For contribution and primary distribution of television, i.e., television transmission to broadcasting stations, parallel transmission links that include codecs are often set up for reliability. However, this configuration still faces the following issues: 1) during normal periods, the reserve link is totally wasted and 2) when a failure occurs, the disrupted signal continues to be transmitted until the system switches to the reserve link. In addition, in digital video transmission, automatic assessment of received video quality is an important issue. To address these issues, the authors developed a processing system for parallelly transmitted video signals, which mainly consists of the following three elements: 1) when both links are normal, outputting the average signal of both links reduces compression coding noise and improves picture quality compared to only one link (efficiency); 2) comparison of the pictures from the two links enables failure detection in either link, to switch to the normal link (support of failure detection); and 3) comparison of the two normally decoded pictures enables evaluation of picture quality (automatic coding noise evaluation). This unique system improves the reliability and operational efficiency of conventional parallel video transmission links.

Multimedia contents transmission and management system "VAST-web" is proposed. It employs store-and-forward transmission technique to maintain the contents quality. It also has a central management function of contents stored at remote locations so that contents query and contents pull model as well as contents push model are supported. A novel transmission protocol "SVFTP" is also introduced, which is a core technique in VAST-web. Its throughput performance is evaluated theoretically and experimentally to show it is well-suited to large volume multimedia contents transmission. Besides, its pipeline transmission capability provides VAST-web system with great flexibility for media playback.

MPEG-2 is an international standard specifying a normative bitstream syntax that decoders must recognize and that allows flexible selection of detailed coding parameters at the encoder. The compression performance is therefore largely dependent on the encoder design and the difference in coded picture quality is present even among encoders developed by different codec makers at identical bit-rates. Conventional MPEG-2 encoders were also designed for high picture quality transmission at an adequate bit-rate, and the overhead portion occupancy in a coded bitstream can be ignored in the final picture quality. However, the unexpected increase in overhead portion occupancy might cause fatal picture quality degradation at extremely low bitrates. To overcome this problem, we investigated an optimal design for an MPEG-2 encoder for use in HDTV digital terrestrial broadcasting where the available bit-rate is limited to less than 0.2 bit/pixel. In our study, advanced key technologies which have not been clearly recognized until now were introduced into possible optimization points, picture type selection macroblock coding mode selection and rate control, and a significant coding gain versus conventional encoding schemes was confirmed in coding experiments.

In this study, the phenomena related to collisions between two phase-version-waves in an array of van der Pol oscillators are investigated. Behavior of the two phase-inversion-waves after they collide with each other is classified by computer simulations. Further, the mechanisms of the complete extinction and reflection of the two waves by using the relationship between phase states and oscillation frequencies are explained.

Proposes some reversible variable length codes (RVLCs) which can be decoded instantaneously both in the forward and backward directions and have high transmission efficiency. These codes can be used, for example, in the backward reconstruction of video signals from the data last received when some signal is lost midway in the transmission. Schemes for a symmetrical RVLC requiring only a single code table and for an asymmetrical RVLC having short average code length are introduced. They compare favorably with other reversible codes such as B2 codes in several aspects.>

An efficient technique for obtaining a variable length code (VLC) resistant to synchronization loss due to channel errors is proposed. Bit errors in the channel lead to incorrect decoding of a VLC and result in error states for continuous codewords. In this paper first a precise value is found for assessing the ability of a VLC to recover synchronization from the error states. Next a new transformation for converting a code into another of the same efficiency (equivalent transformation) is introduced, and several VLCs with an identical efficiency are compared through estimation of synchronization recovery in order to find an error-resistant VLC. Based on the equivalent transformation, an efficient method for finding an error-resistant VLC with high recovery performance from among multiple VLCs is described.>

Integration of video services are addressed. The view that various types of end-to-end quality of service (QOS) for video communications, ranging from videophone to high-definition television (HDTV), should be supported to utilize broadband integrated services digital network (B-ISDN) services and video data is expressed. End-to-end QOS is recognized as a function of terminal capability and network performance. The key feature of B-ISDN is that both terminal capability and network performance are selectable and controllable. In order to capture the basic characteristics of end-to-end QOS, it is necessary to conduct experiments using a prototype system. A prototype system comprising an asynchronous transfer mode (ATM) switch and video codecs is presented. The ATM switch is based on distributed-memory-switch architecture and it will provide for nonblocking cell-switching capability with a very low cell-transfer delay. Developed codecs conform to H.261 with an additional function of controlling average coding bit rate. The coding bit rate is chosen as a parameter of terminal capability and the cell-loss ratio is chosen as a parameter of network performance. From experiments using a prototype system, a relationship between coding bit rate and cell-loss ratio is obtained.>

An efficient recovery method using error concealment is proposed for video packet loss in fast packet switching networks. In this method, the receiver detects the damaged picture area caused by packet loss from the structured picture data received, makes error concealments, notifies the transmitter, and continues decoding. The transmitter, having received the notice, calculates the affected picture area in the local decoded picture and continues encoding without using this affected area. In this selective recovery method, video signals are not stopped even if a long propagation delay exists, no additional information is transmitted to error recovery and conventional coding algorithms can be used. The proposed method is suitable for multipoint communication. Simulation results show the affected picture area is localized for a considerable time attesting to the method's effectiveness.>

Seeing-while-talking has been a dream of mankind for over a 100 years since the invention of telephone. In the past, various trials were performed in spite of the difficulty in installing the network for the actual service. However, with the progress of ISDN and the advancement of digital signal processing technology, the environment has been changing rapidly. In this paper, an integrated visual communication system is described for the enhanced communication service at 64 kbits/s, the fundamental bit rate of ISDN. The roles of state-of-theart compression of the audio and video signals are discussed and an integrated transmission method based on the priority of the information content is proposed.