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Bluetooth® Questions - Webinar 4th Dec 2019

Below are some questions asked during the Bluetooth® webinar on 4th Dec 2019. 

Recording link:


3rd Party Tag Support:

Can you use small Bluetooth® devices like the ‘Tile’ range of keyring/wallet products?

  • It is possible for us to support Tile tags, but the way they send data is somewhat unusual. It requires a Bluetooth® connection, it does not just beacon it's serial.
  • 3rd Party tags can be supported, his is covered here: 3rd Party Bluetooth® Tag Support
  • In general, it is possible for us to integrate tags that 'beacon'. Integration effort (cost) is relatively low.
  • It is also possible for us to support connecting to other Bluetooth® devices, but this kind of integration is more complex and hasn't yet been put in place.

What sort of range is achievable? 

What sort of range have you been able to achieve inside a factory environment? Between a Bluetooth® end node and gateway (Remora2/Eagle) Is 195m realistic or is this optimistic line of site conditions?

The 195m value is line of site conditions. 

Bluetooth® range is dependant on a variety of factors - so the best way to gauge the range you will get in your specific environment is to test. 

The Bluetooth® Technology website does an excellent job explaining the various factors that impact Bluetooth® Range

Understanding Bluetooth® Range

The link above explains how to use the calculator on this page to get range estimates

For how this relates to our devices, see here: Bluetooth® Range and Battery Life

Guppy line of sight range tests are available here: Guppy Bluetooth® Range vs Battery Life

It also explains how the range and battery life impact each other. 

Battery Life

What sort of battery life could we expect from an end node (Guppy and SensorNode) if it was chirping every 10 minutes?

Battery life questions go hand in hand with range so the battery life so this is covered here:

Guppy Bluetooth® Range vs Battery Life

On default settings 

5 years for the Guppy (2 second beaconing) on 2 x AAA Energizer Ultimate Lithium

4 years for the SensorNode (2s beaconing), 3 x AA Energizer Ultimate Lithium.

An important fact to note here is that a 10 minute chirp interval is very long

The G120 scans continuously, all the time, so it is unlikely to have trouble picking this up. 

However given there is an energy cost to scanning, on the Remora2 this is done periodically. 

There is a configurable Scan Period - how often to scan, and Scan Interval - how long to scan for. 

E.g 10 min period and 20 second interval - every 10 minutes the Bluetooth® module is turned on for 20s to listen for any nearby Bluetooth® tags. 

You can envisage scenarios where you had a 10 minute scan interval, and 10 minute beacon interval, you could miss the beacon completely. 

E.g. Tag beacons at 1005, gateway scans at 1010, Tag beacons 1015, Gateway Scans 1020 and they always miss each other. 

For this reason, in practice the scan interval needs to be at least 3 x the beacon period - so for the Guppy, which beacons every 2sec, a scan interval of 10 seconds on the Remora2 is more than enough. 

The 10 minute interval would require a 30 min scan interval!! This uses up a lot of Remora2 batteries.

This is important to note as some tags will advertise great battery life - at a very infrequent beacon interval! So they are saving energy doing this, but it is being 'stolen' from the Remora2!

Which Gateway does a Guppy Talk to?

If you had multiple gateways in the same environment, does the Bluetooth® end node send data to both gateways or does it choose the one closest? The scenario could be that I want to know where abouts in a building an asset is and there may be multiple gateways to ensure coverage.

In short - any within range - so in this case both if they are both in range. 

It is important to note that the Guppy and SensorNode tags beacon. This is sometimes referred to as a 'ping' or 'chirp'.

Put simply, they do not connect to the gateway devices. They simply shout 'I'm here!!' every 2 seconds by default (this can be configured). If they are within range of a gateway, they gateway will pick this up. 

The gateway devices - G120, Remora2, Eagle. Maintain a list of all tags that they can currently see - and report this to the server periodically.

In this example both gateways would report this if they were both in range. 

If this is an issue there are a few ways to get around this. 

  1. Place the gateways a large enough distance apart so there is minimal overlap.

  2. The RSSI of the Guppy is included in the information sent to the server as part of the tag list - so on the server side you could identify which gateway the Guppy is closer to based upon which is reporting the stronger RSSI.

  3. In the Bluetooth® settings on our devices, you can set an RSSI tag filter. So only tags that the gateway receives with strong signal (i.e. likely closer) will be included in the list that is sent to the server. This in effect limits the overlap.
    This only works if all tags are identical, and set to transmit at exactly the same power. So use caution. 

Beacon Based on Movement. 

Is there a mode where the device only chirps when it is being moved, but sleeps when it is not moving?

  • No this does not currently exist. 
  • The Guppy Bluetooth® currently doesn’t have an accelerometer – but it is catered for in the PCB design.
  • For large orders we can run devices with an accelerometer and accommodate this type of thing in FW. 
  • We wouldn’t set it to not chirp, but we would set it to set a flag when on the move. So this can be detected. 
  • Given the 5 year battery life of the Guppy with 2s beaconing - it isn't all that neccessary to sleep the device when not moving. Battery life is not at a premium..

The gateway devices can be configured to scan on trip start, trip end, and at varying intervals based on being in/out of trip as well. 

Maximum number of Tags to a Gateway

The maximum number of tags the gateways can support is 512. This is the maximum tag list size on these devices. As for the theoretical maximum, that is dependant on many factors. Imagine you were in a room of crowded people that were all shouting, and you were trying to listen to every single one of them. Inevitably, the people closer to you will drown out the people farther away from you, but if you listen for long enough you may hear the people farther away when those closest to you are taking a breath. The same is true for Bluetooth®, and the maximum number of devices that could be picked up by a gateway is dependant on:

  • The beaconing rate - beacons are less likely to clash if they beacon less frequently, but that also means if they do clash then you have to wait longer for a chance to pick them up again
  • Background noise - other bluetooth® and wifi devices may interfere with signals
  • The scan length - the longer the scan length, the less of a problem clashing is. For example, if tags are beaconing every 1s, and the scan length is 15 second, then there are 15 chances for the beacon to get through to the scanner. 

Accuracy to Gateway

What is the accuracy of the beacon to the gateway?

Do multiple gateways improve position accuracy? 

Context - what positional information can be shown for the tag - i.e. can the gateways locate them to a specific region etc. 

If a single tag is reporting to a single gateway, all that will be reported is that tag's ID + RSSI (signal strength indication) along with any other data (temp, battery voltage etc) specific to the tag. Some tags, like the Guppy and Sensornode also report their transmit power.

The best that can be determined/achieved with RSSI is that you could approximate the distance of the tag from the gateway. With the assumption higher RSSI = closer, lower = further away.

This has potential pitfalls however, if tags are transmitting at different powers, they could be in the exact same position but the gateway will pick up different RSSIs. That is why some tags, like our Guppy and Sensornode, also send their transmit power.

None of this positional estimation is done on the device - it is done server side. 

For example, in Telematics Guru, if a tag is in the Gateway's list of devices it can see, the tag is simply reported at the gateway's position. 

If you have very good range in one area, tags might be getting picked up from 200m away from the gateway, but will be displayed at the gateway's location. 

If you have poor range, the accuracy is in some ways better - since the tags will be at most this shorter range away.

With multiple gateways, the server could potentially do some triangulation, and compare the RSSI seen by each gateway, to get a better position  - but this will require significant effort on the server side and may not be reliable in practice. 

Best to keep it simple and reliable!

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