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Bluetooth 5.1 Angle-of-Arrival Antenna Array Design

There’s new research from University of Porto, Portugal on Design and Experimental Evaluation of a Bluetooth 5.1 Antenna Array for Angle-of-Arrival Estimation.

Experiments were conducted on a circular antenna array in an anechoic chamber and in a real-world environment to evaluate the quality of the retrieved data. The setup included four beacons advertising a Constant Tone Extension (CTE).

The researchers used a combination of ways to process the data including a non-linear recursive least square method, an unscented Kalman filter, non-linear least square curve fitting, a Gaussian filter and Multiple Signal Classification (MUSIC).

The paper explains how reducing computational complexity is critical in order to achieve real-time processing on edge devices. Accuracy is affected by noise originating from multi-path effects, differences in oscillators between transmitter and receiver, behaviour of the RF switch and slight variations in impedances of the antenna tracks between antenna pairs. There’s much more noise in the real-world environment than in the anechoic chamber.

The researchers conclude that they found it difficult to reduce the error in the obtained phase measurements and identify which packets were reflections.

This paper demonstrates that processing of AoA IQ data is non-trivial. Processing in real-time for a more than a few assets is a challenge. This is why, while many AoA reference kits’ can be used to demonstrate AoA, the accompanying software often isn’t scalable to the required number of assets.

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Sensoro Beacons No Longer Manufactured

We have been informed by Sensoro that the SmartBeaconAA and SmartBeaconAA Pro are no longer being manufactured. We have just sold out of our stock so these beacons are no longer available.

SmartBeacon AA Pro

The SensoroAA Pro was a great, robust, waterproof beacon with a great battery life. If you you are now looking for something similar from an alternative manufacturer we suggest you consider the Minew i3.

Research into Bluetooth Beacon Security

There’s recent useful research into Bluetooth beacon security from The University of Hong Kong. The paper on Security and Privacy of Wireless Beacon Systems explains how widespread deployment of Bluetooth beacons can cause them to be an attractive target for adversaries.

The paper covers security issues and privacy concerns and classifies the possible types of attack.

The three main reasons for attacks are for free riding services, user profiling or service disruption.

Understanding adversary motives, capabilities and the potential impact allows for defence mechanisms and planning for remedial actions.

Measuring Distance with Bluetooth LE

There’s a useful recent Webinar at Nordic Semiconductor on Measuring distance with the Nordic Distance Toolbox. The Nordic Distance Toolbox (NDT) provides ways to measure the distance between two Nordic SoCs. An SoC (System on a Chip) is the main chip found in beacons and Nordic is one of the main manufacturers.

The webinar covers the theory of distance measurement based on radio phase, RSSI, Round Trip Timing (RTT) and processing such as Inverse Fast Fourier Transform (IFFT). Practical performance is measured and the conclusions are:

  • Phase based ranging gives best accuracy but is range limited maximum range is limited to 8 to 10m (in the office environment)
  • RTT gives lower accuracy (Standard deviation 3.8m) but can be used up to the maximum Bluetooth connectivity range that can be several 100 metres
  • High precision with a median 3 filter gives the best accuracy (Standard deviation of 37cm)

The presentation PDF is also available.

Using the SoC radio to determine distance is power-hungry, relatively complex to develop and, as the above shows, doesn’t result is very good accuracy. If you want to measure distance it’s simpler, more accurate and more battery-efficient to use a dedicated hardware-based distance sensor. For example, the IBS03R uses a dedicated time of flight (TOF) sensor to achieve accuracy of +-25mm and a battery life of 1.8 to 2.8 years.

New Bluetooth LE Book

There’s a new book Develop your own Bluetooth Low Energy Applications by Koen Vervloesem. It introduces Bluetooth Low Energy and shows how to programming with Python and the Bleak library on a Raspberry Pi or PC, with C++ with NimBLE-Arduino on Espressif’s ESP32 development boards and with C on Nordic Semiconductor’s nRF52 boards.

Koen has a blog where you can read an abridged version of the book. He explains Bluetooth Low Energy, the Bluetooth stack, advertising and connecting. You can also view the samples on GitHub.

Python and Bluetooth on Linux

Barry Byford has a new blog post on D-Bus and Bluez. It documents his experiences creating a BLE central client on Linux. Barry deliberates over dbus-python and pydbus. He then provides an example how to create a Bluetooth GATT connection, converting D-Bus typed data to python types and interacting with a BBC micro:bit.

While you are on Barry’s site, read his notes from workshops and further notes on using Bluetooth.

Beacon Re-Designs

We are increasingly seeing beacon manufacturers providing updated versions of their beacons, not to provide extra functionality but to instead simplify the designs so as to reduce the component count or use fewer or cheaper semiconductors. The semiconductor manufacture crisis has resulted in a shortage of semiconductors that has resulted in component shortages and price rises. Beacon re-designs are an attempt by manufacturers to keep prices lower and in some cases prevent an existential crisis for a particular beacon model.

System on a Chip (SoC)

Some manufacturers are using simpler versions of the System On a Chip (SoC). These typically have less memory or have less functionality. Often the more-capable functionality wasn’t even used in the older beacon variant. Other times, things can be done in software that were performed in hardware. There’s also a trend to remove crystals that provide timing and instead perform this in software. Some manufactures are switching between SoC hardware manufacturers, for example from Nordic to Texas Instruments that requires a total hardware and software re-design.

Care needs to be taken when purchasing beacons especially when purchasing just a few samples and much later purchasing a larger quantity. Changes in hardware design mean that you won’t necessary get the same behaviour. This can affect aspects such as range and battery life. Doing things in software rather than hardware often affects battery use. At BeaconZone we are taking special care to ensure that current stocks of items behave as previously, if necessary specifying a particular variant when re-stocking.

Introduction to Bluetooth Direction Finding

The Bluetooth SIG, the owner of Bluetooth standards, has a useful video introduction to Bluetooth® Location Services and High-Accuracy Direction Finding. It’s the 4th video from Embedded World 2020. Strangely, you need to view direct from the Bluetooth SIG site because this video isn’t available direct from Vimeo.

Martin Woolley, Senior Developer Relations Manager, provides a high level overview and explains how direction finding differs to positioning using RSSI signal strength. He describes how Bluetooth Angle of Arrival (AoA) and Angle of Departure (AoD) make use of multiple angles to provide accurate location.

Martin dives deeper into direction finding theory and phase sampling. He explains how Bluetooth uses Frequency Shift Keying (FSK) of the radio carrier signal that necessitates use of a Constant Tone Extension (CTE) to enable direction finding. It’s explained how Bluetooth Controller IQ sampling fits into the Bluetooth stack.

View G2 AoA Gateway Kit

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Fingerprinting Positioning Using Multiple Advertising Slots

There’s interesting research from Spain on Multi-Slot BLE Raw Database for Accurate Positioning in Mixed Indoor/Outdoor Environments. It looks into fingerprinting with beacons simultaneously advertising six slots rather than one slot.

Fingerprinting is where you first measure the signal levels at various known points and then later compare new data with the old to work out the position. This is usually performed with one signal from each beacon. The researchers increased this to six signals to attempt to improve positional accuracy.

Tests were performed at the campus of the University of Extremadura in Badajoz in the Physics and Mathematics buildings and also outside. Beacons were set up to transmit four slots using the Eddystone protocol and two using the iBeacon protocol. Different transmit powers were used for each slot. Measurements were performed using three different smartphones with a custom developed Android application. The resultant data is available on Zonodo.

The researchers compared a simple Nearest Neighbours algorithm (NN) using all the slots, the one slot with the highest transmission power and the average of all slots from the same beacon. The results showed that using all the slots or just one per beacon gives similar results for accuracy, floor, and Tag ID recognition. Results using the averaged values increased the accuracy by 10%.