Asynchronous Cooperative Protocols for Inter-vehicle Communications
Sarmad Sohaib, Daniel K. C. So · InTech eBooks · 2011
Inter-vehicle communication is envisioned to play a very important role in the future, improving road safety and capacity.This can be achieved by utilizing cooperative relaying techniques where the communicating nodes exploit spatial diversity by cooperating with each other (Laneman et al., 2004).This alleviates the detrimental effects of fading and offers reliable data transfer.The source node broadcasts the signal to the destination node directly, and also through the relay nodes.Both the direct and relayed signals are combined at the destination.However, conventional cooperative communication systems require frame or symbol level synchronization between the cooperating nodes.The lack of synchronization results in inter-symbol interference (ISI) and degrades the system performance.This problem will be more severe in inter-vehicle communication as maintaining synchronization in fast moving nodes is very difficult.In this chapter, we present the major asynchronous cooperative communication protocols that can be employed for inter-vehicle communications.These are the asynchronous delay diversity technique (Wei et al., 2006), asynchronous space-time block code (STBC) cooperative system (Wang & Fu, 2007), and asynchronous polarized cooperative (APC) system (Sohaib & So, 2009;2010). Conventional cooperative communication system modelA three node cooperative network containing the source (S), relay (R) and destination (D) nodes is shown in the Fig. 1.The information will be transmitted from the source node to the destination node directly and also through the relay node.Both the direct and relay signals are combined at the destination using combiners (Brennan, Feb 2003).In general, there are two kinds of relaying modes; amplify-and-forward (ANF), where the relay simply amplifies the noisy version of the signal transmitted by source, and decode-and-forward (DNF), where relay decodes, re-encodes and re-transmits the signal.The conventional ANF channel model is characterized by transmitting and receiving in orthogonal frequency bands or time slots (Laneman et al., 2004; Sohaib et al., 2009).Here we consider the ANF scheme with the relay node transmitting at the same frequency band as the source node, but in subsequent time-slot. Asynchronous Cooperative Protocolsfor Inter-vehicle Communications 2 www.intechopen.com