Radio-Frequency Impairments Compensation in Ultra High-Throughput Satellite Systems

Abstract

The quest for massive satellite throughput is relentless, motivating the transmission of broadband signals at multiple Giga-Baud rates. Building low-cost, low-complexity user terminals is essential. These competing drivers conspire to cause analog radio-frequency (RF) components to exceed their tolerance limits. Specifically, analog mixers, anti-aliasing filters and amplification in quadrature frequency-conversion architectures create direct-current (DC) offset and in-phase/quadrature (I/Q) imbalance that is strong and frequency-selective. This paper provides two characterization models of analog RF impairments when the frequency offset is present. Novel digital compensation algorithms with immunity to frequency offset are presented, categorized into equalization with image-rejection capability and image cancellation. Adaptive techniques are utilized that operate without a priori knowledge of RF impairments. Two optimization methods are proposed for the multicarrier scenarios that are useful when using known data samples for factory calibration or in decision-directed mode during field re-calibration. Special consideration is given to estimating the frequency offset during initial factory calibration. Extensive computer simulations reveal that the proposed compensators are robust to frequency offset, provide lossless attenuation of imbalance-induced image and remove DC offset, under numerous scenarios. Cases include when the desired carrier is plagued by image interference from more than one source and on-board high-power amplifier is operated near saturation.