Longer range distance measurement synchronisation.

RE: Longer range distance measurement synchronisation.

Jason — Fri, 04 Aug 2023 12:59:39 GMT

Thanks, I'd not seen those range tests before. Unfortunately I cannot use the nrf21540. I ordered the (hopefully) final PCBs this week. So I have to work with what I have.

I repeated the test. This time being more careful to maintain line of sight. and got results upto 50m. Which is probably as far as I walked. It was too bright to use my laser pointer to verify the figures unfortunately.

I will continue testing but I think it's unlikely I can promise my customers any more than 10m (30ft) reliably. Assuming they put it in their pocket etc. But it's still a useful feature, so I will try to include it.

Thanks again for your help. It's much appreciated.

-Jason

RE: Longer range distance measurement synchronisation.

PaKa — Fri, 04 Aug 2023 12:21:54 GMT

So for the Bluetooth range, we test several 100 meters with the standard DKs in line of sight, Comparing range with Bluetooth Low Energy of the nRF21540 DK and the nRF52840 DK. The range will be highly depending on the environment so walls and similar will shorten it. Same for the PCB design and the antenna.

Don't use phase based to estimate the range of the RTT as that will be overly pessimistic.

You can use other synchronization mechanisms if you want, proprietary protocols will also work as long as you can get the synchronization good enough. We only offer the Bluetooth scanner/advertising sample but as the ranging is proprietary running in the timeslot API you can use any radio standard for the synchronization.

RE: Longer range distance measurement synchronisation.

Jason — Fri, 04 Aug 2023 12:12:51 GMT

I see, thank you.

Then I cannot expect the 100ft range I had hoped for.

I just tested RTT with the example again. Making a histogram of the number of samples for each metre.

I walked away from the device and back again. Not very scientific. But it looks like the range was already struggling beyond 10m and was fairly bad by 20m. I will repeat the test.

Is there any easy way to synchronise except scannable advertising? It uses a lot of power to scan.

Perhaps PAwR is worth a try?

Thanks for your help.

RE: Longer range distance measurement synchronisation.

PaKa — Fri, 04 Aug 2023 11:32:19 GMT

The phase based ranging works reliably out to 8-10 meters, for longer ranges you should use RTT only. At longer ranges you are more likely to get incorrect resolutions for the range with the phase based ranging due to multi-path and similar.

The RTT ranging requires that you can communicate over non-coded PHY so using coded PHY for the advertising will not increase your ranging capabilities.

RE: Longer range distance measurement synchronisation.

Jason — Fri, 04 Aug 2023 07:35:01 GMT

I did a test with the nrf_dm example with +8TX power and I can see that the range returned by ifft is good enough, and that the high-precision returns nan when the range is large. I think the estimates are about right

I've not tested RTT mode yet. And I've not got CODED phy advertising to work (yet)

It seemed to have poor reliability at this relatively short range however. I'm not sure if RTT will be more suited to longer ranges I'm not sure if the non-CODED scannable adverts are the problem, or it its because of the DM calculations.

I will try to get CODED phy scannable adverts working and try to test RTT also today.

RE: Longer range distance measurement synchronisation.

Jason — Thu, 03 Aug 2023 18:24:06 GMT

Hi Amanda, Thank you.

I realised that I had misunderstood the webinar, specifically that the phase calculations themselves require 2-way communications.

I had failed to comprehend this when I first watched it. I thought they were just referring to the synchronisation step, but instead it's actually happening during the DM timeslot also. In order to do the phase calculations.

So I can't expect this to work at vast ranges, even if I can do one-way synchronisation.

My goal is to have a reliable 30m (100ft) *outdoor* range. And it would be great if I could get the synchronisation using the 12 periodic adverts that I'm already sending and receiving every second.

I can see several possibilities.

Change the example to use CODED phy and then look for ways to reduce the time spent scanning.
Find a way to get synchronisation from my existing periodic adverts.
Try the callbacks from PAWR (periodic adverts with responses)

I can see that there are callbacks listed in bt_le_ext_adv_cb which might be what I need.

	/**
	 * @brief The Controller indicates it is ready to transmit one or more subevent.
	 *
	 * This callback notifies the application that the controller has requested
	 * data for upcoming subevents.
	 *
	 * @param adv     The advertising set object.
	 * @param request Information about the upcoming subevents.
	 */
	void (*pawr_data_request)(struct bt_le_ext_adv *adv,
				  const struct bt_le_per_adv_data_request *request);
	/**
	 * @brief The Controller indicates that one or more synced devices have
	 * responded to a periodic advertising subevent indication.
	 *
	 * @param adv  The advertising set object.
	 * @param info Information about the responses received.
	 * @param buf  The received data. NULL if the controller reported
	 *             that it did not receive any response.
	 */
	void (*pawr_response)(struct bt_le_ext_adv *adv, struct bt_le_per_adv_response_info *info,
			      struct net_buf_simple *buf);

Obviously I'm not sure what to try.

Any suggestions or advice are greatly appreciated.

Kind regards,

-Jason

RE: Longer range distance measurement synchronisation.

Amanda Hsieh — Thu, 03 Aug 2023 16:28:49 GMT

Hi,

I am working on your case and will update it later.

Regards,
Amanda H.