Showing papers on "Communications system published in 1985"

Structuring computer-mediated communication systems to avoid information overload

Abstract: Unless computer-mediated communication systems are structured, users will be overloaded with information. But structure should be imposed by individuals and user groups according to their needs and abilities, rather than through general software features.

Error-control techniques for digital communication

Abstract: This practical handbook provides communication systems engineers with guidance in the application of error-control coding It emphasizes the fundamental concepts of coding theory while minimizing the use of mathematical toolsdemonstrates the role of coding in communication system designshows the performance gains achievable with codingillustrates how codes should be used and how to select the right code parametersdiscusses the decoding techniques that should be considered and how they are implementedand examines how detailed performance results are obtained

Data and voice communications system

Abstract: A high speed and relatively error free communications system is disclosed which enables the high speed transmission of data at a 19.2 kilobit per second rate. The data is transmitted over the same communications medium as voice transmissions, the data transmission being virtually imperceptible to the user of the analog telephone system. Connection to and from the data terminals is made through an RS232C interface. A spread spectrum technique is utilized which "whitens" the signals of the data terminal regardless of whether the terminal is idle, transmitting or receiving data. Virtual error free transmission is achieved by interleaving bits, so that noise does not destroy the data, and by error detection and correction techniques which assure that the data, as received, is identical to that transmitted. By using a variable pseudo random code, privacy of data communications are enhanced and cross-talk is substantially eliminated. The resulting system is one that can use a single twisted pair wire for transmission and is capable of transmitting data at a high rate of speed while leaving the analog voice transmission resident and unaffected on the line.

Information display scheme for subscribers of a subscription television system

Abstract: An information display scheme for displaying subscriber unique information to subscribers of a subscription communications system. The system comprises template page receiving means coupled to the communications system for receiving a template page as a format for the subscriber unique information, storage means coupled to the template page receiving means for storing the template page and logic means coupled to the communications system and to the storage means for locally generating and maintaining at least some of the subscriber unique information. The logic means combines the subscriber unique information with the template page for display to the subscriber.

Digital transmission over cross-coupled linear channels

Abstract: For a multiuser data communications system operating over a mutually cross-coupled linear channel with additive noise sources, we determine the following: (1) a linear cross-coupled receiver processor (filter) that yields the least-mean-squared error between the desired outputs and the actual outputs, and (2) a cross-coupled transmitting filter that optimally distributes the total available power among the different users, as well as the total available frequency spectrum. The structure of the optimizing filters is similar to the known 2 × 2 case encountered in problems associated with digital transmission over dually polarized radio channels.

Digital transmission over cross-coupled linear channels

Abstract: For a multiuser data communications system operating over a mutually cross-coupled linear channel with additive noise sources, we determine the following: (1) a linear cross-coupled receiver processor (filter) that yields the least-mean-squared error between the desired outputs and the actual outputs, and (2) a cross-coupled transmitting filter that optimally distributes the total available power among the different users, as well as the total available frequency spectrum. The structure of the optimizing filters is similar to the known 2 × 2 case encountered in problems associated with digital transmission over dually polarized radio channels.

Local area network

Abstract: A communications system suitable for use as a local area network (LAN) is provided wherein the network has a ring topology comprising a plurality of nodes 10 each of which is connected to adjacent nodes by links 14 and 15. Each node comprises a Link Interface Unit (LIU) 11, a Network Interforce Unit (NIU) 12 and a Terminal Interface Unit (TIU) 13. By providing forward and reverse links 14, 15 between nodes the system is capable of reconfiguring itself after link or node failure such that the failed equipment can be bypassed to minimize system disruption. Link Interface Units (LIU) 11 are also capable of bypassing their own node if a node failure is detected. System control is decentralized with each active node contributing to system control such that prime-failure sites are avoided. System protocol depends upon a token passing scheme where only the node 10 currently holding the token is entitled to transmit data and once it has finished its transmission the node 10 passes the token to the next node 10 in the ring. The system operates under a strict timing regime wherein a system cycle of substantially fixed period is established and the first rotation of the token around the ring during the system cycle is used to initiate transmission of the highest priority data with subsequent rotations of the token initiating transmission of data of progressively lower priorities. Accordingly, the timeslots available for transmission of each data type have variable-boundaries determined by the system load.

Synchronous packet voice/data communication system

Abstract: A packet communications network and apparatus for communicating information in voice and data packets transmits and receives voice and data in accordance with standardized frames of a standardized communications format such as a standard DS-1 type trunk. An apparatus is coupled to multiplex standardized channels into a single channel wherein voice or data signals are packetized into independently addressable packets synchronized on, for example, the DS-1 frame. The network includes voice and packet data concentration apparatus operable in a multiple node trunk environment to concentrate signals into independently addressable synchronously switchable packets, thereby to provide an efficient (high data capacity) interface between trunk terminations. Up to four times as much information can be transferred between nodes with the ability to switch between nodes as compared to conventional TDM and PCM communication without compression without the ability to switch between nodes.

Electronic audio communications system with voice command features

Abstract: An advanced electronic communication system is provided for the deposit, storage and delivery of audio messages. A Voice Message System (10) interconnects multiple private branch exchanges (12) of a subscriber with a central telephone office (22). Individual subscriber users may access the Voice Message System (10) through ON NET telephones (18) or OFF NET telephones (24). The Voice Message System (10) includes an administrative subsystem (60), call processor subsystem (62) and a data storage subsystem (64). The Voice Message System (10) enables the user to deposit a message in data storage subsystem (64) for automatic delivery to other addresses connected to the system. The Voice Message System (10) also enables the user to access the system through voice commands which are received and compared to prestored speaker independent digital templates. Once an authorized user has accessed a system, the system allows the authorized user to determine if any messages have been in the data storage subsystem (64) for him. After accessing the system, the speaker utilizes voice commands to control the system, which voice commands are received and compared to prestored speaker dependent digital templates. In response to these commands, prerecorded instructional messages are deposited in the data storage subsystem (64) for instructing a user on his progress in using the system.

Communication system for videoconferencing

Abstract: A system for videoconferencing saves travel time and money. To enable participants to see each other continually and simultaneously, and to show documents and objects, equipment is needed, the costs of which vary with the number of locations to be interconnected, and with measures taken for reducing the needed transmission capacity and the outfit of each terminal. As in known videoconference systems, such as studio, or working place systems, the video and audio signals are switched and/or mixed in the inventive system. The necessary equipment, however, is no longer needed at the respective locations, if a central station for videoconferencing is provided which includes this equipment only in a volume actually necessary for the conference. Each of the connected participant locations only comprises terminal units, the same which are needed for a picture telephone system. In addition, both the video and the audio reception can individually be controlled from each location.

Performance of Noncoherent Direct-Sequence Spread-Spectrum Communications Over Specular Multipath Fading Channels

Abstract: The performance of coherent direct-sequence spread-spectrum communications over specular multipath fading channels is investigated. The average probability of error of the correlation receiver is derived for an arbitrary number of paths with deterministic or random gain coefficients. The gain coefficients, delays, and phase angles of any two distinct paths are modeled as mutually independent random variables. Numerical results for several values of the system and channel parameters are presented.

Modern communications and spread spectrum

Abstract: From the Publisher: This state-of-the-art text is written for first year graduate level courses and provides an introduction to the basic principles of communication systems. The text also provides a comprehensive introduction to the new and rapidly growing area of spread spectrum communications. In addition,the text is a useful reference source for practicing engineers from which they can gain ready access to many of the analytical results available for the analysis of communications systems. Problems are provided at the end of each chapter and answers to a number of the problems are included at the end of the book.

Fast acquisition burst mode spread spectrum communications system with pilot carrier

Abstract: A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmitted carrier and receiver local oscillator (LO), the transmitted carrier ferquency is related to the pilot frequency. The receiver phase-locks the pilot carrier to the local oscillator, thereby providing an IF data signal with reduced frequency error. The IF data signal is multiplied by sine and cosine demodulating signals related to the local oscillator frequency to produce inphase (I) and quadrature (Q) components of the received data signal. The I and Q signals are applied to code matched filters, which produce filtered or decoded signals the amplitudes of which are related to the phase error between the demodulating signals and the IF carrier. A logic arrangement responds to the decoded signals to generate a control signal which step-corrects the demodulating signal to the correct phase. Correction can occur within one or a few bit intervals, thereby allowing burst mode communications while maintaining high throughput for the multiple users of the communication system.

Adaptive communication network and method

Abstract: A communication system for use in a network of interconnected communication paths such as electrical power lines utilized for distributing electrical power. The system includes two or more remote units and a master unit, each having an associated address, which are connected to the network. The remote units are each capable of initiating a down link message sequence wherein a data package containing data, such as data relating to power consumption, is transferred from one of the remote units to the master unit. The down link message sequence may include the transmission of one or more messages containing the data package by the remote units with the particular path taken being a function of network conditions. The master unit acknowledges receipt of the data package by initiating an up link message sequence wherein the remote units transmitting during a down link sequence are informed of the receipt. In addition to addresses and data package the messages include information regarding network conditions. By way of example, a message may include information which indicates the amount of noise present in the message path between the transmitting remote unit and the master unit and information which indicates the number of message transmissions required to transfer a data package from the transmitting unit to the master unit. Remote units ascertain network conditions for selecting optimum message paths by examining messages received on the network, including messages not directed to the receiving remote unit.

Communication system having message repeating terminals

Abstract: A system is provided for communicating between terminal units joined on a power distribution network. The terminal units in the system are capable of interfacing with external devices to which they are attached, of communicating with other terminal units, and of functioning as repeater units. When a message is received by a terminal unit, it determines whether the message is intended for itself or for another terminal unit. If it is intended for another terminal unit, it amplifies and retransmits the message. The system also includes means for determining the shortest communication path between one unit and an intended recipient terminal unit. When a previously established communication route is no longer effective, the system automatically determines a new communication route.

Power line carrier communications system transformer bridge

Abstract: A power line carrier communications system transformer bridge/repeater for receiving on a power line communications network a series of original message bit streams generated by a transmitting module and for relaying on the power line communications network corresponding relayed message bit streams to receiving modules. The transformer bridge/repeater includes coupling means adapted for connection to a power line communications network for receiving original message bit streams and for coupling relayed message bit streams onto a power line communications network. Processor means is connected to the coupling means and is responsive to certain predetermined ones of the original message bit streams for generating a corresponding relayed message bit stream.

Performance of Reed-Solomon Coded Frequency-Hop Spread-Spectrum Communications in Partial-Band Interference

Abstract: This paper is concerned with the performance of a Communications system which utilizes frequency-hop spread spectrum, diversity transmission, Reed-Solomon coding, and parallel error-correction and erasure-correction decoding. Both binary signaling and M -ary orthogonal signaling are considered. The goals are twofold. First, it is desirable to provide good performance in partial-band Gaussian noise interference by use of coding and diversity with an efficient error-correction algorithm. Second, it is necessary to totally neutralize narrow-band interference (regardless of the power level or statistical distribution of the interference) in order to have an effective spread-spectrum system. Through an analysis of the effects of partial-band interference on a frequency-hop spread-spectrum system with diversity, it is shown that the use of ReedSolomon coding with a parallel errors and erasures decoding algorithm accomplishes these goals. The paper also investigates the accuracy of the Chernoff bound as an approximation to the true performance of a frequency-hop spreadspectrum communication system with diversity; side information, M -ary orthogonal signaling, and Reed-Solomon coding. The performance results presented in the paper are based on analysis and computer evaluation. Approximate results based on the Chernoff bound are also given. It is shown that the Chernoff bound for M -ary orthogonal signaling gives a very poor approximation for many cases of interest. This is largely due to the looseness of the union bound.

Analysis of Traffic Access Control Strategies in Integrated Service Networks

Abstract: A common digital transmission facility provides service to a community of heterogeneous users generating traffic with differing intensity, message length, and bit rate. In order for this type of integrated communication system to handle its traffic demands with high efficiency and flexibility, close control of access and switching at the input node is required. We propose, analyze, and compare two different strategies for managing the access of two types of traffic, a blockable wide-band (WB) type of traffic and a queueable narrow-band (NB) type of traffic, sharing the transmission resource dynamically. The first strategy assigns preemptive priority to the WB traffic over the NB traffic, whereas the second strategy employs a wide-band to narrow-band bit rate compression mechanism. Exact analytic models are developed, and solution methods are presented and implemented. It is shown that the best combined performance is obtained when the two strategies are adaptively combined according to the offered load.

Rapid Acquisition for Direct Sequence Spread-Spectrum Communications Using Parallel SAW Convolvers

Abstract: In this paper, a technique is described which uses multiple surface acoustic wave (SAW) devices in parallel to reduce the acquisition time of a direct sequence spread-spectrum communication system. Analysis of system performance in both the search and lock modes is presented, and key quantities such as probability of false alarm, probability of correct detection, mean dwell time, and mean time to lose lock are derived.

Electronic audio communications system with voice authentication features

Abstract: An advanced electronic telecommunication system is provided for the deposit, storage and delivery of audio messages. A Voice Message System (10) interconnects multiple private branch exchanges (12) of a subscriber with a central telephone office (22). Individual subscriber users may access the Voice Message System (10) through ON NET telephones (18) or OFF NET telephones (24). The Voice Message System (10) includes an administrative subsystem (60), call processor subsystem (62) and a data storage subsystem (64). The Voice Message System (10) enables the user to deposit a message in data storage subsystem (64) for automatic delivery to other addressees connected to the system. The Voice Message System (10) also enables a user to access the system to determine if any messages have been stored in the data storage subsystem (64) for the user by first entering an identification code and then speaking a password. The password is compared to a speaker dependent template stored in the system. Pre-recorded instructional messages are deposited in the data storage subsystem (64) for instructing a user on the user's progress in using the system. A Universal Control Board is a programmable electronic digital signal processing means for controlling certain functions of the administrative subsystem (60), call processor subsystem (62) and data storage subsystem (64).

Security and communication system

Abstract: A security and communication system permits the location of signaling portable radio frequency transmitters which may be carried by individuals. If an individual signals with his portable frequency transmitter, a first signal is sent including a first individual identification code to identify the particular portable transmitter. The first signal is picked up by at least one of a plurality of radio frequency relays each positioned in a predetermined location. Such relays immediately transmit a second signal including the first identification code and also a second identification code to identify the individual relay that is transmitting the second signal. Thus the signal sent by the individual relay identifies the location and the specific identity of the particular portable radio frequency transmitter which is sending the signal.

Communication system with operation-procedure guiding function by speech

Abstract: In a communication system, the user can be instructed by a speech message to execute an operation according to the procedure for each of various different services. The switching system within the communication system identifies the kind of service which the user wants and then supplies speech information in a conversational mode to the communication terminal device, thereby instructing the user to execute an operation procedure for the service on the communication terminal device. Therefore, the user can enjoy a desired service even if he has no preliminary knowledge of the operation procedure for the service.

Vehicular data transfer communication system

Abstract: A data transfer communication system capable of handling both node-to-node data transfer messages originating at any transmitter and transmitted to a specific receiver on the network and functional command messages originating at any transmitter and broadcast transmitted to an unspecified number of receivers on the network. Receivers are programmed to receive and acknowledge receipt of correspondingly addressed node-to-node type messages and certain correspondingly addressed functional command type messages with their unique addresses in a predetermined field location of the transmitted message. By utilizing pulse width modulation techniques, binary logic signals and a unique start signal are defined and have a dominant hierarchy that allows for bit-wise contention of the common data bus. In that manner, when contention of the data bus is resolved a higher priority message continues to be transmitted while losing contender delays its transmission until after the higher priority message is completed.

Predictive communication system filtering arrangement

Abstract: A digital communication system includes a predictive decoder (30) that is operative to convert received digital codes into a predictively decoded signal, e.g., speech signal, and to generate a set of predictive parameter signals and a signal representative of the communication system bit rate. A set of filter control signals is generated (325) responsive to the communication bit rate signal. The predictively decoded signal is passed through a filter (335) which modifies the output signal responsive to the filter control signals and the decoder predictive parameter signals to improve the output signal quality. The filter control signals selectively alter the predictive parameter signals to optimize the predictively decoded signal modification for the current transmission bit rate.

Mobile radio communications system with join feature

Abstract: Cooperation between two repeater transceivers of a radio trunking system causes a mobile radio transceiver to join or rejoin ongoing communications. To join ongoing communications, a radio transceiver attempts to acquire a free repeater communications channel by transmitting call signalling identifying a group of transceivers to be contacted. If the group to be contacted is already communicating on another repeater communications channel, the calling radio transceiver is forced to leave the communications channel it is trying to acquire and to begin scanning communications channels in search of call signalling identifying it. Meanwhile, the repeater permitting the ongoing communication interrupts the ongoing communications briefly and transmits the call signalling identifying the group of transceivers to be joined (including the radio transceiver which is to join the ongoing communications). The radio transceiver to be joined detects the call signalling transmitted by the repeater, locks onto the repeater channel over which the call signalling is being transmitted, and joins the ongoing communications. Land line callers are also permitted to join ongoing communications.

Multipriority communication system.

Abstract: A data communication system (10) allocates use of a common data communication medium (14) shared by a plurality of stations (12A-12D). During each transmission cycle, the communication medium (14) carries data packets of varying priority which each station (12A-12D) receives. The stations (12A-12D) are allocated use of the communication medium (14) during one or more priority intervals as a function of the priority of the packet which the station is ready to transmit. Each station (12A-12D) is synchronized to a transmission cycle period which is divided into subperiods. Certain types of packets are relegated to transmission and reception within predetermined subperiods.

Spread spectrum communications. Volume 1, 2 & 3

Abstract: The design and operation of spread-spectrum (SS) communication systems are examined in an introductory text intended for graduate engineering students and practicing engineers. Chapters are devoted to an overview of SS systems, the historical origins of SS, basic concepts and system models, antijam communication systems, pseudonoise generators, coherent direct-sequence systems, noncoherent frequency-hopped systems, coherent and differentially coherent modulation techniques, pseudonoise acquisition and tracking in direct-sequence receivers, time and frequency synchronization of frequency-hopped receivers, low-probability-of-intercept communication, and multiple-access communication. Graphs, diagrams, and photographs are provided.

Beam pointing error as a significant design parameter for satellite-borne, free-space optical communication systems

Abstract: The issue of pointing errors between satellite-borne, free-space optical communication systems is examined. The single-axis pointing error distribution is described as a Gaussian function and is used to define a probability of burst error for the pointing subsystem. A relationship between the rms standard deviation of the pointing error distribution, the probability of burst error, and the Airy far field beamwidth is deduced. It is shown that the system beamwidth and antenna diameter are limited by the probability of burst error. Additionally, it is found that typical terminal designs have less temporal communication system availability than one specifically designed to account for the influence of burst errors.

Cordless communications system

Abstract: A cordless communications system wherein transmission is made and received via magnetic lines of induction comprises a base station and at least one mobile station wherein the base station receives and transmits voice or data signals at different frequencies. A PIGLER unit is selectively disposed between the base station and mobile station so as to extend the range of the communications system.

An Adaptive Digital Suppression Filter for Direct-Sequence Spread-Spectrum Communications

Abstract: This paper describes the structure of a digital implementation of the Widrow-Hoff LMS algorithm which uses a burst processing technique to obtain some hardware simplification. This adaptive system is used to suppress narrow-band interference in a direct-sequence spread-spectrum communication system. Several different narrow-band interferers are considered, and probability of error results are presented for all cases. While, in general, the results show significant improvement in performance when the LMS algorithm is used, certain disadvantages are also present and are discussed in this paper.