Estimation Of Carrier Parameters In Multipath Fading Channel Of INET System

With the development of telemetry technology and the research of aeronautical aerial telemetry system,it is recognized that there are still many shortcomings in the existing telemetry system.So the development plan of the integrated Network Enhanced Telemetry(iNET)project is initiated for the new generation of telemetry network,and the SOQPSK-TG transmission system with high spectrum utilization is adopted to improve the performance of the telemetry system.However,in the process of information transmission,the reliability of communication will be affected by some factors,such as noise,multipath fading and unavoidable interference.Especially in multipath fading channel,the synchronization of partial response SOQPSK-TG signal plays a vital role in the transmission performance.At the same time,in telemetry communication system with high performance channel coding,it is of great significance to study how to obtain accurate synchronization of SOQPSK-TG signal at low signal-to-noise ratio.On the basis of introducing the characteristics of SOQPSK-TG transmission signal and the current research status of carrier parameter estimation in aeronautical telemetry system at home and abroad,the classical carrier parameter estimation algorithms in additive white Gaussian noise channel is studied in this paper,and these algorithms are modified to multipath fading channel environment of telemetry system.In order to meet the needs of wide estimation range and high precision estimation,a joint estimation algorithm is proposed.For carrier synchronization of coded SOQPSK-TG signals at low signal-to-noise ratio,a code adied carrier synchronization algorithm is studied.Firstly,the classical time-domain autocorrelation estimation algorithm and frequency-domain periodogram estimation algorithm in additive white Gaussian noise(AWGN)channel are studied.A carrier parameter estimation algorithm based on eye diagram and information entropy is proposed.Then,BPSK signal is taken as an example to be simulated and analyzation.At the same time,it is extended to the case of M-ary modulation for further analysis.Secondly,the multipath fading channel and its channel model are introuced,and these estimators of the classical time-domain and frequency-domain estimation algorithms for AWGN channel are modified to make them suitable for the environment of multipath fading channel.Simulation and analyses of the modified algorithm under the typical multipath fading channel of aeronautical telemetry are carried out.The simulation results show that the modified classical time-domain estimation algorithms have high estimation accuracy,but their estimation ranges are relatively small.The modified classical frequency-domain estimation algorithms have large estimation ranges,but their estimation accuracy is relatively low.Then,aiming at the problem that the modified classical estimators in multipath fading channel can not take into account both the estimation range and the estimation accuracy,two kinds of carrier frequency offset estimation algorithms in cascade mode are proposed,which are based on two-step frequency offset estimation algorithm in time domain and a frequency offset estimation algorithm combined with time-frequency estimation algorithm.The simulation results show that the estimation range of the two-step frequency offset estimation algorithm based on time domain is twice as wide as the original modified classical time domain estimation algorithm,and the estimation accuracy can reach the modified Cramer-Rao bound(MCRB).Time-frequency combined frequency offset estimation algorithm can estimate accurately when the normalized frequency offset is in the range of [-0.5(10),0.5],and its estimation accuracy is close to MCRB.Finally,for iNET system with high performance channel coding,the code-aided carrier parameter estimation algorithm is studied.At first,the pilot sequence is used for rough estimation,and then the compensated signal is used for fine estimation pilot and the decoded soft information.The simulation results show that the code adied estimation algorithm can achieve ideal synchronization performance at low signal-to-noise ratio.Compared with ideal synchronization,the performance loss of bit error rate is less than 0.2d B.