=Paper=
{{Paper
|id=Vol-3248/paper19
|storemode=property
|title=An Overview of Ultra-Wideband Technology and Performance Analysis of UWB-TWR in Simulation and Real Environment
|pdfUrl=https://ceur-ws.org/Vol-3248/paper19.pdf
|volume=Vol-3248
|authors=Meilin Qian,Kai Zhao,Binghao Li,Aruna Seneviratne
|dblpUrl=https://dblp.org/rec/conf/ipin/QianZLS22
}}
==An Overview of Ultra-Wideband Technology and Performance Analysis of UWB-TWR in Simulation and Real Environment==
https://ceur-ws.org/Vol-3248/paper19.pdf
An Overview of Ultra-Wideband Technology and
Performance Analysis of UWB-TWR in Simulation
and Real Environment
Meilin Qian1,* , Kai Zhao2 , Binghao Li2 and Aruna Seneviratne1
1
School of Electrical Engineering and Telecommunications, University of New South Wales (UNSW), Sydney, Australia
2
School of Minerals and Energy Resources Engineering, University of New South Wales (UNSW), Sydney, Australia
Abstract
The Ultra-wide band technology (UWB) offers the benefits of robust interference immunity and flexible
data rate at low power consumption within the short distance communication area. From a indoor
localisation/positioning perspective, UWB also beats other ranging techniques due to its high resolution
in time and space, obstacle penetration capability and fine grained ranging/localization accuracy. This
paper presents an overview of UWB related technical specifications, applications, two main transmission
techniques (i.e., Impulse Radio UWB and Frequency Modulation UWB), relative communication standards,
regulated channel distribution and commercially available UWB chips. Then it provides some insights
for several popular UWB-based ranging and positioning techniques and their corresponding advantages
and disadvantages. Finally, we briefly introduced a simulation model and a real working prototype that
highlights the high precision of UWB-TWR in distance based systems.
Keywords
Ultra-WideBand (UWB), Impulse Radio UWB (IR-UWB), Frequency-Modulation UWB (FM-UWB), Time
of Flight (TOF), Two Way Ranging (TWR), Time Difference of Arrival (TDOA), indoor positioning,
simulation
1. Introduction
As the development of wireless communications for Internet of Things (IoT), the Ultra-wide
band (UWB) technology has been recognized as a highly promising technology for short
distance communications. Compared with other wireless communication technologies, UWB
provides high energy efficiency and flexible data rates [1]. Due to its fine-grained ranging and
good obstacle penetration capabilities [2, 3], UWB also plays an important role in the field of
indoor positioning and localization services. In fact, UWB represents a wireless communication
technology that has no carrier signals. It uses very narrow pulses (i.e., non-sinusoidal pulses at
nanosecond or microsecond level) to transmit data bits over extremely wide bandwidths [4].
According to the Federal Communications Commission (FCC) regulations in 2002 [5], UWB has
to satisfy one of the following two conditions: the signal bandwidth must be at least 0.2 times
IPIN 2022 WiP Proceedings, September 5 - 7, 2022, Beijing, China
*
Corresponding author.
$ meilin.qian@unsw.edu.au (M. Qian); kai.zhao@unsw.edu.au (K. Zhao); binghao.li@unsw.edu.au (B. Li);
a.seneviratne@unsw.edu.au (A. Seneviratne)
0000-0003-0091-9116 (M. Qian)
Β© 2022 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR
Workshop
Proceedings
http://ceur-ws.org
ISSN 1613-0073
CEUR Workshop Proceedings (CEUR-WS.org)
carrier frequency, or the signal must occupy at least 500 MHz of the spectrum. Further, within
the frequency range of 3.1 GHz to 10.6 GHz, the maximum radiation power of UWB signals has
been legally stipulated to be -41.3 dBm/MHz which assumes the noise is also integrated within
the same bandwidth [6]. This is illustrated by the following Power Spectral Density (PSD) for
UWB technology with a spectrum mask limited by FCC [7] included as well, as shown in Fig. 1.
Figure 1: Typical transmitted power spectral density of UWB signal.
With the prevalence of Global Navigation Satellite Systems (GNSS) service and the growth
of outdoor positioning and navigation systems [8, 9], there is no universal solution for indoor
localization yet, despite numerous ranging/positioning methods being proposed [10]. There are
five different types of positioning technologies, ranging based, angle based, Cell ID/approximate,
fingerprinting and dead reckoning in general. Notably, ranging and angle based techniques
are both rely on precise estimation of the absolute/relative position of the unknown node
with respect to a reference node with the given location. There are five widely acceptable
distance/angle measurement methods [11, 12], namely Received Signal Strength Indicator
(RSSI), Time of Arrival (TOA) or Time Difference of Arrival (TDOA), Angle of Arrival (AOA)
and Two Way Ranging (TWR). There are still some other techniques, such as using a centroid
algorithm based on the wireless connectivity between nodes [13]. This eliminates the need
for fine granularity of localization. The inherent characteristic of UWB signal makes TDOA
and TWR become the most suitable ranging approaches for positioning/localization services,
particularly in the indoor environments [1, 14], as they can provide high accuracy and robust
immunity to multi-path fading effect at low power consumption. Although TOA and TDOA
work differently, TDOA can be implemented by two TOA measurements. This paper focused
on TWR only and more details are elaborated in section 3.
The ranging performance and positioning accuracy of UWB technology have been analyzed in
a plethora of works. However to the best of our knowledge, these studies have not been exposed
to a comprehensive performance analysis and comparison of a UWB based working prototype
and a simulation model at the same time. In our work, we do this using a TWR based UWB
positioning system. The remainder of the paper is structured as follows, we explore the inherent
signal characteristic of two transmission techniques (i.e., Impulse-Radio UWB and Frequency-
Modulation UWB) used by UWB signals in section 2. In addition, several IEEE standards that
are specified for UWB communications particularly, channel distribution regulated by FCC
and most commercially available UWB chips and their manufacturers are also included in this
section. A technical overview of two ranging based techniques (i.e., TDOA and TWR) performed
by UWB technology and corresponding applications in positioning systems can be found in
section 3. Section 4 is dedicated to evaluate the system performance of a simulation model and a
real working prototype that are both using UWB nodes as a range finder and TWR mechanism
to perform distance measurement. In the end, we wrap up with some conclusions in section 5.
2. Overview of UWB transmission techniques
2.1. Impulse Radio UWB
Impulse Radio UWB (IR-UWB) replies on the impulse radio signal generated within an extremely
short duration (i.e., sub-nanosecond level) to transmit data packets continuously. Typically,
the impulse radio signal is a high-order Gaussian pulse that occupies an ultra wide frequency
spectrum [7, 15]. This is a particular type of transmission using carrierless modulation as the
radio signal usually propagates in the originally allocated channel. There are several different
modulation schemes that can be applied to this type of baseband signal, namely Pulse Amplitude
Modulation (PAM), On-OffKeying (OOK), Pulse Position Modulation (PPM) and Pulse Shape
Modulation (PSM), Pulse Width Modulation (PWM), etc. In fact, the first four modulation
methods mentioned before are the most popular ones to be employed in the IR-UWB system. In
order to increase the interference immunity and multiple access feature to the UWB signal, the
randomising technique would be necessary to be applied and it can be categorised into two
different types, i.e., time-hopping and direct-sequence [16].
Due to the inherent signal characteristic of IR-UWB system, this transmission technique
can provide high resolution in time and space. Therefore, it can also be used by a range finder
to perform localisation with high accuracy [17]. The duty cycle of this type of UWB pulse is
normally very low and even less than 1% sometimes, which improves the energy efficiency
profoundly via intermittent operation [18]. Because of the capabilities of fine-grained ranging
and low power consumption, the IR-UWB technique has been recognised as revolutionary
advance in the area of radio communications. However, the problem of time synchronisation
between different nodes within the same wireless sensor network would be significantly affected
by its low duty cycle as well [19]. In addition, in terms of the UWB pulse generation, it is
critical to consider the balance between the peak value of the provided voltage and the signal
coverage. In details, the higher peak voltage results in the higher bit energy and the lower
communication range [20]. Due to the challenge of time synchronisation and very restrictive
UWB power limitations, the modulation approach of frequency hopping was introduced.
2.2. Frequency-Modulation UWB
The FM-UWB technique is inspired by the double frequency modulation scheme [21] that can
be divided into two different steps. One is called subcarrier generation that applies Binary
Frequency Shift Keying (BFSK) modulation method to transfer the baseband signal into an
analog triangle wave with two different carrier frequencies. The other step which is also called
radio frequency modulation is to have this triangle waveform achieve the control voltage of a
Voltage-Controlled Oscillator (VCO). The control voltage spreads out widely which makes the
output signal across a very wide frequency spectrum after modulation. Due to the feature of
constant envelop modulation, the peak value of voltage would not be very high which suits for
low-voltage applications. Unfortunately, the FM-UWB system always generates a continuous
waveform which means the duty cycle cannot be as low as IR-UWB. Thus, the energy efficiency
would be decreased significantly compared with the IR-UWB system. In order to resolve this
issue, Chen et al. [22] proposed a novel modulation scheme for UWB signal so that the frequency
modulation can be operated at certain time intervals. In addition, the data rate of FM-UWB
system is restrictedly limited because of the short duration of modulation and corresponding
low modulation index.
2.3. Comparison of IR-UWB and FM-UWB
Due to highly accurate ranging capability and good energy efficiency feature, IR-UWB has a
wider range of applications in secure mobile IoT networks. The comparison between IR-UWB
and FM-UWB has been summarised in Table 1.
Table 1
Comparison of IR-UWB and FM-UWB
Type IR-UWB FM-UWB
Signal short duration pulse Wideband FM
Energy efficiency better worse
Sensitivity worse better
Operation range better worse
Obstacle penetration
better worse
capability
multiple IR nodes
Anti-interference feature worse
work better
Low data rate,
Application high data rate, Low data rate
fine ranging
2.4. UWB standards
Based on these two different modulation schemes mentioned before, the IEEE 802.15.4a standard
proposed in 2015 defines operation mode of the physical layer for UWB signal transmission
and it integrates the benefits of fine ranging, certain penetration capability and high energy
efficiency [23, 24]. Later in 2020, the standard was upgraded to IEEE 802.15.4z to enhance
some existing functions (i.e., alleviate the time synchronisation problem) and also support more
undiscovered features, such as simultaneous ranging and encrypted communication with high
security protection via adding a Scrambled Time Sequence (STS) sequence [25, 26].
2.5. Channel distribution for UWB signal
Since UWB signal usually occupies a very broad frequency spectrum, the bandwidth must
be shared between UWB devices and other wireless technologies. Given that, UWB signal
operates in the industrial, scientific and medical (ISM) radio bands. In order to immune the
signal interference from other technologies, the FCC limits the maximum radiation power for
UWB transmission which directly affects the signal coverage or operation range that can still
achieve high resolution in localisation services. According to the legally regulated maximum
transmitted PSD, the typical UWB signal coverage is ranging from 30 to 120 metres [27, 28].
In general, the frequency spectrums allocated for UWB transmission and the maximum
transmission power vary with different countries. Fig. 2 briefly shows the UWB operation
range in several different countries [29]. Since the higher frequency aggravates the attenuation
effect of wireless signal, channel distributed over a relatively low frequency spectrum would be
preferred.
Figure 2: Frequency spectrum allowed in several different countries [29].
2.6. Commercially available UWB radio chips
Most commercially available UWB radio chips from industrial manufacturers are briefly sum-
marised in Table 2.
3. Overview of UWB ranging and positioning techniques
3.1. TWR
Essentially, UWB performs distance measurement by leveraging the Time of Flight (ToF) mech-
anism. It can be achieved by calculating the time difference of two timestamps captured
separately, before and after the UWB signal travels from one transceiver to another [30].
To be specific, the anchor sends out the first poll message to initiate the ranging request at
π‘π‘π΄π΅ . When it is received by a tag, the reply message will be generated and sent back after
a period of time from the signal reception to the generation of a new signal i.e.,π‘πππ . The
anchor receives the reply message at π‘ππ΅π΄ . Then, ToF can be calculated by using this equation,
Table 2
An overview of UWB radio chips from different manufacturers
Supplier Product name Band Standard Released Date
Decawave DW1000 3.5-6.5 GHz HRP Nov 7, 2013
Decawave DW3000 6β8.5 GHz HRP Jan 2019
NXP NCJ29D5 6β8.5 GHz HRP Nov 12, 2019
NXP SR100T 6β9 GHz HRP Sept 17, 2019
Apple U1 6β8.5 GHz HRP Sept 11, 2019
TSINGOAL TSG5162 6β8.5 GHz HRP 2019
Bespoon B-UWB-MEK1 3.25-4.75 GHz HRP Mar 2021
3 dB 3DB6830 6-8 GHz LRP N/A
UWH-1100-A-
Zebra 6.35-6.75 GHz LRP Jan 2018
00AA
ULP IR-UWB
Imec 6.2-8.2 GHz HRP N/A
radio
Microchip ATA8350 6.2-7.8 GHz LRP Feb 2021
Microchip ATA8352 6.2-8.3 GHz LRP Feb 2021
3.1-10.6 GHz
RivieraWaves
CEVA (depending on HRP Jun 2021
UWB
radio)
π‘π ππΉ = (π‘ππ΅π΄ βπ‘π‘π΄π΅
2
)βπ‘πππ
. Assume that the UWB signal transmits at the speed of light, so that
the distance between two UWB transceivers can be computed directly using the following
formula, πππ π‘ππππ = π‘π ππΉ * ππ ππππ ππ πππβπ‘ .
However, this method has a very restrictive requirement that the clocks of the transmitter
and receiver device must be synchronised which becomes a huge challenge in terms of the real
implementations. Since the UWB pulse usually takes an extremely short duration (i.e., within
the sub-nanosecond regime) to transmit, the time synchronisation obviously can hardly achieve
the same time resolution as the UWB pulse generation does. In that case, the measurement
accuracy would be sacrificed significantly (i.e.,1 nanosecond of time deviation leads to 30 cm
distance error).
To cope with the preceding time synchronisation error, TWR method with no need of time
synchronisation was proposed. TWR is almost the most common distance estimation method
that needs two UWB devices (i.e., one is the transmitter and the other one is the receiver)
to communicate with each other. Obviously, the data packets can be transmitted in both
direction, as the name suggests (i.e., Two Way Ranging). Assume we have two UWB devices
and they can be called βanchorβ and βtagβ respectively. Initially, TWR was achieved by a round
trip of travelling which means the anchor sends out the poll message and the tag replies
after the signal is successfully received, as shown in Fig. 3. Thus, ToF can be calculated by,
π‘ βπ‘
π‘π ππΉ = πππ’πππ΄ 2 πππππ¦π΅ .
However, the clock drift caused by device B may lead to a large ranging error in the end.
An alternative method was proposed to mitigate the effect of clock drift via leveraging one
more message to be transmitted from anchor to tag again, as presented in Fig. 4. It is called
Symmetric double-sided two-way ranging (SDS-TWR) scheme.
Figure 3: TWR mechanism [31].
Figure 4: Symmetric TWR mechanism [31].
Unfortunately, the performance of SDS-TWR is still affected by clock drift sometimes, and it
may also be impacted by the frequency drift occur during the crystal warm-up phase and this
potential error mainly depends on the UWB device itself. An Alternative double-sided two-way
ranging (AltDS-TWR) can be used to resolve this issue and improve the accuracy performance
[32]. In fact, the clock offset between the transmitter and receiver can also be estimated based
on the measurement of carrier frequency offset. Therefore, another approach of Single Sided
Two-Way Ranging (SS-TWR) was recommended by Decawave and it can achieve the same
accuracy as AltDS-TWR scheme [33]. The benefit of TWR mechanism is it does not require
time synchronisation but at the cost of more energy consumption for extra message exchange
compared.
Overall, all different version of TWR mechanisms can be employed for distance estimation
only. If the tag device is always moving with an unknown location and a few anchors are
deployed at fixed but different locations, the anchor can be considered as a reference node, so
that the distance between the tag and anchors can be measured respectively using the TWR
technique. Finally, the mobile tag can be localised using the trilateration algorithms.
3.2. TDOA
Unlike TWR technique that can only be used for ranging, Time Difference of Arrival (TDOA) is
a very popular positioning/localization technique [34]. TDOA is severely affected by the time
synchronisation problem of the anchors, while it has no requirement for the synchronisation
of mobile tags. TDOA technique can remain low power consumption compared with TWR
technique, since it is a one way communication approach. Assume we also have one moving
tag and four fixed anchors with reference location this time, the message sent from the mobile
tag will be received by all anchors within the communication range. The alternative way is
the anchors send the request to the mobile tag but at different time instant so that the tag can
successfully receive all these messages and obtain the location of itself. TDOA highly relies on
the fine granularity of time which implies that the clock between the anchors must be strictly
synchronised. Another advantage of this technique is the latency of a TDOA base system would
be lower than that of a TWR based system.
3.3. AoA
The Angle of Arrival (AoA) positioning technique is based on the direction of UWB signal
propagation and there are several AoA algorithms that can be compatible with this angle based
solution [35, 36, 37, 38]. The angle measurement replies on multiple antennas (i.e., antenna
array) or rotation of a single antenna, for example, Beta Phase Difference of Arrival (PDoA) Kit
provided by Decawave. We need at least two referenced nodes in the 2D domain to obtain the
intersection angle at the moving target lying in between two reference nodes. In fact, there are
two different ways to perform AoA measurement using UWB signal, and one of them is to infer
the direction of the UWB tag based on distance difference measured by the base stations, which
is similar with the TWR technique. The other one is two joint base stations share the same
time clock to calculate the arrival time difference of the same transmitted signal. Then, the AoA
of source signal can be also computed based on the relative position between two antennas
embedded on two base stations respectively. This can be regarded as a special TDOA scheme,
to some extent.
Given the inherent UWB signal characteristic of high timing resolution, it is more efficient to
incorporate the AoA measurement with ToF or other timing based localisation techniques than
using AoA only. The reason for that is AoA based UWB localization systems require pairwised
devices to make a difference.
3.4. TWR vs TDOA vs AoA
An overview of all these techniques in terms of positioning/localization service has been
presented in Table 3. Particularly, the out-of-area positioning capability can be reflected by the
positioning accuracy out of the area enclosed by the preset UWB anchors.
Table 3
Overview and comparison of positioning methods
Method TWR TDOA AOA
Accuracy High High Low
Power High Low Low
consumption
System capacity Low High High
Synchronisation No Yes No
requirement
Out-of-area
No Yes Yes
positioning
3.5. Accuracy performance analysis
The accuracy performance of all the previous ranging/positioning techniques can be affected
by several different aspects and all potential errors are summarised and organised in Fig. 5.
Figure 5: Overview of all potential ranging/positioning error in terms of the TOF, TDOA and AOA
technique performed by UWB.
β’ With respect to the algorithm selection, it is better to choose AltDS-TWR rather than
simple TWR scheme to optimise the accuracy performance.
β’ The ranging/positioning accuracy would normally be severely affected when metals are
close enough to the UWB target device.
β’ Typically, the system calibration error is determined by the quality of the UWB device
[39].
β’ During the signal propagation phase, non line of sight (NLOS) condition and fast/slow
fading might occur which depends on the actual environment [40].
β’ The synchronisation error caused by multi-user interference and malicious attacks are
usually not immutable and can be reduced via Time-Division Multiple Access (TDMA)
[41, 42], etc.
4. Performance evaluation using simulation model and physical
implementations
4.1. Functional description for the simulation model
In order to evaluate the simulation performance without going through a time-consuming
process of physical implementations, we developed a OMNET++ based network simulator
which emulates the real activity of physical UWB devices that might be moving or remain
stationary. The initial motivation to create this simulation model is to provide an easier way to
evaluate the accuracy performance of TWR and the delay performance under different system
capacities, therefore it can be used to detect obstacles and avoid collisions in the end. It is hard
to be done in reality since physical implementations usually take such a long time and need
much more efforts than simulates a network model. All essential parameters that are manually
configured in the model have been listed in Table 4. The data rate, packet size, data slot duration
and maximum transmission range are set according to the datasheet of Decawave 1000. While
the update interval is expected to be as short as possible, in order to reduce the end-to-end
delay between the transmitter and receiver nodes.
Table 4
Configurable parameters used in the simulation model
Parameter description Values
Map size 200 x 200 m
Moving speed of the vehicle node 8.3 m/s
Walking speed for the tag on 1.5 m/s
worker
Update interval 10 ms
Max transmission range 100 m
Data rate 110 kbps
Radio model 802.14.5 UWB impulse radio
Processing delay 0.25 ms
Packet size 96 bits
Data slot duration 2.084 ms
Control slot duration 0.2 ms
This model is developed on the Omnet++ platform to get higher flexibility of module design. In
general, this model emulates the real behaviour of UWB devices including time slot reservation
and distribution, and ranging data transmission when performing TWR in the practical use.
Figure 6: Structure of the network simulation model and node constitution.
As shown in Fig. 6, the simulator constructs a 2D scene with configurable length and width,
including five UWB nodes and each of these so called application nodes contains three different
layers of implementation according to UWB TWR technique. They are application layer, mac
layer and radio layer respectively. The application layer is used to generate ranging packets to
perform TWR mechanism. The mac layer is mainly for data packet encapsulation and timeframe
distribution and time slot allocation, to be more specific, a TDMA-based medium access control
protocol is used in this work. The last one is the radio layer and it is designed to convert the
message from bit by bit values to radio frequency signal. It also limits the signal transmission
and reception scheme (i.e., imposing the restriction of communication range). Overall, each
layer is represented by a compound module comprising abundant of nested submodules that are
encapsulated one by one to become the upper level module. The same principle applies to the
statistics and medium module as well. The statistics module is dedicated to capture all timing-
related data so that the overall delay can be calculated after each run of simulation activity.
In addition, the medium module gives some necessary restrictions on the signal propagation
which makes it behave like real transmission through the channel.
In terms of the timeframe structure, each frame has five control slots to be used for making
reservations for five nodes respectively and ten data slots in total. The data transmission scheme
is the all the packets that need to be transmitted have to queue in the mac layer, in which case,
an empty queue in the mac layer means there is no need of transmission at all. Oppositely,
as long as the message queue comes up with any information that needs to be sent out, the
reservation request will be made and the corresponding control slot representing the specific
node will be filled out intuitively. This helps the data slot allocation for later ranging packets to
be forwarded without interruptions.
4.2. Simulation result
As specified in the configuration file, node 0 is the anchor and the rest four nodes are considered
as tags within this application scenario. Two of the four nodes represent one moving vehicle
with a constant speed of 8.3 m/s and the rest two nodes represent two walking workers with
another constant speed of 1.5 m/s. The vehicle and the other two workers are moving towards
different directions, whereas node 0 remains stationary. The distance should be measured
between node 0 and the rest four nodes intermittently (with the update interval of 10 ms). The
ranging performance is depicted in Fig. 7.
Figure 7: Distance between node 0 and the rest 4 moving nodes.
Y-axis represents the distance result and has the unit of metre. While X-axis represents the
simulation time which starts from 0 every time when we run the simulation. The running time
is set to be 100 seconds. To obtain a clear and organised view of all measurements, we set two
different threshold to discern the βCritical Zoneβ, βWarning Zoneβ and βSafe Zoneβ in terms of
the node 0 surroundings. The brown dotted line forms the boundary between the critical zone
and warning zone, which has the distance value of 40 m. Similarly, another horizontal line in
the color of lime is set to be 80 m to separate the warning zone and safe zone. In general, the
variation of distance result entirely conforms with our expectation.
4.3. Experimental setup for the physical implementations
To scrutinise ranging accuracy of UWB based system that performs TWR mechanisms as the
distance measurement technique, Decawave 1000 was selected with an antenna embedded
inside. We developed our own UWB anchor and tags using DW1000 chipset. The aim of this
experiment is to verify the ranging performance of UWB chips in collision avoidance systems.
After detailed manual configuration, each of these device can be treated as the anchor during
the TWR process, and the other one or two devices can work as the tag.
In this work, we conducted two experiments, the only difference is the number of the tags
which can be called βTargetβ as well. In the first experiment, there is only one target device, so
called βTargetβ; however, there are two targets in the second experiment and they are βTarget 1β
and βTarget 2β respectively. In both experiments, the same ranging mechanism, SDS-TWR was
adopted by all related UWB nodes. Also, the vehicle with four nodes included always remains
stationary in both experiments, but the workers are walking around the vehicle all the time. In
that case, the tag device will be always moving.
In the real working prototype, each worker carries one UWB device, which can be called βtagβ.
It is installed on the top of the head. However, each vehicle has four UWB anchors installed at
four corners of vehicle which is nearly in the shape of a rectangular. Every time of message
exchange, the ranging result to be obtained is the distance measured between the tag and one
of the anchor on the vehicle. Within each run, the tag device will take turn to connect with
the four anchors embedded on the vehicle one by one and carry out the distance measurement
separately but in an organised way.
4.4. Experimental result
The result of the first experiment is shown in Fig. 8. In the second experiment, the distance
between Target 1 and one of the vehicle anchor is illustrated in Fig. 9. Another distance which
is measured between Target 2 and one of the vehicle anchor is depicted in Fig. 10.
Figure 8: Distance between the target and one of the vehicle anchors (1st experiment).
In all the above Figures (i.e., Figures 8 to 10), Y-axis means the measured distance intuitively
with the unit of metre and the X-axis represents the simulation running time which is reset to 0
whenever we rebuild the network. Same as the previous result section, two threshold values
of 3 m and 5 m are set to separate the critical zone and warning zone, the warning zone and
safe zone respectively. The final distance results are exactly shown as we expected in both
Figure 9: Distance between the Target 1 and one of the vehicle anchor (2nd experiment).
Figure 10: Distance between the Target 2 and one of the vehicle anchor (2nd experiment).
experiments.
5. Conclusion
In this paper, we presented an evaluation of a UWB system using TWR, through simulation and
and compared it with a prototype system. It also includes an overview of UWB related technical
information and the positioning techniques.The initial results show that UWB/TWR definitely
occupies significant superiority, both in terms of high accuracy, ease of implementation and
good energy efficiency, when tested with a widely available UWB chip-set. We believe that it
will be true for most other UWB chips. Based on these observations, it can be concluded that,
the use of UWB really provides a practical solution for indoor positioning and contributes to
a comprehensive quantum leap. In the future we intend to investigate the scalability of the
ranging based UWB system and itβs viability in the harsh environment such as underground
mines.
Acknowledgments
This paper is generated to provide background information for a research project, called "DeepIoT
β A New Hybrid Wireless IoT Platform for Underground Mines". This project received grant
funding from the Australian Government.
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