KDDI and Fujitsu Develop Practical-Use High-Efficiency Amplifier for Mobile WiMAX

KDDI Corporation, Fujitsu Limited, and Fujitsu Laboratories Ltd. have announced their joint development of a high-efficiency amplifier applicable for mobile WiMAX (IEEE 802.16e-2005) which offers industry-leading levels of power efficiency. The new amplifier is a result of joint development efforts which Fujitsu and KDDI started in May 2006 to develop a mobile WiMAX-applicable high-efficiency amplifier.

Background of Development and Results
In order to reduce costs required for infrastructure and operation in preparation of implementing a mobile WiMAX system, KDDI has been exploring ways to make base stations smaller and more energy-efficient. In particular, amplifiers dictate the performance of base station equipment. High-efficiency amplifiers can enable various benefits for base station equipment such as downsizing, lighter weight, greater power efficiency, less noise, and moving closer to becoming maintenance-free. Improved efficiency of amplifiers will also make it possible to realize downsizing and lower cost of infrastructure that is collateral to base stations, such as equipment for power sources and air conditioning.

Using a gallium-nitride(1) (GaN) HEMT(2) device that was developed by and later further enhanced by Fujitsu Laboratories, by optimizing the design of the amplifier circuits for higher efficiency and making modification improvements to its digital pre-distortion technology(3) which already has a proven track record in 3G systems, Fujitsu succeeded in developing a prototype transmitter amplifier that achieves power efficiency of roughly 30%(4) with 25 watt (25W) power output at 2.5 gigahertz (2.5GHz) operational frequency band, which is double the level of conventional amplifiers(5). The development of this prototype paves the way for practical use of GaN HEMT-based high-efficiency amplifiers.

Anticipated Benefits and Future Developments
The deployment of this new amplifier technology is expected to reduce the size and power requirements of outdoor base stations by roughly half compared to conventional amplifiers, enabling a significant reduction in equipment space requirements and the downsizing of back-up batteries, and thereby making a major contribution to reducing the costs of constructing base stations for mobile phone carriers when they begin to deploy mobile WiMAX.

Fujitsu is proceeding to strive toward enabling the practical use of the new amplifier for mobile communication base stations including for mobile WiMAX mobile communication base stations. From this year, in addition to embedding the new power amplifier into systems, Fujitsu plans to initiate a standalone business for power amplifiers.

Glossary and Notes
1 Gallium nitride HEMT: A gallium nitride (GaN) semiconductor is more resistant to breakdown due to electrical fields than conventional semiconductor materials, such as silicon (Si) or gallium arsenide (GaAs). When used in a HEMT structure, it enables high-speed operation at high voltages.

2 HEMT (high electron-mobility transistor): A field-effect transistor that takes advantage of the fact that electrons at the junction between two different compound semiconductors move more rapidly than when they are within conventional semiconductors. Fujitsu led the industry by pioneering development of this transistor structure in 1980.

3 Digital pre-distortion technology: Distortion compensation technology in which a signal that can offset the distortion generated by an amplifier is added in advance to the amplifier's input signal.

4 Power efficiency of roughly 30%: Refers to efficiency for OFDM-16QAM signals.

5 Double the power efficiency of conventional amplifiers: Refers to comparison of amplifiers that are used with currently available 3G systems.