GDR 99 - Communications Systems

Satellite Revolution


Section Articles
• Nato & European Digitisation • The Tactical Infosphere • Satellite Revolution • C21 Battle Innovation • Systems Expert

As an increasing number of satellite systems become available, high capability military systems are being supplemented by commercial satellites for administrative and logistical support. Racal's Andy Lovett reports.

Satellite data links are essential for modern military operations. In the UK critical beyond line of sight communications are currently provided by the SKYNET 4 satellites at principally SHF (-8GHz) with additional limited UHF frequencies. These are designed to be secure for both data and voice and are resilient under jamming conditions. However, they are expensive and consequently there can be only limited numbers of terminals available for use.

Support links are required for efficient administrative and logistical communications. These systems may or may not provide secure voice and data services. During peacekeeping operations, when forces are deployed to remote regions at very short notice, there is an increasing need to use terrestrial, cellular or satellite radio services to make international calls for support. "By the end of the next decade, the Pentagon estimates nearly 70 per cent of defence communications could be routed through commercial satellites." (1)

Advantages of data transfer via satellite


Globalstar is an international system for global personal communications, based on a constellation of 48 satellites in low earth orbit

The nature of satellite communications means that they have to be pre-deployed and are therefore available for global or regional operations with only a minimum of ground equipment needing to be deployed to establish a seamless network between the operation in theatre and operational control. Land-based systems need to have links established that are much more difficult to complete at short notice in what could possibly be hostile territory.

Other inherent advantages are the size of the communications footprint compared to a ground-based network. The satellite system gives global or regional access together with increased redundancy offered by the many alternative network paths. The following two examples serve to illustrate military use. The US Army used Panamsat communications links in support of drug interdiction operations in Bolivia and Peru. For mobile communications the military achieved good results from off-the-shelf Inmarsat portable satellite terminals. The US DoD Defense Information Systems Agency (DISA) has purchased a gateway and airtime on the Iridium network. This will be used as an unsecured network for non-critical calls from remote peacekeeping stations or to allow sailors to call home from ships at sea.

However, although commercial satellites hold great promise they can fall short in several technical, operational and policy requirements, that include assured access, control of assets, interoperability and the defence of communications assets.

Adapting a commercial system to meet the military requirement will always increase its cost. When the US Congress directed the DISA to use commercial systems to provide the high-volume data information service needed for command and control in Bosnia the cost of a $500 commercial satellite receiver grew to more than $150,000. This was because cryptographic devices were incorporated and the equipment had to be ruggedised for use in mountainous terrain.

Present systems (2)


The Globalstar user is in direct contact with the satellite via a hand-held system, that provides speech and low data rate up to 10s kb/s

First generation 1990s: This was the first global commercial system developed from the Inmarsat-M system and became the Aero-H on wide-bodied airliners and business jets and was extended into narrow-bodied aircraft by the Aero-I system. Speech and low data rate up to 10s kb/s are provided.

Second generation 1998-2000: These are hand-held systems that provide similar services as the lnmarsat system. The user is in direct contact with the satellite via a hand-held set. Iridium is the first available system; Globalstar and ICO, with similar functionality, will be available by 2000.

Globalstar: The first eight of an eventual 48 LEO satellite systems were launched in early 1998 and the first voice call was placed in June. Call hand-offs from beam to beam and satellite to satellite have been proven and integrated system tests will extend into 1999.

ICO: The ICO system will be available in mid-2000 and consists of 10 satellites in two planes with two in-orbit spares in medium earth orbit of 10,000km. The user segment links directly with the satellites that feed into the ICONET, a network of 12 interconnected access nodes on the public phone networks. ICO will be integrated with national cellular systems such as GSM. The higher MEO orbit means at least two satellites are in view at all times, minimising the number of blocked calls; the system needs fewer earth stations; and the reduced number of regional gateways means the military can expect greater security.

Future systems

Third generation 2002-2006: There are various names for the Universal Mobile Telecommunications System (UMTS): the ITU calls it IMT 2000 and satellites are expected to be an integrated part of a cellular system. Worldwide adjacent terrestrial and satellite frequency bands have been allocated, making a single-mode transmitter/receiver possible for both types of transmission with attendant cost reduction. Although the terrestrial activity is progressing, the satellite part has yet to be defined but the concept is to embrace multimedia services at variable bit rates of at least 144kb/s. Candidates for such a system could be developments of current systems such as Horizons from Inmarsat and INX from Iridium. A total of seven satellite proposals have been made. Other candidate systems will be the second-generation GMPCS or SPCN.

Fourth generation 2004-2010: Mobile Broadband Systems (MBS), Ka bands multimedia. The major change in frequency will be to provide considerably greater bandwidth although rain attenuation becomes significant at Ka band and the high cost of low-power Ka band amplifiers is an unresolved issue. Fade countermeasure techniques employing digital signal processing need to be developed to enable closure of link budgets that will require novelty in system design and technology for services that may require bit error rates as low as 10 to the power of 10. At Ka band the required link budget means that the compromises needed to resolve proximity of the power amplifier to the antenna and the antenna beam width and tracking requirements are all technically more difficult to achieve, particularly on a highly mobile platform such as an aircraft.

The capabilities of mobile Ka have been investigated by several parties notably the NASA Advanced Communication Technology Satellite (ACTS). The eighth UHF Follow-on (UFO-8) was positioned over the Pacific, followed by the completion of in-orbit testing of the 20/30GHz military global broadcasting system (GBS) package. One key event was the joining of forces by Teledesic (Boeing / Gates / MacCall) and Celestri (Motorola).

(1) Defence Procurement analysis, autumn 1998. (2) Definitions from the University of Surrey Centre for Communications Research

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Such a service to consumers looks to be delayed, earth stations at an acceptable cost to support the private user seem as far away as ever. Instead corporate intranets and enterprise networks seem to be a more likely scenario. Another area that may be at or just beyond the state-of-the-art is an on-board digital processor required to switch traffic efficiently among narrow Ka band spot beams. The sheer number of bits per second to be processed requires power that pushes satellite bus requirements to or beyond the limit of current commercial buses. The key may be the use of 0.25mm CMOS technology.

In spite of significant problems, in the commercial world very large companies are planning Ka systems. These include Teledesic, Skybridge (Loral and Alcatel), Astrolink (Lockheed Martin) and Spaceway (Hughes).

The addition of third- and fourth-generation systems will provide users with an extensive capability and the potential to create a global command and control system with extensive data fusion capability. Some commercial systems will have additional features to provide a greater measure of security while other military systems may well use techniques first developed commercially.