Frequency Hopping Waveform Design for Secure Integrated Sensing and Communications

TL;DR

The paper tackles privacy and security in integrated sensing and communications by introducing random frequency agility and random PRI agility (RFPA) combined with channel reciprocity-based key generation (CRKG) to obscure Doppler and PRIs. It presents a generalized RFPA-FH-ISAC waveform, a hybrid information embedding framework (involving ASK, PSK, index, and spatial modulation), a sparse-matched filter receiver, and a CRKG-based secret-generation pipeline, all analyzed via ambiguity functions. Key contributions include a detailed AF-based performance assessment, a low-complexity sparse decoding approach, and a high-entropy CRKG scheme that avoids a central authority while enhancing secrecy in wiretap ISAC channels. The results show improved range and velocity estimation, reduced clutter, and significantly elevated secure data rates, indicating strong practical potential for secure 6G ISAC deployments.

Abstract

We introduce a comprehensive approach to enhance the security, privacy, and sensing capabilities of integrated sensing and communications (ISAC) systems by leveraging random frequency agility (RFA) and random pulse repetition interval (PRI) agility (RPA) techniques. The combination of these techniques, which we refer to collectively as random frequency and PRI agility (RFPA), with channel reciprocity-based key generation (CRKG) obfuscates both Doppler frequency and PRIs, significantly hindering the chances that passive adversaries can successfully estimate radar parameters. In addition, a hybrid information embedding method integrating amplitude shift keying (ASK), phase shift keying (PSK), index modulation (IM), and spatial modulation (SM) is incorporated to increase the achievable bit rate of the system significantly. Next, a sparse-matched filter receiver design is proposed to efficiently decode the embedded information with a low bit error rate (BER). Finally, a novel RFPA-based secret generation scheme using CRKG ensures secure code creation without a coordinating authority. The improved range and velocity estimation and reduced clutter effects achieved with the method are demonstrated via the evaluation of the ambiguity function (AF) of the proposed waveforms.

Figures (8)

• Figure 1: Proposed Scheme Block Diagram: Alice and Bob engage in secure RFPA-FH-ISAC using channel reciprocity-based secret generation, while Eve passively eavesdrops on Alice's messages and uses the reflected echoes from the target to estimate its location and velocity.
• Figure 2: The proposed secure RFPA-FH-ISAC Waveform.
• Figure 3: An illustration of the grouped sample points for Alice and Bob as determined by the proposed algorithm, using either $\Phi_{T_l} = 4$ or $\Phi_{f_l} = 4$.
• Figure 4: Achievable bit rates v.s the number of transmit antennas, $M$, for different information embedding schemes and PSK constellation sizes.
• Figure 5: BER v.s Eb/N0 (dB) for communication between Alice and Bob (A & B) and Alice and Eve (A & E) across SotA FHCS and various individual information embedding schemes.