Showing papers on "Communication channel published in 1981"

A new achievable rate region for the interference channel

Abstract: A new achievable rate region for the general interference channel which extends previous results is presented and evaluated. The technique used is a generalization of superposition coding to the multivariable case. A detailed computation for the Gaussian channel case clarifies to what extent the new region improves previous ones. The capacity of a class of Gaussian interference channels is also established.

An achievable rate region for the multiple-access channel with feedback

Abstract: An achievable rate region R_{1} \leq I(X_{1};Y|X_{2},U), R_{2} \leq I(X_{2}; Y|X_{1},U), R_{1}+R_{2} \leq I(X_{1}, X_{2};Y) , where p(u,x_{l},x_{2},y)= p(u)p(x_{l}|u)p(x_{2}|u)p(y|x_{l},x_{2}) , is established for the multiple-access channel with feedback. Time sharing of these achievable rates yields the rate region of this paper. This region generally exceeds the achievable rate region without feedback and exceeds the rate point found by Gaarder and Wolf for the binary erasure multiple-access channel with feedback. The presence of feedback allows the independent transmitters to understand each other's intended transmissions before the receiver has sufficient information to achieve the desired decoding. This allows the transmitters to cooperate in the transmission of information that resolves the residual uncertainty of the receiver. At the same time, independent information from the transmitters is superimposed on the cooperative correction information. The proof involves list codes and block Markov encoding.

Data encoding for television

Abstract: A transparent data transmission system for encoding data to be transmitted by way of the scan lines of a television video signal, includes interface circuitry for receiving data from a number of input devices each operating at a particular data rate, and encoding processing circuitry which takes the data received by the interface circuitry and arranges it into separate data groups so that each group corresponds to the particular input device which originated the data. The data groups are then inserted, by way of timing circuitry, into corresponding data channels defined in a selected scan line of the video signal. Also, a data channel bit map is defined over a portion of the selected scan line, and data identifying each of the input devices which is providing data to the interface circuitry is inserted into the data channel bit map. Accordingly, when the encoded video signal is decoded to extract the inserted data groups together with the channel bit map, the decoding circuitry can determine, in accordance with the data channel bit map, if a null character contained in the extracted data was provided by an input device to the encoding interface circuitry and, if it was, the decoding circuitry can then allow the null character to be distributed for further processing. The overall transmission system therefore exhibits true transparency.

Capacity, Cutoff Rate, and Coding for a Direct-Detection Optical Channel

Abstract: It is shown that When Pierce's pulse-position modulation scheme with 2Lpositions is used on a self-noise-limited directdetection optical communication channel, there results a 2L-ary erasure channel that is equivalent to the parallel combination of L "completely correlated" binary erasure channels. The capacity of the full channel is the sum of the capacities of the component channels, but the cutoff rate of the full channel is shown to be much smaller than the sum of the cutoff rates. An interpretation of the cutoff rate is given that suggests a complexity advantage in coding separately on the component channels. It is shown that if short-constraint length convolutional codes with Viterbi decoders are used on the component channels, then the performance and complexity compare favorably with the Reed-Solomon coding system proposed by McEliece for the full channel. The reasons for this unexpectedly fine performance by the convolutional code system are explored in detail, as are various facets of the channel structure.

Combined Source-Channel Coding of Images Using the Block Cosine Transform

Abstract: An approach is described for exploiting the tradeoffs between source and channel coding in the context of image transmission. The source encoder employs two-dimensional (2-D) block transform coding using the discrete cosine transform (DCT). This technique has proven to be an efficient and readily implementable source coding technique in the absence of channel errors. In the presence of channel errors, however, the performance degrades rapidly, requiring some form of error-control protection if high quality image reconstruction is to be achieved. This channel coding can be extremely wasteful of channel bandwidth if not applied judiciously. The approach described here provides a rationale for combined source-channel coding which provides improved quality image reconstruction without sacrificing transmission bandwidth. This approach is shown to result in a relatively robust design which is reasonably insensitive to channel errors and yet provides performance approaching theoretical performance limits. Analytical results are provided for assumed 2-D autoregressive image models, while simulation results are provided for real-world images.

Local area communication network utilizing a round robin access scheme with improved channel utilization

Abstract: Disclosed is a local area communication network based upon a broadcast communication system comprising an inbound channel and an outbound channel, a plurality of stations connected to both the inbound and the outbound channels, transmitting on the outbound channel which utilizes an access protocol where the the access protocol used by the stations connected to the bus is a distributed algorithm and is based upon a conflict-free round robin (RR) access scheme. The time required to switch from one active user to the next in a round is minimized (on the order of carrier detection time, and is independent of the end-to-end network propagation delay. This improvement is particularly significant when the channel data rate is so high, or the end-to-end propagation delay is so large, or the packet size is so small as to render the end-to-end propagation delay a significant fraction of, or larger than, the transmission time of a packet. Moreover, some features of the present invention make it particularly suitable for voice applications. In view of integrating voice and data, a voice/data protocol is described which allows it to meet the bandwidth requirement and maximum packet delay constraint for voice communication at all times, while guaranteeing a minimum bandwidth requirement for data traffic. The voice/data protocol constitutes a highly adaptive allocation scheme of channel bandwidth, which allows data users to steal the bandwidth unused by the voice application.

Selective video reception control system

Abstract: A system for controlling a channel/band selective microcomputer programmed indirect frequency synthesis tuner is disclosed. Separate groups of VHF, UHF or CATV channels are programmed by means of a key switch having various positions of engagement corresponding to individual groups of channels. Following key switch selection of a given group of channels, any number of channels within that group may be programmed for viewing by means of channel UP and DOWN selector keys. A RAM is used to store "saved" and "skipped" channels for each key switch position. A backup non-volatile MNOS memory is provided for preserving stored data in the event AC power is removed. Also provided is programmable raster blanking for audio-only channels thus eliminating unwanted video snow. Front panel LED indicators inform the programmer of the status of each channel during television receiver programming. The television receiver is turned on by viewer selection of either the channel UP or DOWN control resulting in tuning to either the lowest or highest "saved" channel. The OFF function is activated anytime an attempt is made to advance past either the highest or lowest programmed channel by providing either a channel UP or DOWN command, respectively. Thus, television receiver control is by means of a single user selector. A wired remote controller with a speaker is also provided.

Characteristics of a digital mobile radio channel

Abstract: A field test has been made in order to better understand the digital mobile radio channel. At the mobile receiver (450 MHz, 1200 bits/s) recordings were made of the digital signal and the field strength. These recordings were later analyzed by a computer. Some existing models for digital channels have been tested. Theoretically motivated probability density functions for the fading envelope have also been considered. A new model for the digital channel is proposed. This model is a memoryless binary symmetric channel (BSC) with field strength dependent crossover error probability. This model fits very well to the recorded data.

On the T-user M-frequency noiseless multiple-access channel with and without intensity information

Abstract: Two specific noiseless multiple-access channel models, the T -user M -frequency multiple-access channel with and without intensity information, are studied in this paper. Information-theoretic bounds on the transmission rate for both models are presented. Constructive coding schemes are given for both channels which achieve zero error probability and whose rate sum is close to the information-theoretic bounds. Although the problem is formulated in terms of frequencies, the results are applicable to any signaling scheme where M orthogonal signals are used in each signaling interval including time partitioning of the interval.

Subsampling of a DPCM speech channel to provide two “self-contained” half-rate channels

Abstract: We consider the following channel-splitting problem: it is required to split a B-bits/s speech-code sequence into two “self-contained” B/2-bits/s components, either of which can be used to reproduce acceptable speech; also, if both components are available at a receiver, it must be possible to reproduce speech with full B-bits/s quality. We propose a solution where for interesting values of B, the speech quality resulting from half-rate receptions approximately equals that from conventional full-rate receptions at B/2 bits/s. In the proposed solution, 3.2kHz speech is sampled at 12 kHz and coded using PCM or differential PCM. The output sequence of code-words is split into odd- and even-word sequences. A full-rate receiver with access to both of the subchannels simply reconstitutes the output sequence prior to decoding, while a half-rate receiver with only the odd (or even) subchannel estimates the even (or odd) components by nearest-neighbor interpolation.

Integrated alarm, security, building management, and communications system

Abstract: A fully integrated alarm, communication, and building management system has a central control station and a plurality of remotely located sensing and controlling devices. Each remote device has an individual digital address, which is a parallel address present on a plurality of parallel lines. The parallel address is converted to a serial address and sent to the various remote locations where it is then reconverted to a parallel address and decoded to determine the specific device being interrogated. A multiple amplifier system is provided at the central control unit and provides communication capability involving remotely located loudspeakers and microphones. The amplifiers are provided in a dual channel arrangement so as to provide a fail-safe arrangement and a failure detector is located in each channel such that if a selected amplifier channel fails, the back-up or redundant channel is immediately switched into use. A number of controlling devices or actuating devices may be employed which operate in conjunction with the sensing devices and a programmable read only memory, or a programmable multiplexer, located at the central control unit. Each remotely located controlling or actuating device also has associated with it an individual parallel digital address and upon the occurrence of a signal from a sensing unit indicating a condition other than a normal condition and a specific address programmed into the programmable read only memory or the multiplexer a command signal will be issued to the remotely located actuating or controlling device causing such device to operate in a predetermined manner.

Bounds on the performance of protocols for a multiple-access broadcast channel

Abstract: A general model is presented for synchronous protocols that resolve conflicts among message transmissions to a multiple-access broadcast channel An information-theoretic method is used now to show that if only finitely many types of conflicts can be distinguished by the protocol, utilization of the channel at rates approaching capacity is impossible A random-coding argument is used to show that if the number of conflicting transmissions can be determined (which requires distinguishing infinitely many types of conflicts) then utilization of the channel at rates arbitrarily close to capacity can be achieved

Asynchronous multiple-access channel capacity

Abstract: The capacity region for the discrete memoryless multiple-access channel without time synchronization at the transmitters and receivers is shown to be the same as the known capacity region for the ordinary multiple-access channel. The proof utilizes time sharing of two optimal codes for the ordinary multiple-access channel and uses maximum likelihood decoding over shifts of the hypothesized transmitter words.

Channel interface circuit with high speed data message header field translation and direct memory access

Abstract: The subject channel interface circuit functions in a multiprocessor environment to provide a high speed interface between a processor and the communication channel which interconnects all the processors. The communication channel carries data messages, which messages contain a header field specifying source, destination and control information. The subject channel interface circuit is programmable and serves to dynamically translate the header portion of the data message as it is received and thereby determine whether this data message is to be stored in the processor memory. If the data message is to be stored, the channel interface circuit immediately converts the header field into a hardware address, which is used to activate a specific location in processor memory. The data message is then inputted (via DMA) to this memory location and the appropriate buffer pointers are reset. Thus, the subject channel interface circuit performs all the data receiving tasks, including message storage and linking, without requiring the involvement of the associated processor.

Electrically alterable double dense memory

Abstract: An electrically alterable double dense memory is provided which includes a field effect transistor having first and second spaced apart diffusion regions of a first conductivity defining a channel region at the surface of a semiconductor substrate having a second conductivity. First and second floating gates are disposed over the first and second diffusion regions, respectively, and each extends over an end of the channel region. First and second dual charge injector structures or enhanced conduction insulators are disposed between the first and second floating gates and a common control gate of the transistor. A word line is connected to the control gate and first and second bit lines are connected to the first and second diffusion regions. By applying appropriate pulses to the word and bit lines, a selected floating gate can be charged to alter the conductivity of the end of the channel region associated with the selected floating gate and then discharged at will. In this manner binary digits of information are stored in each of the two floating gates and altered as desired. By applying appropriate voltages to the control gate and to one of the first and second diffusion regions, the stored information or charge condition of the floating gate associated with the other of the first and second diffusion regions can be determined.

An Efficient Selective-Repeat ARQ Scheme for Satellite Channels and Its Throughput Analysis

Abstract: In this paper, we investigate a selective-repeat ARQ scheme which operates with a finite receiver buffer and a finite range of sequence numbers. The throughput performance of the proposed scheme is analyzed and simulated based on the assumption that the channel errors are randomly distributed and the return channel is noiseless. Both analytical and simulation results show that it significantly outperforms the go-back- N ARQ scheme, particularly for channels with large roundtrip delay and high data rate. It provides high throughput efficiency over a wide range of bit error rates. The throughput remains in a usable range even for very high error rate conditions. The proposed scheme is capable of handling data and/or acknowledgment loss. Furthermore, when buffer overflow occurs at the receiver, the transmitter is capable of detecting it and backs up to the proper location of the input queue to retransmit the correct data blocks.

Joint source and noisy channel trellis encoding (Corresp.)

Abstract: In a trellis encoding communication system the decoder is a time-invariant nonlinear filter with finite memory (sliding-block code), and the encoder is a trellis search algorithm matched to the decoder. A coding theorem is established for a trellis encoding of a stationary and ergodic source over a discrete memoryless noisy channel which shows that such communication systems can perform arbitrarily close to the source distortion-rate function evaluated at the channel capacity.

The Marketing Channel as an Equilibrium Set of Contracts

Abstract: Nash bargaining theory and recent developments in economic contract theory are employed in the analysis of the marketing channels. Individual dyadic contracts involving payment schedules between members of a simple 3 level channel are investigated with particular reference to monitoring problems and intrachannel power relations. The interrelations between individual contracts are examined and the equilibrium set of contracts constituting the channel derived. The performance of the channel in terms of risk sharing, allocative efficiency and the distribution of gains is then evaluated. It is found that the risk aversion of channel members and the cost of monitoring and enforcement affect channel efficiency, and that under certain types of interdependencies and externalities, the nature of the power structure is crucial to channel efficiency.

Satellite communications system with frequency channelized beams

Abstract: A digital communications satellite (12,44) receives signals from a plurality of narrow input spot-beams (14) of an uplink. It regenerates, multiplexes and routes the signals for transmission in a plurality of narrow output spot-beams (42) of a downlink. The uplink beams (14) each include a plurality of frequency re-use channels (18), while the downlink beams (42) each have only a single wide-band channel. The satellite (12,44) may multiplex the signals either before or after routing them. The spot-beams (14,42) may be fixed or scanning.

Coding of arbitrarily varying multiuser channels

Abstract: The capacity region for the arbitrarily varying multiple-access channel is determined. A region of achievable rate triplets for the arbitrarily varying general broadcast channel is then given. Finally a region of achievable rate triplets for the general broadcast channel is given including as special cases all capacity regions known until now for broadcast channels.

Decentralized control of linear multivariable systems

Abstract: A strongly connected decentralized control system may be made single channel controllable and observable with respect to any channel by decentralized feedbacks. It is noted here that the system example considered by Corfmat and Morse to illustrate this fact is already single channel controllable and observable, with respect to one of the channels. An alternate example which fits into the situation is presented in this item.

Peripheral systems employing multipathing, path and access grouping

Abstract: A data-processing system is connected to a peripheral system by a plurality of channel paths. These channel paths are named as members of path groups. Each path group has one or more channel paths. Within each path group, communications between the data-processing system and the peripheral system are multipathed among the paths in such path groups. Devices within the peripheral system are selectively assignable to access groups for exclusive use within one or more of such path groups; a given path group selectively provides communication paths for each device in an access group. Each access group includes one or more path groups. Temporary suspension and reassignment facilities are disclosed. Both devices and channel paths can be either in a grouped or ungrouped state. The assignment function to access groups is particularly useful in interleaved channel transfers for ensuring subsystem integrity.

Simultaneous transmission of voice and data signals over a digital channel

Abstract: A transmission system comprises apparatus for the transmission of voice signals only, data signals only, or a combination of both voice and data signals in a multiplexed stream of eight bit time slots over a single, bidirectional digital channel for a point-to-point connection In the combined mode, the encoded voice signals, using low bit rate voice encoders, are assigned to four bit positions of the eight bit time slot; the data signals are assigned to the remaining four bits Up to two bit positions normally used for data may be used for signature bits, thereby identifying whether the multiplexed stream comprises voice signals only, data signals only, or a combination of both voice and data signals Also, a minimum of one "1" bit per eight bit time slot is thereby guaranteed

Battery-saving arrangement for pagers

Abstract: A pager or other selectively-addressed electronic device powered by a small power cell operates in four different modes and at two power levels, depending on signals received and a timing sequence. The device can stay active continuously, be activated at intervals or remain in a powered-down state. The address code assigned to a particular device would be transmitted at a predetermined time interval following a sync signal, thus the device can be powered-down until the approximate time period in which its address code could be transmitted. The system provides increased channel efficiency since information codes are superimposed on actual address codes, and there is no dead time in a channel while there are address codes waiting to be transmitted. The system is particularly well adapted to time multiplexing.

Method and apparatus for automatic control of electronic equipment

Abstract: An electronic device, such as a video tape recorder (VTR), is set into a desired, but complex mode, such as automatic recording of a desired program, by manual scanning with an optical wand or other scanning instrument of one or more code groups printed on a selection card. Respective selection cards have code groups thereon for selecting, for example, mode, channel, day of week, recording start time (including AM or PM), and recording end time. Code signals provided from the scanning instrument are processed in a data processing circuit, which can be provided as a microprocessor and included in the VTR to provide control signals to the VTR in response to information contained in the scanned code groups. Alternatively, a combination of an FM receiver and high fidelity audio recorder can be set into an auto record mode or other complex operating mode by scanning of selection cards with a scanning instrument associated with such combination.

Method and apparatus for calibrating a linear array scanning system

Abstract: A linear image sensor and the video channel associated with the sensor are calibrated to maximize the video signal available. The sensor is limited in output by saturation of the CCD analog shift registers in the sensor. The channel is limited by the range of the analog-to-digital converter in the channel. The useable video signal is maximized by calibrating the sensor relative to its saturation condition and by adjusting the gain of the video channel relative to the range of the analog-to-digital converter. The sensor is calibrated by adjusting its exposure to illumination. The adjustment may be made by adjusting the illumination source or by changing the sampling interval for the sensor. The gain is adjusted by using a variable gain amplifier. A microprocessor monitors the digitized video signal and controls the exposure and gain to calibrate the sensor and channel.

Service integrated digital transmission system

Abstract: A service integrated transmission system for transmitting, over a light transmission path, digital signals having a transmission band whose upper limit frequency corresponds to the maximum bit rate of the signals to be transmitted, the transmission being effected by simultaneously transmitting, over the transmission path, digital signals having a high bit rate only in an upper part of the transmission band and digital signals having a low bit rate only in a lower part of the transmission band. The system includes a transmitter at one end of the path which separately multiplexes low bit rate signals into a narrowband signal and high bit rate signals into a broadband signal, combines those multiplexed signals, and modulates a light source with the combined signal. A receiver at the other end of the path converts the modulated light signal into a demodulated electrical signal, separates the two multiplexed signals, and then demultiplexes each of the latter signals.

Channel Instability in a Braided Sand Bed River

Abstract: The Gila River of central Arizona is representative of braided, sand bed rivers in alluvial valleys that have inherent unstable behavior and destructive channel migration. The 112-year record of channel conditions along a portion of the Gila River provides data for the construction of locational probability maps for main flow channels. Zones of stability and hazardous instability alternate with each other at 3.2 km (2 mi) intervals. During the past century the overall sinuosity of the main flow channel has remained close to 1.18, despite numerous changes in actual location. Spatial and temporal variation of sinuosity have occurred in subreaches as a result of sedimentation behind a dam and fluctuations in the density of phreatophyte growth, which both affect the hydraulics of flood flows. Unstable zones of the channel correspond to the surface of the sediment wedge behind the dam and areas dense phreatophyte growth. Stable zones correspond to areas controlled by bedrock or man-made structures, as well as locations determined by these external factors plus the requirement to maintain a consistent sinuosity. Channels such as that of the Gila River do not meet most assumptions of equilibrium and are best understood through probabilistic approaches with an assumption of catastrophic adjustment.

Pad holder and display

Abstract: A point of purchase flexible pad holder and display includes an upper clear plastic section which may snap into a pricing channel or be suspended from a peg and a lower separable double-sided, front and back, adhesive section with the front of such section being employed to secure a tear-off pad while the back may secure the holder as a whole or separated in a variety of display locations. The connection and structure of the two sections enables stable support of the pad, ease of insertion into the pricing channel, and also ease of clean separation of the two sections. The back may also secure a second pad so that when the first is exhausted the holder need merely be turned around on the pricing channel or peg to present the second pad to the purchaser.

Multipoint packet data communication system using random access and collision detection techniques

Abstract: In a data communications systems having a communications channel (3) for interconnecting a plurality of transceivers (1) and (2), each of said transceivers (1) and (2) including means (80) for transmitting a signal having transitions, there is provided a means (20) responsive to the presence and absence of a signal on said communications channel (3) during a transition of a signal transmitted by said transmitting means (80) for providing a collision detected (CD) signal if there is destructive interference with the transmitted signal on said communication channel (3) during a transition of said transmitted signal and means (48) responsive to said CD signal for terminating said transmitting of said signal. In the event the channel (3) is busy prior to a transmission from the transmitter (80) there is provided a carrier sense circuit (14) for indicating the channel is busy and a non-persistent control circuit (45) and a random number generator (90a) and a delay circuit (90b) responsive to the carrier sense circuit (14) and the collision detector circuit (20) for interrupting and delaying the transmitting of each of the transceivers (1) and (2) for a random period of time.