[in Japanese]

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In this paper, the ISDB-T SFN relay station coupling wave canceller is studied in a multipath channel. A new algorithm to compute an adaptive FIR filter of the coupling canceller is derived and its implementation method, Channel Pre-estimation (CPE), is proposed. The simulation results show that compared with conventional coupling canceller, the new system achieves great system performance improvement and can work in a deeper frequency selective fading. In addition, a simplified IFFT method is proposed to reduce the hardware complexity and processing time, while guaranteeing the system performance.

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The technical parameters and conditions for transmitting digital terrestrial television broadcasting (DTTB) signals in cable TV networks were experimentally investigated. Indoor and field tests were conducted to evaluate the robustness of orthogonal frequency division multiplexing (OFDM), the standard modulation scheme for DTTB in Japan, signals in multichannel cable TV transmission. Experimental results showed that the carrier-to-noise ratio of 24 dB, a composite triple beat of-44 dB, and single carrier interference of-35 dB are required to keep the bit error rate less than 1×10^-4 without Reed-Solomon forward error correction. Adjacent channel interference tests were conducted between the OFDM signal and several types of possible cable TV signals : NTSC-VSB-AM, 64 QAM, MUSE-AM, and MUSE-FM. For each signal type, the range of relative signal power level to the OFDM signal, at which adjacent signals do not affect the OFDM signal, was derived.

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We propose a method of cancelling the coupling loop interference at a relay station in a Single Frequency Network (SFN) in Digital Terrestrial Television Broadcasting (DTTB) using an Orthogonal Frequency Division Multiplexing (OFDM) signal. This loop from a transmitting antenna to a receiving antenna can distort and oscillate the signal. The loop is cancelled by a replica of it generated by a frequency-domain adaptive cancellation algorithm. The method covers both QAM-OFDM (Quadrature Amplitude Modulation-OFDM) and PSK-OFDM (Phase Shift Keying-OFDM). Computer simulation demonstrated that this method effectively cancels the loop.

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A new approach to achieve SFN that uses OFDM is described. In the SFN emvironment, especially in a relay one, delay spread is sometimes longer than the guardintervals. This results in not only inter-symbol interference (ISI), but also inter-carrier interference (ICI), since orthogonality is lost. To avoid this, the relay station must remove the delay, since the symbol timing is simultaneous among stations. However, this is impossible, because the relay station reuses the received signal. We have thus changed the strategy to transmit the signal on different symbol timing. This is simplly achieved by inserting an additive delay at the relay station, and it makes possible to decrease an additive delay. Therefore, we can spread the region where ICI is avoided. Also described is a method to eliminate ISI by using the Viterbi algorithm. Experimental results showed that the service area becomes larger, because torelable delay becomes longer than in the conventional system. Moreover, the BER characteristics are imprived even in the service area of a conventional system, because strong frequency-selective fading does not occur when using the proposed system.

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Many TV broadcasters now use a progressive scanning format and an HDTV system to produce programs. However, standard TV receivers are still used in most homes. We have thus developed a broadcast system that uses the 480 p format for the source picture and the 480 i format for the receiver. We use progressive scanning coding because of its coding efficiency and room for improvement. The B-picture is not used as a prediction reference ; we use only the interlaced scanning lines in the B-picture to remove redundant information. We use 8 x 4 DCT instead of 8 x 8 DCT for coding the residual to realize this method. Experimental results showed that the proposed coding scheme performs better than other coding schemes such as two kinds of interlaced scanning coding and progressive scanning coding in MPEG-2.

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The digital terrestrial television broadcasting system in Japan is called ISDB-T. It uses OFDM and timeinterleaving to facilitate reception for mobile and portable users. This paper describes the performance of mobile reception. The signal strength in the field was first measured by a moving experimental car for the Shiba experimental station. It was found that the propagation model of the UHF TV band in an urban area is similar to that of the GSM typical urban area model. Therefore, it was used in the computer simulations which calculated the transmission performance in mobile reception. When the modulation method is DQPSK and coding rates are 1/2, 2/3, and 3/4, required carrier-to-noise ratios (C/N) in the multipath fading channel are respectively 10 dB, 13 dB, and 15 dB. Correct reception rates were studied in the field trials of mobile reception. When the modulation method is DQPSK and coding rates are 1/2, 2/3, and 3/4, required receiver input levels for correct reception time rates of 90% were respectively 24.5 dB (μV), 28 dB (μV) and 30 dB (μN).

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[in Japanese]

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[in Japanese]

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With the advent of digital video and digital broadcasting, copyright protection of video data has become an important issue. A novel method is described for digitally watermarking video data that is based on the discrete wavelet transform. The watermark is embedded in a multiresolution representation of each frame in the uncoded video by using controlled quantization. The watermark can be extracted directly from the decoded video without accessing the original video. Experimental results showed that the proposed method gives the watermarked image better quality and is robust against MPEG coding and re-coding. Also described is multiple watermarking with regard to generational copy control for video contents.

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A method is proposed for retrieving images from a database using an index color. It is based on a new method for automatically picking index color in images. This method can be used to represent an effect similar to looking at the most several index colors instead of original images. The index color for an image is selected by collecting the colors and picking noticeable one. A method is also proposed for retrieving images as using index colors. This method is very useful, because we can retrieve images based on our impression of images as represented by index colors.

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Digital video compression schemes have been evaluated to determine which is the most suitable for storaging and transmitting broadcasting contents. Various types of digital compression devices have been proposed and developed for the transmitting and storaging video images, and some of these are now being applied to broadcasting applications. We investigated the application of digital video-compression techniques to digital-broadcasting contribution, distribution, and transmission, and conducted a subjective evaluation of cascaded combinations for broadcasting systems. On the basis of this work, we have developed a system for assessing the quality of compressed digital pictures, in which picture degradation is calculated in realtime and takes account of human visual perception. In this system, noise sensitivities considered in spatiotemporal frequencies in relation to picture brightness. This approach improves the accuracy of picture quality assessment for many types of degradations in comparison with the conventional picture quality scale method.

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A method is proposed for automatically generating an image-retrieval algorithm corresponding to keywords in a quary. It uses vector quantizers and an N-out-of-M detector in the feature space. The objects corresponding to a keyword are assumed to have common features, and the background image is considered to be random noise. The parameters for the vecotor quantizers and detector are determined through training. First, all quantizers are assumed to be scalars, and the parameters are determined using the genetic algorithm. These quantizers are then grouped into vectors quantizers, and their parameters are optimized by clustering. A practical experiment showed that the proposesd method can retrieve images corresponding to keywords.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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