The Research Of Broadcast And Opportunistic Routing Protocols In Low-Duty-Cycle Wireless Sensor Networks

In wireless sensor networks (WSNs), most of applications need to disseminate data packets from the sink throughout the network or deliver the event information from sen-sor nodes to the sink. Hence, it is important to design effective broadcast and routing protocols. Due to the effects of low-duty-cycle sleep/wake scheduling and unreliable wireless channel, broadcast and routing in low-duty-cycle WSNs are different from pro-tocols in other types of networks.Conventional broadcast protocols for WSNs have the following drawbacks: a node may collect incomplete broadcast progress information; a node may have poor ability to handle the time-varying property of a broadcast process; a node may not fully uti-lize the overheard information. Conventional opportunistic routing protocols for WSNs overlook the time-varying property brought by independent duty cycling. When a node handles different waking-up orders of neighbor nodes, the routing strategy needs to be properly adjusted.In this paper, we investigate how to handle the time-varying factors and propose fast and efficient broadcast and opportunistic routing protocols for low-duty-cycle WSNs.The main contributions are:1. Propose an efficient status-based broadcast scheme with coordination of obli-gated senders: Conventional status-based broadcast schemes do not have high broadcast efficiency due to inefficient coordination between potential senders to the same receiver, which induces a large amount of collisions and redundant transmissions. We propose an efficient overhearing scheme based on novel infor-mation encoding and analyzing mechanisms. A node can collect more accurate broadcast progress information. Potential senders can better coordinate with each other without inducing additional message overhead. As a result, the broadcast speed and efficiency can be improved. The proposed scheme can also handle the quadrilateral topology problem in sparse networks, and balance the broadcast speed and efficiency according the application requirements. Results obtained from both simulations and implementation in a testbed show that our proposed scheme outperforms conventional status-based broadcast protocols.2. Propose a flooding scheme with network coding under a schedule-based spanning tree: Flooding under a schedule-based spanning tree is an appropriate scheme in low-duty-cycle WSNs. The broadcast nature of wireless radio can be utilized by scheduling nodes with a common parent to simultaneously wake up. We propose a scheme to exchange rank information (the number of innovative encoded packets)between neighbor nodes. Based on real-time information, a receiver determines which neighbor nodes can provide innovative encoded packets. To guarantee low duty cycle of the receiver, the receiver limits the number of nodes to overhear from. Then, the receiver selects an optimal overhearing node set with a limited cardinality based on a dynamic programming algorithm with polynomial com-plexity, which can maximize the expected rank increment within a sleep/wake cycle. Simulation results show that our proposed scheme outperforms existing schemes in terms of broadcast delay and energy consumption.3. Propose a network coding-based flooding with a mobile sink: In low-duty-cycle WSNs, there is usually one static sink node as a single source in conventional flooding schemes. We use a mobile sink to travel around the monitoring area of a WSN. When the mobile sink travels to a position, it can serve as a new source of flooding. With multiple sources simultaneously forwarding the data packets,the speed of flooding can be accelerated. We model the process to deliver multi-ple encoded packets from the source to a node on the tree as a Markov process.Then, we analyze and estimate the expected delay from the source to each node.The flooding tree is divided into several branches and the mobile sink can travel along a branch or switch to another branch. We consider all the possible traveling orders of the branches for the mobile sink and determine an optimal trajectory for the mobile sink, which can minimize the overall expected flooding delay. Sim-ulation results show that our proposed flooding scheme with a mobile sink can significantly reduce the flooding delay.4. Propose a shortest-latency opportunistic routing scheme with independent duty-cycling: In opportunistic routing, a sender dynamically determines a relay from a candidate node set depending on the real-time network conditions. Due to the effects of independent duty-cycling, the sender may handle different waking-up orders of the candidate nodes when it forwards data packets at different time in-stants. Conventional opportunistic routing protocols overlook the time-varying property of the waking-up order of the candidate nodes. In this paper, we inves-tigate the dynamic behavior of waking-up order and theoretically analyze how to obtain an optimal candidate set for each node, which can minimize the end-to-end latency. Then, considering the realistic scenarios, we propose an opportunistic routing which jointly considers global and localized optimizations. Based on the relatively stable global information (such as network topology and scheduling pe-riod information), an original candidate set is constructed. Then, by considering the time-related factors (such as real-time link quality and wake-up order infor-mation) in the local context, a further optimization for the original candidate set can be achieved. Experiment results show the proposed scheme can significantly improve the performance of opportunistic routing.