10.2 Related Works on Broadcasts in VANETs
Earlier works on broadcast protocols in VANETs mostly assumed the ideal propagation model, i.e., whether a packet reception is successful merely depends on a fixed transmission range. Examples include the UMB (Korkmaz and Ekici 2004) and SB (Fasolo et al. 2006). They designate the furthest node that receives a packet as the relay node to maximize the one-hop progress (Korkmaz and Ekici 2004) or minimize the one-hop delay (Fasolo et al. 2006).
However, as shown by empirical studies, the wireless channel in VANETs is far from perfect (Taliwal et al. 2004). Instead, channel fading is the primary challenge and has a major impact on broadcast reception rates (Torrent-Moreno et al. 2004, 2006). The suggested realistic propagation model on the highway is the Nakagami model (Torrent-Moreno et al. 28–25 Sept., 2005), where the packet reception probability (PRP) of single broadcast decreases with the distance, which aggravates the “broadcast storm” problem. The probability-based methods (Ni et al. 1999; Wisitpongphan et al. 2007b) simply let each node rebroadcast a packet with some probability. However, the probabilistic forwarding decision still results in redundant rebroadcasts and does not solve the broadcast storm problem.
10.2.1 Opportunistic Forwarding in VANETs
As we have seen in the previous chapters, opportunistic forwarding (Biswas and Morris 2005; Zorzi and Rao 2003) is a promising way to deal with lossy links in multihop wireless networks. ...