A Hybrid Approach to the Move From C-Band

Broadcast distribution has depended on satellite connectivity for decades because it can deliver content reliably and cost effectively to hundreds or thousands of affiliates. 

In the United States, the reallocation of a portion of the C-band spectrum for 5G and other cellular services has reduced the spectrum available for satellite services and prompted broadcasters to consider alternatives.  

Despite the near-ubiquity of IP connectivity and increasingly competitive pricing, satellite distribution retains an important advantage. A well-designed satellite link can be engineered for 99.999% availability, equivalent to approximately five minutes of outage per year.  

Individual fiber services are often specified at availability levels between 99.9% and 99.99%, representing approximately nine hours and one hour of annual downtime, respectively. Dual, geographically diverse fiber connections can approach satellite reliability, but fully diverse paths serving a large affiliate network are not always available. 

That level of reliability is difficult to match across a widely distributed network. The challenge comes when broadcasters consider moving services from C-band to Ku-band. 

Ku-band introduces operational and logistical challenges, including its greater susceptibility to rain fade. Atmospheric absorption caused by water increases with frequency. Therefore, wetter and more tropical parts of the United States can experience significantly deeper fades at Ku-band than at C-band.  

A satellite link budget must be robust enough for every downlink location. One way to accommodate heavier rain fade is to use more robust modulation and error connection, accepting a substantial reduction in data throughput. Another is to require larger receiving antenna at locations most affected by rain. 

Neither option is likely to be attractive to a broadcaster or its affiliates. A hybrid satellite and IP distribution system offers another approach: continue using satellite as the primary distribution path while using IP to maintain service during a severe Ku-band rain fade. The IP path, however, must do more than recover a few missing packets.  

With DVB-S2, the transition between quasi-error-free (QEF) reception and complete loss of signal can occur within a margin of only 0.5dB to 1dB. Rain fades may exceed 10dB. Under those conditions, requesting occasional missing or corrupted data will not maintain service. It is simpler and more effective to deliver the complete service required by the affiliate over IP for the duration of the fade.  

That distinction also makes the approach more manageable. An affiliate may receive a satellite multiplex containing many services but require only one or two of them. Delivering only those services over the backup path reduces the IP capacity needed at each site.  

Protocols such as RIST and SRT are already used for reliable video transport. Additional resilience can be added through geographically diverse IP connections, load balancing or SMPTE 2022-7 path protection when duplicate steams are available across separate routes. 

If the satellite and IP versions originate from the same encoder and multiplexer, the two paths can be aligned and seamlessly merged at the receiver. The downstream decoder then receives an uninterrupted transport stream as the satellite signal deteriorates and returns after the weather passes. 

IP does not have to replace satellite. It can be used selectively when raid fade disrupts a Ku-band signal.  

A properly designed hybrid satellite and IP distribution system can support a move from C-band to Ku-band, with IP providing an alternate path when weather disrupts the satellite signal.