Showing papers on "Communication channel published in 1979"

A New Method to Determine Effective MOSFET Channel Length

Abstract: An accurate and convenient method to determine an effective MOSFET channel length is proposed. This method is based on a computer aided evaluation of an intrinsic MOSFET channel resistance without using special test devices. N-channel silicon-gate MOSFETs were fabricated, and the channel length and its range of device to device scatter were evaluated . To define an effective channel, a simple model of the source-drain (S-D) diffusion layer is proposed. This model shows that the expected transition layer resistance between the S-D diffusion layer and the inverted channel layer agrees with the experimental results. The accuracy of this method is also discussed. It is found to be better than 0.1 µm.

Interactive cable television system

Abstract: An interactive cable television system, such as a one way system, simultaneously provides both regular television programmings for one or more television reception channels and subscriber selectable multi-information television programming for a designated common one of those channels to a plurality of subscribers. Each individual subscriber having a multi-information interface network connected to the multichannel television receiver input may independently choose between reception of the regular television programming on any of the channels, including the designated common channel, and reception of the multi-information television programming which comprises a plurality of multi-information packets. Each packet comprises a plurality of simultaneously transmitted different information message signals which are related in real time and content to each other but which are transmitted at a different frequency from each other and from the associated frequencies of the television reception channels. The interface network, which includes a plurality of selection keys, converts the associated frequency of the desired information message signal in the transmitted packet to the common designated channel frequency to enable television reception thereof in accordance with the key selected. Another subscriber having the interface network may independently choose to receive either the regular television programming on that, or another channel, or a different information message signal, while subscribers not having the interface network may still receive the regular television programming. Labels for the selection keys may be visually presented on the television screen during reception of multi-information programming and may be dynamically varied in accordance with message content, such as in a decision tree or memory accumulation type of programming format.

Simulation of the urban radio propagation channel

Abstract: A simulation program for the wide-band response of the urban multipath propagation channel has been developed. The program enables the generation of a sequence of "impulse responses" of the channel that would be observed by a moving vehicle communicating with a fixed station. The program incorporates empirical parameters covering four types of urban areas and three frequencies (in the 0.5-3- GHz range) and can be used in design of urban communication systems.

Combined Source-Channel Coding of Images

Abstract: A combined source-channel coding approach is described for the encoding, transmission and remote reconstruction of image data. The source encoder employs two-dimensional (2-D) differential pulse code modulation (DPCM). This is a relatively efficient encoding scheme in the absence of channel errors. In the presence of channel errors, however, the performance degrades rapidly. By providing error control protection to those encoded bits which contribute most significantly to image reconstruction, it is possible to minimize this degradation without sacrificing transmission bandwidth. The result is a relatively robust design which is reasonably insensitive to channel errors and yet provides performance approaching the rate-distortion bound. Analytical results are provided for assumed 2-D autoregressive image models while simulation results are described for real-world images.

Analysis of Direct-Sequence Spread-Spectrum Multiple-Access Communication Over Rician Fading Channels

Abstract: This paper is concerned with the performance of biphase direct-sequence spread-spectrum multiple-access communication for a general class of fading channels. The channels considered are those for which the channel output consists of a strong stable specular signal plus a faded version of this signal. Such channels, which are referred to as Rician fading (or Rice fading) or specular-plus-Rayleigh fading, are the result of a transmission medium which gives rise to a major stable communication path and a number of additional weaker communication paths. The fading channel is modeled as a general wide-sense-stationary uncorrelatedscattering (WSSUS) channel-a model which is general enough to exhibit both time and frequency selectivity and to impose no restrictions on the fading rate. For the general WSSUS model, results are obtained on the average signal-to-noise ratio at the receiver output in terms of the spread-spectrum signature sequences and the covariance function for the fading process. These results are then specialized to each of two important classes of WSSUS channels: time-selective fading channels and frequency-selective fading channels. Numerical evaluations are presented for specific examples of each of these two types of channels. Analytical expressions are derived for a spread-spectrum multiple-access system with random signature sequences, and the use of these expressions in preliminary system design is discussed.

A Generalized Multiplexer Theory

Abstract: A general direct analytical design process is presented for multiplexers having any number of channels with arbitrary channel complexity, bandwidths, and interchannel spacings. The theory assumes initially that independent doubly terminated designs are available for the individual filters, and formulas for modifications to parameters associated with the first two resonators are developed to match the multiplexer. These formulas are approximate, and the Iimitations of the theory are indicated with several computed examples. The theory is applied to the design of a five-channel interdigital multiplexer. A first-stage immittance compensation scheme is described which improves the design for limiting cases, but the theory of complete immittance compensation which handles even contiguous channel operation is reserved for a companion paper.

Hydraulics of a large channel paved with boulders

Abstract: Experience is described of a 41 m wide by 308 m long, open channel on a 0.052 slope, constructed of loose boulders and through which flows up to 140 m3/s are passed. A new expression for the Darcy ...

High speed digital communication receiver

Abstract: An improved high speed digital communications diversity receiver using a forward adaptive transversal filter equalizer, having a plurality of weighting sections in each diversity channel to provide a combined weighting signal, wherein the required complex multiplications and correlations needed for weighting purposes are performed at IF frequencies, while the time-delayed combining operations for providing the desired combined weighted output signal are performed at baseband frequencies. Such an arrangement reduces the number of tapped delay lines normally needed for such transversal filter equalizer operation and further reduces the signal losses incurred in operating delay line devices at intermediate frequencies so that fewer large gain-bandwidth product amplifiers are required in the system than the number required in previously available systems using such forward transversal filter equalizers.

Access-control disciplines for multi-access communication channels: Reservation and TDMA schemes

Abstract: Reservation and TDMA schemes are studied for governing the access-control discipline for a network of terminals communicating through a multi-access broadcast channel. A single repeater is employed to allow a fully connected network structure. A channel can be characterized as inducing a Iow propagation-delay value, as for terrestrial radio or fine networks, or as being associated with a higher propagation-delay value, as for a satellite communication channel. A synchronized (slotted) communication medium is considered. Messages are composed of a random number of packets, governed by an arbitrary message-length distribution. The process describing the number of reserved message arrivals within each time frame is assumed to be a sequence of i.i.d, random variables, governed by an arbitrary distribution. (A Poisson arrival stream thus becomes a special case.) The reservation access-control disciplines studied in this paper employ message-switching distributed-control procedures. The performance of each access-control scheme is evaluated according to its delay-throughput function. In particular, schemes are developed to adapt their structure, or protocol, dynamically to the underlying fluctuating network traffic-flow values. A fixed-reservation access-control (FRAC) discipline is studied, employing a fixed periodic pattern of reservation and service periods. The reservation periods are used for the transmission of reservation packets as well as for the integrated service of other groups of network stations. The latter stations can access the channel during these periods, using any proper access control procedure. As a special case, message-delay distributions and moments under a TDMA scheme are obtained. Using dynamic estimates of the underlying message traffic parameters, a dynamic fixed-reservation access-control (DFRAC) scheme is obtained. An analytical technique, which employs a Markov ratio limit theorem, is presented for the derivation of the delay-throughput performance curves of dynamic demand-assignment reservation schemes. To illustrate its application, asynchronous reservation demand-assignment (ARDA) schemes are developed to adapt automatically to the underlying network traffic characteristics. Such schemes establish reservation slots dynamically according to observed network service demands and queue sizes.

A conceptual model of the relationship between channel characteristics and discharge

Abstract: Regression equations with the form y = f(q), where y is a channel characteristic and q is a discharge of a particular frequency are widely used in fluvial geomorphology. They imply that channel geometry is related to a dominant discharge. For this to be so, the river must be ‘in regime’ i.e. its characteristics must fluctuate about a mean condition which is effectively stationary at the time scale considered. The static regression-dominant discharge approach does not fully describe the relationship between channel characteristics and discharge and an alternative model is proposed with the form y(t) = ∞h(u)- q(t-u)du. This model states that channel form is a product of the whole series of discharges experienced by the channel. The dominant discharge-static regression approach provides a working approximation of the relationship between channel characteristics and discharge only when temporal variations in q are small or when y is insensitive to variations in q.

Multiprocessor mechanism for handling channel interrupts

Abstract: The disclosure relates to multiprocessor handling of plural queues of pending I/O interrupt requests (I/O IRs) in a main storage (MS) shared by plural central processors (CPs). An input/output processor (IOP) inserts I/O IR entries onto the queues in accordance with the type of interrupt. The entries in the queues are only removed by the CPs, after their selection by a system controller (SC) for execution of an interruption handling program. An I/O interrupt pending register in I/O interrupt controller circuits in the SC is used in selecting CPs to handle the I/O IRs on the queues. The bit positions in the pending register are respectively assigned to the I/O IR queues in MS, and the order of the bit positions determines the priority among the queues for CP handling. An I/O IR command from the IOP to the SC sets a corresponding queue bit position in the pending register and controls the addition of an entry on the corresponding queue in MS. If a bit is set to one, the corresponding queue is non-empty; if set to zero, the queue is empty. A broadcast bus connects the outputs of the bit positions of the pending register to each of the CPs. In each CP, acceptance determining circuits connect to the broadcast bus and accept the highest-priority-unmask non-empty-state bit position being broadcast. From this, the CP sends the SC an accepted queue identifier signal and an accept signal when the CP is in an interruptable state. The CP also sends to the SC a wait state signal if the CP is then in wait state. Selection determining circuits in the SC receive the accept, wait (if any), and queue identifier signals from all accepting CPs and select one accepting CP per accepted queue at any one time. The selection circuits can perform the selection of plural CPs in parallel, and send a select signal to each selected CP. An inhibit register in the interrupt controller in the SC inhibits selected bits on the broadcast bus to all CPs except the selected CP for the selected queue identifier. The inhibit on any bit is removed when the selected CP ends its acceptance of the corresponding queue, so that any CP can select the next entry on the corresponding queue. When any selected CP finds it has emptied a queue, it activates a reset line to the SC which resets the corresponding bit in the pending register to indicate the empty state.

Improvements in Block-Retransmission Schemes

Abstract: Consider the case where an n -digit block encoded word cannot be decoded reliably and a second block of n redundant digits is sent to allow the receiver to make a new try based on the combined information received. Two classes of schemes are proposed and analyzed which give significantly better performance than is obtained by sending a repeat of the first block, yet do not require excessive decoding complexity. One approach is to consider small sub-blocks of the original n -digit code as the data digits of a short rate one-half code. The other approach is to treat the first sending as the data digits of a systematic convolutional code of short constraint length. Comparisons are made for the white Gaussian noise channel and the erasure channel. The comparisons are limited to an assessment of the improvement gained after two sendings. Procedures using length 4 sub-blocks and using convolutional codes with constraint lengths as short as 2 or 3 digits yield considerable improvement over block retransmission. For the case of the erasure channel, a very simple decoding rule is devised for the convolutional code case.

Receiver with a channel swapping apparatus

Abstract: A television tuning system includes apparatus for swapping or exchanging a presently selected channel for a previously saved channel when a user operates a switch provided for that purpose. The apparatus is arranged so that the saved channel is unaffected by channel selections so that it may be used by a user to quickly return to an originally selected channel after scanning other channels, e.g., during commercial interruptions, as well as to follow the progress of two programs, e.g., two sporting events on different channels.

Occlusion of body channels

Abstract: A method for obstructing channels, ducts and other hollow spaces in human and animal bodies is disclosed comprising inserting a device having a portion thereof adapted to swell at least 20% in size when in contact with the fluid of the human or animal body, the device being in a shape matching and cooperating with the channel to be obstructed.

Apparatus and method for receiving digital data at a first rate and outputting the data at a different rate

Abstract: A system is disclosed wherein a series bit stream of digital data, at a relatively high bit rate, is received and the data is recorded on a multiple channel recording medium. During the recording of the data, the data is divided into frames of words each having N bits. Each word has a parity bit added so that each word has N+1 bits. In addition, the data for each channel is recorded in frames where each frame includes a synchronization word followed by fixed plurality of data words. Since each recorded frame includes more bits than the originally received data bits per frame, the recording bit rate for each channel is substantially higher than the incoming data bit rate per channel. All frames from the various channels are recorded simultaneously so that the synchronization words from channel to channel are in alignment. During the read-out process, all of the channels are simultaneously read so as to provide a plurality of reconstructed data channels, each including a serial stream of data bits. A decoder is provided for each channel and the various decoders are controlled by a common decoder control circuit. For each channel, the decoder circuit detects the synchronization word and then sequentially stores the data words in designated locations of a read/write memory. After all of the synchronization words in the various channels have been detected, an offset delay takes place before the reading operation commences. This offset delay is sufficient to permit the writing into memory operation to continue within the decoders until one of the decoders has written a specified number of data words into its memory. This is done to compensate for tape skew. Thereafter, all of the memories are simultaneously read in sequence from a given memory location to form reconstructed data frames for each channel. These data frames include only the original data words and no parity or synchronization bits. These frames are then combined into a single output data stream at a bit rate substantially less than that of the original incoming data stream. In addition, the read-out operation provides circuitry for determining whether the data signals obtained from one of the channels recorded on the recording medium has exhibited a signal loss, as from a tape defect. In such case, a change-over circuit will look to a different channel to provide a clock signal for operating the decoder for that channel.

Computer monitoring system

Abstract: A computer monitoring system connects into the channel, serving as a link between a CPU and peripheral devices. Channel signals are extracted in a channel interface module, altered to be compatible with the logic in a data collection module and sent to a data collection module along with event codes generated within the channel interface module to indicate certain sequences and/or combinations of signals occurring on the channel. The data collection module is programmable to select those peripheral devices it wants to monitor and the type of information to be collected.

Digital radio transmission system

Abstract: A digital radio transmission system for compensating for co-channel or adjacent channel interference or signal level variations and distortions is provided. The system includes apparatus for transmitting a digital signal having a first signal level from a first location to a second remote location, apparatus for monitoring at the second remote location the bit error rate of the received digital signal and apparatus for changing the level of the transmitted digital signal when the received bit error rate is different from a predetermined value.

Conflict resolution by retransmission delay on shared communication medium

Abstract: An apparatus for enabling communications between two or more transceivers when a plurality of transceivers share a common communication medium or channel. The geographical locations of the transceivers are such that the propagation delay between any source to destination pair is relatively a small function of the transmission duration or packet time. In order to prevent two or more transceivers from simultaneously transmitting over the common medium, each transceiver requires a control apparatus. The simultaneous transmission by two or more transceivers is not very likely due to different start times. However, if such start times differ by less than the propagation delay between the transceivers then interference will result. Hence the control apparatus includes a means of resolving such contention interferences by providing a retransmission delay to govern the transmission.

The capacity region of the two-way channel can exceed the inner bound

Abstract: Introducing the two-way channel Shannon (Proc. 4th Berkeley Symp. Math. Stat. and Prob., 1961) layed the foundation to the theory of multi-user communication. Shannon gave an inner bound for the capacity region of this channel. We prove by example that the capacity region of the two-way channel is in general larger than its inner bound. This gives a partial solution of open problem I of van der Meulen's [(1977) IEEE Trans. Inform. Theory IT-23] survey paper.

Flow and flow routing in upland channel networks / L'écoulement et le calcul du cheminement de l'écoulement dans les réseaux des canaux montagneux

Abstract: This paper is based on the premise that the distribution of discharge source areas in relation to the channel network may have a significant effect on the form of the basin hydrograph, and that, in consequence, it is of value to investigate routing models for application to the channel networks of upland catchments. The channels of such networks are generally small, steep and rough with complex flow through a sequence of pools and riffles or rapids. The gulp dilution gauging method provides a useful technique for investigating the bulk properties of flow over complete channel reaches. At least for low to medium flows it is shown that average flow velocities increase nonlinearly both downstream and with increasing discharge, in a manner that is not compatible with traditional analysis in terms of uniform flow equations. The dilution gauging measurements may be used to provide parameters for a nonlinear kinematic routing model. The model is applied to channel networks of two small British basins (≃...

Tie down anchor

Abstract: A tie down anchor and fastening device includes an elongated continuous channel defining a continuous T-slot with a slider block slidably mounted within the channel and including a connecting member extending through the slot externally of the channel with gripping means carried by the slider block for engagement with the internal walls of the T channel upon tilting or pulling the slider block into engagement with the walls of the channel adjacent the slot.

Method and apparatus for rotating priorities between stations sharing a communication channel

Abstract: A method and apparatus for rotating priorities among stations on a communication channel, and particularly on a contention channel where a plurality of active stations are provided, each capable of seizing use of the channel. Counter means at each station contains an indication representative of the station having highest priority to the channel Each station establishes a priority rank for itself based upon the contents in the counter means. The indication is sequentially altered to provide priority to other stations. The priority indications in the counter means are synchronized each time a station seizes use of the channel, and may also be synchronized periodically if no station seizes use of the channel.

The multicoil II airborne electromagnetic system

Abstract: A helicopter-towed electromagnetic (EM) system has been developed with two orthogonal transmitter coils. Units currently in service have either two or three orthogonal receiver coils. The associated software yields in-phase and quadrature channels which are generally free of the conductive response of overburden and of the magnetic induction response of magnetite. These geologic noise sources can mask the response of bedrock conductors for all previously developed airborne EM (AEM) systems. The new technique involves energizing conductors with two orthogonal transmitter coils, both operating at approximately the same frequency (e.g., 900 Hz). The subtracting of the secondary field components of one maximum-coupled coil pair from the other yields in-phase and quadrature difference channels. These channels may contain as much as an order-of-magnitude increase in the signal/noise (S/N) ratio for bedrock conductors in a geologically noisy environment.The new system can also indicate whether a steeply dipping conductor is thin (e.g., width less than 3 m) or thick (greater than 10 m). The thickness parameter provides a new criterion for conductor sorting, complementing the usual parameters of conductance and strike-length.The geophysical data are digitally recorded, and the profile records and maps are plotted by computer. The traces include the basic recorded data, the EM difference channels, a channel of resistivity, and a channel of conductance. The conductance channel essentially is an automatic anomaly selector calibrated in mhos.The usual application of the system is for metallic mineral prospecting. However, the system has also been used for sand and gravel detection using two well separated frequencies. For such applications, apparent resistivities are computed for each frequency and are displayed as channels on the profile record and as contour maps.

Bore telemetry channel of increased capacity

Abstract: Apparatus and method for signaling within a drill hole without disturbing an ongoing drilling operation. High data rates are achieved by using phase and/or amplitude modulation techniques which enable information transfer rates well in excess of the data bit rates being transmitted. The modulation technique provides a multi-level signal which makes optimum use of the amplitude/phase space available. The ability of the invention to substantially increase the carrying capacity of the communication channel is based upon the dispersive characteristics of electromagnetic propagation in a bore hole, wherein the lower frequencies propagate at a slower velocity, and with less attenuation than the higher frequencies. The relative effects of losses over the path length and the added signal-to-noise ratio required for the modulation techniques disclosed in this invention are balanced against each other in such a manner that data rates otherwise achievable only at higher frequencies can be obtained at lower frequencies with a net increase in usable path lengths for equivalent available signal powers and data rates. In accordance with this invention the number of signal states, e.g. phase levels and amplitude levels, for a given signal frequency are selected so as to maximize either the signal path length for a given carrying capacity of the signal channel, or the carrying capacity of the channel for a given path length.

The helical-scan magnetic tape recorder as a digital communication channel

Abstract: The properties of a magnetic tape recorder are viewed in terms of a digital magnetic recording/playback channel which exhibits fading (reduction of playback-signal level) and nonlinear behavior. A method is presented whereby channel nonlinearity may be quantified in a format useful for signal and receiver design. Measurements show this nonlinearity to be relatively small for symmetric two-level signals. Deep fades (dropouts) are the most significant source of errors in digital tape recordings. Fading is considered as multiplicative noise on an essentially linear channel, and measurements are made of the fade probability distribution and an associated additional time dispersion. While the fading process appears to occur relatively slowly (compared with the bit period), neither its probability distribution nor its associated dispersion encourage the use of a receiver which is able to adapt to the changing channel characteristics. Finally an attempt is made to ascribe the fading process to repeatable variations in head-tape separation, and a corresponding probability distribution for this separation is obtained. A helical-scan video recorder was used throughout the measurements because of its low cost and its potential as a high-density storage facility.

Electrooptical switching in thin film waveguides for a computer communication bus.

Abstract: A new crossing multimode channel waveguide electrooptical switch is described here. It has a 21-dB on-state/off-state difference at 10 V of applied voltage, 0.4-dB insertion loss, 2.2-pF capacitance, and a total length less than 1.5 mm. It will be useful for providing a switching network for realizing an integrated optical computer communication data bus where electric signals from computers are converted into optical signals, switched by these switches, and then received and reconverted into electrical signals by a detector array.

Perceiving surprising words in an unattended auditory channel

Abstract: This study addresses two related issues, the degree to which unattended auditory material is interpreted, and the processes by which the direction of attention is controlled. Subjects shadowed a pr...

Repeater trunking system

Abstract: Arrangement for establishing communication between a first mobile radio station and a second mobile radio station through a repeater over a radio frequency channel selected from a plurality of such channels. In an idle mode, a mobile station searches the channels for a predetermined group signal identifying it as belonging to a particular group of mobile stations. When that predetermined group signal is received on a channel, the mobile station is enabled on that channel so that it can communicate with a call originating mobile station belonging to the same group. In a call originate mode, a mobile station searches for an idle or unused channel identified by the absence of a busy signal. When an idle channel is found, the call originating station transmits a busy signal. The repeater, hearing the busy signal, transmits an acquisition signal. This acquisition signal is detected by the call originating mobile station which thereafter transmits a predetermined group signal for enabling other mobile stations in the common group on that same channel.