The Bell System Technical Journal - new TOC TOC Alert for Publication# 6731005
- Combined source and channel coding for variable-bit-rate speech transmissionel abril 30, 2014 a las 7:38 pm
Motivated by potential applications to mobile radio, we studied variable-bit-rate speech communication through Gaussian-noise and Rayleigh-fading channels. For convenience we used a constant signaling rate of 32 kb/s and adjusted the source-coding and channel-coding rates in response to changing transmission quality. When the channel quality was good enough, we used all 32 kb/s for speech transmission. When the channel quality was lower, we reduced the source rate to 24 or 16 kb/s and introduced channel coding to control distortion due to transmission errors. We concentrated on specific source and channel codes that could be implemented with hardware of modest complexity. The source code was embedded differential pulse code modulation, which is amenable to variable-bit-rate operation and economical to implement. For error control we introduced punctured convolutional codes and a Viterbi decoder with only 16 states. Although the source/channel codec was simple, it offered good performance. Speech quality was at the level of normal telephony when the channel was good; the error-correcting codes extended by up to 13 dB the range of channel signal-to-noise ratios that support adequate quality. Our performance estimates were based on a new analysis of transmission errors in embedded differential pulse code modulation and on computer simulations of speech transmission through fixed and fading channels.
- A compatible high-definition television systemel abril 30, 2014 a las 7:38 pm
A compatible HDTV system with the potential of having significantly better picture quality than the present NTSC color TV system is proposed. It realizes an increase in horizontal and vertical resolution and has considerably less crosstalk between the composite signal components compared to the NTSC signal. The increased resolution will allow a display as large as present home projection televisions with a sharper-looking and more detailed image than is possible with the present NTSC system. Also, the elimination of crosstalk adds to picture quality. A large screen size together with improved image quality should provide the user with a feeling of realism and involvement. This system also allows the use of more detailed graphics and more text per page for new services such as teletext.
- Total Network Data System: Central Office Equipment Reports for Stored Program Control Systemsel abril 30, 2014 a las 7:38 pm
Stored Program Control System Central Office Equipment Reports (SPCS COER) is one of the earliest of the family of Operations Systems. Deployed on a centralized time-shared system, it produces engineering and administrative reports for Stored Program Central Office Equipment. This paper describes the user needs that motivated the design of SPCS COER. It traces the development of the system from a joint experiment of Bell Laboratories and the New York Telephone Company's Manhattan Engineering Department to the present system serving over 2800 electronic central offices from three centralized Amdahl V6 computers. We explain the functional system design from the user's point of view and outline the structure of the software, emphasizing the “tools” approach that is central to the development. The project management featured a research and development style, which we call the “whole-job” approach and discuss in some detail. Finally, we explore possible future directions for the project.
- Total Network Data System: Equipment systemsel abril 30, 2014 a las 7:38 pm
This article describes a set of five systems collectively called the Total Network Data System Equipment Systems, which support a number of network administration and engineering functions in the operating telephone companies. These systems are run by the operating telephone companies on large mainframe computers. In an average telephone company they support the management of the collection and distribution of over 50 million individual items of network data each week. They also provide reports to assist in the engineering and administration of No. 5 Crossbar switching offices, and the load balancing of all local switching systems. Initial development of these systems occurred in the early to mid-1970s. They are installed in all Bell System operating telephone companies and Bell Canada. Currently, on-line record base updates and inquiries and on-line viewing of report outputs are being developed.
- Comments on “Three-stage multiconnection networks which are nonblocking in the wide sense,” by F. K. Hwangel abril 30, 2014 a las 7:38 pm
Two theorems presented in this paper are incorrect. Theorem 2 stated by Hwang can be reformulated as follows.