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How Green is Your Base station?
Peter Kenington, Technical Chair
- OBSAI Up until recently, the term ‘green’, when applied to an organisation or an individual, would have brought to mind characteristics such as naivety or inexperience (as in: ”you’ll have to forgive him, he’s a bit green”). In the environmentally conscious age in which we now live, being seen as ‘green’ is the height of praise for an organisation and most now strive to be seen as such by their customers. In the communications sector, it is necessary to be every bit as vigilant as in higher-profile carbon-emitting industries, such as transport or power generation, if the mobile operators are to be seen to play their part in tackling these environmental issues. Base-station efficiency, in particular, has been the subject of much recent debate in the industry – not least amongst the operators, who are increasingly conscious of their environmental impact and the emphasis placed upon this by lobby groups and consumers.
One example of this trend is the substantial part of operator O2’s website which is dedicated to the environment, environment issues and climate change – this would not have been the case a few years ago. You probably knew, for example, that phone chargers use electricity even when they’re not connected to a mobile phone, however you probably didn’t know that the impact of this laziness or carelessness is an additional 50,000 tonnes of CO2 each year in the UK alone[1]? O2 are not the only operator to be concerned for the environment and this concern is being reflected more widely across the mobile industry.
Environmental concerns are increasingly evident in an operator’s procurement policy for its base-station equipment: energy efficiency has gone from a largely ‘don’t care’ issue to one of great importance; likewise for base-station size and consequently the amount of material used in its manufacture.
One significant enabler in this area is the advent of open standards for base-station equipment and the OBSAI (Open Base-Station Architecture Initiative) standard in particular. In defining an interface at digital baseband, between the baseband card and the RF transceiver module in a base-station (known as the ‘RP3’ interface), OBSAI has enabled a new generation of power-efficient modules to be created. Perhaps more importantly, it has opened up free market competition in the RF module area and this is helping to drive up efficiencies and thereby to drive down power consumption and the overall carbon footprint of a base-station transceiver system (BTS). Techniques such as digital predistortion have now largely replaced feedforward in modern base-stations and this has been enabled by OBSAI’s adoption of a digital baseband, rather than an analogue RF, interface to an RF module; digital predistortion is typically more efficient than feedforward as a method of meeting the required spectral emissions requirements in a transmitter.
Improving power efficiency has a number of knock-on environmental benefits for the base-station as a whole. Improved efficiency leads to a removal of the need for air-conditioning systems, which further reduces power consumption.
Improved efficiency also leads to a reduction in the battery back-up requirement. Together these reduce or eliminate the need for some environmentally-unfriendly materials, such as refrigerant gasses, lead and sulphuric acid.
Finally, a BTS with a reduced battery size, smaller heatsinks, fewer fans and no air-conditioning is physically smaller and requires fewer materials to construct and house. This helps to reduce costs as well as having obvious environmental benefits.
To give some idea of the environmental benefits of improved BTS efficiency, Nokia Siemens Networks recently released details of the environmental benefits of their Flexi BTS family, which utilises OBSAI interfaces internally. When compared with typical previous-generation WCDMA base-stations, the power reduction claimed for the Flexi BTS is 60%. Based on the number of WCDMA base-stations installed globally by the end of 2005 and a typical usage pattern over 24 hours, this corresponds to an annual saving of 230MW. This translates to an annual reduction in CO2 emissions of 740,000 tons. A further 60,000 tons of CO2 is estimated to be saved from reductions in air-freight, through the 80% reduction in weight of the Flexi product.
So what will happen next? The use of a digital interface will continue to be a key enabler for efficiency-enhancing improvements in the transceiver space. It will allow, for example, switching transmitter and RF synthesis techniques to be employed; both of these would be far more cumbersome (and less competitive) if they had to be implemented as RF-input/output systems. The influence of OBSAI on this aspect of the marketplace, and on power efficiency in particular, will therefore be felt well into the future. If the term ‘green’ does retain its original (non-colour) meaning in the future, it will increasingly be applied to companies and individuals who do not embrace environmental issues – it is they that will be deemed naïve in the new commercial landscape.
Peter Kenington is the Managing Director of Linear Communications Consultants Ltd. and the Technical Chair of OBSAI. He can be reached at: pbk@linearcomms.com [1] Source: www.O2.co.uk
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