Assume your object is 100m away from where the RSSI is being measured. If the signal reduces by a mere 3dB then the object is now majically 140m away. 3dB is a very small RSSI variation. A person obstructing the path could reduce the signal by 10dB, so the object is now 300m away.
Out of doors there are problems too. I often test radio comms in the streets around where I live. There is a location about 300m away from my house, where the signal drops by 10dB if I cross from one side of the road (5m) to another, so on one side of the road I am 300m from home and on the other (5m away) I am 900m from home ?
Possibly things might improve with a lot of gateways and a lot of transmissions to carry out averaging, but thats hardly a TTN compatible application.
I want to develop a tracking solution for objects and/or people both indoor and outdoor.
For outdoor GPS would be the go-to solution, using LoRa as the data carrier. This is all clear and beyond the scope of this forum post.
For indoor location I was thinking about using BLE beacons with the Nodes periodically scanning for beacons and reporting their RSSI’s.
Then I saw the Things Indoor Gateway and it got me thinking. With BLE Beacons I would need about 1 beacon per 10 meters to allow each node to receive at least 3 beacons for triangulation.
Using the LoRa signal instead of BLE would kill two birds with one stone. Firstly the LoRa coverage is guaranteed, but more importantly: I’d need fewer “devices” (gateways or beacons) in the building since the LoRa signal carries further than BLE (right?).
Exact position precision is not that important to me. If I can see on which floor and which corridor the Node is, this would be enough. Even an indication of the strongest receiving gateway could achieve this (1 gateway per corridor).
The detail is still somewhat lacking to be able to make any concrete suggestions - particularly if it’s a generic solution that needs to work in a wide range of indoor environments and building structures / levels / materials.
So buy a few TTIGs and a couple of devices and give it a try.
PS, the phrase “LoRa coverage is guaranteed” is invalid in all known languages, human and digital.
Would my idea of using LoRa Gateways make sense battery-wise? The LoRa Node’s won’t have to scan for BLE Beacons. All they’ll do is send a ping every now and then.
Localisation of devices, indoors and outdoors has a great many applications. Where is that wheelchair in the hospital, where is that pallet of items in a factory, where is the supervisor?
A DIYer could put an RF beacon together for maybe £3, made in volume they could be as low as £1 perhaps. Receivers don’t need to be TTN gateways, simple RF receivers could be plugged into a nearby network connection or connected by Wi-Fi. Given we have devices such as the ESP32 these receivers would be cheap too.
Lots of people come up with the ‘idea’ of using RSSI for a good level of localisation, almost along the lines of “no-one has thought of this before”. Over in the Arduino forums its suggested as an ‘idea’ pretty much on a weekly basis.
If low cost localisation systems are viable where are they?
Hi everyone, I think that the most common industrial approach to this kind of asset/location tracking is UHF RFID. The RFID tags are very cheap (a few cents/pennies) and therefore can be put on almost anything including consumables. The tags do not have batteries so there is no tag-level maintenance.
I have been involved in deploying UHF RFID systems (for livestock traceability) with the backhaul from the RFID reader to central processing over LoRaWAN. It works very well with RFID range up to about 5m depending on the radio and the antenna.
There are also lots of “pistol-style” RFID tag readers for mobile use that backhaul over cellular radio or WiFi. The RFID readers are often built into discrete “airport-security” type gates.
Note: most of the RFID tags and security gates that you see in large retail stores are LF RFID which uses a completely different technology.
First of all, great community! Thanks for helping me out and thinking along!
UHF RFID has also crossed my mind, but given the low range and expensive equipment I don’t see this as a viable option.
For now let’s assume I want to track employees in an office building and wheelchairs in a hospital.
I think the BLE and LoRa approaches are both interesting. I’ll be using LoRa as the communication protocol in both solutions. Here is my pro’s and cons list, feel free to comment and expand the list.
BLE
Distribute simple BLE Beacons across the building that emit a ping periodically. The Node will scan for BLE Beacons and report the detected Beacons, battery state and RSSI over LoRa to the application.
Pro’s:
BLE Beacons are low cost and don’t need any backhaul network connection
No dedicated LoRa Gateways required if there already is decent coverage, can be expanded by adding a Gateway if needed
Nodes can detect if no BLE Beacons are in range and act on this
Precision can be improved by adding more BLE Beacons
Cons:
Many BLE Beacons required to provide full coverage
Nodes have to actively scan for BLE beacons periodically, probably impacting battery life (right?)
BLE Beacons can run out of battery and have to be serviced
No way to know if Beacons run out of battery when no Node picks up their signal
LoRa
Distribute LoRa Indoor Gateways across the building. The Node will emit a ping periodically with its battery state which the Gateways will report to the application along with RSSI.
Pro’s:
With just a few LoRa Gateways full coverage should be achievable, so less equipment in the building
Node does nothing more than emit a ping, so battery life should be great (right?)
LoRa Gateways have to be powered, so no batteries to replace
Cons:
LoRa Gateways have to be powered and connected to the internet
Node cannot detect when it’s out of range of our “own” Gateways
Wheelchair goes to the local park, to the bandstand at the top of the hill, about 1km away, gets line of sight through the window of a 3rd floor window with a gateway - registers ping - no one has the slightest idea where it is.
RSSI, as LoRaTracker says, is the hot solution no-one ships because it hasn’t been shown to work because of physics - LoRa Alliance consider RSSI to be in the 1-2km accuracy range - which is fine for tractors in Kansas but even telling which floor on would be problematic - if the person is one floor up above a gateway, you’re going to have to figure out the profile on the RSSI for that - although probably having the gateways in the same location on each floor may help.
You are definitely in the “buy some stuff, try it out” zone.
Moving devices are beacons, fixed devices scan for them and report via something else, eg, WiFi. ESP32 development board is around $7.
What you’re describing is more the case of when a phone tracks itself relative to fixed beacons. But a phone already has connectivity.
It’s not really clear that there’s a role for LoRa (and especially not LoRaWAN) in your system, as that is typically too small a “pipe” for detectors to use to report their results.
The examples I recall seeing, of using RSSI for the application, seemed to rely on a fair bit of averaging, as in lots of TX RX cycles, to produce an average and reduce errors such as people or objects moving around in the building.
Therein is part of the problem as I see it; use of TTN significantly limits the potential for lots of transmissions and hence averaging.
It is a ‘solution’ I would like to try for myself (as a sceptic) and with a few Arduinos, it would be easy enough to do so.
Hi @markdegroot
I’m afraid your idea would fail because a phenomenon called multipath fading causes the RSSI to vary wildly indoors. So wildly that it would not be possible to draw any conclusions (at all) as to the whereabouts of the transmitter…
not really adding anything new to the thread, but confirming what other experienced people have said above, and given good reasons for:
this can and will not work, because (essentially) … physics.
there are good reasons why indoor location systems, specifically in hospitals, turn to RFID as reliable and cheap solution, possibly complimented by Wi-Fi/BLE tracking of people, maybe some UWB and ultrasonic for specialized systems.
