DVB-RCS

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Digital Video Broadcasting - Return Channel via Satellite (DVB-RCS, also Return channel over system) is a digital broadcasting format created in 1999 by SES and commercialised in 2003. DVB is the technology prevalent in the US under such brands as DirecTV and Dish network.

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[edit] Why needed?

In older systems, interactive video broadcasting was possible, through a physical cable. However, in rural areas of large countries cable connections can be unavailable. The two-way interactive connections are then impossible. In this case there are 2 solutions: 1 = installing a very long cable (which is very expensive) 2 = using a return channel (for the interactive information) over satellite. Solution 2 is also expensive, but cheaper than solution 1. This is because by using a satellite connection you have to pay only the costs of a satellite antenna, and costs for the connection (the user rents bandwidth of the satellite for a certain time).

[edit] Advantages

This technology offers a full datastream to the operator. For example to participate on a tv-game where with older technologies people had to send their answers with sms. Now people can do it with a satellite-datastream.

There can be much users in one time of this technology, which creates a maximum speed of 38Mbit/second (and in some technologies this can be improved by 2Mbit/second).

[edit] Hardware-Implementation

To be able to use this kind of communication, the home-user has to buy a device called "SIT" and a satellite-dish (mostly combined in one device), which is a "Satellite Interactive Terminal" (also called "astromodem" or Satellite modem). The user gets videostreams from the reception of downlink-signals from the satellite. When the user wants to send data himself he sends data to the SIT. This device uses the dish-antenna to create an uplink to the satellite. When the connection is made, the satellite sends his data to the provider. This takes about 0.5 seconds to connect one-way with the satellite (1 second up and down, and another second to the provider for Round-trip delay time).

This technology can also be used for internet over satellite (also possible on tv!). For example the user wants to be in his mailbox. All the graphics of this come via the downlink of the satellite to the users SIT. This is decoded in Phase-shift keying QPSK or GMSK. At the moment the user selects an email from his mailbox, some signals should be sent to the mail-provider. This is via the uplink-channel. At the provider's this is demodulated by a burstdemodulator (using the MFTDMA-protocol via the shedular). From now on the data can be routed over the wired internet (and can go on this way to the mail-provider). The information to the other direction go by a normal modulator.

The used protocol for this is MFTDMA: this stands for Multiple Frequency Time Division Multiple Access. This means that a user gets slots (bursts) that are separated by time and by frequency (this generates a virtual 2-dimensional array). This protocol is implemented so that a user who pays more gets more bursts (and can use more datastream from the satellite-link). A shedular (this is a device from the provider) is used to maintain this bursts (and that there are no doubles).

[edit] Standards

The standard that implements DVB-RCS is ETSI EN 301.790.

[edit] Tests, Evaluations, and Demonstrations

SATSIX

[edit] External links