Showing papers on "Communication channel published in 1977"

A survey of multi-way channels in information theory: 1961-1976

Abstract: The advances in the area of multi-way channels during the period 1961-1976 are described Shannon's two-way channel, the multiple-access channel, the interference channel, the broadcast channel, and the relay channel are treated successively Only channel coding aspects are discussed Thirty-nine open problems are mentioned

Two-user communication channels

Abstract: A discrete memoryless channel with two inputs and two outputs, called a two-user channel, is studied under the communication situation where only separate messages are allowed to be sent between two source-user pairs. An outer bound to the capacity region is obtained by a method similar to that used by the author for the broadcast channel. Two extreme cases of two-user channels are discussed: separate channels and incompatible channels. Degraded two-user channels are introduced and studied in detail; in particular, an achievable region is obtained by combining two regions that correspond to the two different modes of transmission. This idea is extended to the general two-user channel where an achievable region for the general channel is obtained by random coding arguments.

A Quantitative Stratigraphic Model for Alluvium, with Special Reference to Channel Deposit Density and Interconnectedness

Abstract: Channel deposit density and interconnectedness within a ‘matrix’ of overbank fines in stratigraphic sections through alluvium are inversely related to the rates of contemporary channel avulsion and floodplain accretion and to the width of the alluvial plain. Simulated sections through alluvium generated by random channel avulsions and residence intervals reveal spurious local concentrations of channel deposits. Such concentrations may be given misleading non-random interpretations in stratigraphic or exploration schemes based upon incomplete exposures or sparse borehole data.

Stability and Optimal Control of the Packet Switching Broadcast Channel

Abstract: The purpose of this paper is to analyze and optimize the behavior of the broadcast channel for a packet transmission operating in the slotted mode Mathematical methods of Markov chain theory are used to prove the inherent lnstablhty of the system If no control is apphed, the effective throughput of the system will tend to zero tf the population of user terminals ~s sufficiently large Two classes of control pohcles are examined, the first acts on admissions to the channel from active terminals, and the second modifies the retransmlss~on rate of packets In each case sufflc~ent conditions for channel stability are given. In the case of retransm~sslon controls it is shown that only pohcles which assure a rate of retransmlsslon from each blocked terminal of the form off = 1/n, where n is the total number of blocked terminals, will yield a stable channel It ts also proved that the optimal pohcy which maximizes the maximum achievable throughput wtth a stable channel IS of the formf = (1 - k)/n Simulations illustrating channel lnstabdlty and the effect of the opnmal control are prowded

Low-power, infrared information transmission system

Abstract: A low-power infrared information transmission system, the transmitter of which is compact, portable and capable of being powered by a low-voltage battery power source for an extended period of time, utilizes a unique infrared light pulse position modulation technique. The system is capable of transmitting information from a DC signal to a relatively high frequency AC signal. The system is utilized, for example, to transmit medical information from medical electrodes affixed to a patient via a portable infrared transmitter to a receiver unit which monitors and analyzes the patient's condition; to provide a remote control unit such as the controller for a video game or a TV on/off/channel selector, and, to provide a portable communications device such as a portable microphone or telephone set.

Long-Range Acoustic Communication in Anurans: An Integrated and Evolutionary Approach

Abstract: Acoustic communication constitutes an important and conspicuous part of the breeding biology of most anurans: in the establishment and maintenance of territories by males, in facilitating the attraction of conspecific mates to males, in courtship, and in the identification of sex and reproductive state. The aim of this review is to examine the long-range acoustic communication system of anurans through an integrated and evolutionary approach, and to consider the constraints on the system in the context of reproduction. A useful framework on which to build such an approach is provided by the model of a communication system initially developed by Shannon and Weaver (1949), and applied to biological systems by Cherry (1957), Johnston (1976), Moles (1963) and others. This biocommunication system consists of four main elements: the common repertoire (set of signs), the source (emitter or transmitter),the communication channel and associated noise, and the destination or receiver (Fig. 1). Each functional subsystem, emitter complex and receiver complex, is normally contained within the structure of one individual. A message is selected from the common repertoire, encoded and introduced into the channel as a signal. Perturbations of the channel (noise) tend to reduce the intelligence of the signal (information content), which is subsequently accepted by the receiver, decoded and compared with the contents of its repertoire. The result is an output that completes the bio-communicative sequence. The incorporation of redundancy into the message, through synonymy or repetition, helps to overcome the problem of a noisy channel, but at the expense of energy, time and transmission rate.

Delay Analysis of a Time Division Multiple Access (TDMA) Channel

Abstract: The delay performance of a Time Division Multiple Access (TDMA) channel for transmitting data messages is considered. The channel is assumed to be fixed assigned to a station with unlimited buffer capacity and Poisson message arrivals. Each message gives rise to one or more packets for transmission into fixed-length time slots. The steady-state probability generating function of the queue size is derived. A formula for the expected message delay is given. The analysis is then generalized to a nonpreemptive priority queue discipline; expected message delay formulas are given for the priority classes.

Statistical multiplexing system for computer communications

Abstract: A statistical multiplexing system is provided for computer communications, in which asynchronous user messages are transmitted from the individual terminals to the central processor, or other remote location, in random order. The messages are statistically multiplexed, with time slots being assigned in the communication channel as each message is received from the terminals, and with no time slots being assigned for idle periods, which greatly increases channel utilization. A buffer memory is required in the system to temporarily store messages from the terminals at statistical peaks. To improve channel efficiency, several characters for the same terminal may be collected together in the system to form an addressed data sub-block so as to reduce address label requirements. These sub-blocks are assembled into multiplexed data blocks by a microprocessor and stored in the buffer memory. To relieve the microprocessor load, data blocks are transferred from the memory to the transmitter via a direct memory access facility for transmission over the communication channel to the desired destinations. Input rejection controls are provided to avoid overflow of the buffer memory. A demultiplexer is provided in the system which handles multiplexed data blocks received from the remote location and which transfers the received blocks under the control of the microprocessor to the buffer memory by way of the direct memory access facility. The microprocessor initiates positive and negative acknowledgment signals which are sent to the remote location, and it then demultiplexes the correctly received multiplexed data blocks and transfers them to the appropriate output terminal interfaces for distribution to the terminals. The multiplexer is capable of multiplexing messages from both asynchronous and synchronous input terminals. The microprocessor schedules and multiplexes data blocks from synchronous terminals and from asynchronous terminals over the common communication channel to one or more remote locations.

A Passband Data-Driven Echo Canceller for Full-Duplex Transmission on Two-Wire Circuits

Abstract: A digitally-implemented echo canceller operating at a rate greater than twice the highest passband frequency is proposed for fullduplex data transmission on a two-wire circuit. Located at each end of the communication circuit, the cancellers operate independently of the local receivers and do not require synchronization of the two data stations. Economies in storage and A/D conversion, in comparison with voice-type cancellers described in the literature, are achieved by accepting data symbols as reference input instead of samples of the transmitted line signal. Convergence of transversal filter tap weights is demonstrated under a mean-squared error criterion, and use of the real passband error rather than the complex analytic error is found to lead to the same residual error at the expense of a doubled convergence time. An operational protocol and adaptation algorithm are proposed which make possible both rapid start-up and slower adaptation during double talking. Provision is made for limiting the number and location of active taps on the transversal filter to those actually necessary for replicating the echo channel, resulting in two transversal filter sections of moderate length separated by a bulk delay. Results from a computer simulation of the proposed canceller are offered to demonstrate that convergence of mean-squared tap-weight error follows the predicted exponential characteristic, that the length of the bulk delay can be determined from a single channel sounding under typical channel noise conditions, and that the use of an averaged-gradient algorithm will allow the canceller to adapt, although slowly, to a change in the echo channel during full-duplex operation.

Joint Source and Channel Coding

Abstract: : The advantages and disadvantages of combining the functions of source coding ('data compression') and channel coding ('error correction') into a single coding unit are considered. Particular attention is given to linear encoders, both for sources and for channels, because their ease of implementation makes their use desirable in practice. It is shown that, without loss of optimality, a joint source/channel linear encoder may be used when the goal is the distortionless reproduction of the source at the destination. On the other hand, it is shown that in general there is an inherent and significant loss of optimality if a joint source/channel linear encoder is used when the goal is relaxed to reproduction of the source within some specified non-negligible distortion. (Author)

Plural channel error correcting methods and means using adaptive reallocation of redundant channels among groups of channels

Abstract: Where data is recorded on logically independent sets of parallel channels or tracks, the correction of error of very long (infinite) length cannot be advantageously treated by conventional coding methods unlike finite length error such as single shot or burst noise. To ensure the correction of channels in error from data recovered from a multi-channel storage medium, a fixed number of channels per set are dedicated to error checking bits. In this invention, more than the usual number of channels in error in any one set are made correctable by adaptively reallocating the unused redundant channels in the other set. This is accomplished by encoding and recording in the first redundant channel in each set vertical parity checks limited to that set while encoding and recording in the second redundant channel of each set, the parity of data taken over both sets of channels in a predetermined positively or negatively sloped direction. With this type of parity information so recorded, then the data obtained from up to three known erroneous channels in any one set may be corrected, provided that two sets together aggregate not more than four channels in error. Advantageously, the vertical and cross-parity checking information can also be used to generate an internal channel-in-error pointer for the first erroneous track in each set. Additionally, this data can be made to yield a second internal channel-in-error pointer in at least one of the sets. Lastly, error patterns are identified upon decoding at the intersection of at least two error syndromes one of which is derived from cross-parity checking bits.

A note on Wyner's wiretap channel (Corresp.)

Abstract: Wyner recently introduced the concept of a wiretap channel and showed that by transmitting at a rate less than capacity on the main link it was possible to keep the wiretapper's information about the entire message equal to zero. It is shown that it is possible to send at capacity on the main link and still keep the wiretapper's information equal to zero on many, large, arbitrary portions of the message.

Combined heat exchanger reactor

Abstract: A one-piece, integral, high strength, combined heat exchanger-reactor comprising a monolithic honeycomb structure wherein the channels thereof are divided into two or more groups; group one carrying one fluid and group two carrying another fluid which differs from the first in composition and/or temperature and/or pressure and/or direction of flow, the main design feature of the combined heat exchanger-reactor (CHER) being that group one channels extend outward parallel to the channel axis and perpendicular to the cross-section of the honeycomb and each channel of this group one being in thermal contact through common walls with channels of group two while each channel of group one is separated from other channels of group one by the intervening voids formed by the presence of the channels of group two. The extended ends of the channels of group one extending from one or both ends of the honeycomb are manifolded at one or both ends so as to form a separation of the entrances and/or exits of the extended group one channels from the recessed group two channels thereby permitting the entry and/or exit of fluid in group one channels while preventing entry of the same fluid into the group two channels thereby permitting the independent passage of different fluids through the different channel one and channel two systems, the common wall which exists between channels of the different groups allowing heat conduction from the fluid in one group of channels to the fluid in the other group of channels. In this manner, very precise concentration and/or temperature control may be maintained over the fluids and/or catalysts which exist in the different channel groups, enabling one to perform complex reactions, either self-induced or catalytic, in the reactor with greatly enhanced yields and/or selectively due to the refined temperature and/or concentration control which is made possible by the present invention.

Variable-viscosity flows in heated and cooled channels

Abstract: An asymptotic description is given of Newtonian fluid flow in a channel which is suddenly heated or cooled. The viscosity is assumed to be purely a function of temperature. The asymptotic approximation is that the downstream viscosity at the channel wall differs by an order of magnitude from that in the upstream flow. Although we make the drastic assumption that viscous dissipation is negligible, we can analyse flows where the viscosity depends either algebraically or exponentially on the temperature.

Method of assigning a radio channel to a calling mobile body of mobile communication system and radio channel assigning system therefor

Abstract: The service area of the system is divided into a plurality of overlapping radio zones and a mobile-system base station is installed in each zone. The mobile-system base stations are assigned with a common control channel and each station is assigned with a plurality of speech channels which are commonly controlled by the control channel. Where a mobile body originates a transmission, the intensities of signals received by respective stations which have resulted from a signal transmitted by the mobile body are compared so as to designate an idle speech channel of a station which has received a signal having the maximum intensity among mobile-system base stations including the idle speech channel.

Method for providing virtual addressing for externally specified addressed input/output operations

Abstract: A method of addressing memory in a digital computer where a plurality of devices are connected to a single input/output channel to the digital computer communicate with the digital computer by externally specifying the memory address of the data word or words to be transferred to or from the digital computer More specifically, the invention provides a method for treating the externally specified address coming from one of the multiple devices external to the digital computer as a virtual address Thus, an input/output process operating in the digital computer may operate within the digital computer's system virtual address space This method allows input/output processes to be able to utilize the address mapping subsystem of the central processor of the digital computer The method of memory addressing utilizes a subchannel page table for each one of the multiple devices connected to one input/output channel in addition to a channel page table utilized for each individual input/output channel

A General Model for the Performance of Disk Systems

Abstract: The performance of a disk system is often measured in terms of the length of the waiting line or queue of requests for each of the system's spindles. Thus it is natural to formulate and analyze queueing models of disk systems. While most disk systems have certain characteristics, such as channel interference and concurrent seeks, in common, previous analyses have always been begun from scratch, without exploiting this commonality. We introduce a general queueing model for disk systems, which incorporates the characteristics common to most disk systems, and use it in the approximate analyses of models of the IBM 2314 and 3330 disk systems. Comparisons with simulation statistics show that the approximations made are very good over a wide range of arrival rates and system parameters. We also show how to use the analytic results to investigate performance differences between devices.

Control system providing for the transfer of data in a communications processing system employing channel dedicated control blocks

Abstract: Data is transferred between a main memory in a data processing system and communication channels under the control of communications control blocks provided in an auxiliary memory, each of which control blocks includes a starting address, range and status information so as to enable the transfer of data to data blocks included in the main memory as indicated by the starting address in the control blocks. A predetermined number of control blocks is allocated in the auxiliary memory for each communications channel and the transfer of all such data is performed utilizing as many of the predetermined number of control blocks as required for the channel until the transfer is complete as indicated by the last such control block utilized in the transfer. Control blocks are loaded in the auxiliary memory under control of the central processor of the system and are periodically accessed by the processor to determine the status of data transfer operations. Circuits are provided for preventing the loading in the auxiliary memory of more than the predetermined number of control blocks for a channel and for preventing the execution of a status inquiry for a channel when no control blocks for that channel are in the active state.

Synchronous detection tracking of video disc

Abstract: A videodisc system utilizes a beam of light which tracks the center of an interrupted spiral information channel. The light beam is "dithered" from side to side of the channel in order to determine the relative "direction" of a beam deviating from the center of the channel. The beam oscillates by approximately one-third of the width of the channel. By multiplying the returned signal by the drive signal, a signal is derived whose mean value is positive on one side of the track, negative on the other side and zero when in the center of the track.

An Approximate Analysis of Delay for Fixed and Variable Length Packets in an Unslotted ALOHA Channel

Abstract: In this paper we compute the mean delay for an unslotted ALOHA random access channel for both fixed and variable length packets. The analysis is based on the concept of a user cycle and obtains steady state results. When the channel is "stable", the results seem quite accurate. The input parameters to the model are the number of users, the mean think time, and mean retransmission time. The model yields total traffic, throughput and delay but only the latter is emphasized here. Because of the steady state nature of the analysis, no information is obtained on stability. The results are verified by simulation.

Stepped-bed morphology in arid gravelly channels

Abstract: The stepping phenomenon indicates systematic channel-bed variations that are not identical to the well-known pools and riffles. Channel beds in the Dead Sea area demonstrate that the main elements in a stepped bed are the regular and the rapid segments, which constitute distinct populations. The bed material of the stepped channel is heterogeneous in size, but significant uniformity prevails within the segment types. The cyclic spacing of the segment types deviates clearly from that of pools and riffles in that it is at closer intervals. The coarser the sediment, the more pronounced the segmentation. Stepping may produce variations in flow velocities from subcritical to supercritical and causes the overall flow regime to vary. Widening and braiding of the channels downstream does not replace the steps. Megasteps form in the canyons but are not cyclic. Conditions favoring stepping indicate a coarse fluviatile environment.

On a special class of wiretap channels (Corresp.)

Abstract: The special class of wiretap channels for which a certain quantity \Gamma(R) is constant is examined, and some useful characterizations of its members are given. It is shown that for "symmetric" wiretap channels, \Gamma(R) is equal to the difference between the capacities of the main channel and the channel from the sender to the wiretapper.

Double boron implant short-channel MOSFET

Abstract: Threshold voltage and current-voltage characteristics are presented for a double boron-ion-implanted-n-channel enhancement MOSFET device for high speed logic circuit applications. A 15-Ω. cm-high resistivity p-type

Automatic flight control system with operatively monitored digital computer

Abstract: A dual channel, fail-operative automatic flight control system is disclosed in which each channel includes a totally monitored digital computer for operating upon sensor input data to provide command signals to the aircraft surface control actuators. The operative program for each computer is repetitively executed to effectively provide continuous control. The program is organized into a plurality of tasks to be performed by the computer with program segments associated with the respective tasks and a program routine for determining that all of the tasks have been completed for each program iteration. If non-completion of a task is detected, the program enters a failure routine which stops execution of the program. The program also includes a routine for generating a dynamically varying pattern in accordance with the continuously reiterated execution of the program. The system includes a detector for determining that the correct pattern is being generated and shuts down the system upon detecting a failure of the computer to generate the correct pattern. All of the instructions of the computer instruction repertoire operatively utilized in the system are employed to control the program flow whereby failure of an instruction to operate properly will cause the program to flow into an abnormal path thus causing the task completion program routine to indicate failure and stop the computer. Additionally, the system utilizes further techniques such as dual data and program memory banks to perform redundant computations, all of the techniques in combination providing an automatic flight control system with two autonomous fail-passive channels, the two channels providing a fail-operative system.

Multiplex/demultiplex apparatus

Abstract: An encoding scheme for simplifying frame acquisition and access to an auxiliary channel information bit stream and apparatus for implementing same. A pair of incoming data channels are multiplexed onto three communicating data channels wherein one of the channels contains overhead bits and high speed data bits, a second channel contains auxiliary channel bits and high speed data bits and a third channel contains only high speed data bits. With this format, the operational frequency of the frame acquisition circuit is reduced compared to multiplexing to a single channel and the channel containing only high speed data can be used directly for bit error rate (BER) measurements.

A Survey of Multi-Way Channels in Information Theory:

Abstract: The advances in the area of multi-way channels during the period 1961-1976 are described. Shannon's two-way channel, the multiple-access channel, the interference channel, the broad- cast channel, and the relay channel are treated successively. Only channel coding aspects are discussed. Thirty-nine open problems are mentioned.