A Technique Of Digital Self-interference Suppression Based On Spread-spectrum Full-duplex Communication For Aeronautical Telemetry

With the increase of the number of satellite users in aeronautical telemetry applications,the contradiction between communication traffic and spectrum resources has become increasingly acute.Co-time co-frequency full duplex communication can double the spectrum efficiency by receiving and sendinge signals in the same frequency at the same time,which has attracted widespread attention.Self-interference is the main obstacle to overcome for full-duplex communication.Moreover,the characteristics of the wireless channel change rapidly with time,and the channel change needs to be tracked in real time.In view of the above problems,the main research content of this article is co-time cofrequency full-duplex adaptive digital self-interference cancellation.First,the mathematical model of digital interference cancellation is derived,and the impact of time synchronization and expected signals on digital interference performance is analyzed.Since Recursive Least Squares(RLS)has the characteristics of tracking channel changes in real time,the digital domain self-interference suppression algorithm selects the RLS algorithm to suppress frequency-selective digital self-interference signals.The effect of time synchronization and signal of interst on the digital self-interference suppression performance is theoretically analyzed,The conclusion is that the received signal and the feedback signal are aligned,the receiver has the best cancellation performance;when the gold sequence with the better orthogonality is selected,the digital domain can obtain better cancellation performance;compared with no desired signal in the received signal,desired signal in the received signal will deteriorate the digital selfinterference cancellation performance,but the impact will become smaller with the length of spreading sequence increasing.Second,the effect of time synchronization and signal of interest on digital selfinterference performance by the RLS algorithm was simulated by Simulink.The simulation results show that: as the synchronization offset is 10,the digital interference suppression performance is the best.When the sample offset fluctuates by 2 sample points around 10,the impact on the cancellation performance can be ignored;When no expected signal exists and the signal-to-noise ratio is less than 30 dB,the difference between the cancellation performance under the Rayleigh channel plus the Gaussian channel and the cancellation performance under the Gaussian channel is only about 0.5dB;When the signal-to-noise ratio is 40 dB,the cancellation performance is 38 dB.When the desired signal exists,the value of the ISR has little effect on the demodulation performance of the desired signal.Finally,FPGA implementation and performance testing of self-interference suppression in the RLS digital domain are completed.The first step is introducing the implementation process of each module.Then,under the given test scenario,the RLS self-interference suppression performance test is completed based on the presence or absence of expected signals.The test results are consistent with the theoretical and simulation results.This paper completes the theoretical derivation,simulation implementation and verification of RLS digital interference cancellation.It has theoretical and practical value and can be applied to aerospace measurement and control systems to improve spectrum utilization.