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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]

    Page(s): 0
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  • [Back cover]

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  • Optimum Modulation and Channel Filters for Nonlinear Satellite Channels

    Page(s): 1810 - 1819
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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 xor1-(2x)^{2}/cos xequalizer). 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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  • Single-Ended Transmission Path Measurements

    Page(s): 1971 - 1973
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    New time-domain formulas for the attenuation dispersiondalpha/ domegaand group delay dispersiond^{2}phi/domega^{2}of a transmission path are derived. It is shown how they can be used to measuredalpha/domegaandd^{2}phi/domega^{2}accurately. The formulas involve only output quantities and thus can be used for measurements on very long transmission paths, where the input and output are not simaltaneously accessible. View full abstract»

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  • The Diagnosis and Modeling of Imperfections in Digital Radio Systems

    Page(s): 1973 - 1982
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    In the design and development of digital radio systems there is a need for accurate assessment of degradations resulting from various sub-system imperfections. The modeling technique described here has a wide range of application, and examples show how, in particular, it may be used in the derivation of system distortion budgets. When combined with appropriate experimental test measurements it also provides a powerful diagnostic tool for interpreting and improving the performance of prototype equipments. This important aspect of system development is considered in some detail, again with reference to illustrative examples from laboratory trials. View full abstract»

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

    Page(s): 1968 - 1971
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    An experimental method for the study and trial ofN-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 ofmbits at a rate of fbbits/s and circulating the sequenceNtimes through one regenerator and a coaxial cable loop having a time delaytau > 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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  • The Effect of Selective Fading on Digital Radio

    Page(s): 1870 - 1876
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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 approximately1 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 was2.6 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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  • Multipath Fading Effects on Digital Radio

    Page(s): 1842 - 1848
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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 aBERgeq10^{-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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  • QPSK Direct Regenerator with a Frequency Tripler and a Quadrupler

    Page(s): 1819 - 1828
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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 symbolsm,nands, which denote the intermediate combiner amplitude ratio, the final combiner amplitude ratio and the limiter dynamic range, respectively. Complete regeneration is obtained atm = n = 1ands = infty. Even if this condition is not satisfied, sufficient regenerative performance for practical use is preserved, when0.8 < m < 1.25, 0.7 < n < 1.4ands > 5dB. 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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  • Analytical Model for Initialization of Single Hop Packet Radio Networks

    Page(s): 1959 - 1967
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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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  • Level Division Multiplexing of Service Channels in Multilevel Digital Transmissions

    Page(s): 1946 - 1952
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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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  • Error Rate of QPRS Evaluated in Amplitude-Phase Space

    Page(s): 1802 - 1805
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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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  • Group Delay Estimation with Wideband Signals

    Page(s): 1908 - 1910
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    A new formula for the group delay of a network is derived. The formula is not restricted to narrow-band signals and is valid up to quite large bandwidths. A simple and very sensitive technique for group delay measurement, based on this new relation, is described. View full abstract»

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  • 16 QAM Modulation for High Capacity Digital Radio System

    Page(s): 1771 - 1782
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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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  • Multipath Delay Characteristics on Line-of-Sight Microwave Radio System

    Page(s): 1876 - 1886
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    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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  • A Comparison of Modulation Techniques for Digital Radio

    Page(s): 1752 - 1762
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    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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  • Spectrally Efficient Digital Transmission Using Analog FM Radios

    Page(s): 1837 - 1841
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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

    Page(s): 1953 - 1958
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    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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  • A Multimode Modem for Digital FM Radio

    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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  • The Navy's Use of Digital Radio

    Page(s): 1938 - 1945
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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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  • New Radiation Limits For a Digital Radio World

    Page(s): 1910 - 1915
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    Regulations on radiation limits have been Widely adopted to keep radio transmissions from interfering with each other. Most of them set an upper limit on the total power flux density radiated Within a certain frequency bandwidth,B. But new techniques have given rise to the possibility that some digital transmission systems could cause significant interference to other transmissions without violating the current regulations. This is due to the fact that bursty signals can concentrate most of their energy in a very short pulse with very high power but maintain a low enough average power spectral density, thus meeting the current regulations. New radiation limits are therefore suggested in this paper which set an upper bound on the total energy instead of average power radiated within a certain time period,H, as well as a certain frequency bandwidth,B. It is shown that the current regulations can be easily extended to establish the new limits, and these new limits are essentially identical to the current limits for the traditional continuous-wave signals but can limit the bursty digital signals efficiently as well. Practical consideration for the appropriate length of the time period,H, to be used are discussed, and a few example signals are used to demonstrate the use of the new limits. View full abstract»

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Aims & Scope

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