I chaired a session on green basestations at the NGN and Basestations conference in Dallas in December. The attendance was good, and there’s a lot of thought in the industry going into making more earth-friendly basestations. The panelists included Steve Wang, VP of Taiwan Mobile, Peter Jarich, research director of Current Analysis, Tony Bell of Nokia Siemens Networks, and Bob Sobieck, director of engineering of Cellcom. Here are some of the session’s highlights.

The Objective

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There are about 270,000 basestations in the U.S., with a similar number in Europe and another slew of them in Asia, South America, and Africa. I have never seen a total number, but I guess it must be something like a million worldwide. Wang estimates that telecom overall including wireless contributes about 3% to the annual GDP, but its carbon contribution is only about 1%. Not huge as things go, but any reduction would be a step in the right direction.

The greatest rationale for greening up is money. Most basestations eat a considerable amount of power, and that energy cost is a huge part of the operating capital of cellular carriers. Reducing that power consumption puts more profit on the bottom line and helps improve the environment. However, making those changes is not easy or fast.

Yet most carriers are thinking along these lines, and progress is being made. It is estimated that the number of worldwide cell-phone subscribers approached or just topped 4 billion at the end of 2008. That means more basestations to deal with the service requirements and an even greater expenditure of energy. Growth is definitely in conflict with any green initiative. Clearly, this is a problem to solve.

Saving money is the main benefit, with newer and more efficient equipment for 4G technologies. Other good reasons for going green include an improved company image and goodwill as well as preparation for future regulatory obligations. However, Wang said that even if basestation efficiency was greatly improved, a reduction in total energy might not occur simply because of the growth in the industry and increasing usage.

Key Problems

The main power hogs in a basestation are the air conditioning and heating systems and the transmitter power amplifiers. In most cases, the equipment has to be cooled, and a huge portion of the power consumption goes to air conditioning. While all the equipment produces heat, the main contributors are the power amplifiers.

Since most basestations support multiple wireless technologies that require highly linear power amplifiers, inefficiency is inherent. Most basestations use class AB amplifiers of some sort with efficiencies typically less than 30%. New designs using techniques like pre-distortion feedback compensation have helped in this regard, but not all basestations have adopted these more efficient methods.

An interesting part of this problem is the enormous amount of power lost in the transmission lines. Most of these lines are large coax cables with huge losses between the amplifiers and the antennas on top of the tower. Coax is the only practical feedline, but at high UHF and microwave frequencies, attenuation is many dB. As a result, the power amps need to operate at higher wattages just to overcome the cable losses and emit the power needed to cover the site’s territory.

One promising technique is to put the power amps on top the tower with the antennas and feed them with the low-level digital inputs via fiber-optic cable. That alone would greatly minimize the power needed and wasted. Some carriers are fighting this approach but will no doubt succumb to its sheer efficiency improvement.