Wednesday, 17 December 2008

Satellite based Mobile Internet of the future

Background: The current US military satellite communications network represents decades-old technology. To meet the heightened demands of national security in the coming years, newer and more powerful systems are being developed.

Advances in information technology are fundamentally changing the way military conflicts are resolved. The ability to transmit detailed information quickly and reliably to and from all parts of the globe will help streamline military command and control and ensure information superiority, enabling faster deployment of highly mobile forces capable of adapting quickly to changing conditions in the field. Satellite communications play a pivotal role in providing the interoperable, robust, "network-centric" communications needed for future operations.

Military satellite communications (or milsatcom) systems are typically categorized as wideband, protected, or narrowband. Wideband systems emphasize high capacity. Protected systems stress antijam features, covertness, and nuclear survivability. Narrowband systems emphasize support to users who need voice or low-data-rate communications and who also may be mobile or otherwise disadvantaged (because of limited terminal capability, antenna size, environment, etc.).

For wideband communication needs, the Wideband Gapfiller Satellite program and the Advanced Wideband System will augment and eventually replace the Defense Satellite Communications System (DSCS). These satellites will transmit several gigabits of data per second—up to ten times the data flow of the satellites being replaced. Protected communications will be addressed by a global extremely high frequency (EHF) system, composed of the Advanced Extremely High Frequency System and Advanced Polar System. These systems are expected to provide about ten times the capacity of current protected satellites (the Milstar satellites). Narrowband needs are supported by the UFO (Ultrahigh-frequency Follow-On) constellation, which will be replaced by a component of the Advanced Narrowband System

Lockheed Martin Space Systems, Hughes Space and Communications and TRW have formed a National Team to build the Department of Defense's (DOD) next generation of highly secure communication satellites known as the Advanced Extremely High Frequency (AEHF) system.

The Advanced EHF programme provides the follow-on capability to the Milstar satellite programme. It provides the basis for the next generation military communications satellite system, for survivable, jam-resistant, worldwide, secure, communications for the strategic and tactical warfighter. The system replenishes the Milstar constellation in the EHF band.

Each of these Advanced EHF satellites employs more than 50 communications channels via multiple, simultaneous downlinks. Launch of the first AEHF satellite is planned for April 2008 with the second AEHF satellite scheduled for launch in April 2009.

The fully operational Advanced EHF constellation will consist of four crosslinked satellites, providing coverage of the Earth from 65° north latitude to 65° south. These satellites will provide more data throughput capability and coverage flexibility to regional and global military operations than ever before. The fifth satellite built could be used as a spare or launched to provide additional capability to the envisioned constellation.

Current Status: After being plagued with project overruns and a scaling back of the final system, the US military's next generation satellite communications network is another step closer to reality, with completion of the payload module for the third and final Advanced Extremely High Frequency (EHF) satellite.

Although the EHF band is a relatively lightly used part of the electromagnetic spectrum (30-300 GHz), it is for good reason. Atmospheric attenuation is the biggest problem faced in this band, especially around 60 GHz, however the frequencies are viable for short distance terrestrial based communication links, such as microwave Internet and telecommunication links (which already operate in this band). Millimetre wave radar, probably best known as the radar that can see through your clothes but not your skin, also operates in this band.

Designed to avoid problematic frequencies that are more susceptible to attenuation, but accepting increased overall atmospheric attenuation, are an increasing number of military and civil satellite systems that are using this band for uplink and downlink, as well as inter-satellite communication. Inter-satellite communication is really where EHF equipment shines (no atmosphere, small antennas, high data rates).

Civilian systems are currently around the Ku band (Intelsat), providing data rates of up to 2-4 Mbps (14 GHz uplink, 12 GHz downlink) however these rates have still to trickle into everyday user's hands for remote and mobile Internet access. It is more common that an aggregator will access this link/rate and use that to then portion out local Internet access. Systems such as this are in use for remote Australian territories like Cocos and Christmas Islands, and formed the backbone of Boeing's stillborn Connexion in-flight Internet access. High ongoing access costs (basically a share of the overall cost of the satellite) and limited access slots help keep the technology away from everyday use at this time. Militaries and governments around the globe also lease access on these circuits when they need the added capability, with Intelsat and Inmarsat systems being used in the first Gulf War.

Advanced EHF is designed to provide 24 hour coverage from 65 North, to 65 South across the K and Ka sub bands, and when combined with the prototyped Extended Data Rate (XDR) terminals and systems, will offer up to 8.2 Mbps data rates for around 4,000 terminals in concurrent use per satellite footprint (whether that scales to 12,000 systems in concurrent use globally isn't clear from source material).

Within the tri-satellite constellation, inter-satellite EHF links will allow terminals on opposite sides of the globe to communicate in near real-time without the use of a terrestrial link. Combined with smaller, directional antennas and the various options for anti-jamming technology, it represents a significant military capability for the US.

Already plans are being drawn up for the Transformational Satellite Communications System (T-Sat) which will replace Advanced EHF starting sometime in 2013, however it is already facing funding troubles. This could be problematic, with Advanced EHF still struggling to reach capability and the final launch not scheduled until April 2010. Dropping the fourth satellite of the Advanced EHF constellation has been planned to give the USAF time to implement T-Sat more rapidly.

If GPS and remote imaging (think Google Earth) have proven anything, it is that technology initially developed for military purposes, and extremely expensive for initial civil use, will eventually reach the point where it forms part of our daily lives without us ever being conscious of the massive investment to get to that point.

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