Research On Adaptive Echo Cancellation Algorithms For Single Frequency Repeater And Implementation On FPGA

Signal coverage blind and weak area will inevitably appear in the process of laying communication infrastructure.As an extension of base station,repeater plays an important role in wireless communication system.However,since the transmitting and receiving antennas of repeater are of the same frequency,the signals of the transmitting antennas are reflected by multipath,which is inevitably received and amplified by the receiving antenna to form a feedback loop.When the device gain is greater than the isolation value,communication system will be in a positive feedback state,form a self-excited,even burn the amplifier.Since the echo path is usually unknown and time-varying,adaptive filtering is generally used to estimate the echo noise.The adaptive echo cancellation technology is an important technology to solve echo interference of the same frequency repeater.This paper mainly studies the adaptive echo cancellation algorithms and its implementation.Starting from the basic principle of adaptive filter,this paper deduces the commonly used adaptive interference cancellation algorithms,including steepest descent algorithm,LMS algorithm and NLMS algorithm,compares and analyses the performance of each algorithm.Secondly,aiming at the application of adaptive filtering algorithm in LTE repeater,this paper proposes an LMS adaptive echo cancellation algorithm based on additional reference sequence,and build simulation environment in MATLAB to verify the performance of the algorithm.Then,we build hardware verification platform with LTE-FDD repeater of Fujian helios Communication Technology Co.,Ltd.The core chip adopts Intel's Cyclone V series5CEFA5F23I7.The key implementation modules and interfaces of the proposed algorithm are introduced in detail.And we use Quartus II and Modelsim for joint simulation.Finally,we generate the RBF file and load it into FPGA module.According to the main performance indicators of the same frequency repeater,the board level debugging is carried out through virtual IO and signaltap II.This paper analyzes actual interference cancellation effect of the adaptive echo cancellationalgorithm,and verifies the feasibility of the algorithm.The test results show that with the LMS echo cancellation algorithm based on the additional reference sequence,the feedback echo noise is effectively suppressed,and the output power spectrum is obviously improved.Compared with the transform domain based adaptive filtering algorithm,this algorithm does not need Fourier transform,only use 14018 ALM logic resources and 47 DSP blocks,which has lower computational complexity and consumes less resources.Meanwhile,this algorithm has a wider application range and does not depend on the specific modulation method of the signal processing.