Digital wireless camera systems take the stage at NAB
After several years of R&D field-testing and exhaustive manufacturing to make the electronics portable, several equipment manufacturers, such as the BBC, Grass Valley and Sony will introduce digital wireless camera systems at this year’s NAB convention. The systems deliver on the promises of transmission reliability and production freedom.
Now the size and weight of a large ENG battery, the technology has been tested by two of the major U.S. networks (which have not been identified), which are considering using the digital transmission technology for upcoming political conventions and live sports broadcasts.
Up until two years ago, the necessary encoding technology that mounts on the back of the camera was bulky and not suitable for daily production. The algorithms that allow the technology to operate in the digital broadcast auxiliary spectrum (approximately 1.9-2.7 GHz) were still under development. Without the latter, U.S. broadcasters would have been required to seek a special temporary authority (STA) operating license from the FCC every time they wanted to use the system. It appears that all of those issues have been resolved.
Digital camera systems consist of a DVB-T COFDM demodulator, a digital transmitter and antenna that mounts on the back of the camera and a receiver, usually located in a mobile truck or back at the studio. Due to COFDM modulation, users can employ multiple distributed antennas and a management control unit for uninterrupted transmission and reception. The system automatically switches between antennas to extend the shooting range.
Using either MPEG-2, DV or Wavelet compression, video latency, that is, video frames that become delayed or appear to stutter due to signal processing, has been minimized to the point where the systems are now being considered for a wide variety of live outdoor productions that previously avoided the technology. In general, Wavelet compression reportedly provides the best results, but comes at a much higher cost. Professionals agree that 2-3 frames of delay, which all of the compression-based systems experience, are acceptable for most TV productions.
��We’ve worked very hard to reduce the latency, so that you’re not looking at four or five frames, which is where this technology was a few years ago,” said Chris Tsai, product manager for Sony’s digital wireless camera system. “We think that 2.5 frames is acceptable and manageable for most TV productions today.”
While a user does not need line-of-sight to successfully transmit broadcast-quality digital video, there are still limitations in distance and transmitting through certain obstacles, such as a concrete wall, that can cause a loss in signal strength and the digital transmission to fail. At low power (10 milliwatts), the operating distance usually allotted is 1,800 feet and at 100 mW the distance improves to more than 3,000 feet. Battery consumption is higher in the 100 mW mode.
BBC Research and Development, based in the U.K., has been working with digital wireless technology for more than five years. The BBC showed a shipping Digital Radio Camera system at the IBC2002 convention in Europe. Two NTSC versions of that same system will be exhibited at NAB. Along with the wireless camera system, the BBC’s Research & Development team has been responsible for a series of innovations, including the BBC’s TV text service and Nicam Stereo, the audio system that brought cinema-quality effects to television in the U.K.
The BBC’s camera system, which operates in the 2.38-2.68 Ghz spectrum, currently uses DVCPRO-25 encoding, although development is also underway to provide an MPEG solution which will be switchable with the existing system, according to Mark Popkiewicz, managing director with BBC Kingswood Warren (part of the BBC Ventures Group Ventures) in England. In the past two years, 13 wireless camera systems have been field-tested within the BBC's newsgathering, studio production and mobile production divisions.
Transmission range is just more than 3,000 feet, with a latency of 2.5 frames. Popkiewicz said DVCPRO compression was chosen as the encoding scheme because it produces high-quality pictures that match that of triax cameras. "[Wireless digital signal distribution] requires a significant amount of video content to be transmitted from the camera system," he said. "The high bit rate used in DVCPRO [25 Mbps] makes it ideal for generating high-quality broadcast pictures."
Popkiewicz said a key requirement of wireless digital camera system customers is the ability to intercut pictures directly into live broadcasts. He said the Digital Radio Camera is regularly used to contribute pictures into live broadcasts and recently enabled BBC News to broadcast real-time pictures of a major criminal trial ahead of its competitors. The system has also been used to cover a number of the BBC's live sporting events in the U.K.
Grass Valley’s LDK 200 digital wireless camera system uses wavelet compression to minimize frame delay.
Grass Valley will also show a new digital wireless system to go with its LDK 200 line of SD cameras that it has quietly been developing in Europe for several years. It uses an omni-directional antenna, DVB-T COFDM transmission modulation and runs on very low power.
David A. Stam, product manager for Thomson Broadcast & Media Solutions’ camera business said that they have chosen Wavelet compression to ensure high-quality signal integrity, even under the most demanding RF environments. It has a range of approximately 1,312 feet (line-of-sight), and a frame delay of 1.5 frames. The new Grass Valley transmission system also provides a standard SDI output and is genlocked like a normal studio camera to facilitate its switching with other live or taped footage.
Stam, based in Grass Valley’s Breda, Germany facility (where the camera systems was developed), said Wavelet compression at 18 to 20 Mbps is the only scheme that maintains a 10-bit 4:2:2 digital signal. MPEG-2 compression would have required the use of 8-bit 4:2:0 or 4:1:1 A/D conversion and, "as most professionals know, there is a visible difference between 8 and 10-bit digital video processing."
"The choice of 10-bit processing eliminates such artifacts as contouring on uniform areas like the sky or the green of the playing surface," Stam said. Because the camera system processes the whole picture rather than dividing it into macro-blocks, images processed with Wavelet compression are widely regarded as resulting in a more natural appearance.
“[Images captured with the wireless camera system] are usually free from the familiar artifacts created by MPEG-2, and under difficult reception conditions, the transmission fails more gracefully,” he said.
Wavelet technology is extremely reliable and has been used for more than 10 years by the oil drilling industry to find new deposits -- by stimulating underground pockets with a powerful infrasound signal.
Sony is also introducing a new digital wireless system at NAB. The company has shown a prototype of its MPEG-2-based system for the past two years at various trade shows, both in the U.S. and in Europe. It consists of the WLL-CA50 (transmitter) and WLL-RX50 (receiver) and will ship this summer. An optional DVB/ASI decoder (BDX-D1000) and a cable amplifier (WLL-BA50), used to increase signal distance, are also available.
Using MPEG-2 compression, Sony’s digital wireless camera system is lightweight and mounts on the back of the camera.
Chris Tsai, product manager for Sony’s digital wireless camera system, oversaw a series of tests in February with a prototype Sony system in Chicago, Ill., during coverage of the mayoral primary there. Footage shot with the camera were intercut with other live shots. Tsai said there was very little difference in the appearance of the two sources. “The test went fairly well,” said Tsai, who said the test involved local CBS O&O station WBBM-TV.
Tsai revealed that crews encountered a few interference problems inside a hotel that was filled with disparate wireless electronics devices operating on the 802.11B wireless communications protocol. It caused the camera system to loose signal every so often.
“We did take some hits, but it wasn’t terrible,” he said, adding that the Sony system includes the ability to change the center receiving frequency that enables up to seven wireless camera systems to operate on the same shoot without interference.
Developed at the company’s Atsugi, Japan research facility, the Sony system operates in the 2.4Ghz spectrum, with a delay of about three frames, and is available in two configurations: with diversity or without. The diversity model includes two OFDM demodulators that allow multiple antennas to be used to ensure that as the camera operator moves around the signal is not lost. Tsai said the system’s transmitter alone adds about 2.5 frames, so if someone uses a decoder other than Sony’s, the delay could be higher.
Without the government restrictions placed on U.S. broadcasters, European professionals have used digital wireless systems for the past few years. Acknowledging this, companies like Gigawave Limited (U.K.) and Link Research (U.K.) have also introduced digital wireless camera systems, using both MPEG-2 and Wavelet compression, although those companies traditionally do not exhibit at the NAB convention.
For more information on the products mentioned above please visit: www.bbc.co.uk/rd, www.bbc.co.uk/rd/index.html, www.gigawave.co.uk, www.linkres.co.uk, www.sony.com/professional and www.thomsongrassvalley.com.
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