The Research On Several Issues Of QoS In Wireless Ad Hoc Network

Wireless Ad hoc network is a kind of no fixed facilities wireless network, it is one of the hotspots in the field of wireless communications. Wireless Ad hoc network has many characteristics, such as channel allocation complex、strong network mobility、dynamic changes of network capacity and so on, thus it puts forward very high demands in terms of QoS. In addition, with the wireless communication technology more and more widely used in the real life, multimedia real-time business, like video and audio, also increases demands on the wireless Ad hoc network performance and QoS. So, it is quite difficult to adapt to these requirements for the QoS measures, which are based on the traditional hierarchical design.In this paper, starting from the aspects of adaptive capacity and cross-layer design, I did some research on several issues of ensuring and improving the QoS of wireless Ad hoc network. Firstly, I brought forward the Adaptive Rate Protocol that based on cross-layer design (K-RAP). K-RAP is improved on the basis of the IEEE802.11DCF protocol. While the packet competing channel resources, K-RAP makes it not use the Random Access Mechanism, but judge by its rate and the dynamic classified reference value, in order to determine the packet contention window value. As the result, the higher rate that the packet gets, the earlier it competes channel resources. Secondly, I studied the problem of approximate distances between any two nodes in the wireless Ad hoc networks, for the purpose of providing a reliable basis on routing when the packet was transmitted. And in this paper, I added the distance information into the routing table. Finally, I tried to make the existing wireless Ad hoc network cross-layer adaptive mechanism better. In the improved mechanism, I putted the consideration of time-varying characteristics of wireless channel on a strong focus, and applied the adaptive modulation technique to cross-layer design, which is based on physical layer research, and called channel status prediction.From the simulation results that K-RAP has increased the network throughput under different load conditions, and the average packet delay declined obviously, comparing with the IEEE802.11DCF. The distances information provides so reliable message that reduces the packet loss rate in some kind of special conditions. Comparative analyzing the improved adaptive scheme and the existing AMC/SR-ARQ ideal mechanism, verifies the former that can reduce the packet error rate.