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Trying to fool Beidou.

The Global Navigation Satellite System (GNSS) provides worldwide coverage and is used by soldiers, sailors and airmen. These navigation signals assist commanders controlling movement on the battlefield, mortar rounds and high-precision missiles searching for targets and combat search and rescue teams looking for the lost or wounded. This is all very interesting and certainly quite important. Unfortunately, those weak GPS signals can be susceptible to both jamming and spoofing.

Today all eyes are on the skies in anticipation of new developments to Europe's Galileo satellite navigation programme. The European Space Agency is the project's prime contractor and technical design authority, and is currently managing the programme's [euro] 3.4 billion budget. The European Commission (EC) is negotiating the setting up of industry teams for what it calls 'work packages' to design and build the Galileo GPS satellite constellation.

There are currently 30 satellites planned for the Galileo system, which, when fully operational, will include four in-orbit validation spacecraft. Astrium, a subsidiary of Eads, was the prime contractor and navigation payload lead for the Giove-B satellite, the second of two 'in-orbit demonstration' satellites for the Galileo constellation--this latest bird was launched in 2007 and became operational in July 2008.

Since that time the Giove-B has been broadcasting navigation test signals to earthbound ground receivers, allowing engineers and researchers to perform long-term signal quality measurements. The Giove-B is the first satellite to transmit the Multiplexed Binary Offset Coding modulation standard from space, thus paving the way for this technology's future rollout on the Galileo constellation (Giove-B is a test satellite).

The Giove-B carries three high-precision atomic clocks, including a passive hydrogen maser. This is the most accurate time reference ever orbited in space, with an accuracy of better than one nanosecond per day. The in-orbit behaviour of the maser has thus far proven to be outstanding, boosting confidence that this and other critical new technologies will deliver the superior performance expected of the Galileo system.

The Galileo constellation was not built to compete with the US-designed Global Positioning System (GPS) constellation or Russia's Glonass, but rather as a complement to those, and other, navigation systems, Global navigation systems, although having become an integral part of our everyday lives, and this includes in every sector of the defence industry, are not perfect. Not yet anyway.

The Carpi Diem

In June of this year--at the height of the tourism season--a Swedish couple were driving to their holiday destination on the isle of Capri off the coast of Italy. They quickly typed in the island's name in their car's GPS system and off they drove.

Through no fault of the system, and having not been jammed or spoofed, the couple found themselves in the northern Italian town of Carpi. A simple typographical error took them 650 km off their mark. A forgivable error, without dire consequences, other than a probable 650-kilometre-long heated discussion between driver and navigator.

An ambulance in Britain was transferring a patient to another hospital located 19 km across London, but ended 320 km away in Manchester after blindly following the course set by the GPS. These two events bring a chuckle, if one does not consider--as a result of a spoofed GPS signal--that this could easily have been a cruise missile or GPS-guided artillery round heading for friendly forces.

Spoofing a GPS (or any radio signal) is 'simply' a matter of capturing and analysing the signal, then retransmitting a false signal on the same frequency, but with a higher energy output--thereby overpowering the original signal. The GPS receiver will then be fooled into thinking the new signal is the original and happily send the user towards Carpi (an erroneous waypoint) rather than to Capri (the original destination).

This may sound somewhat elementary, but only the explanation is simplified. Military navigation signals are encrypted, and contain a host of failsafe measures to ensure the original signal remains locked onto the receiver.

In the early days of the GPS satellite navigation programme the radio signal for the civilian population was intentionally degraded to prevent users from obtaining a signal as accurate as that received by military navigation devices. This was called Selective Availability (SA). This practice was officially terminated 1 May 2000 and is no longer a feature of new GPS satellites.

To counter any Selective Availability or spoofing, the Saasm (Selective Availability Anti-Spoofing Module) was included in US military receivers to allow decryption of the higher-precision GPS signal. Although Selective Availability is no longer a concern, anti-spoofing safe-guards are still applied to the military signal to prevent spoofing. By encrypting the P-code (Precision) with a W-code sequence (or algorithm) a 'Y-code' is created, this is the signal (called the P(Y)-code) that is acquired and tracked by authorised military Precise Positioning Service receivers.

The M-Code

Today the M-code (Military-code) is also being used by US forces. This signal was designed to further improve the anti-jamming/anti-spoofing integrity of the military GPS signal. Very little has been published about the M-code--for obvious reasons--but what is known is that it is transmitted on the L1 (1575.42 Mhz) and L2 (1227.60 MHz) frequencies currently in use for the P(Y)-code.

The M-code was designed to be broad-case from a high-gain directional antenna in what is called a spot beam. This beam can be aimed at a specific region of the Earth to increase signal strength (and therefore reception) by a factor of 100. This spot beam capability is expected to be deployed with the GPS III satellites scheduled for first-launch by 2014.

The GPS Modernization programme objectives are to protect military use of GPS by the US forces and their allies and to prevent hostile use of the 'normal' GPS signal during a conflict once it is being jammed. In 1998 a GPS Modernization Signal Design Team was chosen by the GPS Joint Program Office (JPO) to design a signal that [much less than] provides functions, performance and flexibility for an enhanced military radio-navigation service ... [much greater than]

The team included scientists and professionals from Mitre Corporation, The Aerospace Corporation, Arinc and the US Air Force GPS JPO.

One parameter of the new M-code was that it needed better jamming resistance than the Y-code signal, this through a higher-power transmission without creating interference to the C/A or Y-code receivers. The 'M' signal was also required to be compatible with 'prevention jamming'--i.e. guarding against enemy GPS usage, and to be an autonomous acquisition, so a receiver can acquire the M-code signal without access to C/A or Y-code signals.

The M's signal security is based on a next-generation cryptographic algorithm that features a new keying architecture.

The US Department of Defense is upgrading its GPS infrastructure through the GPS III programme, which is being spearheaded by Lockheed Martin. The programme entered its critical design review (CDR) phase in June 2009. The GPS III will undergo 70 individual reviews before the final 'space vehicle' CDR in the fall of 2010.

The GPS III team partners are ITT and General Dynamics. Under the current $ 3 billion contract, the Lockheed Martin team will design and develop two space vehicles with options for up to ten additional production vehicles.

In July of this year Boeing and Iridium announced two major milestones to the High Integrity Global Positioning System programme for the US Naval Research Laboratory. The team completed an on-orbit software modification to computers on Iridium satellites to enable second-generation GPS-aiding signals to be broadcast through the entire Iridium constellation. The Enhanced Narrow-band modification will provide warfighters with rapid, more accurate GPS fixes than are available through the standard GPS constellation.

The two companies reported that the second milestone covered the successful demonstration of GPS signal acquisition in a moving vehicle through a 'substantial' jamming environment.

The High Integrity GPS (iGPS) programme uses signals from both the Iridium low-earth orbit satellite constellation and the US Air Force-operated mid-earth orbit GPS navigational satellites. The iGPS combined constellations have the potential to provide positioning data to within centimetres. Boeing Phantom Works was queried for information on the jamming and spoofing protection, and other details of the iGPS programme but, due to the sensitivity of the programme and the significance of the system to US warfighters, understandably, very few details were released.

On the Ground

Rockwell Collins has been providing its Defense Advanced Global Positioning System Receiver (Dagr) to US forces since the programme's inception in 2003. The Dagr provides precise timing to synchronise tactical radios, missile platforms and situational awareness navigation systems. The new Dagr system incorporates improvements to its anti-jam capability and features enhanced operational capacity in GPS-denied environments.

Novatel is one company that has been very active in the development of the Galileo system. In September 2008 the company released the new GNSS-750 quadruple constellation choke ring antenna, which provides the ability to receive signals from all existing and emerging satellite systems. The GNSS-750 can track satellites that are below the viewer's horizon and will be able to acquire and track signals from all four constellations--Galileo, Compass, GPS and Glonass.

The GNSS-750 antenna operates on these frequencies:

* GPS L1/L2/L2C/L5

* Galileo Ll/E5a/E5b/E6/Altboc

* Glonass L1/L2/L3

* Compass B1/B2/B3 and

* L-band Sbas/Omnistar/CDGPS.

By mixing signals from five separate navigation systems one is guaranteed improved reception opportunities and increased security from either jamming or spoofing.

Distance = Vulnerability?

On any day, a web search 'GPS jammers' will provide years of reading and research. One can find plans for hobby-built home-made systems that can pump out as much as eight Watts to create a GPS denial-of-service umbrella covering hundreds of miles, not to mention Yahoo groups tackling GPS hacking and forums outlining problems encountered when building a GPS jamming system.

One online retailer boasts its GPS/GSM jammer [much less than] ... will jam all GPS and GSM signals up to a distance of 50 metres. When activated, it immediately blocks all types of tracking and navigational devices [much greater than]. Scary words--but can this be true? What effect could this have in the battlespace?

In an indirect response, Thales Avionics in France produces the Topshield antijam solution for helicopters. The Topshield guards against multiple low-cost jammers and high-grade jamming by ground stations. The Topshield unit was built to respond to the future M-code and spot beam modernisation of GPS and is suitable for attack, transport and maritime rotorcraft.

The Topshield system provides antijam immunity above 90dB using null steering to cancel multiple jammers and beam forming for concentrated satellite connection through Space Time Adaptive Processing. The unit simultaneously addresses the L1 and L2 bands.

On 10 August 2009 Lockheed Martin reported the last in a series of eight modernised GPS Block IIR (GPS IIR-M) satellites was delivered to the US Air Force for launch on 17 August from Cape Canaveral in Florida.

The birds built under this satellite moderinsation programme were designed for the US Air Force's GPS Wing, Space and Missile Systems Center and will deliver increased GPS signal power and supply two new highly-accurate military signals that include enhanced encryption and anti-jamming capabilities.

Quality Assurance

Despite spread-spectrum modulation, GPS signals are susceptible to interference due to their extreme low transmitting power (around 160 dBW). Many anti-jam GPS receiver systems try to mitigate interference by phase shifting, spectral filtering or adaptive beam forming. To test the effectiveness of these techniques Spirent provides a variety of equipment, including the GSS8000 GPS/GNSS simulator, which combines signals from all satellites in view into one single RF output. This system can test spectral filtering and non-spatial anti-jam techniques.

Spirent offers dual-frequency signal simulators to transmit into anechoic chambers for testing Controlled Radiation Pattern Antennas, and the company's GSS7765 Interference Simulation System allows testing of multiple, simultaneous interference sources across the AM, FM and CW bands as well as limited white noise or other waveforms.

The Global Navigation Satellite System is a reality today and the civil and military programmes are being upgraded and modernised for tomorrow. Jamming and spoofing efforts will continue, but with so little information (secrets) on those two subjects being shared, anyone interested in distuption is forced to simply build one's own jam/spoof system or buy something from the Internet to put those real-world systems to the 'test'. The only caveat to this concept is, on a battlefield, any jammer or spoofing transmission paints an easy target on many fire control systems.

How Many Eyes?

The US GPS constellation currently has a 24-bird-strong flock of satellites providing worldwide coverage. The Obama Administration has earmarked $ one billion for GPS and related Positioning, Navigation and Timing (PNT) programmes. Under this wing is the GPS III programme (and the next-generation operational control segment), which is currently entering critical design review (as of June 2009) by Lockheed Martin Space Systems, ITT and General Dynamics. The US Air Force Space Command's 2nd Space Operations Squadron based at Schriever AFB in Colorado manages and operates the GPS constellation for both civil and military users.

Glonass, the Russian counterpart, currently has 20 operational satellites, with 24 'modernised' (Glonass-M) birds slated to be aloft by end-2010 and a total of 30 scheduled to be online by 2011. Latest successful satellite launch (the 20th) was on Christmas Day 2008. Glonass signals provide accuracy of around 1.8 metres. Although once a somewhat ailing programme (India almost 'bought' the system), Russia has so far spent more than $ three billion for the system's 2002 through 2011 modernisation effort. In February 2009, Fugro, a Dutch company, began broadcasting its G2 (precise point positioning) service, which provides decimetre-level accuracy using Glonass and GPS signals.

Galileo, Europe's navigation system, is still in the contract-awarding phase for the fully-operational capability system development. The second in-orbit demonstration satellite went online in July 2008 (see above). Planned are 30 satellites.

Compass is China's answer, and the second modernised Compass satellite was launched in April 2009 just two years after the programme's official inception. The Compass (or Beidou-2) system is slated to have ten birds in the sky by end 2010 for regional service, with a worldwide capability of 35 satellites in place by 2015 or 2020. One 'hiccup' has arisen in that the Compass signals currently 'overlay' some portions of Galileo satellite signals (notably Galileo E1A, El and E6 birds). This provides complications in that European forces may not be able to jam GNSS signals of adversaries without jamming friendly forces' signals.

IRNSS (Indian Regional Navigational Satellite System) is under development by the Indian Space Research Organisation. The programme is in reaction to the belief that GNSS signals may not be available in hostile situations. Seven satellites were approved in 2006 with first launch slated for 2009. The navigation signals would be transmitted in the S-band frequency of two to four GHz and broadcast through a phased-array antenna.

Author's note: Beidou is the Chinese name for the Big Dipper constellation, or Northern Dipper, as given by Chinese astronomers to the seven brightest stars of the Ursa Major constellation.

Overview of GPS Performance

The US Air Force GPS Operations Center at Schriever AFB in Colorado is manned continuously. The command produces both prediction models and post-assessment models of GPS accuracy using software called the Giant (GPS Interference And Navigation Tool). This chart only represents the signal in space errors (signal interuption coverage), and does not reflect a receiver's physical obscurants (building, foliage, etc). GPS signals are also often affected by ionospheric disturbances and solar activity.
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Title Annotation:Navigation
Author:Keggler, Johnny
Publication:Armada International
Date:Oct 1, 2009
Words:2571
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