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Satellite Interference: Tech To The Rescue

by Bob Potter

Interference costs satellite operators millions of dollars each year. Solutions such as sophisticated, cost effective tools are now available that allow operators to plug leaks that cost the loss of revenue as a result of interference. The good news is that the expense of interference mitigation tools can be recovered in less than a year by increasing revenue and lowering costs.

Conservative estimates for a fleet of three satellites lists the cost of interference at $2M per year. This total consists of lost, or reduced, revenue due to; delay of the start of services; transponders directed to operate in backed off mode that results in less power and/or bandwidth available for sale; and spectrum that is used for interference mitigation. Then there are the increased labor expenses that include overtime and purchases of other external services.

To understand how modern tools help to reverse this issue from an expense into profit we first have to understand the causes and reasons for the interference.

The Satellite Users Interference Reduction Group (SUIRG) categorizes satellite communication interference into five main groups, these are:
  • 1. User Error
    • a. Human Error
    • b. Equipment Failure
  • 2. Crosspol Leakage
  • 3. Adjacent Satellites
  • 4. Terrestrial Services
  • 5. Deliberate Interference

User Interference
This is usually accidental as a result of operator error, equipment malfunction, or due to poor cable shielding. These interference types are, in most instances, relatively easy to find, however, it usually takes a disproportionate amount of the satellite operator’s manpower and time to locate.

Crosspol Interference
This is usually caused by; incompatible modulation types (such as FM TV) transmitted in the opposite polarization field to digital services on the crossopol; poorly aligned antennas in bursting networks; and lack of training/experience of the uplink operators. The first example involves unusable capacity in which the company of the interfering service compensates the other party. The second and third types are extremely time consuming and labor intensive in both equipment and training.

Adjacent Satellite Interference
This type of interference is generally accidental, due to operator error, or poor inter-system coordination. Frequently, this can be resolved between the satellite operators. Unfortunately, this type of interference is becoming more prevalent as two degree spacing between satellites in the geostationary arc becomes more common.

Both of the affected satellite operators want full use of the spectrum on a non-interference basis. However, this again consumes a disproportionate amount of manpower and time to resolve, resulting in loss of useful spectrum and ultimately, of revenue.

Terrestrial interference
This is the result of; existing terrestrial microwave systems; new microwave systems that have commenced service following deployment of the satellite; or civil or military radar systems. This situation is usually time consuming and difficult to resolve, especially in the military arena. In general, as the terrestrial systems usually have priority, this becomes dead capacity on the satellite.

Experience reveals that with military interference, if proof of source can be indicated, the military is cooperative in removing the cause, if at all possible.

Deliberate interference
This type of interference is usually geopolitically motivated. It is, generally, relatively easy to locate, but almost impossible to remove without political intervention, which can prove difficult.

Recent (SUIRG) reports of cost of interference to a satellite operator reveal that $2M per year is a conservative amount. In order to reduce the loss of revenue, satellite operators need to take a holistic approach to their interference mitigation processes. Geolocation systems are not the panacea for interference that one may think. They are simply one of the tools of the trade to assist and help with interference mitigation.

When interference occurs, payload operators first have to ensure that the user is still active, and that their service is operational. Following that, the operator needs to address the removal of the interference by first determining the source, and then shutting down the transmission.

In the ideal world, interference would be detected and resolved before it affected the existing client of the satellite.

For this to become a reality there first needs to be coordination among planning and live operations, with an open, automated interface between the tools that planners and payload operators use.

With this open interface planners can see what is occurring on the satellite, and operators can observe what should be on the satellite. The result is that the CSM system can locate unauthorized carriers, which potentially can become interferers by occupying the frequency space that is needed for a new customer.

An unauthorized carrier is easily detected when live traffic is overlaid with a planned mask. Frequency planners can readjust the uplink schedule, or frequency plan, and payload operations can locate the source of interference and have it removed. All this is achieved before there is an impact to the new uplink service, and there is no loss of revenue due to delays in the new service.

Digital Spectrum Analyzers (DSA) can find interference occurrences within live carriers before the interference becomes a real issue, resulting in loss of revenue. For this to be affective a feature of the DSA needs to locate interference under the entire live carrier bandwidth, and then be able to analyze it.

With knowledge that interference is occurring, and having access to the analysis of the interference, the payload operator can work to remove the obstruction. This can yield fast results, without affecting the existing service. In fact, it may not ever be known that a small interference signal was present.

The positive result is not having to move the existing service to another frequency slot. This enables the planners to reserve less spectrum for interference mitigation, and make it available for revenue generation.

When the live service is affected by interference, and the operator needs to move the service to a new slot, the operator needs to view the satellite frequency plan and test scenarios. These determine what would happen to a transponder operating point if the serviced was moved to a new frequency.

Graphical analysis tools within the planning system are used to test the new transponder, and observe the frequency plan, transponder noise floor, and operating point if the operator were to move the service to the new slot.

This ensures that correct operation of the transponder is maintained, and the temporary movement of a service that is suffering interference does not affect existing services.

Once the operator has quickly resolved the issues of the existing customer, their attention can turn to the removal of the interference.

One of the DSA carrier’s features also allows for fast resolution of crosspol issues enabling the operators to determine if the interference is coming from the other pol. By using the feature to remove the digital carrier on the crosspol, the performance of the copol antenna is easily observed.

With access to the Earth station database within the planning system the operator resolves the issue quickly and easily with no interruption to services to complete an antenna check.

The interference analysis provided by DSAs acts as a fingerprint. The payload operator uses this information to search the CSM and the planning databases to research the past, present and future services for a “match”. SUIRG reports regarding causes of interference indicates that 98 percent of known interferers are past, present or future customers of the satellite operators.

As a result, most of the interference occurrences can be found and dealt with by inexpensive searches of carrier lifetime databases.

New initiatives such as the SUIRG sponsored Unique Carrier Identifier, or CarrierID provide for use of overhead bits to uniquely identify a modem. Operators can use DSAs to extract the CarrierID and pinpoint the location of the modem quickly resolving interference issues. With the decreasing costs of planning systems and DSAs, a modest investment for an integrated system can save a small operator as much as 50 percent of the cost of interference. This can translate to as much as $1M per year.

Satellite interference is generated from multiple sources; typically most are from operator error or equipment malfunction. When there is an interference incident, it can take anywhere from minutes, to months, and even up to a year of investigation to resolve the problem. This results in lost revenue and increased costs.

The smart investment of an integrated payload planning and operations system can yield huge savings amounting to payback of the cost of the system in less than a year.

About the author
Bob Potter is the President of SAT Corporation and is an expert in interference technologies and solutions.