Key Technologies Of Adjacent Channel Interference Suppression In Spectrum Symbiosis Systems

In recent years,with the application of new wireless communication technologies and the emergence of a large number of communication nodes,the number of users in the limited airspace and frequency domain has increased dramatically.Interference between adjacent channel has become more and more frequent.Take military communications as an example,high-power transmission signals from command vehicles,ships,and aircraft will cause interference to the desired signals at the co-site receiver,resulting in poor sensitivity and shortened communication distances.In civil communications,the signals transmitted by LTE base stations will interfere with Wi Fi and navigation signals,resulting in frequency conflicts.Adjacent channel interference(ACI)worsens the background noise,aggravates the unnecessary consumption of spectrum resources,intensifies the frequency conflict,and seriously restricts the effective utilization of the existing communication system.This dissertation focuses on the key technologies of ACI suppression in spectrum symbiosis systems,and optimizes the communication performance by suppressing ACI.The main contributions are as follows:(1)An ACI suppression method based on signal reconstruction and cancellation at the receiver is proposed.Firstly,an auxiliary branch is added to the receiver,and the nonlinear parameters are estimated by using the demodulated signal and the received interference.Then,the ACI is reconstructed using the baseband signal and estimated parameters.Finally,the reconstructed signal is subtracted from the received signal to eliminate the ACI.The simulation and experiment results show that the proposed method can effectively improve the signal to interference plus noise ratio(SINR)of the desired signal and reduce the mutual interference between co-site devices.(2)The ACI suppression effect under the constraint of frequency offset is studied.First of all,it is proved by theoretical derivation that the frequency offset will cause two parts of the system error to increase: one is the demodulation error of the baseband signal,and the other is the residual error after subtraction,that is,the total residual interference increases.Secondly,the closed expression of ACI suppression capability under frequency offset constraint is given,and the relationship between SINR,observation length and interference suppression effect is analyzed.Finally,the simulation verifies the effectiveness and feasibility of the compensation method based on the pilot sequence,and the relationship between the length of the pilot sequence,the SNR and the accuracy of the frequency offset estimation are given.(3)In order to alleviate the dependence on the high-speed analog to digital converter(ADC)of the auxiliary branch,an low-speed sampling rate ACI suppression method is proposed,which employs the spectral inversion of the main-lobe of the interference.Firstly,the main-lobe of the interference is extracted by a band-pass filter and digitized by a low-speed ADC.Then,the out-of-band side-lobes are recovered by the spectrum inversion to obtain the whole interference.Finally,the reconstruction and cancellation of ACI is completed by using the recovered signal.Simulation and experiment analyze the relationship between inversion error and ACI suppression performance.The results also verify the relationship between inverse filter order,SNR and ACI suppression effect.The essence of the proposed method is to exchange the limited loss of interference suppression effect for the reduction of ADC sampling rate,which is beneficial to the application in broadband ACI suppression.(4)Aiming at the cancellation of ACI leakage of the duplex filter,a low-complexity ACI suppression method is proposed.The proposed method can directly use the ADC output signal of the receiving branch(ie.,the side-lobes of the interference)to reconstruct the interference,which can effectively reduce the receiver circuit complexity and cost.In the parameter training stage,the nonlinear parameters of the system are estimated by using the training sequence and the side-lobes of the interference.Then the reconstruction and cancellation of ACI are completed by using the estimated parameters and the transmitted digital sequence in the interference suppression stage.This method simplifies the auxiliary branch structure,no additional RF filter and ADC are needed,and provides a new method for constructing a low-complexity ACI suppression receiver.In this dissertation,the reconstruction and cancellation of ACI are used to alleviate the interference of the spectrum symbiosis systems,which can increase the SINR of the desired signal and improve the spectral efficiency of the system.The research results can be applied to scenarios such as heterogeneous communication,symbiotic communication,electronic countermeasures,and electromagnetic compatibility,which can better promote the effective use of existing communication systems.