Outline
                   Access schemes in satellite networks
                   FDMA implementation
                   FDMA properties
                   Examples
                    
                       Important note: Slides present summary of the results.  Detailed derivations 
                       are given in notes.
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      Satellite access
      Two types of access
           o Access to transponders (FDMA and polarization)
           o  Multiuser access to bandwidth of a transponder
      Transponders
           o  large bandwidth (36, 54 or 72MHz)
           o  Shared between multiple users using FDMA, TDMA or CDMA 
              access schemes 
      Two types of bandwidth assignment
           o  Pre-assigned (fixed) 
           o  Assignment on demand 
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      Multiplexing vs. Multiple Access
    Multiplexing (Mux)                                     Multiple Access (MA)
         o Common in all long distance                            o  Methodology for sharing same 
            communication                                            communication resource between 
         o  Aggregation of signals from multiple                     multiple users
            users                                                 o  Implemented at the transponder
         o  Performed on the ground (earth station)
         o  Multiplexed signals are modulated on a          Satellite systems use combinations of 
            single RF carrier                                  Mux/MA
         o  Most common: Time Division                            o
                                                                     TDM-FDMA
            Multiplexing (TDM)                                    o
         o                                                           TDM-SCPC-FDMA, etc.
            Inverse process: de-multiplexing
                           Data rates for TDM Mux Standards
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     Example: T1-hierarchy
      
        Multiplexing on T-1 may be
          oChannelized (respects the Mux structure)
          o Non channelized (uses proprietary Mux schemes 
             within T-1 multiplex)                                                Page 5
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      Fundamental principles of access schemes
    Three principle transponder access schemes
          o  Frequency Division Multiple Access (FDMA)
          o  Time Division Multiple Access (TDMA)
          o  Code Division Multiple Access (CDMA)
                                                                              CDMA principle (separation in 
                                                                                      code domain)
                                                     TDMA principle             Note: it is possible to have 
                  FDMA principle                (separation in time domain)     combination between 
          (separation in frequency domain)                                      different access schemes
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