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Communications, Radar and Signal Processing, IEE Proceedings F

Issue 1 • Date February 1988

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Displaying Results 1 - 17 of 17
  • Town crier to world seer: a broadcast odyssey

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1347 KB)  

    A review of the development of broadcasting is given and thoughts are presented for its evolution into the 21st century. Although the terrestrial radio and television networks are unlikely to expand greatly in future, their usage may change, particularly to satisfy new interests in the broadcasting of data or information. Emphasis is placed on the importance of satellites in the next decade, for international programme supply, for delivery of radio and television to the home, and for satellite news gathering. The direct broad casting of television by satellite to the home, starting in 1989 in the UK, also offers exciting new opportunities for carrying higher-definition, wide-screen pictures. It is suggested that in the next couple of decades a slowly changing balance between terrestrial, satellite and cable networks will be seen, with fibre optic connections to the home only starting to make an impact with new services in the next century. Most significant in the near future will be the way in which new delivery technology and new receiver develop ments will increase the choice of programmes and broadcast information services to the user. View full abstract»

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  • Algebraic formulation of Kumaresan-Tufts superresolution method, showing relation to ME and MUSIC methods

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The paper gives a new formulation for the Kumaresan-Tufts (KT) method for enhanced resolution with an antenna array. This formulation shows the relation of this method to the maximum-entropy (ME) method and the eigenvector projection method (MUSIC algorithm). It is shown that the eigenvector projection is a smoothed version of the KT method, and that the KT method is equivalent to the ME method if the signal/noise ratio goes to infinity. This explains the observed increased resolution of the KT method at the expense of a strongly fluctuating pattern. The relation is very similar to the one between Capon's method and the ME method. View full abstract»

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  • Effects of correlated fading on level crossing rates and average fade durations with predetection diversity reception

    Page(s): 11 - 17
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    General expressions for the level crossing rate (LCR) and average fade duration (AFD) are obtained for several diversity combining schemes employing two-branch predetection reception of correlated Rayleigh fading signals. These expressions are obtained from joint and conditional probability density functions (PDFs) of the received signals, and lead to a unified treatment. This simplified method contrasts with the characteristic function approach used in previous investigations. Numerical results are presented for a space-diversity system using horizontally spaced antennas at a mobile station. It is shown that while the angle between the antenna axis and the direction of vehicle motion does not appear in the cumulative distribution function (CDF) of the combined output signal envelopes, it affects the LCR and AFD when the two fading signals are correlated. When the two antennas parallel with the direction of vehicle motion are used, the LCR can be reduced below the value obtainable from signals which fade independently. When the two antennas are perpendicular to the direction of vehicle motion, the AFD is loosely dependent on the antenna spacing and, provided the antenna spacing is not too small, is approximately half that for the no-diversity case. View full abstract»

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  • Formant estimation algorithm based on pole focusing offering improved noise tolerance and feature resolution

    Page(s): 18 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2064 KB)  

    The ability to measure the centre frequencies of areas of resonance (formants) in the short-time power spectrum of speech is of paramount importance in the recognition of voiced speech sounds in a feature-extraction-based continuous speech recognition system. Additionally, the provision of a tracking algorithm, by which the loci of formants with respect to time can be estimated, yields formant transition information which helps identify phonetic features which are of short duration. Noise robustness in formant estimation is an essential attribute for recognition systems which are used in the office environment and in military applications. The novel technique presented in the paper provides a noise-robust method of extracting formant centre-frequency information from the short-time speech spectrum, and consequently improves the signal/noise performance of the associated formant tracking algorithm. Formant estimation is based on modelling the vocal tract frequency response using linear prediction coding (LPC) techniques. However, the estimation of formant centre frequency in any given analysis frame is greatly improved by employing off-axis spectral estimation coupled with a progressive increase in vocal tract model order, which together provide vocal tract pole enhancement. Finally, the use of a formant weighting filter function applied within each frame aids in conferring high noise immunity to the estimation process. The pole focusing technique is shown to offer an improvement of at least 14 dB in signal/noise immunity as a formant frequency estimator over conventional LPC-based spectral estimation. In its application to formant tracking, it is shown that the technique also offers improved separation of formants which tend to merge, besides offering a general improvement in the provision of formant detail, in particular with regard to weak nasal formants. An additional advantage of the technique is its relative insensitivity to choice of vocal tract model order, - hich produces an inherently speaker-independent formant estimation algorithm. View full abstract»

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  • Near-maximum-likelihood decoding of convolutional codes

    Page(s): 33 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1142 KB)  

    The paper describes two novel decoding processes that come close to achieving maximum-likelihood decoding of convolutional codes, without, however, requiring nearly as much computation per decoded data symbol as does the Viterbi-algorithm decoder. The particular application studied is that of a bandwidth-efficient data transmission system, transmitting a rate-2/3 convolutionally coded 8PSK signal over a linear channel in the presence of additive white Gaussian noise. Results of computer simulation tests are presented, comparing the tolerances to additive white Gaussian noise of the new decoders with that of a more conventional near-maximum-likelihood decoder, and also with that of a Viterbi decoder. View full abstract»

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  • Embedded coding technique: principles and theoretical studies

    Page(s): 43 - 50
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (805 KB)  

    In the paper the principles of embedded array codes, which employ a combination of forward error correction and detection (FEC/FED) for error control in an ARQ environment, are introduced. In this scheme a concatenated code with an inner code for error correction and an outer code for error detection is used. A retransmission of the erroneous information packets is requested if the outer code decoder detects the presence of any errors after the initial correction has been performed by the inner decoder. The theoretical expressions for the reliability and throughput efficiency of the system are derived. The performance of the system is analysed and compared with that of a conventional array code. It is shown that the embedded scheme yields high reliability over a wide range of input bit error rates. A system of this type has many practical applications in situations where the transmission capacity of the communication channel varies with time; for example, on meteor-burst or HF (2¿¿30 MHz) radio links. View full abstract»

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  • Adaptive frame synchroniser for digital satellite communication systems

    Page(s): 51 - 59
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1089 KB)  

    The paper presents an analysis of the error performance of a basic frame synchroniser when noise and timing uncertainties exist. The results yield criteria for a new window width and detection threshold strategy, and a new form of frame synchroniser for digital satellite communication systems is described. It is shown that false alarms and misdetections may be minimised using the adaptive window width and adaptive detection threshold strategies implemented using a microprocessor-based system. View full abstract»

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  • Suboptimum adative polarisation cancellers for dual-polarisation radars

    Page(s): 60 - 72
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1476 KB)  

    In the paper some suboptimum adaptive polarisation techniques for the cancellation of partially polarised disturbances are analysed. They are based on suitable use of the estimates of the crosscorrelation between the dual-polarisation received signals. The performances of these techniques are evaluated and compared with that of the optimum setting of polarisation on reception. It is shown that the performances of the suboptimum techniques are affected by a quite limited cancellation loss, and related to the antenna pol arisation basis used on reception Some implementation aspects of these techniques are also discussed. View full abstract»

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  • Space-based radar: narrowing the main-beam clutter spectrum through the use of a high-aspect-ratio antenna

    Page(s): 73 - 81
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (646 KB)  

    With a space-based surveillance radar, the ability to detect slow-moving targets is compromised by returns from the earth's surface illuminated by the main beam of the antenna. An antenna design is presented that minimises the spectral width of main-beam earth clutter returned to space-based radars. The design maximises the aspect ratio of the antenna and aligns its long dimension with the satellite velocity vector. This ensures that the main-beam return is concentrated between two cones of constant velocity (isodops) whose separation. is inversely proportional to the length of the antenna. View full abstract»

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  • State estimation of manoeuvring targets from noisy radar measurements

    Page(s): 82 - 84
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Analytical results for tracking manoeuvring targets from noisy radar measurements are presented. A three-dimensional mathematical model based on the Kalman filtering technique is discussed for the tracking of a manoeuvring aircraft using noisy measurements obtained from a three-dimensional radar. The measurement uncertainties and the manoeuvre characteristics are assumed to be known in polar co-ordinates, and are also assumed to be white Gaussian with zero mean and constant variance. These are coupled to the cartesian co-ordinate system selected for tracking operation. The elements of the covariance and Kalman gain matrices are expressed in terms of those which apply for tracking in polar co-ordinates. The steady-state results are expressed in compact form by appropriately partitioning the covariance matrices. The numerical computations of the steady-state filter parameters of the model are in excellent agreement with those obtained from the recursive Kalman filter matrix equations. Hence these results are of practical interest in developing trackers for tracking manoeuvring aircraft and to eliminate the real-time execution of the complete filter equations. View full abstract»

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  • Algorithm for adaptive error control system synthesis

    Page(s): 85 - 94
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1290 KB)  

    In the paper an algorithm for adaptive hybrid error control system synthesis is presented. The channel is considered as a quasistationary Gilbert model under the constraint that only transitions from one stable state into two adjoining states are possible. The states are ordered according to the decreasing error probabilities. It is also assumed that the channel error statistics are known in advance. Thus, by computer simulation, the optimum codes (i.e. optimal values of the code parameters) are chosen for maximising the throughput for every channel state. During trans mission, identification of the channel states is performed continuously and the optimum code is applied. The criteria for the channel state identification are determined as suitable for block as well as convolutional codes. Channel identification and control are performed on the basis of the number of erroneous blocks within an interval of a given length. The interval lengths, as well as the corre sponding thresholds, depend on the channel state. They are optimised to achieve the minimum probability of error in channel state identification. An illustrative example of the proposed algorithm application for real channel error statistics (i.e. an experimentally obtained error sequence) is given. The approach to optimising the parameters in state identification, as presented, is more general than others found in the literature, since it can be applied to both block and convolutional codes. In the case under consideration, convolutional codes with majority logic decoding are implemented in the hybrid procedure. View full abstract»

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  • Rapid acquisition scheme for spread-spectrum radio in a fading environment

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1221 KB)  

    A modified two-level scheme for coarse code acquisition of spread-spectrum signals in a fading environment is considered. The scheme uses a bank of passive correlators followed by a bank of active correlators. The passive correlators are matched to short sync prefixes, which areinterspersed in the incoming signal. The passive devices correlate over sliding windows (in time), providing a rapid search capability. Threshold exceedances of the passive correlators areused to initiate active correlation over longer time intervals so that high reliability of decision is obtained. The multiple sync prefixes reduce the probability of missing the signal in a fading environment. An analytical model based on queueing and detection theory results is developed, and optimisation of the scheme is treated. A Gilbert model is used to characterise the signal fading on the channel. The performance in the presence of background noise with noisejamming is analysed. Theoretical performance curves and a discussion of the results are also presented. View full abstract»

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  • Book review: Data Communications and Teleprocessing Systems

    Save to Project icon | PDF file iconPDF (172 KB)  
    Freely Available from IEEE
  • ENCAP-4: an OQPSK-type modulation technique for digital radio

    Page(s): 105 - 110
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    A class of OQPSK-type signals (offset quadrature phase shift keyed) is defined which generalises several well known modulation formats. These signals are generated by means of a set of encoding rules which introduce a controlled amount of correlation between the in-phase (I) andquadrature (Q) components and between signal elements in each component. These encoding rulesimply the specification of four generating functions directly related to the eye diagram of the I and Q baseband signals. It is shown that the proposed signal representation provides an efficient means of design and performance evaluation. Advantageous trade-offs between spectral efficiency and power efficiency can be achieved with some of the proposed signals, making them suitable for digital radio applications. View full abstract»

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  • Performance data and limiting conditions of object tracking algorithms in the presence of camera noise

    Page(s): 111 - 113
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (355 KB)  

    The lower performance limits of two different object tracking algorithms relative to the camera noise, quantisation of the image signal, object size and contrast between object and back ground were determined using statistical methods. View full abstract»

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  • Correlation properties of dual-BCH, Kasami and other sequences for spread-spectrum, multiple-access systems

    Page(s): 114 - 117
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (461 KB)  

    Odd correlation functions and average interference parameters for dual-BCH, small sets of Kasami sequences and a new set of sequences are investigated. Results are presented for periods up to 255, and an investigation into the effects of choice of initial phase is included. Results indicate that the new sequences provide a level of multiple-access performance which is on average similar to other sequences, but is insensitive to variations in the statistics of the data used to modulate the sequences. View full abstract»

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  • IEE Conference Publication 281 (Radar 87)

    Page(s): 118 - 120
    Save to Project icon | PDF file iconPDF (353 KB)  
    Freely Available from IEEE

Aims & Scope

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

Full Aims & Scope