Research On Key Technologies Of Nonlinear Interference Suppression In Spectrum Symbiosis Environments

In recent years,the rapid development of information and communication technology(ICT)has not only met the increasing demand for mobile services,but also accelerated the consumption of electromagnetic spectrum resources.With rises of the mobile internet and intelligent terminals,the contradiction between surging access demands and limited spectrum resources has been further intensified,and various electromagnetic devices has also tested the security of the communication.Theoretically,when the frequency band of irrelevant signal is the same or partially overlaps the operating band of the receiver,the irrelevant signal becomes a kind of in-band interference,which prevents the receiver from detecting and acquiring the useful signal.By actively suppressing the in-band interference in the receiver,the useful signal and the irrelevant signal can work in the same electromagnetic spectrum to achieve the purpose of “spectrum symbiosis”.According to different applications,spectrum symbiosis environments can be used to improve the utilization efficiency of spectrum resources,enhance the wireless security,and solve electromagnetic compatibility issues,for achieving comprehensive utilization and control of the electromagnetic spectrum and approaching the development needs of future wireless communication systems.In order to achieve spectrum symbiosis,it is necessary to suppress the in-band interference.However,the hardware employed in the transmit and receive links has inherent non-ideal characteristics,especially the power amplifier,that distorts the signal in a nonlinear manner,degrading the performance of interference suppression.This dissertation focuses on the nonlinear interference(NI)suppression in spectrum symbiosis,the contributions of which are summarized as follows:(1)The NI suppression under constraint of frequency offset(FO)in the spectrum symbiosis environment is studied.The inherent instability of the local oscillator(LO)leads to the FO in the received NI,which severely degrades the estimation accuracy and suppression performance.First,the relationships between FO and NI modeling accuracy,NI suppression performance,and secrecy capacity of the spectrum symbiosis environment are revealed.Then,an NI suppression method under constraint of FO is proposed.Through Taylor series expansion of the NI signal,the nonlinear kernels are reconstructed to transform the time-varying parameters into time-invariant form thus reduce the FO influence on the parameter estimation,which makes the proposed method has the robustness of FO,relaxes the requirement for the stability of the LO,and simplifies the NI suppression process.(2)The NI suppression under constraint of time delay(TD)in the spectrum symbiosis environment is studied.Since perfect time alignment cannot be guaranteed between the local reference signal and the NI signal,the NI parameters are difficult to accurately estimate thus degrades the reconstruction accuracy of the cancelling signal.First,the influences of TD constraint are analyzed,including the NI modeling accuracy,NI suppression performance,and secrecy capacity of the spectrum symbiosis environment.Then,an NI suppression method under constraint of TD is proposed.Through linear interpolation to nonlinear kernels,the proposed method has the robustness of TD,which reduces the accuracy requirements for time synchronization and ensures the parameter estimation.(3)The NI suppression under constraints of time-frequency(TF)errors in the spectrum symbiosis environment is studied.First,the influence of TF errors on the suppression of NI is analyzed.Then,an NI suppression method under constraints of TF errors is proposed,by simultaneously performing linear interpolation on the nonlinear kernel and Taylor series expansion on the time-varying parameters,thus obtaining an NI model with TF errors robustness.The proposed method reduces the limitations of time and frequency synchronization accuracy and also simplifies the NI suppression process.(4)The NI suppression with I/Q imbalance(IQI)in the spectrum symbiosis environment is studied.As the hardware imperfections coexist,especially the combined effects of mixer IQI,power amplifier nonlinearity,and unstable LO,the NI model becomes complicated and difficult to characterize.First,the influences of hardware imperfections on NI is analyzed,and the power levels of various NI components are quantitatively revealed.Then,an NI suppression method with IQI is proposed.The proposed NI model is first based on a memoryless nonlinear model.After comprehensively modeling the effects of IQI and FO,the proposed NI model further expands its memory depth.Next,the brief nonlinear kernels are constructed to characterize all NI components,which overcomes the limitation of the NI suppression under hardware imperfections.This dissertation studies the NI suppression in spectrum symbiosis environments,involving the constraints analysis of non-ideal characteristics,the design of related suppression algorithms and architectures.The research provides a reference and insight for the construction of spectrum symbiosis environments,which can be applied for wireless mobile communications,satellite communications,enhancing electromagnetic compatibility,and electronic warfare.The potential values are of great benefit in both civilian and military usages.