GCI search & multiple cell location

[barbiz]

Hello,

since location accuracy is not enough for us with single cell, we are trying to use multiple cell location.

We tries with %NCELLMEAS = 2 but we don't get multiple cells. Maybe the serving cell has good signal?

Then we tried with GCI search and fw 1.3.4.

%NCELLMEAS = 3,3

and we got those 3 cells (I added newlines for easiness of reading):

%NCELLMEAS: 0,

"0AAE62A2","22201","92B9",65535,0,6254,243,62,19,178936,0,0,

"0319AFA2","22201","92B8",65535,0,6254,295,62,18,178936,0,0,

"0094586F","22210","69D9",65535,0,6354,105,77,29,178973,0,0

so we tried to inject this data into the nrfCloud API:

{
  "lte": [
    {
      "mcc": 222,
      "mnc": 1,
      "eci": 179200674,
      "tac": 37561,
      "earfcn": 6254,
      "adv": 65535,
      "rsrp": -78,
      "rsrq": -10,
      "nmr": [
        {
          "earfcn": 6254,
          "pci": 295,
          "eci": 52015010,
          "rsrp": -78,
          "rsrq": -10.5
        },{
          "earfcn": 6354,
          "pci": 105,
          "eci": 9721967,
          "rsrp": -63,
          "rsrq": -5
        }
      ]
    }
  ]
}

and this is the response:

{
	"lat": 45.39999247,
	"lon": 11.90999508,
	"uncertainty": 2472,
	"fulfilledWith": "MCELL"
}

which does not give any improvement on the original location with SCELL.

Can you help us? Are we formatting the data the wrong way?

Marco

[Cole Hafner]

Hi Marco,

Your formatting is correct. What is the device ID? I can look into the logs and see if I can help you get a better result. 

Thanks,

Cole

[barbiz]

Actually, I am directly calling the API cloud-to-cloud so there is no device id. How can I make my call trackable?

Also, I was wondering: what is the difference between my formatting and passing an array of cells direcly in the "lte" object?

[barbiz]

Hello, any news?

thanks

Marco

[Cole Hafner]

Hi Marco,

I'm looking into this today. 

Thanks for your patience.

Cole

[Cole Hafner]

Hi Marco,

I can reproduce the issue. I see that it makes no difference whether the neighbor cells are included. This could be due to available cell towers in the area or that your SIM is locked down to one carrier with only access to certain towers. Do you have a different SIM that you could try? That may get you higher accuracy. 

Cole

[barbiz]

Dear Cole,

I tried with other SIMs form other providers. But the cells that can be seen do not change much. I managed to add one more cell to the list:

{
	"lte": [
		{
			"mcc": 222,
			"mnc": 1,
			"eci": 52015010,
			"tac": 37560,
			"earfcn": 6254,
			"adv": 65535,
			"rsrp": -78,
			"rsrq": -10
		},
		{
			"mcc": 222,
			"mnc": 1,
			"eci": 179200674,
			"tac": 37560,
			"earfcn": 6254,
			"adv": 65535,
			"rsrp": -78,
			"rsrq": -10
		},
		{
			"mcc": 222,
			"mnc": 1,
			"eci": 179200673,
			"tac": 37560,
			"earfcn": 6254,
			"adv": 65535,
			"rsrp": -78,
			"rsrq": -10
		},
		{
			"mcc": 222,
			"mnc": 10,
			"eci": 9721967,
			"tac": 37560,
			"earfcn": 6354,
			"adv": 64,
			"rsrp": -78,
			"rsrq": -10
		}
	]
}

However, no improvement on the response.

NOTE: I am using Nb-IoT.

I cannot really understand if this is working as expected. The cells in the nearby are actually in a range of 400m (red line on the map)

So I don't understand:

• why single cell location give only 2500m accuracy (if the device was 2500 metres away, it would receive other cells)
• why multiple cell location does not give any improvement.

Thanks & best

Marco

on 

[Cole Hafner]

Hi Marco,

This is very odd indeed. I am passing your findings onto our vendors and will get back to you.

Cole

[barbiz]

Hi Cole,

did you get any news from the vendors?

thanks

Marco

[amessner]

Hi everyone,

We actually ran into the exact same issue.

We use Soracom in Alberta, Canada and when using the GCI search types and mfw_v1.3.4 we do get additional cells as expected. However, when injecting these additional cells into the "nmr" section of the a location request to the nRF Cloud we don't see any improvement on the location either.

Currently we are only evaluating the recent improvements on multicell, so we send the requests directly from the device using a service key.

Thanks
Alex

[Cole Hafner]

Hi Alex and Marco,

Multi cell accuracy depends on a variety of factors: cell density of the area (rural or urban), which cells the SIM carrier is allowed to connect to (irrelevant in 1.3.4), signal strength etc. Sometimes single cell accuracy is just as good, in other cases multi cell is better.

The "uncertainty" response is an estimate of where your device may be relative to the location of the tower, here are some docs. We are working on docs that better explain the details of this.

Alex, will you pass me your device details in a private message? I would like to investigate your specific use case. 

Best Regards,

Cole

[barbiz]

Dear Cole,

I understand, but I honestly think this is an oversimplified explanation.

The cases I am spotting out are very simple: the radio finds three cells, I can spot them on cellmapper and draw the best intersection and provide, manually, a better location than the single cell would allow.

I could do this, theoretically, by a script querying the cloud N times and then making the average.

My question is: why the locations services does not do that? Is there any reason? Or is there any plan to do that?

Or maybe I am wrong: can you please spot out an example where the cloud is actually providing better accuracy with GCI search? (not normal search, we already know that 99% of the cases normal search does not give any further cells)

This would help us to understand how the thing works.

Thanks

Marco

[AndrewKostka]

Hi, Marco: I'm Andrew, I work on the Location Services feature with Cole.
I'd like to offer some more context to the conversation surrounding LTE positioning. First, I think there seems to be a misunderstanding about the term "cell". The term "cell" refers to a specific geographic area that is served by a specific tower, or eNodeB in LTE terminology. Let's look at an example using your original serving tower to see how multicell can improve a position estimate.

Let's take the following request and look at its corresponding cell on CellMapper:

{
 	"lte": [
		{
			"mcc": 222,
			"mnc": 1,
			"tac": 17211,
			"eci": 179200573
		}
	]
}

Finding the corresponding cell on CellMapper means deriving the eNodeB, or tower, ID from the Cell ID. The eNodeB ID here is '700002', and the Sector (or cell) ID is '61'. This is what that cell looks like:

The result we get from nRF Cloud for that data is here:

{
	"lat": 45.4181242,
	"lon": 11.9116044,
	"uncertainty": 796
}

Which correlates to this position:

Now, let's add another nearby cell. Adding another cell from the same eNodeB makes our request:

{
 	"lte": [
		{
			"mcc": 222,
			"mnc": 1,
			"tac": 17211,
			"eci": 179200573
		},
		{
			"mcc": 222,
			"mnc": 1,
			"eci": 179200575,
			"tac": 17211
		}
	]
}

Here's our new cell in CellMapper:

We can see that while this cell has the same serving tower, it is geographically located further to the southwest than our first cell. So, how does this change our results?

{
	"lat": 45.40624738,
	"lon": 11.8985796,
	"uncertainty": 568
}

We can see our new position is over a kilometer further to the southwest, which makes sense given the geographic location of the cells. Additionally, our uncertainty has reduced by about 230M, suggesting we are more confident about the result position.

Unfortunately I wasn't able to find information about the specific cells in your original request on CellMapper, so I can't confirm the location of the actual cells.