Showing papers on "Communications system published in 1969"

Automatic vehicle monitoring identification location alarm and voice communications system

Abstract: In a computer-controlled bus-monitoring system, each of the buses in the system is provided with a two-way radio for communication with the control center on either a voice channel or a data channel. In addition, each bus includes a second receiver for receiving signals from signpost transmitters located along the route, with the signpost information being stored in a temporary storage unit in the bus. The computer continually controls interrogation of all of the buses in the system on a data channel, with the buses automatically replying with the stored signpost location plus the time elapsed since that signpost location was stored in the bus. Deviations from schedule are displayed on a control console at the control center. The bus may be alerted to reply on a voice channel by a special code sent over the data channel with selective calling of the particular bus being provided, and a provision also is made for alerting the control center of an emergency on the bus by automatic data transmission from the bus over the voice channel.

Computer communications system

Abstract: A computer controlled, data communications system is provided for transmitting data between a plurality of external devices. The system comprises up to eight, general purpose, digital computers, each with an associated disc-file storage system. The computers and the disc-file storage units are organized such that communication between the computers is made via the disc-file storage associated with each computer, not directly between the computers themselves. Each group of external devices is coupled to a primary and secondary computer such that upon the failure of the primary computer, the secondary computer will procss the data for its primary group of devices as well as for those external devices for which it is the secondary computer. Each disc-file storage unit is the primary storage for one computer and the copy storage for one additional computer. Upon the failure of a primary disc-file storage unit, a computer can operate with the copy storage unit.

A study of multiaccess computer communications

Abstract: The communications characteristics of multiaccess computing are generating new needs for communications. The results of a study of multiaccess computer communications are the topic of this paper. The analyses made are based on a model of the user-computer interactive process that is described and on data that were collected from operating computer systems. Insight into the performance of multiaccess computer systems can be gleaned from these analyses. In this paper emphasis is placed on communications considerations. For this reason, the conclusions presented deal with the characteristics of communications systems and services appropriate for multiaccess computer systems.

A study of asynchronous time division multiplexing for time-sharing computer systems

Abstract: In order to reduce the communications costs in time-sharing systems and multicomputer communication systems, multiplexing techniques have been introduced to increase channel utilization A commonly used technique is Synchronous Time Division Multiplexing (STDM) In Synchronous Time Division Multiplexing, for example, consider the transmission of messages from terminals to computer, each terminal is assigned a fixed time duration After one user's time duration has elapsed, the channel is switched to another user With synchronous operation, buffering is limited to one character per user line, and addressing is usually not required The STDM technique, however, has certain disadvantages As shown in Figure 1, it is inefficient in capacity and cost to permanently assign a segment of bandwidth that is utilized only for a portion of the time A more flexible system that efficiently uses the transmission facility on an "instantaneous time-shared" basis could be used instead The objective would be to switch from one user to another user whenever the one user is idle, and to asynchronously time multiplex the data With such an arrangement, each user would be granted access to the channel only when he has a message to transmit This is known as an Asynchronous Time Division Multiplexing System (ATDM) A segment of a typical ATDM data stream is shown in Figure 2 The crucial attributes of such a multiplexing technique are:1 An address is required for each transmitted message, and2 Buffering is required to handle the random message arrivals

The Information System

Abstract: An information system is a very complex and sophisticated communication system, but, unlike a telephone system, its major complexity lies not in the switching of lines among various users, but rather in the provision of file structures as a central medium of communication through which relatively complicated data processing takes place. Another difference is that in a telephone system, the several users approach and use the system in essentially the same mode of operation. That is, they are usually transmitters as well as receptors of information. Furthermore, processing of the information that they transmit or receive is usually considered to be a detractive or undesirable property of the communication system, if it in any way modifies the information per se, its meaning or content. The information system, on the other hand, generally has two different classes of users, each of which approaches the system in a different way and for a different purpose, although certain individuals may belong to both classes. Figure 1 presents the model of an information system, and these two classes of people are there labeled Generator and User. The medium of communication, as indicated within the ovals in the center of the diagram are the files. The Generators of information transmit to the files via depositions of various types that may generically be called Documents.

Adaptive Routing Techniques for Distributed Communications Systems

Abstract: The concept of a netted or distributed communications system is significant because it offers a major advantage over conventional communications systems, i.e., a better chance of providing surviving lines of communication after an attack on the system. During and after an attack, however, an effective adaptive routing technique is necessary to adjust the routing tables of the message-switching control system to the changing situation. Previously investigated adaptive routing techniques are shown to be insufficient for the task, and a number of promising alternatives are formulated and investigated such as some stochastic techniques, which use information on messages passing through the network to adjust the tables, and some deterministic techniques, which use dynamic programming or graph-theoretic algorithms to recalculate changes in the tables from observed changes in the network. Each alternative has operational advantages, which make it good for certain types of communications systems, and certain disadvantages if applied to others. Regions of applicability and inapplicability, with respect to the above system parameters, are given for the various techniques. Recommended techniques are specified for two currently proposed applications of distributed communications systems. A number of research areas are pointed out in which further efforts in the analysis and simulation of adaptive routing techniques will have useful payoffs in the design of future distributed communications systems.

Secure communications system

Abstract: A privacy communication system is herein disclosed comprising apparatus for digitizing information to be transmitted, apparatus for logically adding a selected pseudo-random digital code to the digitized information, apparatus for removing the pseudo-random code upon reception and apparatus for synchronizing the transmitted and received pseudo-random codes.

Digital data communications system with means for improving system security

Abstract: For reducing the possibility that unsafe machine operation may result from distorted digital code words representing commands or conditions, a communications system in which both the machine and a central control unit include transceivers which repetitively transmit a digital word sequence consisting of a digital word and its complement. Decoder logic in the other transceiver must recognize both an acceptable digital word and the complement of that word before machine operations will be ordered or initiated.

Satellite communication system

Abstract: An improved communication system using an active transponder to relay microwave signals from any one of a number of transmitting stations to selected groups of receiving stations In a preferred system the active transponder is installed in a satellite spacecraft and is arranged to convert a number of signals, in closely spaced channels, from the transmitting stations in such a manner that the bandwidth of each one of the relayed signals is increased and retransmitted without suffering from the effects of interchannel modulation

Secrecy communication system

Abstract: A secrecy communication system wherein an input signal is sampled at the encoder by electronic sample-and-hold circuits, each of which includes a capacitor to temporarily hold a sample. The input signal is sampled at contiguous intervals and at a rate selected according to the sampling theorem of at least twice the highest frequency component in the input signal. The samples are read from the capacitors in a rearranged abnormal order to obtain unintelligible secured signals. The decoder at a receiver essentially operates in a reverse sequence from the encoder to reconstruct the original input signal. The sample-and-hold circuits are arranged in groups so that while information is read into one group of capacitors, samples are simultaneously read from capacitors in another group.

Communications system with frequency and time division techniques

Abstract: A communication system for a substantial number of subscribers is shown having random access capabilities without the requirement for the usual central exchange. The system uses a frequency division scheme for separating the several communication information channels. The individual subscriber units are interconnected as by means of one or more wires which are also connected to a master clock which continually generates time division digital information consisting of a plurality of pulses and unused time spaces (ones and zeros) including binary circuit code information and synchronizing pulses. A relatively limited band width is required for carrying this control information which is substantially displaced in frequency from the band containing the several communication information channels. These channels are generated by means of a frequency synthesizer in each of the subscriber units, each of which continually monitors the digital control information to determine whether its address is being called and the circuit code representing the channel of the incoming call. Similarly, outgoing calls are initiated by picking up a headset at the subscriber unit which causes an unused channel to be selected, inserting its circuit code into the digital stream and causing the frequency synthesizer in responding to this code to generate the corresponding carrier frequency. The audio information is then converted to single side band (or other) modulation of the particular carrier frequency signal.

Moving object communication control system

Abstract: A communication system between mobile and wayside stations wherein the mobile stations are traveling on a track which is divided into sections by means of an open-type transmission line paralleling the track. A frequency selection and conversion device for each section of transmission line or track is connected to the transmission line to define the length of each section. A series of lower frequency carriers transmitted on the line are allotted respectively to each specific section of transmission line. These low-frequency carriers travel with a low loss along the transmission line and they are selected and converted by their respective frequency selection and converter device to a common high-frequency carrier signal for leaky transmission to a mobile station on the corresponding track section. These signals are used for train control and other communication signals may be transmitted on the same transmission line by a high-frequency carrier signal which is common to all sections, such that the common signal will leak from the transmission line for reception by a mobile station no matter its location on the track.

A model for the local area of a data communication network objectives and hardware organization

Abstract: This paper, together with its companions(1)(2) describes the experimental data communication network being implemented at the National Physical Laboratory. The purpose of the work is two-fold.Firstly, it will act as a model of the 'local area' network assumed, but never analysed in detail, in the NPL proposal for a possible National Data Communication System(3)(4)(5).Secondly, it will provide data communications between a wide variety of devices. These range from computers to teletypes and are spread over the 78 acres of the Laboratory site.

Secure spread spectrum communication system

Abstract: A communication system is protected against jamming by modifying a conventional spread spectrum communication system by inserting errors, in the form of digital noise, into the pseudo-noise digital code used to generate the spread spectrum carrier. A bidirectional system is provided so that when jamming occurs, as a consequence of breaking the corrupted spread spectrum code, the pseudo-noise digital code and/or the percent of errors is changed in a prearranged manner to compensate for the jamming and/or reduce the likelihood of breaking the corrupted spread spectrum code. A conventional correlation receiver is employed to recover the intelligence.

Time division multiplex communications system

Abstract: A closed loop two-wire serial communications system for providing two-way communications between a plurality of serially connected terminal complexes and a central control station. The communications system including a plurality of time multiplexed channels each having switching or multiplexing information, control information and data to effect bidirectional data flow between the terminal complexes and the central.

Predistorted Waveguide Filters for Use in Communications Systems

Abstract: Predistortion is a standard technique for correcting the effects of energy dissipation in filters, making their response conform to that of ideal filters. The problem of dissipation is particularly noticeable in narrowband bandpass filters used in microwave communications systems. Dissipation makes the passband edges slump downward, as shown in Figure 1, which can cause distortion and intermodulation. In predistorting a filter, we allow for dissipation in the initial design. A response approximating the ideal response can be approximated at the price of increased insertion loss. The flat response of predistorted filters is advantageous when used in high-capacity microwave communications systems; however, the filters have an additional property which makes them especially attractive for certain applications in microwave communications systems.

Time division multiplex communication system

Abstract: A time division multiple access communication system including earth stations and a satellite station wherein each earth station includes a paired transmitter and receiver for acquisition and burst synchronization; the transmitter sending first pattern signals, each identifying the start of one signaling frame including a plurality of frequency slots divided on a time basis to identify each earth station, to the satellite for reception and retransmission to the earth stations; the receiver deriving a reference time point from each received first pattern signal, for generating second pattern signals; detecting a time difference between time periods of the first and second pattern signals including a polarity indication of such difference; algebraically adding signals representing such time difference and polarity, a preassigned time interval during which the signal burst is to be transmitted, and the one signal frame and time position therein at which the signal burst is to be transmitted

Digital radio communication systems using repeaters operating at same frequency

Abstract: Communication systems using a repeater or a chain of repeaters each of which receives information during one portion of a cycle of operation and transmits at the same frequency during a subsequent portion of the cycle in a manner to avoid interference. Digital circuitry is provided for transmitting, repeating and receiving digital signals in a manner such that no information is lost and good spectrum utilization and high fidelity are achieved without compounding distortion and noise effects, permitting use of a large number of relatively low-power repeaters. Delta modulator and demodulator means are provided for converting voice or other analog signals to digital signals and for reconverting the digital signals to analog signals. Radio waves of one frequency can be used and a mobile unit can be moved from the field of a base unit to that of a repeater or from the field of one repeater to that of another, without interruption in communication.

Channel reallocation system and method

Abstract: , In a time division multiple access communications system having multiple ground stations and a satellite for communicating signals between ground stations, the channels are periodically reallocated among the several ground stations based upon the traffic load at the time of reallocation. At the reallocation time, a slack group of channels, representing presently available channels, are distributed among the ground stations. The time of the periodic transmission (hereinafter referred to as transmission burst) from each ground station is shifted in time with respect to the time of the transmission burst from a reference station to accommodate the reallocation of channels. The transmission burst times of all stations are not shifted simultaneously but are shifted in accordance with a set of rules which prevents overlapping between transmission bursts from adjacent stations.

Time-frequency-phase in-band coded communications system

Abstract: A communication system which uses a diversity technique to overcome problems of signal fading and multipath distortion. Frequency shift keying (FSK) and differential phase shift keying (DPSK) are employed in combination to code a sequence of signals responsive to a word represented by a stream of input binary digits. The sequences of signals to be transmitted are arranged such that identification of the frequency, phase shift and location of one signal in the sequence uniquely defines the input word.

Third generation destination signing: an electronic route guidance system

Abstract: THE PROBLEM IS ANALYZED OF ROUTING AN AUTOMOBILE DRIVER SAFELY AND EFFICIENTLY FROM HIS ORIGIN TO HIS DESTINATION. PRESENT HIGHWAY ROUTING AND NAVIGATIONAL METHODS ARE EXAMINED IN THE FRAMEWORK OF A SYSTEMS ANALYSIS OF THE HIGHWAY ROUTING SUBSYSTEM. IN THIS CONTEXT, THE FUNCTIONS, CHARACTERISTICS, NORMATIVE OPERATION, AND CONSTRAINTS ASSOCIATED WITH THE PRESENT ROUTING SUBSYSTEM ARE DELINEATED. THE ANALYSIS TRACES THE IMPLICATIONS OF REMOVING THREE MAJOR CONSTRAINTS FROM THE PRESENT HIGHWAY ROUTING SUBSYSTEM. THESE CONSTRAINTS ARE (1) COMMUNICATION WITH DRIVERS PRIMARILY EXISTS AS AN 'OPEN LOOP', (2) COMMUNICATION CANNOT BE INDIVIDUALIZED BUT MUST BE UTILITARIAN, AND (3) THE HIGHWAY AND THE AUTOMOBILE ARE SEPARATE ENTITIES. TECHNIQUES FOR COMMUNICATING WITH DRIVERS, WHICH WOULD EFFECTIVELY REMOVE PRESENT SYSTEM CONSTRAINTS, ARE NEXT EXAMINED AND CONSIDERED IN THE LIGHT OF A FUNDAMENTAL ANALYSIS OF THE ROUTING PROBLEM. EVOLVING FROM THIS ANALYSIS IS A ROUTE GUIDANCE SYSTEM CONCEPT AND A PLAN FOR IMPLEMENTING THE CONCEPT. THE CONCEPT IS CHARACTERIZED BY THESE ESSENTIAL FEATURES: (1) INDIVIDUALIZED COMMUNICATION, (2) UNAMBIGUOUS INFORMATION, (3) UNIQUE CODIFICATION SCHEMES, (4) CAPABILITY FOR CONVERSION TO DYNAMIC ROUTING, AND (5) COMPATIBILITY WITH EXISTING SIGNING TECHNIQUES. THE IMPLEMENTATION PLAN FOR THE CONCEPT CONSISTS OF A MULTIPHASED RESEARCH AND DEVELOPMENT (R & D) PROGRAM WHICH IS CURRENTLY UNDER WAY AT THE BUREAU OF PUBLIC ROADS. INCLUDED IN THE PROGRAM ARE MAJOR STUDIES LEADING TO THE DESIGN OF AN ELECTRONIC ROUTE GUIDANCE SYSTEM. FOLLOWING THE DESIGN OF THE SYSTEM A PROTOTYPE SYSTEM WILL BE INSTALLED ON AN ACTUAL HIGHWAY NETWORK FOR A THOROUGH TEST AND EVALUATION PROGRAM. /AUTHOR/

Communication systems which minimize coding noise

Abstract: The problem of minimizing coding or quantizing noise in a communication system is posed in a general setting. It is shown that if the messages to be transmitted are sample sequences drawn from a discrete-time random process meeting a certain simply stated criterion of “randomness” and if there exists a quantized communication system which is optimal in that it introduces a minimum amount of coding noise, then this optimal system can be realized using a transmitter of special form. Specifically, the optimum transmitter is one which quantizes each message sample according to a scheme that depends only upon the quantized material already transmitted, rather than upon the (unquantized) material that has been previously offered for transmission. It follows that only digital storage is required at the transmitter or receiver. If the receiver is limited, a priori, to have only a given finite amount of storage, and if the system is optimum within this constraint, the transmitter need have only the same amount of storage.

Phase slip corrector means and method for synchronization of pseudorandom generating means in multistation networks

Abstract: IN CERTAIN TWO-WAY COMMUNICATIONS SYSTEMS INVOLVING A MULTIPLICITY OF STATIONS, PSEUDORANDOM SEQUENCE GENERATORS ARE USED TO CODE MARK-SPACE SYMBOLS TRANSMITTED BY WIDE BAND RADIO FREQUENCY WAVES. THE DATA TRANSMITTED ARE ENCODED BY MULTIPLEXING THE INFORMATION WITH THE OUTPUT OF A PSEUDORANDOM SEQUENCE GENERATOR. ONE SUCH GENERATOR IS PROVIDED AT EACH STATION FOR BOTH TRANSMISSION AND RECEPTION. ASSUMING THE DESIGNATION OF A PARTICULAR STATION AS CONTROL CENTRAL, THE PRIOR ART SHOWS ARRANGEMENTS FOR SO SYNCHRONIZING THE VARIOUS PSEUDORANDOM SEQUENCE GENERATORS SO THAT THE SEQUENCE PROVIDED AT ANY OUT LYING STATION WHICH IS RECEIVING WILL LAG, IN REAL TIME, BEHIND THAT GENERATED AND USED FOR TRANSMISSION AT CONTROL CENTRAL, BY AN AMOUNT PROPORTIONAL TO SIGNAL-TRAVEL TIME, I.E., THE DISTANCE BETWEEN THE STATIONS. HOWEVER, ASSUMING SUCH SYNCHRONIZATION, SYSTEMWISE, THERE IS NEED TO MAKE SUITABLE ADJUSTMENTS TO PERMIT A GIVEN OUTLYING STATION TO TRANSMIT BACK TO CONTROL CENTRAL. TWO-WAY COMMUNICATION BETWEEN OUTLYING STATIONS COMPLICATES THE PROBLEM. THE INVENTION HEREIN DISCLOSED SOLVES THE PROBLEM BY SYNCHRONIZING A PSEUDORANDOM SEQUENCE GENERATOR AT CONTROL CENTRAL WITH PRINCIPAL REFERENCE OUTPUTS OF PSEUDORANDOM GENERATING MEANS AT EACH OUTLYING STATION. SUCH GENERATING MEANS COMPRISES A PSEUDORANDOM GENERATOR PER SE AND A DELAY LINE PROVIDING A PRINCIPAL REFERENCE SEQUENCE. THE DELAY LINE IS TAPPED TO PROVIDE ACCESS TO ANY ONE OF A PLURALITY OF TIME-ADVANCED SEQUENCES. WHEN IT IS DESIRED TO TRANSMIT BACK TO CONTROL CENTRAL, A PREDETERMINED TIME-ADVANCE SEQUENCE IS EMPLOYED. OTHER TIME SEQUENCES ARE USED FOR COMMINICATION WITH OTHER OUTLYING STATIONS.

Associative memory control for a switching network

Abstract: A communication system is disclosed in which paths through a multistage switching network are located by reference to information stored in associative memory. Specific methods control the acquisition of the stored information for establishment and termination of the network paths.

Digital communications clock synchronizer for responding to pulses of predetermined width and further predictable pulses of sufficient energy level during particular interval

Abstract: THE DISCLOSURE IS DIRECTED TO LOGIC APPARATUS USED IN CONJUNCTION WITH A DIGITAL COMMUNICATIONS RECEIVER, AND EMPLOYED TO ESTABLISH WHEN CORRECT PULSES, KNOWN AS SUPERVISORY PULSES, ARE BEING RECEIVED FROM ANOTHER COMMUNICATIONS SYSTEM OR FROM ANOTHER UNIT OF THE SAME SYSTEM. OUR DEVICE LOOKS FOR A FIRST PULSE OF THE CORRECT WIDTH, AND BY VIRTUE OF BEING ABLE TO PREDICT WHEN SUBSEQUENT CORRECT PULSES WOULD BE RECEIVED, IS ABLE TO ESTABLISH IF SYNCHRONIZATION EXISTS. IF IT DOES EXIST, OUR DEVICE THEN PROVIDES A CLOCK SIGNAL TO THE RELATED DIGITAL COMCOMMUNICATIONS RECEIVER WHICH IS THEN IN FREQUENCY AND IN PHASE WITH THE CLOCK OF THE OTHER COMMUNICATIONS UNIT.

Subscriber terminal unit for telephone carrier system

Abstract: The disclosure relates to a subscriber terminal for a telephone communication system which is adapted for connection to a cable transmission pair from a central office to supply an additional facility without affecting the original system. The subscriber terminal utilizes a rechargeable battery which furnishes power to its receiver and transmitter sections which operate at frequencies different from those of the physical communication system. The battery is controlled by a charging circuit so as to be charged by the central office power supply during nonoperation of the physical system.

Detection and classification of nonlinearly generated environment interference sources by use of a verifier system

Abstract: A method of locating and classifying electromagnetic interference sources in operational electromagnetic environments of communication systems. Interference sources comprising electrical nonlinearities in mechanical junctions of the structural environment of the communications system are excited by electromagnetic radiation at frequency F1 from system transmitters and by induced signals at frequency F2 from a loop probe held in close proximity to the sources to create harmonic and intermodulation product signals. These signals are sensed on system receiving antennas operating in the operational electromagnetic environment. The levels of the sensed signals determine whether the interference sources are interference contributors, noncontributors or localized interference sources, or parasitic elements.