Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Beam-Based Multiple Access for IRS-Aided Millimeter-Wave and Terahertz Communications

Wei Jiang, Hans Dieter Schotten

TL;DR

This work tackles the capacity bottlenecks of IRS-aided mmWave/THz systems by introducing beam-division multiple access (BDMA), which uses multiple sub-arrays in a hybrid digital-analog BS to form independent beams directed at specific users. The approach combines the orthogonal and non-orthogonal access benefits by assigning one near-far user per slot (FU aided by an IRS) and several near users (NUs) via direct beams, with a hierarchical frame structure enabling robust angle measurements and CSI scheduling. Optimization splits into reflected-beam optimization for IRS-assisted links and direct-beam optimization for NU links, yielding closed-form beamformers and IRS phase designs that maximize desired signal power while suppressing interference. Numerical results show BDMA significantly outperforms FDMA, TDMA, and NOMA in terms of sum spectral efficiency, demonstrating large gains in both moderate and large arrays, and highlighting the practical potential for high-frequency IRS-aided deployments.

Abstract

Recently, intelligent reflecting surface (IRS)-aided millimeter-wave (mmWave) and terahertz (THz) communications are considered in the wireless community. This paper aims to design a beam-based multiple-access strategy for this new paradigm. Its key idea is to make use of multiple sub-arrays over a hybrid digital-analog array to form independent beams, each of which is steered towards the desired direction to mitigate inter-user interference and suppress unwanted signal reflection. The proposed scheme combines the advantages of both orthogonal multiple access (i.e., no inter-user interference) and non-orthogonal multiple access (i.e., full time-frequency resource use). Consequently, it can substantially boost the system capacity, as verified by Monte-Carlo simulations.

Beam-Based Multiple Access for IRS-Aided Millimeter-Wave and Terahertz Communications

TL;DR

This work tackles the capacity bottlenecks of IRS-aided mmWave/THz systems by introducing beam-division multiple access (BDMA), which uses multiple sub-arrays in a hybrid digital-analog BS to form independent beams directed at specific users. The approach combines the orthogonal and non-orthogonal access benefits by assigning one near-far user per slot (FU aided by an IRS) and several near users (NUs) via direct beams, with a hierarchical frame structure enabling robust angle measurements and CSI scheduling. Optimization splits into reflected-beam optimization for IRS-assisted links and direct-beam optimization for NU links, yielding closed-form beamformers and IRS phase designs that maximize desired signal power while suppressing interference. Numerical results show BDMA significantly outperforms FDMA, TDMA, and NOMA in terms of sum spectral efficiency, demonstrating large gains in both moderate and large arrays, and highlighting the practical potential for high-frequency IRS-aided deployments.

Abstract

Recently, intelligent reflecting surface (IRS)-aided millimeter-wave (mmWave) and terahertz (THz) communications are considered in the wireless community. This paper aims to design a beam-based multiple-access strategy for this new paradigm. Its key idea is to make use of multiple sub-arrays over a hybrid digital-analog array to form independent beams, each of which is steered towards the desired direction to mitigate inter-user interference and suppress unwanted signal reflection. The proposed scheme combines the advantages of both orthogonal multiple access (i.e., no inter-user interference) and non-orthogonal multiple access (i.e., full time-frequency resource use). Consequently, it can substantially boost the system capacity, as verified by Monte-Carlo simulations.
Paper Structure (8 sections, 20 equations, 5 figures, 1 algorithm)

This paper contains 8 sections, 20 equations, 5 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model
  3. Beam-Division Multiple Access
  4. Optimization Design of BDMA
  5. Reflected Beam Optimization
  6. Direct Beam Optimization
  7. Numerical Results
  8. Conclusions

Figures (5)

  • Figure 1: Schematic diagram of an IRS-aided mmWave and THz system.
  • Figure 2: Far-field geometry of sub-array $m$.
  • Figure 3: The proposed hierarchical frame structure.
  • Figure 4: Illustration of BDMA for an IRS-aided mmWave and THz system. The signal transmission of the far users are aided by the IRS, while the near users directly access the BS. Without losing generality, this figure only shows the time shifting for two slots and the user grouping with three active users (one FU and two NUs) per slot.
  • Figure 5: Performance comparison of different multiple-access schemes in terms of CDFs of sum spectral efficiency: (a) a $64$-antenna base station with $8$ sub-arrays serving $8$ users, and (b) a $128$-antenna base station with $16$ sub-arrays serving $16$ users.