Outage Probability under I/Q Imbalance and Cascaded Fading Effects



Direct-conversion architectures (DCA) can offer highly integrated low-cost hardware solutions to communication transceivers. However, DCA devices are sensitive to radio frequency (RF) imperfections such as amplifier non-linearities, phase noise and in-phase/quadrature-phase imbalances (IQI), which typically lead to severe degradation of the performance of such systems. Motivated by this, we quantify and evaluate the impact of RF IQI on wireless communications in the context of cascaded fading channels. Novel closed-form expressions are derived for the corresponding outage probability for the case of ideal transmitter (TX) and receiver (RX), ideal TX and I/Q imbalanced RX, I/Q imbalanced TX and ideal RX, and joint I/Q imbalanced TX/RX. The offered analytic results have a relatively convenient algebraic representation and their validity is extensively justified through simulations. Based on these, it is shown that cascaded fading leads to considerable degradation in the system performance and that assuming ideal RF front-ends at the TX and RX induces non-negligible errors in the outage probability that can exceed 20% in several communication scenarios. We further demonstrate that the effects by cascaded multipath fading conditions are particularly severe, as they typically result in considerable performance losses of around or over an order of magnitude.