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Enhancing Next-Generation Urban Connectivity: Is the Integrated HAPS-Terrestrial Network a Solution?

Afsoon Alidadi Shamsabadi, Animesh Yadav, Halim Yanikomeroglu

TL;DR

The paper addresses interference and spectrum sharing in a HAPS-terrestrial vHetNet by formulating a max-min fairness optimization to maximize the network's minimum spectral efficiency, using a joint design of user association and MIMO beamforming, solved with Reformulation-Linearization Techniques and successive convex approximation to yield a tractable SOCP subproblem. The backhaul constraint is incorporated, and the proposed JUBD algorithm converges to a stationary point. Numerical results in urban hotspot scenarios show that vHetNets with optimized beamforming and user association outperform standalone terrestrial networks, with gains increasing as the HAPS antenna array grows and when multi-BS association is allowed. Overall, the work demonstrates the viability of HAPS-enabled vHetNets for 6G and beyond and points to future ML-driven interference management directions.

Abstract

Located in the stratospheric layer of Earth's atmosphere, high altitude platform station (HAPS) is a promising network infrastructure, which can bring significant advantages to sixth-generation (6G) and beyond wireless communications systems by forming vertical heterogeneous networks (vHetNets). However, if not dealt with properly, integrated networks suffer from several performance challenges compared to standalone networks. In harmonized spectrum integrated networks, where different tiers share the same frequency spectrum, interference is an important challenge to be addressed. This work focuses on an integrated HAPS-terrestrial network, serving users in an overlapped urban geographic area, and formulates a fairness optimization problem, aiming to maximize the minimum spectral efficiency (SE) of the network. Due to the highly nonconvex nature of the formulated problem, we develop a rapid converging iterative algorithm that designs the multiple-input multiple-output (MIMO) beamforming weights and the user association scheme such that the propagated inter- and intra-tier interference is managed. Simulation results demonstrate the proposed algorithm's superiority over standalone terrestrial networks and scenario where only the beamforming weights are optimized.

Enhancing Next-Generation Urban Connectivity: Is the Integrated HAPS-Terrestrial Network a Solution?

TL;DR

The paper addresses interference and spectrum sharing in a HAPS-terrestrial vHetNet by formulating a max-min fairness optimization to maximize the network's minimum spectral efficiency, using a joint design of user association and MIMO beamforming, solved with Reformulation-Linearization Techniques and successive convex approximation to yield a tractable SOCP subproblem. The backhaul constraint is incorporated, and the proposed JUBD algorithm converges to a stationary point. Numerical results in urban hotspot scenarios show that vHetNets with optimized beamforming and user association outperform standalone terrestrial networks, with gains increasing as the HAPS antenna array grows and when multi-BS association is allowed. Overall, the work demonstrates the viability of HAPS-enabled vHetNets for 6G and beyond and points to future ML-driven interference management directions.

Abstract

Located in the stratospheric layer of Earth's atmosphere, high altitude platform station (HAPS) is a promising network infrastructure, which can bring significant advantages to sixth-generation (6G) and beyond wireless communications systems by forming vertical heterogeneous networks (vHetNets). However, if not dealt with properly, integrated networks suffer from several performance challenges compared to standalone networks. In harmonized spectrum integrated networks, where different tiers share the same frequency spectrum, interference is an important challenge to be addressed. This work focuses on an integrated HAPS-terrestrial network, serving users in an overlapped urban geographic area, and formulates a fairness optimization problem, aiming to maximize the minimum spectral efficiency (SE) of the network. Due to the highly nonconvex nature of the formulated problem, we develop a rapid converging iterative algorithm that designs the multiple-input multiple-output (MIMO) beamforming weights and the user association scheme such that the propagated inter- and intra-tier interference is managed. Simulation results demonstrate the proposed algorithm's superiority over standalone terrestrial networks and scenario where only the beamforming weights are optimized.
Paper Structure (5 sections, 11 equations, 4 figures, 1 table, 1 algorithm)

This paper contains 5 sections, 11 equations, 4 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. Problem Relaxation and Proposed Algorithm
  4. Numerical Results
  5. Conclusion

Figures (4)

  • Figure 1: Network architecture.
  • Figure 2: Convergence behaviour of the proposed Algorithm \ref{['alg:alg1']}.
  • Figure 3: Statistical behavior of minimum spectral efficiency. Scenario 1: vHetNet (4 MBSs + HAPS) using JUBD Algorithm. Scenario 2: vHetNet (4 MBSs + HAPS) beamforming optimization with max-SINR based user association. Scenario 3: Standalone terrestrial network (4 MBSs) using JUBD Algorithm. Scenario 4: Standalone terrestrial network (5 MBSs) using JUBD Algorithm. Scenario 5: vHetNet (4 MBSs + HAPS) using JUBD Algorithm with multiple base station association.
  • Figure 4: Probability distribution of UEs associated with HAPS.