Waveform Learning under Phase Noise Impairment for Sub-THz Communications

TL;DR

This paper proposes a waveform design for sub-THz communications that is robust to phase noise and low PAPR, utilizing geometric constellation shaping, pulse filtering, and neural network demappers to improve performance under hardware impairments.

Contribution

It introduces a novel waveform optimization method that incorporates phase noise robustness, PAPR reduction, and neural network demappers for enhanced sub-THz communication performance.

Findings

Achieves up to 2.5 dB reduction in Eb/N0 under strong phase noise.

Reduces PAPR by up to 1.2 dB while maintaining BLER and spectral efficiency.

Demonstrates robustness of the proposed waveform in practical PN scenarios.

Abstract

The large untapped spectrum in sub-THz allows for ultra-high throughput communication to realize many seemingly impossible applications in 6G. Phase noise (PN) is one key hardware impairment, which is accentuated as we increase the frequency and bandwidth. Furthermore, the modest output power of the power amplifier demands limits on peak to average power ratio (PAPR) signal design. In this work, we design a PN-robust, low PAPR single-carrier (SC) waveform by geometrically shaping the constellation and adapting the pulse shaping filter pair under practical PN modeling and adjacent channel leakage ratio (ACLR) constraints for a given excess bandwidth. We optimize the waveforms under conventional and state-of-the-art PN-aware demappers. Moreover, we introduce a neural-network (NN) demapper enhancing transceiver adaptability. We formulate the waveform optimization problem in its augmented Lagrangian form and use a back-propagation-inspired technique to obtain a design that is numerically robust to PN, while adhering to PAPR and ACLR constraints. The results substantiate the efficacy of the method, yielding up to 2.5 dB in the required Eb/N0 under stronger PN along with a PAPR reduction of 0.5 dB. Moreover, PAPR reductions up to 1.2 dB are possible with competitive BLER and SE performance in both low and high PN conditions.