Home Articles Global navigation satellite system: GNSS Interference – The debate rages on

Global navigation satellite system: GNSS Interference – The debate rages on

Stephanie Wan
Youth for GNSS (YGNSS) Project Lead
Space Generation Advisory Council
[email protected]

For the younger generation, 'GPS' has become a ubiquitous term synonymous to how one can whip out their smart phone and simply 'Google' for an answer. However, the term Global Navigation Satellite Systems (GNSS) is a topic that the general public knows very little about and would require a thorough search.



If you ask the users about Russia's GLONASS, the planned European Galileo or China's COMPASS GNSS systems, some may recognise one or two at the most, depending on their nationality and region. In addition to global systems, there are also the regional Japanese QZSS, Indian IRNSS and additional satellite-based augmentation systems that exemplify the intricacies of GNSS. This often results in questions like why do we have multiple redundant systems in place. In a commercialised world with multiple options for one product, I want one choice: a GNSS receiver that is interoperable and compatible with all systems around the world.

Unless directly associated with GNSS, a majority of the public takes GPS technology embedded in smart phones, time stamps in financial transactions and navigation devices, for granted. Most of us do not realise how GNSS infrastructure, technology and policies have become infused into our international and domestic economy and society. While protecting the GNSS spectrum from interference has always been an issue, the wireless broadband company LightSquared has become a heated topic in Washington, D.C., where its interest in placing high powered satellite transmissions adjacent to a low power GPS signal will have global consequences.

GNSS Policies
As the sole fully operational GNSS system since the 90’s, the United States has led in shaping GNSS policies.

Free for Users
GPS was originally developed in the 1970's as a positioning, navigation and timing system primarily for military support purposes; but the shooting of the Korean Air flight 007 by USSR in 1983 (where the civilian plane accidentally flew over Soviet air space) led President Ronald Reagan to realise that precise navigation for civilian use was needed to prevent similar mishaps in the future. He issued a statement guaranteeing that the GPS signals would be available at no charge to the world when the system became operational. This decision led to opening up of commercial markets where 95% of the GPS units sold today are meant for civilian use, resulting in tens of billions of dollars worth of direct economic benefits. President Reagan's successors have continued the national policy of keeping civilian GPS free of direct user fees. As a result, an earlier European GNSS business concept for a private public partnership (PPP) to charge users a fee eventually dissipated after realising that it could not compete with a free GPS. The everyday user would find little difference whether their navigation device was created solely for 'civilians' as opposed to both civilian and military use as long as it provided precise measurements.

Selective Availability (S/A)
As GPS became fully operational in 1995, it proved to be an invaluable tool for military, civilian and commercial use and it wasn't long before other space faring nations recognised the social benefits of creating their own independent systems. Nations dependent on the US Air Force-operated system highlighted an international issue – that GPS was nonetheless a US military asset and Selective Availability (S/A) or the option to intentionally degrade public GPS signals for national security reasons, could be turned on at any time. As a response to civil and international user concerns, the United States discontinued the use of S/A in May 2000 and in a September 2007 statement further committed to remove S/A from future GPS satellites. Nonetheless, the European Union and China found national value in continuing investments to build an independent system of their own while Russia continued to modernise its GLONASS system.This has resulted in a state of 'co-operation' between the GNSS providers to prevent conflicting operational uses.

International Cooperation
Rather than creating a competing GNSS sector, the 2004 US PNT policy language has changed its earlier stance of refraining from foreign PNT service dependency to the 2010 US space policy that encourages cooperation with foreign GNSS services "to augment and strengthen the resiliency of GPS". This 2010 language further encourages engagement "with foreign GNSS providers to encourage compatibility and interoperability and promote transparency in civil service provision". To facilitate discussions, the ICG was established in 2005 as an informal international body for GNSS providers, member states and interested organisations to gather for the purpose of promoting cooperation and discussing matters of mutual interest regarding GNSS systems. The five meetings that have taken place so far have resulted in providers adopting the policies mutually beneficial for all citizens of the world open service access and also in creating a desire for interoperable and compatible GNSS systems.





Interference Issues
With global dependence on GPS and other GNSS signals, disruptions to the radio navigation signal technology could have major consequences that can come in the form of statestate, state-domestic and stateindustry conflicts. State-to-state disruption can be resolved through bilateral or multilateral negotiations within the International Telecommunications Union (ITU). Spectrum interference on the space segment would be negotiated to ensure the protection of national frequencies. Moreover, multilateral and bilateral agreements are reinforced through national laws and regulations.

Domestic interference issues have emerged in the form of intentional jamming or signal spoofing with each individual instance causing a ripple effect that is noticed on a local scale. For instance, a trucker can illegally buy a USD 30 jamming device online that prevents employers from tracking his location or a fisherman can spoof his receiver into giving false readings to enable him to fish in restricted waters and feign ignorance. The trucker's use of a jammer can take out GPS for several kilometres resulting in traffic problems for drivers and airports in the area. Increasing use of jammers has blocked cell phone coverage in several cities. Such vulnerabilities are difficult to trace and reinforce and can become exacerbated if there are no means for mitigation. While these issues are currently seen in GPS receivers, it is highly likely that other GNSS receivers in the market will also be affected once they are fully operational.

The LightSquared Debate
Interference issues with a satellite company's business model are often solved at a technical level where the government closely examines the technical data prior to granting the necessary approvals. In the United States, satellite orbital location and frequency requests for private companies are granted through the Federal Communications Commission (FCC). The US wireless broadband company, LightSquared, recently emerged on the GPS community's technical and policy radars with its plans to place terrestrial towers transmitting high powered adjacent signals to GPS, which resulted in interference with GPS signals. Having realised the dire consequences of this system for the GPS user community, US government agencies and a broad GPS industry coalition has come together to oppose these plans.The Federal Communications Commission issued LightSquared a Conditional Waiver of the Ancillary Terrestrial Component (ATC) Integrated Service Rule that would allow it to deploy a nationwide 4G-LTE terrestrial network for broadband services. This waiver was conditioned on the completion of technical studies to examine potential interference with GPS.

The industry-led Technical Working Group studies conducted thereafter showed that LightSquared's operating plans would interfere with virtually all types of GPS receivers. High precision GPS receivers used in commercial, industrial, professional and scientific applications are particularly vulnerable. A large number of GPS dependent commercial firms and sectors created a coalition to 'Save Our GPS' and called for the denial of an operating license to LightSquared. The company has invested several billion dollars into its business plan and continues to take the position that GPS interference is a minor, easily rectifiable issue. However, the GPS community, facing disruption of GPS measurements in the United States, does not share this view. There are no feasible or affordable options to upgrade existing or even future GPS receivers to enable co-existence with LightSquared's terrestrial network, operating at power levels that are billions of times greater than the adjacent band of GPS signals.

While this is currently an ongoing issue under US jurisdiction, the European Commission has raised concerns over the potential harmful interferences LightSquared's satellite placement would have on Galileo navigational equipment. If Light- Squared's plan is approved, other GNSS receivers will face similar interference concerns. FCC's action to grant LightSquared a waiver, which would normally have been rejected based on technical findings, has been elevated to a political level with keen international and congressional interest in its outcome.

The use of GPS has become inherent in our everyday lives with some even going to the extent of calling it an 'invisible utility'. The promise of interoperability and compatibility of all GNSS systems will only strengthen our international dependence. With the growing demand for broadband and a continued reliance on GNSS, the Light- Squared issue serves as an example for other GNSS providers as they work with their satellite companies to ensure that necessary spectrums are protected. From agricultural management for farmers to disaster management and of course, everyday location-based service applications; it is difficult to imagine a day without GPS/GNSS.