Research On The MAC Layer Cooperative Forwarding In Wireless Sensor Networks

Providing reliable and energy-efficient communication in Wireless Sensor Networks (WSNs) is a challenging problem. This is because, in reality, the link conditions in wireless networks can be highly unreliable due to many factors such as interference, attenuation, and channel fading. To forward a packet reli-ably, it may need retransmissions at each hop. This results in undesirable delay as well as waste of energy. Cooperative Forwarding (CF) is proposed to combat fading channels, thus improving the robustness, end-to-end latency and ener-gy efficiency in wireless networks. The idea behind cooperative forwarding is to take advantage of the broadcast nature of wireless communication, involv-ing multiple neighbors of the sender into local forwarding. Since the wireless medium is shared, each node can overhear data packets sent by its neighbor. Therefore, multiple neighbors could cooperatively cache the overheard data packet. When the intended receiver fails to receive the packet correctly, those neighbors could deliver the packet to the downstream node. Cooperative for-warding can be implemented at different layers. E.g., some existing literatures tackle this issue from the physical layer perspective, where the receiver is ca-pable of combining and decoding the signal from several simultaneous trans-missions. For the low-cost, low-power, resource-constrained WSNs, it is more practical to implement cooperative forwarding at the MAC layer. This disser-tation studies how to apply the MAC layer cooperative forwarding in WSNs to improve the routing performance. The main contributions of this thesis are as follows:(1) We study the problem of efficient GOR for multiconstrained QoS provi-sioning in WSNs. Recent work exploits multipath routing to guarantee both reliability and delay QoS constraints in WSNs. However, the mul-tipath routing approach suffers from a significant energy cost. In order to improve the energy efficiency, in this work, we exploit the geographic opportunistic routing (GOR) for QoS provisioning with both end-to-end reliability and delay constraints in WSNs, which can be formulated as a multiobjective multiconstraint optimization problem. We look in depth at the properties of the multiple objectives. Based on the analysis and obser-vations, we then propose a heuristic efficient GOR (EGOR) algorithm for QoS provisioning in WSNs.(2) We study the problem of contention-based geographic cooperative forward-ing in WSNs. Contention-based geographic forwarding (CGF) is a state-free communication paradigm for data delivery in multihop WSNs. First, the sender broadcasts an RTS packet to all its neighbors, including the lo-cation of the destination as well as its own location and the identifier of the DATA packet. The sender’s neighbour who receives the RTS and has positive packet progress towards the destination will contend to serve as the nexthop receiver. The contention process is usually achieved by timer-based contention. Once the nexthop node is decided, the unicast between the sender and the specific nexthop node follows. We present the intel-ligent CGF (ICGF) to combat the channel variation. IGCF combines the advantages of both cooperative and contention-based forwarding, involv-ing multiple neighbours of the sender into the local forwarding to improve the transmission reliability. ICGF differs from existing work in that it ex-tends the cooperation scope intelligently, by sending one additional control message on demand. For this reason, the probability of cooperation void in ICGF is decreased and the single-hop packet progress is increased, con-sequently, improving the end-to-end data delivery delay, energy efficiency and data delivery ratio.(3) We study the robust forwarding for reactive routing protocols in WSNs. Reactive (also referred to as on-demand) routing protocols are designed to reduce the bandwidth and storage cost used in table driven protocols. This strategy applies the on-demand procedures to dynamically build the route between a source and a destination. We present the design of a robust for-warding extension (RFE) for reactive routing protocols in WSNs. RFE can augment most existing routing protocols to combat the channel variation. We introduce a biased backoff scheme during the route discovery phase to find a robust virtual path, which can provide more cooperative forwarding opportunities. Along this virtual path, data packets are greedily progressed toward the destination through nodes cooperation.(4) We study the scalable and energy efficient broadcasting over CHs in multi-hop cluster-based WSNs. In large-scale sensor networks, grouping sensor nodes into clusters has been considered as an effective way to achieve net-work scalability and robustness. Broadcasting over cluster heads (CHs) is often necessary for routing protocols to establish routes in cluster-based wireless sensor networks (WSNs). However, inter-cluster communication between CHs has not been sufficiently investigated in the existing litera-ture. Specifically, most solutions either assume that CHs have longer radio ranges than ordinary nodes so that they can communicate directly, or that only one-hop clusters are constructed. These are not always realistic as-sumptions since the CH may be a regular sensor node and the sink is often not directly reachable. Consequently, CHs communicate with each oth-er by using multi-hop communication through the sensor nodes inside the clusters. We design a cooperative forwarding based distributed heuristic broadcasting over CHs (BOCH) protocol.