Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Millimeter-Wave Radar Beamforming with Spatial Path Index Modulation Communications

Ahmet M. Elbir, Kumar Vijay Mishra, Abdulkadir Çelik, Ahmed M. Eltawil

TL;DR

This paper addresses joint radar sensing and communications (ISAC) in mmWave MIMO by introducing spatial path index modulation (SPIM) into hybrid beamforming. It develops a low-complexity SPIM-ISAC design that selects radar and communications spatial patterns, using a radar-dedicated column and pattern-dependent communications columns, governed by a trade-off parameter $\eta$. The authors derive MI expressions for both SPIM-ISAC and conventional mmWave-ISAC, provide an asymptotic closed-form for the latter under massive arrays, and validate the approach through simulations showing notable gains in spectral efficiency and controllable radar beampatterns. The results suggest SPIM-ISAC can significantly improve performance with limited RF chains, though extensions to multi-target/multi-user scenarios remain for future work.

Abstract

To efficiently utilize the wireless spectrum and save hardware costs, the fifth generation and beyond (B5G) wireless networks envisage integrated sensing and communications (ISAC) paradigms to jointly access the spectrum. In B5G systems, the expensive hardware is usually avoided by employing hybrid beamformers that employ fewer radio-frequency chains but at the cost of the multiplexing gain. Recently, it has been proposed to overcome this shortcoming of millimeter wave (mmWave) hybrid beamformers through spatial path index modulation (SPIM), which modulates the spatial paths between the base station and users and improves spectral efficiency. In this paper, we propose an SPIM-ISAC approach for hybrid beamforming to simultaneously generate beams toward both radar targets and communications users. We introduce a low complexity approach for the design of hybrid beamformers, which include radar-only and communications-only beamformers. Numerical experiments demonstrate that our SPIM-ISAC approach exhibits a significant performance improvement over the conventional mmWave-ISAC design in terms of spectral efficiency and the generated beampattern.

Millimeter-Wave Radar Beamforming with Spatial Path Index Modulation Communications

TL;DR

This paper addresses joint radar sensing and communications (ISAC) in mmWave MIMO by introducing spatial path index modulation (SPIM) into hybrid beamforming. It develops a low-complexity SPIM-ISAC design that selects radar and communications spatial patterns, using a radar-dedicated column and pattern-dependent communications columns, governed by a trade-off parameter . The authors derive MI expressions for both SPIM-ISAC and conventional mmWave-ISAC, provide an asymptotic closed-form for the latter under massive arrays, and validate the approach through simulations showing notable gains in spectral efficiency and controllable radar beampatterns. The results suggest SPIM-ISAC can significantly improve performance with limited RF chains, though extensions to multi-target/multi-user scenarios remain for future work.

Abstract

To efficiently utilize the wireless spectrum and save hardware costs, the fifth generation and beyond (B5G) wireless networks envisage integrated sensing and communications (ISAC) paradigms to jointly access the spectrum. In B5G systems, the expensive hardware is usually avoided by employing hybrid beamformers that employ fewer radio-frequency chains but at the cost of the multiplexing gain. Recently, it has been proposed to overcome this shortcoming of millimeter wave (mmWave) hybrid beamformers through spatial path index modulation (SPIM), which modulates the spatial paths between the base station and users and improves spectral efficiency. In this paper, we propose an SPIM-ISAC approach for hybrid beamforming to simultaneously generate beams toward both radar targets and communications users. We introduce a low complexity approach for the design of hybrid beamformers, which include radar-only and communications-only beamformers. Numerical experiments demonstrate that our SPIM-ISAC approach exhibits a significant performance improvement over the conventional mmWave-ISAC design in terms of spectral efficiency and the generated beampattern.
Paper Structure (12 sections, 1 theorem, 22 equations, 4 figures)

This paper contains 12 sections, 1 theorem, 22 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Communications Receiver
  4. Radar Receiver
  5. Problem Formulation
  6. SPIM in ISAC
  7. Hybrid Beamformer Design
  8. Performance Analysis
  9. Numerical Experiments
  10. Communication Performance
  11. Radar Sensing Performance
  12. Summary

Key Result

Proposition 1

Consider the mmWave-ISAC system with massive antenna array deployment (i.e., $N_\mathrm{T}\gg 1$). Then, the MI for conventional mmWave-ISAC system is where $\gamma_1$ corresponds to the strongest path gain.

Figures (4)

  • Figure 1: The SPIM-ISAC architecture processes the incoming data streams and employs spatial path index information $s_0$ in a switching network, which connects $N_\mathrm{RF}$ RF chains to $\bar{M} = M+1$ taps on the analog beamformers to exploit a single path for the radar target and one of the $M$ spatial paths for the communications user.
  • Figure 2: MI versus SNR when the path gains $\gamma_{1} = \gamma_{2} =0.5$ and the radar-communications trade-off parameter $\eta = 0.5$.
  • Figure 3: MI versus the first path gain $\gamma_{1}$ when $\mathrm{SNR} = 20$ dB and $\eta = 0.5$. Note that $\gamma_{2} = 1-\gamma_{1}$.
  • Figure 4: Azimuthal beampattern when $i=1$ (top) and $i =2$ (bottom) for various values of the radar-communications trade-off parameter, $\eta = \{0,0.3,0.5,0.8,1\}$. Here, the path gains $\gamma_{1} = \gamma_{2} =0.5$.

Theorems & Definitions (2)

  • Proposition 1
  • proof