E. Nemer and A. Said (USA)
I/Q imbalance. Analog demodulation.
In digital video broadcast systems, such as those used in satellite and terrestrial transmission (DVB-S, -T), an analog tuner is used at the user site to down-convert the signal and provide a first stage of demodulation that yields the baseband quadrature (I and Q) components. Due to imperfect analog demodulation and A/D mismatch, the 2 quadratures will be off-balance in both phase and magnitude. This in turn has a negative effect on the signal SNR, as well as on the operation of the internal loops in the receiver. This paper describes a novel time domain method for balancing the I and Q quadratures at the front end of the receiver. The proposed solution consists of 2 iterative feedback loops operating independently, and without apriori knowledge of the transmitted symbols. Simulation on the DVB-S constellations - QPSK, 8PSK and 16QAM - shows the scheme is robust in severe channel impairments and yields a significant improvement of the cluster variance at the receiver output.
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