Estimating a location of a first mobile communication unit (220) in a cellular wireless communications system (200) comprises comparing a first signature from the first mobile communication unit with known signatures. The first signature may comprise control information, a set of observable cells and received power level information for the first mobile communication unit (220). A location estimate is provided from the known location of a known signature in a database (410), if that known signature matches the first signature. The comparison may be a correlation to determine the degree of matching. Context information may link two or more known signatures in the database (410), the known signatures having been obtained in temporal succession from one mobile device (258) in use in the system. The context information may be used in the comparison.