Wireless cameras
Aug 1, 2009 12:00 PM, By Anthony Sangiovanni
Today’s wireless cameras offer new creative and logistical options to content providers.
Figure 1. Camera control system set-up
Select figure to enlarge.
Wireless cameras are not new to the market, but improvements to the technology behind them are changing the TV production landscape and the way they're being used. The premise behind using wireless cameras has always been the promise of delivering new ways of allowing creative freedom during TV production.
Unfortunately, there have also been many compromises to the production process with respect to the on-set compatibility of wireless cameras to their wired camera counterparts. Issues such as on-air reliability, system latency, line of sight or limited range, format capability, and lack of remote camera control features have limited the proliferation of wireless cameras into the TV production world. Recent advances in wireless technology and the addition of enhanced features, along with increased demand for up-close, inside-the-story content for both reality TV and sports production, will also increase the demand of content producers for the creative freedom and flexibility they have desired for so long.
Let's examine some of the limitations that have traditionally hampered the use of wireless systems and how these issues have been addressed.
On-air reliability
When wireless video systems were first introduced in the mid-1990s, these systems' signals were transmitted via analog signal modulation. The systems (many of which are still in use today) required line-of-sight transmission to avoid multipath of the received signals. In many cases, especially in sports production or fan-cams, there were two people involved in the transmission process — the cameraman and the person holding the transmit antenna pointed to the remote receiver site.
The introduction of digital COFDM transmission has eliminated the need for a second person to ensure that a multipath condition does not exist. In fact, with COFDM transmissions, multipath of the transmitted signal to the receive antenna actually helps increase the robustness of the received signal.
System latency
Wireless systems usually have latency, or delay of the received signal, with respect to real time to contend with. This causes problems for content producers because cutting from a wired to a wireless camera interferes with the continuity of events, especially with content that involves motion. For example, try tracking two cars racing into a turn with a wired camera. Halfway into the turn, the director cuts to a wireless camera that has a lot of system latency. As a result, now instead of an image of two cars completing a turn, those two cars would just be getting into the turn.
Imagine viewers' reaction to that. They would think they were watching an instant replay. Recent advances in encoding methods have allowed some wireless systems to achieve one frame or less of system latency, including the transmission of HD formats.
Line of sight or limited range
As explained above, digital COFDM technology has solved the line-of-sight requirement. Maximum-ratio-combining diversity receivers have addressed the range limitations, while also increasing coverage area. Maximum ratio combining is different from traditional diversity systems that would switch from one antenna to another when the signal is lost. Instead, as the name implies, all of the antenna input signals are combined to make multiple weak receive signals into one stronger signal.
Currently, there are multiple input receivers available on the market from two to as many as six antenna inputs. Any of these available systems trump a single input receiver's sensitivity and performance.
Format capability
Transmission of HD signals requires much more bandwidth than SD signals do. Trying to squeeze MPEG-2 encoded HD signals into existing DVB-T channels is a challenge because to do so requires a higher order of modulation, such as 64QAM. By using these other modulation methods, the robustness of the transmitted signals are compromised. Advances in both transmission coding schemes (stretched and/or dual pedestal modes) or other emerging encoding technology (H.264/MPEG-4) have allowed higher data rate HD signals to be transmitted within normal DVB-T channels, at a lower order of modulation, such as QPSK or 16 QAM. This results in more robust receive signals.
Remote camera control
One limitation of wireless cameras has been remote control operation versus their wired counterparts within the production process. While there have been a few camera control options available, these systems have had many feature limitations because they communicated from the remote panel, directly to the camera, without any provisions for bidirectional communication that would normally occur if the camera was wired. This resulted in limited availability of remote control functions, such as iris and pedestal/color gain.
Today, remote wireless camera control systems exist that feature bidirectional communication between the remote panel and the camera. Such systems allow remote operators to have access to every feature that the camera and/or remote panel is capable of, including the use of the camera manufacturer's own panel, instead of using a generic remote control panel.
These technical advancements have allowed wireless cameras to seamlessly integrate into many applications that traditionally were only achievable with wired cameras.
Applications
Both home viewers and live spectators of today's sporting events want to get into the game as much as possible. Better graphics, more statistics and additional camera angles have been added to enhance the production value of the event, thus enhancing the overall viewer experience. However, the means to gather these additional camera angles can create logistical and/or technical challenges.
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