Difference between revisions of "FAQ"

I know where cell tower x exactly is but OpenCellID shows another position

There are two main reasons for discrepancies between the actual position of a cell tower and the position reported by OpenCellID:

1) Cell towers and cells are two different things

It is very rare that only one antenna emitting a 360-degree GSM signal is mounted on a physical cell tower. More often, several antennas are mounted on a cell tower, many of them having 3 or 4 per network access type (GPRS, UMTS, LTE...).
In this case, each antenna serves one segment of the full 360 degrees circle. A sample cell tower, with each antennae emitting signals at 120 degrees, is shown here:

This is where the big discrepancy between the number of cell towers and the number of cell IDs comes from:

Vodafone, for example, reports less than 40.000 cell towers ("Basisstationen") in Germany but OpenCellID reports more than 290,000 Vodafone cell IDs in Germany as of August 2014: Vodafone in Wikipedia, OpenCellID statistics

This means that on average one cell tower carries more than seven antennas (= cells).

After understanding that cell towers and cells are not the same, let's see what that means for the computed GPS positions of each cell ID.

Imagine that many cell ID measurements have been collected, equally distributed in one of the pie slices. In this case, the average of all recorded GPS positions would be as indicated in the graph above (e.g. "centre of area 1"). This would then be the position reported by OpenCellID.

In the case where OpenCellID knows which antennas belong to the same cell tower, this information could be used to average the positions of all cell IDs (antenna sectors) of one cell tower; this would then give a precise position of the cell tower. Unfortunately, OpenCellID has very little knowledge about the numbering schemes of the different GSM network providers and network access types today. In the case that you can provide such information for one or the other networks, this would be very helpful for improving the data quality of OpenCellID.

2) The measurements of cell towers are not always distributed equally around a cell tower

There are countless situations where it is not easy to approach a cell tower from each side by car, bicycle or as a pedestrian. Just imagine a cell tower on a hill where just one road passes by on one side:

file

In this case, the measurements will not be equally distributed around a cell tower, meaning that most of the measurements may be coming from just one side of the cell tower. As a result, averaging the GPS positions of all these measurements will most likely not accurately locate the centre of the respective cell tower's segmented area.

I am an OpenStreetMap mapper. How can I also map cell towers?

OpenCellID mainly collects MCC, MNC, LAC, and CID information combined with a GPS position.
In most cases, it is not possible to obtain this data by going to a cell tower for various reasons:

• the cell tower might be on a rooftop which is not accessible
• there is no sign at the base station indicating such information
• there are many antennas all together and it is not possible to find out which antenna has which cell ID

In addition, one of the basic rules of OSM is to map visible things. This is not the case here as MCC/MNC/LAC/CID are not visible in most cases.
Therefore, only a very small number of cell towers is currently mapped in OSM with MCC/MNC/LAC/CID tags.

The most effective way to contribute to OpenCellID is to use one of the smartphone applications listed here and to collect measurements while mapping something else.
The Keypad-Mapper 3, for example, has a built-in feature to record cell tower data while mapping house numbers / addresses.

How to extract all cells of one country from the cell_towers.csv file?

Due to the size of the cell tower file it is not possible to use common programs like Excel or Microsoft Word for this task.

One way to extract the required data is as follows:

1. Download cell_towers.csv file here.
   
2. Install the free Windows software CSVed.exe on your windows PC.
   Last version we tested successfully was version 2.3.2 (2014). It creates a shortcut on your desktop during its installation.
   
3. Run CSVed.exe and load the CSV file.
4. Use "Filter & Dups" feature for filtering and saving the required data; filtering the data takes a few minutes but works perfectly well.
5. Open the extracted data with Excel or any other CSV-compatible software for further examinations.

A big thank you to Sam Francke for this great tool!

What is a CLF format?

CLF files contain information about mobile network cells.
They were used in some Nokia mobile phones for logging cell data: cell Id, LAC, MCC, MNC, location, etc.
OpenCellID supports the import of CLF files as a source of information on cell locations. During the upload of the data it can be defined if the uploaded data is measurements or if the file contains precise information of cell tower positions which would then override the average of all GPS positions of all measurements of a given cell.

The following versions are supported: 2.0, 2.1, and 3.0.

CLF version 2.0

Files have the following format:
CellId(hex.)+LAC(hex.)+MCC+MNC<TAB>data
(plus symbol means that values are not separated; <TAB> — tabulation character)
Example: 239731EF26202<TAB>City Square

CLF version 2.1

Files have the same format as in version 2.0 but cell ID and LAC are stored as decimal values.

CLF version 3.0

This format uses more information about cells. It has the following format:
MCC+MNC;CellId;LAC;RNC;Latitude;Longitude;Ratio;Data;RFU
Cell ID and LAC can be decimal or hexadecimal.
Example:
26202;07812;03101;00000;45.894375;31.51312;0;City Square;0

LAC vs. RNC

One RNC can handle multiple LACs. RNC ID does not necessarily have a connection to LAC ID - it depends on how the network is planned. For example, you can find in the same RNC (12) LACs 33, 21 and 78 - with no connection between them. No relative connection of RNC IDs and LAC. This is based on how to plan the network. LAC depends on paging. RNC ID is same as site IDs. It only serves as identification.