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Communications, Radar and Signal Processing, IEE Proceedings F

Issue 6 • Date December 1988

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Displaying Results 1 - 19 of 19
  • Representation of radar sea clutter

    Page(s): 497 - 500
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (665 KB)  

    Sea clutter data obtained with a land-based X-band radar are analysed in terms of a correlated gamma-distributed noise model. Results obtained with both vertical-vertical and horizontal¿¿horizontal transmit-receive polarisations are shown to be broadly compatible with the model. As a test of the assumptions inherent to the model, we next simulate textures having the same autocorrelation function as the original image data. General agreement is again observed; discrepancies can be ascribed to specific failures of the assumptions. View full abstract»

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  • Level crossing rate and average fade duration for time diversity reception in Rayleigh fading conditions

    Page(s): 501 - 506
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (605 KB)  

    Time diversity, in which the same data are transmitted several times, is attractive in digital land mobile radio and is simple to implement because only one antenna is required. Expressions for the level crossing rate (LCR) and average fade duration (AFD) are derived in this paper for a system in which each data symbol is transmitted twice (two-branch diversity). As far as LCR is concerned, the expected diversity advantages can be obtained for a data repetition period, normalised by the maximum Doppler frequency, of about 0.2. For a large data repetition period, the AFD is halved. Measured values of LCR and AFD, obtained from 900 MHz signals received at a base station site, are in good agreement with the predicted values. View full abstract»

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  • New class of double inductive binary error correcting codes based on the class of Reed¿Muller codes

    Page(s): 507 - 512
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    A new class of binary codes is introduced. The codes have length n = 1.5 · 2m (m ¿ 3), and have a similar `double inductive¿ structure to that possessed by the class of Reed-Muller (RM) codes. The new codes are structured such that their length-to-distance ratio n/d = 2m, m ¿ 2. For rates less than 1/2, the new codes have a higher rate than the next Reed-Muller code of the same order and length n = 2 · 2m. View full abstract»

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  • Performance of time-frequency coded spread spectrum systems operating over noisy fading channels

    Page(s): 513 - 519
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (779 KB)  

    The performance of time-frequency coded spread spectrum systems (TFCSSS) is considered when the systems are operating over noisy fading channels. Systems employing the random addressing technique of Viterbi [1] and the addressing scheme developed more recently by Einarsson [3] are examined. An exact expression is derived for the word-error probability associated with the Viterbi scheme. This expression provides the tightest known upper bound to the performance of the Einarsson addressing scheme. Also in the paper the question of the most appropriate way of using power is considered, and it is shown that if the possibility of using an increased transmitter power exists, it is better to increase the power per transmission chip to a higher level and keep it constant, irrespective of the number of users occupying the chip, rather than to use a power level that increases with the number of users occupying the chip. View full abstract»

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  • Performance of slot synchronous time-frequency coded spread spectrum systems

    Page(s): 520 - 527
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    The operation of slot synchronous time-frequency coded spread spectrum systems is considered, and an exact closed-form expression is derived for the probability of error. This exact expression is, in general, very difficult to evaluate, and as an aid to estimating system performance, three new upper bounds are derived. These bounds are such that the degree of difficulty of computation increases with increasing tightness of the bounds. The bounds are, however, all relatively easy to evaluate. Simulation results relating to error probabilities are presented and compared with values computed from the various bounds. View full abstract»

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  • Effect of channel errors on source coded image data and the provision of adequate protection of transmission bits

    Page(s): 528 - 538
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1843 KB)  

    The effects of channel errors on image data coded by means of a zonal transform coder and a threshold transform coder have been studied and experimental results obtained. These form the basis for the selection of a suitable error protection technique. The results have been used in conjunction with five error protection schemes as follows: (i) parameter adjustments only (ii) equal importance protection through Hamming block coding (iii) equal importance protection through Hagelbarger convolutional coding (iv) percentage subimage protection (SIP) using Hamming block codes (v) Percentage subimage protection (SIP) using Hagelbarger convolutional codes. These schemes were selected to provide continuity from one to the next, thus helping in the observation of various trade-offs in the characteristics of the overall transmission systems. A sixth scheme is proposed which turns attention away from the more trditional methods of error protection. This scheme involves maximum likelihood decoding of the Huffman coded image, and thus it can only be applied to codes of the threshold transform type. Although this scheme gives a much improved error protection, its main disadvantage is that it requires considerable data storage and significant search times when decoding the data. The results have been used to deduce the best system for transmission of source coded image data over a channel with a specified error rate and to indicate the preferred technique for the protection of the data. View full abstract»

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  • Formant estimation system based on weighted least-squares lattice filters

    Page(s): 539 - 546
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1063 KB)  

    A formant estimation system using the adaptive weighted least-squares lattice (WLSL) algorithm and novel formant labelling techniquesis presented in the paper. In the WLSL, the likelihood variable, which can be considered as a statistical measure of the non-Gaussian component of the speech signal, is used to deweight time intervalsin the speech waveform which correspond to glottal excitation. A short analysis window coupled with optimal frame position placement, determined by the local minima of both the likelihood variable and the residual, is used to emulate glottis-closure, closed-phase analysis. The algorithm, which can also be considered as a special form of robust linear prediction analysis, offers an improved performance (i.e. a less biased formant frequency) in comparison to the frame-based linear prediction analysis. After formant candidates have been frame extracted from the spectral estimates for each of the waveform, a clustering procedure is first used to produce line segments of possible formants. A rule-based labelling mechanismis then applied to these segments to provide final formant trace estimates. Experimental results show the labelling algorithm proposed here offers improved formant labelling accuracy. View full abstract»

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  • Performance of a 16-ARY DEQAM modem employing a baseband or RF predistorter over a regenerative satellite link

    Page(s): 547 - 557
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1270 KB)  

    The paper presents the results of a series of computer-simulation tests that determine the effects of bandlimiting (nonlinear distortion with and without predistortion) on the tolerance to additive white Gaussian noise of a digital modem. The modem transmits a 16-ary differentially encoded quadrature amplitude modulation (16-ary DEQAM) signal over a regenerative satellite link, where the high power amplifier (HPA) on board the satellite transmitter may introduce AM-AM and AM-PM conversion effects into the 16-ary DEQAM signal. Four different bandwidths of the transmitted signal are tested, together with different levels of output back-off in the HPA at the transmitter. The arrangements achieving the most efficient use of the power are selected. There sults show that a surprisingly good improvement in performance can be achieved by using predistortion of the 16-ary DEQAM signal to reduce the nonlinear distortion of the high power amplifier. View full abstract»

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  • Conference report: Radar 87

    Page(s): 558 - 559
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    First Page of the Article
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  • Optimum threshold diversity reception of binary noncoherent frequency shift keying

    Page(s): 560 - 562
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (310 KB)  

    The optimum diversity rule for reception of binary non coherent frequency-shift keying in slow and nonselective Rayleigh fading (multipath) and additive non-Gaussian noise is derived for the critically important threshold case (of small nonvanishing signals and large sample size). The relevant expression for the probability of error illustrates the significant improvement achieved, even with a small number of diversity channels, i.e. 20¿¿30 dB gain from two to five channels for 10-5 error probability. View full abstract»

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  • Analysis and application of the excision CFAR detector

    Page(s): 563 - 575
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1346 KB)  

    The presence of interfering signals in the sample set used by a cell-averaging CFAR detector can cause a drastic degradation in its performance. A detector that alleviates the problem by excising strong signals before the cell-averaging operation is proposed and analysed. This detector suffers almost no degradation in performance, in comparison with a conventional cell-averaging detector, when it operates in an environment of homogeneous noise such as thermal noise with the possible addition of wideb and jamming. The proposed CFAR detector can be used in both radar and communications receivers. The paper presents a mathematical analysis of the operation of the excision CFAR detector resulting in explicit formulas for probabilities of detection and false alarm. An application that includes a binary postdetection integrator for discrimination against randomly occurring pulse interferences is presented, and its performance is evaluated numerically. Procedures for the determination of the detector's parameters are discussed. View full abstract»

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  • Integration of channel coding and modulation in the ARQ protocols

    Page(s): 577 - 584
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (890 KB)  

    The integration of the modulation operation in the structure of some automatic-repeat-request protocols is analysed. Continuous phase modulation schemes are considered together with block and convolutional codes. The optimum structure of channel coding and modulation is determined through a computer search. The results show that a net improvement in the throughput and error probability can be achieved by using this technique with respect to the classical protocols. View full abstract»

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  • Some new retransmission strategies for multipacket slotted ALOHA protocol

    Page(s): 585 - 593
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (957 KB)  

    In the paper some new strategies for message retransmission in the slotted ALOHA protocol with multipacket messages are described. These strategies use the information given by the positive or negative acknowledgments received for each packet of a message to reduce the probability of new overlappings among the same messages. Their application to some retransmission protocols of interfered messages, such as classical ALOHA, stop-and-wait, go-back-N and selective protocols, is considered. The results show that a net improvement can be achieved by using these retransmission strategies. View full abstract»

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  • Optimum patterns for frame alignment

    Page(s): 594 - 604
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1115 KB)  

    The paper considers optimum frame alignment patterns of given length and Hamming distance. After reviewing previous work, we proceed to specify, with supporting analysis, good patterns for the overlap region. For applications where this criterion is insufficient, an analysis of the search mode is also presented. This leads to a study of the choice of optimum pattern for a system as a whole, where patterns are selected against a new objective measure. By way of example, reference is made to CCITT specifications on frame alignment. View full abstract»

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Aims & Scope

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

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