Showing papers on "Communications system published in 1971"

Communications system for electric power utility

Abstract: An electric power utility communication system is disclosed comprising a plurality of geographically distributed group control units and groups of terminal processor units, with each such terminal processor unit within a group coupled to a respective group control unit through the neutral conductor of the power utility distribution lines. Availability of the neutral as a communications link is achieved by inserting a parallel resonant circuit between the neutral and ground at each ground point in the system. Alternately, the signal generating and/or receiving equipment may be connected between the conventionally grounded neutral and deep earth ground, to develop the communications signal across the earth impedance. Communications information is transmitted over the neutral by coded high frequency signals to the terminal processor units which have electronic logic capacity to accept and perform command functions, interrogate meters, and transmit information back over the neutral to their respective group control units. Overall control is achieved by a central computer controller coupled to each group control unit by conventional transmission means, and which generates and receives coded signals through the group control units.

Digital data communication system

Abstract: A digital data transmission system comprising a plurality of interconnected switching units, each such unit having connected thereto at least one transmission loop, and each such loop having at least one digital device attached thereto. The system provides controllable buffering of digital data thereby allowing digital devices having different data transfer speeds and storage capabilities to communicate asynchronously. The system allocates communication resources upon request but only creates actual communication paths when the requesting device is transmitting data. Thus system resources need not remain committed between bursts of data.

Tdma satellite communications system having special reference bursts

Abstract: In a satellite transponder communications system operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst, and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the compressed block of data until a multiplexer requests the block of data for inclusion into the earth station''s transmitted burst. The arrangement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory. A comparable system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules.

A new equalizer structure for fast start-up digital communication

Abstract: The use of transversal filters for automatic equalization has made possible high-speed data communication over voiceband telephone channels. Recently much attention has been focused on the possible use of the high-speed data sets in private line multiparty polling systems. However, for such applications, it is necessary to reduce the start-up time of the present automatic equalizer drastically. This paper examines the start-up time (settling time) of the transversal filter equalizer for two important classes of data communication systems: Class IV partial-response systems and single-sideband Nyquist systems. (The latter represents the limiting case of vestigial-sideband systems with small roll-off bandwidth.) It is shown that in single-sideband Nyquist systems the input signals to the gain controls of the transversal equalizer may be nearly orthonormal. Consequently the equalizers may have a short settling time. It is also shown that the equalizer settling time is much longer in Class IV partial-response systems, because such systems use controlled intersymbol interference and the input signals to the gain controls are highly correlated. The possibility of reducing the settling time of the automatic equalizers is examined. A new equalizer structure is developed based on the following principles: (i) Equalizer settling time can be minimized by making the input signals to the gain controls orthonormal, and (ii) Such a minimization does not change the noise power, the mean-square equalization error, the convexity of the gain control adjustment, and the feedback control loops in the equalizer. These principles are general in that they apply regardless of the type of modulation — single-, vestigial-, or double-sideband (SSB, VSB, or DSB) — or the signaling scheme (Nyquist or partial-response). Application of these principles to Class IV partial-response systems is considered. For private line systems and systems where amplitude distortions in the communication channels are not severe (delay distortions can be arbitrary), the new equalizer can be implemented by simply adding a prefixed weighting matrix to the conventional transversal equalizer. Analysis and computer simulation show that the use of such a new equalizer can residt in a significant reduction in the system's start-up time.

Multiple-access techniques for commercial satellites

Abstract: The unique multipoint interconnection capabilities of satellite communication networks place a burden on the communications system designer to achieve highly efficient transmission capacity in the face of a very wide range of network requirements. The ability of various types of multiple-access systems to meet these requirements is the subject of this paper. INTELSAT, recognizing that the frequency division multiplex-frequency modulation, frequencY division multiple access (FDM-FM-FDMA) method it currently uses has advantages in some applications but is not optimum for the multiple-access environment, has supported the development of two-digital multiple-access communications techniques: single channel per carrier frequency division multiple access (SPADE) and time division multiple access (TDMA). These two techniques are discussed in detail and the paper concludes with a presentation of a promising multiple-access technique of the future which includes time division switching on board the satellite.

Switching system for tdm data which induces an asynchronous submultiplex channel

Abstract: A TDM multiplex communications system for effectively transmitting voice, or high speed, and signalling information or low speed data, between a plurality of stations by employing an asynchronous sub-multiplex channel for the low speed data transmission. The sub-multiplex channel comprises one or more time slots of the equally divided time slot intervals of the normal multiplexing time frame, and is available for use by any connected station of the incoming highways to the central switch, having signaling information or low speed data ready for transmission. Each of the connected stations of the incoming highways having voice or high speed data is assigned, for synchronous operation, particular ones of the remaining time slots, in cyclic fashion, within the multiplexing time frame. Since the submultiplex channel is arranged so that the sending or receiving station address is carried beside the data to be transmitted, any data rate is acceptable thereby.

Tdma satellite communications system with an aperture window for acquisition

Abstract: In a satellite transponder communication system operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst, and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the block of data until a multiplexer requests the block of data for inclusion into the earths station''s transmitted burst. The arragnement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory. A system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules. Acquisition of the proper burst time within each frame is accomplished by sending out a low power signal and monitoring its phase relative to the received frame reference. Apertures are provided to insure that no two earth stations are simultaneously in the acquisition mode.

Emergency distress signaling system

Abstract: A system for addition to a conventional dispatched vehicle twoway radio communication system to enable an operator to notify a central dispatcher of an emergency condition arising after the operator leaves the vehicle. The system includes a unit which plugs directly into the microphone input of the conventional system and which is responsive to a signal transmitted from a portable transmitter carried by the operator for playing a prerecorded emergency message through the transmitter of the conventional radio system.

Central address distributor

Abstract: An address-coded communication system is disclosed wherein the size of the address set required in the system is reduced essentially to the maximum number of stations communicating at any time, as contrasted with requiring an address set size equal to the number of stations located in the system. Specifically, a central address distributor is provided which distributes available identifying address codes on the transmission medium in a manner which makes such address codes available to communicating stations for the duration of a link. In one embodiment, a station desiring to go on line makes a bid for an identification address from the central address distributor and by means of a special handshaking technique, the central address distributor assigns an identification address to that user. When such station terminates the call, it returns its assigned address to the central address distributor so that such address can subsequently be re-assigned to another station or user. Special subperiods are assigned within a period for both sending addresses being distributed from the central address distributor, and for returning the addresses from the stations to the central address distributor after use. In another embodiment, the central address distributor continuously polls the stations of the system to determine which addresses are in use at a given time. This is accomplished by generating addresses at the distributor and inserting the addresses, one at a time, into a special polling subperiod which is sent around the entire system. If this address is removed from the transmission line and absorbed by a station or mutilated by the system and therefor not returned to the central address distributor, then it is assumed the address is in use. On the other hand, if this address returns on the line to the central address distributor, this indicates that the address is not in use and, consequently, is placed in a storage register containing available addresses. The available addresses are subsequently sent by the distributor on the line in designated address distributor subperiods from which any station can remove and use an address on a first come basis. In this embodiment, after a station terminates a call and is through using an address, it need not return the address directly to the central address distributor since such distributor is continuously polling the stations to determine which addresses are in use. The central address distributor permits reduction of the size of the address set required, resulting in economizing on system bandwidth and increased system efficiency.

Tdma satellite communications system

Abstract: In a satellite transponder communications system operating in a time division multiple access mode, each earth station transmits data in a burst format All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications A single earth station sends out the reference burst as well as its normal burst, and in the case of multi-transponders and multi-transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the block of data until a multiplexer requests the block of data for inclusion into the earth station's transmitted burst The arrangement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory A comparable system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules

Data-Aided Carrier Tracking Loops

Abstract: An innovation which improves the capability and performance of certain types of phase-coherent demodulators is introduced. This innovation has application in the fields of telemetry and tracking, e.g., relay satellite systems, deep-space communications, and military communication systems. The basic idea of the innovation centers around using the power in the composite signal sidebands to enhance the demodulator's effective signal-to-noise ratio (SNR). The vehicle through which this is accomplished employs the principle of decision-directed feedback. In its simplest form it is shown, for the first-order loop, that the maximum improvement in loop SNR relative to a standard phase-locked loop is 10 dB. The paper explores and illustrates the corresponding improvement realized in detection system efficiency. Extension to higher order loops follows directly from the analysis given here.

Emergency reporting digital communications system

Abstract: A digital communications system which can be used for emergency reporting having a transmitting unit which sends out information signals identifying the transmitting unit and identifying the type of emergency. A relay station located within the area receives and stores the signal and in response thereto electronically dials a predetermined telephone number to a data center, transmits an encoded signal identifying the station and then relays the information sent from the transmitting unit. Assistance or corrective action may then be provided by dispatch from the data center.

Phase-Ambiguity Resolution in a Four-Phase PSK Communications System

Abstract: The constraints of digital satellite communications systems have led to the derivation of a method for resolving the problem of recovered-carrier phase ambiguity in a coherent fourphase phase-shift-keying (PSK) communications system while simultaneously providing synchronization information. This method is described for the general case and a general implementation is given. In addition, implementations are given for two particularly simple special cases.

Digital communication system with reduced intersymbol interference

Abstract: The transmitter of a digital communication system comprises a compensator which controls at least one of the level, frequency and phase of a signal to be transmitted in accordance with a characteristic of the communication system and the condition of the code preceding or succeeding the signal. The level, frequency and phase at the detector of the receiver are designated values.

Subscription communication system

Abstract: A subscription communication system is described wherein each one of many subscribers has his own individual optical communications service link from a common distribution station. As a result, there is positive control over the communications service provided to each subscriber, and information as to the subscriber''s economic accountability for such service is generated right at the distribution station. A service request communications link is also provided from each subscriber station to the distribution station, preferably in the form of an optical signal, and the economic accountability of the subscriber is dependent upon receipt of the request signal. The service and request signals are affected equally by adverse weather conditions, so that the subscriber is not billed for service under weather conditions which are below the threshold of system availability.

Loop communications system

Abstract: A communications system including a central station connected in a series loop with a plurality of remote stations and in which under control of said central station, the remote stations in the order of their physical position transmit data to the central station.

Tdma satellite communications system with improved acquisition

Abstract: In a satellite transponder communications system operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst, and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the block of data until a multiplexer requests the block of data for inclusion into the earth station''s transmitted burst. The arrangement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory. A comparable system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules. Acquisition of the correct burst position is accomplished by sending out a low power signal and, adjusting its phase until it coincides with the proper received burst position. The low power signal is simply a square wave signal which is in phase with the start signal from the burst synchronizer.

Tdma satellite communications system with rapid automatic re-entry following brief outages of earth station equipment

Abstract: In a satellite transponder communications system operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the block of data until a multiplexer requests the block of data for inclusion into the earth station's transmitted burst. The arrangement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory. A comparable system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules. Loss of synchronization at an earth station due to short time transmission interruptions is compensated for by predicting the correct burst transmission time following the end of said interruption.

Tdma satellite communication system with multi-pcm frames per tdma frame

Abstract: In a satellite transponder communications system operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst, and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the compressed block of data until a multiplexer requests the block of data for inclusion into the earth station''s transmitted burst. The arrangement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the word stored in the memory. A comparable system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules. A terrestrial interface module is provided for receiving multiple voice channels and converting same into PCM data frames. The TDMA frame time is greater than a PCM data frame and thus multiple frames of PCM data are transmitted in a single burst, once per TDMA frame. The terrestrial interface module rearranges the digital voice channels so that consecutive digitized samples from the same voice channel are ultimately transmitted in a contiguous format.

The design of a switching system to allow remote access to computer services by other computers and terminal devices

Abstract: An experimental store-and-forward data communication network has been set up within the National Physical Laboratory (NPL) site. The system represents one element of a national data network scheme proposed by NPL.The network is currently offering a data communication service on a trial basis and is operating successfully.Work on an enhanced communication system is in hand. This new system has been organised along strictly hierarchical lines and is intended to meet the requirements of computer to computer communications in a general manner, permitting resource-sharing applications and remote-access computer services to be developed in the Laboratory.

Testing technique for phase jitter in communication systems

Abstract: A method and apparatus for measuring phase jitter by monitoring the period of a communication signal output of a communication system each one-half cycle. At each one-half cycle, the width of the signal output is compared with an average one-half period of the signal. Both digital and analog techniques are disclosed for displaying a peak-per-cycle phase jitter and a cumulative peakto-peak phase jitter of the signal.

Communication system providing combined audio-video service

Abstract: A communication system for combined audio-video service utilizes at the subscriber''s station two separate line circuits, one being the normal audio-only line to the telephone central office and the other, a special six-wire line, extending from the premises to a video switching network and providing both audio and video signals and transmission on all audio-video calls both incoming and outgoing. The video switching network provides switching facilities for combined audio-video calls exclusively for combined service subscribers in the area.

Differentially adaptive communication system

Abstract: A communication system for improved reception of signals over distorted communication channels, multipath environments and telephone cables is disclosed in which phase shift keyed coded pulses are transmitted such that their respective multipath contributions are separable at a differentially adaptive receiver which stores previous samples of the distorted transmitted pulse for use as a reference in a coherent matched filter type detector employing decision feedback to allow coherent detection without channelizing filters in systems using both binary and four phase modulation. The differentially adaptive receiver is employed both in modulator-demodulator type systems and in predetection combination communication systems.

Data communication system incorporating device selection control

Abstract: A data communication system incorporating control means at the transmitting station for selecting which of several output devices at the receiving station will record the transmitted data. Selection of the output device governs the data rate of the transmitted information. Error control means at the receiving station operates to signal the transmitting station to select a predesignated output device for recording messages previously received in error on another output device. The error control means is responsive both to errors induced by the communication channel and recording errors induced by the output device.

Busy bit for time division multiplex signals to reduce signal processing time

Abstract: A predetermined bit location in each time slot word of a time division multiplex signal is reserved for including a signal bit which indicates by its signal state whether or not that particular word is in use for a call connection within the time division multiplex signal communication system. Busy bits on signal paths which are to be interconnected through a network are matched to identify a common available time slot on the paths. Busy bit signal states interact with switching equipment control memory signal states for holding up and taking down call connections.

Data communication system with addressable terminals

Abstract: A system for communicating addressed data over a single channel amongst a plurality of dispersed stations. The channel can comprise any of a variety of communication media such as twisted pair wire, telephone line, radio frequency, etc., singly or in combination. An address generator is coupled to the channel for applying a sequence of address bit signals thereto to successively define a plurality of different multi-bit addresses. Each station monitors the address information on the channel and, will either apply a data word to or extract a data word from the channel for each address appropriate to that station. Each address bit will be maintained on the channel for one address bit period. During each address bit period, one multi-bit data word can be placed on the channel. An address bit format is employed which enables each station to extract both data bit and address bit synchronization from the channel as well as the address and data information.

Serial loop communications system

Abstract: A communications system including a central station connected in a series loop with a plurality of remote stations and in which under control of said central station, the remote stations in the order of their physical position transmit data to the central station.

Wide band multiplexing system

Abstract: A COMMUNICATIONS SYSTEM EMPLOYS TANDEM PHASE MODULATION FOR MULTIPLEXING NARROW BAND ANALOG DATA WITH VERY HIGH SPEED DIGITAL DATA. THE NARROW BAND DATA IS APPLIED AS LINEAR PHASE MODULATION OF THE SYSTEM CARRIER, WHILE THE HIGH SPEED DIGITAL DATA IS APPLIED AS PHASE-SHIFT MODULATION OF THE CARRIER. D R A W I N G