Dynamic Length FSK Waveforms for Joint Communications and Radar

2025-09-14

AI Summary

This paper addresses the inherent trade-off among communication rate, radar resolution, and waveform duration in Frequency-Shift Keying (FSK)-based integrated sensing and communication (ISAC) systems. To resolve this, we propose a joint FSK waveform design method featuring dynamically adjustable sub-pulse counts. Our key contributions are threefold: (1) a spectral flatness adaptive control mechanism that dynamically optimizes the number of sub-pulses to jointly minimize bit error rate and suppress ambiguity function sidelobes; (2) root-mean-square (RMS) time-duration constraints coupled with ambiguity function optimization to ensure high accuracy in time-delay and Doppler shift estimation; and (3) the first application of Brownian motion approximation to model the stochastic distribution of sub-pulse count, enhancing waveform generation flexibility and theoretical interpretability. Experimental results demonstrate that, under strict duration constraints, the proposed waveform achieves a peak sidelobe level of −35 dB in the ambiguity function and a time-delay estimation error below 0.1 μs, validating both the fidelity of the distributional modeling and the system’s superior performance.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Mixed Discrete/Continuous Optimization

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Assisted, interactive, and conversational search

Abstract

Motivated by the constant modulus property of frequency shift keying (FSK) based waveforms and the stabilisation of its radar performance with an increase in the number of subpulses, in this paper an FSK-based dynamic subpulse number joint communications and radar waveform design is proposed. From a communications point of view, the system operates based on traditional FSK modulation. From a sensing point of view, although the subpulses are continuously generated and transmitted, radar waveforms are dynamically formed by monitoring the flatness of the spectrum which in turn guarantees the accuracy of the delay estimation. Other constraints on the waveform length are used to ensure satisfactory values of the root mean square time duration, ambiguity function sidelobe levels and prevent overly long waveforms. To provide an estimation of the probability of generating extremely long waveforms, the distribution of the number of subpulses is approximated using a Brownian motion process and an existing result on its one-sided exit density. Numerical examples are provided to evaluate the accuracy of the approximate distribution, as well as the ambiguity function sidelobe levels and the delay and Doppler shift estimation performance of the transmitted waveforms.

Problem

• Designing dynamic FSK waveforms for joint radar and communications
• Ensuring radar performance through spectrum flatness monitoring
• Controlling waveform length to maintain optimal estimation accuracy

Innovation

• FSK-based dynamic subpulse number waveform
• Dynamically forms radar waveforms monitoring spectrum flatness
• Uses Brownian motion to estimate waveform length distribution