Multicell Geolocation via LTE

RE: Multicell Geolocation via LTE

Albrecht Markus Schellenberger — Fri, 24 Sep 2021 08:24:46 GMT

Hello Jeremy,

[quote user="jdorn"]Do you have any updates on how to improve the reliability of the neighbor measurements? If this is something where I need to share code, I can create a private query and do it there.[/quote]

my apologies for the late reply. It took us some time to analyse your traces.

[quote user="jdorn"]So I figured out that issue, it was a bug on my end. However, I am still inconsistently able to find neighbors. Anecdotally, the find rate seems to have improved from 1 in 10 or 20 to 1 in 3 or 5. Traces for scenarios where neighbors are found and not found are included.[/quote]

To start with, cell mapper locates cells recorded in this log to the middle of Chicago centrum area.

trace-neighbor-found:

It seems that we are on rather strong cell on band 12 in T-Mobile network. Tower is enb id 20934. It has both cell id's 32 and 453. However, all the neighbours which are close to this tower seems to be on different bands (2,41,66). Inter frequency measurements are not active, so these bands are not searched.

trace-no-neighbor-found:

We seem to be on AT&T network at band 12 and there are even less intra neighbours available. The signal level is as high as in T-Mobile network. Tower is enb id 210917.

So the main point here seems to be that the band 12 cells are the best for both T-mobile and AT&T, but apparently there are not too many neighbours on that band/frequency i.e. intra frequency. And the inter frequency neighbour measurements are not active. If you would like to see more cells, maybe bandlock could be used to exclude band 12 or simply allow only 2 and/or 66? Risk is that 2/66 doesn't have Cat-M cells.

To summarise this: neighbour cells measurement service in current modem release is implemented so that there would not be significant increase in power consumption in any scenario. It can detect any LTE Cat-M neighbour cell on the same frequency, or LTE NB-IoT neighbour cell when operating on LTE NB-IoT, but detecting inter-frequency neighbours requires that network is configured to provide information about those neighbours to devices. In this case network has not been configured to do that.

But we are continuously working on improving our software. The %NCELLMEAS functionality was recently introduced with modem firmware 1.3.0, and new features will be implemented in future releases.

I hope this will help you!

Regards,

Markus

RE: Multicell Geolocation via LTE

jdorn — Thu, 23 Sep 2021 20:11:04 GMT

[quote userid="100109" url="~/f/nordic-q-a/79652/multicell-geolocation-via-lte/330199#330199"]Markus[/quote]

Do you have any updates on how to improve the reliability of the neighbor measurements? If this is something where I need to share code, I can create a private query and do it there.

RE: Multicell Geolocation via LTE

jdorn — Mon, 20 Sep 2021 20:25:48 GMT

So I figured out that issue, it was a bug on my end. However, I am still inconsistently able to find neighbors. Anecdotally, the find rate seems to have improved from 1 in 10 or 20 to 1 in 3 or 5. Traces for scenarios where neighbors are found and not found are included.

Thanks again for all of the help.

devzone.nordicsemi.com/.../trace_2D00_neighbor_2D00_found.bin

devzone.nordicsemi.com/.../trace_2D00_neighbor_2D00_found.pcapng

devzone.nordicsemi.com/.../trace_2D00_no_2D00_neighbor_2D00_found.bin

devzone.nordicsemi.com/.../trace_2D00_no_2D00_neighbor_2D00_found.pcapng or so. In addition, it is usually just one neighbor.

RE: Multicell Geolocation via LTE

Albrecht Markus Schellenberger — Mon, 20 Sep 2021 08:56:44 GMT

Hello Jeremy,

[quote user="jdorn"]I have tried adding a 1 second wait, but the hang persisted.[/quote]

as stated in the documentation for lte_lc_neighbor_cell_measurement: Have you registered an event handler of type LTE_LC_EVT_NEIGHBOR_CELL_MEAS in your application?

Regards,

Markus

RE: Multicell Geolocation via LTE

jdorn — Fri, 17 Sep 2021 16:11:54 GMT

I attempted your proposed fix, but my code is hanging. I have included my code snippets and modem traces.

I have tried adding a 1 second wait, but the hang persisted.

devzone.nordicsemi.com/.../trace_2D00_2021_2D00_09_2D00_17T15_2D00_52_2D00_35.870Z.bin

devzone.nordicsemi.com/.../trace_2D00_2021_2D00_09_2D00_17T15_2D00_52_2D00_35.870Z.pcapng

RE: Multicell Geolocation via LTE

Albrecht Markus Schellenberger — Fri, 17 Sep 2021 11:06:12 GMT

Hello again Jeremy,

[quote user="jdorn"]Here are two traces. One shows what my device is doing when it detects a neighbor, the other when it detects no neighbors. These traces were taken within 5 minutes of each other, and the dev kit was not power cycled in between, only reset.[/quote]

the logs are confirming that neighbour cells measurements only are performed in RRC connected mode. During connection modem only results are returned that are available due to normal modem functionality. If there is nothing, then nothing (except the current cell) will be returned. This also stated in the %NCELLMEAS documentation:

"Neighbouring cell measurements are available during a data or signalling RRC connection only when the network has configured measurement rules for the device and the configured criteria is met."

So to avoid this, please use %NCELLMEAS during RRC idle. You can find some more information in the documentation of the Multicell location application.

I hope this will solve your issue!

Regards,

Markus

RE: Multicell Geolocation via LTE

Albrecht Markus Schellenberger — Fri, 17 Sep 2021 08:49:26 GMT

[quote user="jdorn"]I have included both the PCAP and raw trace files for you to look at.[/quote]

Thanks a lot, Jeremy! We will analyse the traces and come back to you.

Regards,

Markus

RE: Multicell Geolocation via LTE

jdorn — Thu, 16 Sep 2021 15:29:07 GMT

Here are two traces. One shows what my device is doing when it detects a neighbor, the other when it detects no neighbors. These traces were taken within 5 minutes of each other, and the dev kit was not power cycled in between, only reset.

I have included both the PCAP and raw trace files for you to look at.

Side note: I am gathering these neighbor cell measurements in the same manner as the Multi-Cell Location Example.

devzone.nordicsemi.com/.../trace_2D00_2021_2D00_09_2D00_16T15_2D00_06_2D00_28.607Z_2D00_SOME_2D00_NEIGHBORS.pcapng

devzone.nordicsemi.com/.../trace_2D00_2021_2D00_09_2D00_16T15_2D00_06_2D00_28.607Z.bin

devzone.nordicsemi.com/.../trace_2D00_2021_2D00_09_2D00_16T15_2D00_08_2D00_50.791Z_2D00_NO_2D00_NIEGHBORS.pcapng

devzone.nordicsemi.com/.../trace_2D00_2021_2D00_09_2D00_16T15_2D00_08_2D00_50.791Z.bin

RE: Multicell Geolocation via LTE

Albrecht Markus Schellenberger — Thu, 16 Sep 2021 07:55:35 GMT

[quote user="jdorn"]Do you know of configuration settings that I can use to make the neighbor cell measurements happen consistently?[/quote]

In connected mode, the network commands the neighbour cell measurements. Hence, the device does not have any influence on that. This restriction is valid during data or signalling RRC connection only.

In RRC idle, the device can always do the measurements with %NCELLMEAS command even when the network has not commanded device to do so. This command should be used for location service purposes.

%NBRGRSRP was implemented only for testing purposes and that will return only those measurement results that are available, as a result of normal modem functionality (controlled by network), which is why this command should not be used for this purpose. %NCELLMEAS was added as a new feature in mfw 1.3.0.

A modem trace will help to analyse if neighbour cells are available at your location. If you would like, please feel free to record one and upload it to the case :-)

Regards,

Markus

RE: Multicell Geolocation via LTE

jdorn — Wed, 15 Sep 2021 14:13:18 GMT

[quote userid="100109" url="~/f/nordic-q-a/79652/multicell-geolocation-via-lte/329633#329633"]How sure are you that there are multiple cells available at your location? It might be good to know that neighbour cell measurements during connection only are done in case the network has requested to do so. There might be some more useful information in the documentation of %NCELLMEAS. [/quote]

Rarely, I will get neighboring cells information when triggering a LTE_LC_EVT_NEIGHBOR_CELL_MEAS event. But occasionally I will. I am in the middle of downtown Chicago. I am 100% confident in the presence of neighboring cells. And I do not believe there is an error at the moment.

According to the information from the %NBRGRSRP documentation, neighbor cells are only measured when "the strength and quality of the current cell signal do not meet the network configured level".

The %NCELLMEAS documentation implies similar with the following line: "Neighboring cell measurements are available during a data or signaling RRC connection only when the network has configured measurement rules for the device and the configured criteria is met."

Do you know of configuration settings that I can use to make the neighbor cell measurements happen consistently?

[quote userid="100109" url="~/f/nordic-q-a/79652/multicell-geolocation-via-lte/329633#329633"]

I’m afraid this is not possible. Getting tracking areas of the neighbour cells or the “normal” cell ID would consume too much time and battery.

[/quote]

Thank you for confirming.

[quote userid="100109" url="~/f/nordic-q-a/79652/multicell-geolocation-via-lte/329633#329633"]There is no option forcing the modem to connect to some specific cell. It will be done upon request by the network only. The closest approach would be manual network selection and band lock, but I’m not sure if those would fulfil your purpose.[/quote]

I agree that these would not help my current issue.

RE: Multicell Geolocation via LTE

Albrecht Markus Schellenberger — Wed, 15 Sep 2021 13:14:03 GMT

Hello Jeremy,

[quote user=""]1) lte_lc_neighbor_cell_measurement() trtiggers an LTE_LC_EVT_NEIGHBOR_CELL_MEAS event, but that event does not always provide neighbor cells. In fact, it rarely does so. Is there a way to make the system return at least a few neighbor cells consistently other than when there is a bad signal?[/quote]

How sure are you that there are multiple cells available at your location? It might be good to know that neighbour cell measurements during connection only are done in case the network has requested to do so. There might be some more useful information in the documentation of %NCELLMEAS.

However, if you suspect that something is wrong, please record a modem trace starting from boot and ending when the neighbour cell measurement has been completed.

[quote user=""]2) The neighbor cell measurements event only provides the physical cell id and the signal strength. I want the LAC/TAC and normal cell id of the towers as well. Is there a way to get this information? [/quote]

I’m afraid this is not possible. Getting tracking areas of the neighbour cells or the “normal” cell ID would consume too much time and battery.

[quote user=""]If the above two items are not possible, could I disconnect from my current cell tower and force a connection to a different tower? If so, how can I do this?[/quote]

There is no option forcing the modem to connect to some specific cell. It will be done upon request by the network only. The closest approach would be manual network selection and band lock, but I’m not sure if those would fulfil your purpose.

Regards,

Markus