Mitigating Satellite Interference through Carrier Identification
A quiet revolution is underway in the fight against satellite interference. Satellite communications is extremely reliable, but the occasional mistake still makes an undesirable impact from time to time. This revolution is all about the adoption of a new Carrier Identification (CID) scheme that will allow for the timely identification of signals that are causing interference in satellite transmissions.
The Satellite Interference Reduction Group (IRG) has long worked to find ways — procedural, technological, legislative, etc. — to reduce and hopefully eliminate the occurrences of satellite interference. The first step in all this, of course, is to identify the sources and causes of interference. Various studies have revealed that the vast majority of interfering incidents are unintentional, and caused by such things as poor system design, equipment malfunction and operator error. Most cases of intentional interference turn out to be politically motivated.
Unintentional sources of interference logically imply that the personnel at the source of the interference are unaware of the problem they are causing. Examples of unintentional interference include: they may be picking up and rebroadcasting local terrestrial interference (increasingly likely with the explosion of Wi-Fi and 3G/4G services), their dish may not be quite large enough to avoid adjacent satellite interference, the dish may become misaligned through wind or other weather conditions, transmit equipment may fail or become degraded, or they may have a subtle error in the setup of their transmit chain (wrong modulation frequency, power level, etc.) Finally, all of the above parameters may in fact be perfect but the uplink in question is actually transmitting at the wrong time due to miscommunication.
Since most of the above examples are not serious enough to inhibit transmission of the uplink’s own signal, they are left completely unaware of the interference they may be causing to others. The lack of awareness is exacerbated by occasional use or ad hoc transmissions, such as SNG or other mobile uses, where the offending transmission has terminated before anyone has either noticed the interference or pinned down the cause.
What is clearly needed is a system that allows for the routine, timely identification of interfering transmissions. Being able to identify exactly who is causing a problem is the first step in getting them to fix the problem.
How it Works
The CID system works by adding a very low power, spread spectrum carrier to the actual carrier being broadcast. This new carrier can be thought of as being “beneath the noise floor;” though its effect is to very slightly (less than 0.1dB) raise the actual noise floor for the primary transmission. As a separate carrier, the CID signal is very robust, and not related to the primary carrier. It is thus not subject to actual problems in the primary carrier such as modulation errors, incorrect frequency, encryption issues, etc.
The ID carrier uses robust modulation consisting of BPSK Spread Spectrum at 112kHz or 224kHz and BCH Coding. The data within this carrier consists of automatic, mandatory information such as a the modulator’s MAC address or a vendor serial number, plus optional user configurable data such as the carrier name, GPS coordinates and uplinker contact info.
Special purpose receivers lock onto this ID carrier and present the data to satellite operators. This data can be accessed if interference problems are detected, and can also be used by a broadcaster to verify conclusively that their signal is on the air.
When a satellite operator investigates a carrier that is causing interference, they may use the output of one of these receivers to identify and contact the uplinker of the interfering signal. A universally accessible and secure database, available via the Internet, will further aid identification, by associating some of the detected IDs to satellite operators that have working relationships with the uplinkers.
Rollout and Adoption
2013 was a pivotal year for CID as the new technology became formally accepted by the DVB (DVB-CID) and was issued as a standard by ETSI. WBU-ISOG also issued resolutions requiring that all new model modulators and codecs starting by January, 2015 include CID capability, and also that SNG, DSNG, and all new uplinks incorporate CID in their transmissions. Another part of the WBU-ISOG resolution calls for all new Request for Proposals for satellite uplinks to include a requirement for CID, beginning immediately. Additionally, the FCC in the United States will begin requiring that all occasional use video satellite transmission have CID beginning June 2016. These approvals pave the way for widespread industry adoption in the years to come.
Most major modulator manufacturers are now offering CID capable modulators, and are demonstrating them at major industry events. CID has been used in a number of high profile transmissions, including the 2012 Olympics and the 2014 World Cup, greatly increasing its exposure and profile to those in the industry.
Finally, the IRG will continue to work with regulatory and political entities (such as the ITU) to lobby for the widespread adoption of CID. Taken together these actions generate momentum for the widespread adoption of CID.
CID performs the same function as a license plate on a motor vehicle. It allows eventual identification of the responsible party, which may be necessary for instances where that vehicle is not operating with acceptable parameters.
Given human nature, it is likely that we operate our motor vehicles in a more safe and lawful manner knowing in the back or our minds that there is a publicly viewable identification on it that can be traced back to us. Likewise, it is likely that when CID is pervasive in the industry, uplink operators will become habitually vigilant toward their own transmissions. CID’s greatest effect may be to alter the overall mindset of uplinkers to ensure ahead of time that their transmissions will not be the source of any interference. In the end, CID will be most effective when it is least used! VS
Roger Franklin is the CEO and Owner of Crystal Solutions, a supplier of Network Management Systems plus Automation (NMS+) for the broadcast and satellite industries Since early 2009, Franklin has been focused on ways to mitigate and prevent RF Interference. His work includes successfully leading the sIRG SCPC Carrier ID Working Group, as well as extensive involvement with the EUI Advisory Committee.