Analysis Of Channel Estimation Based On IEEE 802.11p For V2V Channels

As one of the most important means of transport,cars have increasingly become an important part in people's daily life with the high development of human society.However,in recent years,with the rapid increasing number of cars,traffic accident mortality rates is increasing,which seriously threat to people's lives.Therefore,vehicle safety has been greatly concerned in society.Because of the urgent demand of intelligent transportation and traffic safety,the vehicle-to-vehicle(V2V)communication,as a promising technique of the future intelligent transportation system,has been emerged.The standard of IEEE 802.11p is referred to a dedicated short range wireless communications protocol.It has defined a number of new features to meet the needs of Intelligent Transportation Systems(ITS)applications,which mainly for the data exchanging between fast-moving vehicles and communication requirements or between the vehicles and the roadside infrastructure.Channel estimation(CHE)is an important part of the wireless communication system.Accurate CHE plays a key role in channel equalization,demodulation and decoding.For wireless communication system,wireless signal can be easily affected by communication environment,relative speed and other factors.Channel characteristics are usually complex and changing fast.Therefore,it becomes challenging to estimate the channel impulse response(CIR)accurately and effectively.For vehicle-to-vehicle communication(V2V),since the characteristics of fast-moving vehicle and the protocol itself limitations,the existing 802.11p protocol has some defects in adapting the exact adaptation of V2V channel,which has a dynamic nature.This paper discusses the IEEE 802.11p protocol first,and then analyzes the OFDM conventional CHE algorithm.At last we made summary of CHE techniques based on 802.11p protocol.By analyzing the advantages and disadvantages of existing algorithms,we proposed a two-dimensional CHE algorithm based on 802.11p protocol,which is a joint of time domain and frequency domain algorithm.Since this algorithm based on minimum mean square error(MMSE),it is named two-dimensional LMMSE channel estimation algorithm(2D-LMMSE).2D-LMMSE algorithm uses long training sequence(Preamble)to estimate CIR,and to extend/interpolate to the data field according to the correlation coefficient of time-frequency domain by using the estimated value of CHE algorithm based on Preamble.The time-domain correlation coefficient is related to Doppler,if we make the above mentioned two-dimensional interpolation,it needs to estimate Doppler and may lead to errors.In V2V communication system,the vehicle speed and a relatively large change in the rate will further affect the estimation accuracy.For these reasons,the accuracy of time-domain correlation coefficient obtained by estimating the Doppler will be poor.But considering V2V communication system,it has an available known speed,so we can get a higher precision time,domain correlation coefficient,further improve the accuracy of interpolation.In addition,as the pilot is used for phase tracking at 802.11p protocol,we propose an improved CHE algorithm(2DP-LMMSE)based on Pilot.2DP-LMMSE uses the estimation value obtained from pilot signal to correct the estimation value based on Preamble,and then further improves the accuracy of estimation.The simulation results show that 2D-LMMSE outperforms one-dimensional frequency domain algorithm(1D-LMMSE)and Linear Square(LS)algorithm in faster speed environment which has higher Doppler shift.Then,we make the performance comparison of 2D-LMMSE algorithm and another two-dimensional frequency domain algorithm(2DE-LMMSE)which has Doppler estimation error,simulation results show that 2D-LMMSE have better performance.Finally,with the comparison of 2DP-LMMSE algorithm and 2D-LMMSE algorithm,the results show 2DP-LMMSE algorithm is better than 2D-LMMSE algorithm,especially in high-speed environment.