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Showing papers on "Communication channel published in 1973"


Journal ArticleDOI
TL;DR: In this article, it is shown that a proper front-end design incorporates a high-impedance preamplifier which tends to integrate the detector output, and this must be followed by proper equalization in the later stages of the linear channel.
Abstract: This paper is concerned with a systematic approach to the design of the “linear channel” of a repeater for a digital fiber optic communication system. In particular, it is concerned with how one properly chooses the front-end preamplifier and biasing circuitry for the photodetector; and how the required power to achieve a desired error rate varies with the bit rate, the received optical pulse shape, and the desired baseband-equalized output pulse shape. It is shown that a proper front-end design incorporates a high-impedance preamplifier which tends to integrate the detector output. This must be followed by proper equalization in the later stages of the linear channel. The baseband signal-to-noise ratio is calculated as a function of the preamplifier parameters. Such a design provides significant reduction in the required optical power and/or required avalanche gain when compared to a design which does not integrate initially. It is shown that, when the received optical pulses overlap and when the optical channel is behaving linearly in power,1 baseband equalization can be used to separate the pulses with a practical but significant increase in required optical power. This required power penalty is calculated as a function of the input and equalized pulse shapes.

700 citations


Journal ArticleDOI
TL;DR: This paper shows that e, which depends only on the channel, is convex and gives formulas to determine it exactly and is the natural generalization of channel capacity to this situation.
Abstract: A communication system is studied in which two users communicate with one receiver over a common discrete memoryless channel. The information to be transmitted by the users may be correlated. Their information rates are described by a point in a suitably defined three-dimensional rate space. A point in this rate space is called admissible if there exist coders and decoders for the channel that permit the users to transmit information over it at the corresponding rates with arbitrarily small error probability. The closure of the set of all admissible rate points is called the capacity region, and is the natural generalization of channel capacity to this situation. In this paper we show that e, which depends only on the channel, is convex and we give formulas to determine it exactly. Several simple channels are treated in detail and their capacity regions given explicitly.

452 citations


Journal ArticleDOI
TL;DR: It is shown that, in all cases of practical interest, signaling faster than the Nyquist rate, while keeping fixed the information rate, increases the mean-square error.
Abstract: In this work we report new results relating to decision feedback equalization. The equalizer and the transmitting filter are optimized in a PAM data communication system operating over a linear noisy channel. We use a mean-square error criterion and impose an average power constraint at the transmitter. Assuming correct past decisions, an explicit formula for the minimum attainable mean-square error is given. The possible advantages of signaling faster than the Nyquist rate while decreasing the number of levels to maintain the same information rate are investigated. It is shown that, in all cases of practical interest, signaling faster than the Nyquist rate, while keeping fixed the information rate, increases the mean-square error. Finally, to illustrate the use of the results, application is made to a cable channel where the loss in dB varies as the square root of frequency. Various asymptotic formulas and curves are provided to exhibit the relationships between the quantities of interest.

360 citations


Journal ArticleDOI
David Cox1, D. Reudink
TL;DR: In this paper, a large-scale mobile radio system using dynamic channel reassignment switch the channels assigned to some of the calls in progress to maintain a nearly optimum separation between coverage areas simultaneously using the same channel.
Abstract: Large-scale mobile radio systems using dynamic channel REassignment switch the channels assigned to some of the calls in progress to maintain a nearly optimum separation between coverage areas simultaneously using the same channel. Dynamic channel REassignment produces a significant increase in channel occupancy. For example, in the systems studied, which have a uniform distribution of their fixed channels and were operated against a uniform spatial distribution of offered traffic, the channel occupancy was increased by 2/3 over a pure fixed channel assignment system at a blocking rate of one percent. This corresponds to a channel savings of about 40 percent for the same traffic carried at one percent blocking by the hybrid systems that were studied.

179 citations


Journal ArticleDOI
TL;DR: This paper is concerned with characterizing the link between an airplane and a satellite, and attention is focused on the effect of indirect paths scattered from the surface of the earth.
Abstract: This paper is concerned with characterizing the link between an airplane and a satellite. Attention is focused on the effect of indirect paths scattered from the surface of the earth. Applicable propagation-theoretic and system function-theoretic work is reviewed and integrated. Some new and some known expressions for channel correlation functions are presented for the "steepest descent" channel model.

171 citations


Journal ArticleDOI
TL;DR: A suboptimum but simple and practical receiver is proposed for digital signaling over channels with a relatively long impulse response that consists of a linear adaptive equalizer in cascade with a maximum-likelihood sequence estimator.
Abstract: Optimum nonlinear receivers for digital signaling over channels with a relatively long impulse response become too complex to be practical. In this paper a suboptimum but simple and practical receiver is proposed for such channels. The receiver consists of a linear adaptive equalizer in cascade with a maximum-likelihood sequence estimator. A general method of finding the error probability of a maximum-likelihood sequence estimator (MLSE) in the presence of correlated noise is developed. An upper bound on the performance of an MLSE is also presented for the case when thc actual channel is different from the channel estimate known to the MLSE. The performance of the proposed receiver is analyzed and results of the analysis and computer simulation are shown for a typical telephone channel.

166 citations


Journal ArticleDOI
TL;DR: A model of the control process is presented that should provide new insight into channel processes and a basis for improved strategies for attaining desired levels of coordination.
Abstract: The degree of coordination among activity stations in a channel is a measure of the competitive position of that system. The author discusses problems of channel control. He presents a model of the...

145 citations


Proceedings ArticleDOI
04 Jun 1973
TL;DR: This chapter discusses the use of graded channels in the telephone industry, the introduction of asynchronous time division multiplexing, and the packet-switching concepts introduced by Baran et al., Davies, and finally implemented in the ARPA network.
Abstract: Imagine that two users require the use of a communication channel. The classical approach to satisfying this requirement is to provide a channel for their use so long as that need continues (and to charge them for the full cost of this channel). It has long been recognized that such allocation of scarce communication resources is extremely wasteful as witnessed by their low utilization (see for example the measurements of Jackson & Stubbs). Rather than provide channels on a user-pair basis, we much prefer to provide a single high-speed channel to a large number of users which can be shared in some fashion; this then allows us to take advantage of the powerful "large number laws" which state that with very high probability, the demand at any instant will be approximately equal to the sum of the average demands of that population. In this way the required channel capacity to support the user traffic may be considerably less than in the unshared case of dedicated channels. This approach has been used to great effect for many years now in a number of different contexts: for example, the use of graded channels in the telephone industry, the introduction of asynchronous time division multiplexing, and the packet-switching concepts introduced by Baran et al., Davies, and finally implemented in the ARPA network. The essential observation is that the full-time allocation of a fraction of the channel to each user is highly inefficient compared to the part-time use of the full capacity of the channel (this is precisely the notion of timesharing) We gain this efficient sharing when the traffic consists of rapid, but short bursts of data. The classical schemes of synchronous time division multiplexing and frequency division multiplexing are examples of the inefficient partitioning of channels.

144 citations


Journal ArticleDOI
David Cox1, D. Reudink1
TL;DR: Large-scale mobile radio systems using dynamic channel REassignment switch the channels assigned to some of the calls in progress to maintain a nearly optimum separation between coverage areas simultaneously using the same channel.
Abstract: Large-scale mobile radio systems using dynamic channel REassignment switch the channels assigned to some of the calls in progress to maintain a nearly optimum separation between coverage areas simultaneously using the same channel. Dynamic channel REassignment produces a significant increase in channel occupancy. For example, in the systems studied, which have a uniform distribution of their fixed channels and were operated against a uniform spatial distribution of offered traffic, the channel occupancy was increased by \frac23 over a pure fixed channel assignment system at a blocking rate of one percent. This corresponds to a channel savings of about 40 percent for the same traffic carried at one percent blocking by the hybrid systems that were studied.

138 citations


Journal ArticleDOI
Bert Rosenbloom1
TL;DR: The author presents some simple conceptual models which illustrate possible relationships of conflict to channel efficiency and provides a useful framework for utilization of the findings of empirical studies of conflict in the marketing channel.
Abstract: The author presents some simple conceptual models which illustrate possible relationships of conflict to channel efficiency. These models should provide the decision maker with a useful framework f...

129 citations


Journal ArticleDOI
L.G. Anderson1
TL;DR: An investigation of the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment found a general upper bound on this increase has been found.
Abstract: This paper reports the results of an investigation of the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment. Three dynamic channel assignment algorithms were studied by simulation using a 21-cell hexagonal array as a representative system layout. Detailed results for each algorithm are presented. For the particular system studied, traffic capacity can be increased by approximately 25 percent with dynamic channel assignment. A general upper bound on this increase has been found.

Journal ArticleDOI
L.G. Anderson1
TL;DR: In this article, the authors investigated the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment and found that traffic capacity can be increased by approximately 25 percent with dynamic channel assignment.
Abstract: This paper reports the results of an investigation of the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment. Three dynamic channel assignment algorithms were studied by simulation using a 21-cell hexagonal array as a representative system layout. Detailed results for each algorithm are presented. For the particular system studied, traffic capacity can be increased by approximately 25 percent with dynamic channel assignment. A general upper bound on this increase has been found.

Journal ArticleDOI
TL;DR: A parasimulation approach was used to investigate the effectiveness of a superordinate goal and an exchange-of-persons program in managing conflict.
Abstract: This article examines a laboratory methodology for studying interorganizational conflict between members of a distribution channel. A parasimulation approach was used to investigate the effectivene...


Journal ArticleDOI
TL;DR: This paper presents three algorithms which are in a certain minimax sense statistically optimum, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed.
Abstract: Cellular mobile radio systems have been proposed that use many base stations to provide radio service over a large geographical area. In such systems, a stored-program processor assigns radio channels to base stations in real time, under certain interference constraints. The capacity and the queueing characteristics of the overall system are strongly dependent on the processor algorithms that are used. This paper presents three algorithms which are in a certain minimax sense statistically optimum. The procedures are quite general, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed. The first algorithm provides for the preferential assignment of a "standard" channel. If all standard channels are busy, a "nonstandard" channel is selected in such a manner that the probability of blocking is minimized in that interferable facility most likely to suffer blocking. The second algorithm provides for the transfer of service from non-standard to standard channels whenever standard channels become free. The choice of the particular nonstandard channel to be freed is again made in a manner which minimizes the maximum probability of future blockage. The third algorithm provides for the rearrangement of channel assignments in those instances when all assignable channels, both standard and nonstandard, are busy. Such rearrangement can cause channels to become available under certain circumstances. If more than one rearrangement is possible, again the choice of what particular action should be taken is governed by the goal of minimizing the maximum probability of future blockage. All three algorithms attain short-term optimality by enumeration; that is, each candidate for assignment is considered in turn. Under the condition that the given candidate is selected, the conditional probability of future blocking in each of the server groups is calculated, and the maximum of these probabilities is associated with the candidate. After all candidates have been considered, that candidate which has the minimum associated probability is assigned. These algorithms produce, by definition, an instantaneous system state which is always optimum in the above minimax sense. In systems with large numbers of servers, the system changes state rapidly; thus, occasional short-term errors disappear rapidly, and short-term optimization tends to lead to peak performance in the long term as well.

Proceedings ArticleDOI
25 Jun 1973
TL;DR: The algorithm, although based on branch and bound, has provided optimum routings for circuits with 50 to 60 nets in a minute or two of computing.
Abstract: This paper presents an algorithm for finding optimum routings for interconnection paths in a channel between two parallel rows of circuit cells.The algorithm, although based on branch and bound, has provided optimum routings for circuits with 50 to 60 nets in a minute or two of computing.

Journal ArticleDOI
TL;DR: A simple technique is presented for generating and optimally detecting the honeycomb (hexagonal.) signal set, i.e., the signal set that has the tightest sphere-packing properties and is shown to be slightly superior from an average power standpoint.
Abstract: Selection of a particular signal set array for a bandwidthConstrained multiple phase-and-amplitude-shift-keyed (MPASK) communication system for a linear additive Gaussian noise channel requires consideration of factors such as average and/or peak power versus symbol error probability, signal amplitude dynamic range, simplicity of generation and detection, and number of bit errors per symbol error (Gray code properties). A simple technique is presented for generating and optimally detecting the honeycomb (hexagonal.) signal set, i.e., the signal set that has the tightest sphere-packing properties. The symbol and bit error probability performance of this set is compared to other two-dimensional signal sets that have been investigated in the literature, and is shown to be slightly superior from an average power standpoint. The paper concludes with a comparison of all of these signal sets from the standpoint of the factors listed above.

Journal ArticleDOI
TL;DR: The concept of combining the design of the error-correcting-coding approach and the modulation format is treated in general terms and its effectiveness is demonstrated by a specific implementation referred to as Codem I.
Abstract: The concept of combining the design of the error-correcting-coding approach and the modulation format is treated in general terms and its effectiveness is demonstrated by a specific implementation referred to as Codem I. A new decoding algorithm is presented, which has the interesting property that the only channel measurement information utilized is the relative reliability of each received digit. The effectiveness of this decoding technique is demonstrated by computer simulation over three different channel models for dispersive channels. Comparisons of the performance of Codem I with the more conventional 16-tone (four-phase DPSK) HF modem are obtained by actual field results as well as by computer simulations. Improvement in error probability in the region of two orders of magnitude is demonstrated when both systems are operating under similar channel conditions and at equal data rates. A further improvement is demonstrated when channel measurement information is used to reject a small percentage (typically less than 3 percent) of codewords that are considered unreliable.

Journal ArticleDOI
TL;DR: In this article, the length of the flowing channel in a small clay basin in southeast England was observed once per week over a period of 1 year, and the main controls of the total length of flowing channel were found to be the effective rainfall during the previous week and the length at the time of the previous weekly's observation.
Abstract: The length of flowing channel in a small clay basin in southeast England was observed once per week over a period of 1 year. The main controls of the total length of flowing channel were found to be the effective rainfall during the previous week and the length of stream flowing at the time of the previous week's observation. Variations in the lengths of streams of different orders were studied, first-order streams being found to vary most.

01 Jan 1973
TL;DR: The emphasis of this research is on the development of mathematical programming tools for the design of S/F communication networks with proper design criteria established and expressed in terms of the variables.
Abstract: : The emphasis of this research is on the development of mathematical programming tools for the design of S/F communication networks. An analytical model for the system is first presented and discussed. The design variables (routing of messages, channel capacities, topology, etc.) are then defined and proper design criteria (delay, cost, thruput, etc.) are established and expressed in terms of the variables. Next, various design problems are defined and investigated; the most significant of them here follow: (1) Find the minimum cost channel capacity assignment, given the routing of the messages and the maximum admissible delay T; (2) Find the routing which minimizes the delay, given the channel capacities (and therefore the cost); (3) Find the routing and capacities assignment which minimizes the cost, given the maximum admissible delay T. (4) Find the topology, routing and capacities assignment which minimizes the cost, given the maximum admissible delay T. (Author Modified Abstract)

Patent
18 Oct 1973
TL;DR: An asynchronous bus for self-determined priority of communication among master computer devices communicating with slave devices through said bus where a multi-bit data channel and a multi bit address channel are shared between all of said devices as discussed by the authors.
Abstract: An asynchronous bus for self-determined priority of communication among master computer devices communicating with slave devices through said bus where a multi bit data channel and a multi bit address channel are shared between all of said devices. A logic circuit in each said master device is connected to each of three signal lines common to all logic circuits in all of said master devices. One of the three lines is connected in series in the order of assigned priority between master devices. Means are provided to actuate the logic circuits via the three signal lines to limit access to said bus in the order of assigned priority and to signal to other master units bus availability and to transmit an access granted signal to master units down stream of a user unit with only one logic gate delay per downstream unit.

Journal ArticleDOI
TL;DR: In this article, the authors stress the underlying importance of overall distribution channel behaviour to PDM and the importance of the distribution channel as the arena within which marketing and logistics culminate into consumer transactions.
Abstract: Bowersox et al in their well‐known book on physical distribution management stress the underlying importance of overall distribution channel behaviour to PDM. ‘At the outset it is clear that the distribution channel is of fundamental importance to a treatment of physical distribution, because the channel is the arena within which marketing and logistics culminate into consumer transactions. Therefore, for a proper understanding of physical distribution, one should develop a sound insight into the overall nature of total distribution channels’.

01 Jan 1973
Abstract: This correspondence is concerned with binary processes and presents results with immediate applications in the modeling of digital channels for the purpose of evaluating code performance. It is demonstrated that cluster density can be analytically described from the distributions of intervals between errors. These relations and derived clustering properties hold for any stationary process. Analyses of real error data exemplify the use of these results in regard to channels having dependent inter-error intervals.

Proceedings ArticleDOI
01 Jan 1973

Journal ArticleDOI
TL;DR: It is shown that on moderately dispersive channels the equalizer nearly achieves optimum one-shot performance, and an adaptive version of this equalizer exists, this means data transmission on slowly fading channels is possible at rates above the natural rate suggested by the channel dispersion spread without bandwidth expansion and with small intersymbol interference penalty.
Abstract: The reception and detection of a single digit under known channel conditions are investigated. The probability of error for an optimum one-shot receiver instantaneously matched to the channel state is averaged over an ensemble of dispersive diversity channels. The average probability of error as a function of energy to noise ratio is found to be solely dependent on the ratio of rms dispersion width to data symbol width. For these dispersive channels an implicit diversity effect is qualitatively explained in terms of eigenvalues that depend on the ensemble statistic. The one-shot receiver performance provides a bound for practical receivers. In a comparison with a decision feedback equalizer, it is shown that on moderately dispersive channels the equalizer nearly achieves optimum one-shot performance. Since an adaptive version of this equalizer exists, this means data transmission on slowly fading channels is possible at rates above the natural rate suggested by the channel dispersion spread without bandwidth expansion and with small intersymbol interference penalty. The use of one-shot receiver performance curves can also be used as estimates of equalizer performance in situations where computation of the latter is impractical.

Patent
27 Jun 1973
TL;DR: In this article, a sensitive door edge comprising a channel for mounting on a door facing outwardly therefrom, and a pressure sensitive assembly removably inserted into the channel and projecting outwardly from the channel is described.
Abstract: A sensitive door edge comprising a channel for mounting on a door facing outwardly therefrom, and a pressure sensitive assembly removably inserted into the channel and projecting outwardly therefrom.

Journal ArticleDOI
TL;DR: This paper presents three algorithms which are in a certain minimax sense statistically optimum, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed.
Abstract: Cellular mobile radio systems have been proposed that use many base stations to provide radio service over a large geographical area. In such systems, a stored-program processor assigns radio channels to base stations in real time, under certain interference constraints. The capacity and the queueing characteristics of the overall system are strongly dependent on the processor algorithms that are used. This paper presents three algorithms which are in a certain minimax sense statistically optimum. The procedures are quite general, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed. The first algorithm provides for the preferential assignment of a "standard" channel. If all standard channels are busy, a "nonstandard" channel is selected in such a manner that the probability of blocking is minimized in that interferable facility most likely to suffer blocking. The second algorithm provides for the transfer of service from nonstandard to standard channels whenever standard channels become free. The choice of the particular nonstandard channel to be freed is again made in a manner which minimizes the maximum probability of future blockage. The third algorithm provides for the rearrangement of channel assignments in those instances when all assignable channels, both standard and nonstandard, are busy. Such rearrangement can cause channels to become available under certain circumstances. If more than one rearrangement is possible, again the choice of what particular action should be taken is governed by the goal of minimizing the maximum probability of future blockage. All three algorithms attain short-term optimality by enumeration; that is, each candidate for assignment is considered in turn. Under the condition that the given candidate is selected, the conditional probability of future blocking in each of the server groups is calculated, and the maximum of these probabilities is associated with the candidate. After all candidates have been considered, that candidate which has the minimum associated probability is assigned. These algorithms produce, by definition, an instantaneous system state which is always optimum in the above minimax sense. In systems with large numbers of servers, the system changes state rapidly; thus, occasional short-term errors disappear rapidly, and short-term optimization tends to lead to peak performance in the long term as well.

Journal ArticleDOI
TL;DR: It is suggested that “how” a leadership is exercised and not by “whom” is more crucial, a better alternative being a “democratic” leadership.
Abstract: Examines a number of features of the power and influence structures of distribution channels. Discusses a number of dimensions of the distribution of power and influence in channel systems. Looks at the relationship between the power and influence structure of a channel and channel functioning. Considers the need for a channel leader or centre of influence. Suggests that “how” a leadership is exercised and not by “whom” is more crucial, a better alternative being a “democratic” leadership.

Patent
19 Mar 1973
TL;DR: In this paper, a system for processing signals representative of air speed error and inertial longitudinal acceleration in first and second channels respectively and providing cancellation of the turbulence induced components of the respective signals.
Abstract: A system for processing signals representative of air speed error and inertial longitudinal acceleration in first and second channels respectively and providing cancellation of the turbulence induced components of the respective signals. A windshear detection circuit and filter circuit provide a signal representative of windshear induced acceleration which is subtracted from the inertial longitudinal acceleration signal in the second channel to compensate for windshear induced acceleration.

Patent
05 Dec 1973
TL;DR: Gain control for an optical reader having a scanned photocell array producing a multiplexed analog signal stream by cyclically sampling the signals on channels leading from the cells in the array is discussed in this paper.
Abstract: Gain control for an optical reader having a scanned photocell array producing a multiplexed analog signal stream by cyclically sampling the signals on channels leading from the cells in the array. A memory stores digital coded words, one word for each given channel with each word representative of the response characteristics of a given channel. A multibit digital-to-analog converter receives the multiplexed signal. In synchronism with multiplexing the signals, gain control words are read from memory and each converted to an analog gain control voltage which is applied to the converter in coincidence with the appearance at the converter of the signals from the given channel to which the word corresponds to produce a multiplexed digital stream at the output of the amplifier independent of differences in responses of the channels to the same field of view.