Study On Digital On-frequency Repeater Echo Cancellation Algorithm And The Simulation

The repeater belongs to amplification device and is a radio signal strengthen launchtransfer equipment in the wireless transmission process. Moreover, it is a low-cost, simpleerection, but with a small base station functions cost-effective equipment. In the modernmobile communication network, a large number of repeater equipment that amplify and relaythe wireless signal are used to solve the problem of base station existing a signal blind. Thedigital On-frequency repeater is applied the most widespread, because of its simple structure,low cost, flexible set features. However, since the On-frequency repeater directly sends thereceived benefactor signal after amplifying it, if the isolation of the transceiver antenna is notlarge enough, the signals from the transmitting antenna will couple fed back to the receivingantenna as echo noise, so that the SNR decreased. Especially the echo signal will be amplifiedagain, and thus the formation of self-excited loop. Since the echo path is usually unknown andtime-varying, generally we use adaptive filters to estimate the echo path. Adaptive echocancellation technology is an important technology to solve the echo interference of theOn-frequency repeater.First, this paper introduces the basic structure of digital on-frequency repeater and basictheory of the repeater’s echo cancellation technology. It also introduces the adaptive algorithmand the adaptive filter. In addition, it analyses the tap-weight adaptation of several commonadaptive algorithm.Second, by analyzing the convergence condition of adaptive filter based on Least MeanSquare (LMS) principle, we find that existing adaptive filtering algorithm using delay toeliminate the relevance is not able to guarantee the convergence condition being satisfied inprinciple, even when the outer channel is a single-path or a main path of multipath channel. Atthe same time, the echo cancellation program of plus PN sequence carries out a detailedtheoretical analysis.Besides, to solve the problem that the convergence of adaptive filtering algorithm is not the necessary and sufficient condition of echo signal completely counteracted. We propose anovel algorithm sending the signal into the adaptive estimator after a delaying time to solvethe problem. The novel algorithm conditionally improves the effect of echo cancellation.However, it cannot guarantee the effective elimination of multipath signals when the outerchannel is multipath channel.Then, this paper constructs a simulation platform. And it declares the performance indexof echo cancellation. It simulates the echo cancellation technology using delay to eliminatethe relevance and the improved program in the Matlab environment.Finally, we study on echo cancellation technique of multipath channel，and proposeseveral new principles of echo cancellation for multipath echo channel conditions.