Showing papers on "Communications system published in 1975"

Multipoint data communication system with collision detection

Abstract: Apparatus for enabling communications between two or more data processing stations comprising a communication cable arranged in branched segments including taps distributed thereover. Tied to each tap is a transceiver which on the other side connects to an associated interface stage. Each transceiver includes, in addition to the usual transmitter and receiver sections, a gate which compares the data from the interface stage with the data on the cable and indicates whether such are equal. Should such be unequal, an interference between the transceiver and the cable is indicated, disabling the associated transmitter section. Each interface stage tied to such transceiver also includes an input and an output buffer on the other end thereof interfacing with a using device, such input and output buffers storing both the incoming and outgoing data. The output buffer is connected to a clock-driven shift register which converts the buffered data to a serial stream, feeds such data to a phase encoder, which then connects to the transmitter or driver section of the transceiver. The input buffer is loaded by an input shift register which derives its clock from a phase decoder, the shift register and the phase decoder both connecting to the receiver section. When the station is to start transmitting, the phase decoder detects the presence of other transmissions on the cable and detains the output shift register until no other transmissions are sensed. Once a transmission has begun, if interference is detected and the transmitter section is disabled, a random number generator is used to select an interval of time at the completion of which the next attempted transmission will take place. Concurrently, a counter counts the number of interferences, or collisions, which recur in the attempted transmissions of one data packet and weights the mean of the random number generator accordingly. The input shift register is also connected to an address decoder which enables data transfer to the input buffer only during those times when the data is preceded by an appropriate address.

A Simple Method for Reliability Evaluation of a Communication System

Abstract: Very few techniques exist for reliability evaluation of communication systems where links as well as nodes have certain probability of failure. This correspondence describes a technique by which the reliability expression for such a system can be conveniently derived. It is also shown that using the concept of this correspondence, it is possible to extend all the existing reliability-evaluation algorithms to communication systems with little effort.

Distribution network powerline carrier communication system

Abstract: A distribution powerline carrier communication system for providing distribution automation functions. The communication system includes a distribution powerline, with inductive couplers and frequency translating repeaters cooperating to circumvent signal obstructions, such as distribution transformers, and to increase the signal strength. The inductive couplers pick up the communication signals without metallic contact to the primary distribution lines, and the repeaters change the frequency band of the communication signals, enabling the amplifier gain of the repeaters to be selected without limitation due to undesirable feedback and oscillation.

Fast start-up adaptive equalizer communication system using two data transmission rates

Abstract: Initial Adjustment of a receiver having an automatic adaptive equalizer in a modem communication system is accomplished by employing a data transmission rate lower than normal for an early segment of each burst of signals. At this lower rate, accurate reception is possible without complete adaptation of the equalizer. These same (early segment) signals are used to adapt the equalizer in a decision-directed mode. When the adaptation is completed the system switches to its normal higher rate of data transmission.

Acoustical underwater communication system for command control and data

Abstract: An acoustic communication system is disclosed as a secondary means for command control of underwater operations from a surface unit. The system includes a diving acoustic command control unit for use in the event of prime propagation path occlusion. Self-check verification as well as data read-out upon interrogation is provided from the surface unit to an underwater receiver-transponder. The latter will also respond to acoustic command signals from the diving unit. An early warning blowout detector employs sensors at the wellhead to detect seismic waves, mud pressure wave fronts and mud flow rates resulting from an emerging blowout and in response thereto, transmits an alert signal.

Interprocess communication protocols for computer networks

Abstract: : This thesis focuses on the design and analysis of interprocess communication protocols for networks of computers. Previous research has emphasized system performance at lower levels, within the communication medium itself. This work examines requirements and performance of protocols for communication between processes in the Host computers attached to the communication system. Both the reliability and the efficiency of protocols are discussed. Reliability involves overcoming unreliable network transmission facilities to avoid loss, duplication, or out-of-order delivery of data. Reliability performance goals are defined, and the correctness of different protocol mechanisms in achieving these goals is demonstrated. Consequences of protocol failures (Host crashes) and problems of initializing control mechanisms required for reliable communication are also considered.

Adaptive hybrid circuit

Abstract: Improved isolation between the four-wire receive and transmit ports in a four wire-to-wire converter in a communication system is obtained by utilizing a tapped delay line network in an active hybrid circuit. The active hybrid circuit includes a first amplifier which terminates the four-wire receive channel in its characteristic impedance, amplifies the four-wire received signal, and excites a resistor network that terminates the two-wire channel in its nominal characteristic impedance. A second amplifier and a resistor circuit function as a weighted summer for nulling the received four-wire signal with the signal passing through the resistor network to obtain signal cancellation at the four-wire transmit port when the four-wire receive channel is activated. The tapped delay line network may be connected either between the first amplifier and resistor network or between the first amplifier and the received four-wire signal input of the second amplifier.

Multiple block binary synchronous duplex communications system and its method of operation

Abstract: A multiple block binary synchronous duplex communications system provides for the orderly transfer of data from one location to another utilizing communications facilities. This communications system increases the efficiency of data links with long propagation delays or with long processing times at either end by maintaining a continuous flow of data and responses in both directions. The memory of the communications link is kept full at all times. Data is transmitted in blocks including an identification code. The received data is checked for errors. When errors occur the transmission of data is not stopped; data is continuously transmitted and signals are returned including the block identification of the block containing the error. The block containing the error is then retransmitted when the transmitting station of the communications system is available for this task.

Computer and communications systems employing new architectures

Abstract: Communications and computer systems are described utilizing an architecture which makes possible the transmission and storage of data in an efficient and rapid manner. The system architecture embodies a plurality of communication sites and computer sites which interact with each other by means of matrices having special properties which permit the control, transmission and storage of data in many time and space saving ways. The matrices also serve as a means of governing the activities of the system. A plurality of computer sites act upon the data in the matrices by transforming, processing and transferring data for the communications network and processing loops. The processing loops provide the basic processing for the system and contain processing units which act independently and respond to the matrices. The matrices contain both the data which is to be operated upon and tutors (instructions) for directing the activities of the processing units. The system provides simultaneous services to a large number of users. The system does not contain a central processing unit (CPU) and its associated programs and does not require fetch, put and interrupt actions inherent in CPU programs. The system architecture, by virtue of the hardware and its special configuration, the matrices and their operation, and the response of the hardware to the matrices, confers great flexibility on the system's operations from both the communications and the computer standpoints.

Communication systems using bundle conductor overhead power lines

Abstract: The main properties of power line carrier (p.l.c.) systems, used conventionally for internal communication purposes in electricity supply undertakings, are examined, and an alternative method for use on bundle-conductor lines is proposed. Earlier work, departing from the use of conventional phase-ground or interphase carrier, proposed the electrical separation of the subconductors of a bundle for signal frequencies, but retained the remaining aspects of conventional p.l.c. These include particularly the expensive filter components required to limit the signal, as far as possible, to the desired parts of the power network, together with the frequency and bandwidth limitation imposed on the signal by these filters. The intrabundle communication system proposed uses a simple, inexpensive but highly efficient broadband coupling method which permits signal-isolation between subconductors without inserting additional impedance at power frequency or reducing the power transmission capability of the line. The signal characteristics of the new system are such that interference is reduced by orders of magnitude in comparison to p.l.c., avoiding need for frequency assignment even between adjacent phases. A bandwidth of 1.6 MHz is available. This may be exploited in a variety of ways, including the transmission of data at faster rates, to enhance the reliability and speed of protection signalling, or to provide up to 180 duplex voice channels. Even where one voice channel only is required, the cost of an intrabundle communication system is estimated to be less than that of a p.l.c, system for route lengths of at least 29 km, and allows subsequent increase in the voice channel numbers at low extra cost.

Control center for a communications system with interchannel patching capabilities

Abstract: A radio communication system of base stations, and a telephone system, are linked and controlled by a control center. A housing having a plurality of control modules electrically and mechanically engaged therein, each control module having a front panel with a patch switch and a plurality of indicators thereon, the control modules each adapted to be connected to a transmitter/receiver base station for receiving all communications to and from the base station on an associated communications channel and controlling the operation of the base station, a plurality of buses mounted in the housing and a patch board on each of said modules for electrically connecting any of said modules to said buses upon operation of the patch switch on said module, a phone patch module mounted in the housing and adapted to be coupled to a pair of telephone lines and including a switch for patching any communications channel to the telephone lines upon operation of the switches in the control module for the communications channel and in the phone patch, an operator module mounted in the housing and including a monitor speaker, microphone, and push-to-talk switch and associated circuitry connecting the aforesaid to audio and push-to-talk buses in the housing, and a patch tone encoder module mounted in the housing and supplying a plurality of tones on a tone encoder bus, said tones being utilized by predetermined ones of said control modules to control the base station.

Electronic voting machine

Abstract: A micro processor is connected to a switch operated voting panel and a vote selection indicating device. The voter-selected switch combination is converted to a digital code which is temporarily stored. The vote is recorded in a permanent form upon completion of voting in both a print-out and in an electronic memory. The electrical record can be connected to a communications system for remote tallying and continuous real-time remote readout. The automatic system is fully compatible with present machine voting systems.

Mobile diversity radio communication system

Abstract: A diversity system in a mobile radio communication system provided with a plurality of antenna systems operating over a multipath medium in at least one of the sending path and the receiving path. At the sending path, a carrier wave frequency- or phase-modulated by a digital baseband signal is transmitted from a transmitting antenna. A plurality of receiving antenna systems are switched at a constant frequency higher than the signaling rate of the digital baseband signal but less than the frequency shift width of the frequency modulated wave or less than a product of the maximum phase shift of the phase modulated wave and the signaling rate, so that average-power dispersion in a signal element of the digital baseband signal received at the receiving antenna systems is effectively compressed. Alternatively, the plurality of antennas may be transmitting antennas, and switched at the same rate to achieve compression of average power dispersion in the baseband signal elements.

Improving Parent-Teacher Communication through Recorded Telephone Messages

Abstract: This study assessed the effects of a teacher-parent communication system which used a daily recorded telephone message as a communications link between parents and their children's teacher. A class of 21 first grade students in a rural southern Illinois community served as Ss. A three-part experiment was conducted to determine: 1) if the parents would use such a system; 2) if the use of such a system would have any beneficial effects on learning; and 3) if the inclusion of non-academic information would be of value. The results of the experiment were that 1) the system was used extensively; 2) the inclusion of academic information in the daily message resulted in improved academic performance by every student in the class; and 3) families complied with recorded teacher instructions of a non-academic nature at a much higher rate than they did when these instructions were sent home with the child in memo form alone.

A High-Capacity Digital Communication System Using TE/sub 01/ Transmission in Circular Waveguide

Abstract: In this paper, we describe the characteristics and several parts of a high-capacity digital communications system using the low-loss circular waveguide

Sampled communication system

Abstract: A communication system apparatus and method for increasing the number of users accommodated by one or more communication channels. Time sharing of the one or more communication channels by a plurality of separate groups of users is provided as a function of user access demand, and channel occupancy. The one or more communication channels are periodically sampled by the user apparatus for detection of signals present on the channels whereby the occupancy status of each one of the scanned channels is determined. Transmission of signals from the user apparatus on each individual one of the channels detected as occupied by other users, is prevented for a predetermined length of time after each said detection of occupancy. Transmission of signals from the user apparatus is permitted on the channels detected as clear or unoccupied. The apparatus additionally provides for detection of each channel having signals addressed to the user and for transmission of reply signals from the user on the detected channel. The described system requires no central control station and is not dependent upon the use of special signals transmitted from an active user apparatus for marking an occupied channel. Some or all of the communication channels of the system can be used in common with other existing and conventional communication systems without resulting in interference with the existing communication system.

ELF communications system using HVDC transmission line as antenna

Abstract: An extremely low frequency (ELF) Communication System is disclosed for worldwide communication from land to receiving stations thousands of miles away using the existing DC power transmission lines of the Pacific Intertie power transmission system as the antenna. An ELF communication system requires a very long uninterrupted antenna or a series of long parallel antennas. The transmission lines of the Pacific Intertie DC power system lend themselves to be used as the required long antenna for the disclosed ELF system. The DC lines together with the associated ELF transmitter and coupling devices comprise the global ELF communication system disclosed herein.

Digital data communication system featuring multi level asynchronous duplex operation

Abstract: A communication system using a single transmission line for the simultaneous bidirectional transmission and reception of a plurality of asynchronous digital data signals. At each end of the transmission line, transmitting means are provided for converting a plurality of individual digital data signals into a multi-level signal. The system permits simultaneous bidirectional transmission of these multi-level signals without requiring the incorporation of a clocking signal into the transmitted signals for decoding purposes. Multi-threshold receivers at each end of the transmission line provide for unclocked decoding of a received multi-level signal, the resulting decoded signals being applied to a pulse discriminating filter for removing spurious pulses which may be introduced during the unclocked decoding as a result of phase shift errors in the signals being decoded. A dynamically variable biasing circuit controls the biasing of the receivers in accordance with the instantaneous value of any multi-level signal being simultaneously transmitted from the same end as the receivers so as to cause the receiver thresholds to appear substantially constant to a received multi-level signal, thereby permitting simultaneous bidirectional transmission and reception along the single transmission line.

Aircraft multi-communications system

Abstract: An aircraft communication system adapted to provide a plurality of communication paths from respective inputs to a plurality of outputs, the communication paths being flexible in arrangement and operator control. For use in an aircraft, the system combines an intercom for voice transmission between pilot, co-pilot and passengers, along with channels for external radio reception and transmission by pilot and co-pilot. The system also provides enabling of transducer outputs only upon detection of input signals above a given threshold, and automatic monitoring of aircraft supply voltage conditions with visual and audio outputs. Specific features of the invention include: (a) audio source input circuits feed a common point which is connected to a threshold VOX switch circuit; (b) the VOX switch circuit controls a recorder, additional audio inputs, and a master amplifier circuit inputted from the common point and connectable to output transducers, whereby signals from the audio sources are outputted only when the common point signal exceeds the predetermined threshold; and (c) the audio source input circuits include aircraft power supply high and low detection circuitry.

Time division multiplexed loop communication system with dynamic allocation of channels

Abstract: In a time division multiplexed loop communication system, a plurality of terminals share one or more channels of a multichannel frame, with a second plurality of terminals assigned to different channels. The communications controller may dedicate one or more of the channels to one of the terminals automatically and dynamically. Alternatively, one of a plurality of terminals assigned to a particular channel group can interrupt the controller and become automatically selected for communication.

Vehicle voice data link

Abstract: A communication system operative on a time-shared basis on a single frequency between a plurality of mobile vehicles such as trucks and buses and one or more central base stations and associated dispatcher offices. The communication system provides a data link between the vehicles and the dispatcher for vehicle status information and commands as well as a priority interrupt voice channel on the same frequency for occasions requiring voice communication.

Power line carrier communication system having efficient carrier signal coupling of distribution secondary lines

Abstract: An arrangement of components for a distribution line communication system Two or more independent secondary distribution lines are connected, through distribution transformers, to a primary distribution line Carrier communication signals are transferred between the primary distribution line and one of the secondary distribution lines by a repeater located near one of the transformers The carrier communication signals are propagated directly along this secondary distribution line and through associated service lines to communications terminals located near the electrical loads Coupling apparatus is connected between the two independent secondary distribution lines to provide a path for the communication signals between the repeater and the communications terminals associated with the other secondary distribution line The coupling apparatus provides a low-impedance path for the communication signals and a high-impedance path for signals at conventional electrical power frequencies

Communication system for guideway operated vehicles

Abstract: A communication system for track or guideway operated vehicles is disclosed The system is adapted for two-way transmission between a vehicle and a wayside station and is provided with a transmission line of special configuration along the wayside The transmission line comprises three conductors each having a wave configuration with the waves disposed in three-phase relationship and a return conductor which is also of wave configuration The vehicle transmitter section is provided with an inductive loop which is coupled with the transmission line and is energized with a continuous wave signal This produces signals on the three phase conductors which have an envelope frequency proportional to vehicle speed and a phase relationship corresponding to the relative position of the wave configurations of the phase conductors Thus, vehicle speed may be derived by measuring frequency and vehicle position may be derived by counting cycles or pulses from a given starting point Direction of the vehicle travel can be derived from the phase sequence of the signals in the phase conductors At the base station, the receiver section is provided with means for squaring each of the phase signals and summing the squared signals to develop a continuous signal, ie one which has an amplitude independent of the position of the transmitting loop along the transmission line The two way voice communication channel and a two way data communication channel is also provided utilizing the above mentioned transmission line The transmission line configuration and the configuration of the transmitting and receiving loops are such that the system is immune to far field radiation

Selective call communication system

Abstract: PURPOSE:To prevent augmentation of the power consumption of a communication system, by adjusting the timing of transmission and reception within relatively short period after the power source is turned on so that an intermittent reception is made.

Pulse code modulation radio control system

Abstract: A pulse code modulation communication system adapted in a preferred embodiment to the remote control of a flying model aircraft. The positions of the various control sticks are represented by a digital code which is multiplexed and then transmitted via pulse code modulation of a unique subcarrier signal. The unique subcarrier signal is locked onto by the receiver which, through correlation detection, detects and demultiplexes the digital code for use by the servo motors to position the flight control surfaces of the aircraft.

Lossless network and method for orthogonalizing dual polarized transmission systems

Abstract: A technique is disclosed for restoring the orthogonality of dual polarized signals in frequency reuse communications systems. The technique may be characterized as polarization coding at the transmitter and polarization decoding at the receiver. Coding and decoding is accomplished solely by means of phase shifters and sum and difference networks which are lossless in the dissipative sense. The required phase shifts are determined by defining the transmission media in terms of a transmission matrix. All depolarization effects including those attributable to antennas, feeds and media are lumped into this matrix. The transmission matrix may be determined empirically, and the phase shifts fixed for a given transmission media. Where the characteristics of the transmission media vary with time due to atmospheric and other effects as is the usual case, an automatic, closed loop orthogonalization network is employed wherein a pilot signal is generated at one or both ends of the communications system and used to derive error signals for phase shifter control. The technique disclosed is applicable to systems using either linearly or circularly polarized waves.

Intrinsically safe communication systems

Abstract: The invention is a communications and tone control system for use between safe and hazardous areas. The invention's field terminals operate in hazardous areas and are limited to low, intrinsically safe power levels by the use of zener barriers and current limiting resistors. The limited D.C. electrical power supplied to the field terminal's amplifier is modulated by field initiated communication and control signals. The resulting duplex transmission allows a strong information carrying signal and amplifier power to pass through a single twisted pair at intrinsically safe power levels. All field stations are connected in parallel to a central control system in a safe area allowing the communication system to operate redundantly. The field stations can be selectably connected to a plurality of output devices by tone controlled switching circuits.

Data communication system having a large number of terminals

Abstract: A large number of terminals are connected to a central computer in a loop utilizing a very high speed transmission medium. A sequential stream of message blocks are provided for transmission by the loop. Each message block includes a first portion specifying a terminal address, and a second portion for specifying information data. Each terminal interrogates the address portion of each message block and responds to its own address by either reading the data portion of the message block or loading into the data portion messages to be transmitted. By generating a continuous stream of message blocks, one for each terminal, and using a randomizing scheme for address generation, it is possible to connect a large number of terminals to a data communications system while maintaining a reasonable response time.