Jeremy Hendy, Vice President of Sales and Marketing at Nujira explores how digital transmitters are receiving energy efficient benefits through innovative envelope tracking technology for the broadcast industry.
Energy efficiency is one of the primary design challenges for the $500M broadcast transmitter industry, with transmitter energy costs accounting for 75 percent of the energy bill and carbon footprint for a typical broadcaster.
Digital Terrestrial TV and Radio broadcasts are significant energy consumers, but today's state-of-the-art transmitters operate at only 25-30 percent energy efficiency, with the majority of the energy wasted in the form of heat dissipation.
As new equipment is expected to be in service for 25 years or more, broadcasters are increasingly focusing on energy efficiency and Total Cost of Ownership as a key buying criteria. As a result, an enabling technology known as Envelope Tracking (ET) has come to the fore.
Why Envelope Tracking?
ET technology provides a step change in transmitter efficiency, enabling OEMs to make an efficiency leap of more than 15 points, corresponding to a 35 percent reduction in energy costs and carbon emissions.
Using ET, the power consumption of a 5kW DVB-T transmitter can be reduced from 25kW to 16kW, giving an annual energy cost saving of around $12,000, and reduction in CO2 emissions by around 100 tonnes.
A 400W Envelope Tracking technology demonstrator has been introduced by Nujira for the Digital TV and Radio markets. The transmitter delivers an output stage efficiency of 45 percent for DVB-T OFDM signals over the majority of the UHF band. The ET solution replaces the fixed voltage DC:DC converters used in today's transmitters, and dynamically modulates the supply voltage to the PA device to track the amplitude of the signal.
By maintaining the PA in compression over the entire dynamic range of the signal, rather than just at the peaks, the energy efficiency is maximised.
The power modulator modules deliver improved power efficiency for most digital broadcasting standards, including DVB-T, DVB-T2, ATSC, ISDB-T, DVB-H and DAB, at frequencies from VHF to 2.6GHz or more.
The technology demonstrator, which is a compact 2U-high liquid-cooled rack, incorporating the company's Ultra High Power ET modulator has been developed for high-power air- or liquid-cooled broadcast transmitters. The demonstrator also incorporates 50V LDMOS PA devices, a commercial RF driver, and low-loss RF combiners and splitters.
Measurement results are achieved using adaptive Digital Pre-Distortion algorithms and a DVB-T signal with 8.0dB Peak-to-Average Power Ratio. The frequency range of the technology demonstrator is 450-750MHz.
In addition to reducing the broadcast network operating costs (OPEX) directly, efficient transmitters enabled by ET also have an impact on the capital cost (CAPEX) of installing the transmitter. Specifically, efficient transmitters require much less cooling and also enable the use of smaller back-up power supplies.
Cooling is a major concern for broadcasters for a number of reasons. Firstly, all forms of forced cooling involve moving parts in one form or another (fans, pumps, etc.) and other items such as filters that require regular maintenance. Secondly, mechanical noise can be a concern in many urban transmitter locations: some countries are already starting to pass legislation to control noise levels at such sites. Finally, the cooling plant increases the equipment required on-site and, hence, site rental costs.
Although lower-power transmitters can use air-cooling (either with or without air-conditioning), higher power (or less efficient) transmitters, as required for digital TV broadcast require water-cooling, incurring further cost and complication. Furthermore, as power density increases, a higher proportion of power is required for cooling, adding to the OPEX.
Poor PA efficiency also affects the on-site backup power supply. Higher transmitter power consumption necessitates either larger battery packs or larger diesel backup facilities, both of which again push up equipment and site costs.
It can be seen, therefore, that poor PA efficiency has a significant impact not just on the design of the transmitter itself, but also the cooling and backup facilities required on site, impacting both initial costs (CAPEX) and also long-term operational costs (OPEX). The overall impact on the total OPEX spend of poor PA efficiency is shown in diagrammatic form in Figure 1.
ET delivers attractive efficiency benefits over a wide band of frequencies, and is seeing growing adoption in the broadcast industry. Its benefits are independent of the digital broadcasting standard and broadcast frequency.
The renewal of the global television and radio transmission infrastructure to support the digital switchover and bring new services, creates a real opportunity to use the newest technologies to optimise energy consumption and reduce carbon footprint.
In doing so, broadcasters will reduce the impact of future energy price rises and achieve a measurable return on investment through operating cost savings today.