A new asset tracking architecture integrating RFID, Bluetooth Low Energy tags and ad hoc smartphone applications
Introduction
The efficiency of manufacturing and construction operations can be seriously affected by the amount of time spent searching for misplaced high value things, hereafter referred as assets [1]. The solution of this problem is crucial especially in wide construction sites (e.g., railway or highway constructions) where lost assets must be searched in very large areas. Asset tracking systems represent a promising approach for reducing wasted time and costs.
The mentioned systems allow tracking the locations and movements of physical assets. The most common commercial solutions employ BAR or Quick Response (QR) code tags attached to the assets, or smart-tags such as Radio-Frequency IDentification (RFID, passive and active) tags. More recently, as in the system described in this paper, Bluetooth tags are fruitfully employed.
Indeed, location (or position) information provides great potential for saving labor time that should be otherwise spent searching for misplaced assets: the same time can be more conveniently spent to optimize decision-making throughout the manufacturing and construction activities, thus enhancing efficiency and responsiveness.
The problem of asset localization and tracking is not new: a large number of research works faced it in different scenarios and under various constraints. For instance, the authors of [2] proposed an approach for tracking mobile robots in an indoor environment; the work presented in [3] addressed the problem of localizing assets by means of the joint use of two technologies, namely radio and ultrasonics: the assets to be monitored are equipped with ultrasonic devices and communicate with each other through a wireless sensor network in order to estimate their position. On the other hand, when targets to be tracked are in a wide outdoor environment, the use of GPS, now included in almost all mobile phones, represents the most promising approach to the problem of asset tracking.
In the last 10 years, smartphones have become popular and widely used because of their mobility, friendly user-interfaces, communication interfaces, and their increasing computing power (see, among others, [4], [5] and references therein).
This paper presents a new asset tracking system that integrates a classical tracking solution with the Bluetooth Low Energy (BLE) technology and opportunities offered by smartphones.
Since the current version of the designed platform represents a proof-of-concept tool, all the results have been obtained through simulations. Nevertheless, the proposed platform has been explicitly designed and implemented to be employed in construction sites and its effectiveness was also tested in a real environment, as shown in [6].
The architecture aims at satisfying a three-fold requirement:
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a good level of precision in terms of accuracy of the asset location, aging of the information and completeness of the acquired information (i.e., detection of all the tagged assets) and, at the same time,
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saving smartphones’ resources such as CPU, memory and, in particular, energy;
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saving construction site resources by decreasing the risk of losing valuable assets and minimizing the time spent by foremen looking for them.
To this goal the following issues have been taken into account.
- (a)
Energy consumption: battery lifetime should be adequate to last for an entire working shift, which has usually a duration of 8 h in a construction site. In practice, a foreman provided with a smartphone, must be able to use the mobile device during his whole working shift, without service interruptions due to battery expiration. Consequently, maximizing the smartphone battery lifetime is a crucial issue. Due to the limited energy capacity of mobile devices, solutions requiring significant computational burden should be avoided. Moreover, suitable strategies are needed to properly manage smartphone devices in order to save energy. In fact, tracking the asset position involves the use of GPS and Bluetooth interfaces, which must be switched on and off while preserving performances. Indeed, the on and off switching strategy, proposed in this paper, guarantees that smartphone lifetime is about 8 h, as shown in Section 5.
- (b)
Performance trade-off: An accurate and precise asset localization needs a significant amount of power due to an extensive use of GPS and CPU, which has to run possibly complex algorithms. As concerns tags, increasing accuracy requires a more frequent beacon emission and, consequently, it implies a reduced lifetime of the battery supplying the tag. Therefore, searching for a satisfactory trade-off between energy consumption and localization accuracy represents a crucial issue in the design of an asset tracking platform.
- (c)
User interaction and interfaces: in the recent years smartphones provide user-friendly interfaces. The proposed architecture adopts specific apps, suitably designed to allow an easy interactions between users (in our case, the foremen) and the tracking system.
- (d)
Cost–benefit analysis: the proposed architecture requires almost no additional expensive hardware. Indeed, in a construction site usually RFIDs technology and PCs are available to track assets entering and leaving storehouses. Foremen are already equipped with smartphones to communicate with each other. The BLE TAGs, necessary for asset tracking, are cheap. Consequently, the proposed architecture allows efficiently locating valuable assets within the construction site, so reducing the risk of losing expensive assets and, at the same time, avoiding to waste man-time.
This paper is structured as follows: Section 2 surveys the state of the art in the field, Section 3 describes the proposed architecture in detail, Section 4 introduces the solution adopted to track the position of the asset by means of Bluetooth Low Energy (BLE) tags and the GPS receiver of the smartphone. The energy consumption of GPS and Bluetooth devices was estimated through real measures on mobile phones and the related results are presented in Section 5. An extensive simulation campaign aimed at studying the performance of the proposed solution is described in Section 6. Finally, in the last section conclusions are drawn.
Section snippets
Related works
The importance of tracking misplaced objects and assets, in particular in large areas, is proved by a number of works in the literature addressing possible useful solutions. The approach presented in [7] exploits smartphones for object localization. The proposed method is based on the use of the device camera together with the built-in inertial sensor. The approach, named ComLoc, allows localizing remote objects in real-time by mixing image-based and phone-based localization techniques.
System architecture
According to the characteristics stated in the Introduction, the asset tracking architecture depicted in Fig. 1 was designed and implemented. Two different mechanisms for tagging are jointly used: each asset is tagged by means of both RFID and BLE devices (indicated with “T” in Fig. 1). In more detail, the Asset Management DataBase System (AMDBS) stores within its tables the relations between the assets and the associated tags. In this way, discovering and identifying tags permit to uniquely
Asset tracking function
As stated in the Introduction, the accuracy of the asset location represents a crucial requirement. In this section, the approach employed by the proposed tracking strategy to determine the asset position, is presented as well as its accuracy.
The asset position estimation is achieved by means of the APL Android application, whose tracking algorithm is represented by the flowchart in Fig. 3. The APL checks the presence of BLE tags: upon detecting a BLE tag, the application determines the
Energy consumption analysis
The energy consumption of an architecture based-on mobile devices represents a crucial issue.
In the next subsections the energy required by a smartphone to execute the asset tracking function is analytically modeled and described. Successively, an optimization of the rate at which the GPS interface is switched on and off is performed in order to ensure that the smartphone battery lasts for an entire working shift (i.e., 8 h). Eventually, the energy consumed during a BLE beacon emission is
The implemented simulator
All the results reported in this section have been obtained through an ad hoc simulator, implemented in C++ by the authors, whose pseudo-code is reported in the Algorithm Box 1. It considers the movements (within a construction site) of a foreman who carries a smartphone with both the WOLF and APL Android applications installed on.
The simulator takes into account a number of parameters which can be divided in three main categories: (i) Area-related parameters, indicated with “A”; (ii)
Conclusions
An asset tracking architecture has been presented that jointly exploits the traditional asset tracking techniques and the facilities offered by modern Android smartphones. The paper focused on the use of Bluetooth Low Energy (BLE) and RFID tags and smartphones. The effectiveness of the proposed solution was proved by means of an extensive simulation campaign. The software consists of two Android applications: the Asset Proximity Locator (APL) and Wandering Object Location Finder (WOLF). The
Acknowledgments
The authors want to thank the colleagues of AM General Contractor S.p.A. and Mantero Sistemi S.r.l. for their fruitful cooperation. Finally, a special thank to Prof. Carlo Braccini for his valuable suggestions and precious advices.
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