MAC Mechanism With High Performance And Joining Control Method Based On ZigBee Technology

Wireless Sensor Networks(WSNs) had come to the attention of the research foreland in the world,with which multiple subjects were concerned .It was important to research on netwok protocols with respect to low power comsumption and other characteristics. The focus of this research was concentrated on network layer and MAC (medium access control) layer.Since MAC layer was on the bottom of software in the network protocol stack, which in charge of the proper time when to join wireless channel as the direct controller of the packet transmitting, the performance of MAC layer was crucial to WSNs. However there were many differences between the MAC layer protocols in traditional networks and that in WSNs of which the principal goal was power saving and self-organized ability. The presentation of ZigBee technology was just to address the need. As a low data rate, low power consumption, low cost, wirelesses networking protocol, ZigBee protocol was designed for wireless nerwork link and control of cheap minitype devices in automation and remote control application.In this thesis, the research of MAC protocols in WSNs was provided at first, then the ZigBee standard was introduced focusing on topology, protocol stack and the MAC sublayer service specification and MAC functionality. Secondly, the feasibility of IEEE 802.15.4 in low power, low data rate wireless networks application was verified with network simulator NS (network simulator). Finally, designs of changing contention window length and introducing sleep mechanism were proposed based on analysis of channel joining mechanism in beacon-enabled star topology, furthermore the models of node and channel were given, then the performance of improved network was simulated and presented, and it was concluded that energy was saved while throughput was not lowered by introducing sleep mechanism and reducing contention window length in such networks.