Time-Frequency-Space Transmit Design and Receiver Processing with Dynamic Subarray for Terahertz Integrated Sensing and Communication

TL;DR

This work tackles THz ISAC by introducing a three-dimensional time-frequency-space transmit design and hybrid beamforming built on a dynamic array-of-subarray (DAoSA) architecture. It presents two ISAC precoding algorithms, a vectorization-based (VEC) method and a low-complexity sensing codebook-assisted (SCA) approach, to enable simultaneous high-rate communication and scanning sensing. For sensing, it proposes a wideband DAoSA MUSIC (W-DAoSA-MUSIC) angle estimator and a two-stage S-DFT-GSS method for range and velocity, along with an ISI- and ICI-tackled estimator to cope with CP limitations and high Doppler. Numerical results show centi-degree angle accuracy, millimeter-range accuracy, and decimeter-per-second velocity accuracy, with VEC approaching fully digital performance and SCA offering lower complexity, demonstrating THz ISAC viability and practical design guidance.

Abstract

Terahertz (THz) integrated sensing and communication (ISAC) enables simultaneous data transmission with Terabit-per-second (Tbps) rate and millimeter-level accurate sensing. To realize such a blueprint, ultra-massive antenna arrays with directional beamforming are used to compensate for severe path loss in the THz band. In this paper, the time-frequency-space transmit design is investigated for THz ISAC to generate time-varying scanning sensing beams and stable communication beams. Specifically, with the dynamic array-of-subarray (DAoSA) hybrid beamforming architecture and multi-carrier modulation, two ISAC hybrid precoding algorithms are proposed, namely, a vectorization (VEC) based algorithm that outperforms existing ISAC hybrid precoding methods and a low-complexity sensing codebook assisted (SCA) approach. Meanwhile, coupled with the transmit design, parameter estimation algorithms are proposed to realize high-accuracy sensing, including a wideband DAoSA MUSIC method for angle estimation and a sum-DFT-GSS approach for range and velocity estimation. Numerical results indicate that the proposed algorithms can realize centi-degree-level angle estimation accuracy and millimeter-level range estimation accuracy, which are one or two orders of magnitudes better than the methods in the millimeter-wave band. In addition, to overcome the cyclic prefix limitation and Doppler effects, an inter-symbol interference- and inter-carrier interference-tackled sensing algorithm is developed to refine sensing capabilities for THz ISAC.

Figures (9)

• Figure 1: Based on the DAoSA architecture, the proposed THz ISAC system generates scanning beams toward the $q$th sensing direction and stable beams toward the communication user at the $q$th time slot.
• Figure 2: Performance tradeoff between spectral efficiency and transmit sensing beamforming gain when the signal-to-noise ratio (SNR) $\frac{\rho}{\sigma_n^2}$ = -20 dB.
• Figure 3: Spectral efficiency versus SNR for the communication link.
• Figure 4: Transmit beampattern in the azimuth plane for $\eta = 0$, $\eta = 0.5$ and $\eta = 1$, when the sensing direction is ($-65^{\circ}, 90^{\circ}$) and the azimuth angles of communication paths are distributed between $-60^{\circ}$ and $60^{\circ}$.
• Figure 5: Beam scanning in the azimuth plane, when the transmit beampattern consists of time-varying sensing beams and stable communications beams. The sensing angular windows are depicted by the shadow areas, which can cover all angles from $-90^{\circ}$ to $90^{\circ}$. In this plot, beam patterns at time slots $q = 3, 4, 5, 6$ are exhibited.