The Research On Performance Enhancement Technologies In WLAN

With the development over the past twenty years, the performance of WLAN has been improved greatly. But the demands for rate of WLAN seems increasing more quickly, which becomes more serious with the popularizing of multi-media services and family entertainment. These reasons stimulate researchers to explore more techniques to enhance the data rate of WLAN. Among these potential technologies, D2D is a promising one emerged in recent years, which is able to enhance the level of local data interchanging. So far, the research on D2D mainly focus on improving the performance of cell networks. We would study on how to improve the performance of WLAN by D2D in this thesis.First, we proposed a network structure which uses D2D technology in WLAN. The structure transmits traditional WLAN packets through 2.4GHz/5GHz ISM band, and transmits D2D data through 60 GHz band. The 60 GHz band is used to avoid interfering between D2D links and WLAN links. Another reason for using the 60 GHz band is that information transmission in this band can satisfy the demands of short distance and high rate, required by D2D communications. Then, we proposed a new directional access protocol used in mm Wave band. The use of mm Wave band brings more complexities in realization, mainly because we need directional antenna with high gain to overcome the serious channel attenuation in this band. The proposed protocol can not only avoid the problems of hidden terminals and deafness from which many directional access protocols might suffer, but also can take a best use of the spatial gain brought by using directional antenna and can keep several active links working in parallel. Besides, we present an improved relay protocol through modifying a well-known relay protocol named Coop MAC to make use of the relay opportunities brought by D2D. We first modify the Coop MAC so that it can work well in our proposed framework. Then we proposed a new method to compensate relay nodes for their consumption of resources in the cases of helping other nodes. The principle is that the relays can use the transmission opportunities acquired by helping to forward data from others to send their own packets. Actually, this method enhances the temporal fairness of WLAN, so it can relieve the rate anomaly problem which caused by the low rate nodes in the network and can improve the throughput of the whole system. Finally, we realized the related models mentioned previously in the NS3 simulator and performed some simulations to verify these ideas. The simulation results indicate that the new directional protocol can improve the system throughput greatly compared with other such protocols, and the improved cooperative MAC protocol can not only enhance the performance of relays, but also can improve the temporal fairness of the network as well as improve the system throughput obviously.