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Matzi Kratzi matzikratzi at gmail.com(In a sort-of-answer to the triangulating mail a while ago:) > i wanted to know is it possible to triangulate any gsm cellphone with osmocombb?? Hi, It would be possible triangulate your own position using osmocombb. Assumption 1 (A1): The base stations of GSM are very stable and can keep running for months or years without interruption. Assumption 2 (A2): Osmocombb has a free running quarter bit counter that it never restarts when power is on. The timings of different cells are calculated relative to this free running counter. To be able to triangulate a phone, we need information about the cells in the area: The GSM TDMA system has a periodicity for broadcasted messages such as sync and SI1. The timing of these can be predetermined as an offset relative to the free running counter in A2. Note that the offset includes the propagation time for the signal from the base station to the mobile station. If the position of the mobile phone with osmocombb (MS) is known, one can get the offset for the first base station broadcasts (dt_BS1). If the MS is moved later to at least three other known positions and the same offsets are calculated, one can calculate the actual offset between the MS free running counter and the BS1 without the propagation time included. At the same time the actual position of the BS is calculated. [1] An MS should do measurements on neighbour cells as well, and can therefor do exactly the same calculations for several BS:s at the same time. An interesting aspect of this is that it is then possible to calculate the difference in timing for several BS:s. If the positions and relative timings for the BS:s in an area are known, it is possible to calculate the position of an MS. This time we do the same calculations, but now the relative timings for the BS:s and the position are known and the same for the MS is unknown. An interesting fact is that osmocombb could use the timings for BS:s from several operators to increase the accuracy of the calculations. Assumption 1 can be held for granted. Assumption 2 could be made true if it is not already true. The concept could probably otherwise be used anyway if that is not accepted. 1 http://en.wikipedia.org/wiki/Multilateration MS Mobile station (phone, modem) BS Base station dt_BSx timing offset from the free running timer to base station number x /Matzi