FM OFDM Unifying High Mobility Communications and Sensing

Abstract: Integrated Sensing and Communication (ISAC) is foundational to future sixth generation (6G) systems, demanding waveform co-design that supports both high throughput data transmission and accurate environmental perception. While Orthogonal Frequency Division Multiplexing (OFDM) offers flexibility and backward compatibility, its high Peak to Average Power Ratio (PAPR) poses significant challenges at higher frequency bands. To address this, we investigate Frequency Modulated Orthogonal Frequency Division Multiplexing (FM OFDM) a constant envelope waveform that facilitates robust joint sensing and communication under highly mobile, doubly dispersive channel conditions. We derive a comprehensive input output relationship for FM OFDM in time varying multipath channels, including analytical expressions for Inter Carrier Interference (ICI), Doppler effects, and effective channel gains. Extensive simulations comparing FM OFDM with conventional Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP OFDM) and Constant Envelope Orthogonal Frequency Division Multiplexing (CE OFDM) demonstrate superior range and velocity estimation accuracy of FM-OFDM, particularly at high Signal to Noise Ratios (SNRs) and under high mobility, highlighting its suitability as a unified waveform for high frequency ISAC applications in 6G.