Showing papers on "Communication channel published in 1974"

Power in a Channel of Distribution: Sources and Consequences:

Abstract: This article empirically assesses the relationship between power and the sources of power in a channel of distribution that has a well-defined power source: the franchisor-franchisee channel. In ad...

The Capacity Region of a Channel with Two Senders and Two Receivers

Abstract: A characterization of the capacity region of a two-way channel is given for the communication situation, in which both senders send independent messages simultaneously to both receivers and all senders and receivers are at different terminals.

On the development of dunes in erodible channels

Abstract: A two-dimensional stability analysis of the flow in a straight alluvial channel has been carried out, using the vorticity transport equation. In the analysis an attempt has been made to account for the influence of gravity on bed-load transport, and this turned out to change the stability quite significantly.In the case of instability, the further growth of the dunes has been investigated using a second-order approximation, This nonlinear theory explains the experimental fact that the dunes very soon become asymmetric.

Multiple zone communications system and method

Abstract: A method and system for more efficiently utilizing presently available and prospectively available two-way communication channels for communication between mobile telephones and either fixed telephones or mobile telephones. A large mobile telephone service area is divided into a plurality of smaller zones, and channels are assigned to the zones in a manner which permits the reuse of channels in zones on a non-interfering basis. A control signal is broadcast over a designated one of the channels assigned to each zone by equipment at a fixed station in each zone under the control of a central control unit. Each mobile telephone monitors one of the designated control channels in accordance with the signal reception characteristics thereof. When a call is placed over the designated control channel, a service or talking channel is assigned to serve the call and the mobile unit is remotely tuned to the assigned talking channel. Provision is made for using the designated control channel as a talking channel if necessary, for assigning additional channels to a fixed station on the basis of user density, and for maintaining communications between two parties as a mobile unit moves from one zone to another. A novel mobile telephone unit operable in accordance with the techniques of the present invention and providing simplified call placement and control is also disclosed.

The probability of vessel collisions

Abstract: This article discusses the problem of safe navigation of the English Channel and the North Sea, particularly in the case of very large cargo ships. A fundamental aim of the discussion is to assess the probability of encounters/collisions between large ships and offshore structures in the North Sea. First the English Channel, and then the North Sea are examined, with both collision and grounding probabilities considered. The methods of probability analysis are described, and the results are included.

Nonlinear Long Waves in a Channel of Variable Section

Abstract: The Kakutani equation is extended to include the effect of the variable width of channel, which is important in such a practical problem as refraction.Assuming that the wave profile is that of cnoidal waves and that this profile is maintained throughout the travel, a law of shoaling is derived.A comparison with experimental data shows that the present theory describes very well the shoaling for gHT2/d2>30, while for gHT2/d2<30 the theory of linear surface waves gives good agreement.For 30< gHT2/d2<50, is Hd2/7=const. and for 50< gHT2/d2, it is Hd3/2[≠ gHT2-2≠3]=const. in case of variable depth only.Due to the lack of experimental data, the theoretical result for variable width could not be examined for the present.

Adaptive Equalization of the Slow Fading Channel

Abstract: This paper considers equalization of the slow fading channel for a serial data transmission application. Linear and decision-feedback adaptive equalization techniques are contrasted. The error propagation effect in decision-feedback equalizers is analyzed by a Markov process model. The error probability magnification is computed for both fixed and fading channels and for both binary and quaternary phase-shift-keying (PSK) transmission. The results show that the error propagation effect is small and in regions of practical error probabilities the decision-feedback equalizer is superior to its linear counterpart. Parameters of a practical decisionfeedback equalizer are estimated and a performance evaluation is performed. The implicit diversity gain is shown to be significant and the intersymbol interference penalty is found to be less than 1 dB. Because the intersymbol interference penalty is small, more complex nonlinear processors such as the Viterbi algorithm cannot be recommended for this application. Time jitter effects for the equalizer are included in a calculation of average error probability.

Optimum Run Length Codes

Abstract: To realize the full redundancy reducing potential of run length coding over a collection of picture segments with varying run length statistics, adaptive coding techniques have been proposed. This paper compares results for a previously proposed A -code, for which the block length was varied adaptively, with those obtained using a fixed block length B -code first proposed here. Both codes use variable length codewords integrally related to the code block length. For all pictures analyzed, the fixed block length B -code performed nearly as well as the adaptive A -code. For both, the bit rates were close to the entropy bound. The reasons for these results are discussed. It is Shown that, due to the prevalence of exceptionally long runs, the A -code, which is nearly optimal for exponentially distributed run lengths, performs poorly for actual pictures unless the block length is varied adaptively. The strategy used to implement the A-code adaptively is described. The optimal block length of the B-code,on the other hand, is shown to be largely independent of the picture statistics and need therefore not be varied adaptively. The hardware implementation of both coding techniques, the influence of channel disturbances on image quality, and the problems of error correction and line synchronization are discussed.

Predicting coherent sidelobe canceller

Abstract: A system for instrumenting time sampled predicting interference suppression, particularly in a side-lobe canceller system. Main and auxiliary channel signals are supplied to a canceller loop where correlating weights are sampled just prior to a radar pulse transmission on command of a radar pretrigger pulse. A sampling circuit stores both current and past weights and combines the current weight with the integral of the difference between the current and past weight to form predicting weights over each pulse repetition period. The predicting weights are used to form a translating signal for operating on the auxiliary channel interference signal so that it will cancel the interference in the main channel. By sampling just prior to radar pulse transmission and forming the predicting weights, cross modulation of clutter and antenna scan error can be reduced in order that a side-lobe canceller may be used compatibly with Moving Target Indicators.

Error Performance for Adaptive Transmission on Fading Channels

Abstract: A communication system is analyzed in which the transmission power and/or rate are adjusted to the observed state (attenuation) of a slowly fading channel. The optimum control of power and rate with channel attenuation is determined. Some suboptimum control rules are also investigated. The average probability of error is evaluated for various types of adaptive transmission, imposing different constraints on power, rate, and bandwidth. It is shown that rate control is superior to power control and that simultaneous power and rate control further improves the performance. The most effective power and rate control presupposes a high peakpower-average-power ratio and a high peak-rate-peak-rate-average-rate ratio; with no peak power and bandwidth limitation, arbitrary small error probability is attainable for a given power and average rate.

Blood leak detector

Abstract: A blood leak detector for use with artificial kidney machines. A transparent conduit through which dialysate circulates extends through a block. The block contains a lamp whose light passes through a first channel in the block transversely intersecting the conduit and a second channel in the block at an angle to the first channel and about the same length, avoiding the conduit. Identical 550-560 nm filters and photovoltaic cells are provided at the ends of the channels. The channels provide relatively wide dispersion angles. Circuitry is provided to measure the differential response of the photovoltaic cells and express this in terms of a voltage. An excessive difference between this voltage and a reference voltage will operate an alarm or emergency device. An adjustable light-obstructing screw is provided in the second channel for purposes of calibration.

Modification of routed streamflow by channel loss and base flow

Abstract: The convolution integral is used to compute continuous variations in channel loss and base flow that result from a reservoir release on the North Canadian River in central Oklahoma. The open channel flow hydrograph is routed by using the unit response method and then modified for interaction with the aquifer. Stream losses and gains are evaluated from the arbitrary fluctuations in stream stage by using average values of aquifer parameters. In spite of gross simplification pertaining to the nature of the groundwater system, good agreement with the actual flow hydrograph is obtained.

Channel switching device for mobile radio communication equipment

Abstract: A channel switching device for use in a mobile radio communication system is disclosed. The device is intended for use in systems wherein the service area is divided into a plurality of zones each having a fixed base station and each accommodating a plurality of mobile stations. The base stations have a plurality of frequency-divided communication channels exclusively assigned to them. The mobile stations are provided with a detector and a switching circuit which are responsive to the received signal to controllably switch between channels. When the received signal exceeds a predetermined threshold, only the channels assigned to the zone in which the mobile station is located are selectively switched or scanned. On the other hand, when the received signal falls below the threshold, all the channels in the service area are scanned.

Automatic data acquisition method and system

Abstract: OF THE DISCLOSURE Continuous type analog data sampled at a high rate automatically is acquired in real time from data acquisition units, established at each of a plurality of spaced source stations. For example in seismic operations the units sense ground motion at spaced detector stations and convert resulting electrical signals to digital representations of such motion. A unique response code is set in each data acquisition unit. From a master station in or adjacent the prospect, data frame pulse sets are transmitted along with a series of channel sync pulses. At each unit digital representations of motion are stored upon receipt of each data frame pulse set. Sync pulses are received and counted at each unit following each data frame pulse set. The count of sync pulses at each said unit is decoded and compared with the respective response codes. In response to coincidence between each decoded count and re-sponse code, the stored signal is transmitted to the master station from each said unit.

Method of information transmission with priority scheme in a time-division multiplex communication system comprising a loop line

Abstract: A closed loop communication system in which the terminals are grouped into priority classes. Any terminal can seize a free channel if certain priority conditions exist. A channel (frame) is always preceded by a header comprising a priority request field and a priority grant field. The request field has n bits assigned to the n priority classes; a terminal requiring service sets that bit to "1" which corresponds to its class. Thus, the controller receives a compiled overall request and inserts, for the next cycle, into the grant field an indication as to which priority class or classes are now allowed access to the channel. This is accomplished by shifting the contents of the request field to the grant field. A terminal can only seize the channel if its priority class is allowed for that cycle by the grant field, and if the channel is still free.

Data processor for a loop data communications system

Abstract: A data processor for a time division multiplexed communications system. A plurality of such data processors are connected in series in a loop configuration, each having a data terminal associated therewith, for establishing a connection between data processors in a time division multiplexed channel. Each data processor demodulates the signal on the loop, extracts timing information from the loop signal and locates the channel to be used for establishing the connection between itself and another data processor. Each data processor in addition, regenerates and passes on data not intended for that data processor. Data found in the correct or selected channel is provided to the data terminal which may be a synchronous or an asynchronous device. Data from the terminal is inserted into the selected channel, modulated in accordance with a particular rule and transmitted onto the loop to another data processor operating in the selected channel.

Time division switching system

Abstract: A plurality of 24-channel, 8-bit time division multiplex carrier lines are inserted with coding data in each channels thereof to identify the PCM data being transmitted A first multiplexer unit multiplexes and distributes the PCM data and the address coding data of each channel of a predetermined number of the multiplex lines onto a supermultiplexed highway carrier known as a long digital link Preselected channels of the supermultiplexed highway are used to carry a special channel identification pattern inserted by a channel identification inserter operating within the first multiplexer unit A channel aligner associated with the supermultiplexed highway is used to recognize the special pattern and align all data for being inputted to a time switch which receives a plurality of the supermultiplexed highways The time switch includes a second multiplexer unit and a number of input buffer memory stores for distrubuting and storing the PCM data according to the coding of the channel address data to achieve a lower channel occupancy level per line of the PCM data as PCM information is presented to the input ports of a space switching network on a greater plurality of lines than the supermultiplexed input lines

Channel identification for high speed digital communications

Abstract: A channel identification problem arises in high speed digital communication systems that transmit information over time-dispersive channels such as telephone channels and radio channels. This paper deals with algorithms for performing the channel identification rapidly in conjunction with the signal detection to recover the information. The stability and convergence properties of the algorithms are demonstrated.

Multi-channel data color display apparatus

Abstract: uous monitored data and for driving of a multiple channel display means, with each channel identified by a selected unique color The present invention particularly in one unique aspect uses a conventional commercial television receiver reoriented to present vertical scan lines and appropriate beam controls to generate line display segments in each channel and thereby generate a total display of the monitored data The output of the random access memory means is cyclically and repetitively transmitted in time-spaced relation through a color display control for separating of the signals for display in related display channels and coupling them to a common color driver means In accordance with the present invention, the computer stores the defintion of line segment for each scan line in a storage means and the information is compared with a beam driver control to activate the color driver means accordingly The color driver means is preset to produce a predetermined color presentation in each channel and thereby provide a color-coded presentation The position of each channel can be controlled to produce separate or superimposed graphical displays with the color distinction between the channels The display apparatus may, in accordance with another aspect of this invention, also include means to display alphanumeric data in selected channels In this aspect of the invention, a character memory bank is provided having means to output to a character generator having an internal sequence system to readout the selected character and channel location with an auxiliary decoder to select the color and channel identification The present invention provides a system which can employ the various standard presentation techniques associated with commercial television such as split screen presentation with alphanumeric information The combined computer-display system with a time shared memory provides for programmed version and storage of the monitored information with the necessary versatility in use and processing of the information Thus, the sampling of information is essentially independent of the output processing and display The medical or any other monitored data is sampled at any desired reasonable rate and stored in computer memory which establishes a record of the channel and the display line The computer processing means and the display means are operated through an interlocking control, with the computer establishing the overriding control of the transfer of information to and from memory A horizontal and vertical sync signal generator drives the television display means to cyclically transfer the data from memory into an auxiliary processing system for display The computer, however, may terminate the operation of t

Interference reduction circuit

Abstract: An interference reduction circuit to provide isolation in frequency reuse systems operates on two or more non-isolated signals by cross-coupling the signals such that the interfering signals are cancelled on each channel. In a dual-polarized frequency reuse system, cancellation is effected by adding a sample of an oppositely polarized channel of equal amplitude, but of opposite phase, to the interference. Practical implementation includes closed-loop, digital feedback control to permit dynamic signal-to-interference improvement involving no a priori knowledge of the nature of the incoming signals. The circuit has applications in satellites and earth stations in a communications satellite system.

Optimal Message Block Size for Computer Communications with Error Detection and Retransmission Strategies

Abstract: Error detection and retransmission are used as error control in many computer communication systems. In these systems, random length messages are partitioned into fixed size blocks for ease in data handling and memory management. A mathematical model is developed in this paper to determine the optimal message block size that minimizes the expected waiting time in retransmission and acknowledgment delay and thus maximizes channel efficiency. The model considers two classes of error detection and retransmission strategies: 1) stop-and-wait and 2) continuous transmissions. Using the relationships among acknowledgment time, channel transmission rate, channel error characteristics (random error or burst error), average message length, optimal block size are computed from the model and presented in graphs. The model and the graphs should be useful as a guide in the selection of the optimal fixed message block size for computer communication systems.

Studies in Interactive Communication: III. Effects of Similar and Dissimilar Communication Channels and Two Interchange Options on Team Problem Solving

Abstract: 16 teams of 2 college students each solved four credible “real world” problems for which computer systems have been or could be useful. Each of the 4 problems was solved on four successive days. A team member sent messages either by voice or by typewriter, and every team was tested with all 4 combinations of the 2 message channels assigned to individual team members. Half the teams could interrupt their partners at any time; half could not. Dependent measures were time to solution, number of messages exchanged, total number of words used per team, message length, messages communicated per minute of channel time, and words communicated per minute of channel time. The results show that communication by voice is much more rapid and wordy than is communication by typewriter. Giving Ss the freedom to interrupt had no effect on the time required to solve problems, on the number of words used in the solution of problems, or on the rate at which words were communicated. When Ss had the freedom to interrupt, they ...

Subscription television jamming system

Abstract: A system is disclosed for transmitting television signals which can only be intelligibly received by authorized subscribers. At the transmitter end of the system, a CW jamming signal is inserted in the passband of each subscription television program transmitted to subscriber terminals. At each subscriber terminal, a selected subscription program is frequency converted to a predetermined channel. The predetermined channel is applied, along with a CW signal from oscillator circuits, to first and second signal processors to enable them to respectively extract a jamming signal and a jamming signal error, which are representative of the signal from the jamming oscillator. The jamming signal is utilized by the oscillator circuits to aid in the production of its reference and CW signals. The reference signal is converted by a quadrature phase shifter into first and second quadrature reference signals, which are each applied to a quadrature phase detector and a quadrature modulator. The quadrature phase detector develops first and second quadrature DC control signals as a function of a comparison of the jamming signal error signal with each of the quadrature reference signals. In response to the first and second quadrature DC control signals and its other inputs, the quadrature modulator applies a nulling signal to the second signal processor to cause it to substantially cancel the CW jamming signal from the predetermined channel to enable an authorized subscriber to receive same. The system also includes means which disables the operation of the unscrambling circuits when either a free or an unauthorized pay TV program has been selected.

Automatically presetting channel selecting system

Abstract: A channel selecting system for use in a receiver having a voltage controlled tuning element which has an automatic channel presetting function which utilizes a pulse generator and a binary counter connected to the generator to count the pulses and to generate a binary coded output in accordance with the sum of the pulses. A digital-to-analog converter changes the binary coded output into a linearly increasing tuning sweep voltage which in turn conditions the voltage controlled tuning element to scan the frequency range of the tuner as the tuning voltage increases. As the frequencies are scanned, a detector, connected to the tuning element, senses the presence of a broadcast channel. When a channel is detected, the scan is interrupted and a binary memory is utilized to store the binary coded output which corresponds to the frequency of the detected broadcast channel. A control gate signal generator driven by the detector controls the pulse generator and memory such that the scan is continued until the entire frequency range has been scanned. Channel selection is accomplished by switch means actuatable to address the memory to read out a selected binary code output corresponding to the channel desired which causes the converter to generate a voltage to condition the tuning element to tune to the desired frequency. The voltage control tuning element may comprise several different elements, one for each of a plurality of different frequency ranges. Means are provided for selecting an appropriate tuner such that channels from any of the frequency ranges may be selected.

Isolation-element CCD serial-parallel-serial analog memory

Abstract: A CCD shift register involves a serial input channel and a serial output channel interconnected by a plurality of parallel channels formed in a semiconductor body with separate arrays of multi electrode sets of phase electrodes for receiving alternately isolation element charge packets and information charge packets, overlaying the input, parallel and output channels. A summing gate electrode common to all of the parallel channels is adjacent the output channel. Control means actuates the gate to transfer charge packets from each parallel channel into the output channel and clocks the charge packets to the output. In one aspect, two shift registers are provided with means to inject time samples of an input signal alternately to the two shift registers and to multiplexing the outputs therefrom.

Polyphonic music synthesizer

Abstract: An electronic music synthesizer including a keyboard control system for enabling multiple independent voice channels (voices) to be controlled by the keyboard in a musically pleasing manner. The control system responds to a keyboard of M keys to control N voices where N

Communication networks: Message path delays

Abstract: A communication network is modeled by a weighted graph. The vertices of the graph represent stations with storage capabilities, while the edges of the graph represent communication channels (or other information processing media). Channel capacity weights are assigned to the edges of the network. The network is assumed to operate in a store-and-forward manner, so that when a channel is busy the messages directed into it are stored at the station, where it joins a queue that is governed by a first-come first-served service discipline. Assuming that fixed-length messages arrive at random at the network, following the statistics of a Poisson point process, we solve for the steady-state distributions of the message overall delay time, for the average message waiting times at the individual stations, for the average memory size requirements at the stations, as well as for other statistical characteristics of the message flow along a communication path.

Feedback Communications over Fading Channels

Abstract: A communication system using noiseless feedback for Rayleigh fading channels is proposed. Pilot tone signaling is used to provide channel amplitude and phase information for the detection of antipodal signals. Channel estimates generated in the receiver are fed back to control the transmitter power and rate. Power division and rate control rules are derived, and it is shown that definite performance improvement over diversity systems is obtained. Because of the requirement of small loop propagation delays, the technique is mainly applicable to low data rate multitone modems for short range HF channels.