1. Introduction
In the technology-driven world, radio frequency (RF) Bluetooth devices have become an integral part, enabling seamless communication in smartphones, smartwatches, and Internet of Things (IoT) devices [
1,
2]. In this context, accurate identification of devices is critical to provide security and effective management of network services [
3]. Bluetooth technology, which operates in the 2.4 GHz band reserved for industrial, scientific, and medical purposes (ISM band), uses RF signals for short-range communication [
4], making it ubiquitous in personal area networks and IoT applications [
5,
6]. However, the widespread use of Bluetooth poses challenges in distinguishing individual devices within the crowded RF spectrum, requiring advanced identification techniques based on machine learning, signal spectral analysis, or statistical analysis approaches.
The machine learning approach uses algorithms such as support vector machines (SVMs), random forests, and deep learning to improve the quality of the RF device identification process [
7,
8,
9,
10,
11,
12,
13,
14,
15,
16,
17,
18,
19,
20,
21,
22,
23,
24,
25]. SVMs excel in classification tasks and provide reliable identification by recognizing unique RF fingerprints [
7,
8,
9,
10,
11,
12,
13]. Random forests, known for their robustness, enhance classification accuracy [
14]. Deep Learning, leveraging artificial neural networks, excels at complicated tasks such as classification and regression [
15,
16,
17,
18,
19,
20,
21,
22,
23,
24,
25]. Machine learning techniques, while powerful, come with inherent complexities [
7]. In this regard, the development and training of machine learning algorithms require specialized knowledge and expertise due to their intricate nature [
8]. Moreover, their implementation often requires significant computational resources, making them challenging for applications with limited computing capabilities [
19]. In addition, it is essential to collect a large data set of radio frequency signals from Bluetooth devices for effective training [
17]. However, obtaining this data can be daunting and costly, posing a significant challenge to the use of machine learning for RF device identification [
9]. These factors underscore the need for dedicated expertise, sufficient computational power, and meticulous data collection efforts in the realm of machine learning-based identification methods.
Signal spectral analysis methods, including swept-frequency, vector signal and real-time analysis schemes, are crucial for decoding and exploiting the complex RF signals emitted by Bluetooth devices [
26]. Swept-frequency analysis precisely pinpoints the frequency band and power level of a device, providing nuanced insight. Vector signal analysis delves into amplitude, phase, and frequency, decoding modulation schemes and evaluating signal quality. Real-time analysis continuously monitors Bluetooth signals, providing dynamic feedback on signal stability and fluctuations. In addition, real-time analysis captures signal power, enabling continuous monitoring of RF signals from Bluetooth devices. These techniques provide dynamic insights that facilitate tracking of signal stability, fluctuations, and adaptive adjustments. In the field of wireless communications, these analyses are invaluable because they provide in-depth understanding, comprehensive analysis, and optimization of Bluetooth signals, ensuring efficient and reliable data transmission. In addition, these techniques involve a level of complexity that requires specialized training to ensure their effective use. This complexity underscores the need for skilled professionals who can utilize spectrum analysis tools to their full potential. Furthermore, the limitations of these techniques are evident in their dependence on the sensitivity and accuracy of the equipment used. The accuracy of the analysis highly dependent on the quality and capabilities of the equipment, so it is imperative to invest in high quality tools to obtain accurate results.
In statistical analysis, there are some tools based on probability theory that can be used to distinguish between two systems being analyzed in the time or spectral domains. For example, the Jensen-Shannon divergence (JSD) stands as a valuable statistical metric that measures the similarity between two probability distributions [
27,
28]. When applied to RF noise signals extracted from Bluetooth devices, JSD excels at detecting subtle statistical discrepancies in the signals, and thus its usefulness can be extended to a variety of tasks related to Bluetooth technology. As will be discussed later, JSD applied to noise signals in the Bluetooth frequency band can be used to distinguish devices by statistically comparing their RF fingerprints, enabling the development of secure authentication protocols and facilitating device tracking. In addition, JSD can be used to identify statistical deviations in the RF noise signals from Bluetooth devices when compared to a reference RF noise signal (RF fingerprint), enabling the location of compromised or malfunctioning devices for early intervention. By monitoring RF signal quality, JSD also helps troubleshoot Bluetooth device and network issues to ensure optimal performance.
A notable strength of the JSD when applied to the statistical comparison of noise signals for Bluetooth device identification is its resilience to signal variations, making it ideal for real-world scenarios where environmental conditions can be unpredictable. In addition, its computational efficiency allows for real-time discrimination of many devices, a crucial aspect in dynamic environments. To address the existing research gap on JSD applied to Bluetooth noise signals for device identification, comprehensive studies are needed to evaluate its performance on various datasets and under different environmental conditions.
This paper presents a comprehensive approach to the development of a Bluetooth device discrimination method. This method is based on a statistical criterion, specifically the application of the JSD to analyze the probability density function (PDF) of intrinsic noise and the statistical fingerprints extracted from Bluetooth devices. Considering the mentioned issues, the effectiveness of the proposed system needs to be evaluated and compared with the artificial intelligence based discrimination methods proposed by Uzundurukan
et al. [
9,
17].
The rest of this paper is structured into six sections.
Section 2 defines the five specifications for device fingerprints: uniqueness, universality, persistence, collectability, and robustness. These criteria ensure that each fingerprint is unique, applicable to a wide range of devices, stable over time, easy to collect and robust under various conditions.
Section 3 delves into the specifics of Bluetooth signal processing. It covers the necessary steps such as signal filtering, state detection, and definition of the device RFF based on reference noise signals recorded under controlled conditions when the Bluetooth radio is turned on in each participating device.
Section 4 presents a case study using the noise signal database developed by Uzundurukan
et al. [
9,
17]. It introduces a criterion based on mean squared error (MSE) for determining the number of reference noise signals that must be evaluated to establish a device RFF. It also proposes a method to compensate for the amplitude difference in noise signals provided by the same device recorded by varying the distance between the receiver and the transmitter. This section concludes with a demonstration of the practical application of the estimated RF fingerprints for device discrimination using the JSD.
Section 5 provides a critical analysis of the results, comparing the proposed discrimination method with Uzundurukan’s method when applied to the same case study. Finally,
Section 6 gives the conclusions of this paper.