Morihiko Minowa

Backoff improvement of an 800-MHz GaAs FET amplifier for a QPSK transmitter using an adaptive nonlinear distortion canceller

The use of a nonlinear distortion canceller (NLDC) with a Cartesian feedback loop to improve the output backoff of an 800 MHz GaAs FET power amplifier when a quadrature phase shift keying (QPSK) signal with a rolloff factor of 0.5 is applied is described. This amplifier module uses three GaAs FETs. The amplifiers saturated power is 31 dBm, and its maximum power-added efficiency is 50%. Excellent operation of the NLDC was confirmed within a backoff range of more than 4 dB. Within this range, the out-of-band emission was kept 55 dB below the center frequency level. Since the peak output power coincides with the saturation power at a 4 dB backoff, the NLDC improves the backoff to the theoretical limit.<<ETX>>

Cartesian feedback amplifier with soft landing

The author describe the results of several experiments conducted on a Cartesian feedback amplifier with soft landing. This amplifier uses a new method for adaptively controlling the local signal phase in a Cartesian demodulator. They tested the soft-landing Cartesian feedback (SLCFB) method in the 900 MHz band using pi /4-shifted QPSK modulation to determine its applicability for pocket terminals in Japanese digital cellular systems. They developed a smooth loop-gain control mechanism using a variable gain amplifier with an FET and a continuous phase-shifter control circuit for digital processing in the IF band. They showed that the SL-CFB method can maintain the optimum local signal phase in the demodulator. This method therefore solves the problem at applying CFB amplifiers. They adopted circuit configurations that are easy to incorporate into LSI chips so that the amplifier can be used in compact terminals. The results show that the SL-CFB amplifier is a promising candidate for developing highly efficient linear amplifiers, which are very important in digital cellular telephone terminals.<<ETX>>

Improved output spectrum of linearized class-F power amplifier for digital cellular mobile communications

Describes a class-F power amplifier with an amplitude distortion canceller for a cellular mobile communications terminal. The output spectrum of the power amplifier was calculated for a pi /4-shifted QPSK input signal. Calculated and measured spectra were in close agreement. Out-of-band emission of the power amplifier output spectrum is subject to both AM-AM and AM-PM conversion. The effects of AM-AM conversion can be mitigated by using an amplitude linearizer; however, AM-PM conversion is not compensated. Out-of-band emission levels were calculated as a function of AM-PM conversion to provide an estimation of allowable AM-PM conversion for a class-F power amplifier module. Calculations and measurement clarified that even a class-F power amplifier module having a phase variation of 10 to 15 degrees due to AM-PM conversion transmits a spectrum that satisfies the out-of-band emission standard.<<ETX>>

An indoor bidirectional message paging system with a pocket-size terminal using a direct-conversion FSK modem

The authors describe an indoor bidirectional message paging system which has good frequency utilization and serviceability. The trial system adopts microcells (with a zone radius of 50 to 100 m) and half-duplex communication using the carrier-sense multiple-access with collision detection access method in the 420 MHz band with an occupied bandwidth of 12.5 kHz and a transmission power of 10 mW, according to the Japanese RCR STD-3 standard. Messages of up to 64 alphanumeric or 32 Japanese (Kanji) characters can be transmitted from a pocket-sized mobile terminal using a direct-conversion FSK (frequency-shift keying) modem. The modem enables the size of the mobile terminal to be the same as that of the conventional message pager. The basic concept of this system can also be applied to future microcell public message communication systems.<<ETX>>

Field Experiment of High-Capacity Technologies for 5G Ultra High-Density Distributed Antenna Systems

In fifth-generation mobile communication systems (5G), it is necessary to significantly increase system capacity compared with 4G in order to accommodate rapidly increasing mobile data traffic. Cell densification has been considered an effective way to increase system capacity. However, severe intercell interference degrades the system capacity due to the increase of the line-of-sight environment between the transmission point (TP) and user equipment (UE). We propose large-scale coordinated multi-user multiple-input multiple-output (LSC-MU-MIMO), which combines joint transmission from all the TPs connected to a centralized baseband unit and MU-MIMO. We have investigated the downlink performance of LSC-MU-MIMO via both computer simulation and field experiments and showed that LSC-MU-MIMO can significantly reduce severe inter-TP interference and improve the system capacity of high-density small cells. In this paper, we introduce our recent field experiment results where reception antennas of UEs are mounted on a vehicle driving at speeds of 5 km/h to 40 km/h. We also compare distributed TP deployment with localized TP deployment when fixing the total number of transmission antennas.