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Communications, Radar and Signal Processing, IEE Proceedings F

Issue 5 • Date August 1984

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Displaying Results 1 - 20 of 20
  • Derivation of impulse responses under minimum phase constraints

    Page(s): 425 - 432
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (951 KB)  

    The paper describes several methods of deriving minimum phase impulse response functions given only the amplitude frequency characteristics. The suitability of these methods for use in digital transmission system analysis is considered. View full abstract»

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  • Relative performance of a simple MTI canceller selection rule

    Page(s): 433 - 436
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The performance of an MTI canceller selection rule, which is solely based on clutter suppression, is analysed in terms of incorrect selection probability and average loss in signal-to-interference ratio (SIR). It is concluded that the variation in target signal power transfer, as a function of the target radial velocity, is responsible for most incorrect canceller choices. The resulting loss in SIR is typically around 3 dB, with peaks to 6¿¿9 dB in worst-case situations. View full abstract»

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  • The performance of combined feedforward AGC and phase-locked AFC in a single sideband mobile radio receiver

    Page(s): 437 - 441
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    The paper describes the results of a simulation of a coupled phase-locked AFC/feedforward AGC system with a two tone fading input. The theoretical predictions agree closely with those obtained under laboratory conditions, and show that considerable care should be exercised in the selection of the phase-locked loop bandwidth, normalised to twice maximum Doppler (¿n/2¿d). Failure to do so can result in nonoptimum feedforward AGC performance. View full abstract»

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  • 14/11 GHz, 120 Mbit/s regenerative satellite transponder

    Page(s): 442 - 450
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1170 KB)  

    This paper describes the design, implementation and performance of an experimental 14/11 GHz, 120 Mbit/s regenerative satellite transponder for possible use in the European communications satellite (ECS) system. Quarternary DPSK and CPSK are applied on the uplink and downlink, respectively. Demodulation and modulation are performed directly at RF. Specific components of the regenerative transponder, which are the pulse shaping filter, the differential demodulator, the baseband regenerator, the modulator and the output filter, were developed. Using the developed components, a laboratory model of the transponder was completed and evaluated. Bit-error-rate measurements were carried out with a test equipment simulating the earth terminals. View full abstract»

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  • Nonlinear polarisation-vector translation in radar systems

    Page(s): 451 - 465
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1821 KB)  

    With current technology, the real-time implementation of a multinotch logic-product (MLP) polarisation suppression filter which covers only a moderate area in polarisation space can only be realised as a rather bulky piece of hardware (typically with more than 61 notches). This has led to the development of the concept of nonlinear polarisation-vector translation (PVT), which allows the number of notches in the MLP filter to be drastically reduced without seriously degrading the effectiveness of the overall process. The mathematical representation of the nonlinear PVT process is described in the paper, and a limited theoretical assessment is given of its performance when used in conjunction with a single-notch filter in a target-plus-clutter environment. By way of illustration, some results are included on the suppression capability obtained when using experimentally derived rain data. View full abstract»

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  • Transform coding of images using interleaved blocks

    Page(s): 466 - 472
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (926 KB)  

    A method of coding images based on interleaved blocks is proposed. These block have irregular outlines with both holes and islands. It is shown that if they are designed by the application of `n-cycles¿¿ to a rectangular array, the resulting block shapes interleave perfectly without overlap. Used in transform coding, they substantially reduce the visiblity of block structure at low data rates. Experimental investigations are reported which identified desirable properties of interleaved blocks, in terms of their degree of overlap and interior distribution of pels. The pre-and post-transformations associated with the use of such blocks are easily accomplished by a simple modification of pel addressing routines, this being the only processing overhead incurred. Limited experiments on another form of overlapping block, which merged rather than interleaved with its neighbours, are also reported. These were computationally more involved and tended to magnify interblock contrasts. View full abstract»

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  • Application of gradient adaptive lattice filters to channel equalisation

    Page(s): 473 - 479
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    In this paper, the potential application of adaptive lattice equalisers based on gradient search adaptive algorithms, is examined. The assessment is based on simulations of equaliser performance in data communications systems which provides a comparison of the relative performance of these adaptive lattice equalisers with transversal equalisers. It highlights the critical balance between rapid convergence and degradation due to algorithm noise, which is involved when selecting the algorithm stepsize. Two new adaptive equaliser approaches are suggested, one based on a timed lattice structure feeding a linear combiner. The other is a short timed lattice structure in cascade with a transversal equaliser. Both approaches are shown to offer fast converging adaptive equalisers for data communications applications, which have a converged error performance superior to that of the direct application of a gradient adaptive lattice equaliser. View full abstract»

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  • Optimum MSK-type receivers for CPM on Gaussian and Rayleigh fading channels

    Page(s): 480 - 490
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1153 KB)  

    Power efficient schemes with excellent power spectra are contained among the continuous phase modulation (CPM) schemes. This is a constant envelope digital modulation technique, which in general requires a maximum-likelihood sequence detector (Viterbi detector) for efficient detection. This optimum receiver is sometimes complex. In this paper a parallel MSK-type receiver is studied. It is useful for binary schemes with modulation index h = 1/2. We consider coherent detection of signals transmitted over an additive white Gaussian noise channel and also over a Rayleigh fading channel. The MSK-type receiver can be implemented with only two filters and simple decision logic. Error probability formulas are given both for the nonfading and the fading channel. A simple algorithm giving the optimum filter for the Gaussian channel for high signal/noise ratios is presented. The optimum filter for low signal/noise ratios is also derived. For intermediate signal/noise ratios numerical optimisations are presented, both for the Gaussian and the Rayleigh fading channels. We have also considered diversity schems with ideal two-branch maximal ratio combining and selection combining. The optimum receiver filters are given for some selected schemes. It is shown that also, for the more complex CPM schemes, the loss compared to the optimum receiver is moderate. View full abstract»

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  • Performance of space-based radar in the presence of earth clutter

    Page(s): 491 - 500
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1218 KB)  

    The paper presents some general principles related to the performance of a space-based radar (SBR) using pulse Doppler to suppress the earth clutter. These principles are developed using a heuristic description of clutter as seen from a space-based radar, and illustrated by means of a case study. It is demonstrated that SBR performance varies with look direction and that clear areas exist in the clutter spectrum, where targets can be easily detected. Also, velocity compensation techniques can be employed to enhance detection for certain look directions. View full abstract»

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  • Evaluation of a site diversity model for satellite communications systems

    Page(s): 501 - 506
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (779 KB)  

    Site diversity is one method for reducing rain outages on earth-satellite communications links. A previously proposed prediction model for dual-site diversity, based on simple meteorological concepts that relate diversity performance to single-path rain attenuation, is evaluated against a compilation of 23 measured data sets. Prediction errors for the model are established and then discussed in terms of path elevation angle and rain convectivity. Possible refinements to the model are also mentioned. View full abstract»

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  • Inexpensive multipurpose airborne surveillance radar

    Page(s): 507 - 516
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2120 KB)  

    Airborne radar has now been in operation for over 40 years, and nose-mounted microwave equipment is fitted to the majority of civil passenger jets for the early detection and subsequent avoidance of severe storm centres. The ground-mapping and sea-search equipment described here provides a high-quality operator PPI display without the expense of either a special cosec2 aerial or a stabilised aerial platform. A novel feature is the provision of a permanent flight record on a low-cost audio tape recorder for subsequent playback on the ground or in the air. This may be used for debriefing or archival use without the inconvenience of airborne photography or the expense of carrying an airborne quality video tape recorder. Extensive results of maritime, sea pattern and terrain targets are reported. View full abstract»

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  • Analogue adaptive hybrid for digital transmission on subscriber lines

    Page(s): 517 - 525
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    Duplex transmission of digital signals on the single-pair subscriber line is possible if the signals in the two directions are sufficiently separated. An analogue adaptive hybrid is one method of signal separation. We discuss here the theory of analogue adaptive hybrids. We present a model for the system and the adaptive hybrid, and show the result of simulation. The parameters of the adaptive hybrid converge fast to the correct values if no signal is present from the far end. View full abstract»

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  • Adaptive adjustment of receiver for distorted digital signals

    Page(s): 526 - 536
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1594 KB)  

    The paper presents the results of an initial feasibility study into a novel technique for the adaptive adjustment of the receiver in a digital data-transmission system, operating with additive noise and severe inter-symbol interference in the received signal. The technique is an iterative process and can be used for the adjustment of the linear feedforward transversal filter that is employed ahead of a near-maximum-likelihood detector, and at the same time for the estimation of the sampled impulse response of the channel and filter, to give the information on the received signal needed by the detector. The latter two operations are equivalent to the adjustment of the feedforward and feedback transversal filters, respectively, in the corresponding nonlinear (decision-feedback)equaliser. The equaliser is, of course, a degenerate form of a near-maximum-likelihood detector, being obtained when the latter is reduced to its simplest possible form. The adaptive system operates directly on the estimate of the sampled impulse response of the channel, that must be provided at the receiver, and it requires no other input signals. It employs a root-finding algorithm that determines some of the roots (zeros) of the z-transform of the sampled impulse response of the channel. It then uses a knowledge of these roots to determine the tap gains of the linear feedforward transversal filter and to form an estimate of the sampled impulse response of the channel and filter. The technique can exploit the high tolerance to signal distortion of a near-maximum-likelihood detector in order to reduce the amount of processing of the received signal that is carried out by the adaptive filter to a level appreciably below that required by a conventional nonlinear equaliser. Thus a more cost-effective design of the receiver can be obtained. The paper describes the method of operation of two versions of the adaptive system and presents the results of computer-simulation tests over four different ch- nnels, showing both the rate and accuracy of convergence of the iterative process in each case. View full abstract»

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  • Predictive entropy coding for speech analysis

    Page(s): 537 - 541
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    Entropy coding using codes with a simple structure is used in connection with predictive coding to reduce the transmission rate. The predictive coder uses a quantiser with a large number of levels to minimise the effects of slope overload. An adaptive quantising scheme is used to maintain system operation at a point that yields a minimum redundancy. Experimental results on speech coding show that the adaptive predictive entropy coding scheme achieves a good signal-to-noise ratio (SNR) versus rate performance. At a 2-bits-per-sample (12.8 kbit/sec)rate, a segmental SNR of 14 dB is achieved; at 3 bits-per-sample (19.2 kbit/sec), the segmental SNR is 20 dB. View full abstract»

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  • Adaptive differential pulse-code modulation with adaptive bit allocation

    Page(s): 542 - 548
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (905 KB)  

    A new method of speech coding is described. The method, which is referred to as adaptive differential pulse-code modulation with adaptive bit allocation (ADPCM-AB), is a combination of adaptive differential pulse-code modulation with adaptive first-order prediction and switched pre-emphasis and adaptive bit allocation. The adaptive bit allocation technique is based on the short-term variation of the prediction error. An extensive subjective test has been carried out in which the system operating at data rates of 16 kbit/s and 32 kbit/s has been compared with conventional adaptive differential pulse-code modulation, with fourth-order prediction, operating at the same data rates, and with 7 bit logarithmically companded (A-law) PCM oprating at 56 kbit/s. The analysis of the results of the subjective test indicates that at 32 kbit/s the performance of the system is indistinguishable from that of conventional ADPCM and better than 7 bit logarithmically companded PCM. At 16 kbit/s the performance of the new ADPCM-AB system is preferred to the conventional ADPCM system. In addition, the technique of switched pre-emphasis has been applied to conventional adaptive differential pulse-code modulation, and the resulting modified ADPCM system has been compared with the new ADPCM-AB system. The results of subjective tests indicate that at 16 kbit/s the two schemes are considered to be subjectively equivalent. But, by using long data blocks in connection with the adaptive bit allocation technique, the ADPCM-AB system can be further improved with respect to its perceptual quality and made significantly superior to ADPCM with switched pre-emphasis. View full abstract»

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  • Weibull-distributed weather clutter in the frequency domain

    Page(s): 549 - 552
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    It is shown that Weibull-distributed weather clutter obeys a Weibull distribution after processing by the Discrete Fourier Transform (DFT). Thus the new Weibull CFAR detector should be considered to suppress such clutter in the frequency domain. View full abstract»

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  • A two-dimensional discrete convolution algorithm

    Page(s): 553 - 558
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (781 KB)  

    A theoretical result concerning the discrete Fourier transform is derived and used to develop a transform algorithm for computing two-dimensional convolutions. The use of this algorithm minimises the number of arithmetic operations and the memory requirements in computing a convolution of order (M¿¿N) using a transform processor or program designed for a length No, where M¿¿N0 and N¿¿N0.It is particularly suitable for computing convolutions whose orders are not powers of two using conventional fast Fourier transform processors. Methods of implementing the algorithm are also presented. View full abstract»

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  • IEE colloquium reports IEE Colloquium on Digital television techniques

    Page(s): 558 - 559
    Save to Project icon | PDF file iconPDF (301 KB)  
    Freely Available from IEEE
  • IEE Colloquium on Digitalisation of the TV receiver

    Save to Project icon | PDF file iconPDF (164 KB)  
    Freely Available from IEEE
  • Book review: Digital Communications Satellite/Earth Station Engineering

    Save to Project icon | PDF file iconPDF (102 KB)  
    Freely Available from IEEE

Aims & Scope

The latest version of this title is Radar, Sonar & Navigation, IET.

Full Aims & Scope