摘要:

The paper presents a review of several commonly employed objective speech distortion measures and their relevance to subjective assessments of speech quality. Since many of the objective measures described in the paper have been covered previously in other reviews, we have concentrated primarily on three aspects. First, the philosophy of progressively constructing objective distortion measures in order to incrementally improve their capability to predict subjective quality (typically done at the expense of computational complexity). Secondly, we have concentrated on the use of objective measures as complementary tools to subjective evaluations, and thirdly, on the methods for evaluating the relative performance of different objective measures.

DOI:10.1049/ip-i-2.1989.0045

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Code excited linear prediction (CELP) has been shown [1] to be capable of achieving high quality speech compression at very low bit rates. However, the original method suffers from the two drawbacks that it requires a large amount of computation, and the Gaussian codebook used is not able to reproduce a sharp impulse in the coded residual waveform. The authors present a classified vector excitation coding (CVXC) scheme based on selective modelling of the LPC residual which attempts to overcome both these drawbacks by using separate codebooks for separate excitation types. A further feature of our coder which helps preserve the nature of pulsive residuals, is the use of pairwise nearest neighbour (PNN) matching [2] to generate the excitation codebooks.

DOI:10.1049/ip-i-2.1989.0047

出版商:IEE    

年代:1989

数据来源: IET

摘要:

In the paper the impact of impulsive noise on the symbol error probabilities (SEPs) of 8- and 16-ary CPSK transmissions is analysed. The transmission medium considered is a two-link nonlinear channel. The SEPs are evaluated in terms of up and down link carrier-to-noise ratios (CNRs), impulsive index of the noise (A), and the power ratio of the Gaussian noise-to-impulsive noise (π′). The bandpass nonlinearity (BPNL) considered exhibits both AM/AM and AM/PM conversions. A phase compensating receiver is assumed to compensate AM/PM conversion.

DOI:10.1049/ip-i-2.1989.0048

出版商:IEE    

年代:1989

数据来源: IET

摘要:

One of the problems that arise in the course of designing a pseudo error monitor (PEM) is the necessity of knowing the relationship between the pseudo error rate (Ppe) and the actual error rate (Pe) in the presence of channel impairments. In the paper, the problem is solved analytically for a fairly general system model. A unified analysis of thePpeand thePeof an M-ary CPSK hard limited multilink system with some hardware imperfections, Gaussian noise and cochannel interference per link, is presented. Extensions of the analysis onM-ary DPSK signals and/or on a linear multilink system are discussed, too.Several types of modern PSK communication systems may be seen as special cases of the model considered in this paper, for example, radio relay link and satellite two-link system.It is shown that knowledge of the asymptotic behaviour of the probabilitiesPpeandPeis very useful for PEM design. To illustrate this, details are given for a one-link quaternary CPSK system.

DOI:10.1049/ip-i-2.1989.0049

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A priority oriented channel access scheme for cellular mobile radio telephone systems serving vehicular and portable radio telephone users is described. The calls generated are divided into three different classes: new vehicular calls, new portable calls and hand-off calls. Priority is given to hand-off calls over new calls and to vehicular calls over portable calls. Appropriate analytical models and criteria are developed and used to derive performance characteristics. Blocking and forced termination probabilities for each kind of user are determined as functions of system parameters. Noncompleted call probability is defined as a useful performance measure for each kind of user. The effects of priorities and hand-off procedures on performance characteristics are investigated. General formulas are given and specific numerical results for nominal system parameters are presented.

DOI:10.1049/ip-i-2.1989.0051

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The effect of selection diversity reception on the error performance of the digital mobile radio systems is investigated. The binary frequency shift keying system (FSK) using noncoherent (NC) demodulation, with a limiter/discriminator receiver is considered. All major error causing factors, fading and Gaussian and impulsive noise, are taken into account. The corresponding general expression for the error probability (BER) is derived. This expression is used to analyse the improvements in the BER performance of the considered system gained by theM-branch selection diversity technique.

DOI:10.1049/ip-i-2.1989.0052

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The paper describes a novel carrierphase synchronisation process that has been developed for use in a digital communication system operating over a satellite link and employing unbalanced quaternary phase shift keyed (UQPSK) signals. The satellite is not geostationary and may travel close to the surface of the earth over at least a part of its orbit. Correct carrier phase synchronisation needs to be achieved here as soon as the satellite rises above the horizon, during the time it is transmitting data signals, and therefore without the use of a known training signal. Under these conditions the digital signal is received at a low signal to noise ratio and in the presence of a severe Doppler shift. Correct carrier phase synchronisation must then be maintained as the satellite passes overhead and until it approaches the horizon again. Thus the synchronisation circuits must tolerate also a high rate of change of Doppler shift, albeit at a higher signal to noise ratio.The synchronisation algorithm is in two separate parts that operate sequentially and are both non-data aided. The first part removes the Doppler shift from the received signal and the second part then achieves carrier phase synchronisation, which is maintained over the rest of the transmission.The paper describes the new algorithms and presents the results of a series of computer simulation tests to assess their performances.

DOI:10.1049/ip-i-2.1989.0053

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The author derives a formula for the error probability of partial response frequency shift keying with limiter discriminator integrator detector with and without decision feedback for the satellite mobile channel which contains as special cases the Gaussian channel and the land mobile channel. The author applies the formulae to Gaussian minimum shift keying and compute the error probability as a function of energy to noise ratio and other system parameters (Doppler frequency, maximum Doppler frequency, bandwidth of Gaussian filter and ratio of power in the direct and diffuse signal components).

DOI:10.1049/ip-i-2.1989.0054

出版商:IEE    

年代:1989

数据来源: IET