Exploring the Gain of the Opportunistic Routing in Wireless Network

Opportunistic Routing (OR) has recently been proposed to improve the efficiency of data transmissions in multi-hop wireless networks. In a lossy wireless environment, OR exploits the broadcast nature of wireless transmission medium and opportunistically selects a relay path to deliver a packet to its destination. OR has been implemented and proved to achieve significant throughput improvement in wireless ad-hoc networks.;To further investigate the gain of OR, we first study the gain of adopting OR in hybrid wireless networks that consist of ad-hoc wireless nodes and base stations connected to a wireline infrastructure. We first extend the opportunistic routing algorithm to exploit high speed data transmissions in infrastructure network through base stations. We then develop the throughput bound calculation models for OR in hybrid wireless networks. The developed models are applied to study several hybrid wireless network examples. Through case studies, we identified several factors that have significant impacts on the hybrid wireless network capacity under OR, such as the density and distribution pattern of Base Stations, the number of wireless channels on wireless nodes and BTs, etc.;Secondly, we investigate OR in wireless multicast. To adopt OR in wireless multi-cast, the main challenge is to efficiently share opportunistic relay paths between multiple receivers. We propose an opportunistic overlay multicast design for wireless networks, named Minimum Steiner Tree with Opportunistic Routing (MSTOR). In MSTOR, we first propose an overlay construction algorithm based on the optimal "OR distance" between nodes. We then design the MSTOR protocol and implement it in OPNET by customizing the IEEE 802.15.4 modules. Through OPNET simulations, we demonstrate that MSTOR can achieve a much higher multicast efficiency than the original unicast OR and the traditional minimum multicast-tree based schemes. MSTOR can be easily deployed for multi-cast in multi-hop wireless networks.;To further improve the performance of MSTOR, we proposed a new multicast OR routing scheme NCOM, a Network Coding based Overlay Multicast. NCOM integrates Network Coding (NC), Opportunistic Routing (OR), and cross-layer link scheduling to achieve high efficiency and reliability in multi-hop wireless multicast. In NCOM, the source and receivers are connected by an overlay Steiner tree optimized for the minimum OR distance between nodes. With NC, coded packets are opportunistically transmitted along overlay links. The transmissions of adjacent nodes in the overlay multicast are coordinated by a novel multicast acknowledgement scheme and cross-layer MAC scheduling algorithm. We implement NCOM in OPNET by customizing the IEEE 802.11b modules. NCOM can achieve a higher throughput and lower source transmission redundancy than the existing NC and OR based wireless multicast designs.