A down conversion method for mobile communications by bandpass sampling with interoperation of quadrature signal

摘要

This report proposes a new bandpass sampling method that is suitable for the software radio. The proposed method, which is an extended version of the conventional frequency offset method, derives both in-phase and quadrature signals by using two kinds of sampling timing. The major advantages of the proposed method over conventional techniques are: (1) the proposed method is free from the DC offset, which is caused by the mixture of sampling clock harmonics into the input signal; and (2) its complex number process in the signal detection can overcome the alias problem. Computer simulations demonstrate that the timing difference between the in-phase and quadrature signals results in signal distortion, and that interpolation techniques can reduce the distortion level up to -60dB.