Outage Performance of Line of Sight Decode and Forward Relays in Cooperative VANETs

Cooperative communications boasts attractive performance enhancements in vehicular communication environment. Amplify and Forward (AF) and Decode and Forward (DF) relaying have been proposed and analysed for vehicular networks in recent literature. For the study of performance enhancements in this area vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) channel model is crucial. Vehicular channel is a mobile to mobile channel which significantly differs from the well known Rayleigh or Nakagami-m channel models. To cater the dynamic nature cascaded fading channel models are introduced. Double Rayleigh fading and double Nakagami fading have been used to analyse AF and DF relaying previously. These models mostly govern Non Line of Sight (N-LOS) communication between transmitting pairs. However, we argue that in cooperative vehicular communication scenarios the likelihood of Line of Sight (LOS) relays are significant and can be subjected to further performance improvement. Supported by several previous works based on practical measurements we model the LOS V2V channel by a double Rician fading process. In DF cooperative VANETs it is highly probable that Source (S)→ Destination (D), S→Relay (R) and R→D pairs have different LOS or N-LOS conditions. With these assumptions and arguments, we investigate the outage performance of DF relaying using analytical formulas and Monte-Carlo simulations. Our results indicate that for V2V DF cooperative relaying, outage probability varies in 1 − 10−1 region for N-LOS conditions (in both S→R and R→D links) while LOS conditions improves it towards 1−10−4 region when typical V2V rician K factors are considered. We believe our theoretical analysis could be effectively used to design and improve channel aware routing paradigms for vehicular networks.