US Patent 11051128 Localization of a mobile device

A method comprising: obtaining a respective measurement of a beacon signal transmitted wirelessly between the mobile device and each of a plurality of the reference nodes; for each of a plurality of different reference locations within the environment, distinct from the reference nodes, obtaining a corresponding measurement of a test signal previously transmitted or modelled to have been transmitted wirelessly between the reference location and each of the plurality of reference nodes; for each of the reference locations, determining for each of said plurality of beacon nodes a difference between the respective measurement of the beacon signal and the measurement of the test signal; for each of the reference locations, determining a value of a measure of statistical spread in these differences; and estimating the location of the mobile device in dependence on a comparison of the values of the measure of statistical spread determined for the different reference locations.