"real-time" tracking with the NRF9151

[m4rkw]

I want to achieve as close as possible to real-time tracking with the nRF9151. Because of the shared RF path this is somewhat tricky, LTE and GNSS can't run simultaneously. Initially I was running into the carrier-side RRC timeout but figured out how to make RAI work to get around it.

I've now managed to get the GPS read -> send loop down to roughly one event per 2-3 seconds. I suspect this is probably at the limit of what's possible with this SIP because it looks like almost that entire interval is GPS but I thought I'd post here just in case there are some other tricks I've missed.

For reference I'm using my own server on a very fast connection and the traffic is using DTLS. Obviously I can batch the records to eliminate the gaps but I'm aiming for high resolution near-realtime tracking. With an older device that had a GPS chip that was separate from the modem real-time 1Hz was possible, still hoping there might be a way to get near this with the nRF9151.

Thanks,
Mark

[Øyvind]

Hello, have you seen our Developer Academy Cellular IoT Fundamentals course? There is a lesson called nRF91 simple tracker.  Are you looking at using our location services as well?

A separate GPS device will allow you to have true "real-time" tracking. 

Kind regards,
Øyvind

[m4rkw]

Hi Øyvind

Thanks for getting back to me. I already have fully working tracker firmware with a bunch of features, not sure that course is going to help me much.

I know I can use a separate GPS device and have been considering that, I just wanted to see if there’s anything I can do to squeeze more iteration speed out of the 9151 SIP. It’s possible it might fare better in a vehicle as my bench setup antenna is apparently a bit weak.

Since I fixed the RRC timeout LTE now still blocks GPS for around ~1s per cycle which seems like a lot for transmission on an open DTLS connection. I might try reverting to plain UDP for comparison and see if that reduces.

Cheers,

Mark

[Øyvind]

Hi Mark, as the GNSS operates concurrently with LTE when the modem is in RRC Idle or PSM mode, it depends on what configuration the network grants your device. This varies from network to network. 

Using A-GPS (nRF Cloud location services) will allow current satellite data to be delivered over LTE instead of waiting for satellite broadcast (reduces TTFF from minutes to seconds).

Our modem experts state: 

In good conditions, GNSS will get a fix in ~1s. Basically, the interval depends on how fast RRC connection can be activated, data sent to the network and the RRC connection released. Interval of a few seconds is probably doable, depending on the network. However, this does cause a lot of signaling on the network side as well, so I think we've generally recommended something like 10 second interval to not upset the carrier.

Let me know how that works for you.

Kind regards,
Øyvind