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Communication Technology, IEEE Transactions on

Issue 4 • Date August 1967

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Displaying Results 1 - 25 of 29
  • [Front cover and table of contents]

    Publication Year: 1967 , Page(s): 0
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    Freely Available from IEEE
  • A Sequential Decoding Technique and Its Realization in the Lincoln Experimental Terminal

    Publication Year: 1967 , Page(s): 477 - 491
    Cited by:  Papers (7)
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    Probabilistic codes when suitably matched to modulation-demodulation systems allow communications which realize the theoretical performance predicted by the coding theorem. Sequential decoding is a form of probabilistic coding which allows realization in practical equipment to achieve this end. The Lincoln Experimental Terminal (LET) uses convolutional encoding and sequential decoding matched to a modulation system employing a 16-ary orthogonal alphabet and matched filter envelope detectors, followed by an ordered list of the filters containing the 7 largest outputs. This coding system employing a constraint length of 60 bits and rates of 1 and 2 bits per orthogonal symbol achieves operation at an energy to noise ratio of 6 dB per information bit on an active satellite (Gaussian) channel. The Fano decoding algorithm is employed. After a brief description of this algorithm, the realization of the LET encoder-decoder is presented. The machine using a commercial magnetic core memory, together with about 2000 integrated circuit elements, occupies about 20 inches of 19-inch rack space. View full abstract»

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  • Sequential decoding for efficient communication from deep space

    Publication Year: 1967 , Page(s): 492 - 501
    Cited by:  Papers (17)
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    A system based on sequential decoding and utilizing binary phase-shift keying and 8-level quantized decisions is proposed for deep-space communication. Theoretical analyses augmented by a program of computer Simulation promise operation within 3-4 dB of the channel capacity of an infinite bandwidth additive white Gaussian noise channel. A low probability of erasure is achieved by the suggested use of occasional off-line decoding. A negligible probability of error is readily achieved. Channel coherence is examined and quadratic and decision-directed methods of achieving a phase reference are compared. Extensive symbol interleaving is suggested and an analysis included of the required phase reference signal-to-noise ratio. View full abstract»

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  • A Method for Calculating Phase-Locked Loop Performance Near Threshold

    Publication Year: 1967 , Page(s): 502 - 506
    Cited by:  Papers (6)
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    Although several methods have evolved over the past few years for analyzing the near-threshold behavior of phaselocked devices, none so far have been able conveniently to integrate all desirable aspects of an engineering method which requires both accuracy and simplicity of formulation. This paper contains a method conceptually as simple as the linear and quasi-linear techniques, but with the added advantage that it is much more accurate near loop threshold-an accuracy, by the way, which increases as the order of the loop increases and as the loop bandwidth decreases. For the simple first-order loop, which is the one this method predicts with least fidelity, the result follows the known exact carrier tracking result with a maximum error of less than 0.08 radians in the rms phase error at system threshold. Compared to actual measurements of carrier tracking secondorder loop performance, the method provided excellent agreement, nominally within 0.05 radians at a \sigma ^{2} = 1 . View full abstract»

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  • Error Rates for Digital Signals Demodulated by an FM Discriminator

    Publication Year: 1967 , Page(s): 507 - 517
    Cited by:  Papers (26)
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    The calculation of the error rate resulting from the detection of binary frequency shift keyed (FSK) signals using an FM discriminator low-pass filter detector is described. An example is given using an alternating mark space sequence and the results compared with those obtained using a matched filter. The results indicate that in certain regions the FM discriminator low-pass filter detector yields error rates comparable to the matched filter detector, while in other regions the matched filter significantly out performs the discriminator. An error correction device is described, which when used in conjunction with the discriminator, reduces the error rate of the discriminator detector so that it more closely approaches the matched filter detector. Experimental results are presented to verify the theory. View full abstract»

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  • Frequency Locked Loop FM Demodulator

    Publication Year: 1967 , Page(s): 518 - 524
    Cited by:  Papers (7)
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    A new type of FM demodulator, the Frequency Locked Loop (FLL) is presented. The concept employed in this class of circuits is shown to be applicable in two forms. The first form is realized at the carrier, or IF frequency, to provide an FM detector that has the properties of not requiring a limiter preceding it and also of having a threshold superior to a normal FM discriminator limiter combination. The second form of the FLL is realized at baseband. This form may be added to any existing FM receiver to provide threshold extension properties to the original receiver. In addition to discussing both versions of this new circuit arguments as to the click suppression and threshold extension properties of the circuit are presented. Detailed experimental comparisons of the new circuit with a conventional FM discriminator are made. A comparison is also drawn between the theoretically possible threshold extension of an FLL and that actually obtained with a baseband version of the FLL. View full abstract»

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  • Design of Block-Coded Communication Systems

    Publication Year: 1967 , Page(s): 525 - 534
    Cited by:  Papers (7)
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    The design and performance of frequency multiplexed, phase-modulated communication systems is presented. In particular, the transmitter is assumed to be an ideal phase modulator which modulates a RF carrier with N phase-modulated, sinusoidal data subcarriers, and in general, M binary-valued composite signals. The receiver is a superheterodyne phase-locked loop (PLL) whose output is applied to one of N subcarrier extractors. Each subcarrier extractor consists of a subcarrier tracking loop, a timing loop, and a data detector which operates as a cross-correlator. The paper presents results which allow the design engineer to allocate the total power between N modulated data subcarriers, M binary-valued signals, and the carrier signal. The total power in the distortion component is computed. Finally, a method is given which allows the communications engineer to select the data rate and the modulation factor of each data subcarrier which will minimize the probability that the data detector will err in the decision process. The results are sufficiently general so that they may be used in designing block-coded systems. Such systems have application in various branches of aerospace communication engineering, e.g., channelized communication satellites and deep-space probes. View full abstract»

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  • Optimum Nonlinear Scalar Transmitters and Receivers

    Publication Year: 1967 , Page(s): 535 - 542
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    Optimum designs are obtained for a receiver for processing scalar signals embedded in noise, a scalar transmitter in a given noise environment, and a scalar transmitter for combating noise and crosstalk. An iteration algorithm is given for determining the best combination of transmitter and receiver to combat noise; an approximate best combination is calculated in the small noise case. View full abstract»

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  • The Reduction of Systematic Jitter in a Transmission Chain with Digital Regenerators

    Publication Year: 1967 , Page(s): 542 - 551
    Cited by:  Papers (3)
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    This paper describes methods for the reduction of jitter in transmission chains with regenerative repeaters. These methods are based on the application of pattern transformations to the output signals of successive repeaters. As a result, the coherent accumulation of jitter from signal dependent jitter sources is prevented. Instead, the jitter accumulates on a power basis. It is shown that in this way a significant reduction of jitter is obtained. This result is demonstrated by both theoretical data and measurements on an experimental transmission chain which correspond fairly closely. Furthermore, the realization of the pattern transformations by simple coding techniques is presented in detail. View full abstract»

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  • Observations on the Effects of Pulse Noise in Digital Data Transmission Systems

    Publication Year: 1967 , Page(s): 552 - 556
    Cited by:  Papers (2)
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    This paper presents some observations concerning the type of variability one might encounter in determining error rates in digital data transmission systems subjected to impulse noise. The effects of pulse shape and duration are investigated. It is shown that for signal-to-noise ratios (SNR) greater than -5 dB, a variation of 8 to 1 in the average number of errors per pulse might be encountered as pulse shape is varied. For pulsewidths in the range 0.1 to 4 ms, a variation of 6 to 1 in the average number of errors, per pulse at a given SNR could be expected. Experimental findings relating error rates to pulse duration were supported by analytical studies. The probability of making an error, given that a noise burst has occurred, is determined and a worst case analysis is made, from which a critical SNR is found such that if the noise is below this threshold, no errors can occur. It is recognized that the limitations imposed by the equipment available for study results in a loss in generality. However, the results presented are indicative of the type of variations one might encounter in the case of actual impulse noise on an existing practical system. View full abstract»

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  • Intermodulation Noise of FDM-FM Communications Through a Hard Limiter

    Publication Year: 1967 , Page(s): 557 - 565
    Cited by:  Papers (2)
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    When the multiple signals of FDM-FM communications are passed through a hard limiter, intermodulation products are generated which cause baseband noise. A technique is presented, implemented by a computer program, of explicitly determining this baseband noise as a function of the system parameters of frequency ratio, frequency deviation, and carrier magnitudes. Results are presented as a function of the system parameters using four carriers which are each modulated by four voice channels. The technique presented permits the minimization of the intermodulation baseband noise without the cost of system simulation. View full abstract»

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  • Wideband Troposcatter Radio Channel Simulator

    Publication Year: 1967 , Page(s): 565 - 570
    Cited by:  Papers (2)
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    A versatile troposcatter simulator has been built which can produce radio channels exhibiting frequency fiat or frequency selective fading over a band greater than l0 MHz and centered at 70 MHz. Frequency selective channels with Rayleigh or other fading are available with controllable cross-correlation of the multipath components. In addition, multiple diversity channels with controllable cross-correlations are provided. A method of estimating the delay and attenuation values for modeling a particular path in terms of intermodulation and thermal noise in an FDM-FM system is described. The actual path measurements and the simulated path measurements are shown to be in reasonably good agreement. View full abstract»

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  • A 160-Watt Experimental Thermoelectric Power Plant for Telephone Microwave Equipment

    Publication Year: 1967 , Page(s): 571 - 578
    Cited by:  Papers (1)
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    A field experiment is described which has operated since July, 1964, using commercially available thermoelectric generators to provide power to a transmitter-receiver bay of telephone microwave equipment. The generators are operated at a nominal power level of 160 watts. The purpose of the experiment is to gain experience with thermoelectric generators operating under actual field conditions and to evaluate their potential as primary power sources for systems operating in remote areas. The design approach is presented together with a description of the test site. Data are presented concerning the operating characteristics of the power plant with details of environmental effects on generator operation. The cost of providing primary thermoelectric power at a remote site is shown with a comparison to primary diesel, primary battery, and commercial ac power. Conclusions are drawn regarding the economic and technical feasibility of primary thermoelectric power for systems operating in remote areas. View full abstract»

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  • Use of Commercial Broadcast Stations for Emergency DOD Communications

    Publication Year: 1967 , Page(s): 579 - 592
    Cited by:  Papers (1)
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    This work proves the feasibility of utilizing commercial broadcast facilities for emergency Department of Defense 100 wpm Teletype communications. The test network, which consists of ten stations, extends over the northeastern United States. Teletype communications is accomplished by frequency shifting the carrier of the broadcast station transmitter ±18 Hz. This submodulation technique causes no degradation to the commercial broadcast material and is undetectable on a standard home receiver. The tests that were conducted on this network between the terminals at Rome Air Development Center (RADC) Rome, N. Y., and the Federal Communications Commission Laurel Laboratories, Laurel, Md., proved the reliability and survivability of this communications technique. View full abstract»

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  • Measurement of the Phase Constant for Rock Propagated Radio Signals

    Publication Year: 1967 , Page(s): 592 - 597
    Cited by:  Papers (4)
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    A method is described for determining the phase constant of the rock medium below the surface of the earth. The constant is deduced from the measured phase angle of the mutual impedance between two vertically polarized antennas placed in drill holes extending into the rock. Experiments were conducted at Cape Cod, Mass., using the method to determine the phase constant of the rock between two 1000-foot drill holes, separated by a distance of 6000 feet, at frequencies between 100 and 4200 Hz. Electrically short monopoles were used in the drill holes, with the overburden above the rock serving as a ground plane. Reference phase was derived from nearby Loran-C transmissions received at both the transmitting and receiving ends of the path. The measured phase constants at these frequencies indicate a large loss tangent for the medium. The bulk conductivity was thus deduced to be 1.1 \times 10^{-3} mho/meter, and the measurements did not alone yield an estimate of the relative dielectric constant. View full abstract»

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  • Excitation of Higher-Order Antenna Modes by Multipath Propagation

    Publication Year: 1967 , Page(s): 597 - 603
    Cited by:  Papers (8)  |  Patents (4)
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    Deep fading on microwave line-of-sight radio relay links is known to be caused by two or more rays arriving at the receiving antenna at slightly different angles in the vertical plane. Destructive interference between these rays can produce deep fades (30 dB or more) of the received signal. In the experiment described, it was found that deep fading is often accompanied by strong higher-order mode excitation of the receiving horn-reflector antenna. The particular higher-order mode measured in this experiment was the TE^{Box^{b}}_{02} , which is excited by horizontally polarized rays arriving off the antenna axis in the vertical plane. The TE^{Box^{b}}_{02} mode as well as the dominant TE^{Box^{b}}_{01} mode of the receiving horn-reflector antenna were continuously monitored for the summer of 1966. The experiment was conducted on a 22.8 mile path in New Jersey at a frequency of 6 GHz. Statistical distributions for the received signal level in the dominant mode, as well as statistical distributions for optimum selection of the TE^{Box^{b}}_{01} and TE^{Box^{b}}_{02} signals, are presented. View full abstract»

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  • Design of Space Diversity Receiving and Transmitting Systems for Line-of-Sight Microwave Links

    Publication Year: 1967 , Page(s): 603 - 614
    Cited by:  Papers (11)
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    Severe fading is a substantial factor that impairs the quality or reliability of transmission over line-of-sight microwave relay systems, producing noise bursts and signal interruptions. This paper describes space diversity receiving and transmitting systems developed by the Electrical Communication Laboratory of Nippon Telegraph and Telephone that reduce the effects of such fading. Theoretical research studies and resultant design criteria, an explanation of fundamental circuits, several example of diversity effects, and the application of the criteria to the design of line-of-sight microwave links using space diversity are described. View full abstract»

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  • Unusual Propagation Factors in Point-To-Point Microwave System Performance

    Publication Year: 1967 , Page(s): 615 - 625
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    Practical problems in the microwave propagation field, which are considered extraordinary and are largely related to ground reflection phenomena are explored. The effects of these problems in terms of noise, discontinuities, and delay distortion, with the attendant unsatisfactory transmission of telephone message, data, and television signals, were the motivation for the studies described, The solutions in terms of extra structures and, in one case, space diversity, are not considered general solutions, but rather, those arrived at and proven successful in the cases covered by the study. Considerations of structure dimensions and limitations are discussed. In the space diversity case described, a method of determining antenua spacing intervals is given, and the results reported. View full abstract»

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  • A 12-MHz Transistor Repeater for the CP-12MTr 2700-Channel Transmission System

    Publication Year: 1967 , Page(s): 625 - 637
    Cited by:  Papers (1)
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    A 12-MHz transistor repeater design is described. Phase shift characteristics of transistor circuits are studied as a common problem in extending a bandwidth of the amplifier and repeater system design and experimental data are also presented. View full abstract»

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  • Design of the 46B Cable Carrier Terminal

    Publication Year: 1967 , Page(s): 637 - 642
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    This paper describes the design of the 46B Cable Carrier Terminal. Included is a description of the modulation plan. A unique frequency correction and regeneration plan is used which provides absolute end-to-end synchronization. The noise improvement resulting from the use of an active-tracking (phase-lock) filter rather than a passive filter for pilot pickoff is described. Some general comments are made upon the relationship between level stability requirements expressed in statistical terms and in specific requirements thereby imposed on the circuit design. Measured performance values are given. View full abstract»

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  • Engineering and Application Features of the 46B Cable Carrier System

    Publication Year: 1967 , Page(s): 642 - 647
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    This paper describes a new 24-channel cable carrier system which is end-to-end compatible with the Western Electric N3. The synchronization technique is described, and the method used to provide synchronization when working end-to-end with an N3 terminal is discussed. Level stability, data transmission capability, and general considerations in the layout of the carrier frequency repeatered line are reviewed. View full abstract»

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  • Considerations Affecting the Mitigation of Noise Coupled Between Cable Pairs

    Publication Year: 1967 , Page(s): 648 - 652
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    Certain mitigative measures which can be employed against metallic noise coupled into telephone circuits in the outside plant are discussed. Quantitative restults are given for separate entrance cable, flat gain amplifiers, arid noise suppression coils. The model used appears to be well-suited to the typical impulse noise problem. View full abstract»

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  • Hard-Limiter Intermodulation with Low Input Signal-to-Noise Ratio

    Publication Year: 1967 , Page(s): 653 - 654
    Cited by:  Papers (2)
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    A simple, closed form expression is derived for the normalized power magnitude of major intermodulation (IM) products at the output of an ideal bandpass hard-limiter with low input signal-to-noise ratio, (S/N)_{i} . This expression together with no-noise results obtained by a previous author allows quick plotting of the no-noise and high-noise asymptotes of the IM product magnitude vs. (S/N)_{i} , for any number of equal-power, input CW signals. Lastly, it is shown that for many signals it may be advantageous to operate the limiter at a lower (S/N)_{i} in order to suppress the intermodulation distortion. View full abstract»

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  • Quantizing for Correlation Decoding

    Publication Year: 1967 , Page(s): 655 - 657
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    The increase in error rate due to quantizing is examined for the special case of a digital correlation decoder such as can be used for orthogonal and other block codes. Three types of effect are considered separately: 1) the increase in variance, which is proportional to the square of the quantum interval; 2) a threshold, proportional to the quantum interval, caused by the ambiguity when the received signal correlates equally with two code words; 3) the effect of limiting. Approximations are obtained for small quantizing loss, the case of greatest interest since the object of correlation decoding is high efficiency. For a 7-bit biorthogonal code and a total of 16 quantum levels the increase in error rate is computed as a function of the quantum interval, and an optimum is found. View full abstract»

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  • Comparison of Biorthogonal and Bisimplex Codes

    Publication Year: 1967 , Page(s): 657 - 658
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    A comparison is made between simplex and orthogonal codes which have been modified by adding their individual complements. The bisimplex code thus formed has reduced efficiency so that the power used must be increased to obtain the same error rate as with the same size of biorthogonal code. It is found that the power advantage of the biorthogonal code is significant only when the code words are shorter than six or seven bits. View full abstract»

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Aims & Scope

This Transactions ceased publication in 1971. The current retitled publication is  IEEE Transactions on Communications.

Full Aims & Scope