This paper describes how VSAT networks currently operate in the INTELSAT system. Four classes of VSAT networks (data transaction; circuit‐switched; data distribution; microterminals) are identified, and it is verified that all of them can operate with INTELSAT satellites. Most VSAT networks in operation on INTELSAT today operate in fractional transponder leases. Fractional transponder capacity estimates are presented for a wide range of scenarios and different INTELSAT satellite series. These estimates clearly show increasing bandwidth utilization efficiencies for newer generations of INTELSAT satellites. Provided that VSAT and hub sizes are appropriately selected, efficiencies are already significant with existing satellites.
Two possible ways of increasing the utilization of satellite resources are examined in the paper: demand assignment multiple access (DAMA) and multiple channel‐per‐carrier (MCPC) techniques. The impact of using DAMA in circuit‐switched VSAT networks is quantified.
There are substantial cost advantages in the use of single‐axis or fixed‐mount earth‐station antennas, thus reducing or eliminating the need for autotracking in earth‐stations operating with quasi‐stationary satellites. Such cost advantages are more relevant in small antennas where the tracking system represents a larger percentage of the overall cost. In addition, small antennas are particularly suitable to be operated without autotracking, owing to their wider half‐power beamwidth. This paper describes a model for calculating the antenna pointing loss as a function of the antenna diameter, operating frequency band, satellite station‐keeping tolerances, and the relative geometry between the earth‐station and the satellite. The model has been extensively used in the development of INTELSAT's IBS and VISTA services as well as in domestic leases. Although the model has been developed based on orbital mechanics equations, its emphasis is towards earth‐station and systems engineering applications. Some example calculations and results obtained through an HP‐41 CV programmable calculator are also provided.
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