Showing papers on "Communication channel published in 1984"

Wire-tap channel II

Abstract: Consider the following situation. K data bits are to be encoded into N> K bits and transmitted over a noiseless channel. An intruder can observe a subset of his choice of size μ < N. The encoder is to be designed to maximize the intruder's uncertainty about the data given his μ intercepted channel bits, subject to the condition that the intended receiver can recover the K data bits perfectly from the N channel bits. The optimal trade-offs among the parameters K, N, and μ and the intruder's uncertainty H (H is the "conditional entropy" of the data given the μ intercepted channel bits) were found. In particular, it was shown that for μ = N − K, a system exists with H ≈ K − l. Thus, for example, when N = 2K and μ = K, it is possible to encode the K data bits into 2K channel bits, so that by looking at any K channel bits, the intruder obtains no more than one bit of the data.

The capacity of the white Gaussian multiple access channel with feedback

Abstract: Since the appearance of [10] by Gaarder and Wolf, it has been well known that feedback can enlarge the capacity region of the multiple access channel. In this paper a deterministic feedback code is presented for the two-user Gaussian multiple access channel, which is shown to allow reliable communication at all points inside a region larger than any previously obtained. An outer bound is given which is shown to coincide with the achievable region, thus yielding the capacity region of this channel exactly.

Reliability and Validity of Alternative Measures of Channel Member Satisfaction

Abstract: The authors describe the development of multiple-item measures to capture the construct of channel member satisfaction. Two measures are developed that are found to have high levels of reliability ...

Channel Networks: A Geomorphological Perspective

Abstract: The study of channel networks has been dominated since 1966 by the random model However, recent work has shown (1) that although the topological properties of small networks conform to the random model more closely than those of large ones, even small networks exhibit systematic deviations from topological randomness and (2) that the topological and length properties of channel networks are controlled to a large degree by the spatial requirements of subbasins and the need for these subbasins to fit together in space, by the size, sinuosity, and migration rate of valley bends, and by the length and steepness of valley sides The factors that control the density properties of channel networks vary with the scale of the investigation and the geomorphic processes governing channel initiation Although progress has been made toward a satisfactory stream junction angle model, further work is needed The evolution of channel networks has been investigated by a variety of methods, including the development of conceptual and simulation models, the monitoring of small-scale badland and experimental drainage basins, and the substitution of space for time The morphology of most channel networks is largely inherited from the past or strongly influenced by inherited forms Inasmuch as there is no way of ever knowing the origin or complex history of such networks, the use of stochastic models in their study seems unavoidable

An achievable region and outer bound for the Gaussian broadcast channel with feedback (Corresp.)

Abstract: A deterministic coding scheme is presented for additive white Gaussian broadcast channels with two receivers and feedback from the receivers to the transmitter. The region of data rates at which reliable communication is possible is larger than that of the corresponding channel without feedback. This is the first example showing that the capacity region of degraded broadcast channels can be enlarged with feedback.

ARQ Schemes for Data Transmission in Mobile Radio Systems

Abstract: An important problem in land mobile radio communications is how to provide reliable data communications to the largest number of users. To explore this problem, several existing ARQ protocols are examined which have application to the land mobile radio channel, as well as some new protocol combinations. All protocols are analyzed for several key system performance measures which are verified by experimental means for static as well as fading channels. Finally, a conclusion is reached regarding a new Protocol combination which is found to offer significant advantages over all other protocols explored.

High-Level Modulation and Coding for Nonlinear Satellite Channels

Abstract: Currently, 4-PSK is the prevalent modulation format in use for digital satellite communications. To improve bandwidth efficiency, 8PSK could be used instead, but a higher power would be needed; to improve power efficiency, error-correcting codes could be used, but at the expense of a larger bandwidth. Recently, Ungerboeck [1] has proposed a class of codes in which a constellation of 2M signals is used to transmit information at the rate of log_{2} M bits per symbol, and has shown that coding gains of up to several decibels can be achieved on the additive white Gaussian noise (AWGN) channel with no increase in bandwidth occupancy and a relatively small added complexity. Thus, these codes seem to be particularly attractive for application in the band-limited environment typical of satellite communication systems, provided that the performance gain that they provide on the AWGN channel is not lost over a satellite channel. The goal of this work is to assess the performance of this class of codes when used to transmit 3 information bits per symbol on a band-limited, nonlinear satellite channel. Three modulation formats are considered, namely 16-PSK, 16-QAM, and a 16-ary amplitude-phase keying scheme with two amplitude levels. It is found that 16-PSK outperforms the two other modulation formats, and that the use of these codes can provide a substantial performance improvement even on a satellite channel.

Adaptive communication rate modem

Abstract: In a modem that transmits signals to and receives signals from a remote device at a multiplicity of communication rates, the quality of the channel is monitored, a communication rate is selected based on the channel quality, the desire for an increased rate is indicated, and the increased rate is implemented by the modem when the remote device concurs.

Railroad communication system

Abstract: A radio communication control system for a lead unit and a plurality of remote units is disclosed. The system has a protocol for establishing a communication link between the lead unit and the one or more remote units in the system which prevents any of the units in that system from processing messages or commands from other units in other train systems or processing messages or commands originating from units within a train system which are addressed to other units within the system. The communication system also includes a communications channel contention system for minimizing the probability of multiple units transmitting on the common communication channel at the same time and for insuring that the highest priority communications in each train are transmitted first in time measured from the end of the latest transmission on the radio communications channel. The invention also includes apparatus for verifying the establishment of the communications link by means of signaling through the mechanical coupling in the train and monitoring the radio response. The invention further includes an improved flow rate sensor for use in a remote unit for determining when significant air flows occur into the brake pipe of the remote unit. The invention further includes an air pressure regulation system which prevents the fluctuation of the air pressure in the equalizing reservoir of the lead and remote units consequent from either leakage or change in the ambient temperature.

Method for communicating variable length messages between a primary station and remote stations of a data communications system.

Abstract: A data communications system (Fig. 1) in which variable length messages (Figs. 3, 4 and 5) are communicated between a general communications controller (GCC 104) and a plurality of portable and mobile radios (130, 132, 134, 136, 138). The variable length messages (Fig. 3) include a bit synchronization field (204), a message synchronization field (205) and a plurality of channel data blocks (203) for efficiently and reliably handling long strings of data or text. Each channel data block (Fig. 5) includes an information field (503), a parity field (505) for error-connecting the information field and a channel state field (507) indicating whether or not the radio channel is busy or free. The GCC (104) is coupled to a cellular arrangement of channel communications modules (CCM's 106, 108, 110, 112), which each include a radio transmitter (114, 120, 124) and/or radio receiver (116, 118, 122, 126, 128). The mobile and portable radios (130, 132, 134, 136, 138) communicate with the GCC (104) by way of the CCM's (106, 108, 110, 112).

Deterministic multi-access method for a decentralized mobile radio system

Abstract: A mobile radio system uses a predetermined number of control channels over which a hand-shake routine is performed to determine called station availability, before one of a limited number of talk channels (local and repeater) is assigned for communication between a calling and the called station. After locating an idle talk channel (local channels are searched first), the control channel to which the called station is predeterminedly assigned is attempted to be accessed. Transmission times on the control channel are a function of the called station's identification code, thus creating a logical ring. Provision is made for message based priorities, emergency numbers and high priority for stations having experienced a previous unsuccessful attempt to access a control channel.

Hand-off filter for cellular mobile radio

Abstract: A cellular mobile radio-telephone system incorporates hand-off equipment for effecting a hand-off of communication links coupled to a mobile subscriber transceiver as the transceiver travels from one cell to an adjoining cell. The hand-off equipment includes a filter which smoothes voice channel signals received from the mobile transceivers so as to permit a more precise determination as to when a reduction in signal amplitude indicates the need for a hand-off. The operation of the filter includes long and short term averaging of a sequence of signal samples. Circuitry is also provided for predicting a time of signal fade-out based on differences in the amplitude of successive samples or groups of samples. Also disclosed is circuitry for commanding a change in transmitter gain in a transceiver as a function of signal fade-out.

Method and system for expediting multi-packet messages in a computer network

Abstract: A data communication computer network system is arranged to interconnect autonomous computers with a shared single communication channel to provide point-to-point communication between a plurality of computers. Each computer is connected to a channel control means coupled to the shared channel for establishing and removing the point-to-point communication line. Once a point-to-point communication line is established between a source computer and a designated destination computer, all the information, in the form of data packets, to be transmitted therebetween is transmitted without interruption, by means of successive transmission of the data packets.

Transmission of digital data

Abstract: The transmission of digital data over a data link, particularly an H.F. radio link, can be corrupted by narrow-band, high level interference signals randomly distributed in frequency. The uncorrupted transmission of data can be made more possible by a frequency diversity digital data transmission system in which a signal channel is divided into a plurality of lesser bandwidth sub-channels, each of which is modulated across substantially its entire bandwidth by a multi-level, spectrally efficient modulation scheme, for example 8PSK, 16QAM, 64QAM. In a receiver the sub-channels are examined for narrow-band interference and the data signal is demodulated using a decision algorithm based on the sub-channel outputs, and an assessment of sub-channel reliability.

Simultaneous transmission of speech and data over an analog channel

Abstract: The present invention relates to a technique for recovering each of an entire analog speech signal and a modulated data signal simultaneously received over a transmission channel such as a common analog telephone speech channel. In the received composite signal, the entire modulated data signal is multiplexed within the normal analog speech signal frequency band where the speech is present and its signal power density characteristic is at a low level. Separation of the speech and data signals at the receiver is effected by recovering the modulation carrier frequency and demodulating the received signal to recover the data signal. The data signal is then (a) remodulated with the recovered carrier, (b) modified to cancel phase jitter and frequency offset errors detected during the data demodulating process and (c) convolved with an arbitrary channel impulse response in an adaptive filter whose output signal is subtracted from the received composite data and speech signal to generate the recovered speech signal. To improve the recovered speech signal, a least mean square algorithm is used to update the arbitrary channel impulse response output signal of the adaptive filter.

Paleohydrologic Equations for Rivers

Abstract: Geomorphologists are becoming increasingly active in reconstructing the characteristics of ancient rivers. The features of interest generally are those that describe the former streamflow, such as discharge and mean velocity, and those that describe the channel, for example bankfull width and depth, or meander dimensions. To make these estimates, the paleohydrologist depends on relations derived for modern rivers. Fluvial-geomorphic literature contains many such relations that potentially can be applied to former rivers and their flows.

Integrated buffer management and signaling technique

Abstract: In a private line multiplexing device a multi-priority buffering system is used to control the transmission of supervisory signaling information and normal messages onto an available communication channel. The system includes a multi-priority message buffer, a queue map for logging entries in the buffer, an output time map and a controller. The controller tags incoming data (be it a normal message and/or signaling information) and stores the data into the priority buffer. The tag may include a priority classification, identification, entry-time, etc. Signaling information is assigned a priority I designation while newly generated voice packets are assigned priority IV. As communication channels become available data is shifted, in accordance with a priority algorithm, from the buffer to the channel. Furthermore, the algorithm ensures that stacked messages from a common source are transmitted on a delayed basis.

Slow Frequency Hopping Multiple Access for Digital Cellular Radiotelephone

Abstract: A theoretical analysis of slow frequency hopping is presented together with a comparison to other multiple access techniques. The propagation and modulation models are described and the multiple access protocols are analyzed with an information theory approach. It is explained why the speed of variation of some random variables is important for protocol evaluation. A definition of capacity is given and is first applied to simple systems. Full mathematical evaluations of the protocol referred to as "random SFHMA" are presented for the mobile-to-fixed-station channel, and some simulation results are given for the reverse channel. With realistic propagation parameters ( \alpha= 3.5, \sigma = 8 dB) and with mobile power control, there can be as many as 87 radiotelephone users per cell in a 25 MHz band. A comparison to the traditional FDMA protocol is presented and it is Shown that slow frequency hopping would be more efficient for future high capacity small cell systems.

Simultaneous voice and data communication and data base access in a switching system using a combined voice conference and data base processing module

Abstract: A combined telecommunications and data communications system operates by partitioning data wherein the PCM speech transmission data field is used to contain both digitized speech and other data in the same channel within a frame. Thus the system enables speech and data to be combined in a common information field and to be simultaneously transmitted in the same channel, frame by frame, through a digital switching network. The switching network contains a common port which has a digital interface connected to the port which digital interface can separate and combine the speech and the data fields. The digital interface is connected to a conference module which conference module receives the speech fields via a speech bus. The digital interface is further connected to a data base system which data base system receives the separated data fields via a data tone bus. Through the unique use of a digital interface for combining and separating speech and data fields from the information field of a channel, a conference module and a data base may both be connected to a single port thereby reducing the number of ports and network channels required for simultaneous conferencing and data base access.

An approximate treatment of flow in branches and bends

Abstract: Flow in channel branches and bends is analysed by using elementary hydraulic theory. The results are expressions for the local loss coefficients. The primary purpose is to explore the simplified fl...

Block coded modulation system

Abstract: A block of digital data bits is sent over a band-limited channel using a plurality of modulation signal points drawn from a two-dimensional constellation of available signals. The constellation comprises a plurality of inner signals, and a plurality of outer signals located farther from the origin than the inner signals. One bit of the block of digital data determines whether any of the plurality of signal points will be drawn from the outer signals. If an outer signal will be drawn, at least one other bit of the block of digital data determines which of the plurality of signal points will be an outer signal point.

Method and device for remotely identifying TV receivers displaying a given channel by means of an identification signal

Abstract: A method and device for remotely identifying TV receivers tuned to a certain TV channel and displaying the video signal thereof. An identification signal is introduced in the television signal of the TV channel at its source before its transmission towards the TV receivers. The nature of the identification signal as well as the way of introducing it in the television signal are both selected so that this identification signal is irradiated in the air at the receivers end when these receivers display the video signal of the concerned channel, due to the phenomenom of cathode--ray--tube radiation caused by the presence of high voltages modulated by the luminance information at the luminance component frequencies. Detection of the irradiated identification signal in the proximity of one receiver indicates that it is tuned to the channel in question and displays the video signal thereof. If a different identification signal is introduced in the television signal of each TV channel, it can be determined which channel has its video signal displayed on a specific receiver by identifying the channel corresponding to the identification signal detected in the proximity of such a specific receiver. The method and device may be used for example to detect pirate decoders in a secured television system.

Card information selecting system

Abstract: Card information selecting system capable of accessing a card provided with a plurality of information channels corresponding to different transactions, includes reading means for reading information recorded on the card, selecting means for designating at least one of the information channels, writing means for recording information on the card, and processing means associated with the selecting means for reading information or recording the predetermined information on the selected channel

Method and apparatus for decoding the output signal of a partial-response communication or recording-device channel

Abstract: A maximum-likelihood sequence decoder is used with a partial-response signaling system for processing sequences of sampled values from a communication channel or recording device. The partial-response signals can be duobinary, dicode, or partial-response class-IV. The maximum-likelihood decoding for each sequence can be based upon a two-state trellis. Instead of two survivor metrics for two states, only a difference metric is necessary.

Real time seismic telemetry system

Abstract: A real time seismic telemetry system includes a central station (10) for communication with a plurality of remote data acquistion units (14) The command station (10) has a command unit (34) for controlling the operation of a transmitter (40) for providing instructions to the data acquistion units (14) The data acquistion units (14) receive the data on a receiver (80) and process the data in a logic control circuit (88) Remote data is picked up with a hydrophone (30) and converted to digital data for transmission through a transmitter (78) which is tuned to a discrete channel for each data acquistion unit (14) The command station (10) has a PCM receiver (62) tuned to each of the channels for demodulating the data stream therefrom A digital receiver (66) is provided for synchronizing and processing the data The digital receiver (66) synchronizes both to the bit rate and to the beginning and ending of the digital word such that data contained in the digital word can be multiplexed onto a data bus (68) The data bus (68) is controlled by an external storage/control (70) for storage of the data from all of the digital receivers (66) for all of the discrete channels

System for transmitting data through a troposcatter medium

Abstract: A method of transmitting binary data from one station to another via a troposcatter medium, characterized in that the data is converted to parallel form so that the bits produce distinctive pairs of sine and cosine harmonics having different frequencies, which harmonics are summed in two separated channels that are modulated by rf sine and cosine modulating signals that are combined and transmitted to the receiver, together with a test signal that was periodically inserted in the parallel bits. The receiver supplies the signals to banks of matched filters that produce a first set of signal estimates from which the test signal is detected. A matrix system responsive to the test signal produces from the first set of estimates a second set of signal estimates having lower distortion than the first set. When the system is provided with diversity signal transmission at a different rf frequency, the test signal at the receiver is used to provide weighted diversity channel signals that are summed to provide third signal estimates having less distortion than the second set of estimates.

Kinetics of Movement in Narrow Channels

Abstract: Publisher Summary The “narrow” in refers to the condition in which the diameter of the channel is so small that the molecules or ions in the channel are not able to pass around each other. The no-pass condition gives rise to two different sets of special effects in narrow channels. First, it provides a physical and mathematical constraint that allows the derivation of some general “thermodynamic” type of relations. The three most important relations discussed in this chapter are relation between the flux ratio, the number of ions in the channel, and the dependence of the streaming potential and of the ratio of the osmotic to diffusive water permeability on the number of water molecules in the channel. The second set of results is concerned with the implications of the no-pass condition for the general kinetic description of transport in narrow channels. Two examples discussed in the chapter are the possibilities (1) that the local mobility of an ion may depend primarily on the mobility of the chain of water molecules in the channel that it must push, rather than on its own ion-wall interaction, and (2) that one ion cannot move in the channel without displacing all other channel ions.

Optimal Channel Cross Section with Freeboard

Abstract: Methods from calculus may be used to determine a channel cross section which minimizes hydraulic resistance or alternatively, determines the least cost channel dimensions. In either case, established procedures ignore channel freeboard. The traditional methods of channel geometry optimization are reformulated to include freeboard considerations. The results are shown to revert to traditional solutions when the freeboard parameter is set to zero. A graphical solution is provided to simplify the resulting equations.