Difference between revisions of "FAQ"
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Vodafone for ex. 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: [http://de.wikipedia.org/wiki/Vodafone Vodafone in Wikipedia], [http://opencellid.org/#action=statistics.cells&type=1&dateFrom=&dateTo=&mcc=262&mnc=2&sortBy=1 OpenCellID statistics] | Vodafone for ex. 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: [http://de.wikipedia.org/wiki/Vodafone Vodafone in Wikipedia], [http://opencellid.org/#action=statistics.cells&type=1&dateFrom=&dateTo=&mcc=262&mnc=2&sortBy=1 OpenCellID statistics] | ||
− | This means, that in average on cell tower carries more than seven antennas (= | + | This means, that in average on 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: | 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: |
Revision as of 23:11, 29 August 2014
ContentsI know where cell tower x exactly is but OpenCellID shows another positionThere are mainly two reasons for discrepancies between reality and the position of a cell tower reported by OpenCellID: 1) Cell towers and cells are two different things It is pretty rare that on a physical cell tower only one antenna is mounted which emits the GSM signal in 360 degrees direction. More often several antennas are mounted on a cell tower, pretty often 3 or 4 per network access type (GPRS, UMTS, LTE...). This is where the big discrepancy between the number of cell towers and the number of cell-ids comes from: Vodafone for ex. 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 in average on 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 cake slices. In this case, the average of all recorded GPS positions would be as indicated in the graphics above (e.g. "centre of area 1"). This would then be the position reported by OpenCellID. In case OpenCellID would know 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 which would then give a precise position of the cell tower. Unfortunately OpenCellID today has very little knowledge about the numbering schemes of the different GSM network providers and network access types. In case you can contribute such information for one or the other network, this would be very helpful for improving the data quality of OpenCellID.
There are countless situations where it is not easily possible to approach a cell tower from each side by car, by bicycle or as a pedestrian. Just imagine a cell tower on a hill where just one road passes by on one side: In this case, the measurements will not be equally distributed around a cell tower, which means that may be most of the measurements are on just one side of the cell tower. Averaging the GPS positions of all these measurements will most likely not have the centre of the area of the segment of a cell tower as a result. 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 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. 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. 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:
Thank you very much to Sam Francke for this great tool! What is a CLF format?CLF files contain information about mobile network cells. The following versions are supported: 2.0, 2.1, and 3.0. CLF version 2.0Files have the following format: CLF version 2.1Files have the same format as in version 2.0 but CellId and LAC are stored as decimal values. CLF version 3.0This format uses more information about cells. It has the following format: LAC vs. RNCOne RNC can handle multiple LACs. RNC ID does not necessarily have a connection to LAC ID - it depends how the network is planned. For example you can find in the same RNC (12) LACs 33, 21 and 78 - 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. |