Showing papers on "Data transmission published in 1988"

Performance models of statistical multiplexing in packet video communications

Abstract: Models and results are presented that assess the performance of statistical multiplexing of independent video sources. Presented results indicate that the probability of buffering (or delaying) video data beyond an acceptable limit drops dramatically as the number of multiplexed sources increases beyond one. This demonstrates that statistical or asynchronous time-division multiplexing (TDM) can efficiently absorb temporal variations of the bit rate of individual sources without the significant variations in reception quality exhibited by multimode videocoders for synchronous TDM or circuit-switched transmission. Two source models are presented. The first model is an autoregressive continuous-state, discrete-time Markov process, which was used to generate source data in simulation experiments. The second model is a discrete-state, continuous-time Markov process that was used in deriving a fluid-flow queuing analysis. The presented study shows that both models generated consistent numerical results in terms of queuing performance. >

Digital filter and square timing recovery

Abstract: The digital realization of timing recovery circuits for digital data transmission is considered. A digital algorithm is proposed that can be implemented very efficiently even at high data rates. The resulting timing jitter has been computed and verified by simulations. In contrast to other known algorithms, the one presented here allows free-running sampling oscillators and a novel planar filtering method that prevents synchronization hangups. >

Method and apparatus for routing communications among computer networks

Abstract: An improved method and apparatus for routing data transmissions among computer networks. The computer networks are interconnected with a series of gateway circuits. Each gateway identifies all destination computers to which it is connected and identifies the path or paths to each destination computer. For each identified path, the gateway stores the topological delay time for a transmission, the path bandwidth for the narrowest bandwidth segment of a path and a number corresponding to the reliability of the path. When a transmission is received, the gateway examines the various paths in accordance with a predetermined algorithm which also considers the channel occupancy of each path to determine a best path for transmision. The data transmission is then directed over the best path. If more than one path exists, the data may be directed in multiplex fashion over two or more paths with the amount of data on each path being related to the quality of the path. The routing information to destination networks is broadcast periodically by each gateway circuit to its neighboring gateway circuits.

Digital signal encoding and decoding apparatus

Abstract: Digital data is conveyed along with the analog signal by selectively quantizing the analog signal in response to the level of each of the digital bits to be sent. By determining which quantization function was used, a decoder may recover the embedded digital data.

Multi-channel trellis encoder/decoder

Abstract: A multi-channel trellis encoder/decoder is disclosed for use with multi-channel data transmission systems. For each data transmission symbol interval, trellis encoding is applied across all available channels, and for each data reception symbol interval trellis decoding is applied across all available channels. In comparision with systems employing independent trellis encoding along each available channel, the present invention reduces data throughput delays by roughly an order of magnitude, and reduces implementation complexity by roughly a factor equal to the number of transmission channels. Further, the multi-channel trellis encoder will permit different data transmission rates as well as permitting variations in signal power and/or noise power from channel to channel.

Improved importance sampling technique for efficient simulation of digital communication systems

Abstract: An improved importance sampling technique for the efficient simulation of digital communication systems is proposed. Evaluation of low-probability error events by direct use of classical Monte Carlo (MC) simulation techniques usually involves a very large number of runs. Importance-sampling techniques make the low-probability events occur more frequently. The technique proposed here is based on optimized translations of the original probability densities. The only approximation needed in the optimizations is that of replacing the Q function by the simpler exponential expression. Detailed analytical evaluations of the estimation variances of the classical MC and the conventional and improved importance-sampling approaches for systems with memories and signals are presented and compared, showing the superior performance of the latter. Detailed numerical and simulation results are given. >

Alternating sequential half duplex communication system

Abstract: A message communication system employing one or more centralized communication stations transferring messages through Earth orbit repeater satellites to or from mobile terminals with at least one central communication station having a first transceiver for transmitting a first communication signal to one or more mobile terminals and at least one mobile terminal having a second transceiver for receiving the first communication signal and demodulating it, and for transmitting at a predetermined duty cycle of the second transceiver, a second communication signal to at least one of the central communication stations. The preferred duty cycle over which the second communication signal is transmitted is about fifty percent of the second transceiver duty cycle. The communication system uses Time Division Multiplexed (TDM) communication signals using a number of channels as designated address channels with the remainder being used for data transfer. Information transmitted on the address channels is used by terminals to determine both the presence of a message and its corresponding data transmission or reception channel. In addition the terminals use the reception of the first communication signal to adjust return link transmission frequency to compensate for transmission path errors. The alternating duty cycle allows mobile terminals to use a single set of local oscillators for both transmission and reception modes of operation. To decrease interference with other systems the present system employs a power dispersal modulation function to achieve the footprint of a video signal for high transfer rate digital communication signals.

Trellis coded modulation for transmission over fading mobile satellite channel

Abstract: The combination of trellis coding and MPSK signaling with asymmetry (nonuniform spacing) to the signal set is disclosed with regard to its suitability for a fading mobile satellite communication channel. For MPSK signaling, introducing nonuniformity in the phase spacing between signal points provides an improvement in performance over that achievable with trellis codes symmetric MPSK signaling, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Block interleaving may be used to reduce error and pilot tone(s) may be used for improving the error correction performance of the trellis decoder in the presence of channel fading.

Secondary channel for digital modems using spread spectrum subliminal induced modulation

Abstract: A system and method are provided for use of a secondary channel in high speed (greater than 2400 bits per second) wire line modems to provide low speed (around 110 bits per second) non-interfering communications for control or monitoring functions. The secondary channel is used to monitor, configure and test the modems in the network using commands sent over the secondary channel. Secondary channels are also used in low duty cycle applications such as in alarms or teletype data transmission. The invention provides a spread spectrum secondary channel which occupies the same bandwidth as the primary data channel and is immune to jamming tones that would interfere with conventional frequency shift keying secondary channels. The spectrum spreading is achieved through use of the primary channel's trellis encoder. Phase shifts of 0°, 90°, 180° or 270° are induced depending upon the trellis state. This rotation simplifies decoding which as a result can be done in the reference system of the decoded primary trellis signals instead of the baseband equalizer reference system. The primary trellis decoder automatically resolves the 90° references. There is no penalty in terms of additional circuitry or software because the transmitter spreading eliminates the need for additional rotation in the receiver which is required for non-spread signals.

Analysis and compensation of nonlinearities in digital transmission systems

Abstract: The compensation of channel nonlinearities in digital radio communication systems is considered. A discrete system with memory, inserted between the source and the modulator, is designed with the aim of providing an equivalent channel with a distortionless linear part and no nonlinearities up to a given order. This design is based on a Volterra series model of the channel and on the theory of pth-order inverse systems. Since the compensator design is based on a mathematical model of the channel, the problem of model identification is considered. A modeling technique is described that uses computer simulation and orthogonal Volterra series. Several examples show the performance of this class of compensators. >

Multiplex transmission system

Abstract: In a multiplex transmission system wherein data is transmitted among a plurality of control units connected to a multiplex transmission line in decentralized fashion, communication is performed upon changing the period of the data transmission among the control units and the method of transmission, such as the order of priority of transmission, in dependence upon the travelling state of the vehicle equipped with the multiplex transmission system, the operating states of the control units or the control unit which is a party to the communication.

Adaptive modem for varying communication channel

Abstract: An improved modem system for HF data transmission over a varying communication channel transmits data in packets formatted into successive frames, each having two identical training sequences following a sequence of data. Each training sequence has a time length longer than the expected time length of the multipath dispersion in the communication channel, in order to isolate one training sequence in each frame from multipath interference from the preceding data sequence. The "clean" training sequence allows the receiving modem system to derive very accurate channel estimates for each frame by autocorrelation to the known symbol sequence stored at the receiver. By interpolating across the channel estimates for the current and previous frames, the modem system can track the communication channel by interpolated estimates for any part or any point in time of the data sequence. An improved data recovery algorithm divides the received data sequence in each frame into a series of data blocks, each of which is processed through a respective decision loop using the interpolated channel estimates corresponding to the time position of the data block in the data sequence. The interpolated channel estimate for each data block is used to set the tap values for the filter functions of the corresponding decision loop.

Data transmission in active picture period

Abstract: A method and apparatus for transmitting extended aspect ratio pictures is described. The transmitted pictures can be viewed on an extended aspect ratio high definition screen but can also be viewed on a reduced number of lines on a conventional receiver. The lines not used in the picture viewed on the conventional receiver contain non-visible data relating to picture information. The transmitter comprises a high definition television (HDTV) camera (42) providing a high definition video signal to a standards down-convertor (44). This has a video output with a reduced number of lines coupled to a frame store (46) and a data output connected to a buffer (48). Means (54) combines the data from the buffer (48) with the video signal from the frame store (46). A controller (50) responsive to synchronising information ensures that the data is combined with blank portions of the video signal. The combined signal is then fed to transmitter (53). At an HDTV receiver the front end circuitry (54) receives the video signal. A switch (56) under the control of a data/video detector (58) selects between sending video information to a frame store (60) and sending data to a standards up-convertor (64). The data is used to enhance picture information from the frame store (64), the resultant picture being displayed on an HDTV display.

G.722: a new CCITT coding standard for digital transmission of wideband audio signals

Abstract: CCITT Study Group XVIII recognized the need for a new international coding standard on high-quality audio to allow interconnection of diverse switching, transmission, and terminal equipment and organized an expert group in 1983 to recommend an appropriate coding technique. A tutorial discussion is provided of the adaptive differential PCM (pulse-code modulation) coding method recommended by the group. The discussion covers the subjective performance tests performed, mode initialization and mode switching, data-speed multiplexing, and communication between narrowband and wideband terminals. >

Digital adaptive receiver employing maximum-likelihood sequence estimation with neural networks

Abstract: A maximum-likelihood sequence estimator receiver includes a matched filter (56) connected to a digital transmission channel (58) and a sampler (60) for providing sampled signals output by the matched filter (56). The sampled signals are input to an analog neural network (68) to provide high-speed outputs representative of the transmission channel signals. The neural network outputs (70) are also provided as inputs to a coefficient esitmator (78) which produces coefficients for feedback to the matched filter (56). For time-varying transmission channel characteristics, the coefficient estimator (78) provides a second coefficient output which is utilized for changing the interconnection strenghts of the neural network connection matrix to offset the varying transmission channel characteristics.

Interconnection network for multiple processors

Abstract: A large number (e.g., 20 or more) independent processors are connected by a network that provides high data throughput (e.g., 64 megabits/second). The network has redundant data, arbitration, and status/control buses. The buses extend across a plurality of microstripline backplanes connected together by impedance-matched twisted-pair cables. Data is transmitted in packets, along with status signals that provide error detection information.

High-speed data transmission on an optical fiber using a byte-wide WDM system

Abstract: The advantages and problems of using wavelength division multiplexing (WDM) to transmit byte-wide data in parallel through a single-mode optical fiber are studied. The principle problem which is particular to byte-wide transmission is shown to be bit skew caused by group delays of the different transmission wavelengths. The aggregate bit rate of the byte-wide link is shown to be equal to the aggregate bit rate of the serial link for all byte sizes. >

Encyclopedia of telecommunications

Abstract: R.W. Stubblefield, Packet Switching. S.V. Ahamed, Intelligent Networks. E.J. Sullivan, Acoustic Signal Processing. R.W.P. King, Antennas. W.V.T. Rusch, Antennas, Reflector. Simon Haykin, Communication Systems, Civilian. B.P. Lientz, Computer Networks. P.S. Kreager, Data Communications Networks. J.S. Sobolewski, Data Transmission Media. L.R. Rabiner and J.L. Flanagan, Digital Speech Processing. U.S. Berger, Microwave Communications. H.M. Gibbs, U.J. Gibson, N. Peyghambarian, D. Sarid, C.T. Seaton, G.I. Stegeman, and M. Warren, Optical Circuitry. B.K. Tariyal and A.H. Cherin, Optical Fiber Communications. H.V. Hitney, J.H. Richter, R.A. Pappert, K.D. Anderson, and G.B. Baumgartner, Jr., Radio Propagation. W.J. Weisz, Radio Spectrum Utilization. S.J. Campanella, Satellite Communications. W.K. Jenkins, Signal Processing, Analog. F.J. Taylor, Signal Processing, Digital. R. Yarlagadda and J.E. Hershey, Signal Processing, General. N. Farvardin, Source Coding, Theory and Applications. F.F. Taylor, Telecommunication Switching. H.S. Dordick, Telecommunications. L. Schenker, Telephone Signaling Systems, Touch-Tone. P.K. Weimer, Television Image Sensors. A.F. Alber, Videotex and Teletext. S.B. Weinstein, Voiceband Data Communications. R. Ziemer, Modulation. R. Ziemer, Multiplexing. Index.

Apparatus and method for control of one computer system by another computer system

Abstract: Apparatus and method whereby a first digital computer system may be controlled by a second digital computer system. The two digital computer systems are connected by data transfer apparatus. A program in the second digital computer system constructs a call protocol specifying a routine to be called in the first digital computer system. The data transfer apparatus transfers the call protocol to the first digital computer system, and a program in the first digital computer system performs the call. Also disclosed are a return protocol which may be employed to return data from the called routine to the second computer system, call protocols containing arguments, the use of call and return protocols to call system and user routines, and preferred forms of the call and return protocols.

Facsimile machine having a transmission speed selective shiftdown function

Abstract: A facsimile machine includes a data transmission speed shift down function according to which the data transmission speed is shifted down from its initial speed to one of a plurality of new speeds based on a ratio between the total number of data frames initially transmitted to a receiver and the number of data frames requested for retransmission by the receiver. In this manner, an optimal new data transmission speed may be accurately and expeditiously determined. A parameter memory containing information regarding destination areas to which an error correction mode of operation is to be used may be preferably provided in a facsimile machine having both of an error correction mode (ECM) and a normal mode. With this structure, the ECM mode can be automatically set. In such a facsimile machine having both an ECM and a normal transmission modes, a common buffer memory is provided for temporarily storing coded image information either in the ECM or normal transmission mode.

Multiplexed address control in a tdm communication system

Abstract: A message communication system employing one or more centralized communication stations (22) transmitting messages through Earth orbit relay satellites (20) to mobile receivers (10) utilizing Time Division Multiplexed (TDM) communication signals having signal time frames divided into a series of transmission channels. A predetermined number of the channels are designated as address channels with the remainder being used for data transfer. Information transmitted on the address channels is used by receivers to determine both the presence of a message and its corresponding data transmission channel. Each system receiver (70) scans, and tracks only the communication signal address channels until a message addressed to that receiver is detected, at which time the selected receiver changes channels to the designated data channel for reception of the message. Thus, demodulation of the entire communication signal is not required and processing time and power is reduced for the typical waiting condition when messages are not being received. While a message is being received only a portion of the communication signal need be received, demodulated and decoded. The decoded message is then displayed on a display screen (88) or similar device for the recipient.

Data transmission system.

Abstract: A device is placed intermediate a data transmitter, such as a facsimile machine and the public switched telephone network, and selectively processes the calls in a predetermined manner. The signals sent by the transmitter are monitored by the process intermediary and when a particular type of signal is identified, the device processes this signal in a different manner. For example, a particular type of signal could be a long distance signal whereupon the device stores the long distance number, supplies a current back to the transmitting device indicating that the connection has not yet been made, and then completes a call to a data transmission network with the process intermediary then connecting the data transmission network with the transmitting device after the device has transmitted the long distance number to the data transmission system. The transmitting device believes the data transmission system is the identified receiver and the data transmission system will transmit the required protocol signals to the transmitting device whereafter the signals then are transmitted in the normal manner. The data transmission system will then transmit this signal through the data transmission system to a regional location and then retransmit the data over telephone lines to the receiver. The present invention also relates to the combination which includes modified transmitters, receivers, the public switched telephone network and the data transmission system which cooperate to transmit the data from the transmitter to the receiver in a more efficient manner as well as the process by which this combination transmits the information. A modified data receiver is taught which is actuated by means of a non-telephone communication link and the receiver does not require a dedicated line. The modification can be in the form of a process intermediary for use with existing receivers.

New directions in subband coding

Abstract: Two very different subband coders are described. The first is a modified dynamic bit-allocation-subband coder (D-SBC) designed for variable rate coding situations and easily adaptable to noisy channel environments. It can operate at rates as low as 12 kb/s and still give good quality speech. The second coder is a 16-kb/s waveform coder, based on a combination of subband coding and vector quantization (VQ-SBC). The key feature of this coder is its short coding delay, which makes it suitable for real-time communication networks. The speech quality of both coders has been enhanced by adaptive postfiltering. The coders have been implemented on a single AT&T DSP32 signal processor. >

Data transmission/reception apparatus

Abstract: A data communication apparatus includes a data communication section for preforming data communication according to full duplex communication, a testing section for performing a communication test prior to the data communication, and a transmission controller for determining whether full duplex communication can be performed during a period of the communication test performed by the testing section. The testing section includes a backward signal generator, a backward signal detector, and a control signal analyzer. The backward signal generator and the backward signal detector may be replaced with an echo canceller.

Information transmission system having collective data transmission and collection devices

Abstract: An information transmission system having a plurality of communication control units connected to one another through an information transmission path in a communication network comprises devices for collectively transmitting and collecting broadcasting information to and from selected plural communication control units by sending one information message.

Data transmission apparatus having cascaded data processing modules for daisy chain data transfer

Abstract: In a data transmission apparatus, a plurality of data processing modules are used and required sequence setting is performed to a port sequencer of input/output ports of each data processing module, and the daisy chain transfer of the selective data transfer, the load distribution data transfer, the collective data transfer is combined between the data processing modules, thereby the data transmission is performed efficiently at high speed.

VAMAS Surface chemical analysis standard data transfer format with skeleton decoding programs

Abstract: In surface analysis today many commercial instruments are operated through a computer. This computer is also used for processing the captured data, using routines from a built-in set of options for peak synthesis, peak deconvolution, background subtraction, peak area measurement, quantification in various levels of sophistication, mapping, depth profile presentation, smoothing, differentiation and a host of other functions. However, many analysts wish to process their data on another computer in their own particular way using programs written to their specification and under their full control. They need to encode the data in the data-capture computer into a form suitable for transmission then decode it into the form required in the receiving computer. A standard format for the transferred data would clearly lead to economies in the number of programs required to effect the encoding and decoding. To meet the above requirement, as a result of a series of iterative discussions over the last three years, first within the UKESCA Users Group and then with the VAMAS National Representatives and users and manufacturers within the VAMAS Community as well as the ASTM Committee E-42.11, we have produced a Surface Chemical Analysis Standard Data Transfer Format defined in a standard metalanguage. This Format is intended to be used by those wishing to transfer data from computer to computer via parallel interfaces or via serial interfaces over direct wire, telephone line, local area network or other communications link. It is suitable for AES, EDX, FABMS, ISS, SIMS, SNMS, UPS, XPS, XRF and similar analytical methods. It covers elemental maps, depth profiles and sequences of data resulting from a variety of experiments. Thus the application of the Format is very general.

Guide wire communication system and method

Abstract: A guidance system for guiding a plurality of unmanned vehicles along guide wires. A plurality of data communication circuits are provided which form an extensive network. A traffic control computer composes a coded vehicle instruction for assigning tasks and allocates resources to said unmanned vehicles. The traffic control computer polls the status of each vehicle at varying time intervals and receives a response from said vehicle. The network connecting the computer and the communication circuits prevents reception of data transmissions from more than one vehicle at a time. Other messages are temporarily, stored. Data transmitters generate low frequency, low power signals which have a high data transmission rate. Digital data is converted at the transmitters into cosine waveforms of selected frequencies. The cosine waveforms are transposed into sine waveforms at receivers. Low impedance or high impedance characteristics are imposed upon the guide wires. A low frequency, high gain transmit antenna for each vehicle is prorated.

Adaptable multiple port data buffer

Abstract: A data buffer includes parallel and serial data ports connected to one or more equipment modules that produce output data or respond to input commands. The data buffer also includes a serial control port communicating with a host computer. The data buffer receives and stores output data from the equipment modules via the data ports. The buffer configures each data port to match the data transfer protocol (baud rate, parity checking etc.) of the equipment module to which it is connected in response to input commands transmitted from the host computer via the control port. The host computer may also command the buffer to immediately route incoming data on one data port outward on one or more other selected data or control ports or to store incoming data for later transmission via a selected port in response to an input command. The host computer may additionally command the buffer to periodically transmit a stored data string outward on one or more designated data ports. The data buffer also includes a real time clock producing data indicating current time and date. When the data buffer detects a state change in an input bit at a parallel port, it generates an indicating message including the bit state along with the current time and date and forwards the message to the host computer.

Data transfer unit for small computer system with simultaneous transfer to two memories and error detection and rewrite to substitute address

Abstract: A data transfer unit for a small computer system which has a host computer and main and auxiliary storage units, transfers data between the host computer, and the main and auxiliary storage units. The data transfer unit transfers the data, which is outputted from the host computer, from the data buffer to both the main and auxiliary storage units simultaneously, in an operation mode in which data is transferred from the host computer to the storage units. When an error occurs in the main or the auxiliary storage unit, the data transfer unit transfers the correct data from the other storage unit which is operating normally, to a substitute address in the storage unit in which the error has occured.