Been doing some widespread reading around TWR and TDoA. Various documents all refer to the TWR protocol with its Discovery Phase, using Blink and Range Init messaging, and Ranging Phase, using Poll, Response & Final messaging. Then I came across APS001 v2.2 page 10, this page shows blink being used in the ranging phase. I’m assuming this is a typo unless told otherwise.
Been looking but not actually found any documentation thus far which shows how Discovery (unpaired nodes) and Ranging (paired nodes) should work side-by-side for cases with multiple nodes. i.e. How the system should manage and maintain these two activities and prioritise. Any pointers?
This in part comes down to user application priorities.
Dedicating more air time to discovery will allow faster detection of new nodes and potentially allow a lower power profile since you can more easily detect low duty cycle devices. However it allows less time for actual measurements.
Spending a lot of time measuring allows for a higher update rate or for more active devices but leaves less time for discovery and implies higher power usage.
How best to weight this compromise between flexibility, performance and power will depend on what you are looking for.
Ultimately what messages you send, when you send them and what name you chose to give them is entirely up to you. e.g. as you noted in APS001 “tag blink” is used in place of “range init”. Depending on your system design there may be no reason why these two messages can’t be the same thing. Don’t get hung up on names, look at functionality instead.
There are a lot of different ways you can structure a system to give the same end results.
Most of the application notes and technology descriptions give the simplest or most direct methods of maintaining the network and obtaining the required information, these aren’t necessarily the most efficient or best solutions for many applications. In fact they almost certainly won’t be, generic solutions can always be optimised for a given specific application. Whether that optimisation is worth the effort is a different matter…