Showing papers on "Communications system published in 1981"

Digital and analog communication systems

Abstract: Add this article to private library Remove from private library Submit corrections to this record View record in the new ADS The book presents an introductory treatment of digital and analog communication systems with emphasis on digital systems. Attention is given to the following topics: systems and signal analysis, random signal theory, information and channel capacity, baseband data transmission, analog signal transmission, noise in analog communication systems, digital carrier modulation schemes, error control coding, and the digital transmission of analog signals. Bibtex entry for this abstract Preferred format for this abstract

The evolution of user behavior in a computerized conferencing system

Abstract: Data from 18-month operational trials of the EIES system indicate that the range of features considered valuable in a computer-based communication system increases with the amount of experience gained by using this medium of communication. Simple message systems alone are not likely to satisfy the communications needs of long term, regular users of computerized communications systems. Among the capabilities which long term, regular users find valuable are group conferences, notebooks for text composition, and self-defined commands.

Spread-Spectrum Multiple-Access Communications

Abstract: In a direct-sequence spread-spectrum multiple-access communications system several asynchronous signals simultaneously occupy the same channel. Each of the signals employs a signature sequence which is selected to have certain desirable correlation properties. For multiple-access communications the primary goal is to be able to separate the spread-spectrum signals at the receiver even though they occupy the same bandwidth at the same time. This problem is considered in the sections which follow for various forms of direct-sequence spread-spectrum modulation including binary phase-shift keying, quadriphase-shift keying, and minimum-shift keying. The emphasis is on the analysis of system performance rather than on the selection of signature sequences. Hence this material complements the recent paper of Sarwate and Pursley (1980) which examines in detail the problem of signature sequence selection.

Radio propagation for space communications systems

Abstract: This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. The design and reliable operation of satellite systems which provide the many applications in space and rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds, fog, precipitation, and turbulence cause uncontrolled variations in the signal characteristics which can result in a reduction of the quality and reliability of the transmitted information. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz are reviewed. Particular emphasis is placed on the effects of precipitation on the earth-space path, including rain attenuation, and rain and ice-particle depolarization. Sky noise, antenna gain degradation, scintillations, and bandwidth coherence are also discussed. The impact of the various propagation factors on communications system design criteria is presented. These criteria include link reliability, power margins, noise contributions, modulation and polarization factors, channel crosstalk, error-rate, and bandwidth limitations.

A local area contention network data communication system

Abstract: This disclosure relates to a station for a data transmission network which is adapted to operate in a cyclic mode for contending for access to the network channel along with other stations of the network. The three states of the cycle are the idle state, the packet-being-transmitted state and the acknowlegement period state. Each station will not begin transmission until it determines that the channel is in an idle state. Once the station has determined that the channel is idle, it will then delay for a period of time that is randomly chosen and, if the channel is still idle, will then begin transmission. In this way, contention conflicts between stations is minimized without unduly restricting communication between stations. Following transmission, the channel will again be quiescent a short period of time before the acknowledgement signal is transmitted from the receiver. Each packet of data to be transmitted is of a fixed length so as to provide for synchronization between various stations contending for access to the channel.

Collision avoiding system and protocol for a two path multiple access digital communications system

Abstract: With the advent of digital communications, it is common to transfer packets of information among a plurality of stations, e.g., digital computers. In order to control the transfer of the packets, various protocols have been introduced. However, the efficiency related to known multiples access digital communications system protocols tends to decrease as the digital signal rate increases. To overcome such problems, the instant communications system and protocol contemplate a communications loop having first and second oppositely directed signal paths. At least two stations are coupled to both the first and the second signal paths. A station includes an arrangement for writing a first signal on the first path and an arrangement for reading a second signal from the second path. In addition, the station includes an arrangement for reading a third signal from the first path. The third signal is coupled from the first path to the station by an arrangement which electrically precedes the arrangement for writing the first signal on the first path. If the station has a packet to transmit, it can overwrite a busy control field of the third signal packet on the first path. Having read the third signal on the first path, a logical interpretation may be made within the station as to whether the first path is busy or not busy. If the first path is not busy, the packet may be written on the first path by overwriting the third signal thereon. If the first path is busy, the station may overwrite a request control field of the third signal for indicating that the station was unable to transmit the packet. The packets flow around the loop and are monitored on the second path. Eventually all packets will be transmitted and the request control field may be detected at the receive side of a head station for indicating the event that all packets have been transmitted, in which event a new cycle may be started by initializing each station on the loop and by permitting each station to transmit.

Asynchronous integrated voice and data communication system

Abstract: The asynchronous integrated voice and data communication system includes a continuously variable slope delta encoder and a continuously variable slope delta decoder to convert voice signals to coded signals and vice versa. A packetizer and a depacketizer are employed with each data and voice user to enable each of the plurality of data and voice users to have random access to a fiber optic transmission medium enabling each of the plurality of data and voice users to receive transmissions from all others of the plurality of users. A microcomputer is coupled to each of the voice and data users and the associated packetizer and depacketizer to enable any one of the plurality of data and voice users to establish communication with any other selected one of the plurality of data and voice users.

Integrated alarm, security, building management, and communications system

Abstract: A fully integrated alarm, communication, and building management system has a central control station and a plurality of remotely located sensing and controlling devices. Each remote device has an individual digital address, which is a parallel address present on a plurality of parallel lines. The parallel address is converted to a serial address and sent to the various remote locations where it is then reconverted to a parallel address and decoded to determine the specific device being interrogated. A multiple amplifier system is provided at the central control unit and provides communication capability involving remotely located loudspeakers and microphones. The amplifiers are provided in a dual channel arrangement so as to provide a fail-safe arrangement and a failure detector is located in each channel such that if a selected amplifier channel fails, the back-up or redundant channel is immediately switched into use. A number of controlling devices or actuating devices may be employed which operate in conjunction with the sensing devices and a programmable read only memory, or a programmable multiplexer, located at the central control unit. Each remotely located controlling or actuating device also has associated with it an individual parallel digital address and upon the occurrence of a signal from a sensing unit indicating a condition other than a normal condition and a specific address programmed into the programmable read only memory or the multiplexer a command signal will be issued to the remotely located actuating or controlling device causing such device to operate in a predetermined manner.

Two-way AC power line communications system

Abstract: An AC power line communications system includes means for transmitting data to and receiving data from a plurality of transceivers over a conventional AC power distribution network. A central procession unit is provided to poll a plurality of room control units which are placed in each room or designated area of a hotel, hospital or building complex. The central processing unit conducts this polling sequence by periodically transmitting, over the neutral and ground lines of the power distribution network, and interrogation signal having an address portion and a data portion. Each room control unit is arranged to receive the interrogation signal and to compare the address portion of this signal with an address previously programmed into the unit. If the address portion of the interrogation signal corresponds with the programmed address of the room control unit, the unit transmits a return signal to the central processing unit. The room control units uses the data portion of the interrogation signal to report a number of different features of functions within the room (or area) in which the room control unit is located. A sequence of successive, identical addresses is used to allow the room control unit to accept data from the central processor. The central processing unit processes the data contained in the return signal insuring that the data received by the room control unit coincides wih the data transmitted to it by the central processing unit and permitting a record of the data accumulated by the room control unit to be made. This AC power line communications system is well suited to be used in combination with a room status indicating system to monitor the status of each room in buildings such as a hotel, motel, or hospital complex, to monitor the condition of a smoke detector located in each room of the complex, to remotely control the operation of the heating and cooling equipment in each room of the complex, to convey message-waiting information to each room in the complex and to perform an automatic wake-up operation.

Data communications

Abstract: T WO common carriers are operated under the administration of the Ministry of Posts and Telecommunications in Japan. One is NTT (Ni'ppon Telegraph & Telephone Public Corporation) for domestic services. The other is KDD (Kokusai Denshin Denwa Company, Ltd.) for overseas services. For the past year, NTT has had DDX (digital data exchange) circuitswitched data network and DDX packet-switched data network services, and KDD has commenced ICAS (international computer access service). Data communications in Japan have begun a new era of rapid progress. Their features are summarized as follows. 0 Both domestic and overseas telephone networks allow nonvoice communications as well as voice. Customers can connect their own terminals to the networks via Modems and NCU's. Public-switched telephone and telex networks are available for data communications. 0 Various speed class leased circuit service is provided.

Introduction to communications engineering

Abstract: Communication System Models. Carrier Modulation. Carrier Transmission. Carrier Reception. Carrier Demodulation. Baseband Waveforms, Subcarriers, and Multiplexing. Binary Digital Systems. Block Waveform Digital Systems. Frequency Acquisition and Synchronization. Satellite Communications. Fiber Optic Communications. Appendix A: Fourier Transforms and Identities. Appendix B: Random Variables and Random Processes. Appendix C: Orthogonal Expansions of Signals. Index.

Serial data bus communication system

Abstract: A node device for use in a digital data processing and communications system of the type utilizing a bus organization for facilitating the interconnection of a large plurality of digital data processing devices (user devices) in which redundant cables are employed. The node devices are interposed between the user devices and the redundant cables to permit automatic reconfiguration of the interconnection of the user devices in the event of malfunctioning or severing of one or more of the cable sets within a minimum period of time. The node devices provide the user devices with the structure needed to detect and diagnose system problems and to effect recovery procedures. In accordance with the invention, one of the plurality of nodes functions as the Bus Controller and by sampling the remaining nodes in the system, it determines the priority with which user devices may transmit or receive data over the bus. Each of the nodes employed is substantially identical and any one may be selected to function as the Bus Controller. Each includes a Microprogrammed Controller and necessary firmware to permit the controller to function in conjunction with special purpose hardware including a Programmable Logic Array (PLA) configured to perform a pre-processing function on control line inputs so that poll/response traffic on the active cables can continue with a minimum of delay.

Communications system, in particular a telephone system, for connecting mobile subscriber terminal devices

Abstract: A communications system, in particular a telephone system, is provided for the connection of mobile subscriber terminal devices via radio links, in which a central and/or sub-central location there are arranged storage devices which, for all of the users, each store an item of information concerning the relevant location of a user. The particular stored item of location information is used to control the switch-through of a connection to be established to the mobile user. The subscriber terminal devices include identification read-out devices for reading user identification cards. The subscriber terminal device temporarily receives the user call code stored on the user identification card which provides the facility of passive access to the user. Facilities are also provided for automatic charge accounting.

Scrambler key code synchronizer

Abstract: A method for synchronizing the scrambling sequences of communicating scrambler units of a privacy communications system in a reliable and secure manner. The method is particularly adapted for use in noisy or fade prone transmission environments, and permits late entry of authorized third parties to the system. The method utilizes digital sequences interleaved periodically with scrambled analog information to provide reliable synchronization.

Multipoint packet data communication system using random access and collision detection techniques

Abstract: In a data communications systems having a communications channel (3) for interconnecting a plurality of transceivers (1) and (2), each of said transceivers (1) and (2) including means (80) for transmitting a signal having transitions, there is provided a means (20) responsive to the presence and absence of a signal on said communications channel (3) during a transition of a signal transmitted by said transmitting means (80) for providing a collision detected (CD) signal if there is destructive interference with the transmitted signal on said communication channel (3) during a transition of said transmitted signal and means (48) responsive to said CD signal for terminating said transmitting of said signal. In the event the channel (3) is busy prior to a transmission from the transmitter (80) there is provided a carrier sense circuit (14) for indicating the channel is busy and a non-persistent control circuit (45) and a random number generator (90a) and a delay circuit (90b) responsive to the carrier sense circuit (14) and the collision detector circuit (20) for interrupting and delaying the transmitting of each of the transceivers (1) and (2) for a random period of time.

Distribution network communication system with flexible message routes

Abstract: Each customer location is equipped with a remote terminal which contains a role code identifying the remote terminal as an end device and a plurality of address codes. A plurality of signal repeaters are each connected with certain of the remote terminals through a distribution network. Each signal repeater contains stored route and role codes as well as a unique address code allowing each signal repeater to be additionally addressed as an end device. A central station produces an outgoing communication signal intended for at least one end device. A communication link couples the central station to the power distribution network. The communication signal includes a route code identifying a signal path to the end device, a role code identifying the first device in the identified route, an address code and a message code. Upon receipt of the communication signal by a signal repeater which is not the intended end device, the received route and role codes are compared to the stored route and role codes. If there is a match, the signal repeater removes its role code from the communication signal, inserts the role code of the next device in the identified route and retransmits the signal. The signal is continually modified and retransmitted until the message code is received by the intended end device.

Distributed digital conferencing system

Abstract: In time division communication systems one conference technique is to have a processor combine those samples going to a particular station forming a conference having as many subcombinations as there are stations. This approach, while allowing individual station gain adjustment, suffers from its dependence upon a large number of logic operations for a given conference. A modification of this technique is disclosed which uses a distributed structure such that the individual station ports, under local memory and processor control, operate to combine selected time slot samples into a conference sum unique to the station. In this manner gain values may be assigned on an individual listener station basis while the logic processing for the conference is performed in parallel by the ports involved in the conference.

Synthetic speech communicating system and method

Abstract: A communication system for communicating information between one or more sensors and a remote location which may be fixed or portable wherein the information received is converted to synthetic speech so as to verbally indicate or warn a person or persons at or near the receiver as to the condition sensed or a condition which is developing at a known or indicated remote location as indicated by the output of one or more sensors. The system may also contain a fixed data receiving station and one or more portable units for receiving signals from such fixed station and/or remote sensors wherein the fixed station serves not only to relay the information to the portable receivers but also to process the information it receives. In a particular form of the invention, the fixed station includes a computer or circuits which process the data or signals received from the sensor or sensors and generates synthetic speech signals which are short wave transmitted to one or more satellite or portable stations and generate synthetic speech thereat warning or indicating to a person or persons at or near the satellite receiver or receivers of the condition sensed.

The Use of the Fourier-Bessel Series in Calculating Error Probabilities for Digital Communication Systems

Abstract: Using the theory of spherical symmetric random vectors one can find an expression for the error probability of a wide variety of digital communications systems. These expressions, however, are in the form of Bessel integrals which are usually difficult to solve. In this paper we show how the Fourier-Bessel series can be used to solve the integrals numerically. The calculation error is found to depend on two series parameters which can be manipulated to make the error arbitrarily small. Two examples are used to show the utility of the technique. In the first the probability of error for a CPSK communications system operating in Gaussian noise and cochannel interference is found. In the second the error performance for a multilevel ASK communications system operating in the same corrupting environment is determined. The Fourier-Bessel series technique is a valuable practical tool for solving these and other signal detection problems.

Data communication system

Abstract: A data communication system for general purposes having a new ternary carrier frequency shift keying (TCSK) signal The system is applied to a utility load control by transmission of a sub-carrier of an FM broadcast channel It is decoded by a receiver, SCA decoder, TCSK filter and a two level or binary converter and used to communicate to a pre-programmed microprocessor which enables various load control functions to be performed The general system also is given for a QPSK (quadraphase shift keying) operating system A data transmission filter is split between the transmitter and receiver and is operated in cascade to give individual interference filtering at each end of the transmission while also providing combined action and wave shaping A high accuracy FM decoder using zero crossing detection enables data recovery with simple circuits A novel random time load restoration circuit for ramp-up is disclosed A fail safe relay operator is also disclosed The TCSK employs a novel 19 character hex code format which is 8 bit microprocessor compatible and directly usable for other purposes such as ASCII message transmission Both QPSK and TCSK systems offer command structures of variable length so as to permit truncation of message and reduce total message transmit time

Privacy communication system employing time/frequency transformation

Abstract: A privacy communication system digitizes a voice signal and divides the signal into different frequency bands or time segments and shifts the bands or segments in frequency and/or time under control of a continually changing pseudo-random key word to develop an encrypted transmitted signal having the same time/bandwidth product as the voice signal.

Multistage decoding of frequency-hopped fsk system

Abstract: A recent paper described an unproved decoding scheme for a frequency-hopped multilevel FSK system. We examined this multiple access communication system for possible application in satellite communication and mobile radio telephony. The new decoder, using the known algebraic structure of the users' addresses, reduces mutual interference and achieves a 50 to 60 percent increase in efficiency over conventional decoding. The present paper shows how additional decoding can further increase the efficiency, bringing it very close (within half a percent) to optimum. The scheme makes use of information derived while decoding the messages of other users and thus is especially attractive for the base station, where such information is readily available and does not require a significant increase in complexify. Compared to conventional decoding, the new scheme more than doubles the number of simultaneous users.

Loop communication system

Abstract: A loop communication system, interconnecting a number of nodes around the loop, in which two oppositely directed unidirectional loops service the two directions of transmission. Each of the loops comprises a time division multiplexed transmission facility. Each of the nodes has facilities for connecting the communications on each incoming channel to a utilization device connected to that node, for connecting the communication from a utilization device connected to that node to each outgoing channel, or for repeating the communication from any incoming channel to a corresponding outgoing channel. Assignment of a communication to a given channel is accomplished using a centralized control means which causes the communicating devices to be connected using corresponding channels in the two loops, and using that portion of the loop which has the smaller number of intermediate nodes.

Mailing system interface interconnecting incompatible communication systems

Abstract: An automated mailing system includes a postage value determining system processor, a scale for providing weight indicative signals, a keyboard for operator entry of information relating to a determination of postage, and a plurality of peripheral devices. A peripheral controller interface establishes communications links with the peripheral devices. An incompatible systems interface interconnects a serial communications bus of the system processor and the peripheral controller interface. The incompatible systems interface includes a processor programmed to receive, decode and transmit information from or to the system processor along the serial bus and load or receive information from or to the peripheral controller interface along parallel lines. The communication timing constraints of the serial communications bus for receipt of data signals by the system processor do not permit monitoring of the data transmission by the incompatible systems processor. To accommodate for such timing constraints, system clock pulses of the serial bus are employed at a flip-flop to disable the incompatible systems processor.

Communication apparatus for hostile environments

Abstract: A dual communication system is disclosed including a microphone for mounting for use by a wearer of a protective face mask, the output signal from the microphone being communicated to both a speaker system for local, audible broadcast and to a transmitter for remote broadcast by radio signal.

Acoustoelectric Convolver Technology for Spread-Spectrum Communications

Abstract: Acoustoelectric (AE) convolvers for spread-spectrum communication applications are described with input bandwidth capacities to 200 MHz. These devices offer a unique combination of large processing gain, high dynamic range, small size and weight, and low drive power requirements. The programmable feature of convolvers allows the encoding waveform to be changed from bit-to-bit, thereby providing resistance to repeat jamming and enabling secure communications. The basic concepts of a convolver-based spread-spectrum communications system are reviewed, current convolver capabilities are discussed, and projections are made for future device performance. Deviations from nonideal convolver performance are considered. Special techniques which must be used in the system implementation and evaluation of convolvers are described, and the performance level achieved in a state-of-art convolver subsystem is given.

Method of testing a data communication system

Abstract: A method of testing the implementation of a communication system definition by constructing a model of the communication system definition in a high level computing language such as PL/1; compiling the model and producing an executable machine language program; monitoring and recording messages transmitted by the data communication system; extracting relevant message-related information; using the extracted message unit sequence as input data to the executable machine language program; executing the machine language program and using the results of the execution to give an indication whether or not the messages were constructed correctly according to the communication system definition.

Load management terminal

Abstract: A load management terminal is utilized as an end device in a utility's distribution network communication system The distribution network carries electrical power as well as communication signals The load management terminal is comprised of a power line coupling unit for connecting the load management terminal to the power distribution network A signal receiver and conditioning unit produces a command signal in response to a received communication signal A solid state memory contains preprogrammed instructions and data A control logic circuit performs load control functions in response to the preprogrammed instructions, data and the command signal These load control functions include the opening and closing of load control switches for selectively disconnecting and connecting, respectively, customer loads A cold load pick-up produces power outage information enabling the load management terminal to provide local, load control functions

Chip Waveform Selection in Offset-Quaternary Direct-Sequence Spread-Spectrum Multiple-Access Communications

Abstract: : An offset-quaternary direct-sequence spread-spectrum multiple-access communication system is analyzed. This analysis considers the effect of the choice of chip waveforms on the bandwidth which the system utilizes, the signal-to-noise ratio at each user's receiver, and the constant-envelope character of the transmitted signals. (Author)