Botaro Hirosaki

An Orthogonally Multiplexed QAM System Using the Discrete Fourier Transform

An orthogonally multiplexed QAM (O-QAM) system is a multichannel system with a baud rate spacing between adjacent carrier frequencies; this property is desirable to digitally implement the system using the discrete Fourier transformation (DFT). This paper provides a novel digital signal processing method based on an N /2-point DFT processing in the O-QAM system. A complexity comparison between a digital O-QAM system and a digital singlechannel QAM system shows that the digital O-QAM system using the new method is more economical than the digitally implemented conventional single-channel data transmission system.

An Analysis of Automatic Equalizers for Orthogonally Multiplexed QAM Systems

A simple structure of a per-channel automatic equalizer for an orthogonally multiplexed QAM system is proposed and the performance is analyzed. It is shown that a dual automatic equalizer with T/2 -long tapped delay lines, where T is a period of individual baseband baud, can equalize not only the transmission channel distortions, but the timing deviations and demodulating carrier phase deviations. Despite its high efficiency, the orthogonally multiplexed QAM system has been regarded as overly costly. However, by using the dual automatic equalizer with fairly simple structure, the system is competitive with conventional single channel data transmission systems.

Advanced Groupband Data Modem Using Orthogonally Multiplexed QAM Technique

An advanced groupband data modem based on the orthogonally multiplexed QAM technique is proposed. Its performance is evaluated through experiments. In the proposed modem, data are transmitted by a number of orthogonally multiplexed parallel subchannels. Because of this orthogonally multiplexing parallelism, the proposed modem becomes more immune to Gaussian noises, impulsive noises, and channel distortions, compared to the conventional Class IV partial response VSB modem. Furthermore, the orthogonally multiplexed QAM modem retains high flexibility in multiplexing a variety of data terminals and in carrying out fallback operation to a wide range of data rates. Experimental results demonstrate the robustness of the proposed groupband data modem.

A Maximum Likelihood Receiver for an Orthogonally Multiplexed QAM System

A maximum likelihood receiver for an orthogonally multiplexed QAM (OQAM) system has been derived based on the mathematical structure of an OQAM signal. The resulting receiver provides the minimum variance estimates of carrier and timing phases under the disturbance caused by not only Gaussian noise but also random data. It has also been proven that the carrier and timing joint control system is asymptotically stable almost everywhere in a state space. The equilibrium points are where the parallel synchronization over all subchannels in the OQAM system is established. Simulations have been carried out in order to verify the maximum likelihood receiver performances, where 9600 bit/s data are transmitted over 750-2450 Hz voiceband with 8×8 staggered QAM signal constellations. It has been shown that sufficient eye opening is obtained under 10 Hz carrier frequency offset and 10-4timing frequency stability.

New Dynamism in the Manufacturing Industry: Value-Sharing “Monozukuri”

This paper describes value-sharing Monozukuri, in which a manufacturer and its users have a mutual partnership and exchange valuable information through a product and its services. Manufacturers make products and services by taking into account the usages and lifestyles of the users. In addition, the users may choose better products or better services, finding value in them often by thinking about why the manufacturers designed and made them the way they did. Based on experiences in manufacturing industries in Japan, the concept of value-sharing Monozukuri is presented. Such Monozukuri will contribute to all manufacturing industries as a new form of dynamism.

Suboptimal Maximum Likelihood Timing Estimator for a PCM Regenerative Repeater

This paper introduces a modified likelihood function and then provides the suboptimal maximum likelihood (SML) timing estimator which is applicable to PCM regenerative repeaters because of its structural simplicity. Since the SML timing estimator tracks a difference waveform balancing point, as opposed to its conventional maximum likelihood (ML) counterpart, which tracks a derivative waveform zero-crossing point, its performance is rather immune against channel phase distortion. Analyses and experiments are also presented to validate the SML timing estimator for timing extraction from a band-limited PAM signal.