VSAT (Very Small Aperture Terminal) systems (VS) are the preferred wireless solution for Internet at sea. A VS is the result of the integration of different electronics components:
- Stabilised VSAT antenna
In the field installations other components are used with the objective of facilitating the remote support, or improve system performances:
- Service selector for multiple WAN (Wide Area Network) management
- Spectrum analyser
- Bandwidth optimizer
In addition to the previous listed items, the system integration will require the installation of several other components:
- Cables (e.g., coaxial, power, ethernet)
- Connectors (e.g., N type, RJ45)
- Arbitrator in case of dual antenna systems
Let’s focus on the main components starting from the antenna. The antenna function is to receive and send an electromagnetic signal from the vessel to the satellite. To track the satellite the antenna is stabilized on 3 axis. The tracking of a satellite is obtained knowing the satellite position, the gyro heading, the GPS information (to define the latitude and longitude of the antenna). With this data and a technique called conical scanning (varies depending on model), the antenna can define which is the best position that maximizes the power of the received signal.
When selecting an antenna there are various options (this refers to Seatel antennas for Ku band):
- Dimension of antenna dish, from 75cm (3011 model) to 150cm (6009 model) diameter
- Block Up converter (BUC): 4W, 8W,16W
- Low noise block down converter (LNB: single or quad band)
A typical antenna has the following characteristics:
- Quad LNB compatible with the bands used by most SPs: 10.7Ghz – 14.5Ghz
- Different polarization options: Copol and Xpol. Copol is when TX/RX signals are in the same plane and X-Pol when TX/RX signals are on perpendicular planes. There are some satellites in the Indian and Pacific region that use Copol transmissions
- Minimum 8W BUC: the BUC power will impact the maximum TX speed. When selecting a service is important to check the BUC power to verify if the service can be supported
The other important component of the VS is the modem. The modem will modulate the TX and RX signal providing a specific data speed. Analysing for example one of the most used models, the iDirect X5, we can observe that the modem speed depends on the modulation and can reach 150 Mbps for TX and 24 Mbps for RX. Other functionalities introduced by the modem are for example: error correction and encryption. The modem model will be imposed by the service provider. Is important to remind that the maximum speed reachable in VS depends on various factors, e.g.: modem type, antenna dimension, BUC type, meteo conditions, cable signal loss, service provider, and antenna position.
The last important component of the VS system is the router. The router will provide some functionality like:
- NAT: Network address translation
- VOIP: voice over IP
Once the VS is installed it will provide the following services:
- Minimum data speed: CIR (can be 0Mbps / 0Mbps , TX/RX)
- Maximum data speed: MIR (up to 2Mbps /8Mbps, TX/RX. For higher speeds a customized offer can be produced by the SPs)
- IP addresses
- VOIP line
Some SPs will provide additional services:
- Vessel tracking
- Multiple IPs
- Multiple VoIP numbers
- ABS: automatic beam switching
The services will be available only on the coverage areas where the SPs have satellite coverage. Ku band services are available in most areas of the world but the coverage is not global. The key factors that are important when deciding the service provider for VS are:
- Multiple satellite on the same area to overcame blockage issues
- Support quality
- Cost of the service
In this list the coverage criteria is one the most important point. A great website to understand satellite footprints is provided at the following link from the SatBeams website.
One of the great advantages of VS is that Internet connectivity can be provided in the most remote locations of the world not only at sea. In particular when VSAT technology will be more affordable, it will permit to have Internet services like eHealthcare or eLearning in remote countries where Internet infrastructures will not be available for many years.
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