Satellite systems and networks explained

21 min read

Ship communications, Satellite systems and networks explained

Shipping is frequently described as a conservative industry that is slow to embrace new technologies. In fact, this is not true especially when it comes to the matter of  ship communications. Ships were communicating with the shore via radio from 1899 although initially messages were sent using morse code rather than voice. By the late 1970s, satellite systems and networks were being used by a small number of commercial vessels and many more military ships.

Obviously technological change is only adopted once it has reached a stage where it can meet the unique demands of the maritime industry and in particular prove its reliability and robustness under the harshest of conditions. If shipping has been slower to embrace some aspects of modern technology, it is often because the difficulties and high cost of ship communications across vast distances has meant that ship operators devised ways of minimising the amount of communications needed for commercial purposes.

Few ship operators or their crews are concerned with the high science and engineering of the satellites themselves, but they do need to understand the fundamentals of satellite communications and the radio spectrum.

Satellite communication is in principle no different from radio communication and in fact both systems operate in an identical manner making use of electromagnetic waves. Conventional radio equipment is intended for ship communications between two points only except when a distress signal is being sent. Radio clearly has one characteristic that has been a restricting factor and that is the signal has a very limited range in comparison to satellite networks. While some radio signals can bounce off the ionosphere extending the range this is not as effective as bouncing signals using satellites.

A satellite is an intermediate device in orbit above the earth that enables transmission of data to a ship or receiving data from a ship regardless of the different positions on the surface of the globe of the two parties. The other party can be a shore office or another ship.

All satellites make use of a beam which is a pattern of electromagnetic waves received or 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. The dish itself is hidden from view by the radome cover but viewed up close they are sophisticated pieces of equipment with motors and gearing enabling the dish to maintain a lock on the satellite under all but the harshest conditions.

Most satellite communication systems are structured so ships are required to share channels with others which is perfectly fine for simple ship 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 (although a VSAT service is not necessarily needed for broadband). 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.

Not all ship types or fleet managers need large data flows for commercial reasons but passenger, offshore and container operations frequently do. For passenger vessels this will involve allowing passengers to use computers, tablets and smart phones as well as providing entertainment services. In the offshore industry it enables survey and other data to be transmitted at will and for container ships there is a need for large amounts of data for stowage plans and customer services.

Satellite networks

Competition for marine traffic is fierce and there are many players within the marine communications sector. They are however not all competing in the same market sectors.

Not all satellite systems are identical, there being three main types: LEO (low earth orbit) MEO (medium earth orbit) and GEO (Geosynchronous Equatorial Orbit or more commonly called geostationary). Each of these types of systems have their pros and cons and some ship operators will sign up to services on different systems.

GEO networks

These satellites are the most powerful type of satellite and are located in an orbit 35,768 kilometers above the earth’s surface at a point above the equator. As their speed and direction matches the earth’s rotation they are always fixed giving meaning to the term geostationary. 

The satellites have a large beam and cover a very wide area meaning that fewer satellites are required to cover the same area as other network types. Inmarsat, the first commercial maritime satellite communication system, is of this type and although it is the leading player it is not alone and there are several other players offering maritime communications and VSAT services using GEO satellites including Thuraya which is in the process of refreshing its fleet of satellites the oldest of which is now over 12 years old.

Inmarsat initially operated with three satellites spaced around the equator with each satellite covering approximately one third of the world’s surface but not extending to the polar regions above 70 degrees. Since the 1990s it has had a minimum of four satellites in service.

Inmarsat is currently in its 5th generation of satellites – all of the first four generations were limited to the L-Band with the latest generation operating on Ka-Band. In 2021, two third generation satellites provide maritime safety back-up services only and the fourth (4 L-Band satellites) and fifth generations (5 Ka-Band satellites) also provide maritime safety and fully commercial ship communications. Increasing demand for VSAT and improved 5G connectivity for both commercial and personal use at sea is driving growth in this arena.

Satellite operators are investing heavily in new satellites to increase maritime VSAT capabilities and invariably the new satellites are of the HTS (high throughput satellite) type. In June 2021 Inmarsat announced its new Orchestra service which will take satellite and 5G communications a step further. ORCHESTRA will be a seamless configuration of its L-Band and Ka-Band networks with terrestrial 5G, targeted LEO capacity, and dynamic mesh technologies.

LEO Networks

Closest to earth are the LEO constellations which typically comprise many small satellites orbiting the earth at between 800km and 1,600km above the earth’s surface at speeds which see them completing an orbit normally in under two hours. They are ideal for very high speed, low latency communications, often exhibiting a delay of just 0.05 seconds.

Their small size and the limited coverage of each satellite means that a constellation comprising tens or hundreds of satellites is needed but this also gives the possibility for full coverage of the earth’s surface including polar regions where GEO systems cannot operate.

LEO satellites are much smaller and less costly than other types making them ideal for newcomers.

Conceivably the best-known player in this sector is Iridium which has invested heavily recently to replace the ageing satellites it acquired cheaply in the early 2000s just a few years after the original constellation was established. There were 99 satellites in the original network. 66 in use, some in orbit as spares and some unlaunched

From 2017, Iridium has developed and launched a complete new constellation comprising 66 active satellites, with another nine in-orbit spares and six on-ground spares. The new satellites in the NEXT generation have more data capacity and have been instrumental in Iridium gaining recognition as the only GMDSS service provider apart from Inmarsat.

Iridium has a proven track record in maritime communications and its new satellites and broadband Certus offering along with GMDSS approval will ensure its future. There will likely be competition for future ship communications from the likes of SpaceX’s Starlink network which will consist of tens of thousands of satellites providing broadband connectivity.

The network has been controversial for various reasons including the impact on the environment, several scientists say it will impact visibility of the night sky and competitors have queried the legality of licenses issued to SpaceX, but launches have begun and more than 1,000 satellites were operational by summer 2021. Expected additional ship communication demand from ships as a consequence of growing digitalisation of shipping and also the imminent arrival of e-navigation whether mandated or voluntary is already being anticipated by new service providers.

Advances in satellite technology means that satellites can now be much smaller and less costly than was previously the case. These so-called micro- and nano-satellites have the potential to bring new services and reduced costs for ship operators especially in niche and specialist areas.

MEO Networks

MEO satellites orbit at a lower altitude than GEO, usually occupying the space between 5,000 and 12,000 km. Their relative proximity to Earth means they achieve far lower latency than GEO units, making them suitable for high-speed telephone signals and similar missions.

Depending on their altitude, MEO satellites usually complete one orbit of the Earth in between two and eight hours, although some can take up to 24 hours to orbit. Their smaller size and lower orbit means that between eight and 20 units will be required to provide complete coverage of the Earth.

Although more satellites are needed for a complete earth coverage MEO network, companies such as SES with its O3b constellation and Globalstar are among those investing in this sector and targeting marine customers.

High latitude coverage

The vast majority of merchant shipping trades are carried out in areas between the Arctic and Antarctic Circles which are a fraction over 66 degrees North and South respectively. This is near the limit of the 70 degrees latitudes that are the extremes of Inmarsat’s GEO satellites meaning satellite communications (including GMDSS) at latitudes above 66 degrees cannot be guaranteed. This is one of the reasons the Iridium has been accepted as a GMDSS provider since its LEO network has no latitude limitations and is available right to the North and South Poles.

Maritime activity inside the Arctic Circle has been steadily increasing involving oil and gas exploration, some domestic commercial traffic but most recently growing use of the Northern Sea Route around the top of Russia connecting Asia and Europe. There is also increasing cruising activity inside the Arctic Circle.

As a consequence, Inmarsat is expanding its GlobalXpress network with payload on two satellites planned to be launched by Space Norway and its subsidiary Space Norway HEOSAT as part of the Arctic Satellite Broadband Mission. The satellites carrying the GX payloads are scheduled for launch in 2022.

Iridium has long made much of its truly global satellite network and with its new NEXT constellation satellites it has added broadband capability with its Iridium Certus offering.  

The Satellite and Radio Spectrum

Both conventional radio and satellite communications receive and transmit electromagnetic signals or radio waves. The length or frequency of radio waves varies tremendously and to distinguish between different lengths of waves they are grouped into bands within the radio spectrum. The bands are named under a number or protocols but in maritime circles, the bands used by the Institute of Electrical and Electronics Engineers (IEEE) are most commonly recognised.

Some bands have a wider spread than others and each of the bands is used for a slightly different purpose. Radio communications on Low Frequency (LF), Medium Frequency (MF), High Frequency (HF), Very High Frequency (VHF) and Ultra High Frequency (UHF) bands are all on frequencies below 1GHz which is the lowest 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 now being used to meet the expanding market by making use of the Ka-Band. Inmarsat has invested in five satellites to use Ka-band radio frequencies and deliver mobile broadband speeds of 50Mbps.

L -BAND (1-2 GH)

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 ship 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 for satellite 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 a 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 than 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 using 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 was the first to provide a global Ka-Band VSAT service as its GlobalXpress service came on stream in 2016. The service uses 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.

As more Ka-Band bandwidth becomes available other satellite providers are 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 and coverage over the North Sea, the Norwegian Sea, the Red Sea, the Persian Gulf and the Mediterranean. Ka-Sat covers most of Europe. Yahsat 1b, NewSat Australia, Eutelsat and Avanti Communications also provide Middle East coverage, offering mariners with strictly regional European and Middle East sailings a Ka-Band alternative to Global Xpress.

A notable development is that as new services in different bands come on streams, some providers are operating hybrid services that take advantage of the cheapest network at any given time.

The technologies required to facilitate hybrid networks consist of dual-band satellite antennas, Ku and Ka-Band switchable antennas, and the use of equivalent modem/hub infrastructure.

ISM and wi-fi

Most people are familiar with wi-fi as a means for using smart phones and computers and this uses a particular section of the radio spectrum that is actually within the C-Band covered above. There are a number of unlicensed spectrum bands in a variety of areas of the radio spectrum. Often these are referred to as ISM bands – Industrial, Scientific and Medical, and they carry everything from microwave ovens to radio communications. Many of these bands, including the two used for wi-fi are global allocations, although local restrictions may apply for some aspects of their use. The two bands in particular used for wi-fi are the 2.4GHz and 5 GHz bands.

As the 2.4 GHz band became more crowded, many users opted to use the 5 GHz ISM band. This not only provides more spectrum, but it is not as widely used by wi-fi. Many of the 5 GHz wi-fi channels fall outside the accepted ISM unlicensed band and as a result various restrictions are placed on operation at these frequencies.