High-Def Newsgathering Passes CBS Test
Digital microwave gear successfully supports HD feeds
By Glen Dickson -- Broadcasting & Cable, 5/7/2006 8:00:00 PM
Complete high-definition newscasts might reach viewers sooner than they expect. After extensive testing in New York, CBS believes new digital microwave gear can support HD electronic newsgathering (ENG).
CBS measured HD feeds from an ENG van parked at various sites up to 35 miles away from its receive site atop the Empire State Building, replicating the typical coverage area for ENG operations. With a line-of-sight to the building from the van’s microwave mast, CBS experienced 100% success at HD data rates ranging from 18 to 28 megabits per second (Mbps), says CBS VP of Advanced Technology Robert Seidel.
CBS also tested “bounce” transmissions from various locations within New York’s urban canyons, such as Times Square and Rockefeller Center. The network had similar success with the COFDM (Coded Orthogonal Frequency Division Multiplexed) system, despite the greater multipath interference present in such locations. The reception rate for bounce transmissions was 95% at a data rate of 18 Mbps, 90% for 22 Mbps.
In fact, the new digital microwave gear is deemed reliable enough that it may actually replace satellite newsgathering (SNG) links in locations that previously didn’t allow analog microwave feeds. “In some locations where we used SNG,” says Seidel, “now we can use ENG.”
CBS’ findings are significant. While a few stations produce HD newscasts, the material coming from the field is still standard-def, with the exception of a few HD helicopter cameras. The expense of HD field cameras is one stumbling block to high-def ENG, but the bigger issue is the return path to the station.
Broadcasters are in the midst of an FCC-mandated transition from analog to digital ENG gear, freeing up spectrum for Sprint Nextel. The wireless carrier is spending up to $500 million to compensate stations for new digital microwave gear (B&C, 5/1, p. 28).
While Sprint Nextel is providing only standard-definition equipment, some broadcasters plan to spend more for high-def capability. But since HD video has four to five times the information of SD video—and improving the robustness of a microwave signal generally means lowering the data rate—questions emerged as to whether reliable high-def feeds could be sent in the new ENG channel.
Those questions seem to be answered, says Seidel: “I suspect New York City represents one of the harshest [receive] conditions you will run into.”
CBS transmitted the compressed HD microwave feeds within an 8 MHz transmission channel, or “pedestal,” using transmission gear from Microwave Radio Corp. and HD encoding and decoding technology from NTT Electronics. The COFDM system allowed CBS to test different modulation configurations at a range of data rates; for example, CBS used a 9-Mbps stream for signal alignment and sighting the antenna.
CBS also tested sending HD feeds with a prototype non-COFDM transmission system at a high data rate of 35 Mbps. That system proved reliable for line-of-sight applications, with a 100% success rate for distances less than 35 miles, but unsuitable for bounce applications, with a success rate of only 15%.
CBS shared the test results with affiliates at NAB and demonstrated the Sony XDCAM HD camcorder that it will begin rolling out to its owned-and-operated stations this year. CBS showed what Seidel called a “clean switch,” alternating between a live camera feed and a prerecorded, edited piece stored on an XDCAM optical disk loaded in the camcorder. Because the camcorder has a countdown timer on its monitor, the operator can perform a countdown to the talent to indicate when a switch back to the live camera feed will occur.
“It’s a nice seamless switch in and out of the disk,” Seidel says.
The XDCAM HD gear will replace tape-based Panasonic DVCPRO equipment at CBS’ 17 owned-and-operated stations. Which gets the gear first will be a function of which needs it the most, says Seidel, with WBBM Chicago likely to be first up.
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