TV-BAY August 13 issue 80

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Wireless systems for live events 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, it’s 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 Moore’s 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? Ask the experts 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? Stuart Brown, Broadcast Systems Director, Cobham Broadcast 58 | TV-BAY MAGAZINE: ISSUE 81 SEPTEMBER 2013 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. It’s relatively easy to make exaggerated claims about latency and/or encoding efficiency – often citing the encoder’s 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