Time delay estimation in digital pre-distortion

OFDM communications require extreme linearity of high power amplifiers (HPA) to avoid intercarrier interference (ICI) and subsequent degradation of the BER and quality of service (QoS). Amplitude (AM/AM) and phase (AM/PM) amplifier nonlinearities can be compensated in a number of ways. Nevertheless, digital adaptive schemes based on least squares optimization criteria need estimate the delay introduced by the analog chains in the generation of the error signal. A sufficiently precise HPA input-output time delay estimate (TDE) is necessary before attempting pre-distortion of the amplifier itself. This paper introduces statistical criteria for this initial acquisition stage.