| 摘要 |
The invention relates to navigation systems and elements. A network element (M) comprises a controlling element (M.1) for forming assistance data relating to one or more reference stations (S1, S2) of at least one navigation system; and a transmitter (M.3.1) for transmitting the assistance data via a communications network (P) to a device (R). The device (R) comprises a positioning receiver (R.3) for performing positioning on the basis of one or more signals transmitted by reference stations (S1, S2) of said at least one satellite navigation system; a receiver (R.2.2) for receiving the assistance data relating to at least one navigation system from the network element (M); and an examining element (R.1.1) adapted to examine the received assistance data to find out information relating to the status of said one or more signals of the reference stations (S1, S2) of the navigation system, said information relating to the status of said one or more signals of the reference stations (S1, S2) comprising indication on the reference station (S1, S2) the signal relates to, and said status indicating the usability of the signal. Therefore, the device (R) is adapted not to use in the positioning such a signal which is indicated not to be usable.
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