Study On Channel Estimation And AMC Technology In Vehicular Ad Hoc Networks

In recent years,with the growth of vehicle ownership,the rise of intelligent transportation system(ITS),as one of the typical applications of mobile ad hoc networks,vehicular ad hoc networks(VANET)has become a research hotspot at home and abroad.At present,there are still no unified VANET standards in the world,which are mainly divided into two directions: the Dedicated Short Range Communications(DSRC)standard represented by Europe and the United States and the LTE-V2 X standard based on cellular network in China.This paper mainly studies the channel estimation and adaptive modulation and coding(AMC)technology based on IEEE 802.11 p protocol under the DSRC system to achieve the goal of improving system performance.The details are as follows:(1).The physical layer based simulation platform is built using Matlab 802.11 p protocol,based on subsequent channel estimation and channel quality measurement method.(2).Aiming at the time-frequency dual selection characteristics of VANET channel,this paper proposes an improved channel estimation algorithm by modifying the 802.11 p standard frame structure.The algorithm uses the Lower Modulation and Coding Scheme(MCS)in the transmitter,then joint pilot signal to estimate the channel response of the data subcarrier.Simulation results show that the proposed algorithm improves the performance of 802.11 p standard medium MCS and high order MCS with good Package Error Rate(PER)performance,but the PER performance of low order MCS is less.At the same time,the performance of the algorithm is related to SNR.In the low SNR range of middle order MCS,PER performance improves obviously.(3).AMC technology can effectively cope with the time-varying characteristics of the channel and improve the performance of the system.In this paper,AMC technology is introduced into VANET.Signal to Interference plus Noise Ratio(SINR)is selected as the index to measure channel quality.The channel quality measurement algorithm of VANET is studied.On the one hand,based on the standard frame structure of 802.11 p,the Exponential Effective SINR Mapping(EESM)algorithm is studied,and the value of the adjusting factor b in EESM algorithm is analysised by simulation.On the other hand,aiming at the modified 802.11 p frame structure in the third chapter,an improved algorithm of channel quality measurement based on pilot after equalization is proposed.Compared with EESM,this algorithm is not restricted by the need to use the same kind of MCS in the data domain,and has lower complexity.The simulation in Urban Approaching Non-Line-Of-Sight transmission scenario shows that,compared with fixed MCS,VANET can improve the throughput of the system while satisfying certain PER performance requirements,and ensure normal communication when channel conditions are poor.