Showing papers on "Communication channel published in 1982"

On the transport and modification of Antarctic Bottom Water in the Vema Channel

Abstract: The Verna Channel is a deep passage across the Rio Grande Rise in the South Atlantic through which Antarctic Bottom _Water (AABW) must flow · on its way northward from the Argentine Basin to the Brazil Basin and eventuafly into the North Atlantic. Both dynamic computation and direct current measurement based on recently acquired data indicate that the volume transport of AABW is about 4 X 10° m/sec northward with a standard deviation of about 1.2 X 10° m/sec. There are no known_·exits for AABW below 1 •c out of the Brazil Basin and it is estimated by heat flux balance that if AABW leaves this basin across isopycnals, a diffusion rate of 3-4 cm/sec so directed is required. There is a sharp water mass transition between the two basins across the Rio Grande Rise with J\\ABW in . the Argentine Basin being distinctively fresher and_ colder in the potential temperature range from 0.2 •c to 2.0°C at the. same density. Cold tongues of fresh. water · iidvected into the Verna Channel may be thoroughly ·mixed by lateral eddy diffusion at a rate estimated to be 4 X 10° cm/sec. This process demands a supply of Brazil Basin AABW. from the north consistent with an observed weak southward flow to the east of the much more intense northward jet. Isopycnals show a reversal in slope with·depth within the channel (but not outside) such that the coldest water is in the west at shallow AABW depths but in the. east near the bottom. East of the channel axis there are thick bottom boundary layers which are nearly homogeneous in the vertical but horizontally stratified. We suggest a dynamical, nonmixing, mechanism for producing these features. Dissolved silicate measurements reveal a filament of low concentration, presumably North Atlantic Deep Water, which is located over the channel axis at 2500 m depth. This is some 1000 m above the Rio Grande Rise and 2000 m above the Channel floor.

Multiple-access channels with different generalized feedback signals

Abstract: This paper is concerned with a communication channel with two senders and one receiver, in which each sender observes a private feedback signal. The two feedback signals are not necessarily equivalent to or derived from the signal observed by the receiver. An achievable rate region is demonstrated for this multiple-access channel by means of a new superposition coding scheme. In particular it is shown that a rate region, previously obtained for the multiple-access channel with "perfect" feedback to both senders, remains achievable when the feedback connection to one of the senders is eliminated.

Description of Fasnet — A unidirectional local-area communications network

Abstract: Fasnet is an implicit token-passing, local-area network aimed at supporting high data rates and carrying a wide mix of traffic (data, voice, video, and facsimile). Transmission is unidirectional with stations attaching to the medium passively via directional couplers. A link consists of two lines, one to carry traffic in each direction. Unidirectional transmission provides the potential for efficient operation at high data rates, while the passive medium provides the potential for high reliability. We describe the physical configuration and the protocol and give channel utilization for the condition of continuously queued sources. Mechanisms to control the access of various traffic types are described. Finally, the interconnection of multiple Fasnets is studied for one particular configuration, a ring.

A new frequency channel assignment algorithm in high capacity mobile communication systems

Abstract: A new algorithm for frequency channel assignment in mobile radio communication is proposed. The algorithm uses flexible fixed channel assignment which enables the calls having all their nominal channels busy to borrow channels from the neighboring cells provided that co-channel interference will not result. The borrowed channel cannot be used in three interfering cells; therefore reassignment strategy is used when a call is terminated on a nominal channel to switch a call in progress in a borrowed channel to that nominal one and set free the borrowed channel in the three interfering cells. Thus the traffic carried on borrowed channels is minimized. Also different call switching strategies are proposed to give priority to some channels to be used by the nominal cells and other channels to be borrowed by neighboring cells. These strategies considerably reduce the blocking probability. A simulation study of the algorithm was carried out on 49 hexagonal zones having uniform traffic density. Also a combined telephone and dispatch traffic was included in the simulation study. The results showed that the new algorithm is better than the other channel assignment schemes. This can be applied in high capacity mobile communications systems to utilize the spectrum efficiently.

Measuring user attitudes in MIS research: a review

Abstract: Management information system (MIS) user attitude measurement and research has been motivated by two distinct perspectives, termed the implementation perspective and the information perspective. A survey of the most significant work based on these perspectives is presented. The consensus of this work is that MIS attitudes are related to MIS use, broadly speaking. However, the usage-relevant components of user attitudes are as yet not well understood. More refined attitude concepts and measures are needed. One such concept, that of a user's channel disposition , is advanced as part of a suggested research direction.

Perennial-streamflow characteristics related to channel geometry and sediment in Missouri River basin

Abstract: Geometry, channel-sediment, and discharge data were collected and compiled from 252 streamflow-gaging stations in the Missouri River basin. The stations, with several exceptions, have at least 20 years of streamflow records and represent the complete ranges of hydrologic and geologic conditions found in the basin. The data were analyzed by computer to yield simple and multiple power-function equations relating various discharge characteristics to variables of channel geometry and bed and bank material. The equations provide discharge as the dependent variable for the purpose of making estimates of discharge characteristics at ungaged sites. Results show that channel width is best related to variables of discharge, but that significant improvement, or reduction of the standard errors of estimate, can be achieved by considering channel-sediment properties, channel gradient, and discharge variability. The channel-material variables do not have uniform effects on width-discharge relations and, therefore, are considered as sediment-data groups, or stream types, rather than as terms in multiple power-function equations. Relative to streamflow, narrowest channels occur when streams of steady discharge transport sufficient silt and clay to form stable, cohesive banks but have a small bed-material load of sand and coarser sizes. Stable channels also are associated with relatively large channel gradients, relatively large channel roughness, and armoring of bed and bank by coarse particle sizes. The widest, most unstable channels are ones that apparently transport a large bedmaterial load of sand sizes. The downstream rates of change of width with discharge reflect these trends, indicating that a given bed-material load necessitates a minimum width for movement of tractive material. Comparisons of standard errors of estimate given here with similar results from regional studies are variable. It is assumed, however, that a benefit of this study is that the use of the equations is not limited to the Missouri River basin. Besides the principal utility of estimating discharge characteristics of ungaged streams, the equations given here can be used for the design of artificial channels and can be used as a basis of predicting channel changes resulting from upstream alterations of the basin or channel. INTRODUCTION Numerous studies have related the geometry of alluvial stream channels to the amount and variation of discharge, sediment characteristics, climate and vegetation, and various basin characteristics. In recent years, a practical result of these studies has been the use of channel-geometry measurements to estimate the discharge characteristics of ungaged streams. By correlating variables of channel size and shape to specified flows at gaged sites, the relations, generally expressed as power-function equations, can provide estimates of discharge for the same recurrence frequencies at ungaged sites. Because a value of streamflow is determined, discharge is treated as the dependent variable. Therefore, the channel-geometry technique is the use of channel measurements as an indirect means of evaluating streamflow characteristics at a site. The channel-geometry technique differs from that of hydraulic geometry by relying on measurements taken from an identifiable geomorphic reference point or level in the channel section rather than from the water surface. The size and shape of the channel cross section are assumed to be the integrated resultant of all discharges, water and sediment, conveyed by that channel (Pickup and Rieger, 1979, p. 41; Osterkamp, 1979a, p. 2). Because it is based on channel rather than basin characteristics, the technique provides discharge estimates more closely related to the measured variables than do many of the older indirect techniques of estimating discharge. Most of these older methods use either drainage area, precipitation, and other basin characteristics as a means of evaluating discharge, or they rely on correlation methods of transferring data from gaged sites to ungaged sites in contiguous or nearby basins.

Method and apparatus for scrambling and unscrambling data streams using encryption and decryption

Abstract: Methods and apparatus for scrambling and unscrambling a plurality of data streams having differing data, on a plurality of signal channels, are taught. The data streams may be television programs or other signal information, transmitted in a frame-by-frame manner with discrete synchronizing information, and where some of the data streams may be high priority such as pay-TV program material. All of the data streams are synchronized, an encryption key code is imposed on them, and a data package containing an identifier code for each data stream and a routing code is generated, so that each data stream is assigned at any instant of time to a specific one of the plurality of signal channels. The data package is encrypted in each data stream by being inserted at a specific place therein relative to the synchronizing information. At any authorized receiver the encryption key code is captured and used to decrypt the encrypted data package so as to decode the identifier and routing codes thereof, whereby a given data stream may be tracked no matter on which transmitted channel it appears at any instant of time. Several embodiments for controlling a local oscillator so as to track a given data stream, are taught.

Capacity Consideration in Reliability Analysis of Communication Systems

Abstract: This paper presents a simple method for deriving a symbolic reliability expression of some practical systems such as a communication system having fixed channel capacities of its links, a power distribution system having limited power ratings of its power lines, a transport system which might not allow traffic more than a particular value, or a chemical system in which oil or gas flow through pipes is permissible only up to some safe limits. A system is good if and only if it is possible to transmit successfully the required capacity from source node to the sink node. This paper defines a group as a set of branches such that success of these branches ensures system success, as defined above. All such groups are obtained from a knowledge of the minimal paths of the system graph. The method is computerized and implemented on DEC-20 computer. Two examples are considered and their solutions presented to illustrate the technique.

Bandpass Signal Sampling and Coherent Detection

Abstract: Coherent detectors in radar and communications receivers are generally implemented in the form of two parallel baseband channels which form in-phase (I) and quadrature (Q) components of a received RF/IF signal. Phase errors of several degrees due to imperfect matching of these separate channels limit the performance achievable from signal processors such as moving target indicators (MTI), coherent integrators, Doppler filters, antenna array processors, and coherent sidelobe cancellers. Thus methods in which a single analog to digital (A/D) converter samples and digitizes the IF signal directly, eliminating the need for IF to baseband conversion, have been of recent interest and are the subject of this paper. To obtain accurate coherent detection from IF samples taken near the Nyquist rate requires interpolation based upon a number of stored samples. An algorithm derived from sampling theory is defined and used to demonstrate accurate reconstruction of the original IF signal from digitized samples. In-phase and quadrature components of the signal are shown to be available from processed samples with demonstrated phase errors less than 0.2°.

The feedback capacity region of a class of discrete memoryless multiple access channels (Corresp.)

Abstract: The capacity region of a class of discrete memoryless multiple access channels with feedback is determined, including as a special case the channel considered by Gaarder and Wolf.

Carrier Sense Multiple Access with Message-Based Priority Functions

Abstract: We consider packet communication systems of the multiaccess/broadcast type, exemplified by ETHERNET [1] and single-hop ground radio networks [2], in which all communicating devices share a common channel which is multiaccessed in some random fashion. Among the various random access schemes known, carrier sense multiple access (CSMA) has been shown to be highly efficient for environments where the propagation delay is short compared to the transmission time of a packet on the channel [3]-[5]. In this paper, we describe a new version of CSMA which incorporates message-based priority functions, referred to as prioritized CSMA (P-CSMA). The scheme is based on the principle that access right to the channel is exclusively granted to ready messages of the current highest priority level. It can be made preemptive or nonpreemptive, and is suitable to fully connected broadcast networks with or without the collision detection feature. We analyze the p-persistent protocol of P-CSMA with two priority levels and derive the throughput-delay characteristics for each priority class. Finally, we discuss numerical results obtained from the analysis and from simulation, and thus evaluate the effect of priority functions and preemption on the throughput-delay characteristics for each class.

One way interactive multisubscriber communication system

Abstract: Interactive programming may be provided by the system (26) of the present invention which can enable both manual and automatic selection of various interactive responses from simultaneously transmitted programming on different channels. In a cable television system (20), the channels used to transmit the interactive programming are the midband channels with the selected response being treated by the system converter (26) to convert the individually selected response to a common assigned television channel frequency for ultimate reception and display on the subscriber's television (24, 22). Automatic selection may then be accomplished by the provision of a selection signal from the logic network (48) to a local oscillator (52) which, in turn, generates a beat frequency to be mixed in a mixer (54) with the various midband channel frequencies to convert the selected midband channel frequency to the assigned television channel frequency. The selection signal is either manually selected as a result of the choice or selection manually input by the subscriber via a keyboard (50) or automatically generated as a result of the pulse count value accumulated in memory (64, 65, ) based on the weighted signal value of prior responses. Various band pass filters (36, 58, 60) and switches (34, 56) are employed to pass the appropriate signals in the interactive and conventional programming modes of the system (26).

Optimal asymmetric error detecting codes

Abstract: Some of the properties of codes capable of detecting errors when used on a binary asymmetric (or Z) channel are examined and in fact the maximum cardinality codes are determined. These results are extended to the q-ary asymmetric channel introduced by Varshamov (1973), IEEE Trans. Inform. Theory 19, 92–95) .

Time division multiplex switching network for multiservice digital networks

Abstract: Asynchronous time division multiplex switching network for multi-service digital network. It comprises a plurality of time division multiplex bidirectional highways, a plurality of data transmit and receive stations connected to and associated with said bidirectional highways and a plurality of buses connecting these stations therebetween. The highways convey digital data arranged in a hybrid frame including a time slot part formed of a plurality of time slots containing sample words having a variable number of bits and a packet channel part formed of a plurality of channels for packets having a variable number of bits. Means are provided in each transmit station for converting the sample words in the time slot part and the packets in the packet channel part into a message including the sample word proper, its number of bits, the address of the terminating highway, the number of the time slot in the hybrid frame and a first indicator marking the sample words and, the packet proper, its number of bits, the address of the terminating highway, the number of the packet channel in the hybrid frame and a second indicator marking the packets. The messages are then transmitted and in the receive station, the items added to form the messages are deleted, leaving only the sample words and packets.

Autopilot flight director system

Abstract: Each of three redundant sensor sets (16, 18, 20) provides flight status data to a corresponding one of three flight control computers (22, 24, 26). Each of the computers shares sensor data as well as computed control surface command signals with all other system computers. The command signal outputs from two computers are transduced (34, 36) to mechanical commands which are combined and applied to the appropriate aircraft control surface. The remaining computer output is a mathematical model of the mechanical outputs of the other channels. Fault detection and isolation is accomplished by cross channel comparing sensor data, command signals, model/surface position information and by incorporating channel monitors for detecting generic or common mode flight control computer failures.

Drip irrigation apparatus

Abstract: Drip irrigation apparatus including a main water flow channel having associated therewith along a length thereof a plurality of pressure-controlled drip irrigation emitter units and at least one secondary water flow channel extending generally parallel to the main water flow channel and receiving water from at least one of the plurality of pressure-controlled drip irrigation emitter units, the at least one secondary water flow channel having water outlets disposed along the length of the main water flow channel, intermediate the plurality of pressure-controlled drip irrigation emitter units.

Method and apparatus for speech recognition and reproduction

Abstract: Speech signal analysis for data reduction, as stored for synthesis or recognition, is improved by features including: digital spectral analysis; reduction of channel data and bit allocation by selective summation of groups of contiguous data; using the mean average of the log amplitude to find the deviation for each channel; also using the instaneous shape of the mean value for each channel for pairs of adjacent frames, all combined to find a feature ensemble for each pair of adjacent frames.

MOSFET with perimeter channel

Abstract: A vertical MOSFET device includes a major surface having an active, gate-controlled portion adjacent to an inactive portion. A gate-controlled perimeter channel is disposed at the boundary between the active and inactive portions.

Applications of a peak detection channel model

Abstract: A computer model of a peak detecting magnetic recording channel has been implemented and used for channel design and performance evaluation. The model predicts raw error rate, ontrack and off-track, as a function of linear density, run-length-limited (RLL) modulation code, write precompensation rules, and tapped-delay-line (TDL) equalizer. It assumes noise additivity and validity of linear superposition. and it bases calculations on a measured disk/electronics noise spectrum and digitized isolated transition readback signals from the data track and adjacent tracks. Details of the model are described, and illustrative applications to RLL (d,k) code selection and pulse slimming equalizer design for a specific channel are discussed.

Disk record reproducer

Abstract: PURPOSE:To obtain a highly efficient control function and at the same time to improve the operability for a disk record reproducer, by presetting a desired number of address data to a prescribed channel to reproduce automatically the corresponding data to be reproduced and then changing optionally the order of reproduction. CONSTITUTION:When a next play switch 313 is not operated, no address designating input is not supplied from a counter 314. Therefore an RAM315 delivers the preset channel data in response to the presetting order and reproduces tha preset music. When the switch 313 is operated in an automatic play mode, the clock inputs are supplied to the counter 314 in response to the operating frequency. At the same time, the address designating inputs are applied to the RAM15 from the counter 314 in response to the number of clock inputs. Then the next channel data obtained by jumping one channel for each clock input is delivered from the channel data of the music which is under reproduction. The preset music is reproduced from the channel data corresponding to the operating frequency of the switch 313.

Packet radio in a Rayleigh channel

Abstract: Statistical multiple access is analysed for a number of independent transmitter-receiver pairs exchanging data packets over a shared mobile-radio channel. Rayleigh fading ‘softens’ the channel, resulting in less packet contentions and higher traffic capacity than for the standard Aloha channel.

On Routing Two-Point Nets Across a Channel

Abstract: Many problems that arise in general channel routing manifest themselves in simpler situations. We consider connecting a set of n terminals on a line to another set on a parallel line across a rectangular channel. We show that in any solution to the problem that (almost) minimizes the width of the channel (i.e. the distance between the lines the terminals reside on), (i) a net may require as many as O(vn) jogs, (ii) no net routed from top to bottom need ever turn upward in the middle. We also present an efficient algorithm to obtain minimal jogging in river routing, and provide necessary and sufficient conditions for conflict cycle resolution. These and other results are presented in the context of a general survey on routing from a combinatorial complexity point of view.

Pulse interference cancelling system for spread spectrum signals utilizing active coherent detection

Abstract: A pulse interference cancelling system for spread spectrum signals utilized in a digital noise coded communications system. The system includes a first and second noise coded signal channel located in a noise coded signal receiver which also includes a demultiplexer for providing a pair of received noise coded signals which were initially generated, multiplexed and transmitted to the receiver. First and second coherent detector means are coupled to both signal channels, the first being directly coupled thereto so that no signal delay exists but the second is coupled to the two signal channels by means of respective first and second variable time delay circuits having a delay substantially equal to the bit width of each digital code as well as a vernier delay which is adapted to delay the phase of any received pulse interference in the respective channel so that it is exactly 180° out of phase with the same undelayed pulse interference. Signal summing means are coupled to the outputs of the two coherent detectors which operate to completely cancel the interference pulse signal while leaving the desired noise coded signal at its peak amplitude.

Coding for the Turbulent Atmospheric Optical Channel

Abstract: In the presence of atmospheric or aircraft boundary layer turbulence, an optical channel may need large amounts of link margin to combat fading and beam spreading. Channel coding can reduce the average transmitter power required for reliable communication. This paper analyzes the performance of a coded PPM optical communication system that suffers log-normal fading during transmission. For moderate turbulence strengths, the coding gain in link margin is shown to be substantial.

Flow Retardance of Submerged Grass Channel Linings

Abstract: AN improved method for determining the flow re-sistance of a grass-lined open channel is introduced. This method relates the flow retardance potential of a grass lining directly to physical parameters normally familiar and available to the design engineer. Retar-dance potential is related to flow resistance through an infinite family of retardance curves, with the traditional *n-VR curves' approximating specific members of this curve family. Use of the relations presented reduces the subjectivity required for flow resistance determinations. The method is applicable for general usage and is especially useful in numerical procedures such as the allowable tractive force method for stability design.

ADF bearing and location for use with ASR and ASDE displays

Abstract: An aircraft locating system identifies on a TV format radar display the position of a specific aircraft based on an RF transmission from the aircraft on an RF channel. The locating system includes at least a pair of receive stations located within several miles of an airport and separated by a base line which is in near proximity to at least one runway at the airport or a theoretical extension thereof. Each receive station includes a passive receiver for determining a bearing angle to a source of RF on the RF channel for generating a signal representative of the bearing angle. The locating system further includes a processor which is responsive to bearing angle signals derived from the receive stations for generating line count and line delay information. The line count and line delay information correlate a position determined by the bearing angle signals from at least a pair of receive stations with a frame of reference of the TV display. The system further includes a video mixer which responds to two different input signals. A first input signal to the video mixer is a scan converted radar return signal. The second input signal to the video mixer is the line count and line delay information. The output of the video mixer is used to drive a video display. The video display, subjected to the two identified inputs can highlight a location identified by the line count and line delay information so that for example a person viewing the display would be able to identify which of perhaps plural radar returns shown on the display is associated with an aircraft which is actively transmitting on the RF channel.

Recycling: A Problem in Reverse Logistics:

Abstract: Using a systems approach, this article looks at recycling as a problem in retrologistics. The role and problems faced by various channel members are discussed. As recycling incentives increase, changes in channel structure will probably occur. Marketing has an opportunity to contribute to the understanding and assessment of future changes.

Tidal power plant and method of operating the same

Abstract: A tidal power plant and method of operating the same are disclosed. In tidal power plants the turbines are arranged in channels between the sea and a storage reservoir. Heretofore known constructions of tidal power plants included relatively complex mechanisms for maintaining the turbine or turbines operating for the maximum amount of time, but generally they have failed to exceed a high overall operating efficiency. The present invention seeks to improve upon prior installations by designing a tidal power plant in which the or each turbine is disposed in a main channel between the sea and the storage reservoir. A connection channel is arranged above the main channel containing the turbine. A shutoff device is located at the reservoir side of the turbine and the connection channel to control and direct the flow of water. One of the described arrangements permits the use of a single shutoff device in the form of a sluice gate operable under pressure in order to open the connection channel and to cut-off the turbine, or vice-versa. A further possible arrangement contemplates total isolation of the working region of the tidal power plant to permit inspection and maintenance work when needed.

Multi-channel redundant processing systems

Abstract: A system having a plurality of redundant channels operating in tight synchronism wherein input information received in one or more of said channels is distributed to all the other channels. The received information in each channel is retransmitted to suitable voter circuitry in each channel so as to provide one or more voted outputs in each channel based on the distributed and retransmitted information from all the channels. The voted outputs from all unfailed channels are substantially identical and the voted output from a failed channel will not be identical to that of the unfailed channels.