Showing papers on "Communication channel published in 1976"

Channel Domination and Countervailing Power in Distributive Channels

Abstract: Three hypotheses are discussed: that the power of a channel leader is a result of his control over some power sources, and of dependency of other channel members upon him, and that such power can b...

Cellular radiotelephone system structured for flexible use of different cell sizes

Abstract: The use of plural cell sizes in cellular high capacity mobile telecommunications systems is facilitated by providing dual service availability in an essentially geographically continuous large-cell grid and an overlaid and essentially geographically discontinuous small-cell grid When using certain frequency channel set assignment plans, large-cell antenna sites employ their ordinary channel set assignments whether or not a small-cell antenna site is also present When a large-cell site is operated in the vicinity of a co-channel small-cell site, the respective channels of the large-cell site are operated in a large-cell mode or a small-cell mode as required to cooperate with the overlaid small-cell site When using frequency channel set assignment plans requiring departures from ordinary large-cell channel assignments, the departures are similarly effected on the large-cell site channels that are operated in the small-cell mode Also shown is an arrangement for channel-sharing around the faces of a directional antenna site to reduce the impact of adjacent channel interference

Coding for a multiple-access channel

Abstract: In this paper, coding for a multiple-access discrete memoryless channel is investigated. Block codes which are uniquely decodable and capable of correcting errors are constructed.

Convolutional Code Performance in the Rician Fading Channel

Abstract: The performance of short constraint length convolutional codes in conjunction with binary phase-shift keyed (BPSK) modulation and Viterbi maximum likelihood decoding on the classical Rician fading channel is examined in detail. Primary interest is in the bit error probability performance as a function of E_{b}/N_{0} parameterized by the fading channel parameters. Fairly general upper bounds on bit error probability performance in the presence of fading are obtained and compared with simulation results in the two extremes of zero channel memory and infinite channel memory. The efficacy of simple block interleaving in combating the memory of the channel is thoroughly explored. Results include the effects of fading on tracking loop performance and the subsequent impact on overall coded system performance. The approach is analytical where possible; otherwise resort is made to digital computer simulation.

Sample and hold circuit

Abstract: An electronic circuit suitable to be fabricated in monolithic integrated circuit form for producing at an output terminal an output signal for a predetermined time period of which the value thereof corresponds to the value of a periodically sampled, time varying, input signal applied at an input terminal. The circuit comprises two identical and parallel channels connected between the input and the output terminals such that one channel is in a sample mode while the other channel is in a hold mode and vice versa. Each channel includes a pair of operational amplifiers operatively coupled to an integrating capacitor. The dual channel system provides self compensation for offset voltage and common mode rejection. Thus, no manual nulling adjustment is required. Because self compensation is renewed each sample/hold cycle, the circuit is substantially insensitive to temperature variations over a broad range of temperatures.

Analysis of Digital Errors in Nonlinear PCM Systems

Abstract: The effect of digital errors in linear pulse code modulation (PCM) systems has been considered by several authors for channels with independent errors. In this paper we present a general approach of analyzing digital errors in linear and nonlinear PCM systems with arbitrary channels. The examples given in this paper cover the different standard nonlinear PCM systems and independent channel errors. The technique used for the analysis leads to the conclusion that there are PCM codes less sensitive to digital errors than the standard binary folded PCM code. An example of such a PCM code is given in this paper.

Optical multi-channel digital disc storage system

Abstract: An optical storage system for the simultaneous or random storage of digital information in a plurality of channels, comprising a rotating storage disc which is scanned by a light beam. The digital information of each channel is stored in points along a spiral track comprising interruptions. A concentrical guide track is associated with each channel. The light beam being focussed onto both tracks of each channel for optical addressing. The light beams of all channels are controlled via deflection systems so that, during the interruptions, they are briefly directed onto the guide tracks while following the spiral tracks. From the radial deviation of the moving disc, measured by way of a detector system, control signals are derived by the deflection systems to compensate for undesired radial motions of the spiral-shaped tracks.

DC free encoding for data transmission system

Abstract: A method and apparatus provide for the elimination of any net DC component from the transmission of binary data sequentially in successive clocked bit cells of a transmission channel wherein logical first bit states, e.g., 0's are normally transmitted as signal transitions relatively early in respective bit cells, preferably at cell edge, and logical second bit states, e.g., 1's, are normally transmitted as signal transitions relatively late in respective bit cells, preferably at mid-cell, and any transition relatively early in a bit cell following a transition relatively late in the next preceding bit cell is suppressed. The onset of a sequence of second bit states following a first bit state that might introduce a DC component into the transmitted signal with normal transmission is detected by producing a first indicating signal, and in response to the first indicating signal and the state of a current bit and the state of the next succeeding bit the transmission of signal transitions is modified to eliminate any DC component. Preferably, the end of a sequence of second bit states that would introduce a DC component is detected by producing a second indicating signal utilized to modify the signal transitions at the end of a troublesome sequence, as by suppressing the transition corresponding to the last second bit state in such a sequence.

Cardiac pacing apparatus with electromagnetic interference protection

Abstract: A cardiac pacing apparatus of the type having a first signal processing channel which functions in the demand mode is disclosed including a second signal processing channel for detecting electromagnetic interference and causing the pacing apparatus to revert to a safe operating rate in the presence of such interference. In a preferred embodiment, the second signal processing channel has an enhanced high-frequency response with respect to that of the first signal processing channel in order to optimize interference detection. The second channel may receive an input from either a conventional cardiac sensing and pacing electrode, or else a second electrode, remote from the heart, may be provided for interference detection. When electromagnetic interference is detected by the second signal processing channel, an override of the conventional demand pacer inhibit function occurs and the pacing apparatus is switched to a safe operating rate, which may be either an appropriate predetermined fixed rate or a rate-limited rate synchronous with the detected electromagnetic interference. In an alternate embodiment, the gain of the second signal processing channel is reduced with respect to that of the first channel, and the pacing apparatus is switched to a safe operating rate upon the detection of electromagnetic interference having an amplitude level above that of natural cardiac signals.

Device for carrying observation and/or manipulation instruments

Abstract: The disclosure herein describes a carrier adapted to receive observation and/or manipulation instruments; the carrier consists of a train of articulated segments whose angular displacement is controlled by a series of magnetic clutches; the leading segment is guided from the carrier's proximal end, and the guide angle is repeated automatically at the articulations of all following segments; a central channel in each segment accepts instruments for observation and manipulation. One advantageous application of the present carrier is its use as an endoscope for inspecting a hollow portion in a living body.

Performance of Phase-Locked Loops in the Presence of Fading Communication Channels

Abstract: An approach is presented for the analysis of phase-locked loops whose input signal has passed through time-varying channels. The specific channels considered in detail are the Rice-Nakagami, Rayleigh, and lognormal fading channels. Loop performance is characterized in terms of the steady-state probability density function of the reduced phase error process. The basic parameters which characterize performance include the loop signal-to-noise ratio (SNR) and the variance and bandwidth of the fading components introduced by the channel. Particular channel models are used to illustrate the theory for the firstorder loop. The results are also applied to the analysis of the PSK noisy reference problem in the presence of these time-varying channels.

Digital communications receiver for dual input signal

Abstract: A dual channel receiver system for receiving polarized signals, which system reduces cross-interference between the signal channels by utilizing adaptive filter equalization means responsive to the input received signals and to error control signals for providing a plurality of weighting signals which are used to combine selectively with the input received signals to reduce the errors, including particularly cross-polarization and noise errors therein. The channels each include decision-directed error signal generating means for providing such error control signals. The system also includes means for preventing system failures wherein both received signals fade simultaneously under which conditions data reversal in the channels could occur and wherein one received signal fades under which condition the same data is produced in both channels.

Data processing system including a program-executing secondary system controlling a program-executing primary system

Abstract: Disclosed is a primary data processing system comprised of, for example, a main store, a storage unit, an instruction unit, an execution unit, a console unit and a channel unit for performing primary system programs. The console unit includes a secondary digital computer for performing secondary programs which functions to observe and/or alter the primary system. The functions performable by the secondary system include altering the primary system control state, causing primary commands to be executed, controlling primary data and addresses, and scanning out primary information. The console is connected through a command bus, an address bus and a data bus to the controls and data paths of the channel unit, of the instruction unit and of the storage unit.

Seismic data telemetering system

Abstract: A plurality of data acquisition and transceiver units are connected in series to a central signal processor through a common telemeter link. The telemeter link includes a data channel, an interrogation channel and a control channel. The signal propagation velocity through the control channel may, for example, be greater than the signal propagation velocity through the interrogation channel. The central signal processor sends an interrogation signal through the interrogation channel to the data acquisition units. After a selected delay, a control pulse is transmitted. The delay between transmissions of the two signals is proportional to the differential travel time of the signals in the two channels. Accordingly the signal through the control channel will overtake and intercept the signal propagating through the interrogation channel, at a selected data acquisition unit. When any selected data acquisition unit receives a control signal through the control channel at the same time that it receives an interrogation signal through the interrogation channel, that unit is activated and a desired function is performed. The control signal is a square wave pulse having a width which is adjustable by integral multiples of the differential travel time. By adjusting the width and transmission-time delay of the control pulse, any selected subset of one or more consecutive units may be activated. Each data acquisition unit may have two or more input channels, which are connected in turn through common electronics to the data transmission channel by means of a channel selector or multiplexer. The interrogation signal may exist in one of two or more states. In the first state, in combination with a control pulse, the interrogation signal resets the multiplexer. In the second state, the interrogation signal advances the multiplexer to the next input channel in sequence.

Method for fabricating diffusion self-aligned short channel MOS device

Abstract: A diffusion self-aligned, short channel device may be fabricated by ion implantation of an n-type channel region within a p-type substrate. A p-type dopant is then implanted in and driven through a portion of the n-type channel region to form an impurity region. A diffusion self-aligned n-type channel region is then disposed in the p-type impurity region and in the n-type channel region. The method allows for the simultaneous fabrication of a channel implanted MOSFET as well as a standard MOSFET. The resulting diffusion self-aligned, short channel device is a high gain, high speed small device which can be simply combined and fabricated with channel-implanted depletion devices and low body effect devices in an integrated circuit.

An optimization of modulation codes in digital recording

Abstract: A few new modulation codes(or run-length-limited codes) in digital magnetic recording is presented. Linear density limits of the new codes and the existing codes are evaluated for a typical recording channel. One of the new codes shows the highest linear density limit among the existing codes and is improved over, for example, MFM and 4/5-rate-NRZI codes by about 20% to 30% in the density limit for the channel. A method for constructing the new codes is presented.

Method and system for selectively accessing multiplexed data transmission network for monitoring and testing of the network

Abstract: A method and system for accessing data in a time division multiplex communication network at the multiplexed level without disturbing the transmission of the data. A multiplexed data stream containing a predetermined pattern of framing signals and subscriber data from a plurality of subscriber channels is accessed directly by line accessing means located in the transmission path of the data stream. The line accessing means does not disturb the transmission of the multiplexed data stream, i.e., allows the multiplexed data stream to pass through the line accessing means, but provides a monitored data signal having the same data content as the multiplexed data stream, thereby essentially providing undisturbed direct access to the multiplexed data stream. A control signal designating one of the plurality of subscriber channels as the desired subscriber channel is generated, and framing signals in the multiplexed data stream are detected. The detected framing signals and the generated control signal are utilized to locate the designated one of the plurality of subscriber channels in the monitored multiplexed data stream for monitoring, testing or for use of the data contained in the located channel. Specifically, the located one of the plurality of subscriber channels is monitored so its data framing and content can be observed. For testing purposes, various codes such as a loopback code or a multipoint junction code may be inserted in the designated one of the plurality of subscriber channels in the multiplexed data stream without demultiplexing the data stream or otherwise disturbing the transmission of the stream. In this manner, loopbacks at various points in the system can be effected and test codes such as a pseudo-random code may be transmitted through the loopback and monitored for errors.

Fabrication methods for the high capacity ram cell

Abstract: Disclosed is a process for constructing an array of memory cells. Each cell is constructed to have a high storage capacity and low leakage current. The cells are formed on a surface of a semiconductor substrate. Each cell has a storage region and an adjacent transfer region. The process forms a deep ion layer and a shallow ion layer in the storage region of each cell. At the storage region-transfer region interface, the deep ion layer lies laterally within the shallow ion layer. In the other portions of the storage region, the deep ion layer extends laterally into adjoining channel stops.

Dual action retaining guide for printed circuit card racks

Abstract: A retaining guide for printed circuit cards has the form of a narrow channel member having a bottom wall and vertically-extending side walls. The cards are slidably inserted into this member. The retentive force is exerted upon the cards by the fact that the channel member has a non-linear, undulating configuration as well as a plurality of spaced inwardly-extending contact surfaces of the side walls thereof.

Digital synchronizing signal recovery circuits for a data receiver

Abstract: A data signal stream includes, in a noisy signal channel, periodic word synchronization characters, and each such stream is preceded by a burst of predetermined bit rate information. An approximate bit rate timing signal is derived from the data stream and utilized for producing an initialization pulse when the predetermined bit rate information is detected. In addition, the approximate bit rate timing signal drives a digital phase-locked loop which is preset by the initialization pulse to a digital circuit state defining operation at the nominal frequency of the approximate bit rate timing signal. A stable bit clock signal provided by the phase-locked loop controls the operation of further circuits which are responsive to the baseband data stream for providing an indicator pulse each time that a synchronizing character appears in the data stream. The bit rate clock and the character indicator pulses are employed to operate a timing chain that yields word synchronization pulses in synchronism with the indicator pulses and having an extraordinarily low false-pulse rate as well as evidencing a flywheel effect to maintain word synchronization in the event that a small number of character indicating pulses are missed. If more such pulses are missed, the timing chain is resynchronized.

System for recording and/or reproducing four channel signals on a record disc

Abstract: This system records four channel signals on or reproduces them from a record disc. The four channel signals are combined into sum signals and difference signals, respectively, each composed of two signals. Each difference signal is converted into an angle modulated wave by modulating a carrier from a single oscillator and is multiplexed with each sum signal. The four channel signals picked up from the record disc are reproduced and sounded respectively from four speakers placed at predetermined positions.

Multi-user and wiretap channels including feedback

Abstract: : The concept of the wiretap channel was first proposed by Wyner. He considered the case in which data is to be transmitted reliably over a discrete memoryless main channel to a legitimate receiver. The wiretapper views the output of the main channel through another discrete memoryless channel. It is assumed that the wiretapper knows the code being used and his only handicap is the additional noise in his signal. The problem is to maximize the transmission rate R to the legitimate receiver and the equivocation d of the wiretapper. In this dissertation, the additive white Gaussian noise wiretap channel is introduced and the set of all achievable (R,d) pairs is determined explicitly through the use of certain special properties of the Gaussian channel. Some useful characterizations of a special class of wiretap channels are also explored. A model of the wiretap channel with feedback is proposed. It turns out that with the introduction of feedback, even when the main channel is inferior to the wiretapper's channel, it is still possible to reliably communicate with the legitimate receiver in complete secrecy. The binary erasure wiretap channel with feedback is examined and inner and outer bounds on the achievable (R,d) region are given. Finally, a scheme for enlarging the capacity region of multiple-access channels using feedback is analyzed. It is shown that conditions under which an enlargement is possible are fairly weak, indicating that feedback can almost increase the capacity region. (Author)

Performance of Multilevel Baseband Digital Systems in a Nonlinear Environment

Abstract: A good deal of effort has been spent, in the past few years, to devise numerical algorithms for evaluating the performance of digital communication systems over noisy linear channels, i.e., in the presence of intersymbol interference and noise. In this concise paper we present a method for computing the error probability of multilevel baseband digital modulation systems when the channel is nonlinear with memory. The algorithm is based on a Volterra series expansion of the nonlinearity; with this model, we show that the moments of the disturbance can be computed recursively, and the same techniques in use for linear channels can be applied for evaluating the error probability. This approach can be generalized to consider noise entering the nonlinear channel. The computing algorithms are described in detail, and a complete example is worked out.

Computer modeling of erodible flood channels and deltas

Abstract: The existing computer program for water-surface computation and delineation of the flood limit has been extended to include the effect of channel deformation during a flood. In the new program, the unsteady flow is approximated by successive temporal steady conditions; the change in channel boundary is corrected at each time step. This computer program has been applied to obtain the progressive changes of the channel boundary and water-surface profile during a flood as a result of erosion and sedimentation. By imposing an additional condition for the delta, another computer program has also been developed to compute the progressive growth of the delta of the river mouth and the variation of the delta stream pattern. /ASCE/

Installations for washing a polluted gas

Abstract: The installation comprises at least one trickling channel oriented vertically and whose cross-section diminishes from above to below. A transverse wall is arranged below the lower end of this trickling channel. The invention is applicable to the air coming from painting cabins.

Solar heating system

Abstract: A solar heating system for a building consists of a stressed-skin roof structure which includes at least one layer formed of longitudinally extended channel-shaped beam members, wherein each beam member is generally U-shaped in cross-section and positioned with its open channel directed outwardly of the building. These beam members are placed side by side with their central bight portions lying in substantially the same plane. The open outwardly facing channels of the beams are closed to form a closed channel or air space which is heated from the sun. A heat storage bed is associated with the building and means are provided for selectively circulating air from the closed channels in the layer of beams to heat the storage bed and to return the air from the storage bed to the closed channel. The heat stored in the storage bed is selectively distributed to the interior of the building through a separate air circulating circuit.