Design And Implementation Of Adaptive Interference Cacellation In WCDMA Repeater

Adaptive interference cancellation (AIC) technology appeared as early as 1960s in American military projects. With the development of digital signal processing, AIC is now being widely used in telecommunications, such as the underlying discussed WCDMA repeater, which is a type of relaying equipment used to provide wider coverage. In this paper, AIC technology is implemented in WCDMA repeater to combat its inherent co-channel interference.This paper first introduces the basic theory of AIC technology, and then a MATLAB platform to simulate AIC designs. Therein, the convergence performance of different algorithms is analyzed. After comparing the computational complexity, it is showed that two algorithms, i.e., M-NLMS in the time domain and FFT LMS in the transform domain, are both applicable in real systems.The two above algorithms are investigated afterwards, including the basic theory, simulation tests, and implementation. In the time domain algorithms, a modified NLMS algorithm, called M-NLMS is proposed. Instead of the division in the original NLMS, the LUT-based structure is adopted for the coefficients updating, which significantly reduces the complexity without compromising the performance. The simulation indicates that M-NLMS can combat the multi-path interference in fast speed. The resulted EVM can reduce to 13.6469% even under the SIR of -5db, which satisfies the requirement of WCDMA repeater.Finally, design and implementation of the FFT LMS are presented. This algorithm has the advantages of fast convergence rate and small residual error. It is showed that the resulted EVM can reduce to 7.004% even under the SIR of -5db. With the adoption of time division multiplexing, the number of FFT is reduced during the implementation. Furthermore, the utilization of ROMs for either data storage or data delay saves the hardware resource.From the presented results, it is discovered that the inherent co-channel interference in WCDMA repeater is reduced greatly with the two AIC algorithms, such as jitters in-band removed, suppression out of band increased and EVM restricted within 17.5%. Generally speaking, AIC technology guarantees a significant improvement, which is meaningful for the practical projects.