Ask the experts: your questions on wireless camera systems

Stuart Brown

Author: Stuart Brown

Published 1st October 2013

by Stuart Brown
Issue 81 - September 2013
tv-bay talks to Stuart Brown, Broadcast Systems Director at Cobham Broadcast about your questions on wireless camera systems. What makes wireless camera systems a viable option now as opposed to only a few years ago?
When the COFDM modulation scheme was introduced over a decade ago, it revolutionised event coverage and newsgathering. It meant that digital wireless camera systems could be used for the first time to transmit non-line-of-sight digital signals, which gave producers complete freedom to go live from locations that were previously out of the question with wired systems.
However, its fair to say that early versions of such systems had drawbacks, which meant that the uptake got off to a staged and somewhat troubled start.
Although MPEG-2 served the wireless camera industry adequately for a number of years, the introduction of HD and its vastly increased bit rates put a lot of pressure on the availability of RF spectrum, which was already stretched. Some began to question whether going wireless was actually worthwhile.
Then along came H.264 encoding, which prompted users to take another look at whether H.264 encoding was, or could be made, viable for wireless camera systems. In their earliest manifestations, H.264 encoders were considered too large and power-hungry to be useful for wireless cameras.
However, like most technology advances that loosely follow a corollary of Moores law, encoders soon became far more compact yet more reliable and required less power, using as little as 10W. (If I may, we recently introduced a mini HD transmitter the worlds smallest that consumes only 7 watts!)
Problem solved, then?
At the time, not quite. The resolution of the size and power questions still left concerns over latency, which was a major issue with early versions of H.264 encoders. Such systems typically had latencies in excess of 500ms, which was wholly unacceptable for large multi-camera events because it caused very noticeable lip-sync issues when mixing cabled and wireless cameras. This problem was particularly acute for newsgathering applications because the addition of encoding delays on top of those already present in an SNG encoder and satellite hop made live two-ways very difficult. Fortunately, in the last few years, new encoding techniques have dropped latency to below 100ms, which has not only made H.264 encoding a viable option for wireless communication, but a preferred one.
Are all H.264 systems pretty much the same?
Not necessarily. While H.264 encoding for wireless systems has been widely adopted, it has to be said that not all H.264 encoders are created equal. Its relatively easy to make exaggerated claims about latency and/or encoding efficiency often citing the encoders response to test patterns as proof, only for the user to discover, too often during a live shoot, that the picture quality/encoding efficiency they were meant to achieve came nowhere near the stated claims when the system is used with real pictures. There have been instances in which a deployed H.264 system had to operate at MPEG-2 bitrates to provide acceptable picture quality. Whats the point in that? A well-engineered H.264 system should deliver at least a 30-50% efficiency improvement over a comparable MPEG-2 system. It is that level of efficiency that enables wireless camera systems to thrive. So, what should I look for in a wireless system?
Ive talked about some of the technical issues that have now been overcome, but there are practical considerations that need to be taken into account when deciding if wireless transmission is right for your operation. One of the most important is whether the selected wireless transmitter has a proven, demonstrable ability to recover quickly after loss of signal. This is what hampered so many early attempts at wireless transmission systems. They simply couldnt be counted on when the going got tough. During any deployment a camera is bound to stray out of range or suddenly de-power to indicate the need for a battery change. Both situations are particularly acute when you are in the field covering a live event. A wireless systems must be able to recover instantly and resume operation seamlessly, which, if carefully selected, they now do.
Ease of rigging is also an important factor. There are a number of wireless camera control systems on the market that take an all-in-one approach, meaning that a single unit is used to connect to a camera control panel and generate an RF control signal. This, however, can be an issue if an OB truck is parked some distance from the event (such as a car park in the basement of a stadium). This means that going wireless is difficult because you have to run long lengths of RF cable from the truck into the venue. However, its a given that the longer the length of cable, the greater the loss of signal, which in turn means that the RF power has to be increased to compensate. The problem with that is that it increases the overall RF noise floor, which will impair performance of other RF systems in use, such as talkback. It can even cause RF noise problems with the wireless camera system itself. In our case, we combat this issue by separating the RF unit from the data unit. They are connected using a standard audio circuit and can be separated by several kilometres if necessary. This ensures the RF unit is mounted at the optimum location, and RF power can be reduced as a result.

IP infrastructure is now common in modern OB trucks and is often used to route camera control signals, with all-in-one master control panels gaining favour. Our latest camera control system now has Ethernet connectivity as an option and our wireless camera receiver all have IP streaming in/out capability.
Frequency reuse is also very important because increasing demand for spectrum means that fewer RF channels are available. Our approach allows up to four wireless cameras to share the same 12.5 KHz bandwidth control channel, which has proven to be a substantial benefit to users.

Are there still technical hurdles to making wireless links reliable?
In short, no, not really. The introduction of advanced video compression standards like HEVC H.265 will inevitably benefit wireless transmission in live production. Whether the manufacturer admits it or not, all wireless systems have to trade a certain amount of bit rate to achieve extensions in range. The higher the picture quality required, the lower the achievable range. Its as simple as that. However, improved compression will enable better picture quality to be achieved at lower bitrates, so production teams will not only benefit from increased range at current picture quality thresholds, but improved compression will also enable the use of even higher picture quality settings (such as 1080p) without requiring a tightening of what we would consider normal wireless camera coverage circles. Basically, at normal thresholds you can extend your range much, much further, but if you are transmitting at the highest image settings, you wont have to worry about losing your signal if you cross from one side of the football pitch to the other.
Another important development in terms of wireless connectivity particularly for newsgathering is the ongoing change in satellite technology to meet the increasing desire to utilise Ka-band. Demand for traditional Ku-band access at times outstrips capacity, which can make it expensive. However, the development and deployment of a number of large, multi-transponder Ka-band satellites and Ka-band satellite networks is increasingly offering a viable and economic alternative to Ku-band.

What does the near-term future hold?
Encoders specifically engineered for high capacity broadcast applications that feature IP connectivity via 3G, 4G and LAN to ensure access to super-fast wireless 3G internet connections from even the most remote locations are now on the market and will be a major game changer. The ability to set up an IP-based newsroom and enable field reporters to get on air almost instantly, and wirelessly, is a massive benefit to producers.
Video-over-IP is also having an impact as a viable means of remote newsgathering due to substantial improvements in compression algorithms, encoding technology and wireless connectivity. This will enable the industry to develop even smaller and more economic transmission devices, which will allow journalists to cover news from just about anywhere they can physically reach.
The use of wireless technology by journalists in the field to quickly establish all the technology they need for a live broadcast, including a broadcast quality transmission path for live two-ways; the ability to control a camera remotely from the studio; perform file transfers; use a high capacity internet connection, have access to the base newsroom computer, and offer mobile phone access - all from a single unit will very soon bring live events to our screens - whether its the big one in our living room or the small one we carry around with us in ways and from perspectives we until recently never thought possible.

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