Design and PHY and MAC layer protocols for inter-vehicle communications

Inter-Vehicle Communication (IVC) is an important component of any Intelligent Transportation System (ITS). It provides wireless connectivity among traveling vehicles to exchange real-time road condition and traffic information to support safe driving and traffic management. Vehicles traveling on roads form a wireless mobile ad hoc network that underlines the communication protocol used to exchange the information. Two factors when combined render the current wireless ad hoc protocols not optimal for IVC system implementation. One is the rapid changes of the network topology due to excessive vehicle mobility. The other is the mobile wireless environment under which vehicles communicate among each other. The environment is characterized by multipath fading, shadowing, propagation path loss, and Doppler shift. This environment negatively influences the performance of the system by increasing the bit error rate (BER). This dissertation proposes new Physical (PHY) and Media Access Control (MAC) layer protocols aimed at improving the performance of IVC systems.; A PHY layer design was developed by combining two well known spread spectrum techniques: direct sequence (DSSS) and frequency hopping (FHSS). The design was called hybrid spread spectrum (HBSS). Analytical and simulation analysis showed a signification improvements in the system capacity and BER performance, when HBSS was implemented in IVC systems.; Two current MAC protocols were examined for IVC implementation: Reservation ALOHA (R-ALOHA) and Sense Multiple Access (CSMA). A Monte Carlo simulation was carried out to analyze the capture effect on the R-ALOHA throughput and packet drop rate under transient and steady states. The simulation results showed that the capture phenomena affected the performance of R-ALOHA in the transient state but not in the steady state. Furthermore, two new MAC protocols were developed for IVC systems to guarantee faster medium access to vehicles with emergency messages such as imminent collision warning messages. The two protocols are CSMA with priority and polling (PP-CSMA) and CSMA with priority and pseudo-reservation (RP-CSMA). A computer simulation analyzed the performance of the newly developed protocols under IVC environment. The results confirmed the time improvement in channel accessibility by vehicles with emergency messages.