A new asset tracking architecture integrating RFID, Bluetooth Low Energy tags and ad hoc smartphone applications

Abstract

The paper describes an original architecture aimed at tracking assets within construction sites. The main components are Radio Frequency IDentification (RFID), Bluetooth Low Energy (BLE) tags and smartphones. The core functions are performed by two Android applications, which implement asset tracking and searching. The main merits of the architecture are its ability to maximize smartphone battery lifetime, that can reach an entire working shift, very satisfactory accuracy of BLE tag-smartphone distance estimation (with a mean error around 2 [m]), high probability of detecting all the tags present in the construction site, as well as a suitably short Aging time.

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:

• 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,

• saving smartphones’ resources such as CPU, memory and, in particular, energy;

• saving construction site resources by decreasing the risk of losing valuable assets and minimizing the time spent by foremen looking for them.

Furthermore, the proposed architecture requires hardware which is already available in a construction site (e.g., smartphones for the foremen and PCs): only cheap RFID and BLE TAGs have to be purchased.

To this goal the following issues have been taken into account.

• 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.

• 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.

• 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.

• 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.