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This paper describes an echo cancellation (EC) algorithm used in a mixed mode WCDMA/GSM repeater with digital sub-band filtering. The EC coefficients are estimated iteratively from cross and power spectrums improving the computational efficiency of the estimation. The effect of regularization and spectral normalization on the convergence of an adaptive EC algorithm is investigated. Singular value decomposition (SVD) is applied to the estimation process as a form of regularization, compensating for the bandwidth reduction associated with the sub-band filter. Spectral normalization used in the estimation of the EC coefficients is shown to avoid convergence problems and the frequency- dependent cancellation that affect the baseline approach. Simulation results show echo cancellation of 23 dB across a 60 MHz bandwidth.