Hideto Furukawa

A digital signal processing demodulator with a wide frequency acquisition range

A demodulator capable of variable baud rate (f/sub b/) operation satisfies the requirements for a forward error correcting decoder for satellite communication systems such as VSAT systems. A new method of frequency acquisition, called swept automatic frequency control has a wide f/sub b/-independent acquisition range and prevents false locking of the carrier recovery circuit. The authors have evaluated such a demodulator and confirm that it performs satisfactorily.<<ETX>>

New OFDM Channel Estimation Method by Adding a Virtual Channel Frequency Response

A discrete Fourier transform (DFT)-based channel estimation method which exploits outside of the active frequency band is proposed for orthogonal frequency division multiplexing (OFDM) systems. Usually the DFT-based channel estimation method is degraded due to leakage from non-sample locations of the multi-path timing. In the proposed method, an additional virtual channel frequency response is added outside of the active frequency band so that the total channel frequency response is smooth and periodically continuous in the DFT size. This method decreases the leakage effect in the time domain, and therefore has better performance than conventional time domain methods. Simulation results show that the mean square error and block error rate performance of the proposed method is greatly improved, especially in high signal-to-noise ratio regions, for example, MIMO 4times4,16QAM, R=8/9.

Evaluation of New NLMS and RLS Chip Equalizers using Tentative Decision Data for HSDPA Systems

Equalizers are currently being studied to improve the performance of wideband code division multiple access (WCDMA) downlinks. Especially for high data rate wireless systems (e.g. high-speed downlink packet access (HSDPA)), reduction of multiple access interference (MAI) and inter symbol interference (ISI) are key issues. We propose a new chip equalizer using tentative decision data and show that it has a high throughput performance for HSDPA systems. The normalized least mean square (NLMS) algorithm or the recursive least square (RLS) algorithm is used as the adaptive algorithm for the equalizer because these equalizers are well known to have lower complexity than the maximum mean square error (MMSE) equalizer. In the proposed method, high-speed physical downlink shared channel (HS-PDSCH) data is tentatively determined and used as a training signal to add to the common pilot channel (CPICH). In this paper, we show that the proposed equalizer has a good throughput performance compared with the conventional equalizer, and that the proposed RLS equalizer has a throughput performance that is approximately 73% of the ideal MMSE

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>>