摘要:

The paper examines the performance of a trunk frame organisation which combines circuit and packet switching capabilities. Circuit performance for the proposed organisation is analysed in terms of blocking probability and uses an exhaustive state enumeration technique. Packet performance is analysed in terms of mean delay, using a ‘work’ concept. Finally, the behaviour of the optimal circuit/packet boundary location is investigated and a square-root formula is proposed to identify this boundary.

DOI:10.1049/ip-f-1.1986.0013

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper deals with the problem of improving the performance of the adaptive transform coder which operates on noisy speech. We propose to estimate the short-time spectral amplitude (STSA) of the original speech and to utilise the noisy phase prior to the encoding process. The appropriate minimum mean-square error STSA estimator is derived and the system is examined in encoding speech which has been degraded by uncorrelated additive wideband spectrally flat noise. The above approach improves the quality of the encoded speech in the sense that the output noise level and the irregularities characteristic to the directly encoded noisy speech are reduced. However, the encoded speech loses some of its crispness.

DOI:10.1049/ip-f-1.1986.0014

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A coherent radar digital data collector (CRDDC) has been developed which records I, Q data obtained by sampling the receiver intermediate frequency (IF) of a fan-beam radar with a single A/D convertor. The paper describes the sampling technique which was developed for this application, called the semicoherent Doppler processing technique, which allows operation with radars employing a noncoherent transmitter such as a magnetron. Representative field results are presented for real targets and natural environments such as land and sea clutter. These results employing spectral analysis, which prove the viability of the sampling technique for Doppler processing, were obtained by processing data recorded by the CRDDC at a coastal site in California with an L-band fan-beam radar.

DOI:10.1049/ip-f-1.1986.0015

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A general method for computing the power spectral density (PSD) of an encoded, continuous phase modulated (CPM) signal with correlated data symbols is presented in the paper. The encoder is a finite-state sequential machine which introduces correlation between symbols transmitted in different time slots. The method used is the so-called autocorrelation function method, in which the autocorrelation functon is first computed and then numerically Fourier-transformed to obtain the PSD. A key result is that the autocorrelation function is obtained via a recursive equation that is in keeping with the assumed Markov property of the data source. The computational complexity of the present method is linear in the length of the baseband pulse, and this enables one to calculate the PSD of CPM signals with a long pulse length. Our primary goal is to specifically consider the PSD of convolutionally encoded CPM signals. However, our algorithm is presented in a general format and numerical results are included for a wide class of digital CPM signals.

DOI:10.1049/ip-f-1.1986.0016

出版商:IEE    

年代:1986

数据来源: IET

摘要:

An extension of the Rowe-Prabhu method is presented for finding the power spectral density (PSD) of continuous phase modulated (CPM) signals with correlated data symbols. Correlation between symbols in different time slots is introduced by an encoder which is represented as a finite-state sequential machine. This structure simplifies any procedure for the spectral analysis of modulated signals with correlated data symbols, including the Rowe-Prabhu method. For instance, it allows a sequential computation of some of the matrices needed for this spectral analysis technique. The PSD is expressed in a compact, Hermitian matrix form that is suitable for numerical computation by a digital computer. Examples for convolutionally encoded CPM are given for the purposes of illustration, as treating such signals was the primary motivation in developing the spectral analysis algorithm that is presented in the paper.

DOI:10.1049/ip-f-1.1986.0017

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper presents a study of the significance of phase distortion in digital transmission systems. Beginning with a review of the eye diagram and contour map criteria, we compare their advantages and disadvantages with those of the mean-square error and probability of error criteria. Using the eye diagram and contour map criteria, we then employ cosine rolloff, Cheb$yshev and Butterworth functions as examples, arriving at the conclusion that phase distortion is significant and some form of phase equalisation is necessary for reliable digital transmission.

DOI:10.1049/ip-f-1.1986.0018

出版商:IEE    

年代:1986

数据来源: IET