A novel adaptive equalizer and compensator for direct conversion receivers

Abstract

A novel adaptive algorithm is proposed in this paper to remove I/Q mismatch, the second-order intermodulation (IM2), ISI and AWGN simultaneously in a direct conversion receiver (OCR) by using cascaded adaptive filters. IM2 signals are treated as variable real DC values both in in-phase and quadrature channels separately, so they can be removed simultaneously with only one complex tap incorporated into a complex feed forward equalizer (CFFE). In addition, a real valued adaptive mismatch canceller is employed before the CFFE. Furthermore, a complex decision feedback equalizer (CDFE) is employed to cancel the residual ISI. To accelerate the convergence rates of the taps and to reduce the estimation variance, an internal iterative algorithm is introduced. Simulation results are provided to verify the superior performance of the proposed method.