摘要:

Quality-rating tests have been conducted to determine the subjective quality of PAL- and SECAM-coded colour television pictures after passage through a 70 Mbit/s DPCM digital coder and decoder. The assessment methods employed comprised both the traditional single-stimulus quality-grading method and a double-stimulus continuous quality-rating method specifically intended for assessing small impairments, such as are introduced by digital codecs. The double-stimulus method is shown to be highly suited to the evaluation of such impairments. After removal of the residual impairment (due, for example, to scan structure and flicker) and assuming an error-free environment, the digital codec was found to introduce a basic impairment of about 1/20 imp for PAL coded pictures and about 1/10 imp for SECAM coded pictures, irrespective of the assessment method employed. These levels of impairment are compared with the performance of analogue links, of various types and lengths, presently in use for the distribution of television signals.

DOI:10.1049/ip-f-1.1983.0077

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper deals with the design and performance evaluation of optimum and suboptimum multistatic radar receivers. Several detection schemes are considered according to the possible models for the wanted signal: completely known; random phase; Rayleigh amplitude and random phase; and one-dominant-plus-Rayleigh amplitude and random phase. The inherent complexity of the multistatic structure may be alleviated by resorting to a simplified scheme suggested here which envisages a number of peripheral decisions in as many conventional receivers, followed by a central decision based on an OR criterion. The latter design admittedly yields a suboptimum receiver, but an assessment of its performance shows the existence of a wide range of operating conditions of practical engineering interest where performance degradation with respect to the optimum receiver is negligible.

DOI:10.1049/ip-f-1.1983.0078

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Some very recent work on equalisers has led to a simple development of a conventional nonlinear (decision-feedback) equaliser, that involves only changes to the equalisation process itself and can, under certain conditions, give a useful improvement in tolerance to additive white Gaussian noise. The technique is particularly effective when binary data symbols are transmitted, at a high signal/noise ratio, and there is severe amplitude distortion in the received data signal. The paper is concerned with a further development of the technique, suitable for applications where a binary data signal is transmitted at a high rate over a linear baseband channel and where the channel introduces severe amplitude distortion. The channel may be either minimum phase or linear phase, or else it may approximate to some compromise between these two. It is shown that, under the given conditions, the linear feedforward transversal filter that forms the first part of a conventional nonlinear equaliser can often be replaced by a simple two-tap feedforward transversal filter, with either an improvement in performance or, at least, no serious degradation in performance. The paper describes both the new equaliser and a further development of this for the case where the received data signal is sampled at twice the data symbol rate. Finally, results of computer-simulation tests are presented, comparing the tolerances to additive white Gaussian noise of the two new equalisers with those of more conventional detectors, for models of various channels. Three quite different applications have been considered, one of which involves the transmission of digital data at 140 Mbit/s over a length of coaxial cable.

DOI:10.1049/ip-f-1.1983.0079

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A key factor in the planning of any microwave radio-relay system is the repeater spacing achieved for a given quality of service (system outage) due to weather-induced impairment in the transmission path. In the paper the repeater spacing for a high-capacity 19 GHz digital radio-relay system is considered. Naturally emphasis is placed on excess attenuation due to rain, but qualitative judgments of the importance of atmospheric multipath, rain-induced depolarisation, scintillation and snow are also made. Use is made of propagation data and models, and practical observation, derived from related research and development studies. With regard to the quality of service it has been shown that at present it is more appropriate to apportion half of the CCIR recommended nonavailability objective to propagation-induced effects rather than design the system on the basis of reliability criteria.

DOI:10.1049/ip-f-1.1983.0080

出版商:IEE    

年代:1983

数据来源: IET

摘要:

An expression is derived for the bit error probability of minimum shift keying (MSK) and offset quaternary phase shift keying (OQPSK) signals which have been transmitted through nonlinear satellite channels after bandlimiting. The transponder nonlinearity considered in the paper is of the bandpass type, which exhibits AM/AM and AM/PM conversion effects. The effects of up-link and down-link thermal noise are also taken into consideration in the analysis. The resulting expression for the bit error probability is an infinite series containing double integrals. In order to illustrate the usefulness of the method, the error rates of MSK and OQPSK signals are computed for a Butterworth bandlimiting filter hard limiting transponder channel model. The error rates of MSK and OQPSK signals are compared with the error rate of binary PSK signals for this communication system model.

DOI:10.1049/ip-f-1.1983.0081

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A general method for numerical calculation of power spectra for digital FM signals is developed. Arbitrary baseband pulse shape, the modulation index and the number of levels of the data can be used. The probability density function of the statistically independent data symbols can also be chosen arbitrarily. With this method the autocorrelation function is first calculated and then numerically Fourier transformed, yielding the power spectrum. The time required to calculate a power spectrum on a digital computer is extremely small, and the calculations are simple and easy to use.

DOI:10.1049/ip-f-1.1983.0082

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A microprocessor-controlled data transmission system is described for use over VHF and UHF land mobile radio channels. The system is based on ARQ operation of error control, additional information regarding the validity of the received data being provided by a signal strength detector. Direct modulation of an FM carrier is employed, although the system may also be used with subcarrier modulation in order to allow the use of existing voice communication equipment. The terminal equipment is predominantly digital in operation, thereby allowing full microprocessor control. As far as it is able the processor adapts the system to the current channel conditions by varying the coding technique employed and the data block size.

DOI:10.1049/ip-f-1.1983.0083

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The exact least-squares lattice algorithm for channel equalisation is derived without using an explicit time update for the equaliser or predictor coefficients. This avoids the need for auxiliary vectors and scalars within the analysis, which is considerably simplified as a result. The algorithm, which incorporates a growing-fading memory estimator, is developed in the traditional unnormalised form, from which a compact rationalised and normalised algorithm is subsequently derived.

DOI:10.1049/ip-f-1.1983.0084

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Block quantisation is a process whereby groups of continuous variables are quantised in a given number of discrete levels for digital processing. In problems involving block quantisation certain constraints concerned with integer bit assignment that guarantee a realistic solution are difficult to incorporate into the development of algorithms for optimal solutions. In this kind of situation the existing methods produce solutions by an appropriate algorithm which treats the number of bits per sample as a continuous variable, and a correcting process necessarily follows to assign integer bits per sample, thereby presenting the solution in a realistic form. Deviation from optimality, however, is often a common side effect of the entire procedure. In the paper we present a recursive algorithm for optimum block quantisation, based on dynamic programming, by means of which integer bit assignment constraints are easily met. Further to a computational solution, a dynamic programming analytical solution is also derived. Compared with existing analytical solutions derived according to entirely different considerations, it is shown that the new approach, without the integer bit assignment constraint, leads to precisely the same conditions of optimality and results in similar closed-form solutions for the block quantisation problem.

DOI:10.1049/ip-f-1.1983.0085

出版商:IEE    

年代:1983

数据来源: IET

摘要:

CISPR publication 16 describes a simple test procedure for assessing the suitability of a site for the making of RFI measurements. The paper describes an improved test procedure which also enables those features of a site which are detrimental to its satisfactory performance to be identified positively. The new procedure has been utilised to assess the site for the proposed free-field EMI test range at IBM Hursley Park, and some results from this assessment are included.

DOI:10.1049/ip-f-1.1983.0086

出版商:IEE    

年代:1983

数据来源: IET