摘要:

The paper covers the salient features, comparisons and potential of recent developments in analogue signal processing hardware: surface-acoustic-wave (SAW) devices, charge-transfer devices (CTD), and also switched-capacitor filter networks. After describing the operating principles of these devices, their potential for several important signal processing roles is reviewed. Applications are treated where the performance capabilities of the devices overlap. Recent developments in optical and acousto-optical signal processors are reviewed and their future potential is examined. Finally, SAW and CTD performances are compared with available very large-scale integration (VLSI), and the potential of VLSI hardware for digital signal processing (DSP) is discussed.

DOI:10.1049/ip-f-1.1987.0059

出版商:IEE    

年代:1987

数据来源: IET

摘要:

An approach to the selection of an optimum pulse repetition frequency (PRF) in an airborne pulse-Doppler radar is discussed. A radar simulation program is employed, and this is described in outline. A specific example is presented.

DOI:10.1049/ip-f-1.1987.0060

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The paper develops an adaptive antenna algorithm that is highly suboptimal and suitable for use in broadband environments. The algorithm is of the LMS beamforming type and is a variation on a frequency-domain adaptive beamformer. Processing is assumed to take place in frequency bands not exceeding one octave. In this band the complex weight vectorsWkare made a simple analytic function of FFT cell numberk. The system minimises broadband output power subject to suitable look-direction constraints. The algorithm was tested assuming constant sensor errors, full adaptation and a time-stationary environment. Broadband bearing resolution capability was found to be far superior to that with conventional beamforming. The system proved capable of steering multiple broadband nulls –40 to –60 dB in depth. Algorithm degradation occurs when the system is steered at strong sources, but the overall performance is good, particularly when the wanted signal is weak.

DOI:10.1049/ip-f-1.1987.0061

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A speech coding technique has been developed to provide a method of digitising speech at bit rates in the region of 8000 bit/s which is insensitive to the effects of acoustic background noise and bit errors on the digital link. The main aim of the work has been to develop a coding scheme which provides speech quality and robustness against noise and errors that is similar to a 16 000 bit/s CVSD coder, but which operates at half its data rate. The result is a sub-band coder (SBC), with seven bands covering the frequency range 330 to 3200 Hz. The design is unusual in that it does not employ quadrature mirror filters (QMFs) but instead uses parallel finite-impulse-response (FIR) filters which are implemented efficiently with discrete Fourier transforms (DFTs) and prefiltering or windowing which is common to a group of filters. These DFT-based filters naturally provide output samples which are complex baseband vectors, and the quantisers are designed to handle these vectors in an optimum way that would not be possible with the purely real signals from a conventional QMF. The phase and amplitude components of the vectors are coded in ways that attempt to minimise the subjective effects of quantisation distortion and of bit errors between the encoder and decoder. Informal subjective tests indicate that the speech is of good ‘communications’ quality, and the coder can tolerate high levels of acoustic noise and a random bit error rate up to 10%.

DOI:10.1049/ip-f-1.1987.0062

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The concept of ‘quasirandom’ connectivity is put forward, and it is shown that, for an equal total number of nodes and links, this can dramatically reduce the risk of a network being split into several large fragments.

DOI:10.1049/ip-f-1.1987.0063

出版商:IEE    

年代:1987

数据来源: IET

摘要:

An extension to a recently discovered class of burst error correcting codes is described. The differences from the previous codes are detailed, together with enhancements to the decoding algorithm. It is shown that the minimum distance of this class of codes is four, and an example of decoding one of the extended codes is given. The simple nature of the decoder allows these codes to be considered as an alternative to established codes for certain block and error burst lengths. A comparison of these new codes with some existing burst error correcting codes is given.

DOI:10.1049/ip-f-1.1987.0064

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Line coding is shown to provide an effective means of controlling modulation jitter associated with digital pulse-position modulation (PPM), enabling simple phase-locked-loop (PLL) timing extraction circuits to be employed. The combination of a specific 9B2-32 code and a suitably designed third-order PLL with a maximally flat response is proposed and studied for the purpose of obtaining at dependent regenerators both frame and slot synchronisation signals. Jitter accumulation along a chain of such synchronisers is considered and shown to be acceptable, establishing that the combination of 9B2-32 line code and PLL synchroniser is well suited to repeatered digital PPM transmission.

DOI:10.1049/ip-f-1.1987.0065

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The paper describes a number of novel and promising techniques for use in the estimation of a flat fading channel with a rapid fading rate, such as occurs in many land mobile radio systems. The algorithms of the various techniques are first presented, followed by the results of a series of computer simulation tests, carried out on these algorithms when operating with an idealised model of the channel. The quantities measured in the tests include the mean-square error in the channel estimate, with the correct detection of the data symbols, and the error rate in the detected data symbols, with perfect channel estimation and also when operating with a channel estimator. The channel estimate considered here is the one- or two-step prediction of the channel that is fed to the detector. A further aim of this investigation is to study the feasibility of the simultaneous transmission of two bandlimited 4-level QAM (quaternary PSK) signals simultaneously over two independent Rayleigh fading channels to a single receiver, where both signals occupy the same frequency band and no coding or diversity techniques are employed to improve the performance, other than differential coding needed to avoid prolonged error bursts. The results obtained suggest that it should be possible to achieve the satisfactory coherent detection of a single Rayleigh-fading 4-level QAM signal, under conditions of even quite severe and rapid fading, but for the simultaneous transmission of two independently Rayleigh-fading signals over the same frequency band, the appropriate diversity techniques will be required to reduce the resultant depth of the fades. The techniques proposed here should make it possible to achieve a significantly more efficient use of bandwidth in cellular mobile radio systems than is possible by conventional methods.

DOI:10.1049/ip-f-1.1987.0066

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Robust Eckart and Wiener filters used in time delay estimation have been considered previously. In the present paper results are extended and generalised to include two Hassab-Boucher filters, employed in the generalised crosscorrelator. These filters optimise two different criteria. Explicit solutions are derived for the ε-contaminated model and thep-point ε-contaminated model for the input signal and noise power spectral densities (PSDs). Theoretical results, numerical examples and computer simulations show that robust filters are less sensitive to the variations in the input PSDs and that they optimise the worst-case conditions.

DOI:10.1049/ip-f-1.1987.0067

出版商:IEE    

年代:1987

数据来源: IET

摘要:

An approach to image data compression using the 2-D lattice modelling method is presented. In addition to the 2-D lattice predictor, this realisation includes uniform quantisation and entropy coding of the prediction errors of the predictor. Results show that coded pictures with an signal/noise ratio of 30.5 dB can be obtained at an information rate of 0.8 bit/pixel.

DOI:10.1049/ip-f-1.1987.0068

出版商:IEE    

年代:1987

数据来源: IET