VSAT technology is used for two-way satellite communications for Internet, data and telephony, typically in rural areas and harsh environments – in our case, in maritime environments.
Normally VSAT solutions in the maritime market are delivered as a package, including satellite space segment, equipment and phone and internet services.
VSAT services historically have operated at Ku-band and C-band for the commercial market, using satellites located at the GEO orbital location. Due to the location of the satellites in combination with the movement of vessels, stabilised antennas with tracking are required. A stabilised maritime VSAT antenna typically has a circular antenna (often concealed within a dome) that is 2.4 metres or smaller in diameter.
Data rates typically range from 64 Kbps up to 8 Mbps, but lower and much higher data rates are available. A remote maritime VSAT system typically consists of two parts:
An antenna and transceiver that is placed outdoors (typically inside a dome) – in maritime this can be referred to as the ‘Above Deck Unit – ADU’.
An indoor unit that interacts with the outdoor unit and controls the antenna – in maritime this can be referred to as the ‘Below Deck Unit – BDU’.
VSAT services can enable a guaranteed level of bandwidth for the transmission of data or voice at broadband level speeds. These exclusively reserved channels are determined by the following elements, which are important to understand in determining what VSAT solution is best for your needs:
Normally, VSAT services are supplied with either dedicated or shared bandwidth. In a shared environment, the free bandwidth is typically shared between the users. The number of users that compete for the available bandwidth is defined within a Contention Ratio. Within a ‘Contended Service’, a contention ratio is given to users as an indication of the number of subscribers who share the fixed amount of bandwidth within a network.
The higher the contention ratio, the greater the number of users that may be trying to use the bandwidth available at any one time and, therefore, the lower the bandwidth speeds. For example, within a contention ratio of 50:1, the maximum number of other users you could be sharing the bandwidth pool with at any one time is 49.
Committed Information Rate
Within a shared bandwidth pool, a Committed Information Rate is a way of guaranteeing bandwidth to the individual end users, ensuring you will get a minimum bandwidth at all times. Usually expressed in kilobits per second (Kbit/s or Kbps), the Committed Information Rate (CIR) can refer to the average or minimum amount of bandwidth guaranteed to the user under the contract, usually known as a ‘Service Level Agreement’ (SLA). The Burst Information Rate (BIR), or Maximum Information Rate (MIR) is the theoretical maximum to which bandwidth can increase as it becomes available.
VSAT Frequency Band
There are three VSAT radio frequency bands that communication and military satellites operate within, these frequency bands determine the link quality and coverage area:
C-band is primarily used for voice and data communications as well as backhauling. Because of its weaker power it requires a larger antenna compared to Ku-band, usually 2.4m for maritime use. However, due to the lower frequency range, it performs better under adverse weather conditions on the ground. In addition, C-band typically has large beams and makes it possible to provide ‘Global’ coverage with only three satellites.
Ku-band is used typically for consumer direct-to-home access, distance learning applications, retail and enterprise connectivity in addition to maritime. The antenna sizes are much smaller than C-band because the higher frequency means that higher gain can be achieved with smaller antenna sizes. Networks in this band are more susceptible to rain fade, especially in tropical areas.
Ka-band is primarily used for two-way consumer broadband and military networks. Ka-band dishes can be much smaller and typically range from 60cm-1.2 metres (2′ to 4′) in diameter. Transmission power is much greater compared to the C, X or Ku-band beams. Due to the higher frequencies of this band, it is more vulnerable to signal quality.