Category: RSSI

Improving Safety on Construction Sites

Researchers from Spain have recently developed a safety system that uses Bluetooth Low Energy (BLE) to ensure the correct use of Personal Protection Equipment (PPE) on construction sites. This innovative system is not only robust and reliable but also easily adaptable to various dangerous machines.

The system is built on RSSI (Received Signal Strength Indicator) information transmitted by BLE devices arranged in a particular rig combined with a Bayesian distance estimator. The aim is not merely to signal risky situations caused by the misuse of PPE but to intervene swiftly and robustly to eliminate the safety risk.

The researchers have built upon previous results on the statistically sound measurement of distances and closeness in construction sites. By collocating several BLE transmitters near orthogonally, they have managed to reduce interferences while avoiding the cost of more advanced technologies.

The practical contributions of this research include the design of the system, a working prototype and a thorough statistical analysis for finding the optimal parameters for both the software and the equipment. The research shows that using several orthogonally collocated BLE transmitters improves robustness and overall performance without requiring more complex and costly equipment.

The improvements are most significant as the number of transmitters increases. Using a diversity of devices is better when these devices are noisy and it also enhances the robustness of the solution. An arrangement of orthogonal BLE beacons allows for an increased rate of advertising messages, and an extended Kalman filter plus a discrete filter can benefit from that increased flow of data, providing a simple and efficient approximation to the problem of safety estimation.

The use of an additional beacon to notify the correct use of the PPE, implemented inside a wearable microcontroller, is a very flexible solution. It allows for different local implementations using various sensors and measurements without the need to modify the RSSI-only method in the receiver, and with any number of users. The system can be easily integrated into a wide variety of dangerous machines and tools such as angle grinders, concrete mixers and pneumatic drills.

Why is There Variation of RSSI?

We sometimes get asked whether a beacon is faulty because a customer is seeing a lot of fluctuation in the Received Signal Strength Indicator (RSSI) values, even in a seemingly stable environment and with no change in distance. The short answer is: this is normal. The reason for this lies in the complex nature of radio signals and how they interact with the environment.

Radio signals are susceptible to a variety of factors that can affect their received strength. When a beacon sends out a signal, it doesn’t just travel in a straight line to the receiver. Instead, it disperses in multiple directions and can bounce off walls, floors and other objects.

Reflections can cause the signal to take different paths before reaching the receiver. Each path can have a different length and, therefore, a different time delay. This results in a phenomenon known as multipath fading, where multiple copies of the signal arrive at the receiver at slightly different times. This can cause fluctuations in the RSSI values you observe.

While reflections are a primary cause of RSSI fluctuation, they are not the only one. Other physical changes in the environment can also contribute to this variability. For example, the presence of people moving around can affect the signal, as the human body is mostly water and can absorb radio frequencies. Similarly, other electronic devices emitting radio frequencies can interfere with the signal, causing further fluctuations.

To get a more accurate understanding of the signal strength, it’s advisable not to rely on a single RSSI value. Instead, you should look at many RSSI values over a period of time and calculate the average. This approach helps to mitigate the effects of temporary fluctuations and provides a more stable and reliable measure of signal strength.

Many people, particularly researchers, have looked into the intricacies of RSSI and its variability. Various algorithms and methods have been developed to improve the accuracy of RSSI-based distance estimation and location tracking. For those interested in a deeper understanding or potential solutions to this issue, we recommend looking at the articles tagged RSSI and RSSIStability on our blog.

BLE Beacons for Sample Position Estimation in A Life Science Automation Laboratory

There’s new research into BLE Beacons for Sample Position Estimation in A Life Science Automation Laboratory. In life science automation laboratories, monitoring and managing the position of samples is crucial. One emerging solution for sample position estimation in these settings is the use of Bluetooth Low-Energy (BLE) beacons.

Historically, many fingerprinting models that harness received signal strength (RSS) data have been proposed for indoor positioning. However, a large number of these methods require an extensive installation of beacons. In contrast, proximity estimation, which relies solely on a single beacon, emerges as a more apt solution, especially for vast automated laboratories.

The intricacies of the life science automation laboratory environment present hurdles for the conventional path loss model (PLM), a prevalent method of proximity estimation based on radio wave propagation. Addressing this challenge, the paper introduces BLE sensing devices crafted specifically for sample position estimation. The proximity estimation rooted in BLE beacon technology is explored within a machine learning framework. Here, support vector regression (SVR) is employed to capture the nonlinear correlation between RSS data and distance. Concurrently, the Kalman filter is applied to reduce deviations in the RSS data.

Experimental outcomes spanning diverse settings underline the superiority of SVR over PLM. Remarkably, SVR achieved 1m absolute errors for an impressive 95% of test samples. The addition of the Kalman filter augments stable distance predictions, effectively smoothed the raw data and mitigated extreme value impacts.

When estimating positions between parallel workbenches, the framework achieved an average mean absolute error (MAE) of just 0.752m across 12 test positions. And for position estimation on workstations, identification accuracies beyond 99.93%.

In conclusion, for labs aiming to enhance sample position estimation, the BLE beacon paired with an IoT node presents a flexible sensing solution. By integrating machine learning, particularly SVR, and the Kalman filter, this framework offers increased accuracy in both corridors and labs.

How Far Can a Bluetooth Beacon Measure Distance?

A common misconception is that beacons can measure distance. In reality, beacons, with the exception of some specialist social distancing beacons and sensor beacons with an additional distance sensor, are designed to send signals rather than receive them.

Instead, measuring distance happens on the receiving end. Devices such as smartphones are equipped to detect these beacon signals. When a beacon sends out its Bluetooth radio signal, the receiving device knows the received signal strength (RSSI). This RSSI can be used to infer the distance between the beacon and the device.

In the proximity of a few metres, the variation in RSSI is significant enough to deduce the distance with a reasonable degree of accuracy. However, as the distance increases, the variation in RSSI becomes less pronounced. This means that while you can determine if a beacon is close or far away, pinpointing an exact distance becomes challenging.

For example, the iOS programming API, CoreBluetooth, provides classifications for the detected beacon signals. These classifications are ‘immediate’, ‘near’, and ‘far’. They don’t give a precise measurement in metres or feet but rather a general idea of the beacon’s proximity.

In terms of maximum range, depending on the specific beacon, it can be detected from distances up to 50m or even 100m. However, as mentioned earlier, at these longer ranges, the RSSI doesn’t provide a clear indication of exact distance. Instead, it offers a more general sense of whether the beacon is nearer or farther away.

Location System Anchor Optimisation

Researchers from Department of Computer Science, University of Jaén, Spain have a new paper on OBLEA: A New Methodology to Optimise Bluetooth Low Energy Anchors in Multi-occupancy Location Systems.

This paper introduces a new methodology called OBLEA, which aims to optimise BLE anchor configurations in indoor settings. It takes into account various BLE variables to enhance flexibility and applicability to different environments. The method uses a data-driven approach, aiming to obtain the best configuration with as few anchors as possible.

The OBLEA method offers a flexible framework for indoor spaces where the occupants are fitted with wrist activity bracelets (beacons) and BLE anchors are set up. The anchors then collect and aggregate data, sending it to a central point (fog node) via MQTT.

A dataset was generated with the maximum number of anchors in the indoor environment, and different configurations were then trained and tested based on this dataset. The best balance between fewer anchors and high accuracy was chosen as the optimal configuration.

This methodology was tested and optimised in a real-world scenario, in a Spanish nursing home in Alcaudete, Jaén. The experiment involved seven inhabitants in four shared double rooms. As a result of this optimisation, the inhabitants could be located in real time with an accuracy of 99.82%, using a method called the K-Nearest-Neighbour algorithm and collating the signal strength (RSSIs) in 30-second time windows.

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Monitoring Sheep Location Using Bluetooth Beacons

There’s new research from Scotland, UK on Calibration of a novel Bluetooth Low Energy (BLE) monitoring device in a sheep grazing environment. Knowing an animal’s location and proximity can offer insights into landscape use, animal performance, behaviour and social contacts. However, the technologies currently used to collect these data are costly and challenging to implement, particularly due to the low value of individual animals and typically large flock sizes.

A device was specifically designed for a study to assess the relationship between the Received Signal Strength Indicator (RSSI) of a BLE beacon and BLE reader and to develop a distance prediction model. This model was then applied in a static situation and on-sheep studies, using a multi-lateration approach to determine a beacon’s location within a field setting. A purpose-built Wearable Integrated Sensor Platform (WISP) was developed for the study, featuring a BLE reader and other sensors. It was designed to report the identity and RSSI of the 16 ‘closest’ beacons seen for each duty cycle.

The findings revealed that the height of the device had an impact, with fewer beacons reported at a shorter distance in WISPs at the lower height of 0.3 m. RSSI can vary greatly based on factors like transmission power, device orientation, enclosure and the operating environment.

Using the distance prediction and adjusted distance prediction, beacon locations could be estimated for most of the beacons. Not all beacons could be located due to issues such as being reported by too few WISPs or the resulting multi-lateration circles not intersecting.

The study suggests that BLE can potentially be used for sheep localisation in outdoor environments. The multi-lateration approach is dependent on receiving RSSI readings from multiple readers at a similar timepoint, it could offer more information about localisation and movement than simple proximity ranges or presence/absence. Locating a sheep to within about 30 m in a field environment represents a significant step forward.

Can I Set the Maximum Distance the Beacon Transmits?

Many people inquire about adjusting the transmission distance of a beacon. They often wish to either conserve battery or restrict the range at which a beacon is detectable.

While some third-party platforms and SDKs offer distance settings, it’s a misconception to think you can directly set the distance. What you’re actually adjusting is the transmission power, which in turn influences the transmission distance. But since this involves radio waves, which are prone to reflections and interference, it’s impossible to guarantee that a specific power will equate to a precise distance.

When using an app to detect beacons, you can employ the Received Signal Strength Indicator (RSSI) to focus on those within a desired range. However, it’s challenging to precisely correlate RSSI with the actual distance.

Some wonder if they can set the distance in terms of centimetres, similar to NFC. Typically, this isn’t feasible because even at their lowest power setting, most beacons transmit over a distance of about a metre.

Rather than asking if the transmitter’s distance can be minimised, it might be more practical to configure the receiver to disregard detections from further away. By using the RSSI value on the receiving app or another Bluetooth scanning device, you can filter out distant beacons. Specifically, you can dismiss detections with an RSSI below a certain threshold, allowing you to focus on detections within a centimetre range.

We have an article on Choosing the Transmitted Power.

Using Beacons To Detect Human Movement

There’s an innovative use of beacons mentioned in the research paper on Developing a Human Motion Detector using Bluetooth. Beacons and its Applications (PDF).

Most motion sensing applications usually place a sensor beacon on the things that will move. The accelerometer in the beacon reports movement. The research paper describes an alternative method of detecting movement of a person, an elderly person in this case, based on the change in blocking of the beacon signal over time. This has the advantage that the beacon doesn’t need to be worn. Also, it doesn’t have to be a accelerometer beacon as any beacon can be used.

The problem with using the strength of the beacon signal (RSSI), is that it varies over time even when there’s no change of blocking in the room. This is due to radio frequency (RF) noise and reflection. The authors of the paper looked into smoothing of the data to filter out such variance in the data:

The report concludes that when averaging over three or more RSSI values, it’s possible to minimise the RF variance and reliably detect the variance caused by human movement in the room.

Another, more reliable, way of detecting movement is to use a beacon with built-in PIR such as the iBS02PIR, M52-PIR, IX32 or MSP01.

Using Bluetooth Metadata to Infer Social Context

Researchers from Idiap Research Institute and EPFL, Switzerland have been looking into the use of smartphone data, include Bluetooth metadata to try to infer social context, for example whether someone is alone or not.

The paper Understanding Social Context from Smartphone Sensing: Generalization Across Countries and Daily Life Moments (pdf) attempts to better understand human behaviour and mental well-being. The paper focuses on the use of passive smartphone sensors, including Bluetooth, to track the social context of individuals over time. In the past, this field of research has been limited by the fact that most studies have only been conducted in one or two countries and often focused on specific contexts such as eating or drinking.

This paper aims to overcome these limitations by using a new, extensive and multimodal smartphone sensing dataset that includes over 216,000 self-reports from more than 580 participants across five different countries – Mongolia, Italy, Denmark, the UK and Paraguay. The goal is to explore the feasibility of using sensor data to infer whether a person is alone or not and to examine how behavioural and country-level diversity influences this inference.

The sensor data comes from 34 different sensors, divided into continuous and interaction sensing modalities. Continuous sensing includes types of activity, step count, Bluetooth, WiFi, location, cellular, and proximity data, while interaction sensing involves app usage, touch events, screen on/off episodes, and notifications. In terms of Bluetooth, the study used both normal and low-energy Bluetooth capturing data on the number of connected devices and received signal strength indicators (RSSI).

The study’s key findings suggest that sensor features can be used to infer the social context. The research also found that models partially personalised to multi-country and country-specific data achieved similar accuracy levels, typically ranging from 80% to 90%. However, the models did not generalise well to unseen countries regardless of geographic similarity.

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Using Packet Loss to Infer Location

There’s new research from the University of Illinois titled Packet Reception Probability: Packets That You Can’t Decode Can Help Keep You Safe (pdf). Many existing systems estimate distance using the Receiver Signal Strength Indicator (RSSI) which is negatively impacted by sampling bias and multipath effects. As an alternative, the study uses Packet Reception Probability (PRP) that utilises packet loss to estimate distance.

Localisation is achieved through a Bayesian-PRP approach that also includes an explicit model of multipath. To facilitate straightforward deployment, there’s no need for any modifications to hardware, firmware, or driver-level on standard devices and only minimal training is required.

A variety of devices were used including Bluvision iBeeks, BluFi, a Texas Instrument Packet Sniffer, a laptop, and Android smartphones (Nexus5x). 60 iBeacons were deployed in a library and 38 in a retail store. The Texas Instrument Packet Sniffer, connected to a Windows laptop was used for packet reception from beacons. Android phones were equipped with a purpose-built Android app.

PRP was found to provide metre-level accuracy with just six devices in known locations and 12 training locations. Combining PRP with RSSI was found to be beneficial at short distances up to 2m. Beyond distances of 2m, fusing the two is less effective than using PRP alone because RSSI becomes de-correlated with distance.