Abstract:
Communications apparatus, such as a multibeam satellite communications system on-board a satellite, or terrestrial communications system, and methods that use a data routing technique that is based on the assignment of one or more codes corresponding to a destination beam. In particular, data routing is performed based on a CDMA code. The communications apparatus and methods allow simplified processing of the data address and routing of the data.

Description:
BACKGROUND 
     The present invention relates generally to satellite communication systems, and more particularly, to a communication system and processor embodying a code division multiple access (CDMA) code address data routing method. 
     The assignee of the present invention manufactures and deploys satellites that orbit the earth and which carry communication equipment. Conventional on-board processors process data communicated by way of the satellite communication equipment to demodulate, decode and individually interpret an address header. It would be desirable for the processor to not require address header processing. It would be desirable for routing to be performed based on a CDMA code. AT&amp;T VoiceSpan has conceived a CDMA on-board processor, but it is not believed to utilize a CDMA spreading code as the router destination address. 
     It is an objective of the present invention to provide for a communication system and processor embodying a code division multiple access (CDMA) code address data routing method. 
     SUMMARY OF THE INVENTION 
     To meet the above and other objectives, the present invention provides for a communications system and a method that does not implement address header demodulation, decoding or interpretation to communicate. Instead, a data routing process is performed based on the assignment of one or more codes corresponding to a destination beam. In particular, data routing is performed based on a CDMA code. The communications system and method allow simplified processing of the data address and routing of the data received by the communications system on-board the satellite. 
     The present invention may be advantageously employed in a satellite-based communication or data routing system. In addition, the present invention may be used in terrestrial fiber router applications, for example. 
     An exemplary communication system comprises a satellite having a multibeam communication system disposed thereon. A plurality of ground-based user terminals  14  communicate with each other by way of the multibeam communication system. A network control center controls the multibeam communication system and communicates by way of the communication system with the user terminals, and wherein the network control center transmits status messages to the multibeam communication system and user terminals that assign a unique CDMA code to each destination beam address. Each transmitting user terminal utilizes a spreading code appropriate for the destination downlink beam in which the recipient terminal is located to spread and transmit messages destined for the recipient terminal. The communication system on-board the satellite removes the unique CDMA code used as the destination beam address as part of the on-board routing function. The despread downlink signal can be formatted so that it is readable by all terminals in the downlink beam or uniquely addressed to individual terminals within the beam. Addressing of messages to individual terminals within the destination beams may be done with additional CDMA codes to uniquely identify the intended recipient terminal or it may be done with TDM headers or FDM frequency assignments as appropriate for the signals to which the destination beam CDMA code is applied. 
     An exemplary data routing method comprises the following steps. Status messages are generated at the network control center that assign a unique CDMA code to each destination beam address. The network control center transmits the status messages to the user terminals. Each user terminal obtains an appropriate code address from the status messages, preferably during user registration and authentication. Each transmitting user terminal uses a spreading code associated with the code address that is appropriate for the downlink beam in which the recipient terminal is located to selectively spread and transmit messages destined for it. A recipient terminal further demodulates and decodes the downlink signal to identify messages addressed to it. A reference signal may be transmitted from the network control center to aid power and code time synchronization at the user terminals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
     FIG. 1 illustrates an exemplary satellite based communication system in accordance with the principles of the present invention. 
     FIG. 2 illustrates details of the satellite based communication system shown in FIG. 1; and 
     FIG. 3 illustrates an exemplary method in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawing figures, FIG. 1 illustrates an exemplary (and preferred) satellite based communication system  10  in accordance with the principles of the present invention. However, it is to be understood that the present invention may be used in terrestrial fiber communication systems  10 , for example. 
     The communication system  10  comprises a satellite  11  that carries a communication system  12  employing a plurality of communication antennas  13 . A plurality of ground-based user terminals  14  communicate with each other by way of the communication system  12 . 
     A network control center  15  controls the communication system  12  on the satellite  11  and also communicates by way of the communication system  12  with the user terminals  14 . The network control center  15  preferably transmits status messages  15   a  to the user terminals  14  by way of the communication system  12  on the satellite  11 . 
     One of the communication antennas  13  of the communication system  12  onboard the satellite  11  comprises a multibeam transmit (downlink) antenna  13   a . The multibeam transmit antenna  13   a  produces a plurality of downlink beams that cover a predetermined area of the ground that include locations of the plurality of user terminals  14 . Another communication antenna  13   b  on-board the satellite  1  comprises a multibeam receive (uplink) antenna  13   b.    
     The communication system  12  includes an uplink receiver (RCVR)  21  that includes the multibeam receive (uplink) antenna  13   b . The uplink receiver  21  is coupled to a CDMA router  17  comprising a despreader  17 . The CDMA router  17  or despreader  17  is coupled to a downlink transmitter (XMIT)  18  that includes the multibeam transmit antenna  13   a . A processor  16  is coupled to the CDMA router  17  or despreader  17  and supplies unique CDMA codes thereto. 
     Referring to FIG. 2, it illustrates details of the satellite based communication system shown in FIG.  1 . The processor  16  is coupled to the despreader  17 . The despreader  17  is coupled between the uplink receiver  21  and the downlink beam transmitter  18 . The downlink beam transmitter  18  is coupled to the multibeam transmit antenna  13   a.    
     In the satellite based communication system  10  implemented in accordance with the present invention, the processor  16  assigns a unique CDMA code to each destination beam address. The output of the despreader  17  is connected to the destination downlink beam transmitter  18 . A user terminal  14  utilizes a spreading code appropriate for the destination downlink beam. Uplink signals destined for other downlink beams are not despread and merely contribute to re-transmitted noise by a small amount determined by the characteristics of the spreading code set that is utilized. Signals from all other uplink beams are summed after despreading into the downlink channel to accomplish the beam to beam routing enabled by the destination beam CDMA code. The communication system  10  on-board the satellite  11  may also transmit a reference signal to aid user terminal power and code time synchronization. 
     User terminals  14  preferably obtain the code addresses from the status messages  15   a  broadcast by the communication system  10  on the satellite  11  that are sent from the network control center  15  during user registration and authentication. However, it is to be understood that the code addresses may be obtained using means other than the transmitted status messages  15   a.    
     This technique of broadcasting status messages  15   a  to user terminals  14  to transmit the code addresses eliminates need for additional data packet address and routing table processing on-board the satellite  11 . This technique also reduces the complexity of multi-beam multicasting communication systems  10  where an uplink terminal  14  distributes data to multiple separate destinations and point-to-point connectivity communication systems  10  in which service is provided for a terminal  14  to transmit data to another individual terminal  14 . 
     FIG. 3 illustrates an exemplary method  30  in accordance with the principles of the present invention. The exemplary method  30  is employed with a satellite-based multibeam communication system  10  that provides a communication link between a plurality of ground-based user terminals  14 . A network control center  15  communicates by way of the multibeam communication system  12  on the satellite  11  with the user terminals  14 . The exemplary method  30  comprises the following steps. 
     Status messages  15   a  are generated  31  at the network control center  15  that assign a unique CDMA code to each destination beam address. The network control center  15  transmits  32  the status messages  15   a  to the user terminals  14  by way of the communication system  12  on the satellite  11 . Each user terminal  14  obtains  33  an appropriate code address from the status messages  15   a  broadcast from the network control center  15 , preferably during user registration and authentication. Each user terminal  14  uses  34  a spreading code associated with the code address that is appropriate for the downlink beam in which it is located to selectively receive and despread messages destined for it. A reference signal may be transmitted  35  from the network control center  15  to aid power and code time synchronization at the user terminals  14 . 
     Thus, a communication system and processor embodying a code division multiple access (CDMA) code address data routing method have been disclosed. It is to be understood that the described embodiments are merely illustrative of some of the many specific embodiments which represent applications of the principles of the present invention. For example, although a preferred embodiment of the present invention is designed for use with a satellite communication system, the present invention is applicable for use with terrestrial fiber routers, for example. Clearly, numerous and other arrangements can be readily devised by those skilled in the art without departing from the scope of the invention.