Showing papers on "Fading published in 1973"
TL;DR: The issue of signal selection in binary data transmission is presented and the question of the relative utility of linear frequency sweeping (LFS or chirp), compared to PSK and FSK, in terms of error probability and spectrum usage, is discussed.
Abstract: The issue of signal selection in binary data transmission is presented. The question of the relative utility of linear frequency sweeping (LFS or chirp), compared to PSK and FSK, in terms of error probability and spectrum usage, is discussed. The transmission media considered are the coherent, partially coherent, Rayleigh, and Rician channel models. Theoretically, LFS has unconditionally superior characteristics in the partially coherent and fading cases, for certain ranges of channel conditions. This is due to the more negative values of cross-coherence parameters possible with the LFS signal set over the FSK signal set. For the fading channel, theoretical supremacy of LFS over FSK depends upon the specular-to-Rayleigh signal power ratio and the adjustability of in-phase cross coherence, with a constraint upon quadrature phase cross coherence. From a practical standpoint, coherent reception of the LFS signal set has severe limitations. These are manifested primarily in two aspects: the need for phase synchronization of a chirp signal set, and the fact that the optimum value of cross coherence is highly sensitive to synchronization channel signal-to-noise ratio (SNR), and/or spectral-to-Rayleigh signal power ratio. The latter would require that modulation characteristics track the channel conditions in order to achieve the supremacy in performance theoretically predicted by optimization of the cross-coherence parameter in LFS.
199 citations
TL;DR: A simple device to simulate the Rayleigh distributed fast fading encountered in mobile radio is described and a design is given whose performance is shown to agree very closely with theory.
Abstract: A simple device to simulate the Rayleigh distributed fast fading encountered in mobile radio is described and evaluated. The Rayleigh envelope statistics are obtained by adding two independent Gaussian noise sources in quadrature. The theoretical spectrum of the received signal is approximated by shaping the spectrum of the noise sources with filters. A design is given whose performance is shown to agree very closely with theory.
102 citations
95 citations
TL;DR: The difference in the performance of the two systems was shown to be primarily due to time delay inherent in the remote antenna switching technique.
Abstract: A theoretical and experimental comparison of performance has been made between two types of predetection switching space diversity mobile radio systems. This comparison was made at a frequency of 840 MHz using simulated Rayleigh fading for a vehicle speed of about 80 mi/h. The switch diversity system was a conventional receiver antenna switching technique with two simulated physically separated receiving antennas and a single transmitting antenna. The feedback diversity system used a single receiving antenna with two simulated physically separated transmitting antennas. The transmitting antennas were switched remotely from the receiver. The difference in the performance of the two systems was shown to be primarily due to time delay inherent in the remote antenna switching technique.
57 citations
TL;DR: A simple device to simulate the Rayleigh distributed fast fading encountered in mobile radio is described and a design is given whose performance is shown to agree very closely with theory.
Abstract: A simple device to simulate the Rayleigh distributed fast fading encountered in mobile radio is described and evaluated. The Rayleigh envelope statistics are obtained by adding two independent Gaussian noise source in quadrature. The theoretical spectrum of the received signal is approximated by shaping the spectrum of the noise sources with filters. A design is given whose performance is shown to agree very closely with theory.
52 citations
01 Dec 1973
44 citations
TL;DR: It is shown that on moderately dispersive channels the equalizer nearly achieves optimum one-shot performance, and an adaptive version of this equalizer exists, this means data transmission on slowly fading channels is possible at rates above the natural rate suggested by the channel dispersion spread without bandwidth expansion and with small intersymbol interference penalty.
Abstract: The reception and detection of a single digit under known channel conditions are investigated. The probability of error for an optimum one-shot receiver instantaneously matched to the channel state is averaged over an ensemble of dispersive diversity channels. The average probability of error as a function of energy to noise ratio is found to be solely dependent on the ratio of rms dispersion width to data symbol width. For these dispersive channels an implicit diversity effect is qualitatively explained in terms of eigenvalues that depend on the ensemble statistic. The one-shot receiver performance provides a bound for practical receivers. In a comparison with a decision feedback equalizer, it is shown that on moderately dispersive channels the equalizer nearly achieves optimum one-shot performance. Since an adaptive version of this equalizer exists, this means data transmission on slowly fading channels is possible at rates above the natural rate suggested by the channel dispersion spread without bandwidth expansion and with small intersymbol interference penalty. The use of one-shot receiver performance curves can also be used as estimates of equalizer performance in situations where computation of the latter is impractical.
40 citations
TL;DR: A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio and has been found to give a significant improvement to both voice and data signals.
Abstract: A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio. The input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit. The system has been measured on simulated Rayleigh fading channels and has been found to give a significant improvement to both voice and data signals.
33 citations
Patent•
13 Sep 1973TL;DR: In this paper, a method for communication transmission in common channel operation of a directional radio network, in particular a PCM directional network, was proposed, in which operation of all transmitters of the radio-relay links takes place during fade-free periods at lower power than usual and upon the occurrence of fading in a particular path, automatically increasing the transmitting power in this path, the increase being effected at the remote transmitter over a return or auxiliary channel from the receiver concerned by fading to the associated remote transmitter.
Abstract: A method for communication transmission in common channel operation of a directional radio network, in particular a PCM directional network, in which operation of all transmitters of the radio-relay links takes place during fade-free periods at lower power than usual and upon the occurrence of fading in a particular path, automatically increasing the transmitting power in this path, the increase being effected at the remote transmitter over a return or auxiliary channel from the receiver concerned by fading to the associated remote transmitter.
33 citations
TL;DR: A novel feature of selective diversity is that, for moderate SNR, the error probability decreases to zero as a strong inverse power of L , the order of diversity, which contrasts with behavior of conventional systems in which increasing L causes the error probabilities to decrease to a nonzero lower bound.
Abstract: A feedback scheme for regulating error probability on slowly fading communication channels is described and analyzed. In this selective diversity system, only the best R of L available diversity subchannels are used, the selection being revised from moment to moment. Comparison with conventional diversity transmission on an 8-channel system shows a performance improvement ranging from 20.8 to 9.5 dB, where the low figure corresponds to constant power operation of the transmitter and a typical value of round-trip delay. A novel feature of selective diversity is that, for moderate SNR, the error probability decreases to zero as a strong inverse power of L , the order of diversity, which contrasts with behavior of conventional systems in which increasing L causes the error probability to decrease to a nonzero lower bound. The implication is that the figures quoted above can be improved indefinitely by increasing the order of diversity.
28 citations
TL;DR: Results of a flight test program involving a KC-135 jet airplane, the synchronous ATS-5 L -band satellite, and a ground station are presented, finding CW tone-ranging performance was determined in both the thermal noise and multipath environments.
Abstract: Results of a flight test program involving a KC-135 jet airplane, the synchronous ATS-5 L -band satellite, and a ground station are presented. Tests included over-ocean multipath measurements and one-way tone ranging within the 1545-1655 MHz frequency band. Amplitude characteristics, polarization, power spectral density, and selective fading properties were measured for sea-reflected and composite signal channels. CW tone-ranging performance was determined in both the thermal noise and multipath environments. Comparison of experimental results with theoretical expectation is given.
TL;DR: BPM is shown to maintain its inherent 2-3 dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.
Abstract: System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming 1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and 2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2-3 dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.
TL;DR: Tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.
Abstract: This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "twoway diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.
TL;DR: Quantitative results show that a worthwhile improvement in quality of reception can be obtained with small numbers of antennas, and there are advantages to be gained if, in future receiving systems, the diversity technique is incorporated directly into the receiver design.
Abstract: Diversity reception techniques can help to combat fast fading in urban areas, and this paper describes some predetection combining systems designed to be compatible with existing standard receivers. Quantitative results show that a worthwhile improvement in quality of reception can be obtained with small numbers of antennas. There are advantages to be gained if, in future receiving systems, the diversity technique is incorporated directly into the receiver design.
TL;DR: Quantitative results show that a worthwhile improvement in quality of reception can be obtained with small numbers of antennas, and there are advantages to be gained if, in future receiving systems, the diversity technique is incorporated directly into the receiver design.
Abstract: Diversity reception techniques can help to combat fast fading in urban areas, and this paper describes some predetection combining systems designed to be compatible with existing standard receivers. Quantitative results show that a worthwhile improvement in quality of reception can be Obtained with small numbers of antennas. There are advantages to be gained if, in future receiving systems, the diversity technique is incorporated directly into the receiver design.
TL;DR: A bound on the probability of error is obtained for an M -ary direct-detection optical communications system consisting of an amplitude-stabilized source, a lognormal atmospheric channel, and a photocounting detector array.
Abstract: A bound on the probability of error is obtained for an M -ary direct-detection optical communications system consisting of an amplitude-stabilized source, a lognormal atmospheric channel, and a photocounting detector array. Equal-energy, equiprobable, orthogonal signaling, and fiat independent fading at all detectors is assumed. The result reduces to that obtained previously in the absence of fading. A comparison is made with the analogous solution for the heterodyne array receiver.
TL;DR: A performance analysis of a digital radio-relay system during fading periods, and results seem to indicate the feasibility of the frequency reuse technique.
Abstract: The planning of a digital radio network requires an evaluation of the effect of quite a large number of interfering sources. These in turn are dependent upon many parameters, such as the network structure, channel arrangement, antenna patterns, and so on. This paper presents a performance analysis of a digital radio-relay system during fading periods. The possibility of attaining a required fading margin is analyzed when many co-channel and interchannel interferences are simultaneously present, both for long-haul and shorthaul radio relay systems. A comparison is presented between two possible techniques for the reusing of the same frequency band in each hop, by taking advantage of the cross-polarization discrimination (XPD). The reduction of the XPD expected during fading periods is also taken into account. Binary and quaternary coherent PSK modulations are considered, with realizable filters (of the Butterworth type), both at the transmitter and at the receiver. The error probability calculations were performed with a combined analytical and computer simulation approach. The results seem to indicate the feasibility of the frequency reuse technique.
TL;DR: Using simulated Rayleigh-fading FM signals, the baseband performance of a diversity system that uses a separate pilot is studied, and an approach to a constant asymptotic baseband SNR for large expansion ratios is shown.
Abstract: Using simulated Rayleigh-fading FM signals, the baseband performance of a diversity system that uses a separate pilot is studied. The effect of various RF/audio bandwidth expansion ratios is included. These results show an approach to a constant asymptotic baseband SNR for large expansion ratios, with diversity increasing this asymptote by 5 dB in the case of moderate to large interference and/or RF noise levels (9 to 15 dB below the carrier), to over 10 dB in the case of lower impairment levels (21 to 27 dB below the signal level). Assuming the usual hex-cell radio coverage plan, and a propagation law of the form r^{-n}, n = 3 or 4, bandwidth expansion ratios of about three to six seem to yield the most efficient RF spectrum utilization in many practical situations. The number of required channel subsets (cells) is strongly influenced by the propagation law ranging from about 19 for n = 3 , to about 7 for n = 4 .
08 May 1973
TL;DR: In this article, field investigations and analyses are conducted to define the characteristics of equatorial scintillation fading and its effects on satellite communications (SATCOM) systems, and a data base for use in evaluating optimum SATCOM techniques is generated.
Abstract: : Field investigations and analyses are conducted to define the characteristics of equatorial scintillation fading and its effects on satellite communications (SATCOM) systems. A data base for use in evaluating optimum SATCOM techniques is generated.
TL;DR: In this article, a model of a spaced-receiver drift experiment is presented in which radio fading is produced by reflections from a perfectly reflecting wavy ionosphere, and the model is shown to be capable of simulating many aspects of observed ionospheric drift records.
TL;DR: In this article, a low cost switched diversity receiving system was developed for use in UHF-FM mobile radio, where the input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit.
Abstract: A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio. The input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit. The system has been measured on simulated Rayleigh fading channels and has been found to give a significant improvement to both voice and data signals.
01 Aug 1973
TL;DR: A method is presented for adaptively adjusting the parameters of a double MTI canceller to minimize the effects of frequency-shifted clutter spectra, and the technique is implicitly gain normalized, such that changing power levels do not affect system performance.
Abstract: A method is presented for adaptively adjusting the parameters of a double MTI canceller to minimize the effects of frequency-shifted clutter spectra. The technique is implicitly gain normalized, such that changing power levels do not affect system performance. The use of ?look ahead? methods and ?fading memory? filtering allows for real-time tracking of the center frequency of the clutter spectra.
TL;DR: Tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.
Abstract: This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "two-way diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.
TL;DR: In this paper, the diurnal variation of phase and amplitude of the NWC-22.3kHz signal was investigated in terms of waveguide modes interference and a good agreement between theoretical and experimental results was obtained.
Abstract: The diurnal variation of phase and amplitude of NWC-22.3kHz signal is investigated. Typical pattern of the phase variation and amplitude fading during sunrise transition, for the case of the summer season in the northern hemisphere, is interpreted in terms of waveguide modes interference. By considering the second mode propagation besides the first in daylight, a good agreement between theoretical and experimental results is obtained.
TL;DR: In this article, the effects of certain atmospheric conditions upon pulse-code modulation (PCM) data transmission at a carrier frequency of 15.3 GHz were discussed and the performance characteristics of the system, relating to conditions in the channel, were measured and presented in this study.
Abstract: The effects of certain atmospheric conditions upon pulse-code modulation (PCM) data transmission at a carrier frequency of 15.3 GHz are discussed in this paper. Using an amplitude-shift keying (ASK) modulation to transmit 1300000 bit/s across a 9.5 mi line-of-sight path, the performance characteristics of the system, relating to conditions in the channel, were measured and are presented in this study. Theoretical curves of probability of error versus predetection signal-to-noise ratio (SNR), are compared to measured error probabilities; these are obtained at different received signal levels, and under various clear weather conditions ranging from humid to dry. Above 15 dB predetection SNR, the system operates more efficiently than theoretically predicted for ASK modulation over a Rayleigh fading channel. The detected envelope probability distributions are computed for different values of SNR. Results show that drier weather, which causes amplitude fluctuations of a shallow nature, results in greater error probabilities than those for more humid conditions; the term shallow fading is used to describe short term (5-10 min) received signal envelope variations of less than 1 dB. For example, error probabilities for a predetection SNR of 14 dB, ranged from 0.005 to 0.078, from humid to dry conditions respectively. These values fall between the theoretical values of 0.0005 for the nonfading case, and 0.0740 for Rayleigh fading.
01 Oct 1973
TL;DR: In this paper, the performance of the agc weighted combiner is compared with the equal-gain combiner and the maximal-ratio combiner, both as a function of time and fade rate.
Abstract: The conventional agc weighted diversity combiner is implemented on the assumption that the agc system of each receiver is tracking the rf fading envelope perfectly (i.e., such as to maintain the linear i-f output amplitude constant). The departure from optimum (maximal-ratio) combining which results from imperfect tracking is determined by computer solution of the nonlinear differential equation of the agc system for particular deterministic rf fading envelopes. The performance of the agc weighted combiner is compared with maximal-ratio and equal-gain combiners, both as a function of time and fade rate. It is shown that under certain conditions the equal-gain combiner outperforms the agc weighted combiner. It is also shown that by using both the a-m (detected linear i-f envelope) and the agc voltages for weighting the combiner the limitations arising from the response time of the agc system can be overcome. It is also indicated how an optimum diversity selector can be implemented by using both the a-m and agc voltages.
TL;DR: In this paper, a ray-tracing technique for simulating the performance of the mode-averaging diversity combiner (MADC) is described, which extends the methods developed by Croft [1969] to the analysis of frequency-selective fading.
Abstract: A ray-tracing technique for simulating the performance of the mode-averaging diversity combiner (MADC) [Villard et al., 1972] is described, which extends the methods developed by Croft [1969] to the analysis of frequency-selective fading. It is shown that the computer procedure satisfactorily predicts observations made during a test representative of conditions encountered in practice. Using the parameters of this test, the method is applied to the original MADC configuration to investigate the dependence of performance on antenna spacing and ionospheric profile. Two MADC schemes which incorporate alternative methods of forming the running average are described. Their performance is also evaluated for the above parameters and shown to be roughly equal to that of the original. It is concluded that for the given parameters at least, a choice between the three alternative configurations can be made on the basis of convenience.