Kazuki Maeda

Ultrahigh channel capacity optical CATV systems

Summary form only given. It is widely recognized that future CATV systems will require more channels to incorporate new services such as video on demand (VOD). Various CATV systems employing subcarrier multiplexing (SCM) techniques have been proposed, however these systems do not seem to have sufficient capacity for the VOD. In this paper, we show new approaches to ultrahigh channel capacity optical CATV systems using SCM technique and discuss performances of each.

Bit-error rate of M-QAM signal and its analysis model for composite distortions in AM/QAM hybrid transmission

In cable television (CATV) systems that deliver digital video services by employing a hybrid fiber and coaxial network, it is important to consider digital channel deterioration due to composite distortions, as well as the amplitude-modulation vestigial-sideband channel. Furthermore, it is essential to clearly estimate a digital channels quality in designing CATV transmission systems. However, there have been few studies on statistical models and an analysis method to estimate the bit-error rate (BER) of M-ary quadrature amplitude-modulation signals for composite distortions. This paper shows statistical properties of composite distortions and a new BER analysis method to handle them. In the evaluations, the amplitude distributions of composite distortions are given by Weibull distributions with skewness levels of 2.3 for composite second-order distortion and 1.5 for composite triple-beat distortion. We propose a new BER analysis method that uses the Weibull distributions for the composite distortion statistical features and demonstrate the effectiveness of the new BER analysis method in estimating BER by comparing its measurement results to calculation results.

Error statistic of QAM channel in AM/QAM hybrid optical transmission

The error statistic of the QAM channel in an AM/QAM hybrid optical transmission system is measured. Errors occur randomly in optical transmission without clipping. However, errors are found to occur in bursts when the impulsive noise due to clipping degrades the QAM signals BER. The error statistic is critical to properly designing the error correction employed in the hybrid system.

Novel BER analysis method for M-QAM signal in analog/digital hybrid optical transmission

In practical analog/digital hybrid optical transmission, carriers are modulated by video signals or digital data, and the amplitude of a multiplexed signal composed of these modulation signals is more compressed than that of the carriers. This causes a decrease in the frequency of clipping of the multiplexed signal at the laser threshold. Consequently, the BER of the M-QAM signal in a practical hybrid transmission is lower than that of the experimental results for same optical modulation index (OMI). However, it is difficult to prepare many practical modulation signals for experiments in a laboratory. Therefore, there is demand for a BER analysis method for a multiplexed signal that includes modulation signals needs to evaluate the BER and determine optimum OMI in a practical hybrid transmission. In this paper, we describe such a BER analysis method that can effectively estimate the BER in a practical hybrid transmission by using representative profiles of the modulation signals. In practical systems, a black pictures gives the largest averaged amplitude for the AM-VSB signal, and the most severe conditions for clipping occurrences. However, in such systems, the BER was greatly improved over the BER of a multiplexed signal of carriers. Furthermore, BER degradations due to clipping can be neglected for the AM-VSB signals in setting a practical OMI range.