As with all types of wireless transmissions, satellite signals are susceptible to interference. Although satellite communications are highly reliable, the satellite industry is continually looking for ways to increase their robustness. Under the ARTES programme, ESA has been supporting various approaches mitigate interference, including an industry-wide initiative to establish a carrier ID scheme for uplink signals.
Satellite communication signals, like all wireless transmissions, are susceptible to interference. This is accounted for during the design phase and not normally is a problem. For example, telecom satellites positioned in geostationary orbit are carefully separated from each other by fixed distances to prevent interference.
“Modern satellite communication systems are extremely robust,” says John Shirlaw, section head at the Telecommunications directorate at ESA. “Significant interference is rare. But when it does happen, it can be a real challenge for the operator identify the source.” In most cases, interference is caused unintentionally, usually by improperly configured ground equipment. he points out.
Intentional interference is extremely infrequent, but when it does happen it can quickly become headline news. This was the case in the spring of 2014, when Arabsat and Eutelsat reported that broadcast signals from several of their satellites were being jammed. To identify the source, Arabsat and Eutelsat used geo-location techniques to pinpoint the source at a location in northern Ethiopia. Intentional jamming is in contravention of international law, and when it is detected cases are reported to the International Telecommunication Union (ITU), the global broadcasting authority.
Identifying the cause of interference, be it unintentional or otherwise, can be a tough challenge for satellite operators. To solve the problem, an operator needs to geo-locate the source, which requires having access to two satellites whose beams overlap. With various complex calculations, an operator may be able to come up with an ellipse of various cross-points, which should indicate where the source may be.
Military satellites use an array of highly sophisticated techniques to prevent interference, but these are not cost-effective for the highly-competitive telecoms segment. For this reason, ESA is working with industry to develop advanced, low-cost techniques for mitigating interference, both unintentional and otherwise.
Under the ARTES Programme, ESA has been supporting a number activities related to interference avoidance. In one product development project
, under ARTES 3-4, ESA supported the implementation of carrier ID in the next-generation M6100 Broadcast Satellite Modulator developed by Newtec (BE), which was introduced in 2013.
In another ARTES 3-4 project, the Agency is supporting the development of a single-satellite ground-based geo-location system which will be able to localise the source of a signal jammer using just one satellite instead of two.
In a third project, under ARTES 11, EADS CASA Espacio (ES) (part of Airbus Defence and Space) developed an electronically steerable antenna which can be controlled from the ground, making it possible to circumvent intentional or unintentional interference by blocking out signals from specific geographical areas.
In a fourth project
, under ARTES 1, researchers from Thales Alenia Italy, Telespazio, Eutelsat, University of Rome are identifying market opportunities for advanced anti-interference techniques, proposing specific technical solutions, and evaluating the costs involved. These activities address interference on various levels.
With the support of ESA, Newtec implemented carrier ID in its M6100 broadcast modulator.
The Satellite Interference Reduction Group
has been actively promoting carrier ID for telecoms satellites. This is a unique identification code embedded in an uplink transmission which enables satellite operators to identify from where a given signal originates. “Carrier ID is not a magic solution for RFI. It won't solve the problem of intentional satellite jamming,” observes Martin Coleman, director of the association. “But it will make it easier to determine the source of unintentional interference.”
The carrier ID specification was completed in July 2013, and now operators such as Eutelsat
, as well as hardware manufacturers
, have been embracing the new standard, and it is on target to be universally deployed by January 2015.
“When hundreds of millions of viewers around the globe turn to satellite TV broadcasts of such events as the 2014 World Cup, the last thing any operator wants is interference, whatever the cause,” observes Michele Le Saux, head of the Commercial Ground Segment Section at ESA. “That could mean a lot of unhappy customers.”
“Although infrequent, interference can affect all satellite operators,“ she continues, “so an industry-wide approach makes a lot of sense. By working together, we should be able to lower the costs of implementing robust anti-interference solutions significantly.”