Advanced Techniques for Recovery of Satellite Interference
by Adi Rozenberg. Technical editing by Paul Atwell
Current Challenges:
Interference caused to Satellite Ground Station, Receivers and Terminals is long documented in the history of Satellite Communications. Broadcast providers, Telecommunication Services Operations, News & Live Event Producers, and earth station personnel are well-aware of legacy issues. Even the public, watching satellite feeds during a raining day, experience collective futility during the shared occurrence of signal degradation. The Interference can come from many sources; Local RF sources using the application frequency or a harmonic of such, Adjacent Signal Interference (ASI), Weather conditions, Sunspot activity, military radars & overflights, and recently the sharing of some of the 5G and C-band frequencies range. In the United States, this is initiating a migration from those shared frequencies to a different frequency assignment, while squeezing legacy Satellite users into a denser frequency range. To those that want an example of how interference and degradation affect applications and Users, reflect to a time sitting with friends at the local sports bar watching the big game when an afternoon thunderstorm crosses the viewing region. Clouds and rain block the receive signal, the game is replaced by tiling effects, frozen frames, and loss of signal until the storm passes.
Each year the Satellite industry allocates significant budget to predict, monitor and mitigate known problems in advance. Many techniques are applied for prevention and to overcome the interference, beginning with improved error correction schemes like LDPC, reactionary power levels adjustment during inclement weather conditions, transmission symbol rate adjustments, and backup Satellite connectivity, to name a few. But as a rule,” one can only be well-prepared for known events”. Unexpected degradation and interference are still caused by local weather activity, undetermined RF power transmissions, rouge operators and faulty neighboring devices will still induce unpredictable interference to occur. One such example is the uncoordinated testing of 5G transmission applications near an Earth station without proper notice to the station operators. It is then left to the earth station technical team to diagnose the problem, adjust appropriately, or to ride out the interference until the event has passed. Over the duration of the interfering event, the result to viewers can include artifacts, micro- and macro-blocking, frozen frames, and complete loss of signal.
The increased deployment of RF solutions for the origination and distribution of high bandwidth connectivity in cities, suburbs and rural America will increase the overall noise. To this we must also now add the advancing popularity of cellular 5G and all its installations, applications, and yet-to-be-known consequences.
How satellite users can compensate for the problem:
A recent ‘BEST PRACTICES FOR TERRESTRIAL-SATELLITE COEXISTENCE DURING AND AFTER THE C-BAND TRANSITION’ ( https://ecfsapi.fcc.gov/file/1113936500088/C-Band%20TWG-1%20Best%20Practices%20Final.pdf ) does a good job defining the interferences sources and types and what can the earth stations do to mitigate the symptoms. The overwhelming advice is to document the events. Record and monitor locally and then regionally. Attempt to define patters and triangulate sources. Regretfully, the conclusion is that if the source of the interference is undetermined the result may be poor service to the point that it could remain non-usable for minutes, hours, or even days.
As the report suggests, one should monitor for the cause of the interference and work with nearby and related operators to mitigate for possible inferences, but the report also addresses the possibility of unknown, undetermined, and undefined interfering signals. Investment in new filters, a different reception dish, receivers and terminals is also advised by manufacturers and system integrators.
Today planners and operators are looking for alternatives. Some choose to engineer multi-site reception configurations to mitigate problems. Others choose to use a broadband IP delivery of duplicate signals to switch in to place when a problem occurs, while other apply the Filter approach. Operators can compensate for several known or anticipated incursions but cannot anticipate them all.
How does VideoFlow do things differently?
VideoFlow has developed a unique and patent-protected, novel system to address the interference symptoms: corrupted data, impaired signal, missing packets, and even up to a full loss of signal. The VideoFlow RISE service (Reliable Internet Satellite Eco-system) works to identify impaired or missing packets and to replace them with the original packets. Instances of interference will still occur but the RISE clients operating at each receiving Earth station terminal (or IRD) will identify the errored packets or lost packets. Those identified packets are replaced with the originals copied at the source, similar to ARQ solutions, but on the MPEG2 transport level and not within the IP layers. The main attraction and highlighted novelty of the system is the use of any available, low-cost internet connection to recover packets. The connectivity options can include LTE/4G/5G, DSL, DOCSIS/Cable Modem, StarLink, IP Hotspots and many other IP delivery options. The packet recovery is seamless, and the original packets are seamlessly swapped in the place of the missing or corrupted packets. Timing information is preserved and maintained. The outcome is a continuous uninterrupted program from the RISE terminal during and throughout the event.
The original Satellite program stream is not manipulated or modified; no watermarking inserted, no additional bit rate overhead, and no changes in any way. This allows for easy incorporation into legacy uplink transport system. A VideoFlow RISE Origin creates a copy of the uplinked signal and forwards it to a VideoFlow RISE cloud server to be used as the recovery source for tens to hundreds of RISE Clients. The RISE service introduces a marginal 300ms of delay to the delivered Satellite program. This allows for any recognition and delivery of missing or corrupted data packets and promotes the use of the low bitrate, low-cost connectivity to the receiving location.
Initial deployments have demonstrated the system is able to maintain successful, undegraded service performance even as the satellite transmission experiences signal-to-noise ratio over 50%, which well exceeds the threshold for any standard Satellite transmission.
Other hybrid solutions, for example using SRT, incorporate a switch between the Satellite-delivered program and an IP-delivered program. The difference is that SRT requires delivery of the full program to the destination, plus overhead. For example, a 36Mb program will call for 45Mb resulting stream. The switching between ‘good & bad’ is done only after a certain noise level is attained, will introduce an artifact and possibly a shift in the synchronization. During the time before the swap takes place, corruption, degradation and artifacts will present and visible. In comparison, a RISE solution will require only a 4Mb or 5Mb downlink and cause NO artifacts or loss of timing.
Additionally, VideoFlow inherent features and toolsets within the service provides additional, value-added features like ETR290 monitoring for each RISE Receiver, program services monitoring, system and connectivity health and much more. These techniques can be applied to existing and evolving transmission systems to increase operational efficiency.
Why is this important?
For the first time, users can implement a new application into an existing system to implement interference avoidance, provides a pro-active, shielded transmission during episodes of interference and remove headaches from the equation. The earth station personnel can have peace of mind that the resulting signal is delivered error free, verify performance, and can take the time required to identify and address the cause of the interference or disregard it completely.
The overall ecosystem does not change, Satellite is still the primary method of delivery. The VideoFlow RISE service results in a robust and error free outcome, ready to provide more services for years to come.