Code distribution multiple access communication system with user voice activated carrier and code synchronization
AssigneeAgence Spatiale Europeenne
InventorsRiccardo De Gaudenzi, Roberto Viola
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Abstract
A communication system comprising a master control station and user terminals (100), in which synchronization in the outward link is achieved by transmitting a master code (MC) with the same clock frequency and carrier as the communication signals, wherein the master code (MC) is transmitted continuously and with greater power than that of the return link signals, and wherein the user voice activated message transmission carrier is broken during the pauses in a message. The invention relates in particular to a mobile satellite communications system.
Claims14
A process for achieving the synchronization between a user terminal and a master control station in a Code Distribution Multiple Access (CMDA) communication system comprising a plurality of user terminals and a centralized master control station, each user terminal and the master control station being adapted to transmit and receive communication signals over a two-way forward/return link, said user terminal being adapted to transmit voice activated carrier signals, said processing comprising the steps of:
- achieving the synchronization in the forward link by using a master code transmitted uninterruptedly from the master control station, said master code having a higher power level than the return link signals, said master code serving to synchronize the user terminal to the master control station for demodulation of the communication signals;
- and
- achieving the synchronization in the return link by using a synchronization signal transmitted form the user terminal during the pauses in a message when a pause has a duration longer than a predetermined time, said synchronization signal having a duration which should allow the master control station to be locked for further signal demodulation.
A Code Distribution Multiple Access (CDMA) satellite communication system, comprising a plurality of user terminals and a centralized master control station, each user terminal and the master control station being adapted to transmit and receive communication signals over a two-way forward/return link;
- the master control station further comprising means for transmitting uninterruptedly a master code to each of said plurality of user terminals;
- each user terminal further comprising master code acquisition and tracking means adapted to acquire the master code from the master control station and track same for producing a user code control signal,
- user code generator means responsive to said user code control signal for generating a user code to be used in achieving the signal demodulation,
- voice activated means adapted to be responsive to the user voice for activating the carrier to be used in achieving the signal modulation for transmission, said voice activated carrier being thereby interrupted during the pauses in a message,
- means adapted to produce a synchronization signal for transmission to the master control station when a pause has a duration longer than a predetermined time, said synchronization signal having a duration which should allow the master control station to be locked for signal demodulation,
- code tracking means in the master control station adapted to be responsive to said synchronization signal for locking the master control station to allow further signal demodulation.
Dependencies are inferred from the claim text.