Showing papers on "Telephony published in 1980"

Silencing echoes on the telephone network

Abstract: Echo of a trasmitted signal can occur in the telephone network and is sometimes a disturbing phenomenon. Various methods of echo control have been used for over 50 years but recent introduction of transmission delays in excess of 300 ms, over satellite circuits, has resulted in a general reexamination of suppression methods. This led to development of the echo canceller. Adaptive echo cancellation is accomplished by automatically synthesizing a replica of the echo path response, convolving the incoming signal with the replica and subtracting the resulting echo estimate from the echo path output. Transmission is not thereby interrupted in any way and two-way information transmission proceeds normally with little or no echo. Detailed mathematical formulations for the convergence properties of such devices allow understanding of the effects of various hardware configurations and input signal properties. Echo cancellers may be applied to the network in a number of ways and the development of a VLSI canceller chip promises inexpensive implementation of these applications. Worldwide tests have shown the effectiveness of cancellation methods for satellite transmission.

Improved decoding Scheme for frequency-hopped multilevel FSK system

Abstract: We have recently examined, for possible application to digital mobile radio telephony, a digital spread-spectrum technique employing multiple frequency-shift keying (MFSK) modulation with code-division-multiple access (CDMA) by frequency-hopping over a common bandwidth. The system uses the cellular approach where all mobiles within a cell communicate with a fixed base station in the cell. An analysis of base-to-mobile transmission shows that mutual interference limits the number of users which the system can accommodate at a given error rate. This paper describes a new decoding scheme to reduce mutual interference which makes use of the well-defined algebraic structure of the users' addresses. Analysis of the new decoder at high signal to noise (s/n) ratio shows it to outperform conventional decoding, allowing a 50 to 60 percent increase in the number of users who can simultaneously share the system at a given error rate. We describe a simple implementation of the decoder using shift registers.

Control system for telephone switching system

Abstract: A telephony system with automatic test calling. Test access circuitry connected to port circuits enables the test call circuit to select actual ports for a test call and monitor the test call signals. Test calls are initiated either on a periodic basis on in resonse to a fault condition. Any portion of the telephony system therefore can be used in a test call.

Automatic telephone message interception system

Abstract: An automatic telephone message interception system which is connected in series between a telephone instrument and incoming telephone lines. The system intercepts an incoming call and, upon the detection of a code signal on the telephone lines, connects the lines to an information storage device without causing the telephone instrument to ring. The system disconnects the storage device from the telephone lines and restores the system to its original condition upon the detection of another code signal on the telephone lines. In the event a code signal is not detected after reception of an incoming call, the system connects the telephone lines to the telephone instrument, which then operates in a normal manner.

Telephone traffic in mobile radio communication system using dynamic frequency assignments

Abstract: Traffic characteristics of a mobile radio communication system using a dynamic channel assignment scheme which has all channels available at all base stations are derived. In the system with one channel, the traffic characteristics in each zone are exactly obtained. For a multichannel operation, some approximation methods are proposed and some simple examples are also presented.

Back-End Network Approaches

Abstract: This review of existing back-end networks emphasizes the relationship of their storage aspects to the more general concept of local computer networks.

Integrated circuits for telephony

Abstract: Many integrated circuits for large-scale application to telephone networks have been designed, including subscriber line interfaces, antialiasing filters, analog-to-digital-to-analog converters, and tone receivers. This paper summarizes in a unified fashion both interfacing and functional requirements for these devices, as well as the related circuit and technology approaches which have been utilized.

Speech-band data modems

Abstract: Speech-band data modems allow the analogue telephony network to be used for digital data communication. New techniques and technology are permitting further exploitation of the network in terms of higher data rates and efficient bidirectional transmission

A low-power NMOS transmit/receive IC filter for PCM telephony

Abstract: A very low-power single chip NMOS implementation of the transmit and receive PCM filters used in telephony applications is described. The circuit utilizes doubly-terminated switched capacitor low-pass and high-pass filters and meets accepted requirements without trimming. The filters have low idle-channel noise, consume only 20 mW of power, and are realized in a small area of silicon. Design of the overall architecture, the individual filter sections, and the operational amplifiers in NMOS technology is described.

An Electronic Hybrid with Adaptive Balancing for Telephony

Abstract: A new form of adaptive balancing hybrid is proposed for application to the two-wire to four-wire interface of a local digital switch. It is similar to an echo canceller but with a single degree of freedom and much simpler circuitry. In this paper a theory of operation of the hybrid is developed, and in a companion paper two circuit implementations and experimental results are reported.

Overview of an A.M.P.S. mobile call processing system

Abstract: The use of mobile communications systems is rapidly increasing as the mobile public's thirst for fast, reliable information expands and the economic pressure of less fuel at higher cost is felt. Aiming at this market, an A.M.P.S. call processing logic and 10- kilobit-per-second data modem was designed for Bell Telephone Laboratories cellular telephone market trial in Chicago. This paper reviews some of the goals and results of the project and describes the system.

Synchronized Clock for DMS-100 Family

Abstract: The advent of digital telephone switches, interconnected by digital carrier systems, makes it possible to route and transmit telephone and data signals virtually without deterioration over many links and through many switching nodes. No bits of the digitized speech or data, however, should be lost en route; an economical method to ensure this is to operate the entire digital telephone system (of a country) synchronously. A highly stable master frequency reference is established from which all digital switching centers derive their clocking, either directly by national distribution of the reference frequency, or through the means of the (pulse-code modulation) PCM transmission systems which interconnect the switches. Operating considerations require that the synchronized clock systems of every switch can survive outages of equipment or synchronizing links without major impact on telephone service. The present paper is concerned with the design and performance of the synchronized clock system as an integral part of a large digital telephone switching office. Clocking and synchronization hardware and software algorithms have been developed to allow a switching office to be synchronized by external reference standards or over digital carrier links. The components of the synchronization system of an office are distributed in peripheral interface hardware, digitally controlled clock hardware, and a feedback algorithm implemented in the software of the switching computer. Steady-state and dynamic behavior are analyzed for a single switch and a timing network. Mathematical analysis is supported by simulation results. Special attention is given to quantization effects and maintenance considerations.

Playcable: a Technological Alternative for Information Services

Abstract: Various technical alternatives for providing consumers with digital information services were explored during the late 1970's. Such systems as Teletext and ViewData specifically address the unique technical challenges associated with the broadcast and telephone communications media. Strong promotions by European governments have resulted in the establishment of defacto transmission and display standard for both of these systems. The situation in the United States is different in many respects, since government intervention is quite unlikely. Experimentation in the United States is currently underway to determine the optimum approach to delivering digitally based services to the consumer's home in an economical and appealing way. Currently, the cable industry in the United States is experimenting with a new service called PlayCable. This system addresses the new market segment of information services by offering advanced home video services eclipsing in graphics, sound and interactive capabilities previous services tested. The PlayCable concept is a method of distributing personal computer s6ftware via a CATV system. Technical details o1f the PlayCable CATV data transmission system are presented, highlighted by the headend computer system, which can become the basis for a host of future CATV services. Utilizing the wide bandwidth spectrum available on a CATV system, a time and frequency division multiplexing scheme is employed to transmit the services. This data transmission scheme will be shown to be spectrally efficient, frequency agile and cost effective in providing a large variety of entertainment, education and information services to the consumer. Four field trials using this sytem are currently in operation in the United States. Designed to not only test the technological and cost advantages of providing these services via cable, but also the field trials will test the marketing potential for digitally based software.

BANCS Special Feature the Concept and Implementation of BANCS

Abstract: With BANCS, each operating telephone company within the Bell System can engineer its own message-switching network. Five modular components facilitate both central support and future expansion.

The First Electronic Speech Circuit Opens the Way to the Fully-Electronic Telephone

Abstract: This paper shows how the speech circuit in a conventional carbon microphone may be replaced by a new monolithic integrated circuit, leading to the implementation of a fully electronic set.

Voicecharacter switching telephone set

Abstract: PURPOSE:To transfer required data to other telephone subscribers, by using a control procedure in which continuous transmission is made after the data received via a telephone line is stored in a memory and the transferred data is displayed on a display device at transfer. CONSTITUTION:When a telephone line 8 is connected to a telephone set 6 via a switch 7, an audio communication is made, and when a switch 7 is switched to an MODEM5A, the transmission of data is enabled. A CPU9 is connected to an MODEM5A, CRT display device 5B, keyboard 5C, memory 10 and input/output interface 13 with a data bus 14 and voice communication and character (data) communication are made, and the content of memory is displayed and the control of on-line such as data transfer via a telephone line to other telephone terminals is executed with a program according to the state such as telephone set and keyboard key input. The display of the memory content at off-line, insertion of data and deletion are made.

Digital TV signals fibre=optics channel transmission procedure - has image and sound signals converted into pulse position modulated signals

Abstract: Combined transmission of television picture and sound signals via a light (fibre-optics) guide connection provides high quality reception without incuring high assembly and design costs. In the system, the picture and sound signals being transmitted in partic. between a central point to a branch or subscriber connection, are converted into a pulse position modulated (PPM) signal(s) the latter being transmitted following combination to a time multiplexed signal. The time-multiplexed signal transmitted specif. to the branch (subscriber). consists of a pulse train comprising four TV signals including sound signals, a TV telephony signal (as reqd). 48 monodural (program) signals corresp. to 24 stereo aural signals and one digital telephony signal.

Automatic guiding method by telephone

Abstract: PURPOSE:To automatic guidance service for information on telephone numbers, etc., by voicing information extracted from the data base of a host system by using a small-size key pad for a conventional telephone set as a terminal. CONSTITUTION:A user calls a host system 9 by using a telephone set 1. Then, the system 9 voice an input-operation request message, such as ''input the key word'', from the telephone set by way of a signal converter 8, a controller 4, a voice synthesizer 7, and a telephone switchboard 10. The user connects a key pad 2 for data entry to the telephone set 1 and inputs and sends the key word. With the key word signal, a data base 5 is searched for data which corresponds to the key word. The accent and voice parameter of the obtained telephone number, name and address are extracted by a character string voice converter 6 to synthesize voice at a synthesizer 7, thereby sending voice answer information to the telephone set 1 via the switchboard 10.

Message translation arrangement for telephony system with romote port groups

Abstract: A telephony network with a digital central office and one or more remotely located digital satellite units Each digital satellite unit connects to a number of remote subscriber lines and monitors these lines to establish communications through interconnecting spans and a digital satellite interface at the digital central office The digital satellite interface includes a programmed controller that communicates with the remote digital satellite units connected to it, with call processing equipment in the digital central office and with maintenance processing equipment in the digital central office Supervisory information and voice data information, in digital form, pass through span equipment that interconnects port group highways in the digital central office and the interconnecting spans The span equipment strips messages from and inserts messages into signalling time slots on the interconnecting span

Interface for passing to a packet-mode transmission connection from a digital transmission connection of another mode

Abstract: This interface comprises a first reception logic level (1) of the digital link (2) and a second packeting logic level consisting essentially of a single memory (20) which write-addresses itself via an addressing register (22). The invention applies to data transmission and to telephony.

Electronic Systems and Equipment for Evolving Loop Plant

Abstract: This paper discusses a French plan for enhanced subscriber service, and some of the systems and equipment that will meet these goals on existing loop plant. Since 1972, the French PTT has been installing digital central offices at the national, regional, and local levels. Coverage is expected to reach 10000000 lines by 1985, so that when integrated services can be offered, the nation will be ready to take advantage of them. A PTT-sponsored program, directed toward all-digital subscriber loops, has revealed four principal phases. The first of these is already in progress: both digital and analog pair-gain systems are now being installed on existing loop plant. Soon to come is the second Phase: residential subscribers will be able to obtain two-channel subscribercarrier installations, with the carrier channel supporting data services, independent of the voice service on the same loop plant. Integrated Services Digital Networks, the third phase, should stretch the French loop plant to maximum capacity. When the demand for broad-band services overrides the capabilities of the existing copper pair plant, fiber optics cable installation will be fully planned and implemented as the fourth phase.

Design and technology for FM cellular portable telephone equipment

Abstract: Introduction of portable service to the 850-MHz cellular system is anticipated as an extensive service of mobile telephone. This paper describes design and technology for the 850-MHz cellular hand-carried portable equipment.

Consumer telephone I: A switch to electronics: Telephone systems will go completely electronic as reed relays are displaced by digital electronic switching

Abstract: Discusses the changeover to digital electronic switching happening in many countries especially in Western Europe as reed relays are replaced in telephone systems. The progress of the French, Swedish, Italian, West German and British are outlined.

Consumer telephone III: Mixing new with old: An interfacing scheme for analog and digital systems features modular architecture

Abstract: For pt.II see ibid., vol.17, no.3, p.38-40 (1980). A telephone switching system that embodies a unique design philosophy is now into its third year of service. The AXE-10, a digital stored-program-control (SPC) system, is made up of functional modules in individual hardware and software configurations. They are interconnected via strictly defined hardware and software interfaces. This building block principle makes the system generally applicable on all levels of the telephone network and permits smooth introduction of new parts into the system without changing its concept. Also, handling and operation of the system are easier as compared to the monolithic-type systems of earlier generation. The physical design, also modular in nature, using a magazine concept, has reduced testing, shipping and installation times, and at the same time increases reliability by a sizable reduction of interconnection contact points.

New digital automatic gain control for p.c.m. signals

Abstract: A new design for digital automatic gain control for p.c.m. telephony is presented. This new design is capable of processing 30 speech channels. It avoids putting highest gain where there is no speech. It has manual and automatic facilities.

Alternative burst transmission technique for digital telephone reticulation

Abstract: The letter proposes an alternative technique for the burst (ping-pong) transmission systems currently being studied for the digital reticulation of subscriber telephone services. Its main feature is the interleaving of transmit and receive bursts to permit the use of lower burst bit rates for a given transmission distance.