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Powering Bluetooth Sensor Beacons via Micro-Energy Harvesting

Recent research A Comprehensive Study on the Internet of Things (IoT) and Micro-Energy Harvesting from Ambient Sources, from researchers in Spain, discusses the potential of micro-energy harvesting (MEH) as a sustainable power source for Internet of Things (IoT) devices, specifically Bluetooth sensors.

Micro-Energy Harvesting (MEH) is a technology that captures and converts small amounts of environmental energy such as like light, heat, or motion into electrical energy, which can power small electronic devices. The study suggests that MEH could be a sustainable solution for powering Internet of Things (IoT) devices, including Bluetooth sensors, due to their low power requirements.

The benefits of MEH include reducing the need for costly and environmentally harmful battery replacements and enabling the deployment of IoT devices in remote or hard-to-reach areas. The study also points out challenges, such as the small and variable amount of energy that can be harvested, which may not provide a reliable power supply for devices that need a steady source of energy. However, even with small temperature gradients between the environment and the cold side of the thermoelectric generator, it wass possible to make several communications per hour.

Sensor Beacons

Factors that Impact the Cost of a Bluetooth Beacon

One of the factors affecting the cost of a Bluetooth beacon is the quality of the hardware used. The beacon’s components, such as the Bluetooth chip, battery, antenna and casing all contribute to the overall cost. High-quality components typically result in a higher-priced beacon but they also provide better range and longevity.

Larger beacons with longer battery lives tend to be more expensive because they require higher capacity batteries, more efficient Bluetooth chips or both. The advantage is that they need to be replaced less frequently, potentially reducing maintenance costs over time.

The range of features that a beacon supports can also affect its cost. Some beacons are designed to be basic, providing only the core functionality of broadcasting a signal. Others offer advanced features like motion sensing, temperature monitoring or water resistance. These additional features increase the beacon’s usefulness, but they also increase its cost.

Small battery, low cost beacon vs large battery, waterproof, higher cost beacon

The software that accompanies the beacon and the level of customer support provided by the manufacturer also affects the price. Companies that offer the best documentation, apps and customer service charge a premium for their products.

If you require a beacon to be customised to suit specific needs, this also increases the cost. Customisations include unique casing designs, branding and specific firmware modifications.

One thing that doesn’t change with cost is compatibility. All beacons work equally well with Android, iOS and gateways.

Beacon Settings for Asset Tracking

Bluetooth beacons are increasingly being used for asset tracking. Their use in this context differs significantly from their conventional role of in-app triggering. In asset tracking, gateways rather than smartphones are used as detection devices, requiring different configurations for optimum efficiency.

iGS03E Bluetooth to Ethernet gateway

Changing Bluetooth beacon settings requires the manufacturer’s specific application custom-tailored for their devices. These apps adjust the beacon parameters according to specific needs.

A most important setting when using beacons for asset tracking involves is the advertising period. This is the time interval between the broadcasted signals. In the the app detection usecase, a frequent advertising period is required to ensure constant detection by nearby smartphones and particularly for iOS. However, in asset tracking, the scenario is different.

Since gateways, not smartphones, are used for detection, a lower advertising period, ranging from 1 to 10 seconds, is sufficient. Less frequent advertising has the advantage of conserving the beacon’s battery life. It also ensures the server isn’t flooded with duplicate data.

The beacon’s advertising type is another key consideration. iBeacon or Eddystone UIDs are usually used for detection by smartphones due to their compatibility and detection by mobile operating systems. However, when using gateways and servers, the Bluetooth MAC address of the beacon is usually used for identification. Consequently, any advertising type can be selected, eliminating the need for specific compatibility.

Where multiple advertising types are available, it’s essential to ensure that only one advertising type is selected. Even though gateways can utilise any advertising type, using multiple types simultaneously can lead to increased energy consumption by the beacon and more redundant data at the server.

Using Beacons for Industry 4.0

Industry 4.0, or the Fourth Industrial Revolution, is the integration of digital technologies into the manufacturing process to create smart factories. These technologies include sensing, artificial intelligence, machine learning, the Internet of Things (IoT), big data, cloud computing to create more efficient, flexible and customisable manufacturing processes.

A new study by Institute of Technology and Business in České Budějovice, Czech Republic on Possibilities of Using Bluetooth Low Energy Beacon Technology to Locate Objects Internally: A Case Study describes and tests a system capable of locating objects inside buildings using Bluetooth Low Energy (BLE) beacons. The authors conducted a survey of available devices and proposed a low-cost combination of system elements, configured the system, programmed reading gates and web applications for data flow monitoring and finally tested the system in an industrial setting at a manufacturing company in Czechia​.

The testing included scenarios with beacon-equipped metal crates being moved around in three different sections of the industrial hall. The study evaluated the system’s ability to detect the beacons and determine their location.

System architecture

The results showed that in the case of direct visibility, the system was able to determine the distance with an accuracy of 94%. However, the measurements also showed that the signal strength was affected by shielding, resulting in worse measurement results in this case and only able to determine the exact distance only 22% of the time.

Crate with a beacon

During a load test, the system and all its sub-components were subjected to several hours of operation, during which the gateways sent requests and collected data about available beacons, processed the requests and stored them in the database. The web application allowed for real-time monitoring of data flow from the individual gateways and the number of beacons in the individual sections. No problems occurred during testing that would cause the measurements to be interrupted, demonstrating the functionality of all system components​​. The system was considered adequate for most use cases.

IQ to Direction Radiogoniometry

Bluetooth Angle of Arrival (AoA) direction finding, part of the Bluetooth 5.1 specification, improves the accuracy of locating using Bluetooth signals. AoA uses the phase difference of the received signal at multiple antennas in a Bluetooth-enabled device to calculate the angle of the incoming radio signal, which can then be used to pinpoint the direction from which the signal was sent.

IQ data comes into play as part of the signal processing. In radio systems, IQ data represents the peaks and troughs of a waveform. I is for ‘In-phase’ part which can be thought of as a signal’s cos component, while Q is for ‘Quadrature’ which is the sin component. This data is derived from the Radio Frequency (RF) front end of the receiver hardware.

The IQ data is translated into direction for further processing, such as determining signal direction in three-dimensional space. Algorithms such as MUSIC (Multiple Signal Classification), ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) and PDDA (Phase Difference Direction Algorithm) turn the IQ data into a pseudo-spectrum the peaks of which provide the direction.

PrecisionRTLS Location Engine Pseudo-spectrum

Radiogoniometry has many complexities such as multipath propagation where a radio signal reaches the receiver by two or more paths due to reflection or diffraction from structures or objects in the environment. This causes multiple peaks in the plot. This is where anti-interference algorithms come into play that can mitigate the effects of signal interference, such as multipath propagation and environmental noise. These algorithms rely on statistical signal processing techniques and adaptive filtering methods to distinguish between the desired signal and interference, thereby enhancing the accuracy of direction finding.

Beacon Setup Tip: Advertising Type

Bluetooth beacons are tiny devices that transmit small amounts of data over short distances using Bluetooth Low Energy (BLE) technology. They can operate with different protocols, like iBeacon (developed by Apple), Eddystone (developed by Google), and various sensor beacon protocols.

Despite the fact that it might seem these beacons can advertising multiple protocols simultaneously, it’s not quite the case. What they actually do is advertise these protocols one after the other in a very rapid sequence. This is due to the way Bluetooth works; it’s not technically possible to transmit multiple signals at the exact same moment. Instead, the beacon switches between the different protocols very quickly, which to a casual observer, or a smartphone, might seem simultaneous.

This rapid succession is made possible by BLE’s advertising mechanism. Beacons, in their idle state, continuously broadcast their identity, and potentially other information, in what’s called ‘advertising packets’. When they’re configured to use multiple protocols, they broadcast an iBeacon packet, then an Eddystone packet, then a sensor beacon packet, and so on in a cycle. This is repeated at a very high frequency, many times per second.

However, while this flexibility is advantageous in certain scenarios where various beacon protocols are required, it’s not always necessary and drains the beacon’s battery more quickly. This is because each advertising event consumes energy, and broadcasting in multiple protocols effectively multiplies the number of these events.

Many beacons are set up to advertise multiple protocols by default. If you don’t need this functionality, you can optimise battery life by disabling unnecessary protocols. This is done using a manufacturer-provided app. The exact process can vary between manufacturers and beacon models, but it generally involves connecting to the beacon, accessing its settings and then deselecting the protocols you don’t need.

While multiple-protocol advertising can be useful in certain situations, it’s often more battery efficient to only use the specific protocols you actually need for your application.

The Advantage of iBeacon over Eddystone and AltBeacon

iBeacon, Eddystone and AltBeacon are the three main beacon technologies. All of them use the standard Bluetooth Low Energy (LE) advertising format. Bluetooth LE is designed for short bursts of radio that uses little power and is therefore suitable for battery operation. Each of the advertising variants uses a unique advertising packet format that defines what kind of data the beacon transmits.

iBeacon, launched by Apple in 2013, was the first to adopt this technology and created a new wave in proximity services. It uses a simple advertising format, which consists of a UUID (universally unique identifier), Major, and Minor identifiers.

Eddystone, introduced by Google in 2015, offers a more complex advertising packet format with four different frame types: Eddystone-UID (similar to iBeacon’s UUID), Eddystone-URL (broadcasting web address), Eddystone-TLM (telemetry information about the beacon itself), and Eddystone-EID (an encrypted version of Eddystone-UID for secure applications).

Altbeacon, an open-source specification introduced by Radius Networks, provides a simpler format similar to iBeacon.

The functionality of beacon technologies are different on iOS and Android due to differences in the operating systems themselves. Apple’s strict app guidelines and strong emphasis on user privacy limit the ability of apps to perform tasks in the background. For instance, iOS only allows apps to scan for iBeacon formatted advertisements in the background using the CoreLocation library, not CoreLocation. Eddystone or AltBeacon can only be read in background using CoreLocation. Android offers more flexibility for background tasks and can work with iBeacon, Eddystone and Altbeacon.

Although Eddystone and Altbeacon have their merits, iBeacon is the advertising of choice for most scenarios involving smartphone apps due to the integration with iOS.

Close Contact Tracing Using Beacons

There’s new research from Maritime and Ocean University, Republic of Korea on A Close Contact Tracing Method Based on Bluetooth Signals Applicable to Ship (pdf).

While the Covid pandemic is over and we are getting on with our lives, there are still outbreaks that can be particularly disruptive on ships. The cruise market was adversely affected by pandemic and continues to need to be vigilant. Operations on navy and commercial shipping also continue to be affected by on-board outbreaks.

The researchers have devised a system that uses beacons rather than having smartphones detect each another. Mutual smartphone detection is difficult, if not impossible, without using the smartphone contact APIs that are only available to government organisations.

The system identifies risky areas in ships based on the location point encounters. It tracks close contacts using Bluetooth and without WiFi or Internet. A smartphone app provides transmission risk indicators.

View Social Distancing Beacons

Beacon Tx Power

A critical aspect of beacon setup is the transmission power (Tx power) setting, which determines the range of communication and the beacon battery consumption. The Tx power is measured in dBm (Decibel-milliwatt) and indicates the strength of the radio signal. The standard range of TX power settings typically falls within -30 dBm to +4 dBm, the ‘standard’ level being 0dBm.

Lower TX power settings, between less than 0 dBm, are used for short-range. Low power settings conserve battery life by minimizing energy consumption, making them ideal for battery-powered beacons. Higher power settings, above 0 dBm are used for long-range communications. However, it is important to note that higher power settings significantly impact battery life.

A change in ± 3dBm is a halving or doubling of power. An approximate rule of thumb is that this halving/doubling affects the battery in opposite way way. For example, going from 0dBm to -3dBm will approximately double the battery life. This is a very rough approximation because the beacon also uses a small amount of power when not transmitting, which is most of the time because the beacon only transmits for a few milliseconds (ms) every configurable 100ms to 10 sec.

A change in ± 3dBm doesn’t halve or double the range. Instead, the range approximately follows inverse square law with distance. Again this is approximate due to antenna characteristics, obstructions and interference. Signal processing at the receiver can also optimise performance and improve on the usable range.

Our recommendation is to start off with the ‘standard’ level of 0dBm. This will provide the battery life quoted by the manufacturer. If you really need more range then increase the power. If the range is further than you require then reduce the power to obtain a better battery life. You can test the range and received radio level using nRF Connect app on a smartphone.