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VSAT network design

Scenario: Network intended for needed to domestic customers and small businesses, such as internet cafes and village WiFi hotspots. All in remote inaccessible locations in equatorial high rainfall region. Prefer to use a local national C band satellite system. Go to your government and seek approval / radio licence for your project.

Sizing the network: Domestic users each need about 25 kbit/s download and 6 kbit/s upload (2014).  These figures have doubled in the last 10 years and can be expected to increase further as customer expectation run far ahead of what they can afford.  If you expect 100 customers up need a 2.5 Mbit/s outlink (download carrier) and uplink capacity of 600 kbit/s.
Appropriate VSAT hubs operate one outlink carrier (2.5 Mbit/s) and multiple smaller inbound TDMA carriers.  In this case the return links might comprise four 200 kbit/s receivers.
The outlink carrier might use 8PSK modulation and 3/4 rate FEC coding.  Bandwidth needed = 1600 kHz.
The return link carriers might use QPSK 3/4 rate FEC coding.  Bandwidth needed = 4 x 190 kHz.
Total transponder bandwidth needed = 1600 + 4 x 190 = 2.36 MHz.  Ask at least two satellite operators how much it costs to lease this transponder capacity.

Satellite choice: Ideally find one with a beam that just covers your wanted service area. Note that it may be possible to have the teleport hub far away, in a different beam if the satellite transponder cross strap configuration is like that. Choose a satellite which is gives elevation angles of at least 5 deg at C band, preferably much higher, like 30 deg or more. Note that C band, although resistant to rain, suffers from WiMAX C band interference is some areas. Check with your radio frequency licencing authority.

Dish sizes:  Ask the satellite operators what combinations of dish size seem appropriate for your network..  It is important to have some idea of what is practical and realistic. For C band remote sites generally need a 1.8m dish with the teleport hub perhaps 4.5 or 6m dia. Once you have teamed up with a satellite operator they will help you with detailed link budgets and tell you what dish sizes you can use. Thimk about transport and installation work. Is 1.8m acceptable ?  1.2m and Ku band might be easier to install but rain effects are worse and transponder costs may be higher.  Your remote site will need something like a 5W transmit BUC.

Hub equipment and teleport:  The equipment you need at the hub comprises a single large carrier transmitter and four TDMA receivers, plus relevant control computers, routers, etc. Read explanation of TDMA. The hub equipment needs a fast optic fibre link to the terrestrial internet, plus connection to the hub antenna, typically an L band receive cable from the receive LNB and an L band transmit cable to the outdoor transmit BUC.
Talk to VSAT hub manufacturers. Find out costs and make plenty of provision for training as the quality of your service will depend far more on the operational skills of your engineers to manage the traffic as customers demand more and more out of a very limited satellite resource, than on the choice of hardware.

You may choose to either buy your hub rack or rent it.  iDirect have very many hub installed in multiple teleports and you can lease a hub with minimal outlay.  You can even have share of an existing operational VSAT network whereby you have your own PC somewhere and remotely control your network, ad and remove customers etc. This is called VNO or Virtual Network Operator.

Remote equipment: Choose from standard satellite frequency bands and equipment. Avoid unusual frequencies and co-pol operation. At C band, circular polarisation is needed in the tropics to avoid cross-pol interference.  Regarding customer modems, choose ones that work with regular LNB and BUC rather than requiring a BUC/LNB only available from one manufacturer. Think in advance about what happens when your network grows, needs to be merged with other networks, moved to another satellite or becomes obsolete. Can the modem, dish and LNB/BUC be reused on another satellite ?  Maybe experiment or look at several alternative suppliers of remote equipment but install all the same so your hub staff don't get confused giving advice to customers.

Teleport:  One option is to have your own teleport. Most people prefer to share a teleport and install their hub rack at a co-locate teleport facility. You then pay a fraction of the cost of the big dish plus power and share of the 24/7 security staff cover. You control your network from your own office, perhaps with a remote site antenna adjacent with an spectrum analyser to monitor your network for interference and new site commissionings.

If anyone wants to suggest alternative text or additional text above please send me the text in email eric@satsig.net


Page started 9 Feb 2014, amended 2nd Sept 2016.  Eric Johnston