Millimeter Wave Band Holds Promise For HD Video Links
By Paul Kruczkowski, Editor
College football’s BCS National Championship Game is still fresh in my mind, and so are all the other live television events that occur this time of year — the NFL playoffs (where the Steelers disappointed me and the rest of Steeler Nation), the New Year’s Eve celebration in Times Square, New Year’s Day parades, and so on. As I enjoyed the TV coverage of these and other events like them, the engineer in me couldn’t help but think about the technology required to cover them, allowing you and I to enjoy them in the comfort of our homes. Video equipment needs to meet the complex demands of today’s digital video standards, and the wireless link that carries uncompressed high-definition video signals from the camera to a nearby production truck is only the first link of the long chain needed to get that video to the viewer.
Broadcast wireless links typically use unlicensed bands governed by FCC Part 15, because no registration is required for their use. One commonly used unlicensed band is 2.4 to 2.5 GHz, but operating in this part of the spectrum presents several challenges for broadcasters. For instance, as the band becomes more congested, there is greater opportunity for interference. Bandwidth is also limited, and transmitting video at high data rates with simple modulation schemes — like on-off keying using non-return to zero — is a bandwidth hungry process. (SMPTE 292M, often referred to as HD-SDI specifies a data rate of 1.485 Gbit/sec, which supports uncompressed HD video; SMPTE 372M, or dual-link HD-SDI, specifies a data rate of 2.970 Gbit/sec data rate, which supports 1080p and 3D HDTV.) In addition, many camera-mount 2 GHz radios just don’t have the range to reach out to a production truck half a kilometer away.
To sidestep the issues associated with the 2 GHz band, broadcasters have started turning to the 60 GHz millimeter wave band to transport their raw HD video from camera to truck. This unlicensed band, governed by FCC Part 15.255, also requires no registration, and the 57 to 64 GHz frequency range provides 7 GHz of unchannelized spectrum for video links. Unlike the unlicensed lower-frequency bands, the 60 GHz band is naturally interference resistant, due to atmospheric absorption, which attenuates interfering RF signals approximately 16 dB/km, effectively mitigating interference.
Gigalink HD, manufactured by HXI, is one example of an HD-SDI wireless link that enables broadcasters to transport raw, uncompressed HD video at 60 GHz, especially when circumstances prevent the production truck from pulling alongside the cameras shooting the event (but line of site is still available). The rugged link was first used by the military to send real-time high-resolution video of troop movement to command posts in the Middle East under harsh conditions. The technology has been adapted for commercial applications and has been used in 1,500 data link deployments worldwide.
Gigalink HD is an FCC Part 15.255-MPT approved transport solution for SMPTE 292M/372M, with a single- or dual-channel option allowing for up to two cameras or 3D/HDTV broadcasts with an effective range up to 500 meters (1,640 feet). A 5-degree antenna beamwidth works in concert with atmospheric absorption to isolate the link from possible interferers and allow for better frequency usage through multiple local links. Gigalink HD takes advantage of abundant bandwidth at 60 GHz to implement a simple modulation with direct detection using non-return-to-zero, resulting in near-zero latency with delays of only 40 ns. A BER of 1 x 10-12 ensures high-quality video reproduction with no artifacts and carrier quality availability of 99.999%.
The 60 GHz band has inherent advantages for wireless HDTV links when the logistics of the event allow for line of sight to the production equipment. Whether that means beaming uncompressed HD video from stadium top to a broadcast truck in the parking lot, or from the red carpet of an awards show to the studio rooftop across the street, the 60 GHz band offers broadcasters an efficient, effective way to deliver that event to a HDTV near you (and me).