Systematic Raptor Codes for Safety Broadcast in an Unsaturated Vehicular Highway Environment

Active safety broadcast is one of the most fundamental services in intelligent transportation systems. The repetition code proposed in wireless access for vehicular environment (WAVE) standard is inefficient in realistic channel conditions and rapidly changing network topologies. In this study, we propose the use of systematic raptor codes as a forward error correction (FEC) scheme at the MAC layer. This code is optimised for short packet lengths, as are expected in safety applications. We have developed a multi-layered simulator that consists of realistic IEEE 802.11p physical layer results, an analytical random access MAC model and FEC codes implemented at different OSI layers. The model considers safety messages under non-saturated channel conditions according to the vehicular IEEE 802.11p standard. Issues such as the hidden nodes problem, interference and vehicles leaving the communication area are considered. The performance evaluation of raptor codes against repetition codes in the shared control channel with different antenna schemes is also presented.