Application Of Fountain Codes In Vehicular Ad Hoc Network

As an important part of the intelligent transportation system, vehicular ad hoc network not only has the characteristics of non-core, self-organize and multi-hop, but also has the characteristics of high speed, oriented direction and large network scale. A vehicle can transmit information to other vehicle directly in the communication area, and also can use multi-hop router technology to transmit information to the long-distance node with the help of middle vehicles. A vehicle can communicate with road fundamental facilities to upload and download information. Due to the rapid movement of vehicles, the network topology structure changes constantly and information transmissions are strictly affected by the change of the channel conditions. In case of emergency, the requirement for delay of information transmission is much more rigorous. It's very important to choose appropriate coding schemes to enhance the efficiency of information transimission and reduce transimission delay.The packets transmitted by a vehicle in the network is not received by the destination vehicle due to collision or timeout, which is similar to deletion of some coding bits in erasure channel in some probability, so choosing coding scheme which has low complexity, good performance and can adapt to vehicular ad hoc network environment is very important. As one special type of rateless codes, fountain codes can generate code bits constantly, the receiver can decode correctly as long as the receiver receives enough coding bits, and fountain codes can satisfy the demand of vehicular ad hoc network encoding schemes. As two important type of fountain codes, LT codes and Raptor codes been applied to ad hoc network etc.In this thesis, the concept of fountain codes is introduced, and some application situations of fountain codes are given according to the characteristics of fountain codes. LT code, SRLDPC code, Kite code and RA code are then introduced in detail in this thesis. We analyse the characteristics of the four codes. Combining with characteristics of data packets transmission in vehicular ad hoc network, we select suitable coding and decoding algorithms for four type of fountain code in the aspect of information transmission of the vehicular ad hoc network. In order to study the influences of different codes used in vehicular ad hoc network based on data packets, this thesis simulates and analyses the four kinds of codes respectively in vehicle ad hoc network.In this thesis, we design the multiple access relay scheme and parallel transmission scheme according to the network characteristics of vehicular ad hoc network and the characterist ics of fountain code. We design highway scene with the OPNET simulation software and collect the average success recovery bit rate statics and decoding cost statics. The network performance of the four kinds of fountain codes in vehicular ad hoc network were compared. Through comparison and analysis, we get the conclusion that using relay in multiple access relay scheme can improve system performance, the exclusive-or processing at relay can improve the decoding accuracy. Fountain codes can be used to reduce the decoding cost in parallel transmission scheme. The destination node which has completed decoding is transformed into a source node and assist in the transmission of information to the new destination node, the destination node which has been transformed can enhance the average successful recovery bit rate of the new destination node in parallel transmission scheme. Based on the multiple access relay scheme, roadside station dynamic access scheme is proposed in the end of this thesis, we simulate the scheme and get the conclusion that reduing the vehicle speed appropriately can reduce the number of lost packets at base stations, increase the connection time between base station and source vehicle, and increase the average successful recovery bit rate at the destination vehicle.