Difference between revisions of "FAQ"
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+ | ===Signal strength details=== | ||
+ | OpenCellID stores correct values in dBm or ASU (defined in TS 27.007 8.5), but also invalid values as for example 0 that means "no value" or a weak signal, or 99 that means unknown.<br> | ||
+ | Please keep in mind, that the range of the signal depends on the network type. You can find below rules how to calculate the signal in dBm from ASU for different network types: | ||
+ | GSM (in the range of -51dBM to -113dBM; ASU in the range of 0 to 31): <br> | ||
+ | RSSI [dBm] = (2x ASU) - 113 | ||
+ | |||
+ | UMTS (in the range of -25dBM to -121dBM; ASU in the range of -5 to 91): <br> | ||
+ | RSCP [dBm] = ASU - 116 | ||
+ | |||
+ | LTE (in the range of -45dBm to -137dBm; ASU in the range of 0 to 95): <br> | ||
+ | RSRP [dBm] = ASU - 140 | ||
+ | |||
+ | CDMA (in the range of -75dBm to -100dBm; ASU in the range of 1 to 16):<br> | ||
+ | RSSI [dBm] >= -75: ASU = 16, | ||
+ | RSSI [dBm] >= -82: ASU = 8, | ||
+ | RSSI [dBm] >= -90: ASU = 4, | ||
+ | RSSI [dBm] >= -95: ASU = 2, | ||
+ | RSSI [dBm] >= -100: ASU = 1 | ||
===Long CellID vs. short Cell ID=== | ===Long CellID vs. short Cell ID=== |
Revision as of 22:53, 21 October 2014
Contents
Signal strength detailsOpenCellID stores correct values in dBm or ASU (defined in TS 27.007 8.5), but also invalid values as for example 0 that means "no value" or a weak signal, or 99 that means unknown. GSM (in the range of -51dBM to -113dBM; ASU in the range of 0 to 31): UMTS (in the range of -25dBM to -121dBM; ASU in the range of -5 to 91): LTE (in the range of -45dBm to -137dBm; ASU in the range of 0 to 95): CDMA (in the range of -75dBm to -100dBm; ASU in the range of 1 to 16): Long CellID vs. short Cell IDThe formula for the long cell ID is as follows: RNC: the Radio Network Controller If you have the Long CID, you can get RNC and CID in the following way: Example for long cell ID 66808694: I know where cell tower x exactly is but OpenCellID shows another positionThere 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...). 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.
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: 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 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:
A big thank you 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 cell ID 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 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. |