Research Of Csma/Ca Mechanism On MAC Protocol Wireless Sensor Networks

As a new network technology, Wireless sensor network has been come to attention widely. This technology has been applied to the military, health care, environmental monitoring, intelligent household, etc. Media access control (MAC) layer, at the bottom of the wireless sensor network part, decided a radio channel used way and has great influence on the performance of the network. So to speak, the MAC protocol is one of the key technologies to guarantee the efficient communication.In order to let sensor nodes share wireless channel and reduce the probability of conflicts between the nodes, the MAC protocol uses the carrier sense multiple access with collision avoidance (CSMA/CA) me-chanism. In recent years, there have been a lot of wireless sensor network related channel accessed, such as BEB, MILD, MIMD, SD and other al-gorithms based on priority design. These algorithms are good to improve the network performance, but are still needed for improvement in im-proving fairness, time delay, etc. This paper mainly have a deep research on the two kinds of typical wireless sensor network MAC protocols—S-MAC and IEEE802.15.4MAC protocols, and puts forward the corres-ponding improved algorithms according to their respective CSMA/CA mechanism:According to S-MAC protocol in retreat process termination wince timer and with fixed competition window value insufficiency, this paper puts forward a kind of adaptive competition window wireless sensor network MAC protocol, called ACW-MAC. The nodes in this protocol can assessment network load condition and dynamically adjust competi-tion window value to adapt to the changes of network flow according to itself and the history of the neighbor nodes competition channel situation. The simulation on NS-2shows that ACW-MAC has a good performance in throughput, delay and energy consumption. The timeslot CSMA/CA in IEEE802.15.4MAC protocol does not make effective use of CCA detection results, so the nodes need to execu-tive unnecessary longer retreat process. For this reason, the article presents a kind of Enhanced CSMA/CA mechanism called ECSMA/CA. The method during the initialization phase introduces a parameter FT, and the node can choose to retreat a backoff timeslot directly after CCA so as to reduce the node unnecessary longer retreat. Combined with NS-2si-mulation, the performance parameters are compared to verify that the ECSMA/CA mechanism is better than the original timeslot CSMA/CA in case of ACK reply.The results of this thesis can provide certain reference value for the research of wireless sensor networks.