| Vehicular Ad-Hoc Network (VANET) is a new application field of Ad-Hoc networks, which attracts extensive attention in Intelligent Transportation System (ITS). VANET can provide vehicle to vehicle as well as vehicle to roadside unit (RSU) wireless communications, so that on board unit (OBU) located in vehicles can share messages related to traffic conditions or varying applications with not only other OBUs in the same VANET, but also transportation management centre, remote users, and INTERNET or 3G/4G system depending on RSU’s retransmission. VANET is an efficient way to improve the safety, comfort and efficiency of ITS.As a part of Wireless Access in Vehicular Environments (WAVE) communication protocol stack, IEEE 802.11p is a new standard for Medium Access Control (MAC) layer and physics (PHY) layer of VANET. In IEEE 802.11p, licensed spectrum of 5.850GHz-5.925GHz is divided into one control channel (CCH) and six service channels (SCHs), CCH is dedicated for broadcasting traffic safety messages, SCHs are dedicated for transmission of various application messages, Orthogonal frequency Division Multiplexing (OFDM) technique is employed in PHY. Because IEEE 802.11p applies multiple channels, the schemes of channel coordination and access control have great influence on efficiency of VANET. The main research works of this thesis are as follows:Firstly, the purpose and significance of our research works are discussed, and then, the architecture of VANET and IEEE 802.11p protocol are introduced. At last, the research focus at home and abroad of VANET are summarized, the current research status and trends on VANET channel coordination and access control are analyzed in detail.A dynamic queue management algorithm to improve Enhanced Distributed Channel Access (EDCA) channel competing protocol is presented. Based on real time transmission delay detection and estimate to different EDCA access category (AC) queue, the improved EDCA protocol can deliver data frame into appropriate AC queue dynamically according to AC queue’s load and communication quality.A contention-based channel access control (CBCAC) mechanism for VANET is proposed. The improved EDCA protocol is used for channel access control, and a channel reservation algorithm is introduced for service channel assignment. The analysis results show that the performance of proposed channel access mechanism is better in light load VANET conditions.A time division multiplexing channel coordination (TDMCC) scheme for high density VANET is presented, which can adjust CCH interval and SCH interval adaptively according to VANET conditions. Besides, a contention-free Time Division Multiplexing (TDM) channel assignment scheme is provided for SCHs access control. The analysis results show that TDMCC scheme can improve channel utilization both in CCH and SCHs under heavy load VANET environments.Focusing on information security transmission in CCH, an identity authentication scheme based on dynamic bandwidth partition algorithm is proposed. Meanwhile, asymmetric encryption algorithm, chaos scrambling technology and frequency hopping communication are applied to enhance the communication reliability.Physics layer of IEEE 802.11p is analyzed, the integrated IEEE 802.11p PHY communication system and frequency hopping communication system based on dynamic bandwidth partition algorithm are designed respectively, Futhermore, the performance of communication system is tested by MATLAB simulation model.At the end of this thesis, we give a summary for our research work. Some useful conclusions are givn, and further research prospects and issues are discussed. |
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