Cooperative Positive Orthogonal Code-Based Forwarding for Multi-Hop Vehicular Networks

Reliable multi-hop forwarding in vehicular networks is required by many critical intelligent transportation system (ITS) safety applications. Cooperative vehicular multi-hop schemes achieve reliability using broadcast transmissions and multiple forwarding relays at each hop. However, packet duplication must be controlled to circumvent the broadcast storm problem. This paper presents the cooperative POC-based forwarding (CPF) protocol for highway vehicular networks, which extends the repetition-based POC-MAC protocol for multi-hop transmissions. At each forwarding hop, multiple cooperating relays form a virtual relay and schedule their transmissions to correspond to a single POC codeword, thereby adhering to the POC-MAC. CPF exploits spatial diversity while mitigating the effect of hidden terminals. By allocating separate POC-based schedules for multi-hop packets and the periodic broadcast of safety heartbeat packets, the CPF protocol reduces the interference between the two. The performance of the CPF protocol is studied through analysis using a Markov model and through ns-2 simulations.