Recent researches show that inter-session network coding could decrease the number of packets transmission and achieve higher throughput in wireless network compared with traditional forwarding mechanism.In most existing relay mechanisms based on inter-session network such as COPE,relay node demands to collect the messages from its neighbor nodes to get notice of which packets already overheard by them so as to determine whether there exists coding opportunity between or among forwarding packets.However,transmission overhead of this message collection and computing cost of opportunity determination will degrade the performance of these mechanisms.It is observed that coding opportunity at relay node is much more related with the local topology,and the opportunity of encoding three or more packets together is far less than that of encoding two packets together in wireless network with general density.Based on this,a new coding-aware routing mechanism,named TCAR,is proposed.TCAR ignores the opportunity of encoding three or more than three packets together.Each relay node maintains an encoding mapping table being established according to the result of its local topology detection,which can be used to calculate the path cost during routing setup phase,and determine that which two packets can be encoded together during the packets forwarding phase.In TCAR,instead of periodic messages collection,each relay nodes just need once local topology detection,and the encoding determination is much simpler than that of the former mechanisms.Simulation results show that compared with typical inter-session network coding mechanisms COPE and COPE-based routing,TCAR achieves 12% and 7% throughput gains,and keeps the minimum end to end delay.
