Adaptive filter theory
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This paper investigates the reason why the predistorted signal is sampled and feeds back to an adaptation block as reference for digital predistorter (DPD) to be updated in real-time (RT) by comparing a non-real-time (NRT) method with off-time processing. In addition, by deriving a simple algorithm based on gradient descent algorithm with minimum square error criterion, the steady-state condition can be obtained. In simulation, it is confirmed that RT method converges to the exact high power amplifier (HPA) model. Also, RT method can rapidly cope with the change of HPA characteristics caused during the operation, which is a major advantage with emphasis on the operation of real-time update. In addition, RT method shows more accurate performance and stability consistently compared to NRT method.