LONDON — The BBC DAB network is one of the largest in the United Kingdom, covering more than 97% of the UK population.
With rising operational costs and a mandate to cut carbon emissions on U.K. terrestrial platforms by 28% by 2030, the BBC and Arqiva proposed an approach focusing on “good enough” broadcast quality rather than peak performance. This strategy could potentially optimize energy consumption, reducing operational expenses and significantly shrinking the network’s carbon footprint.
Traditionally, radio stations aim for maximum broadcast performance, prioritizing coverage quality without accounting for the energy cost of maintaining peak performances. The BBC and Arqiva’s approach, detailed in a paper presented at the IBC2024, flips this model by identifying a sustainable balance — optimizing transmitter efficiency by reducing the Modulation Error Ratio to more energy-efficient levels without compromising the audience experience. The MER is a crucial metric indicating the quality of a digital signal: the higher the MER, the higher the quality of the received signal. However, a better MER requires higher power consumption.
Arqiva and the BBC investigated whether slightly reducing their MER standard level could achieve noticeable power savings without compromising reception quality. Their idea was to limit the supply voltage to the transmitter’s power amplifiers, thus lowering heat dissipation and, therefore, power consumption. This way, the transmitter would continue operating as usual most of the time. At the same time, it would no longer be able to faithfully cope with signal peaks, thus introducing distortion into the transmitted waveform and reducing the MER.
BBC and Arqiva rigorously tested the effects of reduced MER on reception quality through extensive lab simulations. The question was whether the promising results would be reflected in the field.
The BBC’s DAB network includes over 400 transmitters, installed over several years with different technologies. A careful analysis of the network assessed which transmitters could benefit from the proposed MER reduction to 20 dB, thus granting noticeable power savings.
Balancing quality and efficiency
The base for field tests was an operational DAB transmitter site at Clun in the West Midlands region. This transmitter operates within the BBC UK national SFN network with 600 W effective radiated power; its relevant coverage area includes rural roads and village buildings.
Researchers evaluated reception performance through a series of drive tests in the expected coverage area, including assessing edge-of-coverage and transmitter overlap conditions due to SFN operation. They sequentially configured and tested three MER configurations: the standard MER level of 25 dB, representative of the existing network configuration; the candidate reduced level of 20 dB; and, for test purposes, a significantly reduced level of 15 dB.
The configurations were tested in three reception scenarios: strong dominant single-transmitter coverage, edge-of-coverage single transmitter and transition into an overlap area with multiple transmitters. Each field test scenario was completed by multiple drives along the selected routes for the three different MER configurations.
BBC and Arqiva found almost no measurable difference among the three transmitter MER configurations for scenarios with a dominant, strong single transmitter and an overlap of up to six transmitters. However, they recorded minor differences at the edge of the SFN coverage.
The overall measurement results prove that the difference in reception performance when moving from a MER level of 25 dB to 20 dB is hardly noticeable, comparable to the variability between different drives on the same road. Subjective listener comments showed that the difference between the two MER levels was not perceptible. The change from 25 to 15 dB was slightly perceptible at the extreme edge of coverage locations as a boundary condition. So, reducing the MER to 20 dB appeared as a viable solution.
A pathway to energy reduction
The BBC’s DAB network includes over 400 transmitters, installed over several years with different technologies. A careful analysis of the network assessed which transmitters could benefit from the proposed MER reduction to 20 dB, thus granting noticeable power savings. However, depending on the transmitter design, the changes to the power supply arrangement could require extensive site-by-site modification. The overall benefits could, therefore, be negligible.
The evaluation highlighted that reducing the supply voltage to the transmitter’s power amplifiers best suits the modern Doherty design. This modern type of transmitter can be remotely optimized, saving transmitter site visits and implementing it without further carbon costs. Known for their improved efficiency over traditional transmitters, Doherty-designed transmitters can operate at over 40% overall efficiency, while older systems hardly reach 20%.
The BBC’s DAB network has about 165 Doherty-designed transmitters, which consume approximately 2.3 GWh of energy annually.
While speaking at the IBC2024, Phil Kesby, technology consultant at Arqiva, said that the Doherty transmitters optimization will be fully rolled out in 2024, and that the subsequent expected savings are estimated to be approximately 0.3 GWh/year on the entire BBC DAB network: this equates to a 14% improvement in the overall transmitter system electrical efficiency, at nearly no cost.
Furthermore, this energy-saving adjustment supports net-zero targets and cuts operating costs, a key advantage as energy prices rise and funding for public broadcast infrastructure becomes more limited.
The BBC and Arqiva’s DAB network optimization demonstrates that sustainability doesn’t have to come at the expense of quality. By focusing on a “good enough” strategy, they have cut costs, lowered emissions, and championed energy-conscious innovation in broadcasting.
After receiving a Master of Science in Engineering, the author worked for Telecom Italia and Italian public broadcaster, Rai. Based in Bergamo, Italy, he now spends his time as a broadcast consultant for radio stations and equipment manufacturers, specializing in project management, network design and field measurement.
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