Research Of Speed Estimation Algorithm In Wireless Communication System

In the satellite communication system and mobile communication system,it is necessary to estimate the velocity of the terminal.Because the velocity,which is mainly obtained by the Doppler frequency shift estimation,can be applied to adjust parameters,such as MCS,rate,etc.Firstly,the traditional Doppler Frequency offset estimation algorithms are researched in this paper.Doppler frequency offset estimation algorithms are mainly Crossing-based method,covariance method,maximum likelihood method.In single-carrier and multi-carrier system,each method has its own merits and is suitable for different situations.On this basis,speed estimation for single-carrier satellite communication system and multi-carrier mobile communication system are researched.In the sparse-pilot AWGN single-carrier satellite communication system,we propose a LLR-aided(LLR,Log Likelihood Ration)speed estimation algorithm.The main problem of this system is that the frequency offset is larger than the pilot density frequency,but is less than the symbol frequency.The algorithm first uses power spectrum method to calculate the candidate values of frequency offset,and then exploits the LLR soft decision properties to filter out the correct value of candidate frequency.In the traditional hard decision system,this kind of problem is mainly implemented by getting the candidate frequency with the power spectrum method,and then compensating the received signal by candidate frequency and then using hard decision method to determine whether candidate frequency is the correct frequency.The method shows good performance in the low SNR(Signal noise ration)environment,and is superior to the blind estimation method.Furthermore,this method does not require complete closed loop,which greatly reduces the complexity of closed-loop algorithm.In multi-carrier ground communication system represented by OFDM,Crossing-based algorithm in frequency domain is researched in this paper.Based on the time-domain Crossing-based method in single-carrier communication system,the Crossing-based method in frequency domain is proposed.This algorithm is mainly implemented by calculating the number of frequency-domain channel coefficient positive zero-crossing.This algorithm shows good performance and effectiveness.