09 Sep 2015
Mitigating Satellite Interference with Carrier ID
Geoff Smith, Microwave Division, Luso Electronics looks at the role of the system integrator in mitigating satellite interference using Carrier ID.
RF interference from unwanted signal sources on the ground has long been a problem for satellite operators, and without a means of identifying the source of the interference they used to be powerless to prevent it. RFI severely affects Quality of Service for satellite operators and users, especially in temporary feeder links or services that are only used occasionally.
In recent years, Carrier Identification (Carrier ID, or CID) technology has been developed as a countermeasure against these ‘rogue carriers’ to allow fast identification of an interfering carrier, giving satellite operators the ability to request them to cease transmission quickly and effectively. While this will not solve all RFI problems, it will be a key step towards reducing its impact on the satellite industry.
Carrier ID was sponsored by the Digital Video Broadcast (DVB) group, and has been formalised as a standard by the European Telecommunications Standards Institute (ETSI). It is also being avidly promoted by the Satellite Interference Reduction Group (IRG), which faces the difficult task in ensuring the widespread global implementation necessary for this initiative to succeed. The initiative has the support of five major satellite operators worldwide, ArabSat, Eutelsat, Intelsat, Inmarsat and SES.
The technology is being rolled out across modulators, Digital Satellite News Gathering (DSNG) encoders and modems. Satellite operators, manufacturers, and users all have a role to play in implementing this. The satellite operators need to ensure that Carrier ID is included in their earth station verification test procedures and specifications, but likewise systems integrators should be insisting that Carrier ID is included in their Statements of Work (SOW) and that they are not charging their customers an unfair premium for its inclusion. Indeed it needs to be viewed as an integral part of the system, not an optional extra.
Carrier ID standards
There are currently two types of Carrier ID:
IT Carrier ID (NIT-CID) was developed mainly for DSNG encoders, and uses the initial open format, unencrypted Network Information Table, which is available within the DVB stream. NIT-CID has the advantage of being easy both to implement and to use, and it is available as a free firmware upgrade for most single thread and DSNG encoders. However it lacks resilience as the known carrier must be taken out of service in order for the carrier ID of the interferer to be read. Its application is limited to DVB streamed services, and it will become obsolete as the implementation of DVB-CID becomes the global standard.
DVB Carrier ID (DVB-CID) is a new technology that uses spread-spectrum techniques to add a separate carrier under any Single Channel per Carrier (SCPC) or Multiple Channels per Carrier (MCPC) transmission method carrying streamed content or pure data/IP. This RF signal is added within the modulator, and is independent of the data stream or content. DVB-CID was initially developed by Comtech EF-Data and supported through a specific IRG Working Group. The formalised open industry specification has now become an ETSI Standard. It is intended that NIT-CID will be phased out by 1 January 2018 in deference to the ETSI standard DVB-CID.
How Carrier ID works
Carrier ID superimposes a signature on a satellite uplink signal, which allows satellite operators to identify the source of an interfering carrier. This is injected into the signal by the modulator, which creates two carriers the primary payload carrier and a low-power spread-spectrum CID signal comprising both mandatory and optional data fields, as shown schematically in Figure 1.
Figure 1: Schematic diagram of DVB-CID (Diagram provided by courtesy of Newtec/IRG)
The mandatory field consists of a DVB-CID Global Unique Identifier, for which the format has been defined by modulator equipment manufacturers. Optional information such as GPS coordinates and user contact details can be added by the user. Satellite operators have assumed responsibility for maintaining a secure CID database and monitoring their satellites for the occurrence of RFI.
To lower the impact on the satellite’s throughput, the CID information is spread below the carrier noise floor, as shown in Figure 2, which also shows the interaction of the interfering carrier with the wanted carrier.
Figure 2: Location of spread-spectrum Carrier ID in relation to wanted carrier and interfering carrier (Diagram provided by courtesy of Newtec/IRG)
Special measurement receivers at the satellite operator’s earth station can decode this information, allowing them to make either direct contact with the source of the interfering carrier or via the managing satellite operator of the interfering service.
Adoption of CID
The effectiveness of CID was demonstrated during the 2012 London Olympics, where all satellite transmissions during the event were virtually interference-free thanks to its use and the general awareness of interference itself. Eutelsat also upgraded all its satellites that provide full coverage of Brazil and the Americas to handle CID in the run-up to the FIFA World Cup.
In the USA, the FCC has ruled that it will be mandatory for all SNG, temporary or Occasional Use (OU) video transmissions to have either CID or an earlier identification system known as ATIS (Automatic Transmitter Identification System). It is planned that the industry will work towards continuing this process across all types of SCPC and MCPC carriers worldwide.
The route to making this work is being pioneered by the Arab States Broadcasting Union, which has produced an action plan involving raising awareness, providing training, and introducing a system for earth station approvals, with a view to making CID a requirement. IRG is encouraging other Regional Broadcasting Unions to follow this blueprint and work together to persuade the International Telecommunications Union (ITU) to impose penalties on members creating intentional interference.
Roles of the integrator and the satellite operator
As an integrator of satellite systems, Luso believes that integrators have a responsibility to promote the adoption and implementation of CID, and also that earth station manufacturers should be stipulating DVB-CID as standard on all requests for quotation. Many manufacturers currently offer it only as a premium option, but as development costs should already have been recovered this is not a sustainable approach. In contrast, Luso has a policy of including CID integration, and also advising on approvals and training, as an integral part of its customer offering. It also needs to be noted that the majority of Modulator and Modem manufactures offer CID for free. So there is no cost at source for an integrator!
The industry as a whole needs to be encouraged to support the adoption of CID and the aims of the IRG.
The satellite operators can also help this process by ensuring that earth station verification test procedures, specifications and line-up strategies stipulate CID. In supporting CID, Training also forms a key component, and the Global VSAT Forum (GVF) run a number of training courses on the topic. Integrators, take note!
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About the author
Geoff Smith is Principal Engineer at Luso Electronics’ Microwave Division. Geoff is responsible for engineering, delivery and project management of satellite earth station projects undertaken by the company. He has vast experience in satellite engineering, having spent over 17 years at Arqiva developing the innovative 28.2east DTH system and thereafter installing many earth stations transmitting varying traffic on a global basis. Prior to this role, Geoff developed the SNG truck building business for Advent Communications and managed the design, implementation and maintenance of earth station projects meeting high specifications at low cost. Earlier in his career, he spent over a decade working as a mechanical engineer for British Aerospace with a focus on both stress and structural engineering.
Luso Electronics, a UK based supplier of satcom products, engineering components for machinery and power electronic products, recently opened a new design and manufacturing facility in Luton, England, that delivers fully integrated turn-key installations and microwave products to customers primarily in commercial and military satellite communication markets. Luso’s new manufacturing facility in Luton has already made a significant impact to improving the company’s manufacturing capability and delivery times as well as offering greater flexibility to customers with specific design needs. RoHS compliant satcom products manufactured on site including Vsat antennas, switching systems, waveguide assemblies, filters, diplexers, adapters and associated electronic components. While most European microwave product providers simply supply components, Luso has been designing, developing, testing, installing and servicing tailored microwave and high-quality radio frequency (RF) systems and component solutions since 200
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