The satellite and radio spectrum
Updated 11 Oct 2019
Both conventional radio and satellite communications received and transmit electromagnetic signals or radio waves. The length or frequency of radio waves various 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 (1-2GHz)
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 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.
Used for marine radar systems.
C-band is typically used by large ships, particularly cruise vessels, that require uninterrupted, dedicated, always-on connectivity as they move from region to region. The ships’ 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.
Used for marine radar systems.
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.
There are no official statistics as to the number of vessels equipped with Ku-Band communications but analysts of the market estimate that around 10,000 vessels is a probable number, indicating that a considerable market exists to be exploited.
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 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 Global Xpress service came on stream in 2016. The service uses three 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 2015and offers services in the Americas and the Atlantic Ocean Region. The third satellite in the constellation was launched in August 2015, with global availability announced at the end of March 2016. Each Inmarsat-5 satellite is expected to have a commercial life of 15 years.
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 6-9Gbp/s 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.
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.
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, mentioned 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 microwaves in 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 5GHz bands.
As the 2.4GHz band becomes more crowded, many users are opting to use the 5GHz ISM band. This not only provides more spectrum, but it is not as widely used by wi-fi. Many of the 5GHz wi-fi channels fall outside the accepted ISM unlicensed band and as a result various restrictions are placed on operation at these frequencies.
A system making use of the 5GHz waveband for vessel communication purposes outside of the VSAT system has been developed by Kongsberg. Its Maritime Broadband Radio MBR is a smart antenna designed for use in maritime applications where digital high-speed reliable communication and data transfer are desirable. The housing accommodates 60 individual antennae and needs only connections to power and ethernets. The unit is configured from a web interface that also provides the status of the radio and the network. The network administrator can configure and operate units and adjust network resources from any vessel in the network.
The MBR units use highly-dynamic beamforming and adaptive power control to secure stable communication in maritime operations with signal obstructions, fading and ranges in excess of 50km depending upon the model chosen. The system can securely carry a diverse array of operational information, from real-time video to system data, and remotely-situated teams can work together seamlessly, co-ordinating systems and activities for optimal performance, safety and operational success.
With beamforming, the MBR can direct datagrams to the destination as a multi-directional networked wireless system. Supporting IP transmission, the MBR provides a resilient, high-capacity data link for systems that communicate over IP. The use of end-to-end IP connectivity provides cost efficient integration and an interoperable solution for seamless data exchange. The MBR system has been used for testing autonomous vessels in Norwegian waters but the concept has obvious uses beyond this for vessels operating in relatively close contact.