Bill Hayes /
04.01.2013 09:00 AM
The BBC’s Hybrid System for EFP
Could the network’s MIMO initiative double channel capacity?
The BBC demonstrated its prototype hybrid MIMO-based electronic field production system at IBC last September.
JOHNSTON, IOWA— Last month I spoke at the IEEE Broadcast Technology Society’s Second Annual Graduates of the Last Decade Workshop, in Cagliari, Italy. The focus of the program was next generation broadcasting, a topic that is very near and dear to me, since, in addition to my participation in BTS, I am also involved in groups from ATSC, SMPTE, NAB and FoBTV that are all working in this arena. While the presentations from the program looked primarily at distributing content to consumers, there was one from Peter Moss of the BBC’s R&D group that offered a little extra.

MULTIPLE INPUT, MULTIPLE OUTPUT
Peter’s talk was titled “MIMO Technology in Broadcasting—and an application in Programme-making,” and it is the application in program-making that I wanted to look at. MIMO, which stands for “Multiple Input Multiple Output,” requires at least two transmit antennas and two receive antennas, and the idea is to take advantage of multiplexing gain, diversity gain or both to improve channel capacity. If you look at the channel capacities of existing systems you can see that conventional broadcasting services using a single transmitter/antenna and the most sophisticated coding and interleaving techniques are very close to the Shannon limit. So even if major changes are made in the methodologies, the improvements are small—in theory, we have reached the point of diminishing returns. What Peter’s presentation demonstrated was that, by using MIMO techniques and some clever coding and optimization, channel capacity can be increased significantly, perhaps doubled!

So what has this to do with field production? Well, when we consider that the spectrum crunch is not just about the UHF band as the CTIA’s recent letter to the FCC suggested, yet another reduction in the BAS allocation could be in the offing. Not long ago we retooled our 2 GHz EFP services to reduce the amount of spectrum within the band and the size of individual channels. Spectral efficiency is now (and will continue to be) a driver as we move forward in time. The BBC project looked at applying these same RF techniques and some the techniques described in the developing DVB-NGH (next-generation handheld) standard to develop a high-definition wireless camera that used half the bandwidth of an existing 2 GHz channel. In their case this was reducing the bandwidth from 10 to 5 MHz while maintaining a 20 Mbps data capacity. For the experimental system, the engineering team at BBC were able to “cherry pick” some technologies out of the existing DVB-T2 system, as well as MIMO models from DVB-NGH.

For me the most interesting and intriguing part was using quad polarization for the MIMO transmission. As I understand the system, they created a 4x4 MIMO system using linear polarized antennas (horizontal and vertical)— which we are familiar with from traditional terrestrial broadcasting— combined with circular polarized (right-hand CP and left-hand CP) that are more typical in microwave and satellite systems. This hybrid transmission and receive system not only improved data capacity but also reliability in challenging environments.

The prototype system was demonstrated at the IBC last year, and I have heard nothing but good things about it. While this particular implementation is on a camera-mounted 2 GHz transmitter, there doesn’t appear to be any significant reason why the same techniques could not be applied to 7 GHz or higher frequency systems and with some clever antenna design work, perhaps applied to vehicle or helicopter mounted ENG systems as well.

REVISITING OFDM
Since the development of this system is occurring in the U.K., the underlying modulation technology is COFDM, 16QAM in this case. However, suggesting another look at OFDM is not the heresy that it appeared to be 20 years ago as the United States was moving toward the introduction of a digital television standard. Many of the groups looking into the next generation or terrestrial broadcasting services are revisiting the concept of an OFDM-based system to reach an audience that is considerably more mobile than they were in the past.

I confess that when I first heard about the development of DVB-NGH, I was also hearing about European countries shutting down their DVB-H infrastructure due to a lack of consumer interest. It gave me considerable pause as the U.S. was just starting to roll out the ATSC mobile service after developing and approving a standard at a speed not seen before. I think one of the things that this work has indicated to me is that we may eventually be looking for a broadcast standard that doesn’t differentiate between whether the receiver is mobile or fixed.

Producing HD content, whether for high-end programming or newsgathering, is what the audience expects and the BBC’s “halfRF” system would seem to be a contender for allowing more flexibility in how the work gets done. Peter Moss pointed out that, while the system is still under development, the BBC did actually use the camera on the “One Show, Christmas” special. The camera was set up to view some reindeer, and while it may not have been the camera of choice to jump out of a helicopter with James Bond and the Queen, reindeer are an important star in most Christmas programs, so they obviously have faith in the technology.

Bill Hayes is the director of engineering for Iowa Public Television.



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