Showing papers on "Communication channel published in 1991"

On the extraction of channel networks from digital elevation data

Abstract: Channel networks with artibtrary drainage density or resolution can be extracted from digital elevation data. However, for digital elevation data derived networks to be useful they have to be extracted at the correct length scale or drainage density. Here we suggest a criterion for determining the appropriate drainage density at which to extract networks from digital elevation data. The criterion is basically to extract the highest resolution (highest drainage density) network that satisfies scaling laws that have traditionally been found to hold for channel networks. Procedures that use this criterion are presented and tested on 21 digital elevation data sets well distributed throughout the U.S.

The land mobile satellite communication channel-recording, statistics, and channel model

Abstract: The communication channel between the MARECS satellite at 26 degrees W and a cruising van was measured and recorded in European areas exhibiting satellite elevations from 13 to 43 degrees . Different environments and mobile antennas were tested. The results of an extensive statistical evaluation include spectra of the fading amplitude; probability density, and distribution of the received signal power; and the percentage of time for fade and nonfade periods. Based on the physical phenomena of multipath fading and signal shadowing, an analog model of the land mobile satellite channel which can readily be used for software and hardware fading simulation is developed. The most important parameter of this model is the time-share of shadowing. The Rice factor which characterizes the channel during unshadowed periods, can vary from 3.9 to 18.1 dB. Block error probability density, error gap distribution, and block error probability are discussed. >

The Use of Influence Strategies in Interfirm Relationships in Industrial Product Channels

Abstract: The authors seek to extend theory and empirical findings on interfirm influence strategies by examining their use in channel relationships between suppliers and distributors of industrial products....

A physical mobile radio channel model

Abstract: A model is presented for the time- and frequency-selective outdoor mobile radio channel. which is based on the physical process of wave propagation in a statistical fluctuating medium. The reduction of this complex scattering problem to a set of relations containing the pertinent statistics for conducting communications system analysis is developed. Characteristics of the propagation process, e.g., delay power spectra, amplitude distribution (Nakagami-m-distribution), and correlation functions, are derived in parameterized form from physical considerations. The method allows a classification of real configurations (environments) into several classes and the extraction of the relevant parameters in direct comparison with measured data. The method is applied to typical channel situations in Switzerland. The mathematical modeling of the classes is demonstrated. >

Efficiency of packet reservation multiple access

Abstract: Packet-reservation multiple access (PRMA) is viewed as a merger of slotted ALOHA and time-division multiple access (TDMA). Dispersed terminals transmit packets of speech information to a central base station. When its speech activity detector indicates the beginning of a talkspurt, a terminal contends with other terminals for access to an available time slot. After the base station detects the first packet in the talkspurt, the terminal reserves future time slots for transmission of subsequent speech packets. The influence of several variables on PRMA efficiency, defined as the number of conversations per channel, is examined. The number of channels is the ratio of transmission rate to speech coding rate. It is found that with 32-kb/s speech coding and 720-kb/s transmission (22.5 channels), PRMA supports up to 37 simultaneous conversations, or 1.64 conservations per channel. The number of conversations per channel is at least 1.5 over a wide range of packet sizes (8 ms of speech per packet to 34 ms) and for all systems with 16 or more channels (transmission rate >or=512 kb/s, with 32-kb/s speech coding). Other factors studied are the sensitivity of the speech activity detector, the retransmission probability of the contention scheme, and the maximum time delay for the transmission of speech packets. >

Multiple call control method in a multimedia conferencing system

Abstract: A method for use in a multimedia conferencing arrangement to control multiple concurrent calls where each call comprises one or more channels. A first call among a first set of user stations and a second call among a second set of user stations are merged into a single call comprising a plurality of channels among at least three user stations from the first and second sets. The plurality of channels of the single, merged call corresponds to a combination of channels of the first and second calls and may include a signalling channel, a voice channel, and one data channel for each data channel of the first and second calls. The method is also applicable to calls including image or video channels.

Multiple media delivery network method and apparatus

Abstract: A multiple media system having a central site and a remote site for customizing video and audio presentations comprising a communications channel, a studio processor, a scheduling processor, a network processor, a transmitter, a communications processor, a video processor, and optionally a matrix switch, a cue processor, a matrix-switch processor and a system monitor. The studio processor generates one or more content data signals. The content data signals maybe analog or digital, and include text signals, phototext signals and/or audio signals. The scheduling processor generates a schedule data signal, which includes a unique identifier, accounting, administrative and scheduling data. The network processor generates a communication signal which includes the one or more content data signals and the schedule data signals formatted with the video signal. The transmitter transmits the communications signal over the communications channel. At the remote site the communications processor receives the communications signal and selects a first content data signal from the one or more content data signals. The video processor mixes the first content data signal with the video signal. The cue processor is coupled to network feed channel through a matrix switch. In response to detecting network-cue signals, the cue processor generates insertion signals. In response to the insertion-cue signals, the matrix processor controls the matrix switch routes the multiple media signal, which includes the video signal with the additional information from the content data signal, to a network communications channel.

Effective bandwidths for the multi-type UAS channel

Abstract: The Uniform Arrival and Service (UAS) model is one of several appropriate to modelling traffic offered to a multi-service communication channel. We exhibit, via asymptotics and a range of specific examples, that it is possible to assign a notionaleffective bandwidth to each source, dependent not only on its mean bandwidth but also on its burstiness and on the channel. The effective bandwidth can be calculated quickly and efficiently using the results of Anick, Mitra and Sondhi and reduces the multi-service network to the more familar, and well understood, form of a traditional circuit-switched network.

Channel assignment for cellular radio using neural networks

Abstract: The channel assignment problem, i.e. the task of assigning channels to radio cells in a spectrum-efficient way, is solved by a neural network algorithm. This algorithm is inherently parallel and does not rely on a particular structure of the interference graph. The results obtained so far indicate that the algorithm can be used to obtain an optimum solution. It was applied successfully for inhomogeneous interference conditions and channel demand. Cochannel and cosite constraints were taken into account, and the extension to any other technical restrictions will be possible in an obvious way. The examples studied to date are of a relatively small size; the question remains of how the algorithm behaves when applied to larger and more complex examples. The disadvantages of the algorithm are its long calculation time compared to graph coloring algorithms and the difficulty of finding appropriate parameters. However, the algorithm was not optimized for speed, and the parameter search may be a question of experience. >

Delay jitter control for real-time communication in a packet switching network

Abstract: A study is made of the feasibility of bounding the delay jitter for real-time channels in a packet-switched store-and-forward wide-area network with general topology, extending the scheme proposed in previous papers. The authors prove the correctness of the solution, and study its effectiveness by means of simulations. The results show that the scheme is capable of providing a significant reduction in delay jitter, that there is no accumulation of jitter along the path of a channel, and that jitter control reduces the buffer space required in the network significantly. >

The HDSL environment (high bit rate digital subscriber line)

Abstract: The author presents a tutorial on the physical environment in which high bit rate digital subscriber line (HDSL) transceivers will have to evolve and succeed. Special attention is given to the most damaging impairments that are encountered in subscriber lines, such as propagation loss, linear distortion, crosstalk, bridged taps, and impulse noise. Somewhat less important impairments, such as change of gauge, temperature variation, and thermal noise, are also briefly described. The author concludes with a discussion of the capacity of a twisted-pair channel in a crosstalk-dominated environment. >

Least sum of squared errors (LSSE) channel estimation

Abstract: A least sum of squared errors (LSSE) channel estimation algorithm is presented for estimating a channel impulse response from a known training sequence. Optimum training sequences are found and tabulated for different channel responses and training sequence lengths. The effect of channel estimation errors on the performance of some data detectors is also investigated. A simple approximation for the expected degradation in performance with channel estimation errors is derived.

Improved call set-up and spectrum sharing in radio communication on systems with dynamic channel allocation

Abstract: The call set-up technique of this invention is characterized by the use of channel information from both base station and subscriber terminal in determining the radio traffic channel upon which to set-up a new call. Communication between the base station and subscriber terminal is carried out on a signalling channel until the traffic channel is chosen. Calls are set-up so that they proceed on the radio channel which, of a set of channels under consideration by the subscriber terminal, contains the least amount of interference as measured at the subscriber terminal. The set of channels under consideration by the subscriber terminal is a subset of the entire set of channels allocated to the service. This subset is comprised of those channels having little interference, as measured by the base station, and which, additionally, are not reserved exclusively for stationary, fixed-allocation services in the geographic location of the base station. The call set-up technique thereby assures that calls proceed on channels containing little interference from the viewpoint of both base station and subscriber terminal. The technique also facilitates sharing of the radio spectrum with stationary, fixed-allocation services because there is no need to program each subscriber terminal to avoid the spectrum allocated to the fixed service.

The application of nonlinear structures to the reconstruction of binary signals

Abstract: The problem of reconstructing digital signals which have been passed through a dispersive channel and corrupted with additive noise is discussed. The problems encountered by linear equalizers under adverse conditions on the signal-to-noise ratio and channel phase are described. By considering the equalization problem as a geometric classification problem the authors demonstrate how these difficulties can be overcome by utilizing nonlinear classifiers as channel equalizers. The manner in which neural networks can be utilized as adaptive channel equalizers is described, and simulation results which suggest that the neural network equalizers offer a performance which exceeds that of the linear structures, particularly in the high-noise environment, are presented. >

A method of operating a communications system, a communications system and a secondary station for use in the system

Abstract: A method of operating a communications system, particularly a FDM-TDD cordless telephony system, in which, in order to expedite handover, a portable secondary station builds up a record of the status and quality of the other FDM channels in the system by every 1 in n (where n is an integer greater than one) TDD frames monitoring another FDM channel. The value of n is adaptive in that, as the quality of its existing channel deteriorates, the value of n decreases, thereby updating its record more rapidly. At handover, the secondary station is able to choose immediately an acceptable alternative channel, thereby avoiding the time overhead of scanning all the other FDM channels.

Method and apparatus for dynamic distribution of a communication channel load in a cellular radio communication system

Abstract: A method and apparatus is provided for dynamic distribution of a communication channel load of sectorized-antennae or omni-directional antennae of cell sites in a cellular radio communication system. The channel load is distributed by narrowing an antenna (102) beamwidth of an overloaded sector of a cell site (100) and widening an antenna (104) beamwidth of an adjacent sector of the cell site (100). In an alternative embodiment, the channel load is distributed by reducing power of an antenna (124) of a cell site (120) which is adjacent to an overloaded cell site (100). Alternatively, the channel load is distributed by increasing power of an antenna (118) of a cell site (116) which is adjacent to an overloaded cell site (100). Subsequent to the channel load distribution, each of the subscriber units in the overloaded (100) and adjacent cell sites (116, 120) are handed off to the particular cell site which is best able to service the subscriber units.

Real-time communication in multi-hop networks

Abstract: A scheme is developed for providing predictable interprocess communication in real-time systems with (partially connected) point-to-point interconnection networks, which provides guarantees on the maximum delivery time for messages. This scheme is based on the concept of a real-time channel, a unidirectional connection between source and destination. A real-time channel has parameters which describe the performance requirements of the source-destination communication, e.g., from a sensor station to a control site. Methods to compute guarantees for the delivery time of messages belonging to real-time channels are examined. Problems associated with allocating buffers for these messages are addressed, and a scheme which preserves delivery time guarantees is developed. >

Modulation and coding for information storage

Abstract: Many of the types of modulation codes designed for use in storage devices using magnetic recording are discussed. The codes are intended to minimize the negative effects of intersymbol interference. The channel model is first presented. The peak detection systems used in most commercial disk drives are described, as are the run length-limited (d,k) codes they use. Recently introduced recording channel technology based on sampling detection-partial-response (or PRML) is then considered. Several examples are given to illustrate that the introduction of partial response equalization, sampling detection, and digital signal processing has set the stage for the invention and application of advanced modulation and coding techniques in future storage products. >

Blind equalization of digital communication channels using high-order moments

Abstract: The authors describe algorithms for blind equalization of digital communication channels of the quadrature-amplitude-modulation (QAM) type. These algorithms are based on the fourth-order statistical moments of the received data sequence. The first of the two is a linear least-squares-type algorithm. The second algorithm is of the nonlinear least-squares-type. The algorithms use the fourth-order statistical moments of the symbol sequence to explicitly estimate the channel impulse response. The estimated impulse response is used, in turn, to construct a linear mean-square error equalizer. The performance of this equalizer is not optimal in any sense, but it is adequate for channels with mild intersymbol interference or when the number of data points available for estimating the channel response is very large. >

A new method of channel identification

Abstract: A method of channel identification is proposed that exploits the spectral correlation properties of pulse- and carrier-modulated signals to identify channels in the presence of arbitrary noise and nearly arbitrary interference Although a pilot or training signal is required, no replica of the transmitted pilot/training signal is needed at the receiver The price paid for this simplicity and the tolerance to extreme channel corruption from noise or interference is that the method is slow That is, relatively long averaging times are needed for measurement of the spectral correlation of the received signal >

Method and apparatus for displaying channel identification information

Abstract: A subscriber terminal includes a receiver for receiving a television signal including video, audio and data information. A channel of the television signal may be selected for display on the television. A memory stores channel identification information such as channel identifiers. The channel identifiers include at least one display character. A processor establishes a relationship between channel identification information and channel numbers associated with channels of the television signal. An on-screendisplay control circuit controls the display of character information on the television and has the capability of overlaying the channel number and the channel identification information on the video portion of a selected channel displayed on the television for a predetermined period of time. Program identification information such as program titles may also be displayed. Alternatively or additionally, the channel identification information may be displayed on a display such as an LED display of a subscriber terminal.

Device for the transmission of digital data with at least two levels of protection and corresponding reception device

Abstract: A device for the transmission of digital data with at least two levels of protection, of the type providing for the distribution of the data to be transmitted in the form of digital elements in the time-frequency space and the transmission of symbols each formed by a multiplex of N orthogonal carriers modulated by a set of the digital elements, and transmitted simultaneously, the device including channel .[.encoding.]. .Iadd.encodes .Iaddend.means comprising at least two types of modulation and/or at least two encoding efficiency levels. This enables to optimize the use of the transmission channel by assigning differentiated transmission techniques to portions of data of a same digital train as a function of the different levels of protection sought, against transmission errors.

Multi-channel digital receiver for global positioning system

Abstract: A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit and multiple channel circuits, with each channel circuit including a carrier and code synchronizing circuit and multiple digital correlators with dynamically adjustable code delay spacing. The sampling circuit provides high-rate digital samples of the incoming composite signal to each receiver channel. Within each channel, the synchronizing circuit detects cycle slips in a locally generated carrier reference signal as well as phase drift in a locally generated PRN code signal. The correlators compare the digital samples with a locally generated PRN code to produce early, late, and/or punctual correlation signals which are used to adjust the local PRN code. A non-linear sampling technique may be used to provide increased sensitivity in the presence of continuous wave interfering signals.

Method for assigning channel reuse levels in a multi-level cellular system

Abstract: In a radio frequency communication system employing channelization, such as a cellular TDMA system, and having a plurality of reuse channel levels, such as multiple frequency reuse patterns, each level having at least one associated reuse channel, a method and device comprising: determining relative interference for a reuse channel of a first reuse level (100) in relation to relative interference for a reuse channel of at least a second reuse level (105) resulting in a reuse level gradient and assigning the subscriber unit (115) to at least one reuse level in response to the reuse level gradient.

Dynamic channel allocation method

Abstract: A dynamic frequency allocation method of a digital, mobile, portable telephone system wherein in communications between a plurality of base stations which are connected to a public telephone network and/or a private branch exchange and which respectively generate synchronization in an independent manner and mobile stations receiving service therefrom, each base station uses a communication signal transmission channel including a frequency and a time slot pair respectively selected from a plurality of frequencies and a plurality of time slots related thereto to implement a multichannel time division multiplex/time division duplex communication. Each of the base and mobile stations receives a communication signal of a different station communicating with synchronization independent of the pertinent station by use of a different time slot at the same frequency of the channel used by the station to receive a communication sent thereto so as to measure an interval or a distance between the time slot used by the different station and the time slot assigned thereto. Based on the measurement result, a chance of a collision between these two time slots is estimated such that depending on the estimation result, the pertinent station detects free channels not being used by any other stations to conduct a channel transition to one of the detected free channels.

Computer models for fading channels with applications to digital transmission

Abstract: The authors describe computer models for Rayleigh, Rician, log-normal, and land mobile satellite fading channels. All computer models for the fading channels are based on the manipulation of a white Gaussian random process. This process is approximated by a sum of sinusoids with random phase angle. These models compare very well with analytical models in terms of their probability distribution of envelope and phase of the fading signal. For the land mobile satellite fading channel, results of level crossing rate and average fade duration are given. These results show that the computer models can provide a good coarse estimate of the time statistic of the faded signal. Also, for the land mobile satellite fading channel, the results show that a 3-pole Butterworth shaping filter should be used with the model. An example of the application of the land mobile satellite fading channel model to predict the performance of a differential phase-shift keying signal is described. >

Method for frequency sharing in a frequency hopping communications network

Abstract: A frequency-hopping packet communication system without a master clock or master control unit is based on use of a receiver's frequency hopping timing and identification to control communication. A frequency-hopping band plan, involving the number of channels and the pseudo-random pattern of frequency change and nominal timing of changes, is universally known to each node in the network. Frequency-hopping is implemented by the division of communication slots and the accumulation of slots into epochs, wherein each epoch equals the total number of available slots (number of channels times the number of time frames per channel). A transmitting node tracks the preestablished frequency-hopping pattern for its target receiver based on previously-acquired information. The transmission node identifies a receiver node and a current frequency channel of such receiver node. The transmission node then checks the frequency channel to determine if available (e.g., not in use and within an acceptable noise margin). If unavailable, the transmission node delays transmission to the identified node to a later slot. During the delay, the transmission node identifies another receiver node and a corresponding current frequency channel. The steps of identifying a receiver node and checking the corresponding current frequency channel are repeated until a node having an available frequency channel is identified. The transmission node then sends a packet to the selected receiver node at a frequency and for a duration defined according to the current slot. Such transmission node tracks the changing frequency of the selected receiver node to maintain frequency synchronization.

Intra-cell call hand-over in radio communication systems with dynamic channel allocation

Abstract: The intra-cell call hand-over technique of this invention is characterized by the use of channel information from both base station and subscriber terminal in determining a standby radio traffic channel upon which to hand over a call. Communication between the base station and subscriber terminal is carried out on an inband or associated signalling channel for the selection of the standby traffic channel. The standby radio channel is the channel, which, of a set of channels under consideration by the subscriber terminal, contains the least amount of interference as measured at the subscriber terminal. The set of channels under consideration by the subscriber terminal is a subset of the entire set of channels allocated to the service. This subset is comprised of those channels having little interference as measured by the base station. The call hand-over technique thereby assures that calls proceed on channels containing little interference from the viewpoints of both base station and subscriber terminal.

Transmitting, receiving, and automatic recording system for programs with time and channel information

Abstract: Scrambled video and audio signals of programs are transmitted from a transmitting system via a communication satellite to a receiving system. The audio signal contains channel, start/end time, and standard time information of the programs. The receiving system has a calendar for generating time information which is corrected according to the standard time information. Desired programs can automatically be recorded by a video tape recorder connected to the receiving system, based on the channel and start/end time information which is displayed. Any received programs which the user of the receiving system does not want to record can be canceled simply by pushing cancel keys.