Research For SOQPSK Signal With Frequency Domain Equalization Technology

In aeronautical communication systems,shaft offset quadrature phase shift keying(SOQPSK)signal with its series of advantages such as complete constant envelope,high spectrum utilization,and high power utilization has been adopted by many international standards.However,with the trend of increasing data rates in the aeronautical communication system,SOQPSK signal will be affected by severe inter symbol interference when transmitted in the multipath fading channel.Therefore,the equalization is required at the receiver prior to detection to compensate the effect of multipath fading channels on the signal.SCFDE(Single Carrier Frequency Domain Equalization)technology can implement equalization with low complexity while maintaining low peak-to-average ratio and low frequency offset sensitivity.Therefore,combining SOQPSK with SCFDE can maximize the constant envelope characteristics of SOQPSK and the anti-fading ability of SCFDE,the research of SCFDE technology based on SOQPSK is of great significance.For SCFDE technology based on SOQPSK,three aspects have been studied in this thesis.For the cyclic data block construction of SOQPSK-TG signal,the following research is done.Firstly,the signal model of SOQPSK-TG is studied,including the signal description and the state vector representation.Secondly,two methods of the cyclic data block construction of SOQPSK-TG signal are studied,the intrafix symbol construction based on zero state and the intrafix symbol construction based on the state vector.Then based on the former two methods,an improved intrafix symbol construction based on the state vector method is proposed.The three methods satisfy circular convolution and continuous phase characteristic by adding an additional intrafix segment;in terms of the length of the required additional symbols,the proposed improved intrafix symbol construction based on the state vector method has the least overhead,reducing the waste of bandwidth.For the receiver of SCFDE system based on SOQPSK-TG signal,the following research is done.Firstly,based on the Laurent PAM decomposition of binary CPM signal and ternary CPM signal,the Laurent PAM decomposition of the SOQPSK-TG signal is studied.Secondly,under the AWGN channel,the four-state simplified demodulation of SOQPSK-TG based on Laurent PAM decomposition is studied and simulated.Then,under the fading channel,oversampling signal and Laurent's PAM decomposition are applied to SCFDE of SOQPSK-TG and they are simulated and analyzed.For the channel estimation of SCFDE system based on SOQPSK-TG signal,the following research is made in this thesis.Firstly,the design of the pilot is studied.Then,several classical channel estimation algorithms are studied.The simulation results show that for the frequency domain estimation LMMSE estimation gets the best performance and the complexity is the highest;LS estimation gets the worst performance and the complexity is the lowest.To avoid the disadvantages of the frequency domain LMMSE channel estimation algorithm,an improved frequency domain LMMSE channel estimation algorithm which only needs to estimate the time domain characteristics and average signal-to-noise ratio(SNR)of the channel is studied.Theoretical analysis and simulation results show that theperformance of the proposed channel estimation algorithm is between the traditional frequency domain LMMSE and the frequency domain LS channel estimation algorithm,however it reduces the computational complexity and a priori information of the channel does not need to be known.