摘要:

The advent of digital VLSI technology demands a reappraisal of the most suitable algorithms for a given processing function. A cost function is developed for making quantitative comparisons between digital algorithm implementations including control and overheads. This provides a tool allowing different implementations of the same algorithm, and also different algorithms for the same function, to be compared. The cost function is chosen to characterise the algorithm and associated logic design independently of the circuit technology that might be used. In this way the techonology options can be introduced separately in designing a practical system. Also, configurations which achieve a higher throughput by using a proportionally larger quantity of hardware or higher logic speed are assessed as having the same effectiveness or cost. As an illustration, the costing is applied to FFT and Winograd Fourier-transform algorithms (WFTA). The results show the advantage gained by minimising the true costs including, particularly, control overheads, instead of just the number of arithmetic operations. Despite its fewer arithmetic operations, the WFTA is shown to be less efficient than the FFT except in the most fully parallel case.

DOI:10.1049/ip-f-1.1984.0012

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Random processes of considerable importance in signal processing often exhibit short-term stationary statistical attributes although in the long term they appear to behave in a nonstationary manner. Image signals belong to this category. In this work we introduce a class of composite-source models as a means of representing consistently signals of this nature. A composite likelihood function is derived, the subsequent maximisation of which yields estimates of the parameters that are associated with the composite-source model. It is a fact, that maximisation of the composite likelihood function is almost intractable by analytical means. However, by introducing optimisation techniques based on dynamic programming, maximum-likelihood estimation of composite-source models is simplified drastically. A graph-theoretic approach is adopted to demonstrate how the principle of optimality enables efficient algorithms for recursive maximum-likelihood estimation to be developed. Algorithms applied for one-dimensional as well as two-dimensional signals are presented. In both cases it is shown that the estimation problem is equivalent to the problem of identifying the maximumlikelihood path which traverses a directed graph of specific structure. Finally, it is shown that composite source models so estimated can be used in image coding systems which require the least transmission rate for prespecified levels of average distortion of the transmitted image signals.

DOI:10.1049/ip-f-1.1984.0013

出版商:IEE    

年代:1984

数据来源: IET

摘要:

AnM-ary decision feedback communication system with the MAP strategy is investigated. The performance of this system is analytically evaluated as follows. First, an approximate lower performance bound is found by means of the Cauchy inequality. Then an approximate lower performance bound is found by means of the Jensen inequality. Finally, the bounds are compared and found to coincide, yielding an approximate estimate of the system performance. The same estimate may also be obtained by means of mean path approximation. Thus, the mean path approximation tends to underestimate the system average transmission time. For verification purposes, the results are compared with those obtained from computer simulation and are found to be in good agreement. Furthermore, the feedback transmission is compared with one-way transmission. It is shown that feedback systems are better than one-way systems in terms of the signal/noise ratio required to achieve a prescribed error probability. The estimated power advantage of feedback systems is between 5.4 dB and 3 dB, depending on the number of possible signalsM; the power advantage decreases asMincreases. The results obtained forM→ ∞ imply that the feedback increases the capacity of an infinite-bandwidth Gaussian channel. However, the last result was not proved with the degree of rigour required in mathematics; rather, we have used approximate performance bounds and computer simulation data in our analysis.

DOI:10.1049/ip-f-1.1984.0014

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The performance of any given modulation on high-frequency channels reflected from the ionosphere will depend on the attenuation and time-frequency dispersion representative for the propagation medium. Spread-spectrum modulation has the basic function of spreading an information carrying signal over a very wide bandwidth. The ionospheric mode will, however, tend to limit the maximum useful bandwidth because of dispersion. The purpose of the experiment was to obtain some practical knowledge of the effect of time dispersion on spread-spectrum modulation and to obtain an indication of the bandwidth offered by the propagation medium.

DOI:10.1049/ip-f-1.1984.0015

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The characteristics of advanced digital transmission systems were measured using newly developed small earth stations and a K-band (30/20 GHz) and C-band (6/4 GHz) communication satellite. Satellite link performance for data, facsimile, video and packet switching information transmission at bit rates ranging from 6.4 kbit/s to 6.3 Mbit/s have been confirmed, using a small K-band (30/20 GHz) earth station and a demand assignment time division multiple access (DA-TDMA) system. A low-capacity omni-use C-band (6/4 GHz) terminal experiment has verified a telephone channel transmission performance by spread-spectrum multiple access (SSMA). Single point to multipoint transmission characteristics of the 64 kbit/s data signals from the computer centre were tested using a receive-only 4 GHz earth terminal. Basic satellite link performance was confirmed under clear-sky conditions; however, evaluation of the satellite link is also described based on rain attenuation and sun-transit interference data. Precise satellite orbit and attitude keeping experiments were carried out to obtain precise satellite antenna pointing accuracy for development of K-band earth stations that do not require satellite tracking equipment. Precise station keeping accuracy of 0.02 degrees was obtained.

DOI:10.1049/ip-f-1.1984.0016

出版商:IEE    

年代:1984

数据来源: IET