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IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 19, NO. 9, SEPTEMBER 2023
9255
Impacts of Wireless on Robot Control: The
Network Hardware-in-the-Loop Simulation
Framework and Real-Life Comparisons
Honghao Lv
, Student Member, IEEE
, Zhibo Pang
, Senior Member, IEEE
,
Koushik Bhimavarapu
, Member, IEEE
, and Geng Yang
, Member, IEEE
Abstract
—
As many robot applications become more re-
liant on wireless communications, wireless network latency
and reliability have a growing impact on robot control.
This article proposes a network hardware-in-the-loop (N-
HiL) simulation framework to evaluate the impacts of wire-
less on robot control more efficiently and accurately, and
then improve the design by employing correlation analysis
between communication and control performances. The N-
HiL method provides communication and robot developers
with more trustworthy network conditions, while the huge
efforts and costs of building and testing the entire physical
robot system in real life are eliminated. These benefits are
showcased in two representative latency-sensitive applica-
tions: 1) safe multirobot coordination for mobile robots,
and 2) human-motion-based teleoperation for manipula-
tors. Moreover, we deliver a preliminary assessment of two
new-generation wireless technologies, the Wi-Fi6 and 5G,
for those applications, which has demonstrated the effec-
tiveness of the N-HiL method as well as the attractiveness
of the wireless technologies.
Index Terms
—
5G, hardware-in-the-loop, multirobot coor-
dination, teleoperation, Wi-Fi 6, wireless control.
Manuscript received 18 October 2022; accepted 25 November 2022.
Date of publication 8 December 2022; date of current version 24 July
2023. This work was supported in part by the Swedish Foundation for
Strategic Research under Grant APR20-0023; in part by the National
Natural Science Foundation of China under Grant 51975513; in part by
the Natural Science Foundation of Zhejiang Province, China under Grant
LR20E050003; in part by the Major Research Plan of National Natural
Science Foundation of China under Grant 51890884; and in part by the
Major Research Plan of Ningbo Innovation 2025 under Grant 2020Z022.
The work of Honghao Lv was supported by the China Scholarship
Council. Paper no. TII-22-4339.
(Corresponding author: Zhibo Pang.)
Honghao Lv is with the State Key Laboratory of Fluid Power and
Mechatronic Systems, School of Mechanical Engineering, Zhejiang Uni-
versity, Hangzhou 310027, China, and also with the Department of
Intelligent Systems, Royal Institute of Technology, 114 28 Stockholm,
Sweden (e-mail: lvhonghao@zju.edu.cn).
Zhibo Pang is with the Department of Automation Technology, ABB
Corporate Research, 722 26 Vasteras, Sweden, and also with the De-
partment of Intelligent Systems, Royal Institute of Technology, 114 28
Stockholm, Sweden (e-mail: zhibo@kth.se).
Koushik Bhimavarapu is with the Department of Automation Tech-
nology, ABB Corporate Research, 722 26 Vasteras, Sweden (e-mail:
koushik.bhimavarapu@se.abb.com).
Geng Yang is with the State Key Laboratory of Fluid Power and
Mechatronic Systems, School of Mechanical Engineering, Zhejiang Uni-
versity, Hangzhou 310027, China (e-mail: yanggeng@zju.edu.cn).
Color versions of one or more figures in this article are available at
https://doi.org/10.1109/TII.2022.3227639.
Digital Object Identifier 10.1109/TII.2022.3227639
I. I
NTRODUCTION
T
HE growing wireless network technologies and the cloud
and edge computing toward Industrial 4.0 enable various
wireless-network-controlled robot platforms that are practically
applied to industrial production [1], [2]. Intuitively, wireless
networks enable higher flexibility of the robotic system and
simplify design and installation processes, and diminish mainte-
nance needs, especially for mobile robots [3], [4]. And wireless
networks make it possible to implement a remote operation,
because the controllers and actuators are deployed over a wire-
less link, such as the teleoperation of the manipulators [5],
[6]. However, wireless communication imposes challenges in
time-critical robot control scenarios, where wireless networks
involved extra latency compared to wired connection [7].
To ensure the robustness and reliability of the robotic system,
simulation and testing for the communication are required dur-
ing the design stage and deployment process of an industrial
robotic platform [8]. Introducing latency or other communi-
cation characteristics into the controller codes to imitate the
profiles of the real network is a common solution for the sim-
ulation [9]. However, the practical communication condition,
particularly the long-term stable performance of a wireless
network, is extremely difficult to be modeled and simulated
[10]. Li and Savkin [11] simulated unmanned aerial vehicle
(UAV) navigation based on the wireless sensor network using
the professional simulation software V-REP in the industrial in-
ternet of things applications. However, a stable and invulnerable
network condition is assumed in the simulation environments.
Despite the simulation method of [11] is able to do long-term
stability tests but has no generalized capabilities to evaluate
different network conditions and communication uncertainty.
The model-based simulation methods are commonly used for
validating the auto guide vehicles (AGVs) coordination, such
as in [12] and [13], while both cannot be used to evaluate the
communication uncertainty.
Hardware-in-loop (HiL) simulation refers to the simulation
technology, which simulates one part of the whole system
with computer modeling while using physical modeling or an
actual system for the other part [14]. In the past few years,
research efforts have been made in HiL simulation for robot
system design and optimization [15], [16]. Zhou et al. [14]
proposed an HiL simulation method for underwater acoustic
This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/
9256
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 19, NO. 9, SEPTEMBER 2023
TABLE I
C
OMPARISONS
B
ETWEEN THE
P
ROPOSED
A
PPROACH AND
O
THER
R
ELATED
S
IMULATION
W
ORKS FOR
R
OBOT
C
ONTROL
Fig. 1.
Diagram of the proposed network hardware-in-the-loop framework.
communication, but without applying it to robots or other
devices. Marco et al. proposed an on-ground HiL simulation
method for prevalidation and optimization of on-orbit robotic
missions. However, the technical requirements of the proposed
approach are the real-time computations and the negligible
latency given by Assumption 1 in [16]. An HiL simulation
system for manipulator control in [17] was built to improve the
system stability by deploying the self-designed PID controller.
Lamping et al. [18] worked on a multiagent UAV system based
on robot operation system (ROS), and they experimented with
control and supervision algorithms on multiple UAVs using HiL
simulation. The majority of these HiL simulation studies for
robotic applications aimed to provide a flexible and easy-to-use
interface for a controller design [19]. Markus et al. [20] from
ABB and NOKIA investigated the capabilities of 5G and LTE
for supporting industrial robotic applications using the traffic-
model-based communication simulation methods. However, the
simulation results are constrained to the specific scenario de-
fined in this article and do not have the ability to evaluate
the impact of network uncertainty. One common constraint of
HiL simulation for robotics, mechatronics, and control is the
limited modeling of the communication condition, especially
for the growing wireless network controlled robots [21]. Lv et
al. [22] presented an HiL simulation framework and conducted
a preliminary study on wireless robot control using Wi-Fi 6. But
it lacks the systematic evaluation of the network performance,
and the simultaneous correlation between communication and
controlisnotelaborated.Thesummarizedcomparisonsarelisted
in Table
I
.
To cover the gap in the literature, a network hardware-in-the-
loop(N-HiL)simulationframeworkshowninFig.
1
isdeveloped
in this article for evaluating the impacts of the wireless network
on robot control systems, considering the scalability of the net-
work interface, and the friendliness to both the communication
and robot developers in the field.
The major contributions can be summarized as follows:
1) A novel N-HiL simulation framework is proposed to
evaluate the impacts of wireless on robot control, which
provides more trustworthy results, while the huge efforts
and costs of testing the entire physical robot system in
real life are eliminated.
2) Two typical latency-sensitive robot control cases, safe
multirobot coordination and human-motion-based tele-
operation, are investigated, and the performance compar-
isons of Wi-Fi 6 and 5G wireless networks are conducted.
3) The correlation between the communication and control
is investigated using the proposed N-HiL method, and a
selection rule is given for choosing the wireless networks
LV et al.: IMPACTS OF WIRELESS ON ROBOT CONTROL
9257
Fig. 2.
Diagram of the overall methodology compared with previous
methods: (a) traditional methodology and (b) N-HiL methodology pro-
posed in this article.
with different profiles for robot control applications in the
design stage.
The rest of this article is organized as follows. In Section II, the
N-HiLframeworkisproposedandthemethodologyisdescribed.
Two case studies are presented in Section III. Sections IV and
V provide the experiments and validations of the coordination
case and teleoperation case using the N-HiL framework. Finally,
Section VI concludes this article.
II. N
ETWORK
H
ARDWARE
-
IN
-
THE
-L
OOP
F
RAMEWORK
A. Overall Methodology
The proposed N-HiL framework aims to provide a reliable
and trustworthy methodology to evaluate the impacts of wireless
on robot systems. The controller design is the essential part for
designing a robot control system, where the simulation in the de-
sign stage could provide a controller tuning according to the con-
trol performance assessment. For most robotic simulation cases
using the traditional methodologies, assumptions under ideal
communication conditions or stable networks are considered, as
shown in Fig.
2(a)
, which provides an over-optimistic network
model and an interpretable tracking behavior between the output
and command by ignoring the network-communication uncer-
tainty. Compared to the previous methods which integrate the
network modeling in the controller for simulation, the proposed
N-HiL framework injects the realistic network hardware into the
simulation as shown in Fig.
2(b)
. In addition, the control adjust-
ment is associated with the communication adjustment based on
the performance assessment both for the network and control in
the N-HiL simulation framework. Driven by the system design
from two representative use cases, the statistical evaluation met-
rics for the control and communication are proposed. The results
from the N-HiL simulation are coanalyzed to adjust the control
strategies and network strategies collaboratively, investigating
the impacts of wireless on robot control. The proposed N-HiL
framework has the following expected benefits: 1) exposing the
issues of the real wireless network condition that cannot be
mimicked by statistical modeling; 2) eliminating the efforts and
costs of building the entire physical robot system for assessment;
3) providing an effective approach for studying the interplay
between the wireless and control strategy; and 4) enabling
the long-term stability test of the communication for a robot
system.
B. System Architecture
The system architecture of the proposed N-HiL framework
includes four parts, as shown in Fig.
1
: simulated controller,
simulatedrobot platform, networksniffer hardware, andthereal-
life network environment.
The essential element of the N-HiL framework is the unob-
trusive network sniffer hardware interface deployed based on an
Ethernet multichannel probe. The sniffer interface is deployed
to connect the simulated controller and the simulated robot plat-
form. The controller includes the robot kinematic forward model
or the dynamic model, which is used to compute the discrete
high-frequency control command in real time. The simulated
robot is driven by the command transferred by the network
hardware interface. The sniffer program keeps on sniffing the
raw packet from the sniffer port continuously in real time to
capture the packets and calculate the latency of the packets as
the unobtrusive latency tester (ULT). The downstream latency
of the packets that are transmitted from source to destination
is calculated using the time stamping of destination output
DOWN_OUT minus the time stamping of source input UP_IN.
The upstream latency of the packets that are transmitted from
destination to source is calculated using the time stamping of
source output UP_OUT minus the time stamping of destination
input DOWN_IN.
The wired Ethernet and the wireless network, Wi-Fi6 and
5G, are implemented as shown in the floor plan of Fig.
1
.
In particular, three test conditions of Wi-Fi 6, short-range,
medium-range, and long-range, are set for the distance be-
tween two access point (AP) nodes (hereafter represented
as Wi-Fi 6 @ short/medium/long). The 5G station used
here is an internal industrial solution provided by Ericsson
AB. For the wired Ethernet network, the interface is con-
nected using an Ethernet cable between port DOWN_OUT
and port UP_OUT. For the wireless network framework,
the master AP of Wi-Fi 6 and the user plane function of
the 5G station are connected to port DOWN_OUT, while
the slave AP and the 5G user equipment are connected to port
UP_OUT.
III. I
MPLEMENTATION OF THE
N-H
I
L F
RAMEWORK
A. Case Study Overview
To investigate the impacts of wireless on robot control, the
corresponding case studies are conducted by deploying the
proposed N-HiL simulation framework. Two of the key concerns
for wireless robot systems in practical application are safety
and accuracy. Multirobot coordination is chosen as the first case
study, which is a representative core problem in mobile robot
fleets. Most multirobot coordination solutions assume good
communication conditions [23], [24]. The unreliable commu-
nication will lead to the delay of the real-time status update or
control command loss of each robot, which final causes collision
and unsafety [25]. The multirobot coordination does need to
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9258
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 19, NO. 9, SEPTEMBER 2023
Fig. 3.
N-HiL simulation framework for safe multirobot coordination.
deploy the test on the proposed N-HiL framework since it is a
key to pretest for avoiding collision and ensuring safety [26].
Moreover, the manipulator teleoperation is chosen as the sec-
ond test case, which is another typical communication-sensitive
robot application [27]. In order to achieve accurate and smooth
control of a multijoint manipulator remotely, the high-frequency
discrete joint commands need to be accurately transferred from
the remote side to the robot controller [28]. The packet loss
and latency introduced by the communication will change the
motion status suddenly, which will greatly affect the control
performance.
B. Case Study 1: Safe Multirobot Coordination
In this case, a centralized multirobot coordination platform
from Orebro University is deployed, in which robots are driven
by generic second-order dynamics and coordinated by heuristic
robot ordering policies [12]. As shown in Fig.
3
, the motion
planner is used to calculate the path and trajectory of each
robot. The modeling method for the coordination avoids the
need for a priority discretization of the environment and allows
robots to “follow each other” through CSs (overlap of multirobot
trajectory envelops). The coordinator decides the robot order in
the CS to avoid collisions and ensure safety. The simulated robot
forward model is driven by the motion command from the con-
troller, and the real-time multirobot motion status is displayed
in a graphical user interface. The modeling method we used
in this article has been validated formally and experimentally in
simulation and with real robots [29]. The robot trajectory tracker
tracks the robot trajectories and sends the real-time robot status
to the controller.
The controller and the robot forward model, as the simulated
robot system, are achieved by Java, running on Ubuntu 20.04 PC.
Here, two agents are designed to forward the robot command
and update the real-time robot status, as illustrated in Fig.
3
.
Agent 1 is responsible to forward the robot motion command
from the controller to the simulated robot model, which is done
over two independent UDP sockets. Agent 2 is responsible to
forward the current robot status from the driven robot model to
the controller. These two agents are programmed by Java and
deployed on a Windows 10 PC. The network hardware interface
Fig. 4.
N-HiL simulation framework for human-motion-based teleoper-
ation.
is deployed between the simulated robot and the agents. To more
closely match the real AGVs, the proposed N-HiL framework
has the feasibility to add more simulated agents with more
APs connections and add more sniffer channels to measure the
wireless network performance.
C. Case Study 2: Human-Motion-Based Teleoperation
In this case, a human–robot motion transfer teleoperation
system is deployed to evaluate the impacts of wireless using
the N-HiL framework. Here, the captured motion data from the
operator are used to control the YuMi robot. The external guide
motion (EGM) interface from ABB provides a motion control
interface with high frequency (up to 250 Hz), which enables
real-time human–robot motion mapping. As shown in Fig.
4
,
the software Axis Neuron captures human motion and sends
the data to the robot controller via ROS serial protocol from
Windows 10 to Ubuntu 20.04. The controller is responsible for
processing and converting the human motion data to robot tool
center point data using the designed mapping strategy [30]. The
robot tool center point data are used to calculate the real-time
joint configuration by the inverse kinematic solver. The motion
controller program is connected to the motion server running on
the simulated robot model via TCP protocol. The motion server
is responsible to control normal motion like linear motion and
joint motion using the given robot target.
The UDP User Communication device is defined for the task
of each arm, which receives the joint values at a high rate.
The EGM motion is activated/deactivated by the motion server.
When the EGM motion is activated, the generated joint value
queue will be sent using Google Protocol Buffers (Protobuf)
based on the UDP protocol. In this case, the communication
between the human motion capture part on the Windows 10
system and the ubuntu 20.04 is connected by Ethernet. The
network hardware interface is injected between the controller
running on a ubuntu 20.04 PC and the simulated YuMi robot
in RobotStudio on a Windows 10 PC. RobotStudio is a mature
commercial simulation software provided by ABB and has been
used for many years in the industry. It is used in this article for
simulating the YuMi robot provides the same configuration of
LV et al.: IMPACTS OF WIRELESS ON ROBOT CONTROL
9259
Fig. 5.
Hardware setup for the experiments of the above two case
studies. The different hardware settings in the red dotted box are the
options for the two case studies, respectively. Case1: safe multirobot
coordination, Case2: human-motion-based teleoperation.
the EGM interface and the IRC5 controller behavior compared
to the real robot.
IV. W
IRELESS FOR
S
AFE
M
ULTIROBOT
C
OORDINATION
To validate the reliability of the proposed N-HiL framework
compared to the previous methods, comparative experiments be-
tween the statistical modeling method and the proposed N-HiL
method are conducted. The statistical modeling model used and
compared to the N-HiL simulation results in the experimental
Section IV is following the simulation methods from [29]. And
the experiments and evaluations under the wireless network
condition are carried out, choosing the Ethernet wired network
performance as the baseline. The hardware setup for the safe
multirobot coordination case is demonstrated in Fig.
5
with
the case1 option. One NUC10 PC running the Open JDK with
Intel(R) Core(TM) i5-10210U CPU @ 1.60 GHz
×
4 processor
is set as the simulated agent. An HP Laptop PC running the
Ubuntu OS with Intel(R) Core(TM) i7-7500U CPU @ 2.70 GHz
×
4 processor is set to simulate the safe multirobot coordination
platform. The ULT PC is another HP Laptop PC to sniff the
network latency from the ET2000 probe. During the simulation
for the safe multirobot coordination case, the maximum CPU
usage case is 5.6%.
A. Experiment Design and Environment
Two practical AGV use cases from the real industry appli-
cations, harbor, and warehouse are chosen for the reliability
validations of the proposed N-HiL framework. Harbor AGV is
with a bigger size and higher moving speed, while the warehouse
is with a smaller size and lower moving speed [31]. Seven robots
are simulated for each case and the map with several obstacles is
set for each case. The collision counts are logged corresponding
to the timestamp for each test. And the collision rate
P
collision
is
calculated based on the total number of critical sections (CS) in
the test. Fig.
6
shows the collision occurrences under 5G network
conditions for the harbor AGV and warehouse AGV multirobot
coordination cases. For the simulation using the statistical mod-
eling that used a Bernoulli distribution, the packet loss rate
(PLR) of 0, 0.1, and the packet latency of 0, 10, 50, and 100 ms
Fig. 6.
Collision occurrences under 5G network conditions for the
harbor AGV and warehouse AGV multirobot coordination.
Fig. 7.
N-HiL simulation results compared with the statistical modeling
for the harbor AGV safe coordination case.
are set as the condition variables, respectively, to conduct the
simulation for both habor AGV and warehouse AGV cases. For
the simulation used in the proposed N-HiL framework, the wired
network Ethernet, the wireless network Wi-Fi 6, and 5G are
tested to evaluate the impacts of wireless on the safe multirobot
coordination. Furthermore, the experiments under the Wi-Fi 6
network condition for safe multirobot coordination are tested in
both Wi-Fi 6 @short and Wi-Fi 6 @long conditions. We clarified
that the N-HiL simulation experiments were conducted in our
laboratories with multiple functional areas for daily tests and
experiments. Most of the laboratories are related to the industrial
field with various industrial devices and equipment, such as
metal control cabinets, motors, programmable logical controller
automation equipment, heavy-duty autonomous mobile robots,
manipulators, etc., where the environment is similar to the
industrial field.
B. Results and Analysis
The experiment results of the harbor AGV case and the
warehouse AGV case are listed in Figs.
7
and
8
. From the results
of the experiment, using the statistical modeling methodology,
9260
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 19, NO. 9, SEPTEMBER 2023
Fig. 8.
N-HiL simulation results compared with the statistical modeling
for the warehouse AGV safe coordination case.
there was no collision in the 10 000 CSs test under the 50 ms
latency set for any case. For the bigger and faster harbor AGV
case, some collisions were raised when the latency is set to 100
ms. The probability of collision
P
collision
is 0.499
‰
for zero
PLR and 100 ms latency. The
P
collision
is 1.789
‰
for 0.1 PLR
and 100 ms latency. Then the simulation results using the N-HiL
framework for the harbor AGV case are listed in Fig.
7
. No col-
lision occurred for the harbor AGV case when communicating
via the Ethernet network. The
P
collision
is 0.904
‰
under the
Wi-Fi6@shortand2.299
‰
undertheWi-Fi6@longconditions.
The
P
collision
is 0.809
‰
under the 5G network condition, which
shows a better performance than Wi-Fi 6. As shown in Fig.
8
,
for the smaller and slower warehouse AGV case, no collision
happened when using the statistical modeling method. When
using the N-HiL simulation method, the
P
collision
is 0.099
‰
,
1.477
‰
, and 2.300
‰
, respectively, under the Ethernet, Wi-Fi 6
@short, and Wi-Fi 6 @long conditions. And the
P
collision
under
the 5G network connection is 0.540
‰
, which shows a better
performance than Wi-Fi 6 for the warehouse AGV case same as
the experiment results of the harbor AGV case.
For the common wireless network condition, including Wi-Fi
6 and 5G, only the latency under 50 ms is considered meaningful.
When we model the communication network using the experi-
ence parameters, even with the probability distribution model,
some uncommon factors for the network, such as congestion
or the sync problem special for certain long-term control cases
cannot be reproduced. The N-HiL simulation framework pro-
vides a more realistic network condition for evaluating the robot
control performance. Compared to the experiment results using
statistical modeling, the N-HiL framework got higher results of
P
collision
.
V. W
IRELESS FOR
H
UMAN
-M
OTION
-B
ASED
T
ELEOPERATION
The experiments in the case study of human-motion-based
teleoperation aim to evaluate the impacts of wireless on robot
control performance. Meanwhile, the correlation analysis from
the control perspective with the communication is investigated.
In this case, the human motion data are recorded and repeated
play at least 60 min for each test, where the human swings his
right arm from one side to the other side. The motion data from
the human side are sent under 125 Hz, and each test continues
for 4 h to get reliable results. Meanwhile, the comparative exper-
iments of using the raw data and the filtered data under various
network conditions are conducted to investigate the effect of
the control strategy on the network depletion from the local
controller side. The hardware setup for the human-motion-based
teleoperation case is demonstrated in Fig.
5
with the case2
option. One special HP Laptop PC running the motion capture
software Neuron Axis is used to produce the human motion data.
OneNUC10PCrunningtheROSissettosimulatethelocalrobot
controller. Another HP Laptop PC running the Robot Studio
is set to simulate the remote YuMi Robot platform. The ULT
PC is another HP Laptop PC to sniff the network latency from
the ET2000 probe. During the simulation for the teleoperation
simulation case in Robot Studio, the maximum CPU usage
is 18.3%. To guarantee the time synchronization among the
multiple computers, we set up a network time protocol (NTP)
server between the ULT PC and the other PCs (including the
simulated controller PC and the simulated robot platform PC).
All the network setup in this work is the local area network,
and the NTP server can provide better than 1-ms accuracy to
synchronize the time, which satisfies the time synchronization
requirements in this article.
A. Comparisons of Wireless Networks
Compared to the wired network Ethernet, four wireless net-
work conditions are implemented in this case to evaluate the
impacts of the wireless on robot motion control performance,
including Wi-Fi 6 with three range-level coupled APs and 5G.
To evaluate the performance of the networks, the latency
L
is
logged using the unobtrusive network sniffer. Moreover, the nor-
malized probability density function (PDF) and complementary
cumulative distribution function (CCDF) of
L
for each test are
calculated and compared from a statistical perspective. Fig.
9
displays the wireless network conditions of Wi-Fi 6 and 5G
using the PDF and CCDF. It shows an obvious different profile
between Wi-Fi 6 and 5G, where the CCDF curves of Wi-Fi6
show “short-head-long-tail” (SHLT) and CCDF curves of 5G
show “long-head-short-tail” (LHST). In 5G, radio transmissions
are carefully scheduled into specified resource blocks within
given time frames by base station, thus the latency is more
bounded. In Wi-Fi 6, however, the transmissions are based on
carrier-sense multiple access with collision avoidance, thus there
are more chances that the device needs to wait for some time
before the packet can be transmitted, which results in a shorter
head and longer tail in the latency distribution.
B. Intuitive Comparison of Control Performance
To analyze the correlation between robot motion and the com-
munication of the network, some key metrics are selected and
defined for the human-motion-based teleoperation case study.
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LV et al.: IMPACTS OF WIRELESS ON ROBOT CONTROL
9261
Fig. 9.
Network performance analysis of Wi-Fi 6 and 5G network
conditions recorded in the experiments. (a)–(d) are the PDF and CCDF
curves of the network downstream latency; (e)–(h) are the PDF and
CCDF of the network upstream latency.
The desired joint position (the commands sent from the re-
mote side) values are defined as
J
d
, while the measured joint
values (feedback of the real joint states) are defined as
J
r
.
J
d
and
J
r
are time-series signals, which are logged corresponding to the
system timestamp with a sample rate of 500 Hz.
The timestamps between the peaks of
J
d
and
J
r
are compared
and subtracted as the motion delay
τ
by (1), and the motion
delay sequence
τ
of all periods in one test is given by (2)
ˆ
τ
i
= arg
max
t
∈
N
i
J
r
(
t
)
−
arg
max
t
∈
N
i
J
d
(
t
)
(1)
ˆ
T
=
ˆ
τ
1
ˆ
τ
2
· · ·
ˆ
τ
P
(2)
where
i
=
{
1
,
2
,
3
, . . . , P
,
}
and
N
i
denotes the
i
th period
of the repeated motion.
The cross-correlation between
J
d
and
J
r
is calculated follow-
ing (3) and the average motion delay
¯
T
is given by (4)
ˆ
R
J
d
J
r
(
m
) =
∑
N
−
m
−
1
n
=
0
J
d
n
∗
+
mJ
r
n
∗
,
m
≥
0
,
ˆ
R
∗
JrJd
(
−
m
)
,
m <
0
.
(3)
¯
T
=
arg
max
m
∈
[
−
T
2
,
T
2
]
ˆ
R
JdJr
(
m
)
.
(4)
Fig. 10.
Intuitive comparison for motion delay
τ
and peak amplitude
error
ε
peak
under Ethernet, Wi-Fi 6, and 5G network conditions, using
raw data and the filtered data.
In order to evaluate the remote-control performance of the
teleoperation, the absolute errors between the peaks of desired
joint values
J
d
and the measure joint values
J
r
are calculated as
the peak amplitude error
ε
peak
by (5), and the peak amplitude
error sequence
E
peak
is defined by (6)
ˆ
ε
peak
i
= max
t
∈
N
i
J
r
(
t
)
−
max
t
∈
N
i
J
d
(
t
)
(5)
ˆ
E
peak
=
ˆ
ε
peak
1
ˆ
ε
peak
2
· · ·
ˆ
ε
peak
P
.
(6)
Further, the average peak amplitude error
E
peak
are calculated
as
E
peak
=
mean
ˆ
E
peak
=
∑
P
1
ˆ
ε
peak
p
P
.
(7)
Corresponding to the network analysis, the above evaluation
metrics of robot motion, the robot motion delay
τ
, and peak
amplitude error
ε
peak
, are also statistically analyzed toward the
network latency
L
.
More intuitive results of the motion delay
τ
and the peak
amplitude error
ε
peak
from the robot motion perspective is shown
in Fig.
10
. The robot motion indicators under the Ethernet
condition are chosen as the baseline, and the robot motion
performance using the raw data and the filtered data is analyzed
under four wireless network conditions. From Fig.
10(a)
and
(b)
, the wireless network leads to a larger
ε
peak
, which means
decreasing the accuracy of robot control. Further, it is clear in
Fig.
10(c)
and
(d)
that the filter reduces the
ε
peak
, improving
the accuracy, but introducing an additional delay. In order to
prove the validity of the simulated YuMi robot model in Robot
Studio, we implemented the same control framework on the real
YuMi robot using Ethernet and compared the key metrics of the
control performance with the N-HiL simulation experiments.
The results on the real YuMi robot show the average motion
delay
¯
T
of 0.3174 s and the average peak amplitude error
E
peak
9262
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 19, NO. 9, SEPTEMBER 2023
Fig. 11.
Statistical analysis of robot motion performance under the four
wireless conditions compared to Ethernet, using the raw data: (a)–(d)
are the PDF curves of the motion delay; (e) is the CCDF comparison of
the motion delay; (f)–(i) are the PDF curves of the peak amplitude error;
(j) is the CCDF comparison of the peak amplitude error.
of 1.9755°, which is consistent with the N-HiL simulation results
under the Ethernet condition.
C. Impacts of Wireless to Control Performance
For the motion delay
τ
of the robot, the PDF curves un-
der the wireless network conditions compared to the Ethernet
condition are shown in Fig.
11(a)
–
(d)
.
It is clearly shown
that the motion delay under the 5G network condition and
the three Wi-Fi 6 network conditions are almost at the same
level while using the raw data. For the peak amplitude error
ε
peak
, the corresponding PDF curves are listed in Fig.
11(f)
–
(i)
.
Fig. 12.
Statistical analysis of robot motion performance under the four
wireless conditions compared to Ethernet, interacting with the control
strategy by deploying a filter on robot controller: (a)–(d) are the PDF
curves of the motion delay; (e) is the CCDF comparison of the motion
delay; (f)–(i) are the PDF curves of the peak amplitude error; and (j) is
the CCDF comparison of the peak amplitude error.
Furthermore, the CCDF curves of motion delay and peak am-
plitude error are calculated and plotted in Fig.
11(e)
and
(j)
. For
the motion delay, the righter the CCDF curve, the greater the
motion delay. For the peak amplitude error, the righter CCDF
curve means the smaller error (negative values). In Fig.
11(e)
,
the motion delays under the Wi-Fi 6 condition are smaller
than that under the 5G network condition, which shows the
advantage of Wi-Fi 6 compared to 5G in this situation for the
high response. In Fig.
11(j)
, the errors under wireless network
conditions are obviously larger compared to the wired Ethernet
condition, and the 5G has smaller errors compared to all Wi-Fi 6
conditions.
LV et al.: IMPACTS OF WIRELESS ON ROBOT CONTROL
9263
Fig. 13.
Representative test showing how the robot motion performance is affected by sudden changes in network conditions: (a) network
downstream and upstream latency of part1 in this test; (b) overall performance of the robot motion and network; and (c) network downstream
and upstream latency of part 2 in this test.
D. Interplay Between the Wireless and Control Strategy
Afterimplementingalow-passfilterontheEGMinterface,the
differences betweenthemotiondelayunder the5G andtheWi-Fi
6aremagnified,whichisreasonableduetotheconvolutionofthe
filter in the control loop. From Fig.
12(a)
–
(d)
, the motion delay
using the raw data under the Wi-Fi 6 @long condition is larger
than in the Wi-Fi 6 @short and Wi-Fi 6 @medium conditions.
And motion delay under a 5G connection is larger than all Wi-Fi
6 conditions. This shows that the motion delay under 5G network
conditions is more sensitive to network latency compared to
Wi-Fi 6. The peak amplitude errors under the wireless conditions
using the filtered data are shown in Fig.
12(f)
–
(i)
, where the
ε
peak
under the 5G network condition and the three Wi-Fi 6 network
conditions are almost at the same level as wired Ethernet. By
comparing the CCDF curves in Fig.
12(e)
using the filtered
data to Fig.
11(e)
using raw data, it is obviously shown that
the implemented filter on the robot side increased the motion
delay under all network conditions, especially the 5G and Wi-Fi
6 @long. By comparing Fig.
12(j)
with Fig.
11(j)
, it is clear that
the filter works, reducing the errors introduced by the wireless
to a level that rivals the performance of wired Ethernet.
E. Impacts of Wireless Network Fluctuation
Fig.
13
shows a test with wireless fluctuation, which aims to
investigate the impacts of the wireless network fluctuation on the
robot control. The wireless condition is changed by involving
extra AP connections with the same radio band, where the test is
separated into part 1 and part 2. In Fig.
13(b)
, it is obvious that the
latency increased in part 2 after introducing radio interference.
This fact also can be proved by the statistical analysis of the
latency
L
forbothupstreamanddownstreaminFig.
13(a)
and
(c)
,
where the CCDF curves have a “longer tail” in part 2 compared
to part 1. The “longer tail” of CCDF means larger latency.
TABLE II
C
OMPARISONS OF
W
IRELESS
P
ROFILES
W
ITH
C
ONTROL
S
TRATEGIES
Corresponding to network performance, the motion delay
¯
T
in
Fig.
13(b)
is increased obviously due to the increased network
latency in part 2.
F. Future Perspectives
Last but not the least, we hope to give some directional
recommendations and suggestions for robot developers and
communication developers in the field so that they can get the
most benefits from the efforts of both sides through the so-called
“control-communication co-design.” From the comparisons in
Figs.
11
and
12
, we can observe that the communication strate-
gies (i.e., wireless network with LHST or SHLT profile) and
control strategies (i.e., using the filter or not) may have opposite
impacts on different control expectations (i.e., responsiveness
or accuracy), as summarized in Table
II
.
1) If users emphasize the control responsiveness, we rec-
ommend disabling the filter in control and choosing the
wireless network with an SHLT profile. In this combi-
nation, the latencies introduced by the control filter and
wireless network are both reduced, with the expense of
low control accuracy.
2) If users emphasize the control accuracy, we recommend
enabling the filter in control and choosing the wireless
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IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 19, NO. 9, SEPTEMBER 2023
network with a LHST profile. In this combination, the la-
tency of the wireless network is longer but more bounded
(i.e., smaller tail), which is beneficial to reducing control
error,andthefilterincontrolcanfurtherreducethecontrol
error caused by the network latency.
Since it is only verified in limited test cases, these recommen-
dations are preliminary. In the future, we will further investigate
some data-driven and even reinforcement learning methods so
that the robot control system can “negotiate” with the commu-
nication infrastructure to achieve the best tradeoffs, especially
when there are multiple objectives to be optimized. Moreover,
current tuning on the robot local controller only involved a
low-pass filter, which is just a small step towards the “control
communication co-design.” In future article, we will employ
more advanced control methods, such as the time-domain pas-
sivity approaches in the N-HiL framework.
VI. C
ONCLUSION
In this article, we propose a novel N-HiL simulation frame-
work to effectively and efficiently investigate the impacts of
wireless on robot control under real network conditions. Two
representative robot applications, which are sensitive to com-
munication latency, safe multirobot coordination, and human-
motion-based teleoperation, are investigated using the proposed
N-HiL framework. The Wi-Fi 6 and 5G wireless networks are
tested and compared, drawing the network profiles of SHLT
and LHST with the CCDF curves. Results show that the
proposed N-HiL framework provides more trustworthy results
compared to the statistical modeling method while eliminating
the huge efforts and costs of building and testing the entire
physical robot system in real life. From the statistical analysis
of the wireless latency and the robot motion performances, a
preliminary answer is drawn on how the wireless networks
affect robot control. Furthermore, the interplay between the
wireless and the control strategy is investigated by comparing
the robot control performances under the wireless with different
latency profiles. The experiment results will be helpful for both
robot developers and communication developers to find the best
tradeoffs between costs and performances.
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Honghao Lv
(Student Member, IEEE) received
the B.E. degree in mechanical engineering from
the China University of Mining and Technology,
Xuzhou, China, in 2018. He is currently working
toward the Ph.D. degree in mechatronic engi-
neering with the School of Mechanical Engi-
neering, Zhejiang University, Hangzhou, China.
He was with the School of Electrical Engineer-
ing and Computer Science, KTH Royal Institute
of Technology, Stockholm, Sweden, as a joint
Ph.D. Student, from 2021 to 2022, under the
financial support from the China Scholarship Council. He developed
dual-arm robotic teleoperation systems based on the motion capture
techniques. He worked on mobile robotics, multirobot coordination, and
network hardware-in-the-loop simulation as a Guest Researcher with
the ABB Corporate Research, Västerås, Sweden. His research interests
include dual-arm robotic teleoperation, human–robot intelligent inter-
face, and safe interaction.
Zhibo Pang
(Senior Member, IEEE) received
MBA degree in innovation and growth from the
University of Turku, Turku, Finland, in 2012, and
the Ph.D. degree in electronic and computer
systems from the KTH Royal Institute of Tech-
nology, Stockholm, Sweden, in 2013.
He is currently a Senior Principal Scientist
with the ABB Corporate Research Sweden,
Västerås, Sweden, and an Adjunct Professor
with the University of Sydney, Camperdown,
NSW, Australia, and the KTH Royal Institute of
Technology. He works on enabling technologies in electronics, com-
munication, computing, control, artificial intelligence, and robotics for
Industry4.0 and Healthcare4.0.
Dr. Pang is a Member of IEEE IES Industry Activities Committee and
a Co-Chair of the Technical Committee on Industrial Informatics. He is
an Associate Editor of IEEE TII, IEEE JBHI, and IEEE JESTIE. He was
General Chair of IEEE ES2017, General Co-Chair of IEEE WFCS2021,
and Invited Speaker at the Gordon Research Conference AHI2018. He
was the recipient of the “Inventor of the Year Award” by ABB Corporate
Research Sweden, three times in 2016, 2018, and 2021, respectively.
Koushik
Bhimavarapu
(Member, IEEE) re-
ceived the B.Tech. degree in electronics and
communication engineering from the Jawahar-
lal Nehru Technological University, Hyderabad,
India, in 2020, and the M.Sc. degree in electri-
cal engineering with emphasis on telecommu-
nication systems from the Blekinge Institute of
Technology, Karlskrona, Sweden, in 2022.
He is currently working as an Associate Sci-
entist on industrial automation with the ABB
Corporate Research Center, Västerås, Sweden.
His research interests include industrial wireless communication net-
works, internet of things, cloud computing, low-latency communication,
and time-sensitive networking.
Geng Yang
(Member, IEEE) received the B.E.
and M.Sc. degrees in instrument science and
engineering from the College of Biomedical
Engineering and Instrument Science, Zhejiang
University (ZJU), Hangzhou, China, in 2003 and
2006, respectively, and the Ph.D. degree in elec-
tronic and computer systems from the Depart-
ment of Electronic and Computer Systems, the
Royal Institute of Technology (KTH), Stockholm,
Sweden, in 2013.
From 2013 to 2015, he was a Postdoctoral
Researcher with the iPack VINN Excellence Center, School of Informa-
tion and Communication Technology, KTH. He is currently a Professor
with the School of Mechanical Engineering, ZJU. His research interests
include bioinspired flexible and stretchable sensors for robot sensing
and human–robot interaction, focusing on key enabling technologies for
Human-Cyber-Physical-System and Healthcare 4.0.
Dr. Yang is the Associate Editor of IEEE J
OURNAL OF
B
IOMEDICAL AND
H
EALTH
I
NFORMATICS
and
Bio-Design and Manufacturing
.
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Elements Of Electromagnetics
Mechanical Engineering
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Oxford University Press

Mechanics of Materials (10th Edition)
Mechanical Engineering
ISBN:9780134319650
Author:Russell C. Hibbeler
Publisher:PEARSON

Thermodynamics: An Engineering Approach
Mechanical Engineering
ISBN:9781259822674
Author:Yunus A. Cengel Dr., Michael A. Boles
Publisher:McGraw-Hill Education

Control Systems Engineering
Mechanical Engineering
ISBN:9781118170519
Author:Norman S. Nise
Publisher:WILEY

Mechanics of Materials (MindTap Course List)
Mechanical Engineering
ISBN:9781337093347
Author:Barry J. Goodno, James M. Gere
Publisher:Cengage Learning

Engineering Mechanics: Statics
Mechanical Engineering
ISBN:9781118807330
Author:James L. Meriam, L. G. Kraige, J. N. Bolton
Publisher:WILEY
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