Toru Maniwa

A highly efficient adaptive digital predistortion amplifier for IMT-2000 base stations

We have developed the worlds most compact, energy-efficient transmitter amplifier for IMT-2000 base station systems that uses an adaptive digital predistorter (DPD). The power efficiency is improved by reducing the output back-off (the margin from the saturation point) of power amplifiers and by suppressing the resulting increase in nonlinear distortion with the DPD. This method uses a predistortion technique that estimates the distortion characteristics of amplifiers by using the least mean square (LMS) algorithm, and it adds a complementary signal to the digital baseband signal with a reverse-characteristic of the distortion. The power amplifiers we have developed achieve twice the power efficiency of conventional types. In this paper, we describe the DPD equipment and the experimental results of a DPD transmitter prototype. Currently, IMT-2000 base station systems equipped with the DPD are being shipped worldwide.

Low correlation antenna design for diversity handset applications

The design of compact diversity antenna for wireless handset applications has been presented. The results obtained demonstrate high potential of such a design for the handset antenna systems realizing various diversity techniques, such as switched diversity, maximal ratio combining and selection diversity. This antenna structure can also be utilized in a MIMO system, where the low mutual coupling between the antenna elements is required. It has been confirmed that the antenna radiation characteristics (radiation gain, directivity and total efficiency) satisfy the specification parameters being demanded for wireless handset applications.