The Research Of CSMA And TDMA Hybrid Access Algorithm In Wireless Sensor Network

Nowadays, wireless sensor networks are widely used in people's daily life and industrial production.With the continuous development of science and technology, the performance requirements of wireless sensor networks are getting higher and higher, the performance of a wireless network depends directly on the wireless transport protocol used. IEEE 804.15.4 protocol is a common wireless transmission protocol, which uses CSMA-CA algorithm access channel. The CSMA-CA algorithm has excellent performance under the condition of few network nodes. However, when the number of nodes in the network increases, the channel quality deteriorates sharply and the data collision becomes serious, making the CSMA-CA algorithm unsatisfied. In order to solve this problem, this thesis studies the CSMA/TDMA hybrid access algorithm based on the standard CSMA-CA algorithm and the idea of TDMA.In this thesis, CSMA/TDMA hybrid access algorithm based on IEEE 802.15.4 protocol is studied, and the Markov decision model of CSMA/TDMA hybrid MAC protocol is established. On the basis of this model, ABSA(Adaptive Big-Slot Assignment) algorithm is proposed.According to the time information received in the data frame, the coordinator estimates the data amount of each sensor node in each big slot,and then allocates the big slot for the sensor node. In addition, two methods are proposed to improve the channel quality in big slot. Firstly, to reduce the network congestion at the beginning of the big slot, at the beginning of each big slot, all the sensor nodes belonging to the big slot are randomly delayed for a period of time, and then participate in the channel competition.Secondly, the priority of the big slot is differentiated, the sensor nodes belonging to the big slot have high priority and the other nodes have low priority. The node with high priority has small BE, whose average back-off time is short. And the node with low priority has large BE, with long back-off average time.In this thesis, the Markov decision model of ABSA algorithm is simulated by Matlab, and the standard CSMA-CA algorithm is compared from the collision probability. The simulation results show that the ABSA algorithm can effectively reduce the collision probability of the data on the channel. In this thesis, NS-2 is used to simulate the ABSA algorithm, which is compared with the standard CSMA-CA algorithm in terms of packet delivery ratio and transmission delay. The simulation result shows that, in the case of high instantaneous network load, the ABSA algorithm is superior to the standard CSMA-CA algorithm in terms of the packet delivery ratio and the transmission delay. Therefore, the effectiveness and feasibility of the algorithm are verified.