Citation: Tran, H.P.; Jung, W.-S.; Yoo,
D.-S.; Oh, H. Design and
Implementation of a Multi-Hop
Real-Time LoRa Protocol for
Dynamic LoRa Networks. Sensors
2022, 22, 3518. https://doi.org/
10.3390/s22093518
Academic Editor: Carles Gomez
Received: 14 March 2022
Accepted: 3 May 2022
Published: 5 May 2022
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Article
Design and Implementation of a Multi-Hop Real-Time LoRa
Protocol for Dynamic LoRa Networks
Huu Phi Tran
1
, Woo-Sung Jung
2
, Dae-Seung Yoo
2
and Hoon Oh
1,
*
1
Department of Electrical, Electronic and Computer Engineering, University of Ulsan, Ulsan 680-749, Korea;
huuphi.tran88@gmail.com
2
Electronics and Telecommunications Research Institute, Daejeon 305-350, Korea; woosung@etri.re.kr (W.-S.J.);
ooseyds@etri.re.kr (D.-S.Y.)
* Correspondence: hoonoh@ulsan.ac.kr
Abstract:
Recently, LoRa (Long Range) technology has been drawing attention in various applications
due to its long communication range and high link reliability. However, in industrial environments,
these advantages are often compromised by factors such as node mobility, signal attenuation due to
various obstacles, and link instability due to external signal interference. In this paper, we propose a
new multi-hop LoRa protocol that can provide high reliability for data transmission by overcoming
those factors in dynamic LoRa networks. This study extends the previously proposed two-hop real-
time LoRa (Two-Hop RT-LoRa) protocol to address technical aspects of dynamic multi-hop networks,
such as automatic configuration of multi-hop LoRa networks, dynamic topology management,
and updating of real-time slot schedules. It is shown by simulation that the proposed protocol
achieves high reliability of over 97% for mobile nodes and generates low control overhead in topology
management and schedule updates. The protocol was also evaluated in various campus deployment
scenarios. According to experiments, it could achieve high packet delivery rates of over 97% and
95%, respectively, for 1-hop nodes and 2-hop nodes against node mobility.
Keywords:
multi-hop LoRa protocol; dynamic network; mobility; real-time scheduling; reliable
transmission
1. Introduction
Recently, interest in LoRa networks has been increasing due to the absence of an
industrial IoT network capable of reliable data transmission at a low price. In keeping
with this need, remarkable research progress has been made on industrial multi-hop LoRa
networks by enabling reliable real-time data transmission and supporting a wide area with
many nodes with the use of a slot scheduling-based data transmission method [
1
]. However,
in industrial applications supporting worker safety, real-time machine management, etc.,
LoRa terminals (nodes) can be attached to mobile equipment or carried by workers. This
requires a data transmission protocol for dynamic multi-hop LoRa networks. However,
designing a reliable and real-time data transmission protocol in a dynamic multi-hop LoRa
network is a challenge because it involves topology maintenance in a slot scheduling-based
approach. This problem gets worse in LoRa networks with a low data rate and a high
probability of message collisions.
So far, many studies designed to deal with reliable data transmission in dynamic
wireless networks have been conducted under three areas of communication technology:
cellular networks, wireless sensor networks (WSNs), and low-power wide-area networks
(LPWANs). The cellular network has the advantage of reliably collecting data while cover-
ing a wide area and can easily support node mobility because it uses a simple star topology
and operates at high bandwidth. However, when a node enters a wireless communication
shadow area, it suffers from reduced reliability of data transmission and high energy con-
Sensors 2022, 22, 3518. https://doi.org/10.3390/s22093518 https://www.mdpi.com/journal/sensors
