9160/NCS: GPS accuracy value, how to interpret, and inconsistency

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Thu, 27 Jan 2022 06:24:14 GMT

[quote user="naiqiang"]Thanks, enabling PSM and eDRX does help. Now the accuracy is as good as before when I ran GPS only.[/quote]

Happy to hear that this provides the accuracy.

[quote user="naiqiang"]Does that mean the network won;t allow me to change it?[/quote]

Yes, that's correct the PSM is controlled by the network. From the document 3GPP 27.007 Ch. 7.38.

The set command controls the setting of the UEs power saving mode (PSM) parameters. The command controls
whether the UE wants to apply PSM or not, as well as the requested extended periodic RAU value and the requested GPRS READY timer value in GERAN/UTRAN, the requested extended periodic TAU value in E-UTRAN and the requested Active Time value. See the unsolicited result codes provided by commands +CGREG for the Active Time value, the extended periodic RAU value and the GPRS READY timer value that are allocated to the UE by the network in GERAN/UTRAN and +CEREG for the Active Time value and the extended periodic TAU value that are allocated to the UE by the network in E-UTRAN.

More information can be found in our AT Command Reference Guide for AT+CPSMS.

Kind regards,
Øyvind

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

bluebeam — Thu, 27 Jan 2022 02:03:23 GMT

Thanks, enabling PSM and eDRX does help. Now the accuracy is as good as before when I ran GPS only.

Now I'm looking at these PSM and eDRX parameters. I wonder if there's any guidance as to how to properly set them and what they mean. Or should I always let the cell network decide that? I print out some logs and looking at the PSM active time which is set at 180s which is way too long for my case. I need to send data every 60s. So that seem indicate that the device will never be in PSM mode. I attempt to set the value to something smaller like 10s or 20s. But I still get the 180s. Does that mean the network won;t allow me to change it? Is there example to for how to set PSM and eDRX parameters?

part of my logs when start to connect to LTE network:

===============

*** Booting Zephyr OS build v2.6.99-ncs1-1 ***
I: APP thread running
I: modem init
D: lte_lc_init
I: AT+CGMR: 0, mfw_nrf9160_1.3.1
, 0
%XMODEMSLEEP: 4
D: lte_lc_psm_param_set
D: lte_lc_psm_req
D: lte_lc_edrx_req
D: lte_lc_connect
%XMODEMSLEEP: 4
D: LTE_LC_EVT_MODEM_SLEEP_ENTER
%XMODEMSLEEP: 4,0
D: LTE_LC_EVT_MODEM_SLEEP_EXIT
+CEREG: 2,"910F","066E4D0F",7
D: LTE_LC_EVT_NW_REG_STATUS
D: LTE_LC_EVT_CELL_UPDATE: id=107891983 tac=37135
D: LTE_LC_EVT_LTE_MODE_UPDATE
+CSCON: 1
D: LTE_LC_EVT_RRC_UPDATE
+CEREG: 1,"910F","066E4D0F",7,,,"00100011","00011111"
I: modem init done
I: cloud init
D: LTE_LC_EVT_NW_REG_STATUS
D: LTE_LC_EVT_PSM_UPDATE: tau=18600 act_time=180(s)
+CEDRXP: 4,"1001","1001","0001"
D: LTE_LC_EVT_EDRX_UPDATE: mode=7 edrx=163.839996(s) ptw=2.560000(s)

=================================

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Mon, 24 Jan 2022 08:06:57 GMT

Hello,

[quote user="naiqiang"]

On the other hand I'm continuing more tests with the cellular radio enabled. I basically took the agps sample project and put the GPS in continuous mode, and run GPS for 1 minute and then send the data over LTE to the NRF cloud portal.

I did not intentionally stop the GPS but I think the cellular radio will block GPS when it needs to transfer data. So there's a few seconds gap for GPS data. It's probably equivalent to a hot start.

What I can see is it seems the accuracy is a lot worse than when there's only GPS turned on. Is this something expected? Does the cellular radio affect the GPS operation in anyway (other than a small gap in time)? In the agps sample code, I see the PSM mode is requested. I did not enable GPS's PSM mode. Other conditions for testing are the same as before.

[/quote]

Our modem responds with the following:

In that case LTE will interfere with GNSS operation. If PSM is not enabled, the modem needs to periodically listen to pagings from the network. Unless eDRX is used, the paging cycle is usually 1.28 seconds.

If both LTE and GNSS are enabled at the same time, it's recommended to use eDRX or/and PSM. eDRX can be used to increase the paging cycle much longer. And when in PSM, modem doesn't need to listen to pagings at all. It should be noted, though, that the device can only be reached by the network when it's listening to pagings. So, the suitable configuration depends on the use case (and what the network supports).

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Mon, 17 Jan 2022 09:06:41 GMT

Hello,

Sorry, the response from the team was not sent for some reason.

In customer's use case when device is moving and GNSS is running on continuous tracking mode, changing dynamic mode could improve accuracy.

See here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/gnss_interface.html#changing-the-dynamics-mode

Dynamic mode can be one of these: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/api.html#dynamics-modes

Regarding antenna, 9160DK onboard antenna is rather good, but using good quality active antenna could improve accuracy. Also it often enables placing the antenna on better location in challenging environment, example higher.

[quote user="naiqiang"]I did not intentionally stop the GPS but I think the cellular radio will block GPS when it needs to transfer data. So there's a few seconds gap for GPS data. It's probably equivalent to a hot start.[/quote]

The GPS can not run when LTE radio is active. As described in the GPS receiver chapter of the nR9160 Product Specification:

Operation is time multiplexed with LTE modem, and it is possible to use the GPS and QZSS receiver to obtain position either while the LTE is in RRC Idle mode or power saving mode (PSM), or when the LTE modem is completely deactivated.

[quote user="naiqiang"]What I can see is it seems the accuracy is a lot worse than when there's only GPS turned o[/quote]

Are you comparing with AGPS?

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

bluebeam — Sat, 15 Jan 2022 05:27:52 GMT

Hi,

Any more update? I'll be nice if there's more info or suggestion.

I did not intentionally stop the GPS but I think the cellular radio will block GPS when it needs to transfer data. So there's a few seconds gap for GPS data. It's probably equivalent to a hot start.

Any thoughts?

Thanks!

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Thu, 06 Jan 2022 08:51:22 GMT

Thanks for providing these details. I will need to forward this to the team and discuss possible solutions.
If you have not heard back from me by Monday, please ping me here 🙂

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

bluebeam — Thu, 06 Jan 2022 00:31:28 GMT

Ok, I did more tests and here's the results.

First chart is from the same setup at my back yard with everything exactly the same. Device is not moving. I did 3 run, each lasts 5 minutes. Then plot the reported accuracy and the 2D-error between the tests. As you can see, the reported accuracy drops to below 2 meter pretty quickly. But the 2D-error bounces up and down in a wide range through out the 5 minutes. It does not converge as you R&D team implied earlier. But it doesn't run off either. So I conclude that in my specific environment the real accuracy is more like 7~8 meter instead of 3 meter. I consider this 'typical' scenario for my project's use cases.

The second chart is from a test done on a roof top. It's the top floor of a public parking garage without cover. There's no taller building nearby. So it's really wide open. The result is much better. Not only the reported accuracy is lower (about 1.5 meter), the 2D-error is generally below the reported accuracy most of the time. Even the part that's elevated is generally under 3 meter. So I'm convinced the device can achieve the specification under ideal condition.

Back to my project's perspective, the remaining question is, is there any way to improve GPS performance under an non-ideal environment? Particularly it the device is moving, ie walking or running but not driving. Does a better antenna help? (this is done with 9160DK with the onboard antenna)

Thanks!

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Mon, 03 Jan 2022 08:54:21 GMT

Yes, please do. It would be good to have more data to compare with what the R&D team has.

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

bluebeam — Thu, 30 Dec 2021 01:13:23 GMT

Thanks! I'll need to collect more data after the holiday...

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Wed, 22 Dec 2021 14:40:26 GMT

Hello, my apologies for the late reply. Our R&D team have replied with the following:

Q: A further questions is, if I need to track position to the accuracy as data sheet specified (ie 3meter), it seems I can only keep the GPS running in continuous mode?

A: Yes, in order to get to 3 m accuracy, the device should be running in continuous mode.

Accuracy is reported with 2D 1-sigma (= with 68% confidence) as said in doc.
Averaging data partly is dangerous. In plot all positions has been treated equally when first are reported with low accuracy value.
in 60 second case first fix is cold/hot fix and accuracy improves over time. We don't get 3m accuracy with the first fix even it is started in continuous mode.

This picture tries to illustrate the case:

2D errors is distance between positions in Test A and Test B. So after 55 seconds distance between position reported in Test A and Test B is less than reported accuracy.. If test would have continue little bit further we may have discovered the true location.

Please note that the DevZone team is currently entering Christmas holidays with lower staff count. Delayed answer / longer response time must be expected

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Wed, 15 Dec 2021 10:51:32 GMT

Hello, and thanks for providing these details. I will need to forward to our nRF91 GPS experts.

Kind regards,
Øyvind

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

bluebeam — Tue, 14 Dec 2021 06:32:59 GMT

Ok the modem firmware version is not v1.2.2-9.... That's the modem library build string. I believe the modem firmware version is 1.2.3 when I use the SLM.

(I wonder if there's an API to read the modem firmware version? I can't find one)

Now I upgraded the modem firmware to the latest 1.3.1. I did the test again. I don't see much difference in the results. Maybe that's limited by the environment I have. I plan to find an open area and test this again to see if I can get consistent results regarding the accuracy.

Can you clarify if this is the right expectation. If I can find an ideal environment (open sky, what else?), then the fixes should converge to the true position and should be within the "accuracy" range?

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

bluebeam — Mon, 13 Dec 2021 19:13:05 GMT

That's in the middle of backyard. It's generally open, with trees and houses at least 30~40 feet away in all directions. But there're some tall trees on one side. The device definitely won't be able to see the horizon. Not sure how important that is. It's open straight up. This is probably not ideal for GPS testing, but quite comparable to actual usage scenario , which will mostly be dense urban/suburban area.

Hardware setups:

no external antenna

9160DK: PCA10090 1.0.0 / 2021.7

modem firmware: v1.2.2-9-g854050c28061

NCS: 1.7.1

Now I realize there's new modem firmware 1.3. I probably try it to see if that makes any difference.

RE: 9160/NCS: GPS accuracy value, how to interpret, and inconsistency

Øyvind — Mon, 13 Dec 2021 13:55:21 GMT

Hello,

[quote user=""]The 9160DK board is placed in a relative open area.[/quote]

Can you please describe the area where you are testing? Please note that buildings and other elements around may cause reflections, which can impact the results.

[quote user=""]Everything looks just like the first set: reported accuracy drops down to 3m or less quickly and the coordinates mostly fall into the radius. Except the average of the coordinates (hence the whole cluster of positions) are at a point quite some distance from the first test. It could be 6~8 meters away, or even more sometime.[/quote]

The numbers sound correct as described in the nRF9160 Product Specification.

What version of the nRF9160 DK are you running? Are you running an external antenna? What modem version and nRF Connect SDK version are you running?

Kind regards,
Øyvind