Coherent Phase Shift Keying (PSK) Modulation Using Low-Power Micro-controllers for Underwater Acoustic Communications

Phase Shift Keying is a single-carrier coherent modulation scheme that requires accurate phase and frequency control. We evaluate two approaches to accurately control the phase of the modulated signals for acoustic transmitters implemented by a low-power microcontroller (MCU) with a low system clock. One approach is to use one hardware timer for the carrier frequency and one software counter for the symbol rate. Another approach is to use two hardware timers: one for the carrier frequency and one for the symbol rate. We provide the detailed implementation on a Texas Instruments’ MSP430F5529 MCU and compare the two approaches for BPSK and QPSK. Our testing results show that care has to be taken to ensure that the symbol phase control is accurate within 0.01% of the carrier frequency.