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.