Satellite Data Telecommunication Handbook (WMO No.1223)

Explanatory note
The Satcom Handbook is now available as WMO No 1223. Satcom service and equipment providers are welcome to add to the directory of suppliers in Chapter 4.

Click here to download the Published PDF Version


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ACKNOWLEDGEMENTS

WMO would like to acknowledge the work of the lead author, Dr Mike Prior-Jones, the present Chair of Satcom Forum, and the contributions of the other members of the Satcom Executive Committee, especially Johan Stander, Sean Burns and Andy Sybrandy. Considerable thanks are also due to David Thomas, from the WMO Secretariat, for coordinating the work and producing the Web version.

1: Introduction and overview

1.1 Introduction

This is the first edition of the Satellite Data Telecommunication Handbook. This handbook is a guide to using satellite telecommunication systems and is provided as an attachment to the Guide to the WMO Information System (WMO-No.1061). It is intended for scientists and managers who are considering using satellite communications to collect data from remote instrumentation located either on land or at sea. The handbook aims to provide an overview of the state of the market at the time of writing (April 2018) so that users can quickly identify which satellite services are appropriate for their needs. Since the market is evolving rapidly, an online version will be made available via the WMO website https://wiswiki.wmo.int/Satcom-Guide and kept up to date as new systems are introduced to the market and older ones are retired.

This is the first publication from the joint WMO-Intergovernmental Oceanographic Commission (IOC) International Forum of Users of Satellite Data Communications, better known as the Satcom Forum. The Satcom Forum is a relatively new international body whose purpose is to provide clear information about satellite communications to scientific users and to liaise with the industry to advocate for appropriate new technical features and suitable pricing structures. For more details about the Satcom Forum, please see https://wiswiki.wmo.int/Satcom.

The editorial approach has been to work exclusively with publicly available information, including marketing brochures, manuals and other published documents. The handbook only considers systems that were in operation at the time of writing; several satellite networks had new services in development while this handbook was being drafted, but as these services were not yet functioning, their final specifications were unknown. The online version includes clearly marked sections contributed by the satellite operators which provide more details about their product offerings.

1.2 Why satellite communication?

Satellite communication is now more than sixty years old. The Soviet Union launched Sputnik I on 4 October 1957, and the first communications satellite was launched by the United States the following year. Since then, satellite communication has become firmly established as one of three basic techniques for long-distance telecommunications, alongside cables and terrestrial wireless networks.
The key benefit of satellite communication is its independence from ground-based infrastructure. This is particularly valuable in hazardous and isolated regions (such as oceans, deserts and the polar regions) and in places where conflict or natural disasters have destroyed the terrestrial infrastructure. For those in need of reliable emergency communications, satellite communications can literally save lives.

For scientific users, particularly meteorologists, hydrologists and marine scientists, satellite communication offers a convenient way to collect real-time data from instruments in the field. Marine science was an early adopter of remote instrumentation, with satellite services making it possible to immediately and reliably collect data from the open oceans. Satellite communication is also used to track marine creatures and larger birds.

1.3 Connectivity options for remote instruments

There are various connectivity options for equipment installed in remote locations:

(a) Physical retrieval. The instrument stores the data locally (for example, on a memory card, USB stick or local hard drive), and the operator visits the instrument periodically to retrieve the data. The operator may have to wait months or years for the data, but there is no ongoing cost apart from the site visits. This option is often used if a regular visit needs to be made to do maintenance work on the instrument.

(b) Cable/wireline/landline. A wired connection is typically a copper or fibre-optic cable, such as a phone line. These connections generally offer the highest data rates and can be reliable provided that the infrastructure is not disrupted. However, cables can be cut by construction work or damaged by high winds or storms. Power failures at the telephone exchange or router sites can also disrupt communications. In addition, in some countries, the landline network offers a poor quality of service and can be expensive. In truly remote regions, a wireline option is usually out of the question.

(c) Terrestrial wireless. Terrestrial networks include common services, such as cell phones and point-to-point microwave transmission, as well as more esoteric means of communication, such as packet radio, meteor burst, ionospheric scatter, tropospheric scatter and high-frequency (HF) (also known as short-wave) radio. Low-power wide-area networks (LPWANs), SigFox and LoRaWAN, for example, are being deployed commercially in some countries and are designed specifically to offer low data rates for telemetry and remote control applications at a low operating cost. Cellular networks are also starting to offer similar long-range, low-data-rate services (for example, LTE Cat NB1, also known as NB-IoT) to cater to this market. Terrestrial wireless systems are still very dependent on a fixed infrastructure, which can be disrupted by natural disasters, commercial failure or civil unrest.

(d) Satellite communication. Assuming that a terminal can obtain a clear view of the sky, satellite services allow connectivity from anywhere in the world, with no dependence on ground-based communication infrastructure. If the system includes its own independent power supply (batteries, solar, wind, and so forth), communications will not be disrupted unless the terminal itself is disabled or destroyed. The drawbacks to satellite communication are the relatively low data rates from small terminals when compared with terrestrial wireless and the possible higher cost per bit transmitted.

1.4 Types of satellite orbit

Communications satellites are commonly classified by their type of orbit. There is a huge variety of possible orbits, but in practice, only a small number of orbit types are used for communications systems:

(a) Geostationary orbit (GEO): Geostationary satellites sit directly above the Earth’s equator and have an orbital period of 24 hours. They are stationary relative to the Earth’s surface, which means that a single satellite can cover a large, fixed area of the Earth’s surface. Terminals do not require any active steering; they can be pointed at the satellite at the time of installation and then fixed. There are two key drawbacks to geostationary orbits: they cannot provide coverage to the polar regions beyond 80 degrees latitude, and they introduce an unavoidable latency in communications. Geostationary orbits are located at an altitude of 35 000 km, and at this distance, the speed at which light travels produces an end-to-end latency of about a quarter of a second. For a two-way link (such as a telephone call), this results in an apparent half-second delay on the line.

Note:The use of geostationary satellites at between 60 and 80 degrees latitude requires special care and attention and should be discussed with the supplier. When approaching 80 degrees latitude, multiple large antennas may be required in order to obtain a sufficiently strong signal.

(b) Low Earth Orbit (LEO): This is a broader classification of the term “orbit” and refers to satellites that are placed much closer to the Earth. An altitude of 300 km is the lowest practical orbit, and typically, LEO satellites orbit at altitudes of between 600 km and 2 000 km. The low altitude offers much lower latency compared with GEO. LEO satellites move rapidly with respect to the Earth’s surface; a typical LEO satellite will be in view of a ground station for 10 minutes on each pass. Providing real-time global coverage requires a large fleet of satellites (called a “constellation”) in slightly different orbits. Iridium and ORBCOMM both take this approach; Iridium had 66 active satellites in its original constellation. There are also networks that use smaller constellations (such as Argos and Gonets). In such cases, it may be necessary to wait for a satellite to come into view (called “waiting for a pass”) before a message can be sent. The message is often stored on the satellite and downlinked* when it passes over a ground station. This type of network design is called “store-and-forward” and can introduce minutes or even hours of delay between the transmission of the message to the satellite and its delivery. Many LEO satellites are in polar orbits, meaning that they pass over both poles and can thus “see” the whole surface of the Earth over the course of their orbital cycle. A key drawback to LEO satellites is that they are subject to small amounts of drag from the Earth’s upper atmosphere and thus tend to have a shorter service life than GEO satellites. The drag slows the satellites down, and eventually they will re-enter the atmosphere and burn up. Positioning thrusters are used to keep the satellites in the correct orbit, but once they are out of fuel, the satellite is either boosted into a higher “graveyard orbit” or put into a re-entry trajectory where it will burn up safely over the Pacific Ocean
Note:In the satellite industry, “uplink” refers to a signal travelling up to a satellite, and “downlink” refers to a signal travelling down to a terminal on the ground.

(c) Medium Earth Orbit (MEO): This term is used to describe orbits with altitudes between 2 000 km and 35 000 km. Global Positioning System (GPS), GLONASS and Galileo navigation satellites are MEO satellites, but this orbit is not commonly used for communications satellites because the terminals require a tracking antenna. However, O3B operates a constellation of 12 MEO satellites that provide high-speed, low-latency broadband to equatorial countries and to ships at sea.

1.5 Antenna issues

All radio systems experience path loss, which is caused by the spreading out of radio signals from the transmitter. The further the signal is from the transmitter, the weaker it becomes, just as light becomes fainter as it moves away from a lamp. This relationship is an inverse-square law; the signal power drops according to the square of the distance. A radio signal sent to a LEO satellite needs to travel at least 300 km, and to reach a GEO satellite, it must travel 35 000 km. Overcoming path loss is key for satellite communications.


There are three approaches to overcoming path loss:
(a) Increase the transmitter power;
(b) Increase the receiver sensitivity;
(c) Use directional antennas.

Increasing the transmitter power is practical up to a point. Satellites are solar powered, and their performance is usually constrained by the amount of electrical power available for the transmitters. On the ground, it is possible to use very powerful transmitters at the expense of electrical efficiency; provided that you have access to mains power or generators.

Receiver sensitivity has improved as electronics technology has advanced. First-generation satellite receivers in the 1950s were cooled with liquid nitrogen to improve their noise performance, whereas now we have sensitive solid-state electronics with superior performance.

The design of the antenna allows the radio signal to be directed into a narrow beam, rather than radiating equally in all directions. The beam can be thought of as a searchlight, as opposed to a bare light bulb. Concentrating the wave into a beam effectively increases the power of transmission in the direction of the beam. The classic parabolic dish antenna design produces this narrow beam; the larger the dish, the narrower and more powerful the beam. The effective amplification of a signal in the direction of the beam as compared to the signal produced by an omnidirectional antenna is known as “antenna gain”.


There is, however, always a trade-off: a directional antenna must be pointed accurately towards the satellite. This is what makes geostationary satellites so attractive; because the satellite appears “fixed” in the sky, a highly directional antenna can be lined up on the satellite and then fixed in position. For other types of orbit, either the antenna must track the satellite (with the consequent cost and complexity), or the user must forego the gain of a directional antenna and operate with a simpler wide-beam antenna with little or no gain. Note that an antenna used on a moving land vehicle, ship or aircraft must be of the tracking type.

Tracking antennas for ships are bulky and expensive because of the need to constantly correct for the ship’s motion. Traditionally they were gyro-stabilised with large rotating flywheels, but modern control electronics can sense the ship’s motion and automatically point the antenna. However, this requires powerful motors to move the heavy antenna rapidly as the ship pitches and rolls.

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2: Satellite systems currently in service

2.1 Introduction

This section only describes systems that were operating and taking on new users at the time of its update. A number of companies were proposing to launch new satellite constellations while the update to this section was being drafted; these will be covered in future revisions once they enter service. Where possible, all descriptions of satellite systems are based on information that was publicly available at the time of the update. Information that has been supplied directly by the satellite industry (and is not otherwise published) is highlighted in the text.

Data rates (speed of transmission) are given in bits, kilobits or megabits, as appropriate. Message sizes are given in bytes (8 bits = 1 byte). International System of Units (SI) prefixes are used for bytes, so 1 kbyte (1 kilobyte) refers to 1 000 bytes and not to the binary kibibyte (1 024 bytes).

The satellite systems considered in this handbook are: Argos, DCS, Globalstar, Gonets, Inmarsat, Iridium, O3B, Orbcomm, Thuraya and VSAT.
 

2.2 Argos (information updated April 2018)

Website:	http://www.argos-system.org/
Type of orbit:	LEO, polar orbit
Number of satellites in operation:	6
Coverage:	global

It was established as a joint French-American project. The original partners were the French National Centre for Space Studies Centre national d'études spatiales (CNES), the United States National Oceanic and Atmospheric Administration (NOAA) and the United States National Aeronautics and Space Administration (NASA). The service became operational in 1978. Argos does not operate its own satellites; it is carried as part of the payload on meteorological observation satellites. As of 2015, the Argos constellation consisted of three United States (NOAA) satellites (NOAA-15, 18 and 19), two European satellites from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) (MetOp-A and B) and one Indian satellite (Satellite with ARGOS and ALTIKA (SARAL)). A third European satellite (MetOp-C) was due for launch in 2018, and a further launch was planned for 2020.

Argos downlinks data from the satellites through a network of ground stations. Messages received by the satellites are stored until the satellites are in range of a ground station (“store-and-forward”). The service has global coverage but can have relatively long latency.

Argos’s key feature is that it allows the use of extremely small, low-powered terminals. It is the only satellite system with terminals that are light enough to track birds. For tracking applications, Argos can also estimate the position of the terminal based on the Doppler shift of the radio signal, which eliminates the need for a separate positioning system such as GPS.

The Argos service is offered in two ways: there is a commercial service available at market rates, and a special, more economical rate for scientific users. The latter rate is determined by an organization called the Joint Tariff Agreement (JTA), which is a subprogramme of the Satcom Forum. (See http://www.argos-system.org/argos-jta/

Argos offers two types of service, Argos-2 and Argos-3. Argos-2 is available on all six satellites, operates at 400 bits per second and has a maximum message size of 32 bytes. The newer Argos-3 service is available on the four newer satellites in the constellation and offers a 4 800 bit per second “high-rate” service, allowing the transmission of larger messages of up to 576 bytes. Argos-3 also offers optional error corrective coding of messages.

A new service, Argos-4, was in development while the update to this section was being drafted, but the specifications had not yet been announced.

Argos is primarily a unidirectional service intended for collecting data from remote terminals. Argos-3 added a two-way service, but it is presently only offered by three satellites. The downlink data rate to remote terminals is 400 bits per second, and the downlink channel of the two-way service is mainly used to acknowledge receipt of messages.
 

2.3 DCS (information updated April 2018)

CGMS Website:	http://www.cgms-info.org/
CMA website:	http://www.cma.gov.cn/en2014/satellites/
EUMETSAT website:	https://www.eumetsat.int/website/home/Data/MeteosatServices/MeteosatDataCollectionServices/index.html
ISRO website:	https://www.isro.gov.in/applications/climate-environment-0
JMA website:	http://www.jma-net.go.jp/msc/en/general/system/dcs/index.html
NOAA website:	http://www.noaasis.noaa.gov/DCS/
Roshydromet website:	http://www.meteorf.ru/
Type of orbit:	Geostationary
Number of satellites in operation:	10
Coverage:	global excluding poles

The Data Collection Service (DCS) is a unidirectional service designed exclusively for the collection and redistribution of environmental data. It is commonly used to collect data from static automatic weather stations but has a range of other applications. It is free to use, which makes it very popular with less wealthy countries.

The service is offered by geostationary meteorological satellites from the following agencies:
(a) NOAA (GOES-E and GOES-W satellites, covering the Americas);
(b) EUMETSAT (Meteosat-8 and Meteosat-11 satellites, covering the Atlantic Ocean, Europe, Africa and the Indian Ocean);
(c) JMA (Himawari 8 satellite, covering East Asia and the western Pacific Ocean);
(d) ISRO (Insat satellites, covering India);
(e) Roshydromet (Elektro-L satellite, covering Russia);
(f) CMA (Feng Yun satellites, covering China).

NOAA, EUMETSAT and JMA coordinate their DCS activities through a joint body called the Coordinating Group for Meteorological Satellites (CGMS). The Indian, Chinese and Russian satellites offer a DCS service only to users within their own countries. However, the other five satellites are available for use free of charge for meteorological, hydrological or geological data collection and redistribution, subject to the approval of the satellite operating agency. This free service is provided on the basis that the data collected is made publicly available via the WMO Information System (WIS).

The basic DCS transmission process is common across all operators. The transmissions are assigned to different users based on an allocated timeslot. The length of the slot depends on the bit rate of the transmission, which depends on both the user’s terminal and the satellite used. DCS transmitters are unidirectional and rely on an accurate clock to remain within their allocated timeslot. There is typically a 15-second guard period before and after each timeslot to allow for clocks that are too fast or too slow, making the total timeslot 30 seconds longer than the maximum time permitted per transmission.

The original DCS protocol operated at 100 bits per second but is now considered to be very old and slow, and the transmitters are quite power-hungry. Newer satellites have allowed the operators to offer higher data rates, but unfortunately these higher-rate services are not standardized:

(a) NOAA offers DCS rates of 300 bits per second and 1 200 bits per second on their GOES satellites in the Americas, with error corrective coding to protect against errors in transmission.

(b) EUMETSAT offers a “standard rate” service of 100 bits per second and a “high-rate” service of 1 200 bits per second on its satellites. The high-rate service also has error corrective coding and is more power-efficient than the service offered by the NOAA system. It has a flexible timeslot allocation scheme, which allows for the sending of large messages of up to 65 kilobytes or of shorter, more frequent transmissions, for example to collect data every five minutes rather than every hour.

(c) JMA offers DCS rates of 100 bits per second and 300 bits per second on its Himawari series satellite in East Asia and the western Pacific Ocean.

2.4 Globalstar (information updated April 2018)

Website:	http://www.globalstar.com
Type of orbit:	LEO
Number of satellites in operation:	24
Coverage:	North America, Europe, Middle East, East Asia, Australia. Limited coverage in Southern Hemisphere. No permission to operate in China or India. Little or no oceanic coverage.

Globalstar is a commercial service originally intended to be used as a mobile phone system. The present constellation of satellites is the second generation, launched between 2010 and 2013. Unlike some of the other LEO systems, Globalstar’s satellites do not have any on-board processing for calls and messages; all the processing is carried out by ground stations. Consequently, Globalstar can only provide good coverage where it has ground stations in operation. This means it has limited coverage at sea and in the polar regions. At the time of writing, the coverage maps showed limited coverage in South America, very little coverage in Africa and no coverage in China, India and central Asia. Globalstar’s traditional focus has been on the North American market, and more than 50 % of its customers are in the United States. Since its coverage is more limited, its strategy has been to compete on price, so its equipment and airtime tend to be cheaper than those of its competitors.

Globalstar’s “duplex” service (voice service) can be used to provide a circuit-switched data service at 9 600 bits per second. There is no packet-switched service; charges are per minute regardless of whether the voice service or the data service is used.

Globalstar also offers a “simplex” service (unidirectional service) that can be used to collect data from low-power terminals. The simplex service has better coverage than the duplex service and in principle offers coverage on all continents except Antarctica; however, Globalstar does not have permission to operate in every country.

A simplex message carries only nine bytes of data, and the service is billed per message. Multiple messages can be grouped together into a “message burst” to send larger amounts of data. The transmitter sends each message burst several times in order to make sure that it is received since it cannot receive an acknowledgement from the satellite. By default, the transmitters send each message burst three times, with an average of five minutes between transmissions (the spacing is randomized to reduce the risk of collisions with other transmissions). Duplicate messages are discarded at the ground station, so the customer is not billed more than once.
 

2.5 Gonets (information updated April 2018)

Website:	http://www.gonets.ru/
Type of orbit:	LEO
Number of satellites in operation:	12
Coverage:	Global

Gonets is a Russian system with polar-orbiting satellites that operates using store-and-forward messaging. It has four gateway stations, all located in Russia. The service operates in the low UHF band, just below 400 MHz. It markets itself very much towards Russian customers.

Gonets provided more technical information about its system in response to a direct request:
(a) Messages are formed from one or more 1.5-kilobyte packets;
(b) Multiple packets can be used to send larger payloads;
(c) The maximum message size depends on the location of the terminal relative to the satellite orbits.

2.6 Inmarsat (information updated April 2018)

Website:	http://www.inmarsat.com/
Type of orbit:	Geostationary
Number of satellites in operation:	11
Coverage:	Global excluding poles

Inmarsat is a commercial service provider that grew out of the marine communications market. It now offers services to land, marine and aeronautical terminals and operates three different satellite constellations.

Inmarsat’s older satellites (Inmarsat-3 and Inmarsat-4 constellations) operate in the L-band frequency range (~1.5 GHz) and form the backbone of Inmarsat’s business. The newer Inmarsat-5 series operates in the Ka-band frequency range (26-30 GHz) and is used to provide higher-data-rate services, which Inmarsat calls “Global Xpress”.

Inmarsat offers many different services. Marine services are mostly branded “Fleet”, and aeronautical services are mostly branded “Swift”.

2.6.1 Land services

IsatHub is a lightweight, portable terminal that offers data rates of up to 384 kbits per second. The terminal includes a Wi-Fi hotspot and is designed to be used with laptops and smartphones. It incorporates an internal battery and can operate for 2.5 hours on battery power.

BGAN is Inmarsat’s medium-data-rate land service. It has a range of terminals, some of which can be vehicle-mounted, and offers data rates of up to 492 kbits per second.

BGAN HDR is a high-data-rate version of BGAN that is intended for television news broadcasts. It claims to offer a maximum data rate of 650 kbits per second. It is possible to “bond” two terminals together and obtain speeds of more than 1 Mbit per second.

BGAN Link is a BGAN service sold for use by corporate IT departments. It offers data rates of up to 492 kbits per second, with a data cap of 30 GB per month. There is also a version called “BGAN Link Backup” that is designed to be attractive for business continuity and to be used only when a terrestrial system fails.

BGAN M2M is a low-data-rate messaging service that can be used on both land and sea. It is typically used for tracking and telemetry applications. Terminals can send messages of 10 or 25 bytes and receive messages of up to 100 bytes. IsatM2M is an older service and may be retired in favour of the newer IsatData Pro.

IsatM2M is a low-data-rate messaging service that can be used on both land and sea. It is typically used for tracking and telemetry applications. Terminals can send messages of 10 or 25 bytes and receive messages of up to 100 bytes. IsatM2M is an older service and may be retired in favour of the newer IsatData Pro.

IsatData Pro is a low-data-rate messaging service that allows users to send messages of up to 6.4 kBytes and to receive messages of up to 10 kBytes. Marine-grade terminals are available for use at sea.
 

2.6.2 Marine services

FleetBroadband is a medium data rate marine service. There is a choice of three terminals of different sizes:
(a) FB150 - 150 kbits per second;
(b) FB250 - 250 kbits per second;
(c) FB500 - 432 kbits per second.

All three terminals also offer voice and SMS capability. The FB250 and FB500 terminals incorporate a GSM base station to allow voice and SMS forwarding from ordinary mobile phones.

FleetOne is a service intended for occasional marine use. It is sold with very flexible airtime terms and can be activated and deactivated whenever the user wishes. A low-cost service called “FleetOne Coastal” is available for vessels under 500 tons operating in coastal waters. FleetOne offers packet data transmission speeds of 100 kbits per second.

Inmarsat-C is a low-data-rate messaging service designed for marine safety applications. It offers packet data transmission speeds of 600 bits per second from a compact, low-cost terminal. There are two versions - “Inmarsat C” and “Inmarsat Mini C”. Inmarsat Mini C uses smaller, lower-power terminals. Inmarsat C is more than 25 years old and is likely to be replaced with a new type of service.

Fleet-77 is Inmarsat’s higher-end marine safety service. It will be retired in 2020, but in the meantime offers data services at speeds of up to 64 kbits per second. The lower-bandwidth Fleet 33 and Fleet 55 services will be retired in 2018.

Fleet Xpress is a high-data-rate service for the marine market that uses the Global Xpress satellite network. It offers downlink speeds of up to 8 Mbits per second and uplink speeds of up to 4 Mbits per second.

2.6.3 Aeronautical services

Swift64 is an aeronautical service that provides a 64 kbit per second ISDN-style circuit. Up to four circuits can be bonded to create a 256 kbit per second channel. It can also offer a packet data service at the same data rates (billed by the byte, rather than by the minute).

SwiftBroadband is the aeronautical equivalent of FleetBroadband, with data rates of 200-700 kbits per second depending on the terminal used.

JetConneX is a high-data-rate aeronautical service that uses the Global Xpress satellite network. It offers data rates of up to 50 Mbits per second to aircraft in flight.

2.7 Iridium (information updated April 2018)

Website:	http://www.iridium.com/
Type of orbit:	LEO
Number of satellites in operation:	66
Coverage:	global

Iridium is a commercial satellite operator that uses a large constellation of LEO satellites to provide voice and data services. Its original constellation dates from the 1990s and is presently being replaced by new satellites. As of mid-March 2018, Iridium had had four successful launches out of a planned total of eight, with the remaining launches due to occur later in 2018. The new constellation is known as “Iridium Next”, and the services that it will provide will be called “Iridium Certus”; these services are not yet for sale commercially. The services discussed in this article are those for sale as of April 2018, which are all operated by the original 1990s constellation.

Iridium’s network design is much more complex than that of most of its competitors. Every satellite is cross-linked to its neighbours by microwave links, allowing calls and data to pass between the satellites. An Iridium-to-Iridium phone call is handled entirely by the satellites and never via a ground station. Iridium’s ground stations are used as gateways to terrestrial networks, either to the phone network or to the Internet.

Because the Iridium satellites are in a low Earth orbit, they move rapidly with respect to the ground and are only in view for ten minutes at a time. The network is designed to hand over calls automatically to another satellite, but this is not entirely reliable, and it is quite common for calls to be cut off after four or five minutes. This effect is more noticeable if the user is in a valley or on a mountainside, where terrain may obstruct the view of the “next” satellite. The Pilot service accesses multiple satellites at the same time using multiple antennas within the module and does not suffer from this handover problem.

Iridium offer several types of data service:

(a) Short Burst Data (SBD) - a two-way message-based service;
(b) Iridium Burst - a one-way broadcast message service;
(c) Circuit Switched Data (CSD) - a 2.4 kbit per second dial-up data service;
(d) Pilot - a medium-data-rate service offering Internet Protocol connectivity at speeds of up to 134 kbits per second.

2.7.1 Short Burst Data

Short Burst Data (SBD) is a message-based service intended for applications which need relatively small amounts of data, a small terminal and low power consumption. SBD messages are relatively small (270 bytes for messages from the network to the terminal, or 340 bytes for messages sent by the terminal) and are charged by the byte, usually with a minimum charge per message. They are passed through the Iridium network with a latency of under 20 seconds, and Iridium’s network centre then delivers them using email or a simple IP socket interface. SBD modems are typically integrated into scientific instruments and consumer products (Garmin’s InReach communicators, for example), and can be integrated with the user’s own equipment if that suits the application. Iridium does sell a fully weatherproofed SBD modem, branded as Iridium Edge, that can be attached to a PC or datalogger.

2.7.2 Circuit Switched Data and Router-Based Unrestricted Digital Internetworking Connectivity Solutions

Circuit Switched Data (CSD) is the data equivalent of an Iridium voice call. It offers a 2.4 kbit per second full duplex stream. This is extremely slow by modern standards but still usable for basic data exchange. CSD can be used to provide extremely slow internet access (“Iridium Direct Internet”) and to access private networks. Iridium’s Router-Based Unrestricted Digital Internetworking Connectivity Solutions (RUDICS) service allows hundreds or thousands of CSD calls to be routed to and from a private network and is intended for customers with large numbers of devices deployed in the field. Iridium sells a portable terminal, “Iridium GO”, which is designed to share a single CSD connection with a computer, tablet or smartphone over Wi-Fi. CSD is also available on Iridium’s handsets or using a modem that is designed for integration into the user’s own equipment.

2.7.3 Iridium Burst

Iridium Burst is a broadcast service designed to send the same message to many field terminals. It is intended to be primarily an alerting service and could be used to send urgent messages, such as tsunami warnings, to many different locations. Because it is a broadcast service, the terminals do not incur airtime charges while waiting for an alert to arrive.

2.7.4 Pilot

Iridium’s highest-bandwidth service is Pilot, which was originally sold in the marine market and now also has a land variant. One Pilot terminal can connect up to three simultaneous voice calls and provides internet access at up to 134 kbits per second. The Land Station version has the same specifications as the marine version. Data is charged by the megabyte and can be bought in bundles for applications that require large quantities. Pilot works by steering multiple beams from the antenna to access several Iridium satellites at once, so having a clear line of sight in all directions around the antenna helps to ensure good performance. As a marine terminal, one key advantage it has over other services is that it contains no moving parts, and unlike a geostationary system, it has no mechanical tracking, making it cheaper and lighter than other services. However, it can only deliver a fraction of the data rate of a geostationary system. Pilot is powered with a voltage of 11-32 V DC (although an AC adaptor is supplied) and consumes approximately 30 W when connected.

Note: The previous version of Pilot was known as Iridium OpenPort. Now Iridium uses “Pilot” to refer to the terminal and “OpenPort” to refer to the data service. The terms are often used interchangeably.

2.8 Kepler (information updated April 2019)

Website:	https://www.kepler.space/
Type of orbit:	Low Earth Orbit (LEO)
Number of satellites in operation:	2
Coverage:	Global

Kepler Communications is a Canadian start-up company operating a constellation of small satellites in polar orbit. They were founded in 2015 and their first two satellites were launched in 2018. A third launch is planned for 2019. Their initial service is a store-and-forward service for moving large volumes of data - hundreds of megabytes per satellite pass. They currently promise data delivery within 12 hours. The service is bidirectional - data can be delivered to a remote site as well as collected from it. The service operates in Ku-band (12-14GHz) and uses currently VSAT-style equipment with motorised antennas that track the satellites. This gives Kepler a relatively high terminal cost (at least $25,000 USD) at present, but their airtime charges are low given the high volume of data they can handle - they claim to have the lowest price per gigabyte in the industry. Kepler offer both marine and land-based terminals, and claim their system is also compatible with existing Ku-band marine VSAT installations. A typical Kepler terminal offers 100Mbit/s downlink and 30Mbit/s uplink, though of course that data may not be delivered to its destination for several hours.

2.9 O3B (information updated April 2018)

Website:	https://www.ses.com/networks/maritime/maritime-powered-o3b
Type of orbit:	Medium Earth Orbit (MEO)
Number of satellites in operation:	12
Coverage:	equatorial coverage to around 45 degrees latitude north and south

O3B is a wholesale satellite operator that provides high-bandwidth, low-latency internet connectivity to telecom providers in less-developed countries. Its constellation is unusual in that it operates with MEO satellites, meaning that a tracking antenna is required at the terminal. The use of MEO satellites allows for lower latency and higher data rates than would be possible on an equivalent geostationary satellite.

O3B was originally an independent company but is now owned by SES of Luxembourg (best known for the Astra series of broadcast satellites). O3B also provides services to the marine market, particularly for cruise ships, where a large amount of bandwidth is needed. O3B states that it offers up to 1 Gbit per second to ships. O3B terminals typically comprise two or more large tracking dish antennas (typically 1.8 or 2.4 m in diameter); two antennas are used to ensure that there is continuous coverage as the satellites drop below the horizon.

2.10 Orbcomm (information updated April 2018)

Website:	http://www.orbcomm.com/
Type of orbit:	Low Earth Orbit (LEO)
Number of satellites in operation:	16 (OG2 constellation), 25 (OG1 constellation)
Coverage:	global excluding poles

Orbcomm operates its own satellite networks (known as OG1 and OG2) and sells terminals and airtime for Inmarsat’s IsatData Pro network. This entry concentrates on OG1 and OG2.

The Orbcomm OG1 constellation was launched in the mid-1990s and uses marine-band VHF radio to communicate with data terminals. It is strictly a message-based service and operates using the store-and-forward delivery method, sending the messages to a series of gateways. OG1 operates at an uplink speed of 2.4 kbits per second and a downlink speed of 4.8 kbits per second to the user’s terminal. Message sizes are not fixed but are typically a few tens of bytes.

The second-generation OG2 constellation became fully operational in 2016, and Orbcomm states that it allows larger message sizes and higher throughput. OG2 operates at an uplink speed of 4.8 kbits per second and a downlink speed of 7.2 kbits per second. Orbcomm publishes relatively little information about how this system works; interested parties are advised to contact the company directly to request the technical datasheets.

Orbcomm’s modems often combine satellite with cellular connectivity. This is particularly valuable if the modem is mounted on a platform that moves between populated and remote areas, as it allows cheaper cellular service to be used where it is available while retaining the satellite as a backup.

2.11 Thuraya (information updated April 2018)

Website:http://www.thuraya.com/
Type of orbit:	Geostationery
Number of satellites in operation:	2 (all services) + 1 offering M2M service only in North America
Coverage:	full services cover Europe, most of Africa (Angola and northwards), the Middle East, central and East Asia (but not Siberia), Australia. Very limited oceanic coverage, confined to areas of the east Atlantic close to Europe, the northern part of the Indian Ocean and parts of the western Pacific between Japan and Australia. M2M services are additionally available in central and North America, excluding Alaska and arctic Canada.

Thuraya is a Dubai-based satellite provider that provides telephony and data services. It offers a range of terminals, from handheld satellite phones to larger self-pointing units that can be mounted on land vehicles or ships.

Thuraya’s data services consist of:
(a) Circuit switched data (essentially a voice channel used for data), 9.6 kbits per second;
(b) GmPRS - packet switched data, 60 kbits per second downlink speed, 15 kbits per second uplink speed;
(c) “Streaming IP” at guaranteed speeds of 384 kbits per second;
(d) Conventional IP at peak data rates of up to 444 kbits per second downlink speed and 404 kbits per second uplink speed.

The CSD and GmPRS services are available on Thuraya’s voice handsets and XT-Hotspot (a portable Wi-Fi hotspot). The high-rate IP services need a dedicated terminal about the size of a laptop computer.

Thuraya also has an M2M service, currently only available on the dedicated FT2225 terminal. Thuraya does not publish the data rates offered by this service, although they are described as “low”, “medium” and “high” at different price points. The M2M service is the only Thuraya service that operates in North America because it is operated in partnership with Ligado and ViaSat.

Thuraya also offers a range of modem modules for integration into other equipment or commercial products. See http://thuraya.com/developer-zone

2.12 VSAT (information updated April 2018)

Most of the services described in this handbook are fully integrated: the user buys a terminal, installs it, buys an airtime contract and is ready to go. This is “retail” satcom; the user can buy a single terminal and does not have to worry about the rest of the system. However, there is also a “wholesale” satcom business, as used by telecom companies, broadcasters and other large companies with complex communications requirements.

In wholesale satcom, the user rents bandwidth on one or more geostationary satellites, typically agreeing to a long-term lease, and provides his or her own terminals. These could be owned by the user (typically on his or her own building, land vehicle or ship) or supplied under contract from a service provider. One very common arrangement is to use a service provider to act as the hub of the network (from a dedicated Earth station or teleport with many antennas serving different customers); the service provider can also provide routing to the Internet, the telephone network or private corporate networks. The high-end satcom industry views any terminal using an antenna 2 m in diameter or smaller as a “very small aperture terminal” (VSAT); these are “very small” by comparison with the 10 m or larger antennas used by telecom providers.

A VSAT ideally suits a situation in which the user has a continuous need to communicate with a remote location. It can be customized to suit the user’s needs but is necessarily complex to plan and install. There are dedicated service companies that will do this for a fee.

There is a type of VSAT that is more suitable for retail customers. This is known as a “Shared VSAT” and is typically sold by a service provider that leases the satellite bandwidth and provides a suitable terminal. These systems are typically used to provide internet access to rural areas and often use contention to share bandwidth between multiple users, meaning that the service slows down as more and more users log on.

 
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3: How to purchase and install a satcom system

This section provides some general principles which may be helpful when planning or specifying a satcom system. It is not intended to be exhaustive, but to provide helpful prompts.

3.1 Deciding on your priorities

With such a diverse range of satellite systems on the market, it is important to carefully consider priorities. It is likely that a compromise will need to be made regarding the data rate available, the size and power consumption of the terminal and the cost of the airtime. Important questions to consider include:

(a) Where in the world does the user need to operate?

(b) Will the terminals be static or will they move around?

(c) Does the satcom system need to work in the polar regions (specifically at latitudes above 70 degrees)?

(d) Will the satcom system be used on a ship, aircraft or other moving vehicle?

(e) How much data does the satcom system need to transmit?

(f) Are the data continuous or “bursty”?

(g) Is occasional data loss in transmission acceptable, or is it vital that every message get through reliably?

(h) Do the data need to be available in real time, or is some delay in receiving them acceptable?

(i) Is it necessary for the satcom system to allow bi-directional communication (sending commands to the remote installation as well as receiving data back from it)?

(j) How long will the system be deployed for?

(k) How often will the remote sites be visited?

(l) What are the environmental conditions at the remote sites? Some services are more robust at dealing with the effects of poor weather than others; heavy rain or snow can sometimes disrupt transmissions.

(m) How important are considerations relating to the operating cost? A simple messaging service sending a few bytes a day can cost around US$ 30 per month. A high-data-rate service sending several gigabytes per month may cost as much as US$ 5 000 per month.

(n) How important are considerations relating to the capital cost? Small terminals can cost a few hundred US dollars, whereas a large VSAT installation might cost millions.

(o) Does the budget allow for any value added services? Some providers can process a user’s data and put it into suitable formats that meet that user’s needs. Some can deliver data automatically to networks like WIS. Some provide management portals to manage data products or billing.

(p) Would a dual-mode terminal be beneficial? It is possible to buy terminals that combine satellite with cellular phone modems and primarily use the cheaper cellular service while maintaining the satellite as a backup. It is also possible to use two different satellite modems for different applications.

It is advisable to draw up specifications for the service needed and then compare the systems on the market against it. It may be necessary to compromise because the initial specification is too demanding, too expensive or technically not feasible.

3.2 Coverage

The first topic to check for in any candidate system is coverage. Network operators publish coverage maps, but it is helpful to check directly with them to verify that there are no coverage issues in any places where terminals are likely to be deployed.

The first key question is: is polar region coverage required at latitudes above 70 degrees? If so, only the following networks provide the necessary coverage:

(a) Argos;
(b) Gonets;
(c) Iridium.

There is a slight grey area: some geostationary networks may work at up to 75 degrees latitude with careful antenna siting, and with appropriate (expensive) equipment, they can be made to work at latitudes as high as 79.99 degrees (as is done at CFS Eureka in the Canadian Arctic with two very large antennas on mountaintops). However, beyond 80 degrees, the curvature of the Earth prevents the terminal from seeing the satellite.

If polar coverage is not required, it is important to look at the regions of the world where the satcom system will be operating. Networks that offer only regional coverage (for example, Globalstar and Thuraya) generally offer lower prices than those that offer global coverage.

If the satcom system will be operating at sea, check the oceanic coverage. Globalstar and Thuraya both have limited ocean coverage but may still be acceptable. For example, Thuraya provides full coverage of the Mediterranean Sea but does not cover the whole of the Atlantic Ocean.

3.3 Power supplies

If the remote site is completely isolated, the user will need to provide his or her own power supply in the form of solar panels, wind generators, diesel generators and/or batteries. In this situation, ensuring that the communications system has relatively low power consumption will eliminate the expense of transporting a large amount of equipment to the site. Note that most systems have a high peak power consumption when transmitting; if only one or two messages are sent per day, the average power consumption will be much lower than if the system is communicating continuously.

Message-based and low-bandwidth systems have relatively low power consumption and are thus more suited to fully autonomous deployments than high-bandwidth systems.

If satellite communication is being used because a high-reliability data-collection service or one that is resilient to failures of terrestrial infrastructure (such as a flood or tsunami warning system) is needed, consider the reliability of the power supply. Using an uninterruptible power supply unit (UPS) or having a backup power system that can run autonomously from solar power or batteries will help to ensure that messages get through even if the public electricity supply fails.

3.4 Look angles

For geostationary satellites, it is vitally important that the terminal have a clear line of sight to the satellite. On open terrain or hilltops, this is straightforward, but in narrow valleys or urban areas, the line of sight can be blocked by hills, mountains or large buildings. Given the latitude and longitude of the intended site, it is possible to calculate the “look angles” to the satellite, the compass bearing (azimuth angle) and elevation angle to which the dish must be aligned. A site visit or careful use of a topographic map can help determine if the intended satellite is going to be in view. One common remedy to issues with look angles is to raise the terminal antenna on a pole, mast or tower so that it can see over the obstruction. In extreme cases, it may be necessary to site the satellite terminal remotely, on a nearby hillside, for example, and run a cable or use a terrestrial radio link to communicate with it from the measurement location.

For satellites in low or medium Earth orbit, the issue with look angles and terrain is less critical but still important. The satellites will appear to move from horizon to horizon relative to the terminal. If part of that arc is blocked by terrain or buildings, the available communication time for that satellite pass will be reduced. A clear line of sight will help to ensure that communications are reliable and that messages are sent and received on the first available satellite pass. Deep valleys or canyons pose particular problems for polar-orbiting satellites, as only one or two satellites in the constellation will have orbits that align with the valley. Siting the terminal as high as possible mitigates the problem.

3.5 Airtime contracts

Many satellite networks started out in the business mobile telephony market (including Globalstar, Iridium and Thuraya), so it is common for the rate to be billed monthly, usually with a standing charge (“line rental”) and a usage charge based on minutes, bytes or messages used. Some rates include a monthly allowance for data. It is common for providers to ask for a minimum contract length (typically 12 months), which may not be convenient for systems that are deployed for a shorter period.

Many government institutions find the monthly billing inconvenient (as it generates many small invoices to be paid), so it may be preferable to ask the provider for a quote for a pre-paid option as an alternative. This is particularly attractive for remote instrumentation that reports regularly, as the user should know quite accurately how much data will be used in a given period. Pre-payment also reduces the providers’ billing costs, so they should offer users a better rate for this option. If a large number of satellite terminals are being run, it is best to have them all on a single contract with a single provider. This reduces the administrative overhead and may prove more cost-efficient. Many providers allow data allowances to be pooled from multiple terminals.

The Satcom Forum aims to work with the industry to ensure that rates are suitable for scientific users, so if users have particular issues with their rate structure or have comments or suggestions as to how their rate structure may be improved, they are requested to get in touch with the WMO Secretariat (wis-help@wmo.int), which will attempt to provide assistance.

3.6 Internet access

Certain satellite systems, such as Inmarsat’s BGAN, Iridium’s Pilot and Thuraya’s Streaming IP offer full internet access. The terminal can be connected to a PC, and internet services (such as the Web or email) can be accessed just as they would be over a landline or cellular connection. However, there are some significant issues that users should be aware of regarding internet access:

(a) Security: depending on the terminal and service provider, users may be connected directly to the internet without any firewall or other similar protection. Users are strongly advised to take security precautions and to use an appropriate firewall (hardware or software) to prevent malicious hackers from accessing remote sites. It is also wise to avoid sending data over the open internet, and it may be advisable to look into the use of a VPN4 or other similar encryption technique to link remote sites with data servers.

(b) Data usage: most modern operating systems (including Mac OS and Windows 10) by default assume that they have constant access to a free, high-bandwidth internet connection. The operating system and any applications running may check for and download software updates or synchronize large amounts of data with cloud servers (OneDrive, iCloud, Dropbox, and so forth), which will result in large amounts of traffic flowing over the satellite link. This will make the link appear slow, as the amount of usable bandwidth for the intended application will be restricted by the large flow of data to and from the cloud servers. If users are being charged per minute or per byte for their data connection, this will also run up a significant bill. In addition to configuring the operating system to treat the satcom connection as a metered connection, users should arrange for their firewall to block all outgoing requests for internet traffic except for their wanted data traffic. Using a non-standard Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) port number will help segregate their own traffic from unwanted internet traffic.

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4: Directory of industry contacts

This directory is not exhaustive and does not imply WMO endorsement of any of the companies concerned. Companies wishing to be listed in future versions should contact wis-help@wmo.int with their proposed entry.