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Communications, IEEE Transactions on

Issue 12 • Date December 1979

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Displaying Results 1 - 25 of 37
  • [Front cover and table of contents]

    Publication Year: 1979 , Page(s): 0
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  • Digital communications by radio

    Publication Year: 1979 , Page(s): 1749 - 1751
    Cited by:  Papers (3)
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  • Correction to "Analysis of a reservation multiple access technique for data transmission via satellites"

    Publication Year: 1979 , Page(s): 1982
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  • Correction to "Fundamental performance characteristics that influence EHF MILSATCOM systems"

    Publication Year: 1979 , Page(s): 1982
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  • Correction to cover of October 1979 Communications, Part II

    Publication Year: 1979 , Page(s): 1982
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  • [Back cover]

    Publication Year: 1979 , Page(s): 0
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  • A Comparison of Modulation Techniques for Digital Radio

    Publication Year: 1979 , Page(s): 1752 - 1762
    Cited by:  Papers (27)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1184 KB)  

    This paper describes and summarizes the characteristics of the modulation techniques most applicable to digital radio. The modulation techniques discussed are on-off-keying (OOK) with coherent and noncoherent detection, quadrature amplitude modulation (QAM), quadrature partial response (QPR), frequency-shift-keying (FSK) with noncoherent detection, continuous phase FSK (CP-FSK) with coherent and noncoherent detection, minimum-shift-keying (MSK), binary and quaternary phase-shift-keying (BPSK, QPSK) with coherent and differentially coherent detection, offset-keyed QPSK (OK-QPSK), M -ary PSK with coherent detection ( M = 8, 16 ), and 16-ary amplitude and phase-shift-keying (APK). Functional descriptions of these schemes are provided and their performance is compared in a series of tables summarizing the results of the literature of the past 20 years. The modulation schemes are compared with respect to ideal (white Gaussian noise) performance, spectral properties, signaling speed, complexity, and the effects on performance of interference, fading and delay distortion. View full abstract»

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  • 16 QAM Modulation for High Capacity Digital Radio System

    Publication Year: 1979 , Page(s): 1771 - 1782
    Cited by:  Papers (9)
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    A computational method allowing the calculation of bit error rate in the presence of filtering and some other impairments is described for 16 QAM modulation; a breadboard working at a bit rate of 140 Mbits/s has been implemented and experimental results are compared with calculated values. The possible use of this modulation type for a high capacity digital radio-relay system is considered. Some parameters are introduced for this purpose, especially the net fade margin parameter. In the case of the 140 Mbit/s system in the 10.7-11.7 GHz frequency band, 4 PSK and 8 PSK modulation types are compared with 16 QAM. System gain, frequency arrangement, nodal capacity and outage performances are evaluated. View full abstract»

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  • Error Probability Upper Bound for Coherently Detected QASK Signals with Cochannel Interference

    Publication Year: 1979 , Page(s): 1782 - 1785
    Cited by:  Papers (3)
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    A simple upper bound to the probability of error for a QASK system with additive Gaussian noise and cochannel interference has been derived using Cramer-Chernoff techniques. Numerical results for the QASK-16 system are given. View full abstract»

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  • Optimum Modulation and Channel Filters for Nonlinear Satellite Channels

    Publication Year: 1979 , Page(s): 1810 - 1819
    Cited by:  Papers (4)
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    This is a comparative study of three modulation schemes: QPSK, Offset QPSK(OQPSK), and MSK, in nonlinear satellite channels with adjacent channel interference. Two kinds of typical satellite channel models are used for performance evaluation: one is an INTELSAT type narrow band model and the other is a domestic type wide band model. The transmitter filter and receiver filter are optimized for each combination of modulation scheme, channel model, and an input back-off condition for nonlinear amplifiers. All the combinations considered here have the optimum division of the Nyquist shaping between transmitter filter and receiver filter in common. The filters are a wide band sharp cut-off transmitter filter with flat inband response and a gently rolled-off Nyquist receiver filter with an aperture equalizer ( x/\sin x or 1-(2x)^{2}/\cos x equalizer). With these optimized filters, comparisons are made with respect to the bit error rate (BER) performance and phase jitter of the recovered carrier. OQPSK and MSK show superior BER performance to QPSK in the wide band model. However, in the narrow band model, QPSK shows the best BER performance among the three modulation schemes. The phase jitter in the recovered carrier is small for all modulation schemes in the wide band model. But, in the narrow band model, the phase jitter in OQPSK and MSK is four times larger than in QPSK. Generally QPSK is the most preferable modulation scheme in the narrow band model: OQPSK and MSK are most preferable for the wide band model. View full abstract»

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  • The Navy's Use of Digital Radio

    Publication Year: 1979 , Page(s): 1938 - 1945
    Cited by:  Papers (2)  |  Patents (5)
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    Since the early 1960's, the Navy has utilized digital data links in support of their Tactical Communication, Command and Control Systems. Most of these systems continue to be used operationally. They include links 4, 11, and 14. These systems, however, lack the ability of combatting the anticipated electronic warfare threat as well as providing the performance required of a modern digital data system. Two new systems are in development that will improve performance as well as meet future threats. They are Fleet Satellite Communications and the Joint Tactical Information Distribution System. The demand of implementing new systems while retaining backward compatibility has suggested using an integrated architecture for the aircraft's communication system. The Tactical Information Exchange System is a communication's system design utilizing programmable multifunction signal processing components interconnected with a BUS architecture that may be the ultimate solution to the Military aircraft communication design problem. View full abstract»

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  • The Specification and Design of Bandlimited Digital Radio Systems

    Publication Year: 1979 , Page(s): 1763 - 1770
    Cited by:  Papers (4)  |  Patents (25)
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    This paper presents an introductory discussion of the factors related to specification and design of bandlimited digital transmission systems. Two classes of band limited signaling pulses are considered: raised cosine and partial response. These signaling pulses are generated by using pulse shaping filters on the output of conventional QPSK, MSK, or QASK modulators. Realization of bandwidth efficient digital transmission systems is reduced to a problem of designing a special class of filters. Performance evaluation indicates information densities of up to 4.2 bits/s/ Hz can be achieved with theoretically no impairment in error performance as compared to the ideal nonbandlimited channel. Computer-aided design methods for realization of the necessary pulse shaping filters are described. View full abstract»

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  • Multipath Fading Effects on Digital Radio

    Publication Year: 1979 , Page(s): 1842 - 1848
    Cited by:  Papers (23)
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    An experimental study of multipath fading effects on an 8-PSK 6 GHz digital radio system was conducted on a 26.4 mi test link near Atlanta, Georgia. Results were obtained for a non-diversity arrangement and a space-diversity arrangement employing a cophasing combiner operating at 70 MHz and fed by two antennas separated by 30 ft. Multipath fading was found to have a significant impact on bit error rate performance, i.e., the digital radio system was fragile by comparison to conventional analog FM radio. Modest in-band linear amplitude dispersion, 0.2 dB/MHz for example, was sufficient to cause a BER\geq 10^{-3} . Such dispersion occurred at (average power) fade depths as shallow as 20 dB. However, average fade depth was a poor indicator of BER performance. The measured hop missed short haul outage objectives by an order of magnitude without space-diversity, and was close to acceptable when diversity was activated. View full abstract»

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  • Direct Phase Regeneration of a 400 Mbit/s QPSK Signal at 1.7 GHz

    Publication Year: 1979 , Page(s): 1829 - 1836
    Cited by:  Papers (1)
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    A theoretical analysis is presented for a multi-hop relay system composed of QPSK-DPR's. A Direct Phase Regenerator (DPR) can regenerate a QPSK signal at carrier frequency. Special attention is given to jitter generation and accumulation. Circuit parameters characterizing jitter generation are clarified and obtained quantitatively. The required upper limit for jitter per DPR is also obtained from alloted C/N degradation in a multi-hop system. Simulation experiments were carried out using a novel 400 Mbit/s QPSK-DPR with less than 1 dB inherent equivalent C/N degradation. The results Show that a hybrid system, consisting of 4 to 9 DPR's and a base band regenerator, is feasible. View full abstract»

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  • The Effect of Selective Fading on Digital Radio

    Publication Year: 1979 , Page(s): 1870 - 1876
    Cited by:  Papers (20)
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    In the course of development of the DRS-8 Digital Radio System a series of digital propagation trials were conducted over a 51 km path at 8 GHz to determine the effect of multipath propagation on a 40 MHz bandwidth digital radio system. It was found that the effects of frequency selective fading result in unacceptably high system unavailability unless adaptive equalization and space diversity are employed. Specifically the results are: 1) Multipath induced outage is much higher than would be predicted from the measured flat fade margin of the equipment. For a nondiversity system, the probability of outage for a single hop in the worst fading month is approximately 1 \times 10^{-3} . This is 700 times the objective for a long haul system and corresponds to an effective fade margin of only 27 dB. 2) The primary cause of outage is inband distortion caused by the frequency selectivity of the multipath fading process. 3) Phase adaptive space diversity combining is very effective in reducing the amount of fading. In addition it affords some increase in the effective fade margin of the radio, i.e., it reduces the severity of inband distortion for a given fade depth. Outage for the System with space diversity combining was 2.6 \times 10^{-4} which is about 18 times the long haul objective. 4) A simple adaptive linear amplitude equalizer in conjunction with the phase adaptive space diversity combining provides an additional improvement of approximately a factor of 20, reducing the multipath outage to levels compatible with long haul availability objectives. 5) This same equalizer when applied to a non-diversity channel provides an improvement of about 2. Thus the preconditioning effect of phase adaptive space diversity combining is necessary to reduce distortions sufficiently that they can be dealt with by a relatively simple adaptive equalizer. These results apply to wideband digital radio which operates over long hops using a two dimensional modulation system such as QAM or multiphase PSK. View full abstract»

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  • Level Division Multiplexing of Service Channels in Multilevel Digital Transmissions

    Publication Year: 1979 , Page(s): 1946 - 1952
    Cited by:  Patents (1)
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    Level Division Multiplexing (LDM) is a technique suitable for the addition of supplementary information within multilevel digital transmissions using either amplitude modulation or frequency modulation. Its principle of operation is based on the addition of a supplementary modulation area outside that normally provided for, which does not produce any worsening of the transmission quality of the main information signal. The supplementary information can be added without identifying the frame of the main information signal, but simply by arranging the supplementary information in a frame of its own, which is completely independent of the frame of the main information signal. An example of application (the addition of 4 service channels within the DSA2 system) shows that the LDM technique is particularly suitable for the addition of service channels in PAM/FM digital microwave radio links. View full abstract»

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  • The Effects of the Amplitude and Delay Slope Components of Frequency Selective Fading on QPSK, Offset QPSK and 8 PSK Systems

    Publication Year: 1979 , Page(s): 1849 - 1853
    Cited by:  Papers (4)
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    Amplitude and delay slope are significant components of inband distortion resulting from multipath fading. In this paper, we present and compare computer simulated results of signal to noise ( S/N ) degradation for probability of error (Pe) of 10-4, due to these distortion components on Quadrature Phase Shift Keying (QPSK), Offset Quadrature Phase Shift Keying (Offset QPSK) and 8 Phase Shift Keying(8 PSK)systems. For all systems the transmitter and receiver filtering is modeled so as to provide a 50% excess bandwidth raised cosine spectrum at the receiver detector input. The QPSK and Offset QPSK systems are studied with bit rates of 44.7 Mbits/s, the so-called T3 rate, and the 8 PSK system is studied with bit rates of 44.7 Mbits/s and 67 Mbits/s, a 67 Mbit/s 8 PSK system having the same modulated frequency spectrum as 44.7 Mbit/s QPSK and Offset QPSK systems. When the frequency spectrum is the same for all systems, then for a given amplitude slope, results show that QPSK is the least degraded, followed by Offset QPSK, then 8 PSK, and for a given delay slope, Offset QPSK is the least degraded, followed by QPSK, than 8 PSK. When the bit rate is the same for all systems, then for a given amplitude slope, QPSK is the least degraded. 8 PSK is less degraded than Offset QPSK for values of amplitude slope less than 0.47 dB/MHz, but more degraded for higher values. For equal bit rates and a given delay slope, Offset QPSK is the least degraded, followed by 8 PSK, then QPSK. By relating degradation results to published information on the occurrence of amplitude and delay slope distortion components during multipath fading, estimates of S/N degradation for a Peof 10-4due to these distortion components as a function of frequency selective fade depth are made. Finally, measured S/N degradations for a Peof 10-4due to amplitude and delay slope on a 44.7 Mbit/s Offset QPSK system with filtering similar to the computer model are presented and compared to the computer simulation results. View full abstract»

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  • A Multimode Modem for Digital FM Radio

    Publication Year: 1979 , Page(s): 1786 - 1793
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    The evaluation of FM radios designed primarily for analog voice traffic, but used for data transmission, requires operation over a wide range of data rates and modulation formats. A versatile full-duplex baseband modem has been built which interfaces with tactical VHF radios and operates from 75 bits/s to 16 kbits/s. The choice of modulation formats, modem implementation, and some performance results are presented in this paper. View full abstract»

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  • Analytical Model for Initialization of Single Hop Packet Radio Networks

    Publication Year: 1979 , Page(s): 1959 - 1967
    Cited by:  Papers (3)
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    Recent studies have shown that packet radio networks (PRNET) can easily be saturated and become unstable unless efficient routing and flow control algorithms are used. To enable point-to-point packet transportation, network stations assign a code (label) to each repeater; the process of assigning such labels is referred to as "network initialization." The initialization procedure assumes that the network topology is not known a priori and is changing with time. Thus, the initialization procedure involves mapping of network topology, determining network structure (labels for repeaters), and transmitting labels to the repeaters. Although many authors have developed analytical models to study channel access schemes, no one has yet addressed directly the initialization issue. In this paper we present two models which enable one to estimate the optimal rates at which repeaters and stations must transmit connectivity information to minimize the network initialization time in a one-hop network. The first model assumes complete interference (all repeaters can communicate directly with each other), while the second (but more complex) model can provide initialization time under partial interference pattern. With these models we illustrate the effects of varying repeater and station transmission rates for small networks. Our most important results are that the network initialization time is relatively insensitive to the station transmission rate, but the repeater transmission rate must be carefully chosen to achieve rapid initialization. View full abstract»

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  • QPSK Direct Regenerator with a Frequency Tripler and a Quadrupler

    Publication Year: 1979 , Page(s): 1819 - 1828
    Cited by:  Papers (1)
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    This paper describes a regenerator for quadriphase phase shift keying (QPSK) signals at the carrier frequency, which is called a "direct regenerator." The direct regenerator proposed here is realized using a tripler and a quadrupler. This regenerator is characterized by the symbols m , n and s , which denote the intermediate combiner amplitude ratio, the final combiner amplitude ratio and the limiter dynamic range, respectively. Complete regeneration is obtained at m = n = 1 and s = \infty . Even if this condition is not satisfied, sufficient regenerative performance for practical use is preserved, when 0.8 < m < 1.25, 0.7 < n < 1.4 and s > 5 dB. To verify the operation principle, an experiment was carried out for 1.7 GHz QPSK signals transmitted at 40 Mbits/s. It is shown that this regenerator has satisfactory decision and reshaping capability in dynamic operation. Using this direct regenerator, decision and reshaping of the QPSK signals can be made without detection. Thus, a repeater can be simplified, compared to a conventional repeater composed of a detector, a baseband regenerator and a modulator. View full abstract»

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  • Spectrally Efficient Digital Transmission Using Analog FM Radios

    Publication Year: 1979 , Page(s): 1837 - 1841
    Cited by:  Papers (1)
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    This paper explores the feasibility of using 4 level FM to enable digital transmission with a spectrum efficiency on the order of two bits per cycle of transmitted bandwidth when used with Frequency Modulated (FM) radios. A hybrid computer simulation was used to assess the compatibility of 4 level FM with the transfer characteristics of commercial FM radios and also to evaluate the performance of 4 level FM modulation under conditions of radio misalignment. It is shown that 4 level FM is able to provide good spectral efficiency without requiring modification or replacement of most current FM radios, It is also shown that 4 level FM performance is relatively insensitive to the transmission degradations typically encountered in fielded systems. View full abstract»

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  • Design and Performances of a 200 Mbit/s 16 QAM Digital Radio System

    Publication Year: 1979 , Page(s): 1953 - 1958
    Cited by:  Papers (17)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    A novel long haul 5 GHz 16 QAM digital radio system, which has 200 Mbit/s transmission capacity within the 40 MHz interleaved channel allocation, is proposed and described. It is designed to be overbuilt on existing FDM-FM routes with an approximately 50 km repeater spacing. To achieve the 5 bit/s/Hz RF spectral efficiency, the 16 QAM modulation and Nyquist cosine roll-off spectral shaping techniques ( \alpha = 0.5 ) are investigated. Then a new signal shaping filter, differential encoding and carrier recovery techniques are presented. Finally, the effects of TWT amplifier nonlinearity on a 16 QAM signal are experimentally investigated. View full abstract»

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  • Error Rate of QPRS Evaluated in Amplitude-Phase Space

    Publication Year: 1979 , Page(s): 1802 - 1805
    Cited by:  Papers (3)
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    A method for evaluating the character error rate for QPRS in the signal space using the classical Bayes hypothesis-testing technique is presented. Since the decision regions are rectangular, analytical expressions for the error rates can be found. This method may be extended to account for the effect of carrier tracking error and, in principle, phase jitter. View full abstract»

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  • Multipath Delay Characteristics on Line-of-Sight Microwave Radio System

    Publication Year: 1979 , Page(s): 1876 - 1886
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    Multipath properties on microwave line-of-sight links for the purpose of applying to microwave systems design are discussed. The theoretical analyses of the fading mechanism and the relation between multipath delay and radio duct parameters are carried out using the ray-optical method. Multipath delay have been measured with the frequency-sweep method and the three-frequency method on several paths in Japan since 1954. These paths are distributed in length from 20 km to 80 km, and include horizontal and slant paths. Through these theoretical and experimental analyses, a number of wave components in multipath propagation, the probability density function of multipath delay, the maximum delay and the relation between multipath delay and radio duct parameters are examined. The estimation method for path-length difference statistics, needed for evaluation of propagation distortion, is quantitatively given. View full abstract»

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  • An Experimental Test Loop to Assist in Designing Digital Microwave Radio Systems

    Publication Year: 1979 , Page(s): 1968 - 1971
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    An experimental method for the study and trial of N -hop digital microwave radio systems is described. The method is particularly useful for those systems where the different disturbances accumulate and do not occur on each hop on an independent basis. The method simulates a digital transmission system by generating an information sequence of m bits at a rate of fbbits/s and circulating the sequence N times through one regenerator and a coaxial cable loop having a time delay \tau > m/f_{b} . The circulating loop can be employed to investigate the influence on noise and error rate in digital radio systems of factors such as: cochannel and intersymbol interference; heavy rain attenuation on one or two repeater sections; additive noise; gain and phase nonlinearities; fading; changes in components and operating conditions within the regenerator; and combinations of these disturbances occurring simultaneously. View full abstract»

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IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia