Study On Multiple Access Technique Based On OPNET

With the increase of network communication and complication of network configuration, more and more higher requirement of spectrum resource is put forward. To satisfy the communication between nodes, sharing resources is a common method, and the multiple access protocol is to solve how the links can serve all the users with sharing resources efficiently and fairly.Random access technique, one kind of contention-type access protocols, solves how to reduce information collision, increase channel utilization and system throughput, like fixed access technique. Random access technique includes ALOHA, CSMA, CSMA/CD and CSMA/CA protocols. This thesis firstly introduces these protocols systems, and analyses utilization of links, then builds models on OPNET. Based on these, we provide theoretic and model analyses of CSMA/CD in Ethernet.This paper researches on CSMA/CA protocol in WLAN, especially on backoff algorithm. The BEB algorithm used in CSMA/CA has an advantage in increasing the network throughput, but it can bring unfair among different nodes. MILD and MIMLD improve the network in different parts, and improve the fair channel access. But the throughput of the network should be improved. So in this paper, we offer a new backoff algorithm, and import an new concept named E[CW]. This algorithm aims to achieve fair channel access without knowledge of the network topology, by self-adapting to changes in the traffic load as well as topological changes in the network. To validate the algorithm, we analyze the implementation of MAC layer in OPNET simulation system, specially the implementation of BEB algorithm. We change BEB algorithm with MILD algorithm and improved algorithm, then simulate the three algorithms respectively. Based on the simulation results, we compare three network performance .The analysis presents that improved algorithm improves the throughput and fairness.For the lack of spectrum resource, the cognitive radio technology offers a new model for spectrum allocation to improve spectrum utilization. this paper analyses the problem faced by cognitive radio networks MAC, offers a TDMA access scheme based on universal control channel, and builds model on OPNET.