摘要:

The paper investigates the application of a simple nonlinear structure to the problem of adaptive channel equalisation. Based on the Bayes decision rule, it is shown that the optimal equalisation solution is an inherently nonlinear problem and, therefore, it is desired to incorporate some degree of nonlinearity in the design of equaliser structure. The approximate realisation of the optimal equalisation solution is implemented using a polynomial-perceptron architecture and simulation results are included to support the theoretical analysis.

DOI:10.1049/ip-i-2.1990.0036

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The performance of limiter discriminator detection ofM-ary FSK signals is analysed at arbitrary modulation indices. It is shown that the error rate performance of limiter discriminator detection can be significantly improved by increasing the modulation index above 1/M. The optimum modulation index that minimises the overall error probability is determined for the casesM= 2, 4 and 8. The analysis is carried out for wideband and bandlimited channels with Gaussian and second-order Butterworth filters. It is shown that the optimum modulation index depends on the signal/noise ratio (SNR), in a wideband channel, and on both SNR and timebandwidth product in a bandlimited channel. Finally, it is shown that the optimum sampling instance in presence of a nonzero phase IF filter can be approximately determined by using only the worst case symbol pattern.

DOI:10.1049/ip-i-2.1990.0037

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A prototype expert system to diagnose faults in a telecommunications network was developed for a large retail, hotel and brewery company. Principal objectives met were that it should run on a PC, should be usable by unskilled persons, would find all straightforward faults and would lead the operator through all the steps needed to activate the relevant maintenance contractor and record the fault in a log. The topology of the network, together with names and telephone numbers of appropriate people to call up at the network nodes, were all stored in files, thus enabling changes to be made without interfering with the knowledge base. A survey is given of applications of expert systems in related fields and the special features of expert systems together with the reasons for choosing to develop one rather than to write a conventional program are discussed. The system was developed for the SAVOIR expert system shell, and details of the knowledge base are given as well as some comments on the suitability of that shell for this task.

DOI:10.1049/ip-i-2.1990.0038

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper studies some novel techniques for simplifying a near-maximum-likelihood detector that operates on a sequence of received samples, each of which carries two new data symbols. The two data symbols may originate from independent sources, and one of these may be an unwanted interfering symbol. In a received sample, the two new data symbols have been multiplied by arbitrary quantities that may vary independently, but smoothly, from one sample to the next. The new techniques are studied for a particular application of near-maximum-likelihood detection in a land-mobile-radio system, which introduces flat fading into the transmitted QPSK data signals. The receiver here employs an arrangement of combined detection and estimation that has recently been developed for use with the given signals. The arrangement enables two QPSK signals to be transmitted simultaneously over any one channel, in place of the one QPSK signal conventionally used, leading to a more efficient use of bandwidth. The paper shows how substantial simplifications may be introduced into the detection process without, however, significantly changing its resultant operation. The new techniques described here are of quite general application to many near-maximum-likelihood detectors, in applications over flat fading or frequency-selective fading channels, or over time invariant channels that introduce intersymbol interference.

DOI:10.1049/ip-i-2.1990.0039

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The speech enhancement problem is approached by the Fourier–Bessel (FB) expansion of the speech and noise. The application of this expansion to the enhancement of the speech signals degraded with additive noise is described. The method is based on the subtraction of the FB coefficients of the estimated noise from the coefficients of the noisy speech. The difference in two sets of coefficients is then used to synthesise the enhanced speech. The inherent lowpass filtering property of the FB reconstruction with a finite number of coefficients is revealed.

DOI:10.1049/ip-i-2.1990.0040

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper describes the determination of the additive white Gaussian noise channel information transmission capacity when the channel input and output are limited by certain constraints. The channel input constraints are those of signal amplitude, or signal amplitude and average power. The input signal amplitude and average power constraints are defined by restricting the channel input to values within the finite interval [—A, +A] and also to have average power equal to some specified value. The channel output constraint is that of signal clipping due to quantisation applied at the receiver. The input signal amplitude/output signal clipping constrained capacity, and the input signal amplitude and average power/output signal clipping constrained capacity are determined separately. It is found that there are unique, optimum and discrete input signal amplitude distributions, taking a finite number of values, and optimum output signal clippings that achieve these capacity values. The optimum input distribution values are also used to determine the optimum amplitude probability density function at the channel output.

DOI:10.1049/ip-i-2.1990.0041

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper deals with some efficient automatic-repeated-request (ARQ) schemes for error control in digital communication systems. The proposed ARQ techniques utilise the redundant information owing to repeated transmission of a same block to perform a soft detection. The M-ary CPFSK schemes are considered in transmisson. Coherent and noncoherent soft detection are used in detecting the M-ary CPFSK signals, in particular noncoherent soft detection has been studied to reduce the receiver implementation complexity. The throughput efficiencies for the proposed ARQ schemes are analytically derived and optimised with respect to the number of blocks' transmitted copies.

DOI:10.1049/ip-i-2.1990.0042

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper presents simple neural circuits as an analogue decoder for plain balanced codes, a soft-decision decoder for the (16, 9, 6, 5, 4) error correcting balanced code, and a harddecision decoder for the (47, 24) quadratic residue code. The authors study the dynamics of a class of very simple Hopfield nets and prove that they can be used as analogue decoders for plain balanced codes. This result is further extended so that the net is able to store constant weight binary vectors. With these nets as basic building structures, the authors then construct simple decoders for the (16, 9, 6, 5, 4) error correcting balanced code and the (47, 24) QR code, respectively.

DOI:10.1049/ip-i-2.1990.0043

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The effects of nonlinear distrotion on the error performance of a 16-QAM signalling scheme, operating in a typical satellite channel, are investigated by means of a computer simulation program. Additive white Gaussian noise is present on both input and output of the TWT amplifier. The results obtained are in good agreement with those obtained theoretically in other works, and show that the noise presence on the up link causes severe system performance degradation. Moreover, the behaviour of a nonlinear system in the presence of up-link cochannel interference is examined. The results clearly show that the symbol error probability depends strongly on the symbol timing difference between the desired and the interfering signal, as well as on the phase difference of their carriers especially for low signal to interference ratios.

DOI:10.1049/ip-i-2.1990.0044

出版商:IEE    

年代:1990

数据来源: IET