Showing papers on "Communications system published in 1982"

The Origins of Spread-Spectrum Communications

Abstract: This monograph reviews events, circa 1920-1960, leading to the development of spread-spectrum communication systems. The WHYN, Hush-Up, BLADES, F9C-A/Rake, CODORAC, and ARC-50 systems are featured, along with a description of the prior art in secure communications, and introductions to other early spreadspectrum communication efforts. References to the available literature from this period are included.

Error Probability for Direct-Sequence Spread-Spectrum Multiple-Access Communications--Part II: Approximations

Abstract: Approximations are obtained for the average probability of error in an asynchronous direct-sequence spread-spectrum multiple-access communications system. Both binary and quaternary systems are considered, and the chip waveforms are allowed to be arbitrary time-limited waveforms with time duration equal to the inverse of the chip rate. The approximation is based on the integration of the characteristic function of the multiple-access interference. The amount of computation required to evaluate this approximation grows only linearly with the product of the number of simultaneous transmitters and the number of chips per bit. The accuracy of the approximation is extremely good in most cases, but it can be improved, if necessary, by an application of a series expansion. Numerical results are presented for specific chip waveforms and signature sequences.

Error Probabilities for Slow-Frequency-Hopped Spread-Spectrum Multiple-Access Communications Over Fading Channels

Abstract: Bounds and approximations are obtained for the average probability of error in an asynchronous slow-frequency-hopped spread-spectrum multiple-access communications system with noncoherent binary frequency-shift-keyed (FSK) data transmission. Both nonselective fading and wide-sense-stationary uncorrelated-scattering fading are considered.

Computer controlled energy monitoring system

Abstract: Centralized data communications system incorporating a plurality of remote stations (11), each having a plurality of information channels (10) associated therewith. A selected remote station and its associated information channels are tone addressed by a central station (23) communicating with a group of remote stations over a respective communications channel (12). The remote stations (11) may have a current sensor (210) connected to one of the information channels for sending data corresponding to the amount of current sensed in an electrical path (212) back to the central station (23) upon being properly addressed. This data, together with data representative of the voltage on the monitored electrical path, is used by the central station to calculate energy consuption. The calculated energy consumption is retained at the central station (23) and used for information and billing purposes. The central station may also send data to an addressed information channel (10) at a remote station for controlling an operation thereat. The central station (23) can also receive data from various parameter measuring sensors (47) at a remote station, e.g. sensors measuring temperature, humidity, fluid flow, etc. which may be connected to other information channels (10) and thus the system may be used as a general purpose data gathering or distributing communications system.

Performing remote operations efficiently on a local computer network

Abstract: A communication model is described that can serve as a basis for a highly efficient communication subsystem for local networks. The model contains a taxonomy of communication instructions that can be implemented efficiently and can be a good basis for interprocessor communication. These communication instructions, called remote references, cause an operation to be performed by a remote process and, optionally, cause a value to be returned. This paper also presents implementation considerations for a communication system based upon the model and describes an experimental communication subsystem that provides one class of remote references. These remote references take about 150 microseconds or 50 average instruction times to perform on Xerox Alto computers connected by a 2.94 megabit Ethernet.

Electronic audio communications system with versatile message delivery

Abstract: An advanced electronic telecommunications system is provided for the deposit, storage and delivery of audio messages to both users and non-users with limited access provided to the non-user under the control of the user. A Voice Message System (10) interconnects multiple private 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). Selected non-users may be allowed access through the OFF NET telephones (24), the scope of the access of the selected non-users being determined by a subscriber user. 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 and to designate the message for priority transmission. The recipient is able to redirect the message from a message originator to a second recipient and the second recipient can re-redirect it to a third recipient. The Voice Message System (10) also enables a user to access the system to determine if any messages have been in data storage subsystem (64) for him. Prerecorded instructional messages are deposited in the data storage subsystem (64) for instructing a user or a selected non-user on their progress in using the system.

Remote level adjustment system for use in a multi-terminal communications system

Abstract: A remote level adjustment system for use in a multi-terminal communications system wherein a plurality of remote terminals are connected to a master terminal by a distribution network for bi-directional transmission of signals. The remote terminals are adapted to transmit and receive signals on the network and respond to a polling signal by transmitting signals regarding transactions at respective sites. Each remote terminal includes circuitry for responding to level-setting signals by transmitting reply signals, and variable attenuation circuitry for adjusting, in response to a level-setting adjustment signal, the power level of the signals it transmits. The master terminal is adapted to transmit and receive signals on the network and includes program and circuit means for transmitting a polling signal. The master terminal further includes program and circuit means for transmitting level-setting signals, for measuring the power level of reply signals from selected remote terminals and deciding whether to adjust the level, and for transmitting a level-setting adjustment signal, if necessary, to command the selected remote terminal to adjust the setting of its variable attenuation circuitry in accordance with a level-setting protocol.

Error Probability for Direct-Sequence Spread-Spectrum Multiple-Access Communications--Part I: Upper and Lower Bounds

Abstract: Upper and lower bounds on the average probability of error are obtained for direct-sequence spread-spectrum multipleaccess communications systems with additive white Gaussian noise channels. The bounds, which are developed from convexity properties of the error probability function, are valid for systems in which the maximum multiple-access interference does not exceed the desired signal and the signature sequence period is equal to the duration of the data pulse. The tightness of the bounds is examined for systems with a small number of simultaneously active transmitters. This is accomplished by comparisons of the upper and lower bounds for several values of the system parameters. The bounds are also compared with an approximation based on the signal-to-noise ratio and with the Chernoff upper bound.

Multicast communication tree creation and control method and apparatus

Abstract: In a multicast network communication system, administration of the communication path making up the multicast tree itself has been separated from control and administration of the network. Creation of a multicast distribution tree and control over the membership thereof, is separately controlled independently from the creation and use of the tree transmission path used to communicate among the members of a multicast set. Transmission distribution trees are set up when a transmission request is received and the properties of the transmission path that is required are known. Transmission paths are created and controlled by all nodes in the communications system, each node having necessary control code and processors for responding to requests from set members to transmit a message to groups of users by creating and activating the necessary tree communication path distribution linkages. A distribution tree is created by the Tree Leader by generating a tree address using a random number generator. A tree address correlator is generated utilizing network and node identifiers unique for the network, and a list of subnodes or users connected for each member of the multicast tree set is generated. Using this information, a tree distribution path is computed to cover all of the subnodes required and a tree set up request message is sent by the Tree Leader along a computed path to each involved subnode. Each subnode returns a message indicating whether the tree address is already in use or is available for use. Successfully negotiated tree addresses are marked at the path link initiation and termination points at each node through the network.

Data under voice communications system

Abstract: A communications system capable of simultaneously transmitting voice and data information The spectral energy of the data signal is smeared by spreading it in a spectrum with energy packed in the lower frequency range under the conventional voice signal frequency in a manner which complements the standard C-message weighting curve The use of the spread spectrum technique also eliminates thumping at the data rate since the harmonics that produce thumping are also spread throughout the bandwidth

Randomized tag to portal communication system

Abstract: Communication between portal units and identification tags is accomplished by continually radiating an interrogation signal consisting of a code pattern from each portal unit followed by a listening interval. Tags within range of such interrogation signal test the incoming signals for frequency, bit duration, bit rate, a preamble code and a facility identifying code. If the tag receives a valid signal to which it has been preprogramed, such signal synchronizes and initiates a plurality of tag responses within a given overall response interval and with each response transmitted during randomly selected time slot. Each tag is provided with its own pseudorandom binary sequence generator and reply counter with the pseudorandom generator sequenced by a signal derived from the carrier signal radiated by the tag. The portal units also test incoming signals for frequency bit rate and bit duration as well as for a preamble code generically indicative of a tag. If the test is passed, the remaining tag response consisting of an identifier and an error correcting code is accepted and passed on to a CPU.

Communication line interface for controlling data information having differing transmission characteristics

Abstract: There is disclosed an office communication system adapted to handle both bursty and continuous data transmission over a single transmission facility to a central switching network. A programmable station controller is used at each station location to interface a number of transmission inputs to the single communication link. The programmable station controller is arranged to statistically multiplex the inputs associated with the bursty data while allowing the continuous data to pass on dedicate time slots. Transmission compatibility between the types of data transmission received from the bursty and continuous data inputs is assured by subdividing the transmission on the single link into frames having four time slots. A fixed number of time slots of each frame are assigned by a central controller to active ones of the continuous data inputs while other time slots of each frame are assigned to the multiplexed bursty data inputs. One of the time slots of each frame is utilized for communicating control information between the programmable station controller and the central switching network controller.

Multi-station token pass communication system

Abstract: A data communication system utilizing a synchronized serial bus (20) for communication between multiple stations (22) connected to the bus. A token is employed such that when owned by a station it allows that station to transmit high-level messages over the bus and command other stations to transmit high-level messages to it if required by the token owner. Fundamental events called primitives are perceived by stations. Each station capable of token ownership embodies the same set of rules, the rules in turn defining the circumstances when perceived events cause a station to change from one state to another. Fundamental sets of rules, or modules, are used in the communication system to achieve a system for the automatic generation of a token list of stations with periodic ownership of the token, as well as for exapansion or contraction of this token list. In addition, automatic change in the token pass handshake protocol is described. The communication system allows bus interconnection to stations having no potential token acess, with communication control provided by master stations which have token ownership capability.

Capacity Consideration in Reliability Analysis of Communication Systems

Abstract: This paper presents a simple method for deriving a symbolic reliability expression of some practical systems such as a communication system having fixed channel capacities of its links, a power distribution system having limited power ratings of its power lines, a transport system which might not allow traffic more than a particular value, or a chemical system in which oil or gas flow through pipes is permissible only up to some safe limits. A system is good if and only if it is possible to transmit successfully the required capacity from source node to the sink node. This paper defines a group as a set of branches such that success of these branches ensures system success, as defined above. All such groups are obtained from a knowledge of the minimal paths of the system graph. The method is computerized and implemented on DEC-20 computer. Two examples are considered and their solutions presented to illustrate the technique.

Radio communication system using frequency division multiplexing for transmission between a master station and a plurality of remote stations

Abstract: A point-to-multipoint radio communication system includes a master station and a plurality of remote stations which communicate with the master station using frequency division multiplexing. Each remote station transmits on a separate frequency, but the respective frequencies of transmission by the remote stations are closely spaced so as to be contained within the band which is centered on a single licensed frequency. Thus, the system may operate with only a first licensed frequency for communication from the master station to the remote stations and a second licensed frequency for communications from the remote stations to the master station.

Power-line baseband communication system

Abstract: A communication system for transmitting baseband digital signals (16) on an electrical power line (12). A pulse generator (14) produces digital signals which are limited to a frequency spectrum of 30 kHz to 300 kHz and applied directly, i.e., without modulation, to an electrical power line. At the receiving terminal (25) an amplifier (32) compensates for attenuation characteristics of the electrical power line and the received signal is then sampled (34) to extract the information from it. To avoid interference when both a transmitting and receiving link are located at a substation, the baseband system incorporates a mimic network to mimic the interference signal erroneously picked up by the receiving link from the transmitting link located at the same substation. The mimic signal is then subtracted from the interference signal to neutralize the effect of the latter. When both a baseband digital communication system and a carrier communication system utilize the same electrical power lines, provision is made for interrupting the baseband digital signal to allow communications via the carrier system.

Bidirectional, interactive fire detection system

Abstract: A Communication System useful for fire detection which transfers data/commands bidirectionally between a controller and connected transponders on a real time, interactive basis. This system makes possible accurate data recovery, whether a transponder has its output shorted, or although multiple transponders are replying and makes possible the remote determination and constant monitoring of transducer sensitivity, at the controller. The sensitivity can be adjusted remotely at the controller, and different transducers can have different thresholds simultaneously, which can be changed collectively or individually to different settings manually or automatically at the controller. The system transmits reference data for supervision of system accuracy. Compensation for long-term changes is provided for both transponders and transducers in this system.

System and method for controlling a multiple access data communications system including both data packets and voice packets being communicated over a cable television system

Abstract: The instant communications system and method for controlling both digital voice traffic and digital data traffic includes a communications path, a source station and a destination station. The source and destination stations are respectively adapted to be coupled to a source station home network and to a destination station home network. The source station is further adapted to transmit a signaling packet on a first transmit control channel. The signaling packet is for signaling a destination station that the source station has an information packet intended for the destination station. The destination station is adapted to detect the signaling packet on a second receive control channel. The signaling packet includes a field for identifying the source station which has the information packet intended for the destination station. In response to the signaling packet, the destination station is coupled to the source home network. Thereafter, information packets may be transmitted from the source station on a third control channel and then be translated to a source station home network channel for transmission to the destination station.

Orthogonal CDMA system utilizing direct sequence pseudo noise codes

Abstract: An orthogonal code division multiple access communications system is disclosed involving multiple users while providing orthogonal operation, meaning that there is substantially zero interference between users. All of the users employ a mutually different time permutation of the same multi-bit direct sequence pseudo noise code with a synchronous time reference for all of the users being established through a central node or station which communicates with all of the users preferably through a loopback synchronous timing scheme. Each pseudo noise code is followed by an extra processing bit that balances the number of one and zero bits in the composite information bit which has the effect of providing a code structure which will have a cross-correlation value of zero with the other time permutated codes which enables the system to operate as an orthogonal system.

Coded Error Probability Evaluation for Antijam Communication Systems

Abstract: We present a general union-Chernoff bound on the bit error probability for coded communication systems and apply it to examples of antijam systems. The key feature of this bound is the decoupling of the coding aspects of the system from the remaining part of the communication system which includes jamming, suboptimum detectors, and arbitrary decoding metrics which may or may not use jammer state knowledge.

Electronic audio communications system with automatic user access features

Abstract: An advanced electronic telecommunications system is provided for the deposit, storage and delivery of audio messages to both subscribers and non-subscribers with limited access provided to the non-subscriber under the control of the subscriber. A Voice Message System (10) interconnects multiple private exchanges (12) of a subscriber with a central telephone office (22). Individual subscribers may access the Voice Message System (10) through ON NET telephones (18) or OFF NET telephones (24). Selected non-subscribers may be allowed access through the OFF NET telephones (24), the scope of the access of selected non-subscribers being determined by a subscriber. 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 subscriber to deposit a message in data storage subsystem (64) for automatic delivery to other addresses connected to the system. The subscriber is also provided automatic features that allow more versatile access to the system. The Voice Message System (10) also enables a subscriber to access the system to determine if any messages have been in data storage subsystem (64) for him. Prerecorded instructional messages are deposited in the data storage subsystem (64) for instructing a subscriber or a selected non-subscriber on their process in using the system. The Voice Message System (10) also enables the subscriber to associate time and date with a message and also recording and delivery of a subscriber input identifier.

Error rate monitoring for digital communications

Abstract: The error rate is an important measure of performance in digital communications system, since it gives an indication of the quality of the received information. This paper provides a tutorial overview of methods of error monitoring under four broad classifications, namely, test sequences, parameter measurements, violation detection, and pseudo-error monitoring. A brief discussion of several approaches towards performance monitoring and the definition of error rate parameters is also given. The various methods are described and compared; but, no one monitor is singled out as the "best" since the final choice depends largely on the specific requirements of a given application.

Transmitter power control circuit

Abstract: In a radio communication system, an adaptive transmitter power control system is described wherein the signal level at each receiver is monitored and a control signal, which is a function of the signal level, is transmitted back to the transmitting station to adjust the transmitter output power, as required. By transmitting the lowest power level consistent with system objectives, the repeater circuits operate in a highly linear mode, and cochannel interference is significantly reduced.

Orthogonal code division multiple access communications systems

Abstract: An orthogonal code division multiple-access communications system comprised of a plurality of transceivers respectively employing orthogonal noise code mate pairs of a type having autocorrelation functions upon detection which when linearly added together compress into a lobeless impulse and wherein the same single time slot is utilized by all of the users in the system. Each user is assigned a different unique noise code pair consisting of code mate pairs that are selected from a subset of multiplexed noise codes whose cross-correlation function value is equal to zero at a time when all the code mate pairs compress to an impulse, i.e. τ=0. The described arrangement enables random access, or direct call-up, to be accomplished with no interference between the users while using different noise codes for each user.

Electronic audio communications system with versatile user accessibility

Abstract: An advanced electronic telecommunications system is provided for the deposit, storage and delivery of audio messages to both user and non-users with limited access provided to the non-user under the control of the user. A Voice Message System (10) interconnects multiple private exchanges (12) of a subscribed 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). Selected non-users may be allowed access through the OFF NET telephones (24), the scope of the access of the selected non-users determined by a subscriber user. 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 user is also able to automatically delete the message after the message has been delivered to the selected recipient. The Voice Message System (10) also enables a user to access the system to determine if any messages have been in data storage subsystem (64) for him. Prerecorded instructional messages are deposited in the data storage subsystem (64) for instructing a user or a selected non-user on their progress in using the system. A FAX transmission device (19) is also provided for transmitting to the system graphic information for deposit, storage and delivery thereof.

Dual bus communication system

Abstract: A dual set of busses is used to provide close coupling between the data and voice services of the CS300 communication system. One of these busses is a time division multiplex bus arranged for communication between port access circuits, and the other bus is a packet-switched data processing bus used for interfacing both with the system peripherals and with the port access circuits. The port access circuits, as well as the faster peripheral circuits, can be connected to either or both busses thereby allowing for the efficient easy interchange of information.

Power-line carrier communications system with interference avoidance capability

Abstract: The operating frequency of a multi-station power-line-carrier-communications system is automatically changed to avoid narrowband interference. Any one of the plurality of stations in the system can initiate a command to shift operating frequency, when the communications signal reception degrades below a predetermined criterion. An interfering signal itself can initiate a shift in operating frequency when the characteristics of the interfering signal are sufficient to deteriorate communications on an existing operating frequency.

Randomized parallel communication (Preliminary Version)

Abstract: Using a simple finite degree interconnection network among n processors and a straightforward randomized algorithm for packet delivery, it is possible to deliver a set of n packets travelling to unique targets from unique sources in 0(log n) expected time. The expected delivery time is in other words the depth of the interconnection graph. The b -way shufile networks are examples of such.This represents a crude analysis of the transient response to a sudden but very uniform request load on the network. Variations in the uniformity of the load are also considered. Consider si packets with randomly chosen targets beginning at a source labelled i. The expected overall delay is then [equation] where the labelling is chosen so that s1≥s2≥.These ideas can be used to guage the asymptotic efficiency of various synchronous parallel algorithms which use such a randomized communications system. The only important assumption is that variations in the physical transmission time along any connection link are negligible in comparison to the amount of work done at a processor.

One way interactive multisubscriber communication system

Abstract: Interactive programming may be provided by the system (26) of the present invention which can enable both manual and automatic selection of various interactive responses from simultaneously transmitted programming on different channels. In a cable television system (20), the channels used to transmit the interactive programming are the midband channels with the selected response being treated by the system converter (26) to convert the individually selected response to a common assigned television channel frequency for ultimate reception and display on the subscriber's television (24, 22). Automatic selection may then be accomplished by the provision of a selection signal from the logic network (48) to a local oscillator (52) which, in turn, generates a beat frequency to be mixed in a mixer (54) with the various midband channel frequencies to convert the selected midband channel frequency to the assigned television channel frequency. The selection signal is either manually selected as a result of the choice or selection manually input by the subscriber via a keyboard (50) or automatically generated as a result of the pulse count value accumulated in memory (64, 65, ) based on the weighted signal value of prior responses. Various band pass filters (36, 58, 60) and switches (34, 56) are employed to pass the appropriate signals in the interactive and conventional programming modes of the system (26).