Key Technology For Nonlinear Correction Of Downsampling Rate Of Terahertz Band Transceivers

With abundant spectrum resources,high transmission rate and excellent security,terahertz communication is one of the key technologies for 6G research.However,terahertz high devices are often characterized by strong nonlinear distortion.Nonlinear correction in the terahertz band faces problems such as excessive observation bandwidth and incomplete nonlinear distortion acquisition,resulting in insufficient correction effect.In view of the above problems,this paper proposes a method for the correction of terahertz band transceiver nonlinearity with reduced sampling rate,and the main research contents include:First,at the transmitter side,a narrowband feedback digital pre-correction method is proposed to solve the problem of insufficient sampling rate of the feedback channel.A bandwidth-limited power amplifier model is established,and the inverse transfer function of the power amplifier is obtained according to the mutual inverse relationship between the power amplifier and the pre-corrector,and the pre-distortion parameters are calculated.The signal nonlinear distortion is compensated at the transmitter side to improve the inband signal quality.The simulation results show a 6% improvement in EVM performance for 64-QAM modulated signals at 3.2 GHz.Second,at the transmitter side,an undersampling digital pre-correction method is proposed to address the problem of high digital signal processing rate of the system,where both DPD model identification and nonlinear correction are performed at the baseband signal rate.The inverse model of the power amplifier at the baseband rate is established,and the pre-distortion parameters are calculated and then the signal is corrected for nonlinearity at the transmitter side.For the 64-QAM modulated signal at3.2 GHz,the EVM metric is improved by about 5.5% level;for the 256-QAM modulated signal,the EVM metric is optimized by 5% level.Third,at the receiver side,a low-rate receive nonlinear post-correction method is proposed for the case where pre-correction cannot be performed at the transmitter side.A symbolic-level nonlinear post-correction model is established to compensate for signal distortion directly at the receiver side.The nonlinear correction parameters are trained using pilot known in the transmitting source,and the nonlinear post-correction model is established with this parameter to improve the linearity index of the received signal.Simulation results conclude that the EVM is improved by 4% for a 64-QAM source with a bandwidth of 3.2 GHz.In this paper,the narrowband feedback digital pre-correction method,undersampling digital pre-correction method and low-rate receive nonlinear post-correction are investigated,and the research results can be applied to ultra wideband terahertz communications to improve power amplifier conversion efficiency and the nonlinear distortion of the received signal,so that high-order modulation with higher spectral efficiency can be used in the terahertz communication system to increase the transmission distance.