Continuous-Phase Frequency-Hopping MIMO Signaling and Processing for ISAC

Abstract

Frequency-hopping MIMO integrated sensing and communications (FH-MIMO-ISAC) supports agile multidimensional signaling but faces challenges in phase-continuous transmission, demodulation without channel-phase information, and coherent processing of multi-frequency echoes. We propose a continuous-phase frequency-hopping (CP-FH) MIMO ISAC waveform with matched communication and radar processing. Information is conveyed jointly by frequency combinations and continuous-phase-modulation symbols. CPM phase accumulation and frequency-hopping linear-frequency-modulation phase compensation maintain phase continuity and reduce spectral leakage. We derive exact inter-element orthogonality conditions, residual cross-correlation bounds, and a bound on averaged transmit-beampattern ripple. For communication, projection-energy demodulation requires no channel-phase information and approximates least-squares detection under weak inter-branch correlation. It separates frequency-combination search from CPM-symbol decisions, reducing complexity while retaining direct joint-search decisions. For radar, structure-matched coherent processing combines space-time-frequency matched filtering, velocity-consistent Doppler focusing, and frequency-aperture focusing to form a three-dimensional coarse-range--velocity--fine-range response. It reduces Doppler-mismatch loss and extra detections from periodic range grating lobes in conventional pulse-Doppler processing. We further derive the joint range response, output signal and noise powers, and receive beampattern. The analysis characterizes target-discrimination limits under periodic ambiguity and shows that the proposed processor preserves frequency-aperture range resolution and full-aperture angular resolution, with equal output noise power under the stated conditions.