The Research Of Transmission Performance Over Wirelsess Ad Hoc 802.11 Networks

From the late 90s of the 20th century, a new kind of network technology in the wireless communication field is developing rapidly, i.e., wireless ad hoc network technology. As one of special kind of wireless communication networks, ad hoc networks have several characteristics, such as independently organized, no center, self organized, multi-hop routing, dynamic topology and so on. However, because of these characteristics, ad hoc network is drastically different from the existing communication systems in the protocol design. This thesis focuses on two aspects of the networks. One aim is to provide a maximum throughput for TCP over ad hoc networks; the other is to improve real time voice transmission over the networks.In this thesis, I investigate the challenges faced by the transport protocol design according to the wireless environment. Extensive works have been carried out to study the performance over it. It is observed that TCP's implicit assumption that any packet loss is due to congestion is not valid any longer in mobile ad hoc networks.Moreover, I study the traditional congestion window mechanism of TCP and propose an adaptive packet size (APS) scheme to work on top of fractional window scheme (FeW). Extensive simulation results demonstrate that APS over FeW outperforms traditional TCP by 100% according to different scenarios, e.g., chain topology, grid topology, and random topology with mobility.Finally, I explore voice transmission and the development of IEEE 802.11 protocol. Most of the studies are priority based that the voice packets have higher priority to access the channel. But for pure voice networks, these schemes are no longer useful since they do not take the intrinsic of the voice into consideration.Based on above observation, the thesis proposes a Burst Queue (BQ) scheme to cooperate with both 802.11b and 802.11e MAC protocols. My simulation results show that BQ scheme can support 50%-100% more VoIP calls and obtain 20%-50% lower delay at the cost of a little higher loss ratio which is tolerable to voice flows.