Multihop Wireless Networks: Opportunistic Routing

7.7 Conclusion

In this chapter we further investigated the transmission coordination problem in opportunistic routing and studied how the strict coordination requirement in ExOR can be greatly eased using network coding. First we reviewed MORE, a well-known state-of-the-art MAC-independent opportunistic routing protocol. After identifying the inadequacy of MORE in dealing with multicast and broadcast, we demonstrated how network coding can be integrated with opportunistic listening in wireless broadcast. In particular, we looked into a class of challenging problem—mobile content distribution (MCD) in VANET, where large files are broadcast proactively from a few APs to vehicles inside an interested area. To combat the lossy wireless transmissions in VANETs we leverage symbol level network coding (SLNC), which exploits symbol-level diversity to achieve better error-tolerance compared with traditional packet level network coding (PLNC). We then qualitatively characterize the advantages of SLNC compared with PLNC from two aspects, namely higher throughput and spacial-reusability. Using two typical MCD applications as examples—popular content distribution and live multimedia streaming, we present two novel push-based broadcast schemes—CodeOn and CodePlay, respectively. The common ideas underlying the two schemes include a prioritized relay selection algorithm that opportunistically maximizes the usefulness of transmitted content, and a simple transmission coordination mechanism that ...