Joint Channel and Mismatch Correction for OFDM Reception with Time-interleaved ADCs: Towards Mostly Digital MultiGigabit Transceiver Architectures

Time-interleaved (TI) analog-to-digital converters (ADCs) are a promising architecture for realizing the highspeed ADCs required to implement "mostly digital" receivers for emerging multiGigabit communication systems. Mismatch between the parallel ADCs comprising a TI-ADC is a fundamental performance bottleneck. While there exist mismatch correction techniques for generic applications of ADC, we illustrate in this paper that mismatch compensation can be subsumed within the overall receiver design for communication applications. We consider an orthogonal frequency division multiplexing (OFDM) link with TI-ADC used after downconversion. We show that mismatch results in frequency selective interference across subcarriers that can significantly degrade the performance of a standard OFDM receiver. However, this performance degradation can be alleviated significantly by joint channel and mismatch estimation and compensation, leveraging already available training or pilot sequences. This eliminates the necessity for dedicated hardware for mismatch correction. Specifically, we present an algorithm for estimating the channel gains and the mismatch, followed by low-complexity linear equalization to suppress the inter-subcarrier interference resulting from the mismatch. Our simulations show that the error floor due to mismatch-generated interference can be eliminated, permitting bandwidth-efficient operation with large constellations.