An Adaptive Echo Cancellation Module for the Same Frequency Repeater Based on LMS Algorithm and FPGA

To extend the coverage of base stations, the same frequency repeater is widely used in modern communication network. However, there exists coupling echo interference between transmitting antenna and receiving antenna of the repeater station, which affects the system stability and the signal quality. The echo interference is in the same frequency with the useful signals of base stations, which cannot be eliminated by traditional frequency-domain filtering. To address this problem, this paper proposes an adaptive echo cancellation algorithm by inducing an additional reference sequences, which is targeted to apply in the hardware platform of Fujian Jingao FDD-TLE same frequency repeater. In this paper, the working principle of the algorithm is described firstly; then the algorithm is analyzed by MATLAB simulation, and finally verified in FPGA. The comparisons between before and after echo cancellation using the proposed algorithm in time domain and frequency domain shows that this algorithm can effectively suppress echo interference, and the output signal spectrum is significantly improved. Compared with the adaptive filtering algorithm based on the transform domain, this algorithm does not need Fourier transform, which has lower computational complexity and takes less resource. Moreover, this algorithm has a wide application scope and does not depend on the specific modulation scheme of the relaying signal.