nrf52840 packet transmitting time measurement for TOA or TDOA

RE: nrf52840 packet transmitting time measurement for TOA or TDOA

Dmitry — Thu, 05 Mar 2020 17:12:41 GMT

In your case UWB would be the best solution. If nevertheless you wish to experiment with TDoA/ToF, try a chip with direction finding (52811 or 52833) - with them you can sample an analog signal and thus get better resolution. Really it's not an easy task and requires a deep understanding of nRF radio transceiver.

RE: nrf52840 packet transmitting time measurement for TOA or TDOA

Thinking_HyunSoo — Thu, 27 Feb 2020 05:11:55 GMT

I really want to implement TOA or TDOA, but since you guys are saying that It is hard and BLE is not intended for this purpose, then is there any other way to check distance between two or multiple BLE devices in every second?

RE: nrf52840 packet transmitting time measurement for TOA or TDOA

Dmitry — Thu, 20 Feb 2020 21:35:48 GMT

IMHO your case is too serious to build it using some hack upon a technology that is not intended for it. Take a look at UWB, it has much better precision and applicable for indoor positioning.

RE: nrf52840 packet transmitting time measurement for TOA or TDOA

Thinking_HyunSoo — Thu, 20 Feb 2020 04:37:17 GMT

Hi
I actually want to use BLE devices in emergency situation to track first responder.
For example, if there is a building in fire, fire fighters are going into the building to save people who cannot escape. but in this case, we even cannot track fire fighters moving in the building.

So my idea is that fire fighters have peripheral BLE devices and fire chief or commander has central BLE device, then the commander can track first responder in the building and give them a proper order.

For tracking first responder, I was tried to get distance between peripheral and central BLE devices. For getting the distance, I tried packet transmitting time for TOA or TDOA.

If this packet time measurement is not available using the BLE softdevice stacks, can you give me any other approaches? I hope you got what i try to do it!

RE: nrf52840 packet transmitting time measurement for TOA or TDOA

Kenneth — Wed, 19 Feb 2020 14:07:24 GMT

There really isn't any support for doing this using the BLE softdevice stacks. The radio is entirely used by the softdevice, and the events that you potentially could use to measure time of travel just isn't available to the application.

Even if you could have access to the radio events, the results would not be accurate, since the main focus of the radio and soc is low power, the delay's are not accurate enough to be used in any reliable distance measurement (e.g. the on-air bit rate is 1Mbps, so depending on when the bit is sampled in the radio, you may have a resolution of up to 1us = 300m).

Best regards,
Kenneth

RE: nrf52840 packet transmitting time measurement for TOA or TDOA

Dmitry — Wed, 19 Feb 2020 10:14:11 GMT

Hi,

sorry, no answers on your questions, just my thoughts..

- a radio wave passes 300m in one microsecond, max timer frequency is 16 MHz, so the best resolution you can achieve is 300/16=18.75m, maybe a bit better with averaging from multiple packets. Is this ok for you? Anyway, RTC crystal is not suitable for this, only HFCLK.
- to implement ToA, you have to synchronize time on your devices with 1/16us accuracy, I can't imagine how it can be done.
- for TDoA, you need at least three base stations and one anchor, seems this is not your case.
- for ToF method (the one you actually going to implement), you don't need to insert any timestamp in your packets. You have to send a packet back to central with constant delay and measure time difference between two ADDRESS events (for sent and received packets).
Anyway, it can be implemented only with direct radio programming, PPI and capture/compare feature, not on top of BLE stack.

Maybe this post will be interesting for you, though it solves a different task.