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VSAT

The primary focus for Time Division Multiplexed Access (TDMA) communications is for IP Based communications over satellite.  Often, applications for various terminals within the network vary based on specific requirements.  Often, for moving (land or ship) or fixed vehicle usage, a smaller antenna is required, typically utilizing stabilized parabolic antennas, or phased array antennas.  These antennas typically have small apertures as required by the low profile requirements.

Smaller antennas have limited focus ability due to their size, and this limits the amount of energy that they can receive, and transmit.  To overcome this, DVB-S2 and DVB-S2 ACM satellite transmission protocols are often used.  DVB-S2 is a second generation specification based on TDMA technology.   In order to lessen the power and density issues encountered utilizing smaller antennas, DVB-S2 ACM is often used to adjust the out-bound coding rates in order to maximize in real time the out-bound transmission.

This can be accomplished by changing the Coding Rate and Modulation Type, allowing the link to reduce the outbound data rate or power levels to overcome changing link structure such as rain fade, antenna blockage, and antenna misalignment, allowing the network to overcome spectral density limitations.

Another feature of TDMA based systems is the Spread Spectrum technique.  In this mode of operation, the transmitted data is divided into multiple sections and assigned to a frequency spectrum within the channel bandwidth.  Each node of the network is assigned spreading sequence, and this signal is then transmitted into the allocated frequency channels, allowing for a greater efficiency within the network.  All nodes within the network can join the network and share the allocated bandwidth, thus eliminating the need for individual carriers to be assigned.

There are several available systems currently available and offered over wide variety of functionality and cost, depending on the actual user requirements.  Various antenna platforms can be incorporated within the network, allowing each platform to access the network utilizing the best available solution for the individual platform.