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Impact of Pointing Errors and Correlated Wall Blockages on Practical Grid-based Indoor Terahertz Communication Systems

Zhifeng Tang, Nan Yang, Salman Durrani, Xiangyun Zhou, Josep Miquel Jornet, Markku Juntti

Abstract

Terahertz (THz) communications has emerged as a promising technology for future wireless systems due to its potential to support extremely high data rates. However, severe path loss, blockage effects, and sensitivity to beam misalignment pose major challenges to reliable indoor THz communications. In this paper, we investigate the coverage probability of downlink transmission in a three-dimensional (3D) indoor THz communication system under structured access point (AP) deployments, with a focus on square and hexagonal grid topologies. A tractable analytical framework is developed to jointly account for human blockages, correlated wall blockages across APs, beam training, and residual pointing error. Numerical results demonstrate that wall blockage correlation significantly reduces the association and coverage probabilities, and its impact cannot be neglected in system performance analysis. Compared with square grid AP deployments, hexagonal grids consistently achieve higher coverage by mitigating correlated wall blockage effects and reducing the distances between user equipments (UEs) and their associated APs. Furthermore, coverage performance is shown to strongly depend on the UE location, with noticeable degradation as the UE moves away from its nearest AP. Residual pointing error is found to introduce substantial coverage loss, especially for longer links. In addition, beam training analysis reveals a non-monotonic relationship between antenna array size and training overhead, highlighting an inherent tradeoff among antenna configuration, beamwidth selection, and beam training efficiency. These findings provide useful insights into the design and deployment of practical indoor THz communication systems.

Impact of Pointing Errors and Correlated Wall Blockages on Practical Grid-based Indoor Terahertz Communication Systems

Abstract

Terahertz (THz) communications has emerged as a promising technology for future wireless systems due to its potential to support extremely high data rates. However, severe path loss, blockage effects, and sensitivity to beam misalignment pose major challenges to reliable indoor THz communications. In this paper, we investigate the coverage probability of downlink transmission in a three-dimensional (3D) indoor THz communication system under structured access point (AP) deployments, with a focus on square and hexagonal grid topologies. A tractable analytical framework is developed to jointly account for human blockages, correlated wall blockages across APs, beam training, and residual pointing error. Numerical results demonstrate that wall blockage correlation significantly reduces the association and coverage probabilities, and its impact cannot be neglected in system performance analysis. Compared with square grid AP deployments, hexagonal grids consistently achieve higher coverage by mitigating correlated wall blockage effects and reducing the distances between user equipments (UEs) and their associated APs. Furthermore, coverage performance is shown to strongly depend on the UE location, with noticeable degradation as the UE moves away from its nearest AP. Residual pointing error is found to introduce substantial coverage loss, especially for longer links. In addition, beam training analysis reveals a non-monotonic relationship between antenna array size and training overhead, highlighting an inherent tradeoff among antenna configuration, beamwidth selection, and beam training efficiency. These findings provide useful insights into the design and deployment of practical indoor THz communication systems.
Paper Structure (16 sections, 6 theorems, 65 equations, 9 figures, 1 table)

This paper contains 16 sections, 6 theorems, 65 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. System Model
  3. System Deployment
  4. Antenna Model and Beam Training
  5. Channel Model
  6. Performance Analysis
  7. Impact of Pointing Error and Wall Blockages
  8. Coverage Analysis
  9. Beam Training Overhead
  10. Numerical Results
  11. Conclusion
  12. Proof of Lemma \ref{['Lemma:1']}
  13. Proof of Lemma \ref{['Lemma:3']}
  14. Proof of Lemma \ref{['lem:PA_exact']}
  15. Proof of Theorem \ref{['Theorem:Coverage']}
  16. ...and 1 more sections

Key Result

Lemma 1

The PDF and the CDF of pointing error loss, $f_{H_{pe}}(h_{pe})$ and $F_{H_{pe}}(h_{pe})$, are approximated as and respectively, where $\rho_1=\arcsin\left(\frac{\omega_{T}}{\sqrt{-\omega_A^2\ln h}}\right)$, $\rho_2=\frac{\sqrt{-\omega_A^2 \ln h-\omega_{T}^2}}{\omega_{T}}$, $\omega_A = \frac{1.06}{N_A}$, and $\omega_1=e^{-\omega_{T}^2/\omega_A^2}$.

Figures (9)

  • Figure 1: Illustration of the considered 3D indoor THz communication system with structured AP deployments, including square and hexagonal grid topologies.
  • Figure 2: Top and vertical views of human blockage for an AP-UE link.
  • Figure 3: Top and vertical views of the pointing error for an AP-UE link.
  • Figure 4: Illustration of the considered three locations of the typical UE, where the red point is Location 1 directly under $\mathrm{AP}_{0,0}$, the blue point is Location 3 at the farthest position from $\mathrm{AP}_{0,0}$, and the green point is Location 2 at the midpoint between red and blue points.
  • Figure 5: The PDF of the pointing error loss $f_{H_{pe}}(h_{pe})$.
  • ...and 4 more figures

Theorems & Definitions (6)

  • Lemma 1
  • Lemma 2
  • Lemma 3
  • Lemma 4
  • Theorem 1
  • Lemma 5