Hybrid Frequency and Phase-Shift Keying Modulation for Energy Efficient Optical Wireless Systems

In this letter, we introduce direct-current (DC) offset hybrid frequency and phase-shift keying (DC-FPSK) modulation for Internet-of-Things based on optical wireless systems. For DC-FPSK, non-negative phase-modulated frequency waveforms are generated by combining frequency-shift keying (FSK), phase-shift keying (PSK) and a DC offset. We propose optimal maximum likelihood and sub-optimal receivers for DC-FPSK. The performance is appraised in terms of Euclidean distance, bit-error-rate (BER) performance and energy efficiency. We determine that combining 4-PSK with conventional DC-FSK is the optimal approach to enhance the energy and spectral efficiencies.