Research On Routing Protocols In Energy Limited Ad Hoc Networks

Due to its autonomy, topological dynamics and distributivity, Ad Hoc network has drawn great attentions as a competitive candidate of future wireless mobile communication networks. Limited energy is an important issue since Ad Hoc nodes usually rely on batteries, which leads to that the lifetime of network cannot be maintained for a long time. Therefore, how to efficiently allocate and exploit limited energy resources to prolong the network lifetime is one of the key issues for Ad Hoc networks. The existing studies show that packets retransmission is main part of network energy consumption. Thus adjusting packets retransmission strategy within network layer routing protocols is an effective way to partly solve energy limitation problem. Through studying the design of routing protocols, this dissertation optimizes the energy consumption of Ad Hoc network, and achieves a feasible solution to the problem that the nodes with limited energy cannot keep working for a long time.This dissertation takes the routing protocols as the focusing dimension under the background of Ad Hoc network application. We thoroughly investigate the influence of routing protocols on network performance. Specifically, for routing discovery, residual energy generation in routing maintenance process and unbalanced problem of energy consumption, we optimize the design of routing protocols by reducing and balancing energy consumption and adopting residual energy protection strategies, thereby prolonging the network lifetime. This dissertation focuses on path finding method, routing strategy in routing discovery process and routing maintenance. The main contributions are summarized as follows:Firstly, path finding method is studied in depth to provide a basis for routing selection and maintenance in routing discovery. The traditional flooding-based broadcast scheme has redundant information, which results in additional energy consumption. We introduce Gossip algorithm into the traditional broadcasting system and a pseudo flooding broadcast is proposed according to the bimodal characteristics of Gossip mechanism. The proposed mechanism guarantees packet arrival rate and reduces redundancy information transmission. Based on this, a dynamic protection domain based algorithm is proposed to guarantee packets arrival rate. Packet controlling cost is reduced effectively and residual energy consumption is decreased substantially. Secondly, routing strategy in routing discovery process is optimized, which is also the core of the entire routing process. This dissertation first gives a theoretical proof that routing protocol design cannot achieve the goal of maximizing network lifetime because of computational prohibition, which indictates that the optimal design for network lifetime is imposible in polynomial time. Therefore, the residual energy of network nodes is one of the most important factors in prolonging the network lifetime. An energy sensing routing protocol is thus proposed for multi-strategy routing selection in term of the residual energy of nodes. By analyzing the influences of node residual energy on the network in different periods of network, a routing protocol with energy consumption equalization and different levels of energy protection is proposed to prolong the network lifetime.Thirdly, considering packets transmission error probability based retransmission mechanism by energy consumption, we further optimize the routing strategy.. Due to high packets transmission error probability in Ad Hoc network environment, more packets retransmission energy is consumed. Therefore, energy consumption part in routing discovery strategy should be considered. Based on this, we propose an optimized energy saving routing strategy with the consideration of packets transmission error probability. Specifically, we derive the cost function of routing discovery strategy with two traditional restrasmission mechanisms named end-to-end retransmission (EER) and hop-to-hop retransmission (HHR). Then we give a more general M-retransmission routing strategy cost function by combining both mechanisms above. Additional energy consumption generated by packets retransmission is added to the routing strategy cost function, thereby achieving an energy saving routing discovery strategy with packets retransmission error probability.Fourthly, on the basis of the above, we design a maintenance strategy for the routing maintenance process to provide reliable packets transmission, Dynamic network environment may cause transmission links interrupted frequently, and thus a high robust routing maintenance mechanism is necessary to repair broken links in time. Traditional maintenance strategy usually works with long reparing period and high energy consumption. We present a local routing maintenance strategy, which controls the broken links in small areas with decreased maintenance period and network energy cost. Furthermore, a prediction based link maintenance strategy is proposed. By sensing key factors that may cause link interruption, dangerous link can be predicted in advance and local maintenance strategy will be triggered before link interruption, leading to the decrease of link interruption probability. Therefore, routing maintenance cost and additional energy consumption are reduced to a considerable level.