Spectral-Efficient Network Design for High-Altitude Platform Station Networks With Mixed RF/FSO System

Ju Hyung Lee, Ki Hong Park, Young Chai Ko, Mohamed Slim Alouini

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


Integrating terrestrial networks with burgeoning high-altitude platform stations (HAPSs) will be a disruptive challenge for beyond-5G systems provisioning large-scale three-dimensional connectivity. Here, we study the problem of forwarding packets between terrestrial terminals and backhaul through multi-HAPS relaying. Considering the limited wireless backhaul, which is the practical constraint of HAPS relaying, dual-hop mixed radiofrequency/free-space optical (RF/FSO) networks are investigated, where backhaul-to-relay and relay-to-user communications employ FSO and RF links, respectively. To maximize the end-to-end network throughput, including downlink and uplink rate, we formulate the optimization problem for variables; the association between aerial and terrestrial terminals, transmit power, and deployment of multiple HAPSs, respectively. We tackle this problem using an iterative algorithm with proposed surrogate functions to efficiently obtain the locally optimal solution. Simulation results corroborate that our proposed optimal method achieves up to 11.3% spectral efficiency compared to the conventional heuristic method. Furthermore, we answer three questions; 1) what the wireless backhaul requirements are, 2) how the number of HAPSs and terrestrial terminals impact the network, and 3) what if a certain user terminal has a particular demand on data rate.

Original languageEnglish
Pages (from-to)7072-7087
Number of pages16
JournalIEEE Transactions on Wireless Communications
Issue number9
Publication statusPublished - 2022 Sept 1

Bibliographical note

Publisher Copyright:
© 2002-2012 IEEE.


  • FSO backhaul
  • HAPS
  • UAV
  • beyond-5G
  • mixed RF/FSO dual-hop transmission system
  • non-terrestrial network

ASJC Scopus subject areas

  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Applied Mathematics


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