| 摘要 |
This invention allows Cooperating mobiles (ground vehicles, aircraft) to be located and identified by Multilateration and Automatic Dependent Surveillance - Broadcast (ADS -B) techniques using the frequency band and the format of the Secondary Surveillance Radar (SSR) signals in high traffic situations, such as those of large airports. Standard messages, transmitted by the mobile on the downlink channel, i.e. to a set of fixed receiving stations, and including the identification code, permit the location of the mobile by multiple time measurements (Multilateration) from a subset of the set of fixed receiving stations; when the message contains the position (GPS and, later, Galileo datum) the mobile may be located with the ADS-B when in view even of a few stations or of a single station. In order to overcome the problem that arises with high traffic, i.e. the superimposition of signals, called garbling, the present invention uses (a) a variable carrier frequency in the downlink channel (b) a time division scheme for the transmission from different mobiles . In this way, the system becomes suitable to the discrimination of overlapped signal; this is obtained by frequency analysis and, in the cases of high traffic in the downlink channel, by super resolution techniques. Moreover, the downlink transmission capacity increases with respect to the present state of the art respecting the bandwidth limits as defined by the international regulations. The present invention includes a signal generation and transmission system with selection of the carrier frequency (called frequency agility) and with selection of the transmission time for each mobile (called time agility or time division multiple access), as well as signal discrimination means in the receiving fixed station. |
