Research On Data Transmission Control Mechanism Of Vehicular Ad Hoc Network

Vehicular Ad Hoc Network (VANET) has gradually entered into people's life in company with the construction of informational transportation. VANET, which aims at establishing a vehicle-to-vehicle/vehicle-to-roadside wireless communication system characterized by open, self-organized, convenient, efficient, environment friendly, is a novel application form of Ad Hoc Networks and wireless sensor network in traffic circumstance. It provides reliable traffic security and comprehensive information services while promoting passage efficiency.Stable and efficient transmission control mechanisms guarantee VANET data transmission. However, current TCP which based on lined-network is unfit for VANET environment. On one hand, it is not capable of distinguishing packet loss adapted from no-congestion issues. Indiscriminate congestion control is one of the main reasons leading to TCP performance deterioration. On the other hand, the excessively radical window increment brings albatross to under-layer and initiates mass of packet loss. For these reasons, this paper centers on TCP performance improvement in VANET and carries out correlative research. Main research and innovation elaborated as follows.1. Carry on further research and analysis of current TCP. Perform intensive classified discussion on many MANET TCP improved schemes. Compare the performance of current TCP with APS-Few, TCP-Few and ADTCP. Our research reveals that inability in network status identification and greed are two influence factors of TCP performance in wireless environment.2. Regarding to the problems of traditional TCP, a scheme known as Adaptive Ad Hoc TCP (A~2DTCP), which based on network status identification and under-layer load alleviation is presented. On the basis of acquiring a clear identification of network status, this mechanism configures the windows increment factor adaptively according to the forward path length. And then, greedy growth of TCP congestion window is limited to avoid congestion. Change the packet size in light of current congestion window and make full use of network resource. The simulation shows that, under vehicular circumstances A~2DTCP upgrade TCP throughput by 102% at most. However, the transmission stability and fairness of this scheme is not up to expections.3. Aiming at issues of A~2DTCP, a scheme named Data Path Transmission Capabilty Adaptive TCP (DPTCA-TCP) is proposed. DPTCA-TCP learns path transmission capability by feedback mechanism. According to that, it adjusts data rate reasonably and stabilizes transmission. In the meanwhile, heuristic algorithms were introduced to simplify network status identification. TCP sender distinguishes pseudo congestion signal by path transmission capability and retransmission timeout record, then responses it appropriately. The simulation shows that DPTCA-TCP increases throughput by 125% at most than traditional TCP, and upgrade fairness by 21% than A~2DTCP.4. Develop the A~2DTCP, DPTCA-TCP modules which are mentioned in this paper based on NS2 simulation platform.