Minew MWL01 AoA Beacon Insights

The MWL01 Beacon is an AoA beacon which means it advertises a constant tone extension (CTS) for angle of arrival detection. An accelerometer detects the degree of movement and adjusts the advertising across three levels between 100ms (fast) -> 250ms (normal) -> 4s (slow) to save battery life. The battery level is provided in the advertising data. Double clicking the button changes the advertising, for example, for SOS notification.

Here are some observations that aren’t immediately obvious in the documentation:

  • While AoA is Bluetooth 5.x, It actually advertises Bluetooth 4.1 rather than 5.x. This makes it suitable for non-AoA applications where it can be detected by non AoA Bluetooth 4.1 receivers. It’s particularly suited for asset tracking because it increases the period between advertising, when not moving, to significantly save battery.
  • You might think the change to 4s advertising isn’t working. Be patient. It takes 5 minutes of normal advertising before it switches to slow advertising. Note that it also takes 5 seconds to go from fast advertising to normal advertising. While the advertising rates can be changed, the times to transition can’t be changed.
  • The beacon that is supplied with the AoA kit is different to that supplied separately. The kit’s MWL01 is fixed to 100ms advertising and can’t be changed. This is because it much easier to evaluate AoA and develop software when the advertising is consistent over time. The kit MWL01 can be upgraded, if necessary, to support the changing advertising period. However, we recommend you keep them as 100ms advertising beacons for ease of testing.
  • The ‘Location Finding’ flag in the AoA advertising is actually an indication of the double button press rather than anything to do with direction finding. This flag stays on for a minute and the blue led flashes during this time. Again, the double button press is only available on the non-kit beacon.
  • The battery level isn’t in the AoA data advertising. The beacon advertises a second connectable broadcast frame that includes the MAC address and battery level every 1s, 1s and 4s in the fast, normal, and slow modes respectively. These times can’t be changed.
  • Unfortunately, Minew are stipulating that the settings and firmware upgrade are only available to people who have signed an NDA with Minew or BeaconZone if you purchased the beacons from us.

Linux, D-Bus and Bluez

Barry Byford has a useful and continually growing introduction to using Bluetooth on Linux. He describes how to use BlueZ, the official Bluetooth stack on Linux, via D-Bus and Python. D-Bus allows communication between multiple processes running concurrently on the same machine. There’s an example how to set up an asynchronous event loop and how to build a Bluetooth Low Energy (BLE) device implementing the Bluetooth Central role.

While you are there, also take a look at Barry’s notes and examples on Creating a BlueZ Pairing Agent and Bluez beacons on the command line.

Beacons, IoT and Platforms

Our article on Beacon Proximity and Sensing for the Internet of Things (IoT) explains how beacons can become part of the Internet of Things. Most implementations need to use a server or cloud IoT platform. However, in working with clients we have seen many problems with most of today’s commercial IoT platforms:

Cost – Many aren’t financially scalable in that costs escalate once the number of sensors and/or sensor reporting frequency is increased. Future costs are also unknown and unpredictable which is unacceptable for many organisations.

Continued Existence – It’s still early days for IoT and it’s not known if today’s platforms will be around for as long as the project. Some early beacon-specific platforms have already closed. Others have been taken over by large companies that have other agendas.

Security – Many projects, particularly those with sensitive data, can’t be run on or through shared public servers, services or platforms.

Control – For some organisations, aspects such availability and reliability need to be controlled in-house.

Functionality – IoT is a nebulous concept covering many specialist areas and industries. It’s difficult for a given IoT platform to cater for all needs. It’s usually necessary to compromise on your required functionality. Many IoT platforms have limited alerts, analytics and dashboards because they have cater for the lowest common denominator and not provide industry specific features.

A solution to these kinds of problem is the use of open source IoT platforms. The current and future costs are known, there’s full control and you are free to extend in any way you wish.

Platforms such as ThingsBoard offer data collection, processing, visualisation, and device management. In the case of ThingsBoard it offers a secure, scalable solution that uses a Cassandra database that’s well suited for storage and querying of time-series data while providing high availability and fault-tolerance.

Thingboard Dashboard Showing Sensor Beacons

If you need more help, consider our development services.

Using Bluetooth RSSI for Visually Impaired Navigation

There’s new research from the University of Bristol on Outdoor Localization Using BLE RSSI and Accessible Pedestrian Signals for the Visually Impaired at Intersections.

The idea is to use Bluetooth received signal strength (RSSI) to enable the blind and visually impaired (BVI) to safely to cross intersections on foot. Audible systems already exist but users find them confusing when crossing complex road intersections. The researchers developed a system called CAS (Crossing Assistance System) that provides pedestrian positioning.

The system uses k-nearest neighbors (kNN) method Support Vector Machine (SVM) with various RSSI features for classification, including a moving average filter, that was able to localise people with 97.7% accuracy.

Transmitting Images via Bluetooth LE?

Some platform providers claim beacons can transmit multimedia data which isn’t strictly true. A beacon sends a small amount of data that typically contains a unique id. When an app sees an id it shows information, such as an image, that is typically obtained from a server.

But what about beacons actually transmitting images? Chong Shao, Shahriar Nirjon, Jan-Michael Frahm or the Department of Computer Science, University of North Carolina has a paper on “Years-Long Binary Image Broadcast using Bluetooth Low Energy Beacons” (pdf). Again, don’t be misled, they don’t mean it takes years to send an image but instead that a beacon might transmit for a long time (which most do).

The researchers have found that with suitable compression schemes, a set of 2–3 beacons is capable of broadcasting high-quality images (75%–90% structurally similar to original images). The image quality improves when more beacons are used.

beaconimageprocessingpipeline

How might you get the data into a beacon? Well, some beacons such as the M52 Plus and iB003N allow arbitrary data to be set in the advertising data.

The images are necessarily very simple but nevertheless this provides a great example of what can be achieved when you attempt the seemingly impossible.

RSSI vs AoA Bluetooth Asset Tracking

In a previous post on iBeacon Microlocation Accuracy we explained how assets can be tracked using Bluetooth Received Signal Strength (RSSI) or Angle of Arrival (AoA). We advised working out what accuracy is needed prior to seeking out an appropriate solution. However, accuracy isn’t always the only consideration and here is a more complete list of factors.

Accuracy

RSSI asset tracking can achieve accuracies of about 1.5m within a shorter range confined space and 5m at the longer distances. RSSI zone-based systems where beacons are found to the nearest gateway, are accurate to the inter-gateway distance that can be of the order of cm. However having such as large gateway density is usually only practical for very small areas.

AoA asset tracking achieves sub-metre accuracy. The accuracy depends most on the distance between the locator and beacon but is also affected by the locator hardware quality, radio signal noise, surfaces causing radio reflections, the accuracy of locator placement and beacon orientation.

Maximum number of beacons

AoA-based asset tracking produces and requires much more data which means the locators and software systems have to deal with more data. The data throughput for both types of system depends on the required minimum latency that in-turn depends on how often the beacons advertise. RSSI-based systems support up to high tens of thousands of beacons while AoA supports thousands of beacons.

Beacon variety and IoT

RSSI-based systems can use any beacon and hence support a large range of sensor beacons that can detect movement (accelerometer), movement (started/stopped moving), button press, temperature, humidity, air pressure, light level, open/closed (magnetic hall effect), proximity (PIR), proximity (cm range), fall detection, smoke, natural gas and water leak.

AoA beacons are more specialised and currently only support limited IoT sensing such as movement (accelerometer) and button press.

Cost

AoA locators, gateways and beacons are more complex and are therefore more costly. AoA also needs more locators/gateways per sq area. Hence, AoA systems are x3 to x4 more expensive than RSSI systems.

Setup effort

The accuracy of AoA requires that locators be more carefully positioned than for RSSI, in particular the site and AoA locator positions need to be carefully measured.

Beaconzone supplies both RSSI and AoA systems. Contact us to determine the best type of system for your needs.

Nordic Semiconductor Wireless Quarter Articles

Nordic Semiconductor, the manufacturer of the System on a Chip (SoC) in many beacons, has published the latest online issue of Wireless Quarter Magazine. It showcases the many uses of Nordic SoCs.

The latest issue of the magazine highlights the use of SoCs in the following Bluetooth solutions:

  • A glucose monitoring system
  • A six-degrees-freedom (6DoF) virtual reality (VR) headset
  • A smart bulb that can be controlled from a connected device or by voice command
  • A smartwatch incorporating Amazon Alexa Voice Service (AVS) functionality
  • A Mouse supporting very low latency PC gaming
  • A Bluetooth LE powered trampoline wearable

There are also interesting articles on:

  • The DECT-2020 standard for IoT
  • How engineering education is evolving to train tomorrow’s IoT innovators
  • How location services can extend beyond supply chains to other use cases
  • How wireless tech increases workers’ safety and boosts productivity

The use of asset tracking solutions in global logistics could create $1.9 trillion of economic value

There’s also an ‘Inside Track’ article on beacons showing how beacon wireless location services are making consumers’ lives simpler.

Inside the Minew LR1 Locator

The Minew AR1 locator has multiple antenna that receive special constant tone extension (CTE) advertising from beacons.

The Minew antenna consists of 12 PCB patches. If you imagine a radio signal hitting the antenna array from the left hand side, the antennas to the right will receive the signal slightly later. The phase difference can be use to determine the angle.

Martin Woolley’s excellent Bluetooth Direction Finding Technical Overview explains the theory. The main concept is based on simple trigonometry:

In practice, if you do this across just two antenna and with one sample the result has very poor stability. Instead, you need to consider all the antenna patches, over time, as well as perform analysis in multiple directions. This requires use of advanced radiogoniometry techniques.

Minew AoA Kit

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Minew AoA Direction Finding Kit in Stock

We now have Minew AoA Direction Finding Kit and beacons in stock. The AoA kit consists of a G2 gateway, 4 locators, 3 beacons and interconnecting cables. It covers an area of 400m². Multiple kits can be used to cover larger areas.

The gateway outputs antenna IQ data that’s sent to your server or BeaconZone’s LocationEngine™ for generation of angles.

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