Citation: Li, S.; Kim, K. S.; Zhang, L.;
Huan, X.; Smith, J. Energy-Efficient
Message Bundling with Delay and
Synchronization Constraints in
Wireless Sensor Networks. Sensors
2022, 22, 5276. https://doi.org/
10.3390/s22145276
Academic Editors: Alvaro Araujo
Pinto and Hacene Fouchal
Received: 23 May 2022
Accepted: 11 July 2022
Published: 14 July 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
Energy-Efficient Message Bundling with Delay and
Synchronization Constraints in Wireless Sensor Networks
Sihao Li
1,2
, Kyeong Soo Kim
1,
* , Linlin Zhang
1
, Xintao Huan
3
and Jeremy Smith
2
1
School of Advanced Technology, Xi’an Jiaotong-Liverpool University (XJTLU), Suzhou 215123, China;
sihao.li19@student.xjtlu.edu.cn (S.L.); linlin.zhang18@alumni.xjtlu.edu.cn (L.Z.)
2
Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3BX, UK;
sihao.li@liverpool.ac.uk (S.L); j.s.smith@liverpool.ac.uk (J.S.)
3
School of Cyberspace Science and Technology, Beijing Institute of Technology, Beijing 100081, China;
xintao.huan@bit.edu.cn
* Correspondence: kyeongsoo.kim@xjtlu.edu.cn
Abstract:
In a wireless sensor network (WSN), reducing the energy consumption of battery-powered
sensor nodes is key to extending their operating duration before battery replacement is required.
Message bundling can save on the energy consumption of sensor nodes by reducing the number
of message transmissions. However, bundling a large number of messages could increase not only
the end-to-end delays and message transmission intervals, but also the packet error rate (PER).
End-to-end delays are critical in delay-sensitive applications, such as factory monitoring and disaster
prevention. Message transmission intervals affect time synchronization accuracy when bundling
includes synchronization messages, while an increased PER results in more message retransmissions
and, thereby, consumes more energy. To address these issues, this paper proposes an optimal message
bundling scheme based on an objective function for the total energy consumption of a WSN, which
also takes into account the effects of packet retransmissions and, thereby, strikes the optimal balance
between the number of bundled messages and the number of retransmissions given a link quality. The
proposed optimal bundling is formulated as an integer nonlinear programming problem and solved
using a self-adaptive global-best harmony search (SGHS) algorithm. The experimental results, based
on the Cooja emulator of Contiki-NG, demonstrate that the proposed optimal bundling scheme saves
up to
51.8
% and
8.8
% of the total energy consumption with respect to the baseline of no bundling
and the state-of-the-art integer linear programming model, respectively.
Keywords:
message bundling; energy efficiency; wireless sensor networks (WSNs); end-to-end delay;
time synchronization accuracy
1. Introduction
A typical wireless sensor network (WSN) consists of a head node with abundant
computing and power resources and a large number of resource-constrained, battery-
powered sensor nodes [
1
,
2
]. As the sensor nodes’ energy is strictly limited by the equipped
batteries, minimizing their energy consumption is critical to the operation of the entire
WSN; for instance, the lifetime of a WSN could be extended by up to 52% through the use
of energy-efficient transmission algorithms and protocols [3].
The number of message transmissions can be reduced by bundling several messages
together and transmitting them in a common data frame or packet [
4
,
5
]. As data transmis-
sion modules consume the most energy [
6
,
7
], message bundling is considered an efficient
technique for reducing the energy consumption of a sensor node [
8
,
9
]. However, message
bundling not only increases the end-to-end (E2E) delay, but also reduces the synchro-
nization accuracy [
10
–
14
]. Various optimal message bundling schemes that investigate
the relationship between message bundling and the E2E delay in the reduction of energy
consumption have been proposed. However, in most of the work, the message bundling is
Sensors 2022, 22, 5276. https://doi.org/10.3390/s22145276 https://www.mdpi.com/journal/sensors
