Showing papers on "Data transmission published in 1992"

Optimum diversity combining and equalization in digital data transmission with applications to cellular mobile radio. I. Theoretical considerations

Abstract: A comprehensive theory for Nth-order space diversity reception combined with various equalization techniques in digital data transmission over frequency-selective fading channels is developed. The channels are characterized by N arbitrary impulse responses possessing random parameters as well as N additive Gaussian noise sources. Various combiner-equalizers that minimize the mean-squared error are determined. Formulas are presented for the attainable least-mean-squared errors and upper bounds on average probabilities of error. The theory is applied to optimize system parameters and to predict performance for QAM data transmission operating over a model for the mobile radio channel. For this model, estimates of average attainable error rates and outage probabilities are provided as functions of system parameters. In the channel models the uncoded data rates as well as Shannon capacity are regarded as random variables. >

Telecommunication display system

Abstract: A telecommunication system provides voice and data communications over a conventional telephone line that can be dynamically switched from voice mode to data mode during a single conversation. Each station includes a telephone for voice communications and bypass relay means for selectively connecting the telephone to the telephone line in voice mode and disconnecting the telephone while operating in data mode. Prior to transmitting data, the originating station first transmits a start signal over the telephone line that includes a rate signal indicating one of the several possible data transmission rates. If a station detects a start signal transmitted by a remote station, a microcontroller directs the bypass relay means and modem to automatically switch from voice mode to data mode in preparation for receiving data from the originating station.

Bandlimited quasi-synchronous CDMA: a novel satellite access technique for mobile and personal communication systems

Abstract: Recent trends in digital communications are opening commercial applications to code division multiple access (CDMA). A novel access technique based on bandlimited quasi-synchronous CDMA (BLQS-CDMA) is described, showing all the advantages of synchronizing conventional direct sequence CDMA to drastically reduce the effect of self-noise. Bandlimitation is achieved with no detection loss by means of Nyquist chip shaping, leading to a simple all-digital demodulator structure. Detection losses due to imperfect carrier frequency and chip timing synchronization are analytically derived and numerical results are checked by computer simulations. Impairments due to satellite transponder distortions are evaluated. The full digital modem structure is presented, together with possible applications to mobile and very small aperture terminal (VSAT) satellite communications. >

Introduction to digital communication

Abstract: (NOTE: Most chapters begin with an Introduction and conclude with Summary, References, and Problems.) 1. Introduction to Digital Data Transmission. Components of a Digital Communication System. Communications Channel Modeling. Communication Link Power Calculations. Driving Forces in Communications. Computer Use in Communication System Analysis and Design. Preview of the Book. 2. Signals, Systems, Modulation, and Noise: Overview. Review of Signal and Linear System Theory. Basic Analog Modulation Techniques. Complex Envelope Representation of Bandpass Signals and Systems. Signal Distortion and Filtering. Practical Filter Types and Characteristics. Sampling Theory. Random Processes. Computer Generation of Random Variables. 3. Basic Digital Communication Systems. The Binary Digital Communications Problem. Signaling through Bandlimited Channels. Equalization in Digital Data Transmission. A Digital Communication System Simulation Example. Noise Effects in Pulse Code Modulation. 4. Signal-Space Methods in Digital Data Transmission. Optimum Receiver Principals in Terms of Vector Spaces. Performance Analysis of Coherent Digital Signaling Schemes. Signaling Schemes Not Requiring Coherent References at the Receiver. Comparison of Digital Modulation Systems. Comparison of M-ary Digital Modulation Schemes on Power and Bandwidth-Equivalent Bases. Some Commonly Used Modulation Schemes. Design Examples and System Tradeoffs. Multi-h Continuous Phase Modulation. Orthogonal Frequency Division Multiplexing. 5. Channel Degradations in Digital Communications. Synchronization in Communication Systems. The Effects of Slow Signal Fading in Communicative Systems. Diagnostic Tools for Communication System Design. 6. Fundamentals of Information Theory and Block Coding. Basic Concepts of Information Theory. Fundamentals of Block Coding. Coding Performance in Slow Fading Channels. 7. Fundamentals of Convolutional Coding. Basic Concepts. The Viterbi Algorithm. Good Convolutional Codes and Their Performance. Other Topics. 8. Fundamentals of Repeat Request Systems. General Considerations. Three ARQ Strategies. Codes for Error Detection. 9. Spread-Spectrum Systems. Two Communication Problems. Types of Spread-Spectrum Systems. Complex-Envelope Representation of Spread Spectrum. Generation and Properties of Pseudorandom Sequences. Synchronization of Spread-Spectrum Systems. Performance of Spread-Spectrum Systems in Jamming Environments. Performance in Multiple User Environments. Multiuser Detection. Examples of Spread-Spectrum Systems. 10. Introduction to Cellular Radio Communications. Frequency Reuse. Channel Models. Mitigation Techniques for the Multipath Fading Channel. System Design and Performance Prediction. Advanced Mobile Phone Service. Global System for Mobile Communications. Code Division Multiple Access. Recommended Further Reading. 11. Satellite Communications. Allocation of a Satellite Transmission Resource. Link Power Budget Analysis. Examples of Link Power Budget Calculations. Low- and Medium-Earth Orbit Voice Messaging Satellite Systems. Appendix A. Probability and Random Variables, Probability Theory. Random Variables, Probability Density Functions, and Averages. Characteristic Function and Probability Generating Function. Transformations of Random Variables. Central Limit Theorem. Appendix B. Characterization of Internally Generated Noise. Appendix C. Attenuation of Radio-Wave Propagation by Atmospheric Gases and Rain. Appendix D. Generation of Coherent References. Description of Phase Noise and Its Properties. Phase-Lock Loop Models and Characteristics of Operation. Frequency Synthesis. Appendix E. Gaussian Probability Function. Appendix F. Mathematical Tables. The Sinc Function. Trigonometric Identities. Indefinite Integrals. Definite Integrals. Series Expansions. Fourier Transform Theorems. Fourier Transform Pairs. Index.

Remote link adapter for use in TV broadcast data transmission system

Abstract: A hybrid transmission system is provided to transmit and receive high-speed digital information in the form of variable length packets using standard television practices and components. The basic building block of this hybrid digital transmission system is the device at the remote location that receives the analog broadcast TV-like signal processed by a standard vestigial sideband video modulator. This device decodes the digital information from the signal and then passes it along as digital information to any form of a data terminal equipment or computer.

Methods and apparatus for uniquely encrypting data at a plurality of data transmission sites for transmission to a reception site

Abstract: In a data transmission system comprising a plurality N of transmission sites and at least one reception site, a set of data at each transmission site is uniquely encrypted by (a) providing each transmission site with a broadcast key unique to that transmission site and a system key that is the same for all transmission sites, the system key comprising a plurality S of bits and each of the broadcast keys comprising a unique plurality B of bits, wherein B is less than S; (b) convolving in a predetermined manner at each transmission site the system key and the broadcast key unique to that transmission site to generate a unique data encryption key for that transmission site; (c) encrypting the set of data at each transmission site with the unique data encryption key generated at that site. The sets of data uniquely encrypted at each transmission site are then transmitted to the reception site. There is stored, in a memory at the reception site, the system key and the of said broadcast keys to enable a selected one of the encrypted sets of data to be decrypted at the reception site. The memory capacity necessary to store the system key and the broadcast keys at the reception site is no greater than ((N×B)+S) bits. Alternatively, a plurality N of data sets at a single transmission site are encrypted in this manner.

System for simultaneous analog and digital communications over an analog channel

Abstract: At a transmitting end, frequencies used to a construct a digital signal are substantially removed from an analog signal by a notch filter circuit to produce an interim signal which is then combined with the digital signal as by combining to produce a composite analog signal that is transmitted to a receiving end. At the receiving end the frequencies used to construct the digital signal are substantially removed from the composite analog signal by a notch filter circuit. In this way the digital signal can be transmitted simultaneously with the analog signal without errors that could be introduced by the analog signal, and with only a slight change to the frequency spectrum of the analog signal. This can be used in telephone communications for sending caller ID digital data over the same line carrying a voice signal. Caller ID data is sent FSK encoded and only those frequency used for the mark and the space are attenuated in the received voice signal before it reaches the telephone's speech circuit. For PSK encoded data method, a single notch filter removes the carrier frequency from the voice signal at the receiving end. In this way, the user is not subjected to the audible frequencies used to transmit the caller ID data, but the overall fidelity of the voice signal is only insignificantly reduced.

Distributed applications processing network

Abstract: A system is described in which a local task (415) running on a local computer (400) can use a remote task (430) running on a remote computer (405). The local task (415) firstly establishes a conversation between a local data transmission agent (410) in the local computer (400) and a remote data transmission agent (420) in the remote computer (405). This conversation is assigned a handle (XmitHandle). The local task (415) can then use this handle (XmitHandle) to call tasks (430) running on the remote computer (405). Data is passed between the local task (415) and the local data transmission agent (410) by the use of a shared memory buffer. Data is similarly passed between the remote task (430) and the remote data transmission agent (420) by the use of a shared memory buffer. The local (410) and remote (420) data transmission agents are connected together in a network which is preferably an SNA network.

Optimum diversity combining and equalization in digital data transmission with applications to cellular mobile radio II. Numerical results

Abstract: For Pt.I, see ibid., vol.40, no.5, p.885-94 (1992). The probability distributions of the data rates that can be supported by optimum receiver structures as well as the distribution of the Shannon capacity are studied. The dependences among the important system parameters are exhibited graphically for several illustrative examples including QPSK. At outage probabilities >

Orthogonal multiple carrier data transmission

Abstract: In this paper, the idea of data transmission by essentially using the discrete Fourier transform (DFT) algorithm, the idea of overlapped but orthogonally sampled multiple data transmission channels, and the idea of subband signal processing by means of DFT polyphase filter banks are combined. The main result in a novel orthogonal multiple carrier (OMC) data transmission system with high computational efficiency and high bandwidth efficiency. Intersymbol interference is avoided by choosing each channel as a Nyquist system. The problem of unavoidable crosstalk between adjacent channels is solved by sampling the equally spaced zeros of the crosstalk impulse response. It is shown that in a critically sampled DFT filter bank the space between the zeros exactly equals one symbol period. The time offset of half a symbol period between the zeros of the real part and the zeros of the imaginary part of the crosstalk impulse response leads to a special staggering technique with time offset. Finally the structure of the polyphase filter banks is optimized resulting in fast Fourier transforms of half of the original length.

Inter-processor communication method for transmitting data and processor dependent information predetermined for a receiving process of another processor

Abstract: In a parallel computer, in order to reduce the overhead of data transmissions between the processes, a data transmission from the virtual space of a process in a certain cluster to the virtual space of a process in other cluster is executed without copying the data to the buffer provided within the operating system. The real communication area resident in the real memory is provided in a part of the virtual space of the process, and an identifier unique within the cluster is given to the communication area. When the transmission process has issued a transmission instruction at the time of data transmission, the cluster address of the cluster in which the transmission destination process exists and the identifier of the communication area are determined based on the name of the transmission destination process. Then, the data is directly transmitted between the mutual real communication areas of the transmission originating process and the transmission destination process. Overhead for the data transmission between the processes can be reduced by avoiding making a copy of the data between the user space and the buffer provided within the operating system at the time of data transmission between the processes.

Achievable information rates on digital subscriber loops: limiting information rates with crosstalk noise

Abstract: The capacity and cutoff rates for channels with linear intersymbol interference, power dependent crosstalk noise, and additive white noise are examined, focusing on high speed digital subscriber line data transmission. The effects of varying the level of additive white noise, crosstalk coupling gain, sampling rate, and input power levels are studied in detail for a set of simulated two-wire local loops. A closed-form expression for the shell constrained Gaussian cutoff rate on the crosstalk limited channel is developed and related to the capacity, showing that the relationship between these two rates is the same as on a channel without crosstalk noise. The study also projects achievable rates on a digital subscriber line, inside and outside of a carrier serving area, with a sophisticated but realizable receiver. >

Analysis of 16-APSK modulation in AWGN and Rayleigh fading channel

Abstract: The error probability for fully differential 16-APSK in a Rayleigh fading channel has been evaluated theoretically and through the use of extensive computer simulation. The optimum ring ratio and detection thresholds have been determined and the results indicate that 16-APSK can be considered as a potential candidate for spectrally efficient digital transmission over practical mobile fading channels.

Process for digital transmission and direct conversion receiver

Abstract: The transmitter uses a synthesized oscillator (1A) whose reference (24) is provided by the clock (H) of the data (P, Q). The demodulation oscillator (13A) of the receiver is a synthesizer which is functionally identical to that (1A) of the transmitter, and its reference (23) is provided by the clock (H, 36) recovered from the received data.

Low frequency audio sub-channel embedded signalling

Abstract: A T1 based digital transmission system includes audio subchannel embedded signalling, instead of "robbed bit" signalling, to transmit signalling information along with voice communications. Signalling bits are produced in a sub-audio range and combined with voice information signals in the audio range. The resultant signal is transmitted over a T1 link to a receiver which recovers the signalling bits and voice information signals. The technique can be applied using adaptive pulse code modulation to increase the number of channels. A digital signal processor can implement channel functions.

Digital transmission of acoustic signals over a noisy communication channel

Abstract: The performance of digital communication over a noisy communication channel is improved. An encoder combines bit modulation with error control encoding to allow the decoder to use the redundancy in the error control codes to detect uncorrectable bit errors. This method improves the efficiency of the communication system since fewer bits are required for error control, leaving more bits available for data. In the context of a speech coding system, speech quality is improved without sacrificing robustness to bit errors. A bit prioritization method further improves performance over noisy channels. Individual bits in a set of quantizer values are arranged according to their sensitivity to bit errors. Error control codes having higher levels of redundancy are used to protect the most sensitive (highest priority) bits, while lower levels of redundancy are used to protest less sensitive bits. This method improves efficiency of the error control system, since only the highest priority data is encoded with the highest levels of redundancy. The effect of uncorrectable bit errors is reduced by adaptively smoothing the spectral parameters in a speech decoder. The amount of smoothing is varied depending upon the number of errors detected during the error control decoding of the received data. More smoothing is used when a large number of errors are detected, thereby reducing the perceived effect of any uncorrectable bit errors which may be present.

Communications method for a shared-medium communications method

Abstract: A communications method for a shared-medium communications network having a plurality of stations connected by a first and second bus. The first bus is for data transmission in one direction and the second bus is for data transmission in an opposite direction. The method includes transmitting data between stations in slots. A station desiring to transmit requests the use of a slot by placing a request signal on the bus in a direction opposite to the desired direction of transmission. A slot is then used on a first request, first use priority except for a least one station which is allocated a slot without regard to the first request first use priority. This allocation provides for guaranteed bandwidth traffic.

Designing teleoperator architectures for transparency

Abstract: The author provides tools for analyzing the performance of various teleoperation systems, including the effects of communication delay. A general multivariable system architecture is utilized which includes all four types of data transmission between master and slave robot; force and position in both directions. It is shown that a proper use of all four channels is of critical importance in achieving high-performance telepresence in the sense of accurate transmission of task impedances to the operator. Achieved transparency and stability properties of two common architectures, as well as a transparency-optimized architecture are quantitatively compared on simplified one-degree-of-freedom examples. >

A system for monitoring parked vehicles

Abstract: A system (10) for monitoring parked vehicles, comprising a portable parking tag (11) for each vehicle and a reading device (12). The portable parking tag (11) includes a non-contact data communications circuit (15) for effecting data transfer via mutual electromagnetic coupling with the reading device (12), a memory (17) coupled to the data communications circuit (15) for storing at least one parking parameter, and an antenna (22) coupled to the data communications circuit (15) for transmitting a first signal representative of each parking parameter. The reading device (12) includes an antenna (25) for receiving the first signal, a reading circuit (26) coupled to the antenna (25) and responsive to the first signal for reading each parking parameter stored in parking tag memory (17), validity verification means coupled to the reading circuit (26) and responsive to the first signal for generating a validity signal, and output means (28, 31) coupled to the validity verification means and responsive to the validity signal for producing a visual or audible output.

Performance limitations of TDD wireless personal communications with asynchronous radio ports

Abstract: A wireless personal communications system, based on a TDMA architecture, using asynchronous ports (radio base stations) and the TDD (time division duplexing) method is evaluated using computer simulations. It is shown that, without port synchronisation TDD methods cannot achieve the uplink quality obtainable by the FDD (frequency division duplexing) method.

Headend processing for a digital transmission system

Abstract: A headend method and apparatus for a digital transmission system is provided which includes inputs for receiving first and second program information from first and second program sources and inputs for receiving first and second control information from first and second control sources. The first and second program information is applied to a switching circuit and a switch control controls the switching circuit to output channels of program information comprising combinations of the first and second program information for output to a subscriber. Processing circuitry allows for selectively providing the first and second control information to the channels output from the switching circuit.

Method of transmitting data from a drillhead

Abstract: A method for remotely monitoring conditions such as carbon monoxide or methane gas concentration, longwall roof support pressure, machine parameters or uncut coal, trona or potash layer thickness in a natural resource mining system such as a longwall or continuous mine system. The method utilizes a plurality of sensors connected to low magnetic moment transmitters, e.g. 0.1 ATM 2 , or high magnetic moment transmitters, e.g. 2.5 ATM 2 , that transmit collected data during multiple short burst transmission periods. Prior to transmission, the data is converted to a digital word format. An algorithm in the transmitter microcomputer ensures that random time intervals exist between data transmission bursts thus preventing a data transmission clash at the central receiver. A microcomputer algorithm in the central receiver protects against data contention caused by simultaneous transmission from several sensors. The data is transmitted to the central receiver either through a natural waveguide pathway or through a utility conductor that is magnetically coupled to the transmitter and central receiver by properly oriented electrically short magnetic dipole antennas. The method can be used, for example, to automatically control the positioning of a plurality of longwall roof supports or to transmit data from a longwall drillhead, along the drill rod, to the central receiver. Data can be communicated between a remote location and a surface area by utilizing a system of repeaters inductively coupled to a utility conductor. Use of the repeater system permits operation of mining machines from a surface computer.

Digital audio data muting system and method

Abstract: A system and method for disabling the output of a data transmission system when a relatively high error rate is detected in the transmitted signal. The error muting technique of the invention functions as the digital equivalent of a leaky integrator with hysteresis. In particular, the signal quality of the received data transmission is monitored, and a predetermined value is added to an accumulator or error counter when an error is detected. This value varies depending upon the nature of the detected error such that more serious errors are given greater error values. The error counter is also decremented by one or some other amount at a programmable time interval in accordance with the maximum acceptable error rate. The error count (accumulator sum) is continuously compared to a programmable error threshold, and if the threshold is exceeded, the output of the data transmission system is disabled, or in the case of a digital audio transmission system, is muted. Once disabled or muted, the output is not reenabled or unmuted until the error counter is decremented all the way down to a lower limit such as zero. In a particular embodiment of the invention, the error counter is decremented at a different rate when the output of the data transmission system has been disabled or muted so that the system may be more or less rapidly returned to normal operation.

Multimedia communicating apparatus

Abstract: Multimedia communication apparatus includes a communication unit that transmits and receives plural types of media information in multiplexed form. When the communication unit is to transmit a first type of media information, a large-capacity transfer speed is allocated to transmission of the first type of media information by first transmission speed selection, but when the communication unit is to receive the first type of media information, a small-capacity transfer speed is allocated to the transmission of the first type of media information, so as to receive the first type of media information and transmit necessary control data. The data transmission speed is flexibly changed dependent on the multiplexed condition of other than data type media information to enable smoother multimedia communication.

VCSE laser transmitters for parallel data links

Abstract: The major issues associated with using vertical cavity surface emitting laser (VCSEL)-based transmitter arrays for parallel data links are examined. An assumption is made that only limited optimization of the individual links is permitted, and to the extent that the required circuits are shared by many channels. An analysis of bit-error ratios, based on measured laser parameter variations across the array, and their theoretical effect on noise margins indicates that a 5-dB penalty may be expected. This leads to a tradeoff between laser tolerances and receiver complexity. Experimental work towards a VCSEL-CMOS transmitter is described. A 622-Mb/s operation is demonstrated with a small hybrid transmitter array. Power dissipation and electrical crosstalk problems are assessed. Block coding of data before transmission significantly improves some aspects of laser transmitter performance. A statistical treatment of crosstalk noise is presented and compared to experimental results. >

Apparatus and method for high speed flexible multiplexing for fibre optic data transmission

Abstract: Disclosed is a method and apparatus for flexibly converting an electrical parallel digital data signal to a serial optical digital data signal for transmission along a fiber optic cable and then subsequent conversion back to a parallel electrical digital data signal. An input conditioner circuit is used to set a ratio between a transmission link clock rate and a sample clock rate such that the ratio determines the number of bits being transmitted for a sample word thus enhancing the flexibility of the device to different sampling rates. Each individual sample word is a frame of data which includes a single frame bit set up in a 4-bit frame pattern. A first frame bit is a sync acquisition bit comprised of an alternating sequence of "0"s and "1"s, a second and fourth parity bit computed from the parity of the previous two words of data, and a third channel identification bit. An output conditioner circuit receives the serial stream of data bits to convert it back to a parallel data format. The output conditioner further must identify and remove the frame bits as discussed above for proper processing. By this, the system can transmit data at flexible sample rates.

Method and system for automatically determining data communication device type and corresponding transmission rate

Abstract: A method and system in a data communications system for automatically determining a data communication device type and a transmission speed associated with the data communication device type. An incoming communication is detected on a transmission line, and transmit and receive hardware are connected to the transmission line. Next, a sequence of different signals in either a first communication protocol or a second communication protocol are transmitted from a first data communication device via a transmission line. The transmission line is then monitored for a response signal from a second data communication device. The response signal is initiated from the second data communication device in response to receipt of a particular signal within the transmitted sequence of different signals. Utilizing the relationship between the response signal and the transmitted sequence of different signals, a data communication device type and transmission speed are determined, and data communications may then be established between the first data communication device and the second data communication device at an optimal transmission speed.

Subscriber distribution networks using compressed digital video

Abstract: Emerging standards for highly compressed digital video create interesting possibilities for providing broadcast and switched video services over fiber in the subscriber loop. Experiments are reported which simulate transmission of 200-400 compressed digital video signals using conventional Fabry-Perot lasers and p-i-n diode lightwave receivers. In addition to featuring a robust, low-cost transmission system, compressed digital video networks can offer significant additional advantages, including provisioning of broadcast and switched-video services on a single optical carrier, offering remote service provisioning, and use of video line concentration to significantly reduce the number of switched-video access lines required on each fiber-loop. >

Computer system having different communications facilities and data transfer processes between different computers

Abstract: A computer system is disclosed in which different type of communication links are provided between different computers. A high speed data communication link between a personal computer (PC) and a midrange computer is disclosed. An application is run on the midrange computer, and simultaneously a different but related application is run on the PC. Then, the PC initiates a write command to write data from the PC to the midrange computer without prior direction from the midrange computer to initiate the write command. Next, the data is written into a buffer pool memory based on memory resident indicators whereby no channel program is required. This expedites the data transfer. The midrange computer application subsequently reads the data from the buffer pool memory. A master/slave relationship is also provided between the midrange computer and another computer or external device for more controlled data communications.

Method for handling of a call coming to a terminal equipment in a digital transmission system, and a mobile telephone

Abstract: A method for handling a call coming via a digital transmission system in terminal equipment suitable for speech and data service, the transmission system including at least one connection element which is a speech transmission connection when the call is in speech service mode and which is a data transmission connection rate-adapted in compliance with the CCITT recommendation V.110 or in a like manner and preferably attached to V.24 interfaces when the call is in data service mode. The terminal equipment starts the connection in speech service mode and automatically changes over to data service mode and initiates a procedure for changing the at least one connection element to a data transmission connection upon receipt, in speech mode, of a predetermined audio signal from the connection. The method can make use of a mobile telephone.