Showing papers on "Communication channel published in 1978"

Interference channels

Abstract: An interference channel is a communication medium shared by M sender-receiver pairs. Transmission of information from each sender to its corresponding receiver interferes with the communications between the other senders and their receivers. This corresponds to a frequent situation in communications, and defines an M -dimensional capacity region. In this paper, we obtain general bounds on the capacity region for discrete memoryless interference channels and for linear-superposition interference channels with additive white Gaussian noise. The capacity region is determined in special cases.

Models for channels with memory and their applications to error control

Abstract: Errors encountered in digital transmission over most real communication channels are not independent but appear in clusters. Such channels are said to exhibit memory, i.e., statistical dependence in the occurrence of errors; and thus cannot be adequately represented by the classical memoryless binary symmetric channel. The existence of memory implies additional capacity. To exploit this through efficient coding schemes, it is necessary to describe and model the underlying statistical structure of the error process. This paper reviews various channel models, noting the interaction between channel modeling and error control.

A Hybrid Channel Assignment Scheme in Large-Scale, Cellular-Structured Mobile Communication Systems

Abstract: This paper considers the problem of channel assignment in mobile communication systems, where the service area is divided in hexagonal cells. In particular, a Hybrid Channel Assignment Scheme is studied and certain results are obtained using GPSS simulation of a model 40-cell system.

A heuristic technique for assigning frequencies to mobile radio nets

Abstract: In preparing or revising an RF channel plan for a group of mobile radio nets operating in the same region, the order in which the nets are assigned channels can be crucial to success. One well-known principle for selecting such an assignment sequence is to rank the channel requirements of the various nets in descending order of "assignment difficulty." This paper describes an easily automated heuristic assignment technique in which the channel requirements that prove themselves to be "difficult," through repeated failures to be assigned channels, rise rapidly toward the top of the list of requirements. The heuristic technique is useful in solving complex frequency-assignment problems that involve cochannel, adjacent-channel, spurious and intermodulation interference; nonrepetitive zone structures; fixed pre-existing frequency assignments; and frequency-resource lists that contain gaps and vary from zone to zone.

The Capacity of a Channel of the Poisson Type

Abstract: In the paper, a Poisson type channel is considered and its capacity is found. It is proved that the feedback does not improve the channel capacity.

On degraded Gaussian two-user channels (Corresp.)

Abstract: Several bounds to the capacity region of a degraded Gaussian channel are studied. An outer bound utilizing the capacity region of the corresponding broadcast channel is obtained. Two achievable regions obtained previously are compared, and a region including both is introduced by using frequency division multiplexing.

Color responsive imaging device employing wavelength dependent semiconductor optical absorption

Abstract: An image sensing element in a solid state imaging device is provided with a plurality of superposed channels disposed at respective distances from a light receiving surface of the device, each of such channels having a different characteristic spectral response due to the differential absorption of light by a semiconductor. By so disposing the channels, the device becomes a color imaging sensor having optimized resolution. The top channel, i.e. the channel nearest the surface of the device, may be either a "surface" channel or a "buried" channel, the lower channel(s) being buried channels. Depending upon the design of the element, either electrons or holes may be accumulated as photocharges in respective superposed channels. The color photocharges generated in respective channels of such an image sensing element are simultaneously moved in a plurality of superposed channels by a multiple superposed channel signal handling device such as a multiple channel charge coupled device (CCD), thus the solid state imaging device does not require special timing networks to correct for phase differences between color signals which result from a common point within an image.

Television system scheduler

Abstract: A television receiver includes a chassis having a digital tuner for generating local oscillator signals for tuning the receiver to respective channels in response to binary signals representing corresponding channel numbers and a signal processing unit for controlling at least one characteristic of the receiver such as the sound level, in response to binary signals representing the controllable characteristic. The receiver also includes a microcomputer including a RAM (Random Access Memory) with at least one memory location for storing binary signals representing the present time and a plurality of memory locations for storing binary signals representing future times and channel numbers of channels to be tuned at those times. A control portion of the microcomputer causes binary signals representing the channel number associated with a future time to be coupled to the digital tuner when the present time matches the future time. A keyboard having ten digit keys for generating binary signals representing the decimal digits between 0 and 9 and two characteristic keys to generate binary signal representing an increase and a decrease in the controllable characteristic is provided to enable user control of various operating modes of the receiver. When a user operates digit keys to form a number within a predetermined range of channel numbers, e.g., 2-83, the control portion of the microcomputer causes a channel to be tuned. Subsequently, operation of digit keys within the predeterined range of channel numbers causes the channel to be changed and operation of the characteristic keys causes the controllable characteristic to change. When a user operates digit keys to form a number not within the predetermined range of channel numbers, the control portion of the microcomputer causes power to be decoupled from the chassis. Subsequently, in response to the operation of a predetermined one of the characteristic keys, the control portion causes binary signals generated in response to the operation of the digit keys to be selectively coupled to either the RAM location associated with the present time or to the RAM location for future selections.

Baseband differentially phase encoded radio signal detector

Abstract: A radio signal is applied to an in phase detector channel and a quadrature phase detector channel. Each detector channel includes, in cascade arrangement; an in phase downconverter means for downconverting the received radio signal to a baseband signal; a sampling means for sampling the baseband signal at a predetermined rate; and a matched filter means matched to the symbol waveform and wherein the sample pulses are stored over a predetermined period of time that corresponds to two data symbols. The sum of the pulses for the first data symbol and the sum of the pulses for the second data symbol are compared to determine if there has been a phase reversal between the two data symbols. The outputs of the in phase and quadrature phase channels are summed, which results in demodulation of the encoded data.

A novel approach to digital beamforming

Abstract: For many sonar applications, the sensor outputs of a hydrophone array are sampled at a rate significantly higher than that required for waveform reconstruction when digital beamforming is used. The reason for this is that the number of synchronous, or ’’natural,’’ beampointing directions is proportional to the beamformer input rate. This paper presents an implementation of a digital beamformer that achieves the desired synchronous beams while minimizing the sensor channel sampling rate requirement. The technique employs zero padding of sensor data followed by digital interpolation filters to achieve vernier beamformer delays. Interpolation filtering can be done either at the beamformer input or output to minimize processing requirements. The resulting structure realizes a hardware savings since both A/D converter and cable bandwith requirements can be traded off against digital processing complexity to achieve an optimal partitioning.

Methods and means for simultaneously correcting several channels in error in a parallel multi channel data system using continuously modifiable syndromes and selective generation of internal channel pointers

Abstract: An apparatus for simultaneously correcting several channels in error is combined with a parallel multi channel data handling system. The apparatus encodes and records vertical parity checks in a first channel and encodes and records parity checks in a second and third channel or equivalent taken over the channels in respective predetermined positively and negatively sloped directions. Upon readback, syndromes from the parity checks and the recorded data are obtained. Correction signals from at least two syndromes intersecting the same error in a known channel in error are formed. The values of the syndromes diagonally intersecting each error in the known channel are continuously modified as the error is detected by inversion of the simple parity. Correction is attained by logically combining the correction signals with the original known channel in error data. Internal pointers to either first or subsequent channels in error are generated as a function of the bit position displacement in the in-channel direction between the occurrence of first and subsequent mismatches of vertical and diagonal syndromes. Internal pointers are generated either in the absence of or to supplement any external pointers.

Digital Processing Techniques in the 60 Channel Transmultiplexer

Abstract: Techniques applied to the digital processing of speech and signaling in a 60 channel FDM to 30 channel PCM converter are presented. Great efficiency is achieved through connecting a particular type of Fourier Transform computer to a polyphase network in which coefficient symmetries are exploited. Digital processing parameter values have been chosen so as to meet specified performance objectives. Realization of a laboratory model is outlined and measured performance is reported. Adequacy of the various options retained for the digital processing is confirmed by the experimental results.

The Effect of Acknowledgment Traffic on the Capacity of Packet-Switched Radio Channels

Abstract: We consider a population of terminals communicating with each other or with a central station over a packet-switched multiple access radio channel. To ensure the integrity of the transmitted data over the multi-access channel, we consider a reliable method using an error detecting block code in conjunction with a positive acknowledgment of each correct message. In this paper, we study the effect on channel capacity of the overhead created by the error-control traffic for both slotted ALOHA [1] and carrier sense multiple access (CSMA) [2]. For this we consider several implementation schemes for the two channel configurations: the common-channel configuration (a single channel for both information traffic and error-control traffic); and the split-channel configuration. The packet delay analysis will be treated in a forthcoming companion paper.

Selection of an Effective Channel Control Mix: A study of the relative effectiveness of two kinds of channel control tools or power sources

Abstract: E channel administration is a major prerequisite for successful performance of marketing plans. Traditionally, manufacturers anddistributors have relied on price and related mechanisms of intermediary markets to secure the required cooperation from other channel members. However, differences in goals, norms, expectations, and perceptions among different members of a distributive channel have often inhibited cooperation and affected detrimentally the execution of channel-wide policies. Activities and decisions have often been fragmented, and economies of scale stemming from channel-wise cooperation have often not been achieved.\" Furthermore, duplication of activities, inefficient allocation of functions in the channel, and \"noise\" in the communications among channel members have often plagued channel management.

Capacity reallocation method and apparatus for a TDMA satellite communication network with demand assignment of channels

Abstract: In a time division multiple access communication system utilizing a satellite for communicating signals between a plurality of ground stations, at spaced times a reference ground station reallocates the total channel capacity of the system among the several ground stations to minimize system blocking and to thereby utilize the available system channel capacity more effectively. To increase the time between successive reallocations, channels are reallocated only when a ground station makes a channel capacity request that is greater than or equal to its corresponding present channel allocation. System blocking is minimized by using a table look-up scheme to generate excess capacity allocation factors for the stations and to thereby determine each station's proportionate share of excess system capacity. An appropriate portion of excess capacity is then added to each station's channel capacity request to provide a new channel allocation for each station. The new channel allocations are transmitted to appropriate ground stations and each station thereafter adjusts its burst duration to correspond to its new channel capacity allocation.

Bounds on the achievable rates of block coding for a memoryless multiple-access channel

Abstract: Block coding for a memoryless two-input single-output multiple-access channel, called a two-user adder channel, is studied. Techniques for constructing codes for this particular channel are presented. Upper and lower bounds on the achievable rates of these codes are derived. These bounds define various two-dimensional regions for the achievable rates of codes for the two-user adder channel.

Multichannel radio communication system for automated power line distribution networks

Abstract: An automated electric power distribution network includes a radio communication system for transmitting multipurpose, multitone signals in one or more signaling channels over the auxiliary channel or channels of one or more commercial broadcast stations. Energy management terminals receive the signals at remote locations served by the distribution network. Radio receivers at the terminals have frequency selective detectors responsive to different multitone signals. The selective allocation of the multitone signals at different remote locations provides different communication links for effecting common or different electric energy usage related responses at grouped or separate locations. Complex address and/or function encoded signal information is reduced by providing the frequency selective reception of the several multitone signaling channels available in a radio or television station auxiliary channel.

The Modeling of Tidal Flow in a Channel Using a Turbulence Energy Closure Scheme

Abstract: A parameterization scheme is developed that is suitable for the modeling of turbulence in marine systems and an application is made to the determination of the tidal structure in an elongated channel The model is used to investigate the practicality of the frequently employed depth-integrated technique and conclusions are drawn about the customary bottom stress parameterization inherent in that approach Additionally, it is shown that the value of the roughness length of the elements at the floor of the channel is of importance in determining the frictional dissipation in the model and an evaluation is made of the tidally induced residual flow in the channel

Loop carrier system for telecommunication and data services

Abstract: A versatile loop communication system is disclosed wherein recurring frames of the ring carrier signal are divided by a movable partition into a dynamically allocated time division channel portion and a data packet communication portion. A common signal channel, in the ring carrier frame, is used to logically connect and disconnect stations for either circuit or packet communication on a common bus extending from terminals located in the loop. The loop controller automatically forms a contiguous group of time division channels or signal bytes at one end of the ring carrier frame. The format of the time division multiplexing channels is such that dynamic time slot interchanges of signal bytes are produced by the controller without the necessity of counting circuitry in the terminals to identify specific channel locations. The dynamic time slot interchange or byte displacement function is provided by additional memory arrangements both for the signals being transported by the ring and control functions in the time division switch located in the controller. The remaining portion of the frame serves as a shared channel for packet header switched data. In order to provide a flexible basis for packet switching, the controller assigns address tags and retains a map of the system.

Design of efficient coding and modulation for a Rayleigh fading channel

Abstract: The design of a coding/modulation structure for digital communications over a Rayleigh fading channel, the structure of the corresponding decoder, and the error rate performance of the resulting system are considered. Emphasis is on the use of constant weight codes for constructing equal energy waveforms for transmission over the channel. The performance gains that are achieved by the integrated coding/modulation approach relative to conventional methods for obtaining diversity are illustrated via some examples. Of special interest is the use of a concatenated coding technique for forming codes of large distance and hence high diversity. A new decoding algorithm is applied to enable efficient decoding of the concatenated code. An example is included that shows a performance increase of several dB resulting from concatenation.

Decentralized control in packet switched satellite communication

Abstract: The problem of access control to a packet switched multi-access satellite broadcast channel is considered in the framework of nonclassical control theory. This viewpoint, with the simple model presented, gives us some interesting results. It is shown under certain assumptions, that because of the inherent delay in information, the optimal control law will be within the class of open loop control laws. By a result in Bayesion decision theory it is shown that randomized decisions will not be necessary. Given an additional minor restriction we find that for "new" pockets only two modes of operation of the channel could be optimal, namely, All Together (every station sends whenever it has a packet) or Round Robin (every station sends whenever it is turn and it has a packet), and an equation for the crossover arrival probability P 0 the channel would switch from All Together (P to Round Robin (P>P_{0}) is given. For collided packets we find that it is optimal to have predetermined assignments of groups of stations to time slots for retransmissions, and a dynamic programming algorithm for determining the optimal grouping is given.

Sift-Out Modular Redundancy

Abstract: A fault-tolerance technique for digital systems, Sift-Out Modular Redundancy, is proposed and designed. An appropriate number of identical channels are provided for each module. The number of channels depend upon the particular application, and all channels are active as long as they are fault-free. Upon the failure of a channel, its contribution to the module output ceases. The configuration tolerates up to L − 2 channel failures, if L is the initial number of channels. Sift-out redundancy is easy to implement, and shows several advantages when compared to existing redundancy techniques.

Method of error control in asynchronous communications

Abstract: Error control, in the form of a modulo 2 division remainder checksum is added to a packet of reformatted asynchronous characters prior to transmission over a data link connecting two data devices such as a host computer and a teletype terminal. At one end of the link, data in asynchronous form, such as ASCII code, comprising seven data bits, start and stop bits, and a parity bit, is originated by one data device. The start, stop and parity bits of each character are eliminated. The remaining data bits for a selected number of characters are then grouped together to form a data grouping and the checksum and other control information bits added, forming an information packet. The information packet is then divided into sections or groups of eight bits. Start and stop bits are added to each group, forming ten bit characters. The ten bit characters are then transmitted over the data link in standard asynchronous format. The process is carried out in reverse at the other end of the link, resulting in the other data device receiving the data in the form originated by the first data device. Sophisticated error control techniques thus may be implemented in asynchronous communications without detrimentally affecting the data capacity of the channel.

Quantizing process with dynamic allocation of the available bit resources and device for implementing said process

Abstract: A coding process, given a total number of available bits per unit time, allocates to each of a plurality of signal channels a number of bits proportional to information in the channel. The process is useful for transcoding BCPCM (Block Coded PCM) voice signals for lower bit rate and conserving transmission channel bandwidth.