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1887

IEE Proceedings F (Communications, Radar and Signal Processing)

Volume 134, Issue 6, October 1987

Volumes & issues:

Volume 134, Issue 6

October 1987

Editorial
Spatial correlation in K-distributed sea clutter
  • Author(s): S. Watts  and  K.D. Ward
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 526 –532
  • DOI:  10.1049/ip-f-1.1987.0090
  • Type: Article
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  • p. 526 –532 (7)
    The compound K-distribution model for sea clutter previously described in the literature provides the foundation for a quantitative treatment of the spatial and temporal correlation characteristics of the envelope of clutter returns. In the paper the compound K-distribution model is extended to cover the spatial characteristics of sea clutter. The relationship of these characteristics to the physical basis of the model is described, and methods for their simulation are discussed. The effects of different radar range resolutions are analysed theoretically and these results compared with observations on real data. Finally, quantitative techniques are derived for optimising radar range resolution to give the best target detection performance in different clutter conditions, and some practical examples are presented.
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Erratum: Subscriber loop noise measurements and calibration
Noiseless encoding of speech signals
  • Author(s): H. Gharavi  and  R. Steele
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 533 –538
  • DOI:  10.1049/ip-f-1.1987.0092
  • Type: Article
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  • p. 533 –538 (6)
    Noiseless encoding strategies based on conditional entropy encoding are proposed for 8-bit μ-law PCM speech, with μ = 255. Specifically, we formulate the conditional probabilities of the current and previous PCM samples to generate the codebook employed in the noiseless encoding process. In addition, we consider a second-order conditional entropy encoding scheme which, when coupled with a state-reduction technique, reduces the size of the codebook. The entries in the codebooks are established with the aid of a training speech sequence, and different sentences are used to test the noiseless encoding performance. For first- and second-order conditional entropy encoding we obtain average transmission rates of 50kbit/s and 40kbit/s, respectively, compared to the original bit rate of 64 kbit/s. These reductions in bit rate are achieved without affecting the recovered speech quality.
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Transmission of log-PCM via QAM over Gaussian and Rayleigh fading channels
  • Author(s): R. Steele ; C.-E.W. Sundberg ; W.C. Wong
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 539 –556
  • DOI:  10.1049/ip-f-1.1987.0093
  • Type: Article
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  • p. 539 –556 (18)
    The digital noise power due to transmission errors is determined for 8-bit μ-law PCM, μ = 255, signals transmitted via M-level QAM, M = 16, 64 and 256, over Gaussian and Rayleigh fading channels. The analytical results apply for various laws that map the 8-bit μ-law PCM signal into the QAM format, and for different binary Gray codes used to represent the QAM signal points. In addition to the theoretical results expressed as overall speech signal/noise ratio (SNR) as a function of channel SNR for different input speech signal levels, simulations for Gaussian and mobile radio channels using speech signals are also presented. From our deliberations we can conclude that the 256-level QAM system employing the best mapping law and Gray code has a gain of about 6dB in overall speech SNR compared to transmission without co-ordination of the speech bits over a Gray-coded link. Corresponding gains for 16-level and 64-level QAM are marginally smaller. By increasing the number of QAM levels from 4 to 256, the required increase in channel SNR per bit to maintain an overall speech SNR of 30 dB is approximately 12 dB. The bandwidth efficiency increases by a factor of four. The theoretical analysis in the paper is approximate. Only the effect of the most likely channel errors (single errors) has been taken into account. The theoretical results coincides well with the simulations, where such approximations were made.
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Logarithmic PCM weighted QAM transmission over Gaussian and Rayleigh fading channels
  • Author(s): C.-E.W. Sundberg ; W.C. Wong ; R. Steele
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 557 –570
  • DOI:  10.1049/ip-f-1.1987.0094
  • Type: Article
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  • p. 557 –570 (14)
    The transmission of 8-bit μ-law PCM signals using M-level weighted QAM (WQAM), M =16, 64 and 256, over Gaussian and Rayleigh fading channels is examined. The weighting process modifies the positions of the QAM constellation points so that the overall distortion in the recovered information-bearing source signal is reduced. The PCM bits are mapped to the WQAM points such that the most significant bits have a lower probability of being in error than the least significant bits. Gray coding of the constellation points is also used. The WQAM systems have been optimised for the same average signal energy per transmitted symbol as for unweighted QAM. Optimised systems have also been derived for the same peak signal energy per symbol. The theoretical and simulation results using speech indicate that 16-level and 256-level WQAM have a gain of up to 3 and 5dB, respectively, over unweighted QAM for the Gaussian channel. The gains due to weighting for 16-level QAM operating over an ideal slow Rayleigh fading channel are up to 5 dB.
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Limiting error bounds for the continuous channel
  • Author(s): A.G. Burr
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 571 –582
  • DOI:  10.1049/ip-f-1.1987.0095
  • Type: Article
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  • p. 571 –582 (12)
    The paper presents an approach by which absolute error bounds may be derived for the continuous channel, thus determining the limits of the performance of a modulation and coding scheme. The code is considered as a set of points in n-dimensional space, and the concept of a sphere-packing in n dimensions based on the regular simplex is used to determine the maximum packing density. The effect of code points on the edges of the signal space is also considered. Upper and lower bounds on the error rate are derived for various code rates and various block lengths (numbers of dimensions). The results are of relevance to combined coding/modulation schemes, and n-dimensional coding schemes, and show that a coding advantage of approximately 2dB is obtained for every doubling of the number of dimensions.
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Prediction of attenuation on satellite-earth links in the European region
  • Author(s): P.A. Watson ; M.J. Leitao ; V. Sathiaseelan ; M. Gunes ; J.P.V. Poiares Baptista ; B.A. Potter ; N. Sengupta ; O. Turney ; G. Brussaard
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 583 –596
  • DOI:  10.1049/ip-f-1.1987.0096
  • Type: Article
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  • p. 583 –596 (14)
    A new method for predicting attenuation on satellite-earth links is applied throughout the European region. Sources of long-term point rainfall data required for the method are identified, and the approach to compiling a rainfall intensity database is described (including conversion techniques for integration time, which are developed and tested). A technique for predicting effective rain height from available meteorological data, which takes into account seasonal and climatic dependencies, is also described and evaluated. Finally, the method is applied to the prediction of attenuation at arbitrary sites in the European region and to the production of contour maps of attenuation for specific satellites. The values predicted at 33 European sites with available attenuation data from the COST 205 programme show excellent agreement, and give lower errors than other methods.
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Trigonometric high-resolution method to resolve two close targets
Asymptotically optimum detection of fluctuating targets in non-Gaussian interference
  • Author(s): E. Conte  and  M. Longo
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 602 –608
  • DOI:  10.1049/ip-f-1.1987.0098
  • Type: Article
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  • p. 602 –608 (7)
    The design of asymptotically optimum detectors (AODs) is considered for a class of fluctuating targets in non-Gaussian interference, as a reasonable alternative to optimum (Neyman-Pearson) detectors, which prove hopelessly complex. The useful signal is modelled as an incoherent train with constant amplitude or with fluctuating amplitude, either from scan to scan or from pulse to pulse. The AOD structure is based on an asymptotical expression of the log-likelihood ratio, which has been derived by a suitable modification of the classical AOD approach; it results in a conventional detector (CD) but for the replacement of the quadratic envelope detection with another zero-memory nonlinearity, depending only on the noise statistics. The invariance properties of the CD with respect to the signal fluctuation model are shown to be preserved in the more general AOD class. As the test statistics are asymptotically normal, the asymptotical AOD operating characteristics are expressed in terms of asymptotical relative efficiency (ARE), thus allowing direct comparison with the CD under the same interference. The ARE for log-normal interference is calculated, showing a potential improvement on the order of at least 20 dB.
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Book review: Advanced Digital Communication: Systems and Signal Processing Techniques
Antenna elements for improved shipboard HF direction-finding
  • Author(s): G. Mönich
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 609 –614
  • DOI:  10.1049/ip-f-1.1987.0100
  • Type: Article
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  • p. 609 –614 (6)
    The situation of shipboard DF antennas is briefly analysed. It is shown that DF errors are worst within the HF range, and then especially to port and starboard. It is shown that this region can be covered by a parallel loop arrangement which must be kept ‘blind’ to the main reradiating structures in addition to the conventional crossed loop DF. Theoretical considerations prove that all structures in a ship's symmetry plane and an idealised ship's hull no longer create bearing errors. Unsymmetrically placed components, which continue to affect the parallel loop, turn out to produce merely a very smooth error curve, which can easily be compensated by computer-stored correction tables during the evaluation process. Polarisation errors, which appear when direction-finding with a crossed loop, are shown to be at a much lower level when using a parallel loop.
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Book review: Radio Receivers
Optimisation of centroiding procedure for noisy measurements
Monogenic function range resolution radar
  • Author(s): P.S. Moharir ; K. Venkata Rao ; S.K. Varma
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 134, Issue 6, p. 620 –628
  • DOI:  10.1049/ip-f-1.1987.0103
  • Type: Article
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  • p. 620 –628 (9)
    Sequences having peaky autocorrelation are useful in range resolution radar and in a homomorphic problem of detecting reflections in seismic exploration. The concept of correlative signal processing for system identification in these applications is extended here to processing based on monogenic signatures. Some sequences having good monogenic signatures are listed. These yield sequence compression equal to the length of the sequences, and peak/sidelobe ratios or merit factors could be superior to those obtainable in correlative processing for the same length of sequences. The problems in developing monogenic function radar are discussed and some solutions proposed.
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Binary-decision approach to fast Chien search for software decoding of BCH codes

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