Showing papers on "Bandwidth expansion published in 1990"
TL;DR: CC are extended to multipulse signaling applied to both self-noise limited, and degraded optical channels and it is seen that gains in bandwidth expansion and peak-to-average power ratios are attainable.
Abstract: Multipulse signaling has recently become an attractive alternative format to single pulse position modulation (PPM) utilized in optical communication systems [1]. In Ref. 2, the author analyzed the performance of short constraint length convolutional codes (CC) with the standard PPM model. In this article, CC are extended to multipulse signaling applied to both self-noise limited, and degraded optical channels. Using this scheme, it is seen that gains in bandwidth expansion and peak-to-average power ratios are attainable.
4 citations
02 Dec 1990
TL;DR: Simulation results for both a Gauss-Markov source and speech samples indicate that the use of the present scheme results inconsiderable improvement not only over uncoded transmission but also in comparison to joint source-channel trellis coding.
Abstract: The authors present a novel tandem source-channel coding scheme consisting of a trellis source coder and a trellis coded modulation (TCM) channel coder. Motivation for the use of TCM, instead of conventional channel coding schemes such as convolutional codes, arises from the fact that, by using TCM, improvement in signal-to-quantization-noise ratio (SQNR) is achieved without bandwidth expansion. Criteria for the choice of TCM codes are discussed, and TCM schemes suitable for this application are presented. Simulation results for both a Gauss-Markov source and speech samples indicate that the use of the present scheme results inconsiderable improvement not only over uncoded transmission but also in comparison to joint source-channel trellis coding. The disadvantage is the additional computational effort and corresponding delay resulting from the use of the Viterbi algorithm at the receiver. >
3 citations
TL;DR: In this paper, the authors proposed a method based on the principle that the transmissible two-dimensional spatial frequency area is matched with the visual characteristics and an improved image sharpness is achieved.
Abstract: Bandwidth expansion of the luminance signal is discussed as a method of picture quality improvement in the NTSC television system. By modulating the high-frequency component over a 4.2-MHz luminance signal using a new subcarrier whose phase is field-alternated and multiplexing the aliasing component resulting from that to a low-frequency component, the transmissible bandwidth of the luminance signal can be expanded, with compatibility to NTSC receivers. A method based on this principle is proposed. Expanding the bandwidth as described, the transmissible two-dimensional spatial frequency area is matched with the visual characteristics and an improved image sharpness is achieved. Experiments confirmed that the bandwidth can be expanded while maintaining compatibility with NTSC receivers. In addition, subjective evaluation tests indicated that there is not much deterioration of image sharpness through the method's deletion of the oblique high spatial frequency component, and that sharpness is improved in pictures including detailed images through the proposed method. A novel phase regeneration circuit is also proposed. >
2 citations
TL;DR: NTSC方式の画質改善の一方法として, 色信号の高域成分をフィールド順次伝送するこの後の視覚研究によれば当時とは異なる結�“が
Abstract: 現行のNTSC方式における色信号の帯域幅は, 規格制定時の視覚特性の研究成果と伝送路帯域の制約から決められたが, その後の視覚研究によれば当時とは異なる結果が報告されている.また, 当時は妥協できると考えられた狭帯域色信号の帯域幅も近年のテレビジョン高画質化傾向に伴い色にじみとして目立つようになってきた.本論文では, NTSC方式の画質改善の一方法として, 色信号の高域成分をフィールド順次伝送することにより狭帯域色信号の帯域を拡大する方式を提案した.本方式の時空間スペクトルを求め, それをもとに本方式の画質やNTSC受像機に対する両立性を検討しだ.その結果, 本方式が良好な両立性を持ち, 時空間周波数に関する伝送帯域の面でも充分な値を持つことが明らかになった.本方式をハードウェアにより実験したところ, 色の鮮やかな縞やエッジを含む画像で画質改善効果が認められた.
1 citations