Technical questions about nRF54L15 before buying it

[madding]

Hello everyone. I'm planning on buying multiple nRF54L15 boards for a college project, which is based on channel sounding. I'm considering rn 1 tag board, along with 1 dev kit, and a possible second dev kit. My technical questions are related to timing, capabilities and other required hardware.

Timing: during normal load, what is the expected timing between Channel sounding "first packet" send and data measurement obtention?

Capabilities: During my search, it became clear that simultaneous multi-reflector channel sounding is impossible (and makes a ton of sense, honestly). If I were to use 2 or more reflectors, would I have to do connect-measure-disconnect or would I be able to hold multiple device connection with different reflectors and measure one at a time? In case it's the first, how would it affect that extra load to timings?

Other required hardware: after looking at the spec for the dev kit, I've seen the embedded antenna it has. Would it be needed/recommended to have an external antenna on the dev kit when being used as a reflector? If so, recommendations are welcome. I've seen the tag, and the whole package looks promising for what I need

Those are my main questions. Any useful comment is welcome. TIA

[Edvin]

Hello,

I can imagine that there are many posts on this forum saying different things regarding channel sounding, as this feature is quite (relatively) new. 

What I can say now is that with the latest SDK, one tag and two DKs (or 3 DKs, or 3 tags, or any combination of these, let us call them A, B and C) it is perfectly possible to do channel sounding measurements between A<-->B and A<-->C "simultaneously". Of course, one at the time, but you don't need to "connect AB -> CS measurement -> disconnect AB -> connect AC -> CS measurement -> disconnect AC" etc. You can connect to both of them, and then do channel sounding on one device, then the other, then the first, etc.

You can use the embedded antenna on the DK. The Tag has two chip antennas, and they can also be used. No need for external antennas. 

The timing is roughly 1 second per measurement, from the top of my head. Don't arrest me on that, it may be 2 or even 3 seconds, and I don't have an application at hand that can test it quickly right now. But be aware of the accuracy of Channel sounding. I don't know what you intend to use it for, but the accuracy is good enough to tell if something is close or far away. For some ranges it is roughly 50cm, but very close it is a bit more, and very far away it is also a bit more. But this will always depend on the surroundings.

So depending on your application that may or may not be accurate enough. It will not give you a 1cm accurate indoor positioning system.

I want to mention a few words on the Channel Sounding roles:

With 3 devices, you can probably do one initiator and two reflectors. The impact isn't really that big, but there are some things to consider:

1: The initiator will use more power than the reflector.

2: The (BLE) Central will use more power than the (BLE) Peripheral.

I don't know whether you are familiar with these terms, but the Central is the leader of the BLE connection, and the Initiator is the leader of the channel sounding procedure. You can mix and match this.

We did have an internal student project where they wanted to measure the position of a tag. They ended up using one tag as a CS reflector, and BLE central. This means that the tag was the leader of 6 (simultaneous) BLE connections, but it was just the channel sounding reflector. The reason for this approach is that if you want to have a star-type "network" topology, the central will control the timing, meaning there will be less collissions on air (because it controls the on air timing). 

The tag was the reflector, meaning the initiators (5 or 6 DKs) would regularly send channel sounding initiator requests. The reason for this is that it is the initiator that takes the initiative to do a measurement, then the reflector just replies to a set of messages (according to the CS specification), and then the initiator does all the calculations (heavy lifting/number crunching). Again, you may be fine with one device being a central and initiator to two peripheral reflectors, but if you want to have more than two devices, then it is beneficial to spread out the load of the calculation to the surrounding devices. Of course, this means that you need to send the distance data from these surrounding devices to one central location if you want to e.g. calculate the position.

So to summarize, I think you should look into having one tag as a BLE central, and Channel Sounding reflector. This gives you a bit more flexibility in case you want to add more reflectors later. 

I hope this made some sense, and that it cleared up a bit, and not just add a lot more confusion. If you get your hands on 3 devices, I suggest that you try to get going with this setup, and see how fast you can get your channel sounding measurements, and how accurate they are.

Best regards,

Edvin