Throughput Maximization of Mixed FSO/RF UAV-Aided Mobile Relaying with a Buffer

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

Research output: Contribution to journalArticlepeer-review

51 Citations (Scopus)


In this paper, we investigate a mobile relaying system assisted by an unmanned aerial vehicle (UAV) with a finite size of the buffer. Under the buffer size limit and delay constraints at the UAV relay, we consider a dual-hop mixed free-space optical/radio frequency (FSO/RF) relaying system (i.e., the source-to-relay and relay-to-destination links employ FSO and RF links, respectively). Taking an imbalance in the transmission rate between RF and FSO links into consideration, we address the trajectory design of the UAV relay node to obtain the maximum data throughput at the ground user terminal. Specifically, we classify two relaying transmission schemes according to the delay requirements, i.e., i) delay-limited transmission and ii) delay-tolerant transmission. Accordingly, we propose an iterative algorithm to effectively obtain the locally optimal solution to our throughput optimization problems and further present the complexity analysis of this algorithm. Through this algorithm, we present the resulting trajectories over the atmospheric condition, the buffer size, and the delay requirement. In addition, we show the optimum buffer size and the throughput-delay tradeoff for a given system. The numerical results validate that the proposed buffer-aided and delay-considered mobile relaying scheme obtains 223.33% throughput gain compared to the conventional static relaying scheme.

Original languageEnglish
Article number9217992
Pages (from-to)683-694
Number of pages12
JournalIEEE Transactions on Wireless Communications
Issue number1
Publication statusPublished - 2021 Jan

Bibliographical note

Funding Information:
Manuscript received March 7, 2020; revised June 19, 2020 and August 19, 2020; accepted September 28, 2020. Date of publication October 8, 2020; date of current version January 8, 2021. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) under Grant NRF-2018R1A2B2007789. This article was presented in part at the IEEE International Conference on Communications, Shanghai, China, in May 2019. The associate editor coordinating the review of this article and approving it for publication was S. Wang. (Corresponding author: Young-Chai Ko.) Ju-Hyung Lee and Young-Chai Ko are with the School of Electrical and Computer Engineering, Korea University, Seoul 02841, South Korea (e-mail:;

Publisher Copyright:
© 2002-2012 IEEE.


  • Mixed FSO/RF communication
  • UAV-aided mobile relaying
  • buffer constraint
  • delay-considered design
  • throughput maximization

ASJC Scopus subject areas

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


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