Feasibility study of physical-layer network coding in 802.11p VANETs

Vehicular Ad-hoc Network (VANET) is expected to play a major role in improving road safety and traffic efficiency in people's daily life. However, the main issue in VANETs remains to be intermittent node connectivity and relatively short contact duration due to the high mobility of vehicles. Physical-layer Network Coding (PNC) that enables data exchange within a much shorter airtime (e.g., twice faster than traditional scheduling) favors the highly-dynamic link condition in vehicular environments and hence appears to be a powerful tool in VANETs. One of the most important challenges in applying PNC to VANETs comes from the Doppler shift due to high-speed vehicle motion, which leads to carrier frequency offset (CFO) and hence introduces inter-carrier interference (ICI) that degrades the bit error rate performance. In this paper, we investigate the impact of motion-induced CFO/ICI on the overall signal detection. In particular, we study whether PNC in VANETs can be made feasible with conventional equalization techniques that suppress the effect of CFO. We found that PNC suffers only a 3 dB SINR penalty in the worst case compared with generic point-to-point (P2P) communications, and generally PNC is feasible in vehicular environments even if the transmission powers of source nodes cannot be finely controlled.