| An Ad Hoc network is a multi-hop and autonomous system consisting of number of mobile nodes armed with wireless radios. With the characteristics such as deployed easily, self-managed without any infrastructure and so on, Ad Hoc networks can be widely applied in areas such as military communication, disaster rescue, environment monitoring and etc. However, due to low-bandwidth resource constrained, distributed contention access and dynamic network topology, the design of channel access protocol and routing protocol is a challenging subject. This dissertation focus on the problems of analytical model of DCF, channel access protocol, cross-layer routing metric, backup routing protocol and routing algorithm suited for multi-raido multi-channel Ad Hoc networks. The major contributions of the dissertation are listed as follows.Most of analytical frameworks for 802.11 DCF scheme in unsaturated conditions are based on Markov model. Based on the Post-backoff procedure introduced in 802.11 protocol, considering the fairness characteristic of DCF serving for all contending nodes, the time interval between two consecutive packet successful transmissions is deduced firstly. Then the average transmission cycle time of a node under the non-saturated traffic assumption is easily obtained, and the mathematical expression for throughput is proposed. The approach is very simple compared with the previous work. Its predictions are validated against extensive simulations and are showed to be in very good agreement.IEEE 802.11 DCF exhibits poor performance as the number of nodes increases due to high collision probability on each transmission. Based on the optimal constant backoff (OCB) window scheme that fixes the backoff window at every backoff stage, a virtual collision solution (VCS) scheme is proposed to reduce the collision probability and to enhance the throughput performance. In our scheme, if more than one node's backoff timer reaches zero, they should enter a virtual collision phase containing several contention cycles. In each contention cycle, every competing node transmits a burst to jam the channel and a node sensing the medium busy should retire from the contention. Moreover, an analytical model is proposed that shows the high efficiency of elimination in VCS with negligible cost. Both analysis and simulation results show that our proposed scheme achieves higher throughput and lowers the collision probability compared to the DCF and OCB.A new metric "CAM" (Capacity of Access to Medium) is presented based on the retransmit strategy of IEEE 802.11 MAC (Medium Access Control) layer protocol. The characteristic of CAM shows that the MAC layer information can be considered as indication of congestion degree around a node. Furthermore, a congestion-aware routing protocol based on the proposed metric is developed. In addition, the simulation shows that the new approach can improve the network throughput and reduce the end to end average delay with less overhead. In the previous Ad Hoc routing protocol, route reply packet missing and the existed route broken due to link failure propel the source node to flood the RREQ packet again for rediscovering a new route, thus increases the network load and consumes the node more energy and bandwidth resource. On the basis of overhearing and MAC cache technique, a new routing protocol named ODMR (On Demand Mesh Routing) is presented that employs the cross-layer approach. By unicast BRREP packet during route reply phase, the routing protocol can set up multiple bypass route to the destination and reduce the frequency of searching route. Through analysis of simulation result, it is demonstrated that the ODMR reduces the end to end delay and flooding search times while enjoying significantly small protocol overhead and higher network throughput as compared to AODV, AOMDV, AODV-BR.It is well known that the performance of wireless Ad Hoc networks is constrained dramatically by interference from neighboring nodes. By assigning orthogonal channels, the nodes within interference range can transmit or receive concurrently. Recent work shows that such interference can be effectively mitigated. A notation named channel utilization percentage (CUP) to measure the contention level of different channels in a node's neighborhood is introduced and the optimal value of CUP for determining whether a channel is overloaded or not is deduced. Then, a channel selection metric, named CSM, which actually reflects not only a channel status but also corresponding node's capacity to seize it, is presented to evaluate the channel assignment. At last, a routing protocol that takes into accounts both CSM value and channel diversity along the path is developed. In addition, the simulation results indicate that our protocol outperforms others in terms of delay, packet delivery ratio and protocol overhead.
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