Koji Matsuyama

A burst GFSK-modem for wireless LAN systems

In this paper, we present a GFSK modem for use in spread spectrum wireless LAN systems. The proposed digital GFSK modem includes open loop automatic frequency control (AFC) to capture burst data completely. The transmission rate is 1 Mbps. It uses a frequency discriminator for detection and an A/D converter for digital processing. We explain the configuration and the operation of the GFSK modem and show the experimental BER and AFC performance results. The AFCs performance was evaluated for frequency offsets in both static and Rayleigh fading environments. We found that our demodulator with AFC synchronized within 8 symbols when the frequency shift was more than /spl plusmn/240 kHz. A digital GFSK modem circuit can be fabricated as a digital integrated circuit using only 3,000 gates.

A pi /4-shifted DQPSK demodulator for a personal mobile communications system

A digital 384-kbps TDMA-TDD microcellular system using pi /4-shifted DQPSK modulation is under development in Japan. To simplify the demodulators configuration using this system and to reduce its power consumption, the authors propose a pi /4-shifted DQPSK demodulator that includes what they call an arctangent differential detector (ATN-DD) and an arctangent automatic frequency controller (ATN-AFC) because they process the phase of the received signal rather than the quadrature components. They present the configuration and the principles of operation of the ATN-DD and the ATN-AFC and show the results of BER and AFC performance testing. In addition, they investigate the most suitable AFC structure. Their study enabled a differential detector and AFC circuit gate-count reduction of more than 60%.<<ETX>>