Wide-band system identification using multiple tones with allpass filters and square-law detectors

This paper introduces a method of wide-band system identification that uses a uniformly spaced set of tones with allpass filters and square-law detectors to obtain estimates of amplitude and phase at the associated discrete frequencies. The bandwidth of the detectors is on the order of the tone spacing and so can be much smaller than the overall signal bandwidth, thereby making feasible the use of low-cost analog RF integrated circuits and/or pure digital signal processing with all of its inherent advantages. Applications of this technique include equalization and compensation for fiber optic and wide-band cellular communication systems.