Showing papers on "Communication channel published in 1993"

The indoor radio propagation channel

Abstract: In this tutorial survey the principles of radio propagation in indoor environments are reviewed. The channel is modeled as a linear time-varying filter at each location in the three-dimensional space, and the properties of the filter's impulse response are described. Theoretical distributions of the sequences of arrival times, amplitudes and phases are presented. Other relevant concepts such as spatial and temporal variations of the channel, large-scale path losses, mean excess delay and RMS delay spread are explored. Propagation characteristics of the indoor and outdoor channels are compared and their major differences are outlined. Previous measurement and modeling efforts are surveyed, and areas for future research are suggested. >

Simulation of multipath impulse response for indoor wireless optical channels

Abstract: A recursive method for evaluating the impulse response of an indoor free-space optical channel with Lambertian reflectors is presented. The method, which accounts for multiple reflections of any order, enables accurate analysis of the effects of multipath dispersion on high-speed indoor optical communication systems. A simple algorithm for computer implementation of the technique and computer simulation results for both line-of-sight and diffuse transmitter configurations are also presented. In both cases, it is shown that reflections of multiple order are a significant source of intersymbol interference. Experimental measurements of optical multipath, which help verify the accuracy of the simulations, are discussed. >

Approximation theory of output statistics

Abstract: Given a channel and an input process we study the minimum randomness of those input processes whose output statistics approximate the original output statistics with arbitrary accuracy. We introduce the notion of resolvability of a channel, defined as the number of random bits required per channel use in order to generate an input that achieves arbitrarily accurate approximation of the output statistics for any given input process. We obtain a general formula for resolvability which holds regardless of the channel memory structure. We show that, for most channels, resolvability is equal to Shannon capacity. By-products of our analysis are a general formula for the minimum achievable (fixed-length) source coding rate of any finite-alphabet source, and a strong converse of the identification coding theorem, which holds for any channel that satisfies the strong converse of the channel coding theorem.

Channel network source representation using digital elevation models

Abstract: Methods for identifying the size, or scale, of hillslopes and the extent of channel networks from digital elevation models (DEMs) are examined critically. We show that a constant critical support area, the method most commonly used at present for channel network extraction from DEMs, is more appropriate for depicting the hillslope/valley transition than for identifying channel heads. Analysis of high-resolution DEMs confirms that a constant contributing area per unit contour length defines the extent of divergent topography, or the hillslope scale, although there is considerable variance about the average value. In even moderately steep topography, however, a DEM resolution finer than the typical 30 m by 30 m grid size is required to accurately resolve the hillslope/valley transition. For many soil-mantled landscapes, a slope-dependent critical support area is both theoretically and empirically more appropriate for defining the extent of channel networks. Implementing this method for overland flow erosion requires knowledge of an appropriate proportionality constant for the drainage area-slope threshold controlling channel initiation. Several methods for estimating this constant from DEM data are examined, but acquisition of even limited field data is recommended. Finally, the hypothesis is proposed that an inflection in the drainage area-slope relation for mountain drainage basins reflects a transition from steep debris flow-dominated channels to lower-gradient alluvial channels.

Decorrelating decision-feedback multiuser detector for synchronous code-division multiple-access channel

Abstract: A decorrelating decision-feedback detector (DF) for synchronous code-division multiple-access (CDMA) that uses decisions of the stronger users when forming decisions for the weaker ones is described. The complexity of the DF is linear in the number of users, and it requires only one decision per user. It is shown that performance gains with respect to the linear decorrelating detector are more significant for relatively weak users and that the error probability of the weakest user approaches the single-user bound as interferers grow stronger. The error rate of the DF is compared to those of the decorrelator and the two-stage detector. >

A Hierarchical Approach to Classifying Stream Habitat Features

Abstract: We propose a hierarchical system of classifying stream habitats based on three increasingly fine descriptions of the morphological and hydraulic properties of channel geomorphic units. We define channel geomorphic units as areas of relatively homogeneous depth and flow that are bounded by sharp gradients in both depth and flow. Differences among these units provide a natural basis for habitat classification that is independent of spatial scale. At the most general level of resolution, we divide channel units into fast- and slow-water categories that approximately correspond to the commonly used terms “riffle” and “pool.” Within the fast-water category, we identify two subcategories of habitats, those that are highly turbulent (falls, cascades, chutes, rapids and riffles) and those with low turbulence (sheets and runs). Slow-water habitats include pools formed by channel scour (eddy pools, trench pools, mid-channel pools, convergence pools, lateral scour pools and plunge pools) and those formed be...

Gaussian multiaccess channels with ISI: capacity region and multiuser water-filling

Abstract: The capacity region of a two-user Gaussian multiaccess channel with intersymbol interference (ISI) in which the inputs pass through respective linear systems and are superimposed before being corrupted by an additive Gaussian noise process is discussed. A geometrical method for obtaining the optimal input power spectral densities and the capacity region is presented. This method can be viewed as a nontrivial generalization of the single-user water-filling argument. It is shown that, as in the traditional memoryless multiaccess channel, frequency-division multiaccess (FDMA) with optimally selected frequency bands for each user achieves the total capacity of the multiuser Gaussian multiaccess channel with ISI. However, the capacity region of the two-user channel with memory is, in general, not a pentagon unless the channel transfer functions for both users are identical. >

Centralized power control in cellular radio systems

Abstract: This paper describes a centralized power control scheme for cellular mobile radio systems. The power for the mobiles in the proposed scheme is computed based on signal strength measurements. All the mobiles using the same channel in this scheme will attain a common carrier-to-interference ratio. The proposed scheme is analyzed and shown to have an optimal solution. >

Network having selectively accessible recipient prioritized communication channel profiles

Abstract: A method for a sender to automatically distribute information to a receiver on a network using devices (such as printers and facsimile machines) and communication channels (such as electronic mail) defined in a receiver profile. The receiver profile establishes the properties and mode for receipt of information for receivers on the network and the profile is published in a network repository for all network users or is accessible by selected groups or individuals on the network. Receivers have additional control over network senders by defining an information filter which further controls sender channel access (to a receiver) by defining some channels as having priority of access such as direct or delayed access, as well as selectively permitting senders to override the receiver profile. Consequently, receiver profiles provide a variable receiver definable link to senders using multiple forms of media as well as multiple hardware platforms and network configurations.

Automatic tuning radio/tv using filtered seek

Abstract: A video processing device for automatic tuning of an audio-video signal (86) in accordance with a topic selection (80) made by a user. A user makes a selection of a subject matter topic from a menu (82) and the necessary tuning is thereafter automatically done under control of a menu control interface (82). In the example of digital information (90) transmitted in the vertical blanking interval of a video signal, the menu control interface (82) automatically adjusts the tuner (88) in accordance with the menu selection made by the user to choose an arbitrary channel and page of information within the channel. The menu or menus can be received from the incoming information, or can be stored in a memory (100).

Automated drug infusion system

Abstract: The present invention relates to a control system for use with an automated intravenous drug and fluid infusion system having plural pumping channels that operate independently for intravenously infusing drugs and fluid. The pumping channels are controlled by a microprocessor-based host controller that monitors each of the channels concurrently. In an exemplary embodiment, the system functions include identifying the particular drug that is to be pumped through a channel, preventing priming of a channel unless verification is provided that the channel is not connected to a patient and initiating the priming of each of the pumping channels independently.

Adaptive data rate modem

Abstract: An adaptive data rate modulator/demodulator (modem) (102), particularly useful for transmitting data over fading communications channels, uses an adaptive data rate technique which supports multiple data rates in the same device. The modem incorporates an adaptive data rate encoder (104) and an adaptive data rate decoder (105) using adaptive, parallel-branch decoding to translate received symbols into corresponding data bits. Significantly, the soft decision metrics of the decoder are also used to provide an estimate W of the signal-to-noise ratio. An optional predictor (232) receives W from the adaptive data rate decoder (105) and predicts the future signal-to-noise ratio to determine the desired data rate for the modem. The data rate is changed automatically and dynamically without interrupting the decoding process. A constant channel symbol rate and a single signal set simplify signal acquisition and synchronization. Incoming and outgoing data are buffered, and the transmission rate is changed dynamically by a memory controller (109) to avert buffer overflows and underflows. An optional adaptive phase-lock loop system (116) maintains synchronization of the decoder at all data rates.

Limits to interfirm coordination through information technology: results of a field study in consumer packaged goods distribution

Abstract: Researchers have suggested that information technology (IT) can reduce coordination costs, leading to increased coordination and cooperation among buyers and suppliers in an industry. However, improved coordination through IT, and the economic benefits from that coordination, may not be fully realized in practice; this conclusion is suggested by a field study in the consumer packaged goods industry investigating the impact of IT on interactions between manufacturers and retailers. New coordination mechanisms are emerging, driven by checkout scanner systems and IT, that permit more tightly coupled logistics operations in the distribution channel. The potential benefits of this increased coordination, through reduction in inventory and more stable manufacturing, are dramatic. However, we have observed considerable resistance by retailers to these innovations. Analysis of our field study results suggests that this resistance is due to the impact of the new coordination mechanisms on bargaining power; retailers perceive that their bargaining power will be eroded under the new coordination structure, and fear that this will preclude their sharing in the economic benefits.

Continuous authentication using an in-band or out-of-band side channel

Abstract: A re-authentication procedure between the modems of a public switched telephone network (PSTN) data connection, which is between a computer facility and a user, provides a secure method for protecting the computer facility against an active wire tap, or spoofing, by an intruder. In particular, the user's modem and the computer's modem perform a re-authentication procedure throughout the duration of the data connection. This re-authentication procedure is transparently performed on a side channel of the data connection. This side channel can either be an in-band channel or an out-of-band channel. The re-authentication procedure comprises an exchange of encrypted information between the two modems. If one of the modems detects the presence of an active wire tap, that modem simply interrupts the data connection.

Bi-directional wire-line to local area network interface and method

Abstract: A bi-directional wire-line to local area network interface, used between a remote host on a local area network (LAN), and a wire-line carrier system. A LAN media access control and physical interface converts outgoing LAN data from a LAN to an outgoing-data packet with a machine readable format. A LAN transmission control protocol and internet protocol stack identifies a protocol type of the outgoing-data packet from the LAN-MAC and physical interface. When the outgoing-data packet does not have a modem control command, a protocol converter correlates the outgoing-data packet to a channel number and depacketizes the outgoing-data packet into outgoing-binary data. Using the channel number, a connection controller and signal transform polls the outgoing-binary data and transforms the outgoing-binary data to a digitized representation of an analog signal having pulse code modulation (PCM). A wire-line carrier interface uses the channel number for multiplexing the digitized representation of the analog signal with frame bits, and also multiplexes any alarm conditions and signalling bits, as an outgoing-wire-line carrier signal. The wire-line carrier interface sends the outgoing-wire-line carrier signal over the wire-line carrier system.

Performance issues and algorithms for dynamic channel assignment

Abstract: Using dynamic channel assignment (DCA) algorithms to select communications channels as needed, time-division multiple access (TDMA) or frequency-division multiple access (FDMA) systems can serve dynamic and nonuniform traffic demands without frequency planning as long as quality is sufficient and equipment is available. Here, performance issues and algorithms for DCA in a TDMA portable radio system are considered. A fixed number of traffic servers (time slots) per radio port is assumed: therefore, the system capacity is hard-limited by the equipment availability, and the DCA efficiency is compared mainly through the signal-to-interference ratio in both the uplink and downlink directions. >

Method and apparatus for parallel decoding and encoding of data

Abstract: The present invention provides a method and apparatus for encoding and decoding data in parallel. The present invention provides a system for decompressing a data stream having multiple codewords. The system includes an input channel that receives the data stream. The system also includes a decoder which decodes each bit of the data stream, wherein at least two of the codewords in the data stream are decoded at the same time, such that the data stream is decoded in parallel.

Demonstration, using sliding-frequency guiding filters, of error-free soliton transmission over more than 20 Mm at 10 Gbit/s, single channel, and over more than 13 Mm at 20 Gbit/s in a two-channel WDM

Abstract: By transmitting trains of 2 14 bit pseudorandom words in a recirculating loop containing strong, sliding-frequency guiding filters, «error-free» (measured BER≤10 -9 ) soliton transmission at 10 Gbit/s, single channel, and at 20 Gbit/s in a two channel WDM is demonstrated, over paths as great as 20 000 km and 13 000 km, respectively

Planform pattern and channel evolution of the Brahmaputra River, Bangladesh

Abstract: Abstract The Brahmaputra is one of the world’s greatest rivers, ranking fifth in terms of discharge and eleventh in terms of drainage area. It also has a very high sediment discharge, ranking third in the world. The river is braided with meta-stable islands and nodal reaches, mobile sand bars, shifting anabranches and severe bank erosion. The dominant discharge is about 38 000 cumecs, which is a high in-bank flow. Islands have top elevations that are adjusted to bankfull discharge, with a spacing scaled on the width of the primary channel. Bar top elevations are adjusted to the dominant discharge and bars are scaled on the width of the major anabranches. The dominant bedforms are large dunes scaled on the third order sub-channels of the major anabranches. Sustained right bank erosion has occurred during the last 35 years, with average rates of about 90 m per year. The left bank shows both erosion and accretion that together produce relatively low rates of net movement. Erosion is faster in island reaches and slower in nodal reaches. Recognition of the geomorphic controls of bank erosion allows its spatial distribution to be related to the development of the braided pattern of the river and a tentative hypothesis is proposed to explain recent trends in both bankline movement and the evolution of the channel planform pattern.

Network echo canceller

Abstract: An echo canceller and method for cancelling in a return channel signal an echoed receive channel signal where the echoed receive channel signal is combined by an echo channel with an input return channel signal. The echo canceller has a first filter which generates first filter coefficients, generates a first echo estimate signal with the first filter coefficients, and updates the first filter coefficients in response to a first filter control signal. A first summer subtracts the first echo estimate signal from a combined return channel and echo receive channel signal to generate a first echo residual signal. A second filter generates second filter coefficients, generates a second echo estimate signal with the second filter coefficients, and updates the second filter coefficients in response to a second filter control signal. A second summer subtracts the second echo estimate signal from the combined signal to generate a second echo residual signal, and provides upon the return channel the second echo residual signal. A control unit determines from the receive channel signal, the combined signal, and the first and second echo residual signals, one of a plurality of control states wherein a first control state is indicative of a receive channel signal above a first predetermined energy level, wherein when the control unit is in the first control state it generates the first control signal and generates the second control signal when at least one of a first energy ratio of the first echo residual signal and the combined signal and a second energy ratio of the second echo residual signal and the combined signal exceed a predetermined level.

Multicarrier modulation transmission system with variable delay

Abstract: A transmission system using multicarrier modulation applies FECC (forward error correcting code) coding and codeword interleaving differently to input signals from a plurality of different data channels to produce encoded data signals having different reliabilities and different coding delays. Bits of encoded data signals having relatively less delay are allocated to carriers that are subject to relatively more attenuation and/or channel noise, and hence that are allocated fewer bits for transmission in each symbol period, to reduce the effects of impulse noise. The data channels can comprise video, data, and control channels transmitted on an ADSL (asymmetric digital subscriber line) two-wire telephone line.

Method and apparatus for time-division plasma chopping in a multi-channel plasma processing equipment

Abstract: A multi-switch processing methodology and a multi-channel time-division plasma chopping device (10) for in-situ plasma-assisted semiconductor wafer processing associated with a plasma and/or photochemical processing equipment. The device (10) comprises a main transfer channel (72) associated with the processing reactor for transferring process gas and activated plasma mixtures into the reactor. A plurality of gas discharge channels (18, 22, 26, and 30) associate with the main transfer channel (72) for independently directing various gases and activated plasma combinations to main transfer channel (72). Process excitation sources (16, 20, 24 and 28) associate with at least one of said gas discharge or activation channels to independently and selectively activate process gases and to control gas activation and flow from the discharge channels to the main transfer channel (72). The method of the present invention performs multi-channel time-division plasma chopping by independently and selectively generating plasma or activated species using a plurality of remote plasma generation process energy sources (16, 20, 24, and 28) associated with the semiconductor wafer fabrication reactor.

Segregation method of dynamic channel allocation in a mobile radio system

Abstract: A method for adaptively allocating channels for connections between base station and mobiles is disclosed. The channels accessible to the base stations for establishing connections with mobiles are ranked in at least one priority list based on transmission loss intervals. Each channel is ranked in the priority list according to their success at previous connections. The amount of power required for a channel allocated from a list associated with a low transmission loss can be set lower thereby reducing the interference associated with the channel and increasing system capacity. A self planned system evolves where channels are allocated for connections based on their past connection history. Thus, the selection of channels which may interfere with calls in neighboring cells or which may suffer substantial interference from a neighboring base is avoided.

Channels with Side Information at the Transmitter

Abstract: In certain communication systems where information is to be transmitted from one point to another, additional side information is available at the transmitting point. This side information relates to the state of the transmission channel and can be used to aid in the coding and transmission of information. In this paper a type of channel with side information is studied and its capacity determined.

Control method and apparatus for wireless data link

Abstract: Methods and apparatus for operating an optical communications system having at least two communicating entities (10,12) In accordance with a method of the invention a first step transmits communication link control information from a first entity to a second entity over a first optical channel having a first data bit rate Responsive to the transmitted communication link control information, a second step of the method transmits data information from the second entity to the first entity over a second optical channel having a second data bit rate that is greater than the first data bit rate The first optical channel is preferably a relatively low-bandwidth diffuse transmission infrared radiation channel The second optical channel is preferably a relatively high-bandwidth infrared channel One of the entities is a network adapter coupled to a wired network The network adapter is preferably ceiling mounted The other entity may be a mobile data processor A plurality of mobile data processors may be served by one network adapter

User interface for defining and automatically transmitting data according to preferred communication channels

Abstract: A user interface to automatically distribute information to a receiver on a network using devices (such as printers and facsimile machines) and communication channels (such as electronic mail) defined in a receiver profile. The receiver profile establishes the properties and mode for receipt of information for receivers on the network and the profile is published in a network repository for all network users or is accessible by selected groups or individuals on the network. Receivers have additional control over network senders by defining an information filter which further controls sender channel access (to a receiver) by defining some channels as having priority of access such as direct or delayed access, as well as selectively permitting senders to override the receiver profile. Consequently, receiver profiles provide a variable receiver definable link to senders using multiple forms of media as well as multiple hardware platforms and network configurations.

Dynamic regrouping in a trunked radio communications systems

Abstract: In a trunked radio frequency communications system, a dynamic regrouping scheme includes an effective user interface, automatic support of multi-site systems, the capability to program individual radio transceivers with multiple new groups dynamically, a fast rate of reconfiguration, instantaneous switch over to prevent radios from residing in immature groups, and a satisfactory mode of operation should the site controller (or site controllers in non-fault tolerant systems) fail. Some of the dynamic regrouping features includes unlimited prestored plans and source and destination groups per plan, regrouping at the plan or destination group level, an advanced user interface, automatic support of multiple sites, fast regrouping at the rate of over 30 radios per second while reducing loading on the system control channel, and fast activation/deactivation. Each plan can be immediately activated or deactivated and users are effectively regrouped together. An alternate control channel is used to regroup transceivers to avoid undue main control channel loading and to increase rate of regrouping.

Optimal detection of discrete Markov sources over discrete memoryless channels/spl minus/applications to combined source-channel coding

Abstract: The authors consider the problem of detecting a discrete Markov source which is transmitted across a discrete memoryless channel. Two maximum a posteriori (MAP) formulations are considered: (i) a sequence MAP detection in which the objective is to determine the most probable transmitted sequence given the observed sequence and (ii) an instantaneous MAP detection which is to determine the most probable transmitted symbol at time n given all the observations prior to and including time n. The solution to the first problem results in a "Viterbi-like" implementation of the MAP detector (with Large delay) while the latter problem results in a recursive implementation (with no delay). For the special case of the binary symmetric Markov source and binary symmetric channel, simulation results are presented and an analysis of these two systems yields explicit critical channel bit error rates above which the MAP detectors become useful. Applications of the MAP detection problem in a combined source-channel coding system are considered. Here, it is assumed that the source is highly correlated and that the source encoder (a vector quantizer (VQ)) fails to remove all of the source redundancy. The remaining redundancy at the output of the source encoder is referred to as the "residual" redundancy. It is shown, through simulation, that the residual redundancy can be used by the MAP detectors to combat channel errors. For small block sizes, the proposed system beats Farvardin and Vaishampayan's channel-optimized VQ by wide margins. Finally, it is shown that the instantaneous MAP detector can be combined with the VQ decoder to form an approximate minimum mean-squared error decoder. >

Comparison of lightning return‐stroke models

Abstract: Five return-stroke models, each allowing the use of measured channel-base current and return-stroke speed as inputs for the computation of channel current distribution and remote electric field, ar ...