Showing papers on "Communications system published in 1987"

Spread spectrum multiple access communication using satellite or terrestrial repeaters

Abstract: A multiple access, spread spectrum communication system and method for providing high capacity communications to, from, or between a plurality of system users, using code-division-spread-spectrum communication signals. The communication system uses means for providing marginal isolation between user communication signals. The marginal isolation is provided by generating simultaneous multiple steerable beams; using an omni-directional antenna with polarization enhancement; using power control devices to adjust the output power for user generated communication signals either in response to their input activity level, or in accordance with a minimum allowable power for maintaining a communication link. The communication system can also employ a means for transmitting a predetermined pilot chip sequence contiguous with the code-division-spread-spectrum communication signals. In further embodiments the communication system employs a plurality of user terminals linked to each other or to other services through one or more terrestrial or satellite repeaters. Multiple satellite repeaters are operable in a new communication mode to obtain further gains in signal isolation.

Universal digital portable radio communications

Abstract: Providing voice and data communications to people away from their wireline telephones has become a major communication frontier. This frontier is being penetrated by evolving approaches to portable communications, e.g., cordless telephones, mobile radiotelephone, and radio paging. However, these approaches have many limitations; none can provide universal portable communications services. This paper discusses limitations of the evolving approaches and considers objectives and approaches for providing more universal digital portable communications as an integrated part of telephone exchange networks. These more universal communications could be accomplished by using demand-assigned radio links for the last thousand feet or so of telephone loops and sharing the remainder of the fixed distribution facilities. Fixed radio ports as integrated parts of telephone distribution networks could be placed throughout service regions. Efficient use of the radio spectrum could be insured by the planned reuse of radio frequencies throughout the regions. The severe multipath radio propagation environment within and around buildings that strongly influences the design of portable communications systems is described in the paper. System configurations and radio link techniques, that can provide reliable communications in the multipath environment, are discussed. Radio system calculations are illustrated for radio ports with 30-ft-high antennas in residential areas. The calculations indicate that radio link availability would be greater than 99 percent for 2000-ft port separations and 5-mW portable transmitters. Reuse of frequencies would require dividing the allocated frequency band into segments for use at adjacent ports. Calculations suggest that link availability in the cochannel interference environment would be greater than 99 percent, if 25 to 35 segments were used in residential areas.

Direction finding localization system

Abstract: The present invention combines the relative insensitivity of the phase angle differences of a radio signal to the signal distortions inherent in an urban environment with digital signal processing techniques to produce an accurate and economical way to locate a mobile transmitter station such as a mobile telephone in a cellular telephone network. Phase angle measurements indicative of the angle of direction of a mobile transmitter station from each of a plurality of land stations are obtained by translated Hilbert transformation and are processed to produce a probability density function. The probability density functions are combined after a CHI-squared analysis to produce an area of uncertainty representing the position of the mobile transmitter station. The radio frequency signals emitted from the mobile transmitter station need have no special characteristic for the localization process. Thus, the present invention may easily work as an adjunct to an unrelated communications system such as a cellular telephone system.

Optimum Combining for Indoor Radio Systems with Multiple Users

Abstract: This paper studies the use of optimum combining to increase the capacity of narrow-band in-building radio communication systems with multiple users. We consider systems consisting of a base Station with numerous remotes in a Rayleigh fading environment and study the problem of more users requiring channels than the number of channels available. A system is described that, with multiple antennas at the base station but only one antenna at each remote, uses optimum combining to suppress interfering signals. We show that this system, with M antennas at the base station, can achieve an M -fold increase in the number of users or tolerate M - 1 interferers from other systems. Thus, with optimum combining, radio communications can be used in high-density, multiple-user environments, such as within buildings, even when only limited bandwidth is available.

Video-telephone communications system

Abstract: An auxiliary unit is used in conjunction with a personal computer based work station for interconnecting the work station to an audio-visual communications network. The auxiliary unit includes a CRT, a camera, a speaker phone circuit, and a CPU for interfacing these elements with each other and with the communications network to permit the transmission and reception of voice, video and computer graphics information.

Method and apparatus for communication of video, audio, teletext, and data to groups of decoders in a communication system.

Abstract: A communication system enabling transmission of individual subscriber teletext messages (12), audio and video to individual subscribers (300a, 300b, 300c) and permitting group communications of audio, video, teletext and data information from a single central subscriber location (302), such as a corporate head office to a plurality of satellite offices, such as field or sales offices of the corporation. A composite signal including the information to be transmitted as well as system wide, individual decoder and group decoder control signals is transmitted. The system-wide control signals include data germane to operation of each of the decoders (24) of this system, including key information needed to decode the composite signal.

Universal Digital Portable Communications: A System Perspective

Abstract: In our highly mobile society, the provision of voice and data communications to a person away from his/her wireline telephone has become a major communications frontier. The early penetration of this frontier has been based on very limited portable communications approaches, e.g., cordless telephones, mobile radio telephones, and radio paging. Each of these approaches only partially satisfies portable communications needs. This paper describes an approach to providing universal digital portable communications integrated into telephone networks. A system configuration employing time-division multiple-access radio link architecture and frequency reuse is described. Issues affecting radio link transmission rates and radio system coverage are discussed. Characteristics and parameters of a possible system to supplement the wire (or fiber) loop are indicated.

Packet switching network

Abstract: A communications system is described in which a large number of endpoints communicate among one another in an orderly and protocol independent manner. The system is based on a short, fixed format packet which is switched among stations and within equipment in a contention-free manner without the use of general purpose processors. The system is distance independent, employs serial or parallel data paths, can use various media and can transport and switch data and digitized voice and video information in the same format and with the same equipment and transmission media. The effect of the system is to enable the construction of large metropolitan area networks which provide complete protocol conversion of all terminal types as well as transmission of data, voice, video and encrypted information.

Strategies for encouraging successful adoption of office communication systems

Abstract: The adoption of new computer communication systems into organizations requires behavioral change. Planning for successful adoption requires knowledge of individual organizational communication patterns and the relationship between those patterns and particular communication system solutions. This paper documents a sequence of studies of organizational communication. Needs for office communication systems were identified, as were social and psychological factors temporarily inhibiting their use. Strategies for assuring smooth adoption of such systems are highlighted.

Computer-controlled electronic system monitor

Abstract: An electric power monitor system for radio communication (trunking and paging repeater base station) systems includes a plurality of input switches, power sensors, a power monitor having a display, keyboard, and microprocessor, a printer port, and communications port. The input switches facilitate alarm inputs, for example, unauthorized entry, flooding, fire, and temperature of the antenna site. The power sensors include bidirectional and unidirectional sensors connected to a communication system having tunable components for producing analog signals indicative of system component performance. The power monitor measures, determines, and reports locally and/or remotely the power output and standing wave ratio of transmitters and antennas, insertion loss of combiners and power to and SWR of antennas and alarms. Specific measurements and computations are: (1) transmitter input power forward to the combiner; (2) reflected transmitter power on the input side of the combiner; (3) reflected power from the antenna side of the combiner; (4) transmitter voltage standing wave ratio; (5) combiner insertion loss (IL) per channel; (6) time and date of most recent channel measurement; (7) antenna voltage standing wave ratio; and (8) combiner power to the antenna. The display shows either single measurements or dual measurements of any selected pair of the foregoing measurements. The measurements are compared to acceptable norms and an alarm system will automatically and remotely signal outside-the-norm measurements of the antenna, combiner, and transmitters as well as the selected environmental conditions.

Radio communication system using synchronous frequency hopping transmissions

Abstract: A frequency-hopping radio communication system is disclosed comprising a control unit which transmits to and receives from each of a plurality of slave stations using a frequency-hopping mode of operation. During a start-up mode, the control unit communicates a starting message to each slave station using a predefined frequency. The message identifies to each slave station a frequency-hopping sequence to be used to select the frequencies from a group of frequencies for transmission to and reception from the control unit. This message also specifies to each slave station unique starting frequencies in the frequency-hopping sequence at which to begin transmitting and receiving. All slave station transmissions are synchronized to the control unit transmissions, thereby preventing any two stations from concurrently using the same frequencies for either transmitting to or receiving from the control unit.

Method and apparatus for enhancing security of communications in a packet-switched data communications system

Abstract: Security of communications in a packet-switched data communications system is enhanced by introducing terminal and host security devices into the system in communicative relationship with a terminal and a host processor, respectively In response to a user-initiated data entry at the terminal, the terminal security device generates an initial data packet indicative of user authorization or not, but which is unsuited for processing by the addressed processor, ahead of additional data packets containing user-entered message data to be processed by the addressed processor The host security device intercepts and processes the initial data packet and, if user authorization is indicated therein, replaces it with an artificial data packet solely to render the additional packets amenable to processing by the addressed processor and thereby to establish a communications session between user terminal and processor-associated database to which access was requested

Developments in the Theory and Application of Importance Sampling

Abstract: The assessment of bit error rate (BER) performance of a digital communication system via computer simulation has traditionally been done using the Monte Carlo method. For very low BER, this method requires excessive computer time. This time can be substantially reduced by using extrapolation based on importance sampling (IS). In applying IS to a complex system, many considerations must be addressed, chief among which is the reliability (variance) of the estimator as a function of the system particulars. We discuss a number of these considerations and, specifically, derive a number of expressions for the variance. We find that the variance improvement may be severely limited by the dimensionality (or memory) of the system. We describe a means for circumventing this limitation through the definition of a statistically equivalent impulse response. For a linear system, this amounts to the ordinary impulse response. The simulation can be structured to estimate the equivalent impulse response using statistical regression. This new approach has been implemented and found to yield significant runtime improvement over conventional importance sampling for linear systems of large dimensionality. We believe this technique will work also for mildly nonlinear systems, as might be encountered in typical satellite Communications.

Telephone communications system with portable handsets

Abstract: This is a telephone communications system having at least one fixed terminal connected by at least one subscriber's line to a telephone exchange and a plurality of portable handsets, the fixed terminal and the portable handsets having infrared transmitters and receivers for exchanging unit charging information and sound data information, the fixed terminal transmitting to a given handset unit charging signals received from the telephone exchange during a call, each portable handset accommodating a support for a programmable read-only memory and logic circuit for deducting from the programmable read-only memory unit charges corresponding to the unit charging signals transmitted by the terminal, each portable handset further transmitting a pay signal to the fixed terminal after having deducted the unit charge fee from the programmable read-only memory, and the fixed terminal further arranged for cutting off the call in case of failure to receive a pay signal after having transmitted a unit charging signal, interference between portable units being avoided by the use of time multiplexed bursts of pulses.

Closed loop, programmable power and communication system

Abstract: A power and communication system for a building, and particularly a residential dwelling wherein there are provided a plurality of receptacles throughout the building, each connected by a cable to source, which may provide different voltages and either AC or DC and having a control interface for selectively switching the desired power to each cable individually. The control interface may also connect each cable to a selected signal transmission line, such as telephone, radio, TV, etc. The cable includes a pair of power conductors and a optical fiber which transmits to and receives from the control interface light signals informing the control interface what power or communication connection is required for a particular receptacle and possibly at the same time providing signal messages to each receptacle. The single optical cable can transmit an interrogating signal to the receptacle, which signal is transferred through a special plug and socket connection have a mating optical coupler to an appliance equipped with a microprocessor programmed for replying by way of light signals sent back to the interface through the same coupler and optical fiber. The control interface is thus informed as to what power and communication connections the appliance requires and to how the appliance should be subsequently monitored.

Control system for microprocessor and software enhanced communications equipment

Abstract: A control system for microprocessor and software enhanced land mobile radio communications systems is provided to increase versatility, capabilities and facilities while providing an easier and more precise control of various radio protocols. As the usage of microprocessors and software is increased in radio communications equipment, additional capabilities, digital protocols and versatility can be desired in such equipment. However, this requires additional and special controls and prior art approaches have limitations with respect to capacity, versatility, size and compatibility with digital protocols. The innovative approach of the invention provides a compact new system to replace prior art multipositional knobs and switches and refines the system of control. The novel control system provides for an efficient utilization of space while achieving outstanding versatility and new operational and control capabilities. This is achieved by advantageously accommodating microprocessors and software based radios by utilizing a multifunctional keypad in combination with a display and command/mode and control switches to access and control a large number of versatile and combined capabilities, operating modes and facilities in a compact form.

Communications system having voice and digital data capability and employing a plurality of voice and data buses in main service unit and serial packetized transmission to and from telephones

Abstract: OF THE DISCLOSURE A communications system having a common equipment unit and a plurality of telephone station sets coupled to the common equipment unit comprises a common equipment unit having at least one trunk interface for coupling at least one central office telephone line to the common equipmeny unit and an analog to digital converter for converting analog signals on the telephone line into digital form, and at least one station interface coupling the common equipment unit to at least one of the station sets by a single wire pair. A plurality of buses couple the trunk interface and the station interface together, the plurality of buses comprising at least one digital voice bus for carrying digitized voice signals, a digital data bus for carrying digital data signals originating from a digital data device and a control data bus for carrying digital data comprising control information for controlling functions in the station sets and for routing the data on the digital voice bus and the digital data bus between at least one of the station sets and the telephone line. The system further includes a controller comprising a microprocessor coupled to the plurality of buses for generating at least some of the control information, the station interface comprising a converter for converting the digitized voice signals, the digital data signals and the control information into serial form for transmission to a selected one of the station sets, and a converter for converting digitized voice signals, digital data signals and control information originating at the station set into parallel form for coupling to respective ones of the plurality of buses.

The application of packet switching techniques to combat net radio

Abstract: The narrow-band Packet Radio system which is the subject of this paper is a highly flexible and survivable data communications system for the Forward Area tactical environment achieved by applying packet switching techniques to Army Combat Net Radio. The User requirements driving this development are outlined. It is important that this system is not viewed as being in competition with other Packet Radio systems, but as one system or building block in an integrated electronic battlefield, hence the emphasis on internetworking. Important design considerations such as survivabifity and the abifity to operate with random network topologies are discussed. A detailed description of the algorithms for Channel Access, Routing, and Network Control which were developed using finite-state-machine simulation techniques is then given followed by a summary of the simulator performance predictions for various scenarios. Packet Radio is a synergism of signal processing and communications protocols implemented on real-time systems. The signal processing requirements and architecture adopted for signaling in the VHF environment are described in the context of the hardware for a prototype network. Early experience resulting from trials and demonstrations with this network are used to point to refinements in the next iteration of system design.

Apparatus and method for obtaining frequency agility in digital communication systems

Abstract: In a communication system that comprises a plurality of subscriber stations in RF communication with a base station having multiple sequentially repetitive time slots, each time slot being assigned to a particular subscriber station, means to change either the frequency or the time slot configurations, or both, in the event of a deterioration of transmission quality caused by modulation change, frequency channel interference, equipment failure, or the like, or by the entrance of additional subscriber stations going on line.

Multipoint data communication with a supervisory system for detecting a malfunctioning remote station

Abstract: A random access multipoint data communication system comprises a central station and a plurality of remote stations. A multiple access channel is established from the remote stations to the central station and a broadcast channel is established from the central station to the remote stations. The central station generates a timing signal for causing each of the remote stations to define commonly shared time slots on the multiple access channel. Each remote station transmits data on a randomly determined time slot of the multiple access channel. The central station periodically and sequentially interrogates the remote stations to return an acknowledgment and processes the returned acknowledgements to determine the presence of a malfunctioning remote station. To avoid data collision, the central station specifies an idle time slot on which the interrogated remote station is requested to send the acknowledgment.

Mobile radio communication system with repeater station grid

Abstract: A mobile radio communication system has base stations 1a, 1b, 1c at the centers of major service areas A, B, C defined by a contiguous array of hexagons or partially overlapping circles, and repeater or one way relay stations 3a-3m at each vertex or intersection point. The repeater stations have directional receiving antennas subtending successive 120° arcs of surrounding minor service areas similarly defined by a ring array of hexagons or circles, amplifiers for imparting a high gain to signals received from mobile units in the minor service areas, and narrow width transmitting antennas for relaying the amplified signals to the base station closest each mobile unit. Such an arrangement enables a substantial reduction in the transmitter output capacity of the mobile units.

A Wireless Network for Wide-Band Indoor Communications

Abstract: We propose and analyze a wide-band indoor communication system that uses radio as the transmission medium either on a stand-alone basis or to supplement a hard-wired network for those situations where complete portability is desired. One principal impairment to such a system is intersymbol interference caused by frequencyselective fading. A novel media-access scheme is proposed which permits the use of resource sharing, wherein a small pool of time slots is effectively shared among all users to provide added protection against channel impairments on an as-needed basis. Our results show that the use of resource sharing and diversity provide excellent protection against intersymbol interference caused by frequency-selective fading with negligible impact on throughput. Furthermore, resource sharing plus diversity can permit significantly higher data rates without large queueing delays. For example, a wireless network with a 10 Mbit/s data rate in a 10 MHz bandwidth using four antennas at the base station has a less than 10-4outage probability at a 10-4BER in buildings with less than 58 ns rms delay spread. A loading of 75 percent is permitted for a queueing delay of less than 20 packet transmission times all but 0.01 percent of the time.

A New Error Control Scheme for Hybrid ARQ Systems

Abstract: This paper introduces the concept of a generalized hybrid ARQ (GH-ARQ) scheme for adaptive error control in digital communication systems. This technique utilizes the redundant information available upon successive retransmissions in an efficient manner so as to provide high throughput during poor channel conditions. A new class of linear codes is proposed for the GH-ARQ system application. The main feature of this class of codes is that the encoder/decoder configuration does not change as the length of the code is varied. As a result, the receiver uses the same decoder for decoding the received information after every retransmission while the error correcting capability of the code increases, thereby leading to an improved performance and minimum complexity for the overall system implementation.

Electronic Communications Systems: Fundamentals through Advanced

Abstract: From the Publisher: All topics have been updated to present the latest information available in this fast-changing field, and completely new sections have been added to cover the following important topics: AM envelopes produced by complex nonsinusoidal signals Quadrature Amplitude Modulation Noise limiters and blankers Alternate signal-to-noise measurements Single-sideband suppressed carrier and frequency division multiplexing Double-sideband suppressed carrier and quadrature multiplexing Microstrip and stripline Light sources, optical power, optical sources, and link budget Trellis encoding CCIt modem recommendations PCM line speed Extended superframe format and wavelength division multiplexing Kepler's laws Clark orbits, and limits of visibility In addition, an entirely new chapter has been added with coverage of: Mobile telephone systems (including AMPS, PSC, and PCSS) This text is written for use in undergraduate level electronic communications courses in which students have prior knowledge of some of the basic electronic principles, as well as an understanding of mathematics through the fundamental concepts of calculus.

Channel unit interface circuit

Abstract: A channel unit interface circuit for interconnecting a two-wire, bidirectional signal transmitting means and a four-wire signal transmitting means in a communication system includes a tip terminal line driver, a ring terminal line driver, a voice sense amplifier, a balance network, A/D signal processing circuit, D/A signal processing circuit, filter network, a voice codec/PCM filter, a channel logic circuit, and a DC-to-DC converter. The channel unit interface circuit is suitable for use with substantially all of the different alarm-signalling techniques utilized by the various alarm companies for connecting their equipment to a channel bank coupled to the four-wire means. The interface circuit simulates a transmission line or cable over carrier in the frequency range of DC to 3.5 KHz with an amplitude variation between +110 to -200 VDC.

System for providing transmitter-controlled actuation of equipment at the receiving end of a communications system

Abstract: A system for providing transmitter-controlled actuation of equipment at the receiving end of a communications system by using an identification signal transmitted for the entire duration of a broadcast and characterizing this broadcast. If the equipment has not been started by the identification signal and if the device is actuated at the beginning or during the broadcast, the further operation of the equipment in a predetermined operating mode is controlled using the identification signal. The equipment at the receiving end may be a broadcast receiver, particiularly a television or radio receiver, or an audio or video recorder. In a particular embodiment, the identification signal is stored when a record or "quick start" key of a VCR is manually actuated, and recording continues until the current identification signal is no longer the same as the stored signal.

Space coherent optical communication systems--An introduction

Abstract: Critical technology and system issues for space optical heteroydyne communication systems using GaAlAs lasers are discussed. Heterodyne systems offers 10-20 dB better receiver sensitivities and thus smaller telescope sizes for the same laser power than direct detection systems. Based on present state-of-the-art technologies, it is concluded that an efficient optical intersatellite link can be realized with a few years of development.

Network measurement of the VMTP request-response protocol in the V distributed system

Abstract: Communication systems are undergoing a change in use from stream to request-response or transaction communication In addition, communication systems are becoming increasingly based on high-speed, low delay, low error rate channels These changes call for a new generation of networks, network interfaces, and transport protocol design The performance characteristics of request-response protocols on these high-performance networks should guide the design of this new generation, yet relatively little data of this nature is availableIn this paper, we present some preliminary measurements of network traffic for a cluster of workstations connected by Ethernet running the V distributed operating system We claim that this system, with its use of a high-speed local area network and a request-response transport protocol tuned for RPC, provides some indication of the performance characteristics for systems in the next generation of communication systems In particular, these measurements provide an indication of network traffic patterns, usage characteristics for request-response protocols, and the behavior of the request-response protocol itself These measurements suggest in general that a key design focus must be on minimizing network latency and that a request-response protocol is well-suited for this goal This focus has implications for protocol design and implementation as well as for the design of networks and network interfaces

Cellular communication system sharing control channels between cells to reduce number of control channels

Abstract: Unnecessary control channels are eliminated in a mature cellular radio telephone RF communications system by sharing control channel transceivers and control channels between original omni-directional cells and subdivisions of those original cells. A control channel is allocated to the original omni-directional cell, and subdivided cell areas are not provided with their own control channels. One or more voice channels are allocated to the original omni-directional cell, and the subdivided cell areas also have voice channels allocated to them. Calls are initiated between mobile transceivers and the original omni-directional cell. Locating receivers associated with the subdivided cell areas determine which subdivisions particular mobile transceivers are located within. Subsequently, calls are handed off fron the original omni cell to an appropriate subdivision.

Radio communication system having autonomously selected transmission frequencies

Abstract: When the disclosed frequency-hopping communication system is initially enabled, it detects another system operating within range by listening for a predefined radio frequency of a fixed duration. When that particular frequency is detected, the system knows that a master system is operating within range and is utilizing a first predetermined group of communication frequencies and, consequently, selects a second, third, etc. predetermined group of communication frequencies. If the particular radio frequency is not detected, the system becomes the master system, selects the first predetermined group of communication frequencies for intra-system communication and begins transmitting the predefined radio frequency to indicate its master status.