10.4 Overview of OppCast

OppCast consists of two types of broadcast phases: fast-forward-dissemination (FFD) and makeup-for-reliability (MFR). Intuitively, the FFD phase uses relatively long hops to advance the WM towards the end of IR for the purpose of fast propagation. The FFD phase is realized via relaying the WM by a series of forwarder nodes that lie successively along the message dissemination direction, where each next-hop forwarder node's distance to the previous one is relatively large. These forwarder nodes thus divide the IR into several one-hop zones. Due to lossy links and the independent reception assumption, however, vehicles within these one-hop zones may not all receive the packet upon one relay node's transmission. Thus we use additional make up transmissions that constitute MFR phases to ensure the PRR of the network. In particular, in the MFR phase of each one-hop zone, a minimal set of makeup nodes are successively selected until the expected packet reception probability of each node within that one-hop zone is larger than a pre defined Pth. In order to satisfy the PRR requirement of the whole network, the reliability of each hop's forwarder node selection is ensured by a retransmission mechanism. By deriving the optimal parameter that controls the length of the one-hop zones, the PRR requirement is satisfied with the least transmission overhead. Note that, we refer to both forwarder and makeup nodes as relay nodes.

The concept of opportunistic forwarding ...

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