Cooperative forwarding for vehicular networks using positive orthogonal codes

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 proposes the Cooperative POC-based Forwarding (CPF) protocol, which extends the repetition-based POC-MAC protocol to handle multi-hop transmissions. Multiple cooperating relays at each forwarding hop schedule their transmissions to correspond to a single POC codeword. The transmission adhere to the transmission patterns of the POC-MAC. The proposed scheme exploits spatial diversity while mitigating the effect of hidden terminals on broadcast transmissions. 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. A Markov model is presented for the end-to-end probability of reception of multi-hop packets. The performance of the CPF protocol is compared with other multi-hop schemes through ns-2 simulations.