On Asymmetrically Clipped Hybrid FSK-Based Unipolar Modulations: Performance and Frequency-Domain Analysis

Envelope detection, commonly used in visible light communication systems or in some radiofrequency receivers, requires the definition of real and unipolar modulations. With the objective of maximizing the energy efficiency of the modulation for a given spectral efficiency (≤ 1 bit/s/Hz, compatible with low power low data rate applications), a hybrid modulation that merges the elements of non-linear and linear modulations (named as hybrid asymmetrically clipped frequency-shift keying (AC FSK)-based modulation) is investigated. Comparing the performance for different linear (amplitude/phase) modulations, it is shown that the use of phase-shift keying (PSK) with 4 or 8 states for the linear part offers the best spectral efficiency vs energy efficiency trade-off. Moreover, a frequency-domain analysis of the waveforms facilitates the implementation of a low complexity quasi optimal harmonic receiver. Finally, a closed-form expression of power spectral density for AC-FSK-PSK modulation is defined, leading to a relevant definition for signal bandwidth and spectral efficiency.