FPGA-Based Implementation of MSK Modulation for Simultaneous Wireless Power and Data Transfer

Minimum Shift Keying (MSK) is highly suitable for band-limited Simultaneous Wireless Power and Data Transfer (SWPDT) systems due to its excellent properties, including continuous phase, constant envelope, signal orthogonality, and minimum frequency separation. This paper presents the implementation of MSK modulation using a Field-Programmable Gate Array (FPGA). Two methods for MSK modulation are implemented and compared. The first method is based on the mathematical properties of the MSK signal; the digital baseband signal is differentially encoded and then converted from serial to parallel to create two distinct signals. These are subsequently multiplied by two orthogonal carriers, and the difference is taken to produce the MSK waveform. The second method leverages the continuous phase characteristics of a Direct Digital Synthesizer (DDS) IP core, generating the MSK waveform in a manner similar to Continuous Phase Frequency Shift Keying (CPFSK). To validate the correctness of both modulation approaches, a simulation was conducted in Vivado using an MSK signal with a 7 MHz center carrier frequency and a 2 Msps symbol rate. The simulation results demonstrate that both methods can accurately and successfully generate the MSK modulated signal.