Design Of Self-interference Analog Signal Cancellation Circuit In Underwater Acoustic Communication System

In underwater acoustic communication system,seawater has great attenuation to high frequency signal,which makes the available signal frequency band is low,leading to the limitation of its available bandwidth.Co-time Co-frequency Full-Duplex（CCFD）can make both transceiver and receiver work simultaneously at the same frequency,which can effectively improve spectrum utilization.In the underwater acoustic communication system,CCFD will introduce self-interference signal whose power is 70～80d B higher than that of useful signals at the receiving end,which will pose a challenge to selfinterference cancellation under the premise of long transmission distance.In this thesis,the analog domain self-interference cancellation technology will be studied and tested for the underwater acoustic full-duplex communication system.The main work are as follows:Firstly,according to the overall demand of the self-interference cancellation module,the requirements of engineering error are determined by theoretical derivation and simulation.First,according to the underwater acoustic propagation channel noise and application scenarios,the total self-interference cancellation is 86 d B,and the analog domain cancellation is 40 d B.Then,according to the overall demand,Theoretical derivation and circuit simulation are used to analyze the ability of self-interference cancellation under different conditions,so as to determine the influence of engineering error on the self-interference cancellation ability.In order to satisfy the self-interference cancellation ability greater than 40 d B,the simulation results show that the delay error should be less than 0.75 μs,the amplitude error should be less than 5%,and the number of rebuild channels should be more than 2.Secondly,the scheme design is finished according to the overall demand,and the key indicators are analyzed to complete the design of the circuit and algorithm.First,the scheme design is determined according to the overall demand,and the key circuit indicators are analyzed.The dynamic range and signal to noise ratio（SNR）of ADC and DAC should be greater than 90 d B.Then,the analog circuit is designed according to the circuit indicators,and the design is evaluated by theoretical calculation and circuit simulation.Finally,the Least Mean Square Error（LMS）algorithm is used as the selfinterference cancellation algorithm.Thirdly,the test platform was build to complete the performance test of analog circuit and self interference cancellation module.First,the analog circuit is tested,and the test results indicate the circuit design settles for the requirements of the index.Then,the self-interference cancellation module is tested.When the single-tone signal with signal amplitude of 0.5V～2V is used for testing,the self-interference cancellation ability of the module is not less than 40 d B.The module has a self-interference cancellation ability of 45 d B when tested with 9k Hz and 12 k Hz dual-tone signals.Final,a signal with a bandwidth of 3k Hz was used for testing,and the self-interference suppression ability was 41 d B.In summary,a analog domain self-interference cancellation module is designed and implemented in this thesis.The module operates from 7k Hz to 15 k Hz and adopts a digitally assisted self-interference cancellation structure.The test results show that the module can achieve 40 d B self-interference cancellation for self-interference signals with amplitudes no more than 2V.This thesis verifies the feasibility of analog domain selfinterference cancellation,which provides a certain reference value for the study of underwater acoustic full-duplex communication system.