摘要:

To reduce the computational requirement which two-dimensional transform coding imposes it is common to combine the one-dimensional form of the process with simple previous-element predictive coding with an assumed fixed value of predictor coefficient for all coefficients. The underlying assumptions of this approach are here examined both theoretically and with reference to experimental data obtained from two widely different real images, and it is shown that it is highly inefficient to apply the prediction process to all of the transform coefficients, because not only is the error sequence variance frequently greater than that of the original coefficient sequence, but also considerable residual correlation exists in the signal to be quantised and coded, thus undermining the basis upon which such a data-compression technique rests.

DOI:10.1049/ip-f-1.1984.0002

出版商:IEE    

年代:1984

数据来源: IET

摘要:

In the paper the results of a study using Fermat number transforms (FNTs) to compute discrete Fourier transforms (DFTs) are presented. Eight basic FNT modules are suggested and used as the basic sequence lengths to compute long DFTs. The number of multiplications per point is for most cases not more than one, whereas the number of shift-adds is approximately equal to the number of additions in the Winograd-Fourier-transform algorithm and the polynomial transform. Thus the present technique is very effective in computing discrete Fourier transforms.

DOI:10.1049/ip-f-1.1984.0003

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The paper examines the performance of a direct-phase regenerator (DPR) with imperfect reference carrier employed in a two-link coherent quarternary phase-shift-keyed (CQPSK) communication system. Additive Gaussian noise (AGN) corrupts the signal at the input to the DPR and the coherent receiver. The referencecarrier phase error is assumed to have a Tikhonov probability distribution, but otherwise the system is considered to be ideal.

DOI:10.1049/ip-f-1.1984.0004

出版商:IEE    

年代:1984

数据来源: IET

摘要:

It is shown that, in situations where part of a correlation function can be predicted, it is possible to include this knowledge when forming a spectrum. The proposed method only requires the form of the known correlation function to be available. The method is an extension of the usual maximum entropy method, but it is demonstrated that it is possible to achieve good resolution in poor signal/noise environments.

DOI:10.1049/ip-f-1.1984.0005

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The maximum entropy method for spectral analysis is extended by assuming part of the spectrum to be known,a priori. It is shown that the extended method is still consistent with the Jaynes principle of maximising the entropy of the process. An example is included which demonstrates that the extended method produces improved results, even when incomplete background spectral information is assumed.

DOI:10.1049/ip-f-1.1984.0006

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A comprehensive review of the theory and practice of analogue and digital correlation systems used in radio astronomy and its related fields is given. The correlators are discussed according to the following classifications: analogue, amplitude-limited, Stieltjes (or random reference), relay, modified relay, polarity coincidence, modified polarity coincidence, and multilevel correlators. The expected performance data and limitations of each type are discussed together with examples of use.

DOI:10.1049/ip-f-1.1984.0007

出版商:IEE    

年代:1984

数据来源: IET

摘要:

In the evaluation of the analogue correlation from the digital correlation of coarsely quantised Gaussian signals, it is necessary to know the threshold levels used in the quantisation. The formulas used in the evaluation normally assume that the levels are accurate and stable. In this paper, errors in digital correlation arising from threshold variations of ±2%, ±5% and ±10% are evaluated for four-level correlators with lower-order correlation products deleted. The classification of the threshold errors into patterns shows that at low correlation coefficients, the largest contribution to the correlation error originates from the threshold of the comparator which detects the sign of the signal. An error analysis for the case of unequal delays in the signal paths is also presented. In the analysis, the comparator outputs of the quantiser are treated as data streams to which individual path delays can be inserted and the effect of any delay differences on the correlation coefficient readily obtained.

DOI:10.1049/ip-f-1.1984.0008

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A zero-crossing-based approximate realtime demodulator is described. Output digital samples, generated through linear interpolation of a suitably approximated piecewise linear model of the modulating signal, are passed through an usual reconstruction filter to recover the original modulating signal. Details of a simple microprocessor-based implementation of the demodulator are presented along with an estimate of the sample error bound for a sinusoidal modulation. A good compromise between constructional simplicity and overall output distortion is an important feature of this digital demodulator which is well suited for application in the areas of industrial telemetry and underwater communication.

DOI:10.1049/ip-f-1.1984.0009

出版商:IEE    

年代:1984

数据来源: IET

摘要:

This paper introduces a new class of codes that have been called ‘unequal error locating codes’. These codes are basically error locating codes but are studied by considering error patterns of various magnitudes lying in different sub-blocks of unequal lengths of the block length of a code. Lower and upper bounds on the number of parity-check digits required for such codes are derived. First, the codes locating random errors are considered and then a similar study is carried out for codes locating burst errors. Both cases are illustrated.

DOI:10.1049/ip-f-1.1984.0010

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A novel approach to split-band systems for speech-coding applications is proposed and evaluated. This differs from the conventional filter-bank implementation of sub-band coding (SBC) in that a blocktransform method is employed to perform the spectral analysis and synthesis. It is shown that substantial savings in terms of system delay and complexity can be achieved using this approach.

DOI:10.1049/ip-f-1.1984.0011

出版商:IEE    

年代:1984

数据来源: IET