Research And Optimization Of IEEE 802.15.4 MAC Layer Protocol

IEEE802.15.4standard is a new protocol defined for low-rate wireless personal area networks, which supports more cheaper, smaller, power-efficient application. In the IEEE802.15.4standard, Medium Access Control(MAC) layer is a control message for all the packets received and sent with the array controller and put directly on the wireless channel, it determines nodes in wireless sensor networks using the kinds of rule in order to achieve satisfactory network performance. Therefor, MAC layer protocol for wireless sensor networks is one of communication to ensure that the key factor. So, the main of this paper is to study IEEE802.15.4MAC layer protocol performance and optimization studies.At first, this paper studies the performance IEEE802.15.4MAC layer protocol binary exponential backoff algorithm. Research show that BEB algorithm in the fewer nodes of network, the obtained node contention window is too large, reducing efficiency, and when the number of nodes in the network are more successfully sent after each data node will minimize contention window, causing excessive data conflicts. Meanwhile BEB algorithm always successfully transmitted to a node with the greatest competitive priority channel, the channel leading to unfair phenomenon. In tackling these questions, the paper proposes a new backoff scheme for IEEE802.15.4, which uses Probability judgment based on Network Load and Exponentially Weighted Moving Average (PJNLJEWMA) method. According to a real-time monitoring of current network status by probability judgment of network load, this method dynamically adjust backoff exponent by EWMA when Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) begins. The simulation experiments on NS2platform show that the PJNL_EWMA algorithm not only improves the throughput of the network, but also reduces the packet loss rate and the collision ratio, significantly improve the network performance.Secondly, According to multiple services in the dynamic networks, BEB algorithm can not distinguish between different services priorities and provides high-priority service fast access channel to provide QoS guarantee. The paper proposes a new backoff scheme, which uses Probability Judgment based on Network Load and Adaptive Service Distinguishing Backoff (PJNL_ASDB) scheme that could judge network status with Probability mechanism and use adaptive dynamic backoff scheme to distinguish service by introducing weighting parameter,thus it can implements reasonable backoff. The model of two-dimensional discrete-time Markov chains numerical results and NS2simulation show that the PJNL_ASDB scheme is not only ensure the demand of high priority transmission and is able to improve the network performance of low priority.At last, from the perspective of the game theory, a detailed analysis of the IEEE802.15.4MAC layer protocol channel access performance. According to the characteristics of multiple services in the wireless sensor networks, the channel contention processes are modeled as a dynamic incomplete information game. In this model, Nash Equilibrium is obtained by solving utility function of network performances, throughput and transmission delay is compromised with goal programming method. In addition, this paper propose a adaptive service distinguishing backoff (ASDB)scheme, which could use adaptive dynamic backoff method to distinguish priority services according to current networks status. The scheme guarantees the demand of high priority transmission and is able to improve the network performance of low priority. Simulation results show that ASDB scheme can not only implements compromise of throughput and transmission delay, and improve performance of the whole network.