摘要:

The realisation of a Walsh network is proposed. This network is built from a set of Walsh functions which are either odd or even binary value functions in their defined domain. The network is employed as an adaptive equaliser for which an algorithm for recursively adjusting the tap gain coefficients minimising the mean-square estimation error at the output is proposed. Some desirable properties of the covariance matrix of the equaliser are discussed. Examples of equalisation of a practical channel demonstrate the effectiveness of the Walsh equaliser.

DOI:10.1049/ip-f-1.1983.0024

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The author has concluded that a vector-signal processor which notionally adapts the location of a multinotch logic-product polarisation suppression filter in polarisation space such that it coincides with the location in polarisation space of the unwanted incident field samples could represent a rather severe load in terms of processing time. Consequently he has developed the alternative approach whereby the processor transforms the incident-field polarisation vectors to that fixed location in polarisation space at which the filter achieves maximum suppression. To help illustrate this new development and its significance within the virtual polarisation adaptation (VPA) concept there is a brief but comprehensive recapitulation of VPA principles. As well as explaining the polarisation-vector transformation process, the paper gives an outline of the mathematics involved and how the process would be applied as a tool for improving target detection capability through the suppression of unwanted signals. It is likely that the rather simple arid elegant technique which is involved may have application in fields other than radar, and it lends itself well to real-time implementation.

DOI:10.1049/ip-f-1.1983.0025

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Bandlimited SSB-FM is analysed in terms of its complex zeros, leading to expressions for the spectral components of both modulated and demodulated signals as a function of the zeros. These confirm that direct distortionless reception is feasible if the modulating signal is sufficiently small. The characteristics of the bandlimited SSB-FM signal and the demodulated signal are analysed, and it is shown that demodu lation distortion caused by overmodulation consists mainly of positive ‘clicks’. These occur simultaneously with envelope dips, and their frequency may be taken as a measure of distortion noise. Computer simulation provides illustrative examples concerning the use of SSB-FM for speech transmission through a conventional SSB channel, and bounds on the frequency deviation are obtained for this example. The effects of both realistic IF filters and mis-tuning at the receiver are also investigated. The results suggest the potential of narrowband SSB-FM for applications such as mobile radio.

DOI:10.1049/ip-f-1.1983.0026

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper describes simple prediction techniques for compensating the effects of carrier phase and frequency offsets normally encountered in high-speed data transmission systems over distorted voice-band channels. Computer simulations are used to show how the techniques can be used to overcome the problem of large delays in decision-directed carrier phase-locked loops and hence improve the phase and frequency lock of such systems. The various prediction techniques are compared at their steady-state RMS prediction error in the presence of ± 10Hz frequency offset.

DOI:10.1049/ip-f-1.1983.0027

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A technique for reducing the bandwidth requirement for the transmission of digital shore-based marine radar data is presented. It is found that the removal of ground clutter, run length encoding and scan-to-scan averaging results in a reduction of about a factor of 20, allowing the use of a 10 kHz telephone line in place of a microwave-link communication system with no loss of image quality.

DOI:10.1049/ip-f-1.1983.0028

出版商:IEE    

年代:1983

数据来源: IET