Masked Modulation: High-Throughput Half-Duplex ISAC Transmission Waveform Design

TL;DR

The paper tackles the sensing-communication tradeoff in ISAC by introducing MASked Modulation (MASM), a half-duplex waveform that mitigates range glint (mainlobe fluctuation) under a duty-cycle constraint. It formalizes metrics for mainlobe fluctuations, AESL, PESL, and energy efficiency, and derives an optimization framework that links the mask design to the discrete Fourier transform spectrum via $\|\mathbf{F}\bm{m}_{\rm t}\|_4^4$; for constant-modulus signals, zero IRGI is achievable with certain $(N,\rho)$ through Singer cyclic difference sets. The work characterizes sidelobe performance and proves the existence of masks that are both mainlobe-fluctuation-ideal and pesl-ideal (notably Singer CDS), while also extending MASM to slow-time, frame-level designs. Numerical results corroborate the theory, showing reduced mainlobe fluctuations and competitive sidelobe performance relative to full-duplex and PRF staggering, enabling ~50% communication throughput with si-free long-range sensing. Overall, MASM offers a principled, practical pathway to high-throughput, long-range ISAC in 6G settings.

Abstract

Integrated sensing and communication (ISAC) enables numerous innovative wireless applications. Communication-centric design is a practical choice for the construction of the sixth generation (6G) ISAC networks. Continuous-wave-based ISAC systems, with orthogonal frequency-division multiplexing (OFDM) being a representative example, suffer from the self-interference (SI) problem, and hence are less suitable for long-range sensing. On the other hand, pulse-based half-duplex ISAC systems are free of SI, but are also less favourable for high-throughput communication scenarios. In this treatise, we propose MASked Modulation (MASM), a half-duplex ISAC waveform design scheme, which minimises a range blindness metric, termed as "mainlobe fluctuation", given a duty cycle (proportional to communication throughput) constraint. In particular, MASM is capable of supporting high-throughput communication ($\sim$50% duty cycle) under mild mainlobe fluctuation. Moreover, MASM can be flexibly adapted to frame-level waveform designs by operating on the slow-time scale. In terms of optimal transmit mask design, a set of masks is shown to be ideal in the sense of sidelobe level and mainlobe fluctuation intensity.

Figures (10)

• Figure 1: Qualitative performance comparison between proposed masm waveforms and conventional isac waveforms.
• Figure 2: Illustration of the reception processing in \ref{['range_profile']}. We focus on the $0$-th pri $\bm{x}_0$ throughout the treatise, although all results also apply to other pris.
• Figure 3: Illustration of the mainlobe fluctuation effect of conventional pulse radars. Trapezoidal $\bm{r}_{\rm m}$'s suffer from severe mainlobe fluctuation across many range bins.
• Figure 4: The mainlobe fluctuation of masm under PSK constellations and different transmission masks, compared with the conventional pulse.
• Figure 5: The irgi-to-mainlobe ratio of masm under various constellations and transmission masks, compared with the conventional pulse.

Theorems & Definitions (17)

• Remark 1: ARGI as Conditional Variance
• Proposition 1
• Proposition 2
• Proposition 3: Expected irgi of data payload signals
• Remark 2
• Lemma 1
• Proposition 4: Expected irgi of random masks
• Lemma 2
• Proposition 5
• Proposition 6: Constant aesl