Bluetooth Low Energy Transmitter Research Articles

Protecting Bluetooth User Privacy Through Obfuscation of Carrier Frequency Offset

This brief presents the analysis, design, and measurement results of an integrated circuit designed to prevent tracking the location of Bluetooth Low Energy (BLE) transmitters. Conventional BLE transmitters have unique RF fingerprints due to variation-induced imperfections in the underlying circuits. Coupled with BLE’s wide adoption in mobile devices and tendency to transmit continuously, BLE has become a significant threat to the location privacy of individual users. The primary source of this privacy threat is that BLE transmitters have a unique Carrier Frequency Offset (CFO) that can be easily fingerprinted by passive adversaries. To combat this, a test chip is developed that pseudo-randomly changes its CFO by switching in a binary-weighted set of semi-identical MIM capacitors into the tank of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> voltage controlled oscillator, all while maintaining compatibility with BLE standard specifications. Measurement results reveal that privacy preservation can be improved from only a few seconds with a conventional design, to over a day with the proposed design.

Accuracy Analysis of the Indoor Location System Based on Bluetooth Low-Energy RSSI Measurements

Systems for determining the position of objects inside buildings have a wide range of applications, such as the surveillance of people’s movements in hospitals, and of goods or mobile robots in warehouse spaces or production halls. Hence, there is a need for the development of methods that could be applied for those purposes. This paper presents the results of research on an experimental system for localizing people being evacuated from a building. The proposed solution was designed as a part of the building evacuation management system. The method used for finding location belongs to the class of proximity-type methods and is based on Received Signal Strength Indicator (RSSI) information of Bluetooth Low-Energy (BLE) devices. The devices used to build the system (BLE receivers) and the evacuee’s wristband (BLE transmitters) are low-budget electronic modules. The paper presents preliminary research and the process of selecting data processing methods, as well as the results of tests of the experimental network created for the evacuation system. The results of measurements and statistical analyses of the properties of the RSSI parameter of the BLE signal transmission between the modules used in the designed system are presented. In addition, the results of RSSI measurements and the analyses of RSSI recorded under varying environmental conditions in the building are presented. The choice of the data processing method and its parameters was made with the use of the determined probabilities of the nearest locator node detection. Finally, the performance of the experimental installation of the evacuee tracking system was tested and the effectiveness of the proximity method was evaluated. The experimental tests aimed to analyze the detection range and the impact of shading. They also allowed for determining the mean error and for estimating the maximum position determination error. It should be emphasized that the proposed position estimation method has a very low computational load, allowing the implementation of an extensive real-time system on a typical personal computer. Although the proposed system should be classified as a coarse positioning system, its features such as low cost, simplicity, flexibility, the use of commonly available components and low requirements for computational load make it attractive. Such a system is directly transferable to other applications in, for example, Industry 4.0.

A Safety System based on Bluetooth Low Energy (BLE) to prevent the misuse of Personal Protection Equipment (PPE) in construction

In this paper we address the issue of safety in the use of Personal Protection Equipment (PPE) in construction, industrial, or similar sites where power tools are used. We propose a novel solution that can control actively the power of the tool depending on the worker–tool distance. It is based on RSSI information transmitted by BLE devices arranged in a particular rig, combined with a Bayesian distance estimator. Such an approach minimizes the required instrumentation of the workplace and also the number of configuration parameters; therefore it enables a wide range of applications. Our aim is not only to signal risky situations caused by the misuse of the PPE (either due to its bad fitting or a wrong distance to the tool), but to intervene in a fast and robust way to avoid the safety risk.This solution is built upon previous results on the statistically sound measurement of distances and closeness in construction sites. Here, we contribute with a thorough analysis of collocating several BLE transmitters near orthogonally, which reduces interferences while avoiding the cost of more advanced technologies. We study how many transmitters are needed and what parameters are the best in the Bayesian filter for the optimal performance of the system.Real experiments with a prototype have been conducted in a construction workshop where a person operates a miter saw. The results show how the correct use of the PPE (an earmuff equipped with the BLE transmitters) can be inferred from the distance estimation in a robust and reliable way.

PERFORMANCE ANALYSIS OF BLE 5.1 NEW FEATURE ANGLE OF ARRIVAL FOR RELATIVE POSITIONING

Abstract. The official release of Bluetooth Core Specification, version 5.1 in 2019, provides a new feature for direction determination. It introduces a fine-grained angle measurement capability including Angle of Arriva (AoA) and Angle of Departure, which is deemed essential to the development of Internet of Things applications for localization or relative positioning within the area where Global Navigation Satellite System signals cannot be received. In this paper, we set up a series of experiments to empirically evaluate the direction of the Bluetooth Low Energy transmitter based on the AoA mechanism using the commercialised equipment. The experimental evaluation is performed, for the first time to date, under four different testing environments and other various conditions to inspect the fidelity of angle measurement against the high accuracy given in the specifications. In details, an ideal environment (i.e., anechoic chamber with no multi-path effect), an underground mine, an open area and a typical office area are all tested comprehensively. The experimental results reveal that the ideal environment has the best performance with the minimum error and conforms with the provided datasheet. The worst case occurs on the data collected from the office area. We also find a regular pattern always showing up repeatedly on the error plots based on the measurement results and scrutinize the truthfulness of this rule by adding more innumerable tests conducted in the office. Our results show that the performance of accuracy does depend on the data channel selection due to the multi-path effect.

A fully matched dual stage CMOS power amplifier with integrated passive linearizer attaining 23 db gain, 40% PAE and 28 DBM OIP3

PurposeThe purpose of this paper is to introduce a new linearization technique known as the passive linearizer technique which does not affect the power added efficiency (PAE) while maintaining a power gain of more than 20 dB for complementary metal oxide semiconductor (CMOS) power amplifier (PA).Design/methodology/approachThe linearization mechanism is executed with an aid of a passive linearizer implemented at the gate of the main amplifier to minimize the effect of Cgs capacitance through the generation of opposite phase response at the main amplifier. The inductor-less output matching network presents an almost lossless output matching network which contributes to high gain, PAE and output power. The linearity performance is improved without the penalty of power consumption, power gain and stability.FindingsWith this topology, the PA delivers more than 20 dB gain for the Bluetooth Low Energy (BLE) Band from 2.4 GHz to 2.5 GHz with a supply headroom of 1.8 V. At the center frequency of 2.45 GHz, the PA exhibits a gain of 23.3 dB with corresponding peak PAE of 40.11% at a maximum output power of 14.3 dBm. At a maximum linear output power of 12.7 dBm, a PAE of 37.3% has been achieved with a peak third order intermodulation product of 28.04 dBm with a power consumption of 50.58 mW. This corresponds to ACLR of – 20 dBc, thus qualifying the PA to operate for BLE operation.Practical implicationsThe proposed technique is able to boost up the efficiency and output power, as well as linearize the PA closer to 1 dB compression point. This reduces the trade-off between linear output power and PAE in CMOS PA design.Originality/valueThe proposed CMOS PA can be integrated comfortably to a BLE transmitter, allowing it to reduce the transceiver’s overall power consumption.

(Invited) Cavitas Sensors: Non-Invasive Bio/Chemical Sensing in Human Body Cavities for Medical and Healthcare

Introduction A non-invasive monitoring is important not only for medical inspection in hospitals but also healthcare management in daily life. For 30 years, we have developed several types of detachable sensors into human cavitas sites (conjunctiva, pharyngeal, oral cavity, etc.) with biocompatible materials and harmless device-techniques (Fig. 1). “Cavitas sensors” attached to body cavities such as a contact lens type and a mouthguard (“no implantable”, “no wearable”) are attracted attention for preventive medicine [1]. In this contribution, the cavitas sensors (soft contact-lens [SCL] and mouthguard [MG] biosensors) in human body cavities will be introduced as novel non-invasive biosensing devices. Soft contact lens type glucose sensor The soft contact lens type biosensor was designed for continuous glucose monitoring in tear fluids (Fig. 2) [2]. Biocom-patible poly(MPC-co-PMEH) (PMEH) (Fig. 3) [3,4] and polydimethyl siloxane (PDMS) were employed as the biosensor material. The biosensor consists of a flexible Pt working electrode and an Ag/AgCl reference/counter electrode, which were formed by micro-electro-mechanical systems (MEMS) technique. Glucose oxidase (GOD) was immobilized on the sensitive area by entrapping with PMEH polymer. The contact lens biosensor showed a good relationship between the output current and glucose concentration in a range of 0.03–5.0 mM, covering the reported tear glucose concentrations in normal and diabetic patients. Also, the biosensor was applied to a rabbit for the purpose of tear glucose monitoring. The basal tear glucose was estimated to 0.14 mM. Also, the change of tear glucose induced by the change of blood sugar level was assessed by the oral glucose tolerance test. As a result, tear glucose level increased with a delay of few min from blood sugar level (Fig. 4). The result showed that the contact lens biosensor is expected to provide further detailed information about the relationship between dynamics of blood glucose and tear glucose. Invisible Mouth guard type sensors with BLE transmitter The telemetric mouthguard-biosensor was developed with dental materials integrated with Bluetooth low energy (BLE) wireless module for measurement of saliva glucose [5]. The electrodes were formed on the thinner mouthguard surface which made of a polyethylene terephthalate glycol (PETG) using the same method as the contact lens one (Fig. 5). The BLE module, small potentiostat and battery were mounted and heat-sealed between upper and lower mouth guards. In the investigation of in-vitro characterization, the transparent biosensor showed excellent relationship between the output current and the glucose concentration (Fig. 6). In artificial saliva consisting of salts and proteins, the glucose sensor exhibits high-sensitive detection in a range of 5-1000 µmol/L including glucose concentration of human saliva. We demonstrated the capability of the sensor and wireless communication module to characterize an inclusion in oral phantom that imitative structure of human oral cavity. Stable and long-term monitoring (more than 1 day) using telemetry system was established. Monitoring of real-time changes of glucose concentration in artificial saliva with evaluation system of phantom jaw was demonstrated. The mouthguard device would be useful not only for monitoring of the oral chemical and physical information but also for unconstrained controlling of external device and system [6]. Future potential of cavitas sensors The self-detachable cavitas sensors are expected to allow the non-invasive bio/chemical monitoring, thus improving quality of life in view of the aging of society in near future.

Digital Door-Lock using Authentication Code Based on ANN Encryption

Abstract Nowadays, many houses/apartments are rented out for travelers in sites like Airbnb. A way to give out temporary access key for the guest is necessary for both the guest and hosts convenience. This paper presents an electronic door lock mechanism that able to generate dynamic temporary access key for the guest. The door lock is controlled by a smartphone using the dynamic key which is transferred though Bluetooth Low Energy (BLE) connection. The development of dynamic key utilizes block cipher encryption and fusion methods (Artificial Neural Network) to generate the block cipher keys. The generator produces a unique dynamic key for a specific period of time and nRF8001 proves to be a reliable Bluetooth Low Energy transmitter and receiver.

Adaptive Sequential Monte Carlo Filter for Indoor Positioning and Tracking With Bluetooth Low Energy Beacons

We model the tracking of Bluetooth low-energy (BLE) transmitters as a three layer hidden Markov model with joint state and parameter estimation. We are after a filtering distribution by Bayesian approximation using Monte Carlo sampling techniques. In a test environment decorated with multiple BLE sensors, the tracking relies only on the naturally unreliable received signal strength indicator (RSSI) of the captured signals. We assume that the tracked BLE transmitter does not provide any other motion or position related information. Hence, the transition density is designed to be merely a diffusion where the probability measures are diffused into the neighboring space. This makes the diagonal error covariance factor of the prediction density, namely the diffusion factor, the most important parameter to be tuned on the fly. We first show an experimental proof of concept using synthetic data on real trajectories by comparing three parameter estimation approaches: static, decaying and adaptive diffusion factors. We then obtain the results on real data which show that online parameter sampling adapts to the observed data and yields lower error means and medians, but more importantly steady error distributions with respect to a large range of parameters.

(Invited) Cavitas Sensors: Non-Invasive Bio/Chemical Sensing in Human Body Cavities for Medical and Healthcare

Introduction A non-invasive monitoring is important not only for medical inspection in hospitals but also healthcare management in daily life. For 30 years, we have developed several types of detachable sensors into human cavitas sites (conjunctiva, pharyngeal, oral cavity, etc.) with biocompatible materials and harmless device-techniques (Fig. 1). “Cavitas sensors” attached to body cavities such as a contact lens type and a mouthguard (“no implantable”, “no wearable”) are attracted attention for preventive medicine [1]. In this contribution, the cavitas sensors (soft contact-lens [SCL] and mouthguard [MG] biosensors) in human body cavities will be introduced as novel non-invasive biosensing devices. Soft contact lens type glucose sensor The soft contact lens type biosensor was designed for continuous glucose monitoring in tear fluids (Fig. 2) [2]. Biocom-patible poly(MPC-co-PMEH) (PMEH) (Fig. 3) [3,4] and polydimethyl siloxane (PDMS) were employed as the biosensor material. The biosensor consists of a flexible Pt working electrode and an Ag/AgCl reference/counter electrode, which were formed by micro-electro-mechanical systems (MEMS) technique. Glucose oxidase (GOD) was immobilized on the sensitive area by entrapping with PMEH polymer. The contact lens biosensor showed a good relationship between the output current and glucose concentration in a range of 0.03–5.0 mM, covering the reported tear glucose concentrations in normal and diabetic patients. Also, the biosensor was applied to a rabbit for the purpose of tear glucose monitoring. The basal tear glucose was estimated to 0.14 mM. Also, the change of tear glucose induced by the change of blood sugar level was assessed by the oral glucose tolerance test. As a result, tear glucose level increased with a delay of few min from blood sugar level (Fig. 4). The result showed that the contact lens biosensor is expected to provide further detailed information about the relationship between dynamics of blood glucose and tear glucose. Invisible mouth guard type sensors with BLE transmitter The telemetric mouthguard-biosensor was developed with dental materials integrated with Bluetooth low energy (BLE) wireless module for measurement of saliva glucose [5]. The electrodes were formed on the thinner mouthguard surface which made of a polyethylene terephthalate glycol (PETG) using the same method as the contact lens one (Fig. 5). The BLE module, small potentiostat and battery were mounted and heat-sealed between upper and lower mouth guards. In the investigation of in-vitro characterization, the transparent biosensor showed excellent relationship between the output current and the glucose concentration (Fig. 6). In artificial saliva consisting of salts and proteins, the glucose sensor exhibits high-sensitive detection in a range of 5-1000 µmol/L including glucose concentration of human saliva. We demonstrated the capability of the sensor and wireless communication module to characterize an inclusion in oral phantom that imitative structure of human oral cavity. Stable and long-term monitoring (more than 1 day) using telemetry system was established. Monitoring of real-time changes of glucose concentration in artificial saliva with evaluation system of phantom jaw was demonstrated. The mouthguard device would be useful not only for monitoring of the oral chemical and physical information but also for unconstrained controlling of external device and system [6]. Future potential of cavitas sensors The self-detachable cavitas sensors are expected to allow the non-invasive bio/chemical monitoring, thus improving quality of life in view of the aging of society in near future.

A 1.0-Mb/s 198-pJ/bit Bluetooth Low-Energy Compatible Single Sideband Backscatter Uplink for the NeuroDisc Brain–Computer Interface

Wireless brain-computer interfaces (BCIs) are highly energy constrained because of the need to minimize battery size and weight, as well as the need to minimize the thermal dissipation into the living tissue. We demonstrate an ultralow-power Bluetooth Low Energy (BLE) v5.0 compatible backscatter communication uplink for the NeuroDisc BCI. This backscatter approach is compatible with completely unmodified BLE devices such as PCs, smartphones, and tablets and has an energy consumption of under 200 pJ/bit, over 50× less than commercially available BLE transmitters. This article is the first to present an analysis and demonstration of single sideband (SSB) BLE backscatter, which increases the available channel power by +3 dB while suppressing out-of-channel emissions. An analytic model of SSB backscatter communication is provided, along with simulations showing how nonidealities in the achieved backscatter constellation impact opposite-sideband suppression. The experimental measurements of in-channel gain and opposite-sideband suppression are provided. Additional experiments demonstrate a range of 6 m using a +20-dBm external carrier source and an unmodified Nordic Semiconductor nRF51DK BLE adapter, while uplinking prerecorded neural data sampled at 500 Hz.

Robust Localization for Robot and IoT Using RSSI

Node-localization technology has been supported in the wireless sensor network (WSN) environment. Node localization is based on a few access-point (AP) nodes that comprises positioning information because they are fixed, and a beacon node that comprises unknown positioning information because it is moving. To determine the position of the unknown node, it must use two or three APs that comprise certain positioning information. There are a number of representative range-based methods, including time of arrival (TOA), weighted centroid locating algorithm, received signal strength intensity (RSSI), and time difference of arrival (TDOA) signal, that are received by the receiver. The RSSI method has its advantages. A simple device structure means that the RSSI method is easy to use. Because the structures of previous wireless local area network (LAN) technologies make them compatible with RSSI information, the RSSI method is widely used in the related area of position tracking. In addition, this algorithm has a hardware system that cannot be increased, has the advantage of the miniaturization of the node, and can wear through obstacles. This paper proposes the application of a robust ranging method that can be applied in robots and Internet of Things (IoT) using RSSI, especially in the tracing location of each nursing home patient, where the RSSI method with trilateral technique is used. This paper shows the results of the measured point from the application of the trilateral technique, and it also represents the results of the error distance between the ideal point and the measured point using computer simulation. Finally, this paper presents an estimation of localization using a real experimental device with a BLE (Bluetooth low-energy) transmitter and receiver, and beacon gateway, by applying an RSSI algorithm with the trilateral technique.

A 0.2-V Energy-Harvesting BLE Transmitter With a Micropower Manager Achieving 25% System Efficiency at 0-dBm Output and 5.2-nW Sleep Power in 28-nm CMOS

This paper reports an ultralow-voltage (ULV) energy-harvesting bluetooth low-energy (BLE) transmitter (TX). It features: 1) a fully integrated micropower manager ( $\mu $ PM) to customize the internal supply and bias voltages for both active and sleep modes; 2) a gate-to-source-coupling ULV voltage-controlled oscillator (VCO) using a high-ratio (5.6:1) stacking transformer to improve the phase noise and output swing; 3) an ULV class-E/F2 power amplifier (PA) with an inside-transformer LC notch to suppress the HD3, and finally 4) an analog type-I phase-locked loop (PLL) with a reduced duty cycle of its master-slave sampling filter (MSSF) to suppress the jitter and reference spur. The TX prototyped in 28-nm CMOS occupies an active area of 0.53 mm2 and exhibits 25% system efficiency at 0-dBm output at a single 0.2-V supply. Without resorting from any external components, both the output HD2–49.6 dBm) and HD3–47.4 dBm) comply with the BLE standard. The FSK error is 2.84% and the frequency drift in a 425- $\mu \text{s}$ data packet is <5 kHz under open-loop modulation. The use of negative-voltage power gating suppresses the sleep power of the entire TX to 5.2 nW.

Support Vector Machine Algorithm in a Bluetooth Low Energy Passenger Detection System

Internet of Things (IoT) and Bluetooth Low Energy (BLE) technologies are drawing attention in the trend to integrate electronic devices and services. One example of an IoT application is a smart fare collection/payment system. Because people carry transportation cards nowadays, it is troublesome to tap the card every time, but making payment automatic by eliminating the tapping operation lets a greater number of passengers take public transportation in a shorter time. The first step toward a smart transportation fare collection system is passenger detection. One way to detect a passenge is by received signal strength indication (RSSI). The basic idea consists of adding BLE transmitters (beacons) to the vehicles and comparing intensity (power) between signals transmitted and received. However, due to multi-path propagation and fading effects, RSSI is not sufficiently accurate to calculate an exact location. Therefore, instead of determining the exact position, it is preferable to only check if the passenger is inside or outside the vehicle. In this support vector machine estimation method, RSSI signals are filtered using a moving average filter. Algorithm estimation efficiency was 92.51% (on average) for one beacon, and close to 100% for five beacons.

Real-Time Healthcare Data Transmission for Remote Patient Monitoring in Patch-Based Hybrid OCC/BLE Networks.

Research on electronic healthcare (eHealth) systems has increased dramatically in recent years. eHealth represents a significant example of the application of the Internet of Things (IoT), characterized by its cost effectiveness, increased reliability, and minimal human effort in nursing assistance. The remote monitoring of patients through a wearable sensing network has outstanding potential in current healthcare systems. Such a network can continuously monitor the vital health conditions (such as heart rate variability, blood pressure, glucose level, and oxygen saturation) of patients with chronic diseases. Low-power radio-frequency (RF) technologies, especially Bluetooth low energy (BLE), play significant roles in modern healthcare. However, most of the RF spectrum is licensed and regulated, and the effect of RF on human health is of major concern. Moreover, the signal-to-noise-plus-interference ratio in high distance can be decreased to a considerable extent, possibly leading to the increase in bit-error rate. Optical camera communication (OCC), which uses a camera to receive data from a light-emitting diode (LED), can be utilized in eHealth to mitigate the limitations of RF. However, OCC also has several limitations, such as high signal-blockage probability. Therefore, in this study, a hybrid OCC/BLE system is proposed to ensure efficient, remote, and real-time transmission of a patient’s electrocardiogram (ECG) signal to a monitor. First, a patch circuit integrating an LED array and BLE transmitter chip is proposed. The patch collects the ECG data according to the health condition of the patient to minimize power consumption. Second, a network selection algorithm is developed for a new network access request generated in the patch circuit. Third, fuzzy logic is employed to select an appropriate camera for data reception. Fourth, a handover mechanism is suggested to ensure efficient network allocation considering the patient’s mobility. Finally, simulations are conducted to demonstrate the performance and reliability of the proposed system.

A Coin-Battery-Powered LDO-Free 2.4-GHz Bluetooth Low-Energy Transmitter With 34.7% Peak System Efficiency

This brief reports a 2.4-GHz Bluetooth low-energy (BLE) transmitter (TX) that can operate against a coin-battery voltage discharging from 1.5 to 1 V, corresponding to a 99.2% battery capacity usage. Specifically, a class-B/C push–pull power amplifier with dual feedback control loops is proposed to dynamically adjust two gate biases, ensuring stable output power and low output HD2. The TX fabricated in 65-nm CMOS occupies a die area of 0.5 mm2 and achieves three stable power levels: $\text{P}_{{\mathbf{ out,H}}}$ (2.7 ± 0.4 dBm), $\text{P}_{{\mathbf{ out,M}}}$ (−0.1 ± 0.6 dBm), and $\text{P}_{{\mathbf{ out,L}}}$ (−2.5 ± 0.8 dBm). At $\text{P}_{{\mathbf{ out,H}}}$ , the system efficiency reaches 34.7%. The 1-Mb/s GFSK output ( ${\mathbf{ m = 0.5}}$ ) and HD2,3 comply with the BLE specifications, and the FSK error is 8.2%. A tiny demo board with an antenna, a crystal, and a coin battery (Nanfu LR44) verifies the feasibility of the TX over-the-air, achieving 27.5 h of continuous operation for a 1-dB reduction of the received power.

Timing Channels in Bluetooth Low Energy

This letter introduces timing channels in connectionless Bluetooth low energy (BLE). The proposed standard-compliant enhancement, BLE with timing channels (BLE-TC), improves the energy efficiency of an energy-constrained connectionless BLE transmitter by encoding additional information in the interarrival time between BLE advertisements. BLE-TC is analytically compared with the connectionless BLE standard. Using realistic timing noise that is empirically determined through a proof-of-concept implementation, the results indicate that more than 10% improvement in energy efficiency can be achieved for low-throughput applications, such as smart metering and environmental sensing for smart cities.

A Fully Integrated Bluetooth Low-Energy Transmitter in 28 nm CMOS With 36% System Efficiency at 3 dBm

We propose a new transmitter architecture for ultra-low power radios in which the most energy-hungry RF circuits operate at a supply just above a threshold voltage of CMOS transistors. An all-digital PLL employs a digitally controlled oscillator with switching current sources to reduce supply voltage and power without sacrificing its startup margin. It also reduces 1/f noise and supply pushing, thus allowing the ADPLL, after settling, to reduce its sampling rate or shut it off entirely during a direct DCO data modulation. The switching power amplifier integrates its matching network while operating in class-E/F2 to maximally enhance its efficiency at low voltage. The transmitter is realized in 28 nm digital CMOS and satisfies all metal density and other manufacturing rules. It consumes 3.6 mW/5.5 mW while delivering 0 dBm/3 dBm RF power in Bluetooth Low-Energy mode.

Improving Indoor Localization Using Bluetooth Low Energy Beacons

The paper describes basic principles of a radio-based indoor localization and focuses on the improvement of its results with the aid of a new Bluetooth Low Energy technology. The advantage of this technology lies in its support by contemporary mobile devices, especially by smartphones and tablets. We have implemented a distributed system for collecting radio fingerprints by mobile devices with the Android operating system. This system enables volunteers to create radio-maps and update them continuously. New Bluetooth Low Energy transmitters (Apple uses its “iBeacon” brand name for these devices) have been installed on the floor of the building in addition to existing WiFi access points. The localization of stationary objects based on WiFi, Bluetooth Low Energy, and their combination has been evaluated using the data measured during the experiment in the building. Several configurations of the transmitters’ arrangement, several ways of combination of the data from both technologies, and other parameters influencing the accuracy of the stationary localization have been tested.

A Self-Powering Wireless Environment Monitoring System Using Soil Energy

This paper presents a self-powering wireless environment monitoring system using renewable and cost-efficient soil energy. The D-size (55.8 cm $^{3})$ soil energy cell with carbon and zinc electrodes can produce $\sim 60$ –100 $\mu \text{W}$ , depending on the water contents and microbial reactions in the soil. The $RC$ circuit model of a soil cell is proposed for understanding the electrical characteristics of the cell. The wireless sensing system, including temperature and air moisture sensors, a custom low-power capacitive sensor readout silicon chip, a microcontroller, and a Bluetooth low-energy transmitter, is demonstrated for long-term environmental monitoring solely by the fabricated D-size soil cell. The capacitive sensor readout chip is fabricated in a 0.18- $\mu \text{m}$ CMOS process and only consumes 3 $\mu \text{W}$ . The capacitance readout range is 160–200 pF. The total power consumption of the wireless temperature and air moisture monitoring system is $\sim 20~\mu \text{W}$ and 1 mW in the sleep mode and the active wireless data communication operations, respectively. The new technology can enable remote field environment monitoring with less labor-intensive work and battery replacement.