synchronization information provided by MAC to establish and update route, therefore its memory, communication and computation cost are very small; uses the stochastic method to select the next hop node, which realizes the load equalization to a certain extent, reduces latency under the heavy load. The simulation model is implemented in NS2 and the performance is evaluated, the results show the cross layer route protocol inherits the LD3-MAC outstanding performance,simultaneously implements self-organization of sleep nodes.The study shows that sleep is an effective method of reducing energy consumption and prolongs network life; LD3-MAC integrates media access control mechanism with node synchronization on sleep schedule, utilizes dynamic listening and dynamic duty cycle mechanism, resulting in dynamic sleep of nodes, which provides significant latency reduction and throughput enhancement while ensuring energy savings. The cross-layer route protocol based on LD3-MAC utilizes the information provided by synchronization mechanism to choose route, achieves the self-organization of sleep nodes.