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Showing papers on "Communication channel published in 1975"


Journal ArticleDOI
01 Apr 1975
TL;DR: Roberts investigates methods of increasing the effective channel capacity of such a channel and proposes to consider the channel to be slotted into segments of time whose duration is equal to the packet transmission time, and to require the devices to begin a packet transmission at the beginning of a time slot.
Abstract: This paper was originally distributed informally as ARPA Satellite System Note 8 on June 26, 1972. The paper is an important one and since its initial limited distribution, the paper has been frequently referenced in the open literature, but the paper itself has been unavailable in the open literature. Publication here is meant to correct the previous gap in the literature.As the paper was originally distributed only to other researchers intimately familiar with the area covered by the paper, the paper makes few concessions to the reader along the lines of introductory or tutorial material. Therefore, a bit of background material follows.ALOHA packet systems were originally described by Abramson ("The ALOHA System--Another Alternative for Computer Communication," Proceedings of the AFIPS Fall Joint Computer Conference, Vol. 37, 1970, pp. 281--285). In an ALOHA a single broadcast channel is shared by a number of communicating devices. In the version originally described by Abramson, every device transmits its packets independent of any other device or any specific time. That is, the device transmits the whole packet at a random point in time; the device then times out for receiving an acknowledgment. If an acknowledgment is not received, it is assumed that a collision occured with a packet transmitted by some other device and the packet is retransmitted after a random additional waiting time (to avoid repeated collisions). Under a certain set of assumptions, Abramson showed that the effective capacity of such a channel is 1/(2e).Roberts in the present paper investigates methods of increasing the effective channel capacity of such a channel. One method he proposes to gain in capacity is to consider the channel to be slotted into segments of time whose duration is equal to the packet transmission time, and to require the devices to begin a packet transmission at the beginning of a time slot. Another method Roberts proposes to gain in capacity is to take advantage of the fact that even though packets from two devices collide in the channel (i.e., they are transmitted so they pass through the channel at overlapping times), it may be possible for the receiver(s) to "capture" the signal of one of the transmitters, and thus correctly receive one of the conflicting packets, if one of the transmitters has a sufficiently greater signal than the other. Roberts considers the cases of both satellite and ground radio channels.

1,480 citations


Journal ArticleDOI
TL;DR: A mathematical model is formulated for a "slotted ALOHA" random access system and a theory is put forth which gives a coherent qualitative interpretation of the system stability behavior which leads to the definition of a stability measure.
Abstract: In this paper, the rationale and some advantages for multiaccess broadcast packet communication using satellite and ground radio channels are discussed. A mathematical model is formulated for a "slotted ALOHA" random access system. Using this model, a theory is put forth which gives a coherent qualitative interpretation of the system stability behavior which leads to the definition of a stability measure. Quantitative estimates for the relative instability of unstable channels are obtained. Numerical results are shown illustrating the trading relations among channel stability, throughput, and delay. These results provide tools for the performance evaluation and design of an uncontrolled slotted ALOHA system. Adaptive channel control schemes are studied in a companion paper.

607 citations


Journal ArticleDOI
TL;DR: A Markovian decision model is formulated for the dynamic control of unstable slotted ALOHA systems and optimum decision rules are found and numerical results on the performance of controlled channels are shown for three specific dynamic channel control procedures.
Abstract: In a companion paper [1], the rationale for multiaccess broadcast packet communication using satellite and ground radio channels has been discussed. Analytic tools for the performance evaluation and design of uncontrolled slotted ALOHA systems have been presented. In this paper, a Markovian decision model is formulated for the dynamic control of unstable slotted ALOHA systems and optimum decision rules are found. Numerical results on the performance of controlled channels are shown for three specific dynamic channel control procedures. Several practical control schemes are also proposed and their performance compared through simulation. These dynamic control procedures have been found to be not only capable of preventing channel saturation for unstable channels but also capable of achieving a throughput-delay channel performance close to the theoretical optimum.

250 citations


Journal ArticleDOI
TL;DR: The capacity of a single-input single-output discrete memoryless channel is not increased by the use of a noiseless feedback link, but the capacity region for such a channel is enlarged if a noisy feedback link is utilized.
Abstract: The capacity of a single-input single-output discrete memoryless channel is not increased by the use of a noiseless feedback link. It is shown, by example, that this is not the case for a multiple-access discrete memoryless channel. That is, it is shown that the capacity region for such a channel is enlarged if a noiseless feedback link is utilized.

227 citations


Patent
24 Nov 1975
TL;DR: In this article, a communication system of the type where a central station assigns a limited number of information channels to a requesting one of a plurality of remote stations is disclosed, where the requesting station sends its identification signal along with the request signal to the central station on a signal channel.
Abstract: A communication system of the type wherein a central station assigns a limited number of information channels to a requesting one of a plurality of remote stations is disclosed. The requesting station sends its identification signal along with the request signal to the central station on a signal channel. The central station classifies the requesting station in either a priority or a non-priority queue. The priority queue corresponds to those stations which are continuing an on-going interchange, whereas the nonpriority queue contains those stations which wish to initiate an interchange. Stations are prioritized in the queues on a first-in/first-out basis. The central station constantly monitors the information channels and, as channels become available, assigns the channels first to stations in the priority queue, then to nonpriority queue stations. A channel becomes "available" when the central station detects a pause, such as a momentary release of a push to talk microphone switch, in transmission of that channel. By this transmission trunking method, the system makes optimum use of the limited number of available channels. Additional central station processing provides an acknowledgement signal, which indicates that the request was received and a channel will be assigned as soon as one becomes available. Also, the identification of a requesting station is compared with an associate memory. The memory provides the identifications of all stations to whom the requesting station would transmit. Once a channel is available, it is assigned to the requesting station and to its associated stations, whereby the associated stations are notified of, and prepared for, the impending transmission.

133 citations


Book ChapterDOI
01 Jan 1975
TL;DR: This chapter discusses the recent advancements in the broadcast channels and discusses the m-sender n-receiver network capacity region, which is currently unknown although the m x 1 region is known, and the 1x n region isknown for the special case of degraded broadcast channels.
Abstract: Publisher Summary This chapter discusses the recent advancements in the broadcast channels The reason for work on broadcast channels is that the regions of achievable rates can be exceeded by optimal encoding It turns out that one should neither transmit simultaneously to several channels at the rate of the worst channel nor attempt to transmit information by a time-sharing or time-multiplexing method but rather one should distribute the high-rate information across the low-rate message The capacity region for a broadcast channel is the set of all achievable rates (R 11 , R 12 , R 22 ) The degraded broadcast channel models the situation in which one receiver is farther away than the other receiver The total information flow to the receiver that is being multi-accessed is W l n(l+ (kP/NW)), which tends to infinity asymptotically like l n k Thus, the bandwidth limitation does not prevent the flow of information to the receiver from going to infinity as the number of users grows to infinity The m-sender n-receiver network capacity region is currently unknown although the m x 1 region is known, and the 1x n region is known for the special case of degraded broadcast channels

127 citations


Proceedings ArticleDOI
19 May 1975
TL;DR: There is an increasing demand for access to data processing and storage facilities from interactive terminals, point-of-sales terminals, real-time monitoring terminals, hand-held personal terminals, etc.
Abstract: Terminal access to computer systems has long been and continues to be a problem of major significance. We foresee an increasing demand for access to data processing and storage facilities from interactive terminals, point-of-sales terminals, real-time monitoring terminals, hand-held personal terminals, etc. What is it that distinguishes this problem from other data communication problems? It is simply that these terminals tend to generate demands at a very low duty cycle and are basically bursty sources of data; in addition, these terminals are often geographically distributed. In the computer-to-computer data transmission case, one often sees high utilization of the communication channels; this is just not the case with terminal traffic. Consequently, the cost of providing a dedicated channel to each terminal is often prohibitive. Instead, one seeks ways to merge the traffic from many terminal sources in a way which allows them to share the capacity of one or a few channels, thereby reducing the total cost. This cost savings comes about for two reasons: first, because of the economies of scale present in the communications tariff structure; and secondly, because of the averaging effect of large populations which permit one to provide a channel whose capacity is approximately equal to the sum of the average demands of the population, rather than equal to the sum of the peak demands (i.e., the law of large numbers). This merging of traffic and sharing of capacity has been accomplished in various ways such as: polling techniques, contention systems, multiplexing, concentrating, etc. Many of these are only weak solutions to the problem of gathering low data rate traffic from sources which are geographically dispersed.

108 citations


01 Jan 1975
TL;DR: In this article, the effect of dilute, long-chain, polymer solutions upon the spatial structure of the viscous sublayer in fully developed, turbulent, two-dimensional channel flows was determined.
Abstract: The effect of dilute, long‐chain, polymer solutions upon the spatial structure of the viscous sublayer in fully developed, turbulent, two‐dimensional channel flows was determined. The longitudinal, low‐speed streaks characteristic of the sublayer were made visible by seeping dye through a transverse slot in one wall. Motion pictures yielded a detailed description of the streak formation process and revealed two major differences in the sublayer structure when drag reduction occurs. At a given nondimensional distance from the wall, the average transverse spacing of the streaks increases as the amount of drag reduction increases. The average streak spacing within the viscous sublayer is not a function of the distance from the wall in water flows and flows at lower levels of drag reduction. At high levels of drag reduction, the average spacing varies within the sublayer increasing as the wall is approached.

98 citations


Journal ArticleDOI
TL;DR: In this paper, the capacity region for the general non-degraded discrete memoryless broadcast channel with two components is derived for three different communication situations, in which common and separate information is sent to both receivers, and in another situation, only one Common and one separate message is sent.
Abstract: Three different communication situations are considered for the general nondegraded discrete memoryless broadcast channel with two components. In the most general situation, common and separate information is sent to both receivers. In another situation, only separate information is sent, and in a third, one Common and one separate message is sent. For each communication situation a random coding inner bound on the capacity region is derived. An example is presented which Shows that in the most general situation the inner bound strictly dominates the family of rates obtained by time-sharing. The capacity region for the general situation is characterized by a limiting expression. The relationship with the degraded broadcast channel and the connection with other multiway channels, such as the channel with two senders and two receivers, is shown.

98 citations


Journal ArticleDOI
TL;DR: In this paper, an optimum linear receiver for multiple channel digital transmission systems is developed for the minimum P e and for the zero-forcing criterion, together with a theorem on the optimality of a finite lenght multiple tapped delay line.
Abstract: An optimum linear receiver for multiple channel digital transmission systems is developed for the minimum P e and for the zero-forcing criterion. A multidimensional Nyquist criterion is defined together with a theorem on the optimality of a finite lenght multiple tapped delay line. Furthermore an algorithm is given to calculate the tap settings of this multiple tapped delay line. This algorithm simplifies in those cases where the noise is so small that it can be neglected. Finally as an example the transmission of binary data over a cable, consisting of four identical wires, symmetrically situated inside a cylindrical shield, is considered.

93 citations


Patent
Kuemmerle K A1, Port E1, Zafiropulo P A1
18 Apr 1975
TL;DR: In this paper, a TDM multiplexer is used to combine circuit-switched synchronous data and packetswitched asynchronous data for transmission over a common channel, where the remaining capacity of the TDM frame is used for transmission of store-and-forward traffic which is inserted in the gaps between assigned time slots in the form of an intermittent bit stream.
Abstract: A method and a TDM multiplexer by which circuit-switched synchronous data and packet-switched asynchronous data are optimally combined for transmission over a common channel. Time slots of variable width are assigned to circuit-switched traffic, while the remaining capacity of the TDM frame is used for transmission of store-and-forward traffic which is inserted in the gaps between assigned time slots in the form of an intermittent bit stream.

Patent
04 Nov 1975
TL;DR: In this paper, the left and right channel signals are compared and, when they include significant amounts of correlated information, the relative gain of the center channel is enhanced by boosting the gain of that channel and/or cutting the gains of the right channels.
Abstract: In a stereophonic reproduction system, especially for a cinema, a center channel signal is derived by combining left and right channel signals. In order to harden the center image, particularly in speech, the left and right channel signals are compared and, when they include significant amounts of correlated information, the relative gain of the center channel is enhanced by boosting the gain of that channel and/or cutting the gain of the left and right channels. The test for correlation of information is preferably restricted to speech frequencies and the enhancement of relative gain may be performed only at middle frequencies.

Patent
21 May 1975
TL;DR: In this article, a heat or cold storage system utilizing a plurality of channels dug directly into the earth and filled with rocks which are used to absorb heat and cold for storage, a part of such storage being the rocks themselves and a (usually much larger) part being the adjacent earth.
Abstract: A heat or cold storage system utilizing a plurality of channels dug directly into the earth and filled with rocks which are used to absorb heat or cold for storage, a part of such storage being the rocks themselves and a (usually much larger) part being the adjacent earth. Conduit connections are provided for carrying heat or cold to the rocks.

Patent
28 Oct 1975
TL;DR: In this article, an input/output controller for an information processing system comprising a main memory, a central processing unit, a peripheral controller and a plurality of peripheral units coupled to the central processing units is disclosed.
Abstract: There is disclosed an input/output controller for an information processing system comprising a main memory, a central processing unit, a peripheral controller and a plurality of peripheral units coupled to the central processing unit. In particular, the input/output controller comprises a plurality of physical channels disposed between the peripheral controller and the central processing unit, a plurality of logical channels for transmitting information with the central processing unit, and each uniquely associated with one of the peripheral units. The main memory stores a first table including a physical channel entry containing informaton relative to the plurality of physical channels and a second table including a logical channel entry containing information relative to the plurality of peripheral units. Further, there is included means for storing a channel control program to be executed by the input/output control system for selectively transferring data between the main memory and the peripheral controller by first connecting the input/output control system to a logical channel entry and placing the identified logical channel table into the means for storing for a subsequent execution.

Patent
22 May 1975
TL;DR: In this article, a system for remotely monitoring or determining the channel to which a voltage tunable receiver (or CATV converter) has been tuned includes an encoder for measuring the magnitude of the tuning voltage applied to the tuning section of the receiver and for generating a channel representative digital code in response to tuning voltage.
Abstract: A system for remotely monitoring or determining the channel to which a voltage tunable receiver (or CATV converter) has been tuned includes an encoder for measuring the magnitude of the tuning voltage applied to the tuning section of the receiver and for generating a channel representative digital code in response to the tuning voltage. The digital code thus generated is compatible with remotely located monitoring equipment, and represents the number of the channel to which the receiver is tuned. Since the tuning voltage is not linearly related to the channel number of the station being received, the encoder utilizes a read-only memory or the like for storing a coded representation relating the channel number to the tuning voltage. In a preferred embodiment, the coded representations are sequentially stored as tuning voltage representations in address locations of the memory corresponding to the respective channel numbers. The read-only memory locations are sequentially addressed, and the tuning voltage representations are compared with the amplitude of the tuning voltage currently being applied to the receiver. When the value of the tuning voltage representation equals or exceeds the amplitude of the tuning voltage, the sequential addressing is terminated and the address of the last accessed memory location is stored to provide a coded indication of the channel number of the station being received.

Patent
07 Apr 1975
TL;DR: In this article, an asynchronous digital time division multiplexer and demultiplexer combination at one communication terminal is disclosed that will multiplex first N asynchronous source data signals having a first mixture of different bit rates into a transmitted synchronous data stream having a predetermined fixed data format and a given bit rate greater than the total of the bit rates of the source data.
Abstract: An asynchronous digital time division multiplexer and demultiplexer combination at one communication terminal is disclosed that will multiplex first N asynchronous source data signals having a first mixture of different bit rates into a transmitted synchronous data stream having a predetermined fixed data format and a given bit rate greater than the total of the bit rates of the source data and to demultiplex second N asynchronous source data signals having a second mixture of different bit rates from a received synchronous data stream having the predetermined fixed data format and the given bit rate. The combination includes an automatic channel assignment circuit to assign channels of the two data streams to the asynchronous source data signals in a manner to minimize temporary data memory regardless of the number of different bit rates by assigning the data signals to channels of the associated one of the two data streams so that the bits of each of the data signals tend to have equal spacing throughout the bits of the associated one of the two data streams. The channel assignment control circuit also includes a means to automatically indicate when the total of the mixture of bit rates has exceeded an allowable maximum.

Patent
09 May 1975
TL;DR: In this article, a gain control apparatus is provided for controlling the gain applied to the signals in each channel whereby the total gain of the system remains constant, such that the automatic gain variations in all channels are always complementary.
Abstract: In a sound reinforcement system having a plurality of input channels and input signal sources and at least one output channel, a gain control apparatus is provided for controlling the gain applied to the signals in each channel whereby the total gain of the system remains constant. Gain changes in each channel are proportional to signal ratios such that the automatic gain variations in all channels are always complementary. In a preferred embodiment, the control apparatus comprises means for providing a reference signal having a magnitude proportional to the sum of the amplitudes of the signals in the channels and a plurality of control signals each of which has a magnitude proportional to the amplitude of the signal in a respective one of said channels, and a plurality of attenuating means, each of which is responsive to the ratio of the corresponding one of said control signals to the reference signal.

Patent
Michael Robert Boudry1
08 Jul 1975
TL;DR: In this article, a data transmission system for interfacing a computer with a plurality of data sources which are in groups, each group at an individual remote location, comprising local interface apparatus for the computer and remote interfaces for each remote location are provided for connection by a two-wire channel to sending and receiving means at each remote apparatus.
Abstract: A data transmission system for interfacing a computer with a plurality of data sources which are in groups, each group at an individual remote location, comprising local interface apparatus for the computer and remote interface apparatus for each remote location, wherein individual sending and receiving means at the local apparatus are provided for connection by a two-wire channel to sending and receiving means at each remote apparatus, wherein the local apparatus includes a buffer for each channel to receive input data words one at a time in bit serial form its respective channel, means for polling each buffer in turn until a buffer having an input data word is located when polling stops, and means responsive to an input by the computer of an input data word from a buffer to clear that buffer, send an acknowledge word in bit serial form to the respective remote location and restart the polling.

Patent
25 Jun 1975
TL;DR: In this paper, a tapped delay line network is used to cancel the received four-wire signal with the signal passing through the resistor network to obtain signal cancellation at the four wire-to-wire transmit port when the 4-wire receive channel is activated.
Abstract: Improved isolation between the four-wire receive and transmit ports in a four wire-to-wire converter in a communication system is obtained by utilizing a tapped delay line network in an active hybrid circuit. The active hybrid circuit includes a first amplifier which terminates the four-wire receive channel in its characteristic impedance, amplifies the four-wire received signal, and excites a resistor network that terminates the two-wire channel in its nominal characteristic impedance. A second amplifier and a resistor circuit function as a weighted summer for nulling the received four-wire signal with the signal passing through the resistor network to obtain signal cancellation at the four-wire transmit port when the four-wire receive channel is activated. The tapped delay line network may be connected either between the first amplifier and resistor network or between the first amplifier and the received four-wire signal input of the second amplifier.

Journal ArticleDOI
TL;DR: Results show that the hybrid schemes offer substantial improvement over ARQ and FEC, and that an optimum exists for the number of errors corrected to obtain maximum throughput efficiency.
Abstract: The effectiveness of hybrid error control schemes involving forward error correction (FEC) and automatic repeat request (ARQ) is examined for satellite channels. The principal features of the channel are: large round-trip transmission delay due to the satellite link, and burst errors introduced by the terrestrial links that connect the users to the satellite link. The performance is estimated for two channels described by Fritchman's simple partitioned finite-state Markov model, and is compared to that obtainable if the channel is considered as a binary symmetric channel of the same bit error probability. Results show that the hybrid schemes offer substantial improvement over ARQ and FEC, and that an optimum exists for the number of errors corrected to obtain maximum throughput efficiency.


Patent
22 Oct 1975
TL;DR: In this paper, an improved multiplexer especially adapted for combining a plurality of microwave signal channels for transmission over a common transmission path is disclosed, where a single "directional filter" structure is utilized to combine contiguous or adjacent channels without resort to odd-even channel separation or additional equalization and/or compensation networks.
Abstract: An improved multiplexer especially adapted for combining a plurality of microwave signal channels for transmission over a common transmission path is disclosed. A single "directional filter" multiplexer structure is utilized to combine contiguous or adjacent channels without resort to odd-even channel separation or additional equalization and/or compensation networks. By purposely extending the bandpass characteristics of preselected channel filters so that either or both of their cutoff frequencies extend substantially past their associated channel band edges and well into the reflection loss regions of the adjacent channel or channels the adjacent channel mutual interaction effect is exploited. The resultant interaction between the transmission characteristics of one channel and the reflection characteristics of the adjacent channel yields an overall transmission characteristic for each channel which meets the multiplexer loss, loss slope and group delay requirements while minimizing the need for equalizing or compensating devices.

Journal ArticleDOI
TL;DR: In this paper, an efficient broadband coupling method was proposed to achieve signal isolation between subconductors without inserting additional impedance at power frequency or reducing the power transmission capability of the line, and the signal characteristics of the new system are such that interference is reduced by orders of magnitude in comparison to p.l.c.
Abstract: The main properties of power line carrier (p.l.c.) systems, used conventionally for internal communication purposes in electricity supply undertakings, are examined, and an alternative method for use on bundle-conductor lines is proposed. Earlier work, departing from the use of conventional phase-ground or interphase carrier, proposed the electrical separation of the subconductors of a bundle for signal frequencies, but retained the remaining aspects of conventional p.l.c. These include particularly the expensive filter components required to limit the signal, as far as possible, to the desired parts of the power network, together with the frequency and bandwidth limitation imposed on the signal by these filters. The intrabundle communication system proposed uses a simple, inexpensive but highly efficient broadband coupling method which permits signal-isolation between subconductors without inserting additional impedance at power frequency or reducing the power transmission capability of the line. The signal characteristics of the new system are such that interference is reduced by orders of magnitude in comparison to p.l.c., avoiding need for frequency assignment even between adjacent phases. A bandwidth of 1.6 MHz is available. This may be exploited in a variety of ways, including the transmission of data at faster rates, to enhance the reliability and speed of protection signalling, or to provide up to 180 duplex voice channels. Even where one voice channel only is required, the cost of an intrabundle communication system is estimated to be less than that of a p.l.c, system for route lengths of at least 29 km, and allows subsequent increase in the voice channel numbers at low extra cost.

Patent
21 Apr 1975
TL;DR: An automatic channel assignment circuit in a controlling association with an asynchronous or synchronous digital time division multiplexer and demultiplexer combination at one communication terminal is presented in this paper.
Abstract: An automatic channel assignment circuit in a controlling association with an asynchronous or synchronous digital time division multiplexer and demultiplexer combination at one communication terminal to assign channels of transmitted and received synchronous data streams to asynchronous or synchronous source data signals in a manner to minimize temporary data memory regardless of the number of different bit rates of the source data signals by assigning the data signals to channels of the associated one of the transmitted and received data streams so that the bits of each of the data signals tend to have equal spacing throughout the bits of the associated one of the transmitted and received data streams. Each of the transmitted and received data streams have a predetermined fixed data format with respect to the channels and a given bit rate greater than the total of the bit rates of the source signals. However, the automatic channel assignment circuit provides, in effect, an automatically determined-at-the-time-of-rate-selection a variable data format with respect to the ports. The channel assignment control circuit also includes a means to automatically indicate when the total of the mixture of bit rates has exceeded an allowable maximum.

Patent
04 Dec 1975
TL;DR: In this paper, a three-stage switching network is used to establish a connection between a network input or input channel and a certain network output or output channel by rearrangement of a three stage switching network.
Abstract: Apparatus establishes a connection between a certain network input or input channel and a certain network output or output channel by rearrangement of a three-stage switching network, where, in a specific network condition, each network input or input channel is assigned to a specific network output or output channel. The desired connection is derived by means of successive permutations of the connections within the switching stages until the desired connection has been attained. The apparatus includes a special switching memory wherein the actual network condition is recorded. The organization of the memory is such that the various memory cells are addressed according to the numbering of the interstage links on one side of the central switching stage and each of the cells has a record of which network input and network output is interconnected via the link in question. The apparatus further includes means for the identification of the addresses involved in the desired connection and for the subsequent determination and execution of the necessary permutations, based on these addresses.

Patent
17 Mar 1975
TL;DR: Disclosed as discussed by the authors is a technique for error checking in one channel or a pair of channels of a binary system in which communications is serial-by-character and parallel-by bit, such as in digital computer-controlled magnetic tape peripherals.
Abstract: Disclosed is a technique for error checking in one channel or a pair of channels of a binary system in which communications is serial-by-character and parallel-by-bit, such as in digital computer-controlled magnetic tape peripherals. The system is shown as applied to the group coded recording (GCR) format and standard for half-inch, nine-track magnetic tape used for interchange among information processing systems (the USA Standard Code for Information Interchange). The technique employs equipment which generates and records on the tape, together with a set of information characters, a check (i.e., redundant) character and parity bits, the former resulting from the employment of a cyclic code and the latter being based on odd modulo 2 addition.

Patent
22 Dec 1975
TL;DR: In this paper, a plurality of processing channels each receive one of a number of direct d secondary signal energy rays, each channel includes an A/D converter and computer the logic of which is controlled by a Fast Fourier Transform (FFT) algorithm to produce a pluralityof data outputs each containing the amplitude and phase information of selected frequencies present in the channel input.
Abstract: A plurality of processing channels each receive one of a number of direct d secondary signal energy rays. Each channel includes an A/D converter and computer the logic of which is controlled by a Fast Fourier Transform (FFT) algorithm to produce a plurality of data outputs each containing the amplitude and phase information of selected frequencies present in the channel input. To enhance signal detection and minimize signal strength fluctuations, each of the selected frequency outputs of each channel FFT is compared with each identical frequency output of other channel FFT's. Phase compensation means such as a shift register adjusts the phase relationship between all identical FFT outputs to permit their amplitudes to be constructively added. The individual subtotals so produced are totalled to provide an output representing the combined strength of the multi-path signal energy. In particular, medium interfaces such as an air-sea or air-ground interface, produce wide variations in the incoming direction of the signal energy to be detected.

Journal ArticleDOI
TL;DR: Ahlswede (1974) found a new approach to the coding problem for a channel with two senders and one receiver which led to an alternative characterization of the capacity region of this channel, and this approach seems to be more canonical than the earlier one.
Abstract: The study of multi-way channels was initiated by Shannon in his basic paper “Two-way communication channels” ( Shannon, 1961 ). Ahlswede (1971b) has defined and classified multi-way channels of various kinds and proved simple characterizations for the capacity regions of channels with (a) two senders and one receiver, and (b) three senders and one receiver. Subsequently, Ahlswede (1974) found a new approach to the coding problem for a channel with two senders and one receiver which led to an alternative characterization of the capacity region of this channel. This approach seems to be more canonical than the earlier one, and was used successfully in determining the capacity region of a channel with two senders and two receivers in case both senders send messages simultaneously to both receivers ( Ahlswede, 1974 ). In the earlier paper, Ahlswede conjectured that the results of that paper would hold for any channel with s ⩾ 2 senders and one receiver. A conjecture of the later paper was that its results would hold for any channel with s ⩾ 2 senders and r ⩾ 1 receivers in case all senders send independent messages simultaneously to all receivers. In this paper, we have proved the latter conjecture to be true. The characterization we get for the special case s = 3 and r = 1 is different from that of Ahlswede's (1971b) earlier paper. All of our results are obtained under the assumption of independent sources.

Patent
27 Jun 1975
TL;DR: In this article, a tracking system for a sorting apparatus for sorting pieces of material moving through a sorting zone in a wide path random stream has a light scanning device which makes repeated scans across the sorting zone to detect light reflected from the pieces of materials, and downstream of the scanning device a plurality of deflection devices extending across the scanning zone.
Abstract: A tracking system for a sorting apparatus for sorting pieces of material moving through a sorting zone in a wide path random stream has a light scanning device which makes repeated scans across the sorting zone to detect light reflected from the pieces of material, and downstream of the scanning device a plurality of deflection devices extending across the sorting zone. An electronic control generates timing signals which, in effect, represent a plurality of overlapping analyzing channels extending in the direction of movement of the pieces of material and overlapping one another across the sorting zone. An electrical circuit arrangement for each analyzing channel receives signals from the scanning device and accumulates information relating to pieces of material in that channel and provides a decision signal based on the accumulated information. A control for each analyzing channel is responsive to the decision signal for that channel to actuate a number of deflection devices which extend at least the width of the channel. Because the analyzing channels overlap it is more probable that a piece of material will be within or substantially within one channel for analysis.

Patent
13 Aug 1975
TL;DR: In this article, a phase modulated carrier wave is demodulated by sampling at a rate f s greater than the frequency of the carrier, comparing the phase of each sample with a sample delayed a nominal bit period in one channel, sample delayed less than the nominal bits period in a second channel, and sample delayed more than the bit periods in a third channel to compensate for positive and negative Doppler shift of the channel from its nominal frequency in the second and third channels, respectively.
Abstract: A phase modulated carrier wave, in which a phase reversal represents one of two binary values is demodulated by sampling at a rate f s greater than the frequency of the carrier, comparing the phase of each sample with a sample delayed a nominal bit period in one channel, a sample delayed less than the nominal bit period in a second channel, and a sample delayed more than the nominal bit period in a third channel to compensate for positive and negative Doppler shift of the carrier from its nominal frequency in the second and third channels, respectively. A code word is detected in each of the three channels by comparing each demodulated sample bit with a replica of the code word, and correlating the results separately for each channel. The channel with the highest correlation is selected as the one most closely tuned to the carrier frequency received.