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Dror, E., Jianye Z., Sacks, R., Seppänen, O. (2019). “Indoor Tracking of Construction Workers Using BLE:
Mobile Beacons and Fixed Gatewayes vs. Fixed Beacons and Mobile Gateways.” In: Proc. 27th Annual
Conference of the International. Group for Lean Construction (IGLC), Pasquire C. and Hamzeh F.R. (ed.),
Dublin, Ireland, pp. 831-842. DOI: https://doi.org/10.24928/2019/0154. Available at: <www.iglc.net>.
831
INDOOR TRACKING OF CONSTRUCTION
WORKERS USING BLE: MOBILE BEACONS
AND FIXED GATEWAYS VS. FIXED BEACONS
AND MOBILE GATEWAYS
Erez Dror
1
, Jianyu Zhao
2
, Rafael Sacks
3
and Olli Seppänen
4
ABSTRACT
Automatic resource location monitoring in construction projects empowers managers to
make data driven decisions that improve project workflow. Monitoring data can be
processed to measure workflow quality and thus for better understanding of effectiveness
and efficiency. We compare two methods for deployment of Bluetooth Low Energy (BLE)
beacons for indoor resource monitoring - mobile beacons and fixed gateways (MB) vs.
fixed beacons and mobile gateways (FB). BLE beacons can be fixed to walls or carried by
workers, and can be fixed to material containers and equipment. Using gateways, such as
raspberry pi computers or smartphones, one can easily and automatically monitor resource
locations. Several field experiments were conducted, both in the laboratory and in
construction sites in Finland, Israel, Peru, Netherlands and China. Technical aspects such
as setup, direct cost, feasibility and accuracy were compared for two methods - mobile
beacons and fixed gateways vs. fixed beacons and mobile gateways - and the performance
of each method in providing the data needed for lean construction workflow assessment
was assessed. Both methods are effective in monitoring resource locations but differ in
their feasibility of implementation in construction sites and in the utility of the data they
provide in terms of identifying value adding activities.
KEYWORDS
Gateways, beacons, Bluetooth Low Energy (BLE), lean construction, waste, situational
awareness, indoor positioning
1
MSc graduate, Faculty of Civil and Enviromental Engineering, Technion - Israel Institute of Technology,
Haifa Israel, +972 54 717 0019, erezdror@gmail.com
2
Doctoral candidate, Department of Civil Engineering, Aalto University, Espoo Finland, +358
50 3394574, jianyu.zhao@aalto.fi
3
Professor, Faculty of Civil and Enviromental Engineering, Technion - Israel Institute of Technology,
Haifa Israel, +972 4 829 3190, cvsacks@technion.ac.il
4
Professor of Practice, Department of Civil Engineering, Aalto University, Espoo Finland, +358 50 368
0412, olli.seppanen@aalto.fi
Dror, E., Jianye Z., Sacks, R., Seppänen, O.
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Proceedings IGLC – 27, July 2019, Dublin, Ireland
INTRODUCTION
The real-time location of labour, material and equipment is important information for site
managers and safety managers and enables efficient production planning and work
efficiency assessment. However, given the complexity of construction sites and the
expense of gathering information, construction managers often make decisions with very
limited certainty. Lean construction tools and methods such as the Last Planner System,
visual management, Plan-Do-Check-Act, waste identification and workflow assessment
are already widespread in construction sites, but their full potential remains unrealized due
to limited ability to assess the real status and performance on construction sites. Collecting
data manually is time consuming and inefficient (Navon and Sacks 2007) and therefore
construction managers are forced to make their decisions based on gut feeling or past
experience instead of real-time data (Sacks et al. 2013).
IoT and other technologies enable real-time tracking of labour, material and equipment
and might be suitable for the complex environment of construction sites. There are several
solutions for indoor resource monitoring, including Bluetooth Low Energy (BLE), radio
frequency identification (RFID), Ultra-wideband (UWB), laser scanning, videogrammetry
and more. The solution must be easy to deploy, provide efficient and accurate location
monitoring and be cost effective. The IoT technology chosen for examination in this paper
is BLE beacons. A BLE monitoring system includes four components: BLE beacons, a
gateway, a web service and cloud-based storage. The authors examined two methods of
deployment of such beacons and gateways - mobile beacons and fixed gateways (MB) vs.
fixed beacons and mobile gateways (FB) in the field on construction sites in Finland, Israel,
Peru, the Netherlands and China. The research questions we sought to answer were:
Do the MB or FB methods enable effective and efficient tracking the locations of
resources, such as labour, material and equipment?
What are the advantages and disadvantages of each of the methods?
LITERATURE REVIEW
Production control has been developed over years within the scope of lean construction
(Koskela, 1992). For example, the Last Planner System (Ballard, 2000) and Location-
Based Management System (Kenley & Seppänen 2010), together with their integration (e.g.
Seppänen et al., 2010), have led to positive progress in operations management in
construction. Their success has been successfully recorded in many case studies around the
world (Seppänen et al., 2015). These methods have been tested to improve resource
efficiency through onsite waste elimination (Ballard, 2000) and to shorten project durations
thanks to production control and forecasting (Seppänen et al, 2014).
In order to coordinate the complex flows of labour, materials, space, equipment and
products (Sacks, 2016, Golovina, 2016), the construction industry needs innovative
management processes and software that exploit automated information collection and
intelligent data processing (Sacks et al. 2010, Nath et al., 2015). Production control
methods in construction used to rely heavily on social processes and manual input
Indoor Tracking of Construction Workers Using BLE: Mobile Beacons and Fixed Gatewayes vs. Fixed
Beacons and Mobile Gateways.
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Information Technology in Construction
(Pradhananga, 2013), but this resulted in human errors and inaccuracy (Costin et al., 2012),
which prevent fulfilment of the prospects of lean construction philosophy (Vieira, 2016).
There is a need to develop an intelligent real-time platform where all resources can be
tracked and analysed to support labour management (Lin et al., 2013), and automate the
data recording process (Costin et al., 2012).
Many technologies have been applied for resource tracking in construction, such as
passive RFID (Costin et al., 2012), ZigBee (Liu et al., 2007), BLE (Zhao et al., 2017),
(Dror, 2018), magnetic field (Park et al., 2016), and Global Positioning System (GPS)
(Alarifi et al., 2016). GPS is a mature technology for tracking, but it is not suitable for
indoor positioning (Liu et al., 2007). For indoor positioning, among all the technologies,
Bluetooth Low Energy (BLE) has proved to be cost-effective because of its high degree of
implementation simplicity with minimal infrastructure and ease of calibration (Park et al,
2016), and sufficiently accurate, thus making it, from the implementation perspective, the
preferred technology. However, different solutions applying BLE technology have neither
been thoroughly discussed nor compared for application to the scope of production control
in lean construction. This paper provides a comparative analysis of two BLE indoor
positioning solutions serving the purpose of operations management in construction,
outlining the potential use cases suitable for the respective methods.
METHODS
We examined two different methods for indoor positioning in construction sites using BLE
technology. The two methods used the same principles: a combination of BLE beacons and
gateways. In general, location monitoring systems using BLE sensors comprise four main
components: BLE beacons, gateways, a web application and cloud storage. Each BLE
beacon continuously transmits a universally unique identifier (UUID) that is detected by a
compatible app or operating system running on the gateway. The gateway in turn transmits
the UUID signals and the timestamp to the server via mobile network or Wi-Fi, and the
data is stored in cloud-based storage. The minimum requirements for the gateway are that
it can detect BLE signals and transmit data to the cloud using either mobile networks or
Wi-Fi.
FIXED BEACONS - MOBILE GATEWAYS (FB)
In this method, the beacons are fixed in place on walls or ceilings in the building under
construction, while apps installed on workers’ mobile smartphones serve as gateways. The
beacons transmit the UUIDs, which are detected by the workers’ smartphones, which in
turn send packets of UUIDs, timestamps and signal strengths to the data analysis engine in
the cloud (Figure 1). Additional fixed beacons in site elevators and site offices can be used
to track workers more extensively.
Dror, E., Jianye Z., Sacks, R., Seppänen, O.
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Proceedings IGLC – 27, July 2019, Dublin, Ireland
The method requires one-time installation of the beacons in each location. Figure 2
shows a typical distribution of beacons on a typical floor of a residential building in Israel
(beacons are marked in green). The beacons require neither infrastructure nor external
power source and are fixed in place manually. In the process of positioning the beacons,
the location of each beacon is registered using a designated smartphone app interface,
matching each physical location to a specific UUID.
Most smartphones available on the market today can receive Bluetooth signals and are
connected to cellular networks and are therefore suitable to serve as gateways (Dror, 2018).
In order to use smartphones as gateways, a designated app is needed. In the experimental
setup, an Android app was implemented for this purpose.
Figure 1 BLE tracking system components Figure 2 Typical beacon placement in a residential building
MOBILE BEACONS - FIXED GATEWAYS (MB)
In the MB method, mobile BLE beacons attached to equipment or material containers and
carried by workers send signals to gateways that are fixed in place. The proposed prototype
contains four main parts (see Figure 3): beacons, gateways, cloud storage and a web-based
application. Gateways receive signals from the beacons and transmit them to the cloud
service via Wifi or cellular networks (using dongles) (link 4). The cloud software compares
the signal strength from beacons and determines the location information based on the
strongest signal strength received. The software saves the data in the server and displays
the results on a web-based application through an application programming interface (API)
(link 5). The application aims to provide situational awareness on site from the perspective
of operations management and to update production status based on information from the
Indoor Tracking of Construction Workers Using BLE: Mobile Beacons and Fixed Gatewayes vs. Fixed
Beacons and Mobile Gateways.
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Information Technology in Construction
cloud (link 3 and 5). The prototype enables tracking of labor, materials and tools
simultaneously (link 1).
Figure 3 MB indoor positioning solution scheme
COMPARISON
Each method has its own characteristic advantages and disadvantages. In this section, we
compare the two methods in detail from technical, system and lean construction
implementation perspectives, considering and proposing possible use cases. Both methods
were tested on active construction sites. The MB method was implemented and tested in
construction projects in Finland, China, Peru, and the Netherlands, including low rise
residential buildings and office buildings. The FB method was implemented and tested in
several high-rise residential buildings in Israel.
TECHNICAL AND SYSTEM COMPARISON
Setup & maintenance. Both methods require physical setup onsite. The MB solution
requires setting up the gateways in their fixed positions. The FB solution requires setting
up the beacons in their fixed positions. In both methods the setup process needs around
half a day. Additional maintenance work for the system is anticipated to be as much as 1-
2 hours per week.
Cost. When examining the costs, we consider only the hardware costs of the system and
not the costs related to developing the software or labour for setup & maintenance. The
costs are split mainly between two components: beacons, gateways.
The MB solution requires a beacon for each item that is to be monitored, gateways, and a
power outlet for each of the gateways (in the case studies examined, the gateways were
Dror, E., Jianye Z., Sacks, R., Seppänen, O.
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Proceedings IGLC – 27, July 2019, Dublin, Ireland
positioned in proximity to existing temporary power outlets at no extra cost). The FB
solution requires 4-5 beacons for each apartment, no infrastructure, and no gateway
purchase - worker`s personal smartphones are used as gateways. In both solutions,
additional beacons are needed for material and equipment location monitoring. Each
element is tagged with a beacon and the number of beacons is the same for both solutions.
As an example, Table 1 details the actual costs for a residential building of three floors
with 16 apartments and an entrance floor. The costs assume 15 tracked workers in the
building, working with 20 pieces of equipment and up to 30 material containers at a time
(beacons are reused).
Table 1: Comparison of example project costs
Fixed beacons - mobile gateways
prototype (FB)
Mobile beacons - fixed
gateways prototype (MB)
Hardware
requirements- labor
tracking
65 Beacons
23 Gateways
15 Beacons
Hardware
requirements-
equipment/ material
tracking
50 Beacons
50 Beacons
Total cost
460 €
1,675 €
Feasibility in construction sites. Construction sites are complex environments, with
extensive movement of people and vehicles, use of heavy equipment, frequent change of
labor and lack of infrastructure such as Wi-Fi signal or electricity. The MB solutions
require a stable power supply, which is the biggest obstacle for feasibility testing on site.
Therefore, in the tests of MB solutions, the gateways were placed wherever temporary
power was available. Data was then analyzed to propose a more rigorous gateway
placement strategy for this solution.
The FB solution requires no infrastructure such as Wi-Fi or electricity at all, which
makes it highly feasible for construction sites and enables wide spread monitoring. On the
other hand, it requires collaboration of the construction workers to allow use of their
smartphones. In the case studies, 90% of workers were carrying a smartphones and were
using 3G network that is widely available in the construction site, however some 20% of
the workers objected, expressing discomfort with the idea of using their personal
smartphones to share their locations in the building and on the site.
Coverage & Accuracy. The coverage and accuracy of the system is related to the ability to
position the fixed components: beacons or gateways. The rule of thumb is that the more
fixed components placed, the higher the possible location accuracy will be.
Indoor Tracking of Construction Workers Using BLE: Mobile Beacons and Fixed Gatewayes vs. Fixed
Beacons and Mobile Gateways.
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Information Technology in Construction
In the prototype MB method, positioning of the gateway requires access to temporary
power. This restricted the positioning to specific locations in the construction site. As the
coverage depends on the placement of gateways, location accuracy might be low in
buildings with open layout, such as office buildings.
The FB method enables wide spread of beacons in the construction site because it
requires no physical infrastructure. It thus enables accurate positioning with unlimited
coverage.
Table 2: Technical comparison of the methods
Fixed beacons - mobile gateways
prototype (FB)
Mobile beacons - fixed
gateways prototype (MB)
Setup & Maintenance
+ Short setup time
+ Minimal maintenance
- Application required for the
installation
+ Short setup time
+ Minimal maintenance
+ Easy set-up, no mobile
application required
- Gateways are exposed
onsite so they are in risks of
damage or movement
Cost
+ Low hardware costs
- Higher hardware costs
Feasibility in
construction sites
+ Minimum physical requirements
- High friction with workers
- Requires access to power
Accuracy & Coverage
+ Unlimited coverage
+ High accuracy in closed areas
+ Coverage and accuracy
can be improved based on
data analysis heuristics
- Temporary power
requirements decrease
coverage in most cases
- Internet is required for
gateways (from onsite WIFI
or mobile network dongles)
Reliability
+ 98% accuracy in apartment scale
positioning
+ Accuracy is high and
detection in real time
- Signal coverage is not
perfect due to the limitation
from gateway placement
Data transmission
rate
- Every 5 minutes
+ Continuous
Dror, E., Jianye Z., Sacks, R., Seppänen, O.
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Proceedings IGLC – 27, July 2019, Dublin, Ireland
Data transmission rate. In both methods the BLE beacons transmit their UUID
continuously and the data is transferred through the gateway to the cloud storage.
In the MB method, gateways receive signals from the beacons at a frequency of one
per second. Because gateways are supplied with power all the time, they can provide a
continuous signal scan window, thus making the tracking results very detailed.
In the FB method, because the workers phones serve as gateways, battery drainage
aspects must be considered. Therefore, a decision was made to monitor the workers’
locations every five minutes, resulting in data gaps of 5 minutes. It is possible to minimize
the gap to one minute with little adverse impact on the battery life, but continuous
monitoring is not possible.
USE CASE COMPARISON
Just as different BLE solutions were employed in these two indoor positioning schemes,
the requirements and the functionality of each approach can also be different in practical
use cases. We have considered three use cases (labor monitoring, material and equipment
monitoring, and movement analysis) in Table 3, highlighting the key features of the two
approaches.
Table 3. Use case comparison of FB and MB approaches
Fixed beacons - mobile gateways
prototype (FB)
Mobile beacons - fixed gateways
prototype (MB)
Labor
monitoring
+ High accuracy monitoring
- Requires smartphone
compatibility and application
installation
+ Workers likely to consistently
carry smartphones
+ Workers need carry only beacons that
have been registered.
- Workers might leave beacons on site,
which can cause invalid data
- Limited tracking precision due to lack
of coordinates of floor plan
Material &
Equipment
monitoring
+ Beacons can be used as material and equipment tags. Attaching beacons to
material packaging at time of delivery is straightforward, and they can be
reused.
Movement
data
analysis
+ A movement tendency index can
reflect the workers’ efficiency
+ Gaps in data flow can lead to
gaps in information accuracy
+Time-location analysis can indicate the
uninterrupted presence level at work
locations for workers
CONCLUSION
The wide-ranging series of experiments has shown that both methods are feasible for
resource location monitoring in construction sites. Both provide a robust solution for
Indoor Tracking of Construction Workers Using BLE: Mobile Beacons and Fixed Gatewayes vs. Fixed
Beacons and Mobile Gateways.
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Information Technology in Construction
monitoring labor, material and equipment.The FB method has lower cost and greater
coverage than the MB method. The degree of resolution of location reporting can be greater
with the FB method than for the MB method, since the cost of beacons is significantly
lower than that of gateways. The MB method has lower latency of reporting because the
fixed gateways can communicate in real-time as they do not have the battery life limitations
that apply to smartphones.
Both methods appear to provide sufficiently accurate and complete data for deducing
which tasks are underway at any given moment and thus for updating project and process
status automatically. The location data itself can be communicated visually to construction
managers as an aid to improve their decision making. When it comes to movement data
analysis, both methods provide data that can be processed to yield insights about workers’
movement patterns and the wastes related to movement and waiting. However, the greater
location precision of the FB method is an advantage in this respect, because knowledge of
workers’ presence or absence from the work face location - often defined as a single room
or a single apartment - is necessary to distinguish value adding from non-value adding
activity.
LIMITATIONS AND FUTURE RESEARCH
Both methods share a few implementation limitations. They both require the assent and
cooperation of the workers, they both require setup and some maintenance work, and both
are subject to vandalism or intentional sabotage. Full scale implementation will require
contract terms that ensure cooperation. It is worth mentioning that implementation
processes may vary in some countries. The MB method was tested in China, Peru and
Finland. Users in China and Peru were more willing to invest resources to ensure the
functionality and proper placement of gateways (for example, using power banks instead
of temporary power to keep gateways working). They were also more willing to invest in
the infrastructure to ensure dense placement of gateways and theft protection. Unlike in
China and in Peru, the gateway implementation in Finland was dependent on the
availability of power and there was less motivation to invest time or resources.
Implementation strategies seem to be dependent on the availability of resources and
willingness to invest time and money on new solutions that do not yet have a proven record
of positive return on investment.
Future research should focus on examining the features of the two solutions of BLE
technologies and apply them in suitable real use cases serving the purpose of production
control in construction. Given the success of the experiments with the BLE tracking
technology, numerous specific modes of operation can be contemplated. For example: (1)
attaching BLE beacons to primary equipment, such as cutting saws, ladders, etc., to provide
additional indicators about workers’ operations through the day; (2) attaching BLE beacons
to palettes of materials to understand actual material flows delivered from warehouse to
jobsites; (3) attaching BLE beacons to site managers and providing them a real-time
Dror, E., Jianye Z., Sacks, R., Seppänen, O.
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Proceedings IGLC – 27, July 2019, Dublin, Ireland
interactive monitoring experience for onsite acitivities of workers. All of these can improve
the detail and the reliability of the information provided to the work planning process,
which can then better improve planning and hence productivity. Futhermore, productivity
at work locations could be analyzed in terms of value-adding level and waste spent onsite
calculated from the tracking system. In addition, research should also focus on data analysis
and visualization of the information to define what information site management teams
would like to accuqire to enhance the construction process flow in practice.
ACKNOWLEDGMENTS
The writers gratefully acknowledge the support of Tidhar Construction Ltd., who
collaborated with the bKan research, and the guidance and assistance of Eng. Ronen Barak
and Raz Yosef. Addtionally, this work was supported by Tekes (Finnish funding agency
for Technology and Innovation) grant number 2819/31/2016
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