All satellites make use of a beam which is a pattern of electromagnetic waves transmitted by the satellite. The transmission from a satellite has a defined pattern and the beam can be wide or narrow covering a large or small area on earth. Using a system of varying frequencies and alignment of antennas onboard the satellite, each satellite can have several beams within which all or most of the satellite’s power is concentrated. The antennae on the ship are rarely stationary due to the constant movement of the vessel when under way and thus require the dish to be mobile in all dimensions.
Most ships’ communication systems are required to share channels with others which is perfectly fine for simple communication needs but highly inefficient when dealing with the large quantities of data that some operators generate. This can be overcome by making use of a very small aperture terminal (VSAT) service.
Subscribers to VSAT services are provided with exclusive or semi-exclusive use of satellite channels for sending and receiving voice and data at broadband speeds. Usually they are charged for this on a monthly fixed fee subscription basis (although there may be limits on the data allowed before extra charges apply) as opposed to the rate per Mbit charged when using basic services.
This enables a network to be created that permits the transmission of large quantities of data. The service is ideal for the offshore industry as it enables survey and other data to be transmitted at will and it is also popular among high end and middle rate cruise ship operators who may have similar high volume requirements.
As far as shipping is concerned, the satellite communications era began with the establishment in the 1970s of Inmarsat a not-for profit international organisation, set up at the behest of the IMO to provide a satellite communications network for the maritime community. Initially the service was used purely for commercial purposes allowing voice and telex communication with ships at sea equipped with an Inmarsat A terminal.
Without the advent of GMDSS and the mandatory requirement for most ships to be fitted with at least an Inmarsat C terminal, it is doubtful if the marine satellite communications sector would have expanded at anything like the rate it has. By having an Inmarsat terminal on board, ships immediately gained e-mail as a new method of communication.
Early Inmarsat services were described by an alphabetical reference being Inmarsat A, B, C, D and E. When the letter F was reached, the service was renamed Fleet followed by a number (33, 55 or 77) indicating the size of the antenna in centimetres.
Inmarsat-A was the original Inmarsat service and offered analogue FM voice and telex services and, optionally, high speed data services at 56 or 64kbit/s. The service was withdrawn at the end of 2007.
Inmarsat-B provides voice services, telex services, medium speed fax/data services at 9.6kbit/s and high speed data services at 56, 64 or 128kbit/s. Inmarsat-C effectively this is a “satellite telex” terminal with store-and-forward, polling etc. it can handle data and messages up to 32kb in length, transmitted in data packets in ship-to-shore, shore-to-ship and ship-to-ship direction. Message length for Inmarsat Mini C terminals may be smaller. Certain models of Inmarsat-C terminals with GPS are also approved for GMDSS use. Inmarsat D/D+ is a paging service not regularly used on ships.
Inmarsat-E was a global maritime distress alerting service using small EPIRBs that automatically relayed distress messages to maritime Rescue Coordination Centres. This service has been withdrawn.
Inmarsat Fleet 77 offers voice and the choice of mobile ISDN up to 64kbps or an always-on Mobile Packet Data Services (MPDS) for cost-effective, virtually global communications. Fleet 77 also meets the distress and safety specifications of the GMDSS for voice communication.
Inmarsat Fleet Broadband introduced in 2006 when the first of Inmarsat’s i-4 satellites went into service. It offer a shared-channel IP packet-switched service of up to 492kbit/s and a streaming-IP service from 32 up to X-Stream data rate. X-Stream delivers the fastest, on demand streaming data rates from a minimum of 384kbit/s up to around 450kbit/s. Most terminals also offer circuit switched Mobile ISDN services at 64kbit/s and even low speed (4.8kbit/s) voice services.
Inmarsat does not market its services directly but through service providers who are also able to market the services of other satellite network operators. Because of its GMDSS role, Inmarsat has dominated the marine satellite sector but it is not without competitors in the commercial communications arena. Among those competing, Iridium Communications was a front runner in voice and light data usage and had the advantage of being able to offer a wider pole to pole coverage that Inmarsat could not match due to the differences in the satellite constellations. Iridium has just begun a project under the title Iridium Next and is in the process of replacing its existing satellite network with a series of new satellites.
Since the advent of GMDSS, Inmarsat has become a private company and although committed to maintaining the safety services it is no longer focused solely on the marine sector as it once was. Recently the IMO has decided that the GMDSS communications should be opened up to other satellite operators and in April, Iridium Communications announced it had formally submitted a comprehensive application to the IMO via the US government for the provision of mobile satellite communications in the GMDSS.
Choosing the right band
The radio spectrum is divided into a number of bands some with a wider spread than others. Each of the bands is used for a slightly different purpose. Radio communications on LF, MF, VHF and UHF are all on frequencies below 1GHz which is the point in the spectrum allocated to satellite communications and ship’s radar.
When it comes to communications equipment on board a ship, VSAT mostly requires a choice to be made between systems operating on either C-band or Ku-band frequency. Vessels with modest traffic should opt for Ku-band, which requires less power and smaller antennae. Bigger dishes and more power are needed for the larger bandwidth and better quality of C-band systems.
The attraction of VSAT is that whichever band is chosen the equipment usually comes as part of a lease package with a fixed monthly payment, making for greater control over communication expenditure. On many modern ships the operational element of communication use is expanding rapidly and crews are beginning to expect the kinds of email, internet and calling services that they receive on shore.
Greater bandwidth is on the horizon to meet the expanding market by making use of the Ka-Band. Inmarsat is investing in three satellites to use Ka-band radio frequencies and deliver mobile broadband speeds of 50Mbps.
L-Band (1-2 GHz)
Almost all of the Inmarsat and all of the Iridium services operate in the part of the radio spectrum labelled as L-band which is very narrow and congested. Being a relatively low frequency, L-band is easier to process, requiring less sophisticated and less expensive RF equipment, and due to a wider beam width, the pointing accuracy of the antenna does not have to be as accurate as the higher bands. Only a small portion (1.3-1.7GHz) of L-Band is allocated to satellite communications on Inmarsat for the Fleet Broadband, Inmarsat-B and C services.
L-Band is also used for low earth orbit satellites, military satellites, and terrestrial wireless connections like GSM mobile phones. It is also used as an intermediate frequency forsatellite TV where the Ku or Ka band signals are down-converted to L-Band at the antenna. Although the equipment needed for L-Band communications is not expensive in itself, since there is not much bandwidth available in L-band, it is a costly commodity. For this reason, as the usage of data heavy applications has grown, shipping has turned to more sophisticated technology for commercial communications.
S-Band (2-4 GHz)
Used for marine radar systems
C-Band (4-8 GHz)
C-band is typically used by large ships and particularly cruise vessels that require uninterrupted, dedicated, always on connectivity as they move from region to region. The ship operators usually lease segment of satellite bandwidth that is provided to the ships on a full time basis, providing connections to the Internet, the public telephone networks, and data transmission ashore. C-band is also used for terrestrial microwave links, which can present a problem when vessels come into port and interfere with critical terrestrial links. This has resulted in serious restrictions within 300Km of the coast, requiring terminals to be turned off when coming close to land.
X-Band (8-12 GHz)
Used for marine radar systems
Ku-Band (12-18 GHz)
Ku-Band refers to the lower portion of the K-Band. The “u” comes from a German term referring to “under” whereas the “a” in Ka- Band refers to “above” or the top part of K-Band. Ku-Band is used for most VSAT systems on ships. There is much more bandwidth available in Ku -Band and it is less expensive that C or L-band.
The main disadvantage of Ku-Band is rain fade. The wavelength of rain drops coincides with the wavelength of Ku-Band causing the signal to be attenuated during rain showers. This can be overcome by transmitting extra power. The pointing accuracy of the antennas need to be much tighter than L-Band Inmarsat terminals, due to narrower beam widths, and consequently the terminals need to be more precise and tend to be more expensive.
Ku band coverage is generally by regional spot beams, covering major land areas with TV reception.
VSAT Vessels moving from region to region need to change satellite beams, sometimes with no coverage in between beams. In most instances the satellite terminals and modems can be programmed to automatically switch beams. VSAT Antenna sizes typically range from a standard 1m to 1.5m in diameter for operation in fringe areas and, more recently, as low as 60cm for spread spectrum operation.
Ka-Band (26.5-40 GHz)
Ka-Band is an extremely high frequency requiring great pointing accuracy and sophisticated RF equipment. Like Ku-band it is susceptible to rain fade. It is commonly used for high definition satellite TV. Ka-Band bandwidth is plentiful and once implemented should be quite inexpensive compared to Ku-Band.
Inmarsat will likely be the first to provide a global Ka-Band VSAT service as its GlobalXpress service comes on stream in 2015. The service will be using Inmarsat’s fifth generation satellites, the first of which arrived on station in 2014 and entered commercial service in July 2014 powering regional Global Xpress services for Europe, the Middle East, Africa and Asia.
The second Global Xpress satellite – Inmarsat-5 F2 (I-5 F2) – was launched on 1 February 2015. Once operational, I-5 F2 will deliver Global Xpress services in the Americas and the Atlantic Ocean Region. The third satellite in the constellation is on track for launch in Q2 2015, with global availability expected early in the second half of this year. Each Inmarsat-5 satellite is expected to have a commercial life of 15 years. A fourth Inmarsat-5 is on order for delivery in late 2016.
Fleet Xpress, Inmarsat’s hybrid Ka-band/L-band service, will become available once Global Xpress commences global commercial service. In the meantime, the company has introduced FleetBroadband Xtra (FBX), a regional Global Xpress/FleetBroadband service that is already available in the Indian Ocean Region, powered by the first Inmarsat-5 satellite and Inmarsat-4 fleet. As the second and third I-5 satellites enter commercial service, coverage will expand to the Atlantic Ocean and Pacific Ocean Regions.
As more Ka-Band bandwidth becomes available, there will be several other satellite providers offering Ka-Band VSAT on a more regional basis. Telenor Satellite Broadcasting’s THOR 7 HTS Ka band payload offers 6-9Gbps throughput with up to 25 simultaneously active spot beams. THOR 7, which is expected to launch in Q2, 2015, will provide high- powered coverage over the North Sea, the Norwegian Sea, the Red Sea, the Persian Gulf and the Mediterranean. Ka-Sat will cover most of Europe.
Yahsat 1b, NewSat Australia, Eutelsat and Avanti Communications will also provide Middle East coverage, offering mariners with strictly regional European and Middle East sailings a Ka-Band alternative to Global Xpress. With new services in different bands coming on streams, some providers will be operating hybrid services that take advantage of the cheapest network at any given time. The technologies required to facilitate hybrid networks are already well under development and consist of dual-band satellite antennas, Ku and Ka-Band switchable antennas, and the use of equivalent modem/hub infrastructure.