摘要:

A general class of binary continuous-phase shift keying (CPSK) signals is defined, of which continuous-phase FSK (CPFSK) and continuous-phase chirp (CPC) signals are special cases. The structure and performance of suboptimal average matched filter (AMF) receivers with multibit observation are considered; both coherent and noncoherent detection of binary CPSK signals are investigated. Expressions suitable for numerical evaluation of such suboptimal CPSK receivers in the additive white Gaussian noise (AWGN) environment are given, and simplified expressions are derived for special cases. In particular, the coherent AMF receiver with optimised CPC and CPFSK signal parameters is shown to be equivalent to a generalised inphase and quadrature receiver. The relation between crosstalk and filter orthogonality is clarified for non-coherent AMF detection. Numerical examples for CPFSK and CPC signals are given.

DOI:10.1049/ip-f-1.1981.0021

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The paper describes how asynchronons delta sigma modulation can be used to generate frequency modulation. Present FM modulators have an inherent nonlinearity in the voltage/frequency characteristic, and as a consequence they are restricted to small percentage frequency deviations. The ADSM-FM modulator is inherently linear, allowing a wide percentage frequency deviation to be obtained. When incorporating this ADSM-FM modulator in the design of an FM broadcast exciter a system results which has an order of magnitude improvement in both signal/noise ratio and harmonic distortion compared with conventional designs.

DOI:10.1049/ip-f-1.1981.0022

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The jamming rejection capability of the broadband Frost power inversion array is investigated both theoretically in a qualitative manner assuming small bandwidth and experimentally using simulation as a function of the various parameters. The results obtained are used for designing the transversal filters behind the array elements as well as assessing, in terms of the number of variable weights, the alternative broadband system using several narrowband processors. The frequency distortion introduced by the jammers at various directions is then studied qualitatively.

DOI:10.1049/ip-f-1.1981.0023

出版商:IEE    

年代:1981

数据来源: IET

摘要:

An algorithmic derivation is described for a minimal-order Markov model for the problem of obtaining sliding-window detection probabilities. The advantage of this model over previous ones is the ease with which it may be run on a computer. A computer program for determining detection probabilities is described.

DOI:10.1049/ip-f-1.1981.0024

出版商:IEE    

年代:1981

数据来源: IET

摘要:

A 1-bit adaptive decision-feedback predictive coding (ADFPC) system is derived on the assumption of ‘good’ decisions. The predictor in the ADFPC is made adaptive by projecting the gradient, at each iteration, along the co-ordinate which exhibits the maximum absolute gradient. This gradient-seeking method requires that the stepsize only needs to be optimum with respect to a single coefficient (co-ordinate) during each iteration. A formula for calculating the stepsize at each iteration is obtained via a minimisation of the squared prediction error. Simulation results obtained in the encoding of a 1st-order autoregressive source and a monochrome image (with the analogue sources digitised by a 6-bit quantiser prior to encoding) reveal that the ADFPC is robust and exhibits good performance.

DOI:10.1049/ip-f-1.1981.0025

出版商:IEE    

年代:1981

数据来源: IET

摘要:

An adaptive filter configuration, known as the adaptive line enhancer (ALE), has previously been suggested by Widrowet al. for the detection of sinusoidal signals in wideband noise. Very few results are available in the literature on the analysis and performance of the ALE for the case of correlated noise. In the paper we analyse the ALE response to a sinusoid in 1-pole lowpass noise and show that there exists an optimum value of the decorrelation parameter. An attempt has been made to study the effect of the correlation of the lowpass noise on the coupling between the positive and negative frequency components of the sinusoid, and the response of the ALE to low- and high-frequency sinusoids. The ALE has been simulated using the recently derived lattice structure and the recursive least-squares lattice algorithms. The results agree closely with those of the theoretical predictions.

DOI:10.1049/ip-f-1.1981.0026

出版商:IEE    

年代:1981

数据来源: IET

摘要:

A technique has recently been developed whereby it is possible, without undue complexity and without any adaptive linear prefiltering, to achieve near-maximum-likelihood detection of a sampled digital signal, where there is intersymbol interference extending over several samples of the signal. It is, however, important here that the channel impulse response does not undergo large changes with time, since, when it does, a considerable increase in the complexity of the system may be required to maintain correct operation. The paper describes a development of the detection process whereby correct operation is achieved with a relatively simple system, even when the channel introduces severe frequency-selective fading of the type sometimes experienced over HF radio links. Results of computer-simulation tests are presented, showing the tolerance of a synchronous serial data-transmission system to additive white Gaussian noise, when a 4-point quadrature amplitude modulated signal is transmitted at 2400 bit/s over a model of an HF radio link, with two independent Rayleigh fading sky waves and frequency spreads of 0.5, 1 and 2Hz, and when the novel detection process is used at the receiver. Correct estimation of the channel is assumed throughout.

DOI:10.1049/ip-f-1.1981.0027

出版商:IEE    

年代:1981

数据来源: IET

摘要:

It is shown that Weibull-distributed weather clutter obeys a Weibull distribution after passing through a moving target indicator (MTI) processor realised by a double canceller. Both ground and weather clutter can be thus suppressed by using the method of MTI and new Weibull constant false alarm rate (CFAR) systems.

DOI:10.1049/ip-f-1.1981.0028

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The maximum-likelihood decoding of convolutional codes has generally been considered impractical for other than relatively short constraint length codes, because of the exponential growth in complexity with increasing constraint length. The soft-decision minimum-distance decoding algorithm proposed in the paper approaches the performance of a maximum-likelihood decoder, and uses a sequential decoding approach to avoid an exponential growth in complexity. The algorithm also utilises the distance and structural properties of convolutional codes to considerably reduce the amount of searching needed to find the minimum soft-decision distance paths when a back-up search is required. This is done in two main ways. First, a small set of paths called permissible paths are utilised to search the whole of the subtree for the better path, instead of using all the paths within a given subtree. Secondly, the decoder identifies which subset of permissible paths should be utilised in a given search and which may be ignored. In this way many unnecessary path searches are completely eliminated. Because the decoding effort required by the algorithm is low, and the decoding processes are simple, the algorithm opens the possibility of building high-speed long constraint length convolutional decoders whose performance approaches that of the optimum maximum-likelihood decoder. The paper describes the algorithm and its theoretical basis, and gives examples of its operation. Also, results obtained from practical implementations of the algorithm using a high-speed microcomputer are presented.

DOI:10.1049/ip-f-1.1981.0029

出版商:IEE    

年代:1981

数据来源: IET

摘要:

A new notation is proposed for use in the discussion and analysis of high-purity signal sources. Omissions in the previously accepted notation are rectified and a consistent set of interrelated symbols is suggested.

DOI:10.1049/ip-f-1.1981.0030

出版商:IEE    

年代:1981

数据来源: IET