High-Efficiency Power Amplifier for LTE/W-CDMA System

Long Term Evolution (LTE) systems are attracting attention as next-generation mobile communication systems. Such systems have come to transfer and manage large volumes of data at high speed. Therefore, base stations have urgent requirements for devices that are friendlier to the environment, easier to install and cheaper to run. Further, there are needs to reduce size and power consumption. This can be done with the overlay service which supports both W-CDMA and LTE systems, and which uses antennas that are employed in the conventional 3G service and thus allows system introduction costs to be reduced. Conventional mobile communication systems are composed of a baseband portion and a radio frequency (RF) portion installed in the same building. In recent systems, the RF portion of more and more devices is housed in an outdoor case separate from the baseband portion, and they are connected with an optical fiber. This type of RF unit is generally called a remote radio head (RRH) device. The RRH is also known as remote radio equipment (RRE). Fujitsu has developed multimode technology RRE which supports W-CDMA and LTE for NTT DOCOMO. To achieve small devices with low power consumption, the efficiency of the power amplifier (PA) has been improved by adopting digital pre-distortion (DPD) and GaN Doherty PAs. This paper describes the principle, methods of operation, characteristics and configurations of such devices.