LONDON — Almost all mobile network operators now include in annual reports and on their websites worthy statements, usually in sections touting their corporate social responsibility, about what they are doing or plan to do to reduce the energy costs of running their basestations.

The operators are beginning to take the issues almost as seriously as how to solve the more consumer-oriented problem associated with battery-life and power drain on handsets.

The increasing emphasis on energy savings, more and more wrapped round a desire to be seen as being good corporate “green citizens”, is not wholly altruistic, as energy use equates directly to costs. Running radio networks is getting more expensive and difficult, due to increasing energy costs in developing countries and sheer availability of electrical power in emerging markets.

As operators increase the number of basestations in the infrastructure, so that they can offer third generation networks, wireless services at broadband data rates, power consumption is set to continue to rise.

Operators are therefore looking to equipment suppliers to help them improve basestation efficiency and for the development of more efficient power amplifers and a reducing requirement for blown air and air conditioning in basestations.

Vodafone, for instance, has said it wants to see a 33 percent improvement in the energy efficiency of new network equipment by March 2008, compared to a 2006 baseline. Recent studies indicate that radio networks account for about 80 percent operators’ electricity usage, so there are plans to introduce software controls to minimize the power used for cooling, and turn off selected base stations at non-peak times, while maintaining coverage and capacity.

The hefty power amplifiers (PAs) in basestations account for about half the power they use and generate large amounts of heat, according to Tim Haynes (right), chief executive officer of Nujira Ltd. (Cambridge, England). In particular, current 3G basestations are inefficient partly due to standard-specified use of linear RF power amplifiers.

On average, each fully loaded 3G cell site using traditional PAs is estimated to need 3 kW of power, equating to a cost of some $1,600 a year for a US-based operator, or €2,300 (about $3,200) for an operator in Europe buying electricity at about double the cost of their U.S counterpart. Thus, suggests Nujira, for a typical European operator with a network of 20,000 basestations, the total energy consumption on the same basis would be 58MW (equivalent to a large wind farm) resulting in annual electricity costs of €45 million (about $62 million).

As well as these costs, such a level of consumption is estimated to lead to a carbon footprint of about 11 tonnes of carbon dioxide for each cell site, each year.

Haynes says the latest generation of “Node Bs” starting to be deployed could halve the above figures but that bolder solutions are needed.

“There is no doubt we can make significant impact here with the type of PA modules we have developed, based on our High Accuracy Tracking (HAT) technology, which involves adding a supply voltage modulator and drive software to the processor in a PA,” Haynes said.

HAT is set to become the first commercially available variant of a technique known as “Envelope Tracking”, where the bias voltage of the PA is changed dynamically to ensure that the power output transistors remain in the best possible part of their operating curve, which means they can make a major contribution to improve energy efficiency.

Nujira has spent five years developing the modulator and designing optimum ways to deploy it in a PA architecture, and the company says use of the technology can improve the efficiency of linear amplifiers used in W-CDMA systems from typically around 15 percent to nearer 50 percent.

“We are now producing hundreds of units and sampling major OEM suppliers. The HAT technology is in the early stages of being trialed in networks and we anticipate the first OEM customer will start production of gear using our technology in the second quarter of 2008”, Haynes said. Haynes declined to reveal the names of the eight customers Nujira has attracted so far, except to say, “most are Tier 1 infrastructure suppliers and active globally.”

Haynes adds PAs using the new HAT modulator technology will not only improve power efficiency, but have significant knock-on effects on overall basestation design.

HAT technology can be used in any frequency band and with most modulation schemes, including OFDM-based ones that will be used in mobile WiMAX and the Long Term Evolution version of 3GPP networks such as GSM and W-CDMA. The technique is also applicable for use with a range of RF device process types, working equally well with GaAs FETs and HBTs, silicon LDMOS and GaN.

The potential for such basestation architecture improvements has been helped by the development and definition within the Open Basestation Architecture Initiative (OBSAI) of an interface at digital baseband, between the baseband card and the RF transceiver module, known as the RP3 interface.

“This has been a real enabler, perhaps a catalyst, to novel power efficient modules, and has really opened up free market competition in the RF module area”, said Peter Kennington (right), technical chair of the initiative which counts amongst members most silicon and module makers for basestations as well the leading wireless infrastructure players and operators.

Kennington, who also acts as a consultant, said some companies are looking at switching amplifier techniques instead of linearization , similar to the Class D digital amplifiers now coming in to use in the audio world, while other groups are betting on multi-element steerable antenna arrays or patch antennas to solve the problem of cooling and power efficiency.

Steerable arrays could be deployed to reduce RF losses associated with current generation PAs and the amount of cabling necessary in existing base-station design, said Kennington. “Some of these techniques are perhaps a year away from becoming a reality and the relatively small companies now have the confidence their technology could make it because of the ease with which OEMs could test and deploy the technology because of baseband-RF interface devised by OBSAI.”

However, Kennington said the operators are wary of extra cost and have yet to be convinced the costs involved deploying some of these technologies are justified by the power efficiencies promised.

“It has long been the case that operators are unwilling to pay for the extra even if they see the opex and capex business case, but continue to beat OEMs over the head for not achieving sufficient energy saving efficiencies. They have been seeing incremental improvements over the past five years and to some extent use these savings to pay lip service to their efforts in this area to achieve really significant improvements.”

Chris Larmour, chief marketing officer at mobile network optimization specialist Actix (London, England) agreed. “Some operators, particularly in the developed markets, are genuinely doing their bit, but in general the sector could do a lot better and are not really embracing the opportunities for reducing their costs and thus improving the environment. In developing countries, they have no political pressure to act at all on the green aspects of site reduction.”

“Energy usage is actually increasing, which is not surprising in view of the extra capacity being installed. And infrastructure suppliers are even suggesting there is a business case for replacing a mobile network on energy savings alone. But for operators the near term business model remains what it has always been: revenue minus cost equals profit.”

In a recent report, Actix suggests that large operators such as Deutsche Telekom report energy consumption levels approaching 3,000 GWh, causing some 1.6 million tons of CO2 emission annually. Worryingly, the report suggests that the mobile network energy consumption of an estimated 61 billion kWh worldwide, with each of the millions of basestations producing nearly 10 tonnes of carbon emission a year, will get much worse, and possibly double by 2011.

Larmour admits Actix found the green issue almost by accident and continues to offer the benefits, through a range of optimization programs and network planning projects that allow an operator to reconfigure the design of a radio access network that for instance allows it to turn off some cell sites, as a part of an overall optimization scheme. “It turns out that for 3G at least, turning off some sites and changing some antenna direction can even improve capacity, but that is not the case for GSM,” says Larmour.