Showing papers on "Communications system published in 1994"

Packet data communication system

Abstract: A packet data transmission system is used to link a number of remote hand-held data-gathering units such as bar code readers to a central computer which maintains a database management system. Data packets are sent from the remote units by an RF link to intermediate base stations, then sent by the base stations to the central computer by a serial link. Direct sequence spread spectrum modulation is used for the RF link. The remote hand-held units initiate an exchange using RF transmission to and from the base stations, receiving only during a rigid time window following a transmission from the remote unit. The base stations cannot initiate communication to the remote units, but instead send data to the remote units only as part of the exchange.

Steps Toward Unmasking Secure Communications

Abstract: This work tests the level of security in secure communication systems based on nonlinear dynamics (NLD), or chaos In these systems, a chaotic carrier signal is used in a type of spread-spectrum signaling system, with the added benefit that the hidden information signal is buried at something of the order of −30 dB with respect to the chaotic carrier To investigate the level of security in such systems, an examination was conducted on a test set of chaotic carriers and hidden information signals prepared by the NLD research group at the Naval Research Lab The hidden signals included a triangle wave, a period doubled signal, and a chaotic signal that was different from the chaotic carrier The analysis process was to use NLD forecasting to predict the carrier dynamics, and then subtract away the predicted values to reveal the hidden signal or at least increase its signal-to-noise ratio with respect to the carrier In each case, it was a simple task to determine the power spectrum of the hidden signal once the prediction of the carrier was removed This was then used to create a “comb” filter to extract the correct frequencies from the FFT of the first two signals When this was done, the hidden signals were recreated with almost perfect accuracy In the third case, the hidden chaotic signal had a broadband component, so the spectrum was used to develop a Weiner filter which enabled the hidden signal to be reconstructed with only moderate accuracy, where the overall structure of the hidden chaotic signal was preserved, but the fine structure was lost As a further test, the processing approach was applied to a voice signal hidden in one-dimensional Lorenz data at −35 dB After subtracting away the carrier model, the voice signal was reconstructed with reasonable accuracy, and had the same characteristic structure In this case, no secondary filtering was applied The forecasting approach was then extended to allow for dynamic signal estimation using threshold detection, so that whenever a signal was detected, multiple predictions of the carrier behavior were made into the future This was tested on a square wave embedded at −42 dB in Lorenz data The extended approach was able to reveal the square wave with almost perfect precision, except in a few regions where it temporarily lost synchrony with the carrier This allowed for the elimination of the secondary filtering requirement entirely The final conclusion is that the secure communications systems based on chaotic carriers may be useful to increase privacy, but are not yet capable of providing a high level of security The paper concludes with a discussion of measures which may be taken to improve the security of such systems so that they may be applicable to areas where higher security is required

Hierarchical communications system using microlink, data rate switching, frequency hopping and vehicular local area networking

Abstract: A hierarchical communication system is described in which two wireless local area networks exhibiting substantially different characteristics are employed to link inherently portable or mobile computer devices. A series of radio base stations make up a infrastructure network. The infrastructure network and at least one portable computer device make up the first local area network. The communication on the first local area network is accomplished by spread spectrum frequency hopping communication. A second local area network allows for radio communication between a portable computer device and peripheral devices with built-in transceivers utilized by the portable computer device. The communication in each local area network is controlled by a reservation access communication protocol. The communication protocol facilitates frequency hopping synchronization and supports adaptive data rate selection based upon the quality of communication on the communication channel. The communication protocol prevents interference between communication on the first local area network and communication on the second local area network. In a premises LAN, a series of radio base stations and a backbone LAN make up an infrastructure network. The infrastructure network and at least one mobile computing device make up a higher-power LAN, utilizing a frequency hopping protocol. A lower-power LAN allows for radio communication between a mobile computing device and peripheral devices, utilizing a single-frequency spread spectrum protocol. A vehicular LAN provides for short-range communication between a vehicle terminal and a portable terminal. When out of direct RF range of the premises LAN, the vehicle terminal maintains indirect communication when necessary with the premises LAN via one of several alternate RF channels. A microprocessor, located inside radio units which participate in multiple LAN's, selects the appropriate protocol, frequency band and power level for communicating through the network.

Method for communicating in a wireless communication system

Abstract: A communications system in which information is transmitted in a plurality of time slots grouped into a plurality of superframes which are, in turn, grouped into a plurality of paging frames. A remote station receives paging messages once in each paging frame.

Hierarchical communication system using premises, peripheral and vehicular local area networking

Abstract: A hierarchical communication system is described in which wireless local area networks (LANs) exhibiting substantially different characteristics are employed in an overall scheme to link portable or mobile computing devices. In a premises LAN, a series of radio base stations and a backbone LAN make up an infrastructure network. The infrastructure network and at least one mobile computing device make up a higher-power LAN, utilizing a frequency hopping protocol. A lower-power LAN allows for radio communication between a mobile computing device and peripheral devices, utilizing a single-frequency spread spectrum protocol. A vehicular LAN provides for short-range communication between a vehicle terminal and a portable terminal. When out of direct RF range of the premises LAN, the vehicle terminal maintains indirect communication when necessary with the premises LAN via one of several alternate RF channels. A microprocessor, located inside radio units which participate in multiple LAN's, selects the appropriate protocol, frequency band and power level for communicating through the network.

Stability of linear feedback systems with random communication delays

Abstract: Integral control of large-scale systems implies coordination of activities by information exchange via communication networks. Usually these networks are shared with other users. Thus traffic conditions in the network may introduce time-varying random delays in the control loop with adverse effects on its performance and stability. Hence, the control must be designed to compensate for these delays. Recent work in modelling integrated control and communication systems has shown that the communication specific phenomena inducing random communication delays (such as multirate sampling, vacant sampling and message rejection) may be encompassed by finite-dimensional linear discrete-time models, provided that the plant and the controller are linear and time invariant. Existing approaches to the design of integrated control systems rely on conservative stability tests, because only sufficient stability conditions were found for systems with random time-varying delays. In this paper, necessary and sufficient cond...

Disaster warning communications system

Abstract: The Disaster Warning Communications System is a message relay system designed to provide backup warning of impending natural hazard in areas where normal communications are vulnerable to losses imposed by geographic influence. It has been designed to take advantage of the near-hemispheric communications access of existing geostationary weather satellites. This broad coverage allows a single satellite to provide warning to virtually all the inhabited islands in the hemisphere surrounding the subpoint of the satellite, excluding only the extreme polar areas. By extension, three such satellites can cover the entire populated Earth.

Method and apparatus for determining the transmission data rate in a multi-user communication system

Abstract: A method and apparatus are described for controlling the data rates for communications to and from a base station and a plurality of remote users. The usage of the communications resource whether the forward link resource (from base station to remote users) or reverse link resource (from remote users to base station) is measured. The measured usage value is compared against at least one predetermined threshold value and the data rates of communications or a subset of communications on said communications resource is modified in accordance with said comparisons.

Simulation of communication systems

Abstract: When both a complex system and a complex channel model are encountered, the result is typically a design or analysis problem that cannot be solved using traditional (pencil and paper) mathematical analysis. Computer-aided techniques, which usually involve some level of numerical simulation, can be a very valuable tool in these situations. The purpose of this article is to provide a tutorial review of some of the basic techniques of communication system simulation. The authors consider the basic techniques used to represent signals, generate signals, and model linear systems, nonlinear systems, and time-varying systems within a simulation. They consider the important problem of using a simulation to estimate the performance of a communication system. >

Method and system for the dynamic modification of control parameters in a transmitter power control system

Abstract: In a communication system in which direct sequence spread spectrum modulation techniques are used, interference is generated in communications by remote stations since the communications share the same frequency spectrum. In order to increase system capacity the power level of the remote station transmitters are controlled by the local station. A setpoint in generated at the local station by a power control processor (118) and compared by a comparator (120) with the remote station signal strength measured at the local station by a power averager (114). The result of this comparison is used to generate power level adjustment commands by a command generator (122) which are transmitted to the remote station. The remote station is responsive to the power level adjustment commands for increasing or decreasing remote station transmitter power. In a spread spectrum communication system in which data is encoded at variable data rates, the local station determines via a rate determination processor (116) the rate at which received data was encoded by the transmitting remote station. The data is decoded by decoder (112) at each possible rate with error metrics generated that are representative of the quality of the data decoded at each rate. A rate decision algorithm is used by processor (116) to evaluate the error metrics and make a decision on the rate at which the data was transmitted. A pattern match of rate decisions is used by processor (118) to modify a setpoint so as to closely control the transmitting power of the remote station as a function of the quality of the received data.

Integrated vehicle communications system

Abstract: An integrated vehicle communications system for on-board use within a vehicle which may also communicate with external portions of the system which includes miniaturized, self-contained read/write transponders 20, 22, 30 of the type disclosed in Schuermann U.S. Pat. No. 5,053,774, for providing functions within the vehicle, e.g., for sensing conditions and parameters, The on-board interrogation unit 10 interrogates and receives signals by RF communication provided by on-board antennas 14, 26, 28 between the interrogation unit and respective transponders for read/write responder operation. The processor 33 with display device 34a and/or control circuits 34b carries out on-board functions in response to such interrogation. A transponder 22 may serve as a vehicle operator key by which the system may verify key code, unlock the vehicle doors, as well as select and perform initialization functions including ignition, seat and seat belt adjustment, mirror positioning, and antitheft functions before vehicle entry by the operator. A transponder 30 may access external control data for premises or toll access, and may provide toll or credit or service transactions, as for authorization or verification or toll charge debiting purposes. The system may include also IR links.

Periodic interference avoidance in a wireless radio frequency communication system

Abstract: A hierarchical communication system is described whereby periodic interference can be detected and avoided utilizing constituents' computer controllers and sync signals generated in response to the interference. The use of a predictive sync signal allows radio frequency communication to be optimally timed to efficiently make use of the interference-free time within the periodic interference signal.

Remote control of engine idling time

Abstract: A system for remotely accessing an engine control system and selectively controlling and changing an existing engine algorithm. In a preferred embodiment, the system comprises an on-board vehicle communications system which receives and sends data to a remote central fixed base site. A truck operator contacts the fleet base manager via the on-board communications system and requests, for example, that the engine idle for a specified period of time. The fleet base manager at the remote central fixed based site then transmits data from a computer over a communications channel to the vehicle's on-board communications system. The data is sent through a remote command interface device which translates the data in language recognizable by an engine control device. Based on the data transmitted, the engine control device disables an existing idle shutdown system and permits the engine to remain idle for an amount of time specified by the truck fleet manager.

CDMA communications and geolocation system and method

Abstract: A spread-spectrum CDMA communications system for locating remote units, and for communicating message data between a plurality of remote units and a base station. The spread-spectrum CDMA communications system includes a plurality of base stations and a plurality of remote units. A base station has a spread-spectrum modulator for spread-spectrum processing the message data, and a transmitter for transmitting the spread-spectrum processed-message data, combined with a generic-chip-code signal, from the base station to a remote unit. The base station also has an antenna, and spread-spectrum detectors for recovering message-data communicated from the remote-units. A remote-unit has an antenna, and a detector coupled to the antenna for recovering data communicated from the base station. The detector includes a spread spectrum demodulator. Also, the remote unit has a device for converting the format of the data into a form suitable for communicating over radio waves, a spread spectrum modulator and a transmitter. The base station has a range circuit, which comparers the generic-chip-code signal generated at the base station with the generic-chip-code signal received from the remote unit, for determining a range between the remote unit and the base station.

Microcellular communication systems with hierarchical macrocell overlays: traffic performance models and analysis

Abstract: A hierarchical overlaid scheme suitable for high-capacity microcellular communications systems is considered as a strategy to achieve high system performance and broad coverage. High-teletraffic areas are covered by microcells while overlaying macrocells cover low-teletraffic areas and provide overflow groups of channels for clusters of microcells. New calls and handoff calls enter at both the microcell and macrocell levels. Handoff calls are given priority access to channels at each level. The layout has inherent load-balancing capability, so spatial teletraffic variations are accommodated without the need for elaborate coordination of base stations (wireless gateways). An analytical model for teletraffic performance (including handoff) is developed. Theoretical performance characteristics that show carried traffic as well as blocking, handoff failure, and forced termination probabilities are derived. Effects of nonuniform teletraffic demand and channel allocation strategies on system performance are discussed. >

Allocation method and apparatus for reusing network resources in a wireless communication system

Abstract: In a wireless communication system (106), base stations (118, 120) are connected to a backbone network (116) such as a wired LAN and act as access points and relays for remote stations (128, 132, 136). A remote station registers and performs bidirectionnal communication with one of the base stations designated as its home base station. Base stations have overlapping coverage areas where a remote station is within reception range of several base stations. Such communication system may for instance be a multicell radio LAN using frequency hopping signaling. The method allows to reuse a limited number of network resources such as frequency hopping patterns and assign the same resource to several active base stations. Upon request from a base station, a network controller (110) connected to the backbone network computes a distance index between the requesting base station and the other active base stations and assigns to the requesting base station the same network resource as the one assigned to another base station with the highest distance index. Information about cells overlaps is centralized in a control database (109) and used by the network controller to compute distance indexes.

Multicarrier frequency hopping communications system

Abstract: A multicarrier frequency hopping spread spectrum communications system wherein a transmitting station assigns encoded data symbols to particular ones of a predetermined series of fixed carrier frequencies, the frequency assignments being periodically mixed according to a frequency hopping code, and the encoded data symbols are combined with their assigned carrier frequencies in accordance with an inverse Fourier transform so as to multiplex the encoded data symbols by orthogonal frequency division modulation. A receiving station performs demultiplexing and de-mixing of such multiplexed signals in accordance with the inverse of the multiplexing and mixing performed at the transmitter. The system thereby provides frequency hopping operation without requiring a rapidly tunable and accurately phase controlled oscillator at each of the transmit/receive stations.

Asynchronous transfer mode communication with inverse multiplexing over multiple communication links

Abstract: An asynchronous transfer mode inverse multiplexed communication system is disclosed wherein a series of communication cells are multiplexed over a set of communication links. Each communication cell includes a framing bit of a predetermined framing bit stream for each communication link and a control channel bit of a control message for each communication link. Inbound communication cells from each communication link are aligned according to the corresponding framing bit stream. The control message specifies an ordered list of logical identifiers to indicate a multiplexed sequence of transfer of the communication cells over the communication links.

Wireless direct-sequence spread spectrum TDMA communications system

Abstract: A protocol for wireless direct user-to-user DSSS TDMA digital communication at a data rate of the order of one to several megabits per second in the 902-928 MHz, 2400-2483.5 MHz or 5725-5850 MHz band includes a sequence of transactions, each transaction consisting of a predetermined sequence of subpackets, and each subpacket consisting of a predetermined number of bytes preallocated to a subpacket element or element portion. Network communications among a plurality of stationary and/or mobile users such as personal computers, each equipped with a (Remote Unit) transceiver, are organized and directed by a Master Unit transceiver. Master Unit and Remote Unit transceivers have identical circuitry. Using a first pseudorandom code sequence (M-code), the Master Unit intermittently transmits a DSSS signal enabling Remote Units to synchronize to the Master Unit and so receive scheduling directives. A Remote Unit, while maintaining synchronization with the Master Unit, sends information by transmitting a DSSS signal using a second pseudorandom code sequence (R-code). To facilitate synchronization, the Master Unit also transmits a continuously running DSSS signal using a third pseudorandom code sequence (P-code) which is code-locked and phase-locked to the M-code. A transceiver implementing the protocol in the 2400-2483.5 MHz band includes a microprocessor, external data RAM, Control Logic Section, Analog Section, and Radiofrequency Section.

Script-based data communication system and method utilizing state memory

Abstract: A preprocessing script-based data communications system and method that embeds information regarding the previous state of the system within script data. This effectively imposes a state memory upon what would otherwise be a stateless system. Typically, the scripts processed by this system are similar in structure and format to ordinary HTML scripts, with the addition of several commands that facilitate programming embedded state information. Within systems employing the invention a client is afforded the capability of having one script influence another by exploiting the preprocessor imposed state memory. In addition, the invention provides these advantages to a client without the need for storing state information on a data system server, thereby providing increased system security.

Communication system and method

Abstract: PURPOSE: To provide a circuit connected with the control system of a pair-wire for a variable analog DC input for attaining bi-directional digital communication along the pair-wire for the diagnostic operation of a transducer. CONSTITUTION: This system incorporates a switching circuit for providing the first impedance for a DC signal and a second substantially high impedance while the same pair-wire system is used with a first position to which a capability to accept both a variable DC analog signal and a bi-directional digital communication signal is applied by applying a second switching position. Also, this system includes an analog input signal which is auxiliary to a circuit capable of further control as current feedback to a control algorithm in a microcontroller 59. An auxiliary process transmiter detects a variable related with a pressure, temperature, flow, or several other processes, and connects it with a circuit for the control of a transducer 34. At last, this system includes a new voltage adjuster and a capacity voltage supplying source, and the voltage is used on the two conductors from the controller for supplying a power source to the device.

System and method for integration of a paging server into a private branch exchange environment

Abstract: A communication system and method of use which integrates a paging system into the PBX communication environment providing enhance performance and capabilities. A PBX environment brings together many forms of communication: telephony conversations, voice mail, electronic mail, Fax messages, and others. The paging system, which consists of a paging server, a voice response unit, and end user paging devices, is integrated into the PBX environment making it the focal point of communications. The paging devices provide immediate and visual indication to the user of a request for callback and relative urgency for the callback, and of the arrival of other forms of communication such as a voice mail message, electronic mail, and Fax. The paging system subscriber need only look at his paging device to determine if E-Mail, Voice Mail, or facsimile messages await. Performance is also enhanced for a caller trying to reach a paging system subscriber. Callers only need to dial a single phone number, rather than a phone number for the office and a different phone number to page. Because the paging system utilizes a voice response unit, callers are informed of their options and instructed how to complete their communication.

GestureCam: a video communication system for sympathetic remote collaboration

Abstract: An approach supporting spatial workspace collaboration via a video-mediated communication system is described. Based on experimental results, the following were determined to be the system requirements to support spatial workspace collaboration: independency of a field of view, predictability, confidence in transmission and sympathy toward the system. Additionally, a newly developed camera system, the GestureCam System, is introduced. A camera is mounted on an actuator with three degrees of freedom. It is controlled by master-slave method or by a touch-sensitive CRT. Also, a laser pointer is mounted to assist with remote pointing. Preliminary experiments were conducted and the results are described herein.

Sub-orbital, high altitude communications system

Abstract: A sub-orbital, high altitude communications system comprising at least two ground stations (12) and at least one high altitude relay station (28, 130). Each of the ground stations (12) including means for sending and receiving telecommunications signals (20, 22, 36). The relay stations (28, 130) include means for receiving and sending telecommunications signals (48) from and to the ground stations (12) and from and to other relay stations. Means are provided for controlling the lateral and vertical movement of the relay stations so that a predetermined altitude and location of each of the relay stations can be achieved and maintained. Means are provided for receiving the relay stations so that they can be serviced for reuse.

Optimizing microcell base station locations using simulated annealing techniques

Abstract: The problem of choosing the optimum locations for base stations in a microcell communications system is considered. The factors affecting optimum selection are the non-uniform service areas in complex propagation environments, the mutual coverage and interference of multiple base stations, and the service objective which is usually defined by signal level but may also be defined by delay spread for certain digital systems. This optimization problem is addressed using simulated annealing (SA) techniques which offer a method to achieve near optimum solutions to complex combinatorial optimization problems, This research shows that SA is a viable approach for handling practical base station siting problems in an urban microcell environment. >

Method and apparatus for communicating data in a wellbore and for detecting the influx of gas

Abstract: The present invention relates to a borehole acoustic communication system. The apparatus of the invention comprises a first transceiver at a first communication node and a second transceiver at a second communication node. The data is transmitted in a wellbore between the first transceiver and the second transceiver through a communication channel.

Position enhanced communication system including system for embedding CDMA navigation beacons under the communications signals of a wireless communication system

Abstract: A cellular telephone system having three or more cell sites with each cell site having a source of cellular communication signals and an RF transmitter and antenna for broadcasting the cellular communication signals. A direct sequence spread spectrum waveform carrying navigation signals is embedded in the cellular communication signals, including controlling the signal strength of the navigation signals so that the combined energy of the navigation signals from all cell sites at any location is at least a predetermined energy level below the energy level of the cellular communication signals. Each cell site includes timing for timing the operation of a GPS receiver. An RF signpost system comprising a plurality of low powered RF broadcast stations, one each at a plurality of scattered geographic locations, each low powered RF broadcast station broadcasting a direct sequence spread spectrum digital RF waveform and a modulator to modulate the digital RF waveform with location information identifying the geographic locations, respectively.

Data burst randomizer

Abstract: A method and system, for use in a communication system in which data is transmitted in data frames of a predetermined time duration, for the positioning of the data within the data frames for transmission. A computation circuit computes according to the deterministic code a pseudorandom position for the data within each data frame. A positioning circuit positions the data within each data frame in the computed position.

Transceiver sharing between access and backhaul in a wireless digital communication system

Abstract: A microcellular digital packet communication system is provided for digital communication having a plurality of repeating packet-mode fixed-site transceivers each being at a plurality of different sites and each being capable of communicating on mutually-common frequencies, including for example by means of frequency-hopping spread spectrum, wherein a terminal transceiver directly communicates substantially simultaneously with at least a few of the fixed-site transceivers on the mutually-common frequencies and distributes information packets of a single originating message among the fixed-site transceivers, the fixed-site transceivers forwarding the information packets via multiple communication links to a single destination terminal on the mutually-common frequencies at which the message is reassembled. The system enables reliable handoffs and robust connectivity by maintaining multiple simultaneous communication links between terminal transceivers and repeating transceivers.

Remote data acquisition and communication system

Abstract: A remote data acquisition and communication system includes a plurality of collector devices including a radio transmitter, optionally a plurality of concentrator devices including a radio transmitter, a radio receiver and a memory, a plurality of controller devices including a radio transmitter, a radio receiver and a memory, optionally a plurality of data communications nodes coupled to corresponding concentrator devices via a first communications link, and a data management platform computer coupled to the data communications nodes or the next lower level of devices via a second communications link. The collector devices, concentrator devices and controller devices communicate with one another via RF communications, preferably a single communication channel at a single carrier frequency. The collector devices preferably transmit data to the concentrator devices at intervals of between 4 to 6 hours and in preferred transmission bursts of less than 200 milliseconds, to minimize collisions between transmissions from different collector devices, and the transmitted data is sorted and redundancies discarded for each desired period of data keeping, i.e., typically daily.