Research On Single Carrier Frequency Domain Equalization System Based On FQPSK Modulation

With the continuous development of wireless communications,high-speed data links such as aircraft-to-ground communications and unmanned aerial vehicle(UAV)communications have higher demands on the power efficiency and bandwidth efficiency of communications systems.As an efficient modulation method,Feher-patented quadrature-phase-shift keying(FQPSK)modulation has the characteristics of quasi-constant envelope and efficient spectral efficiency.As an effective single-carrier transmission technology against inter-symbol interference,single-carrier frequency domain equalization(SC-FDE)technology is insensitive to carrier frequency offset and timing offset and have a low peak-to-average ratio(PAPR).Therefore,based on the advantages of FQPSK modulation and SC-FDE,this paper proposes the SC-FDE system based on FQPSK modulation for the first time to provide a solution for high-speed communication data links such as aircraft-to-ground communications and UAV communications.The paper focuses on the design of transmitter and receiver for SC-FDE system based on FQPSK modulation.The key issues of signal design,pilot design,over-sampling multiple design,channel estimation,frequency domain equalization and sequence demodulation are studied respectively.In the aspect of signal design,the implementation of FQPSK modulation based on convolutional code mapping is firstly studied.Secondly,the influence of different over-sampling multiple on the approximation of design waveform and the actual bandwidth occupation are analyzed.Finally,the insertion of cyclic prefix and pilot sequence is studied.By adding cyclic prefix and pilot bit first and then applying FQPSK modulation,the signal waveform can be continuously without discontinuity to obtain efficient spectral efficiency.The receiver selects the corresponding channel estimation,frequency domain equalization and demodulation algorithms for the transmitter design and performs system simulation and analysis respectively.At the same time,this paper studies the impact of non-ideal bit synchronization and over-sampling multiple on system performance.Finally,under the condition of Rice fading multipath channel,the link performance is evaluated and compared with the SC-FDE system based on QPSK modulation.It is found that the system based on FQPSK modulation achieves higher power efficiency and bandwidth efficiency with little loss of error performance.