Research On MAC Protocol And Wireless Greenhouse System In Wireless Sensor Networks

Wireless sensor networks (WSN) is a kind of self-organization wireless network which taking the data as center. The node in network is intensive, huge quantity and covering a large area, and the network topology is dynamic,and the network was self-organization and self-modulation. The energy efficiency is one of the most decisive factors of designing node. The MAC protocol play an important role in WSN and traditional MAC protocol are not suitable for WSN. Therefore research and improve existed MAC protocol, advancing new algorithm of MAC is essential. Under the support of the fund of the Chongqing Science and Technology Committee (Subject No.2005BB2198), the key technique on MAC protocol for WSN has studied in the thesis.From the energy consumption, network topology and efficiency, the difficulty in designing MAC protocol and major sources of energy waste described. The recent representative MAC protocols are also discussed and presented in detail.Beacon conflict and time synchronization problems which exist in IEEE 802.15.4 are analyzed. By analyzing the process of that a node sending or receiving packet, we can see that propagation delay and Processing Delay are primary error which we can set a offset to eliminate in practical application. The idear from LMAC protocol of managing slots are used here, which adopts slots scheduling algorithm to resolve beacon conflict. This algorithm import beacon-only period when all coodinator would send their beacon frame, which make all nodes in the network sleep and wake up at the same time.IEEE 2.15.4 MAC utilizes carrier sense multiple access with collision avoidance (CSMA/CA) whose parameter minimum contention window (CWmin) has influence on the performance of wireless sensor networks (WSN). Proper CWmin length can reduce probability of collision. This paper proposes an adaptive optimization mechanism, ABM (Adaptive Backoff Mechanism) which is based on the condition detection, the offered load and the competing station number. Moreover, a new mathematic method, Signal-Flow Graph Model is used to modeling. The elaborate numerical results show that the energy efficiency mechanism could achieve is 3 times higher than standard CSMA/CA in almost all the different competing stations numbers and offered load. Develop a wireless sensor network system which consist of wireless module, gateway,controlling center,data collectiong module,data extracting module and data transfer module based on ZigBee technology for greenhouse. Micaz development kits are used as experiment platform. The software on Windows platform is developed in C and in TinyOS's is nesC. The result of experiment illustrate that the algorithm can be realized by WSN nodes, which also can provide more flexible and mobile.