摘要:

Conventional cell averaging (CA), greater of (GO) and smaller of (SO) constant false alarm rate (CFAR) detectors are considered when an interfering target is present in the reference noise cells. Threshold compensation techniques used previously to improve the performance of a CA detector have been modified and generalised to include GO and SO detectors. It is shown that, using these methods, good relative improvements are obtained for the GO and CA detectors, especially for a small number of reference noise cells. Only slight relative improvements are obtained for the SO detector, however.

DOI:10.1049/ip-f-1.1986.0037

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper proposes and investigates a new type of nonlinear adaptive canceller of intersymbol interference (ISI) called ‘ACDEC’. The ACDEC uses an automatic equaliser including a decoder of an error-correcting code (AEDEC), to obtain more reliable preliminary decisions than those by the linear equaliser used in the linear adaptive canceller of Gersho and Lim. By using the modified structure and incorporating one more decoder, the tap values of both the canceller's delay line and the adaptive matched filter are correctively updated with reduced final decision errors in the same manner as AEDEC. The theoretical calculation of the error probability in the joint repetitive scheme of both cancelling ISI and decoding indicates that two repetitions, i.e. ACDEC, can provide considerable improvement in the error probability performance in the steady state without excessive complexity of implementation. Moreover, computer simulations show that an ACDEC achieves stable convergence and exhibits better adaptability in noisy and time-varient channels.

DOI:10.1049/ip-f-1.1986.0038

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper presents a method of analysing the performance of a bandlimited 16-ary quadrature amplitude modulation(QAM) signal transmitted through a bandpass nonlinearity (BPNL), exhibiting AM-AM and AM-PM conversions, and in the presence of additive Gaussian noise (AGN) both preceding and following the BPNL. To illustrate the validity and usefulness of the technique, the symbol probability of a bandlimited 16-ary QAM signal transmitted through a typical nonlinear satellite channel is derived and computed for a four-pole Bitterworth filter as a function of various levels of the on-board travelling-wave tube (TWT) back-off from saturation andBTproducts. Finally, as an example, a study of the effect of increased bandlimiting on the system degradation for this communications system model is undertaken.

DOI:10.1049/ip-f-1.1986.0040

出版商:IEE    

年代:1986

数据来源: IET

摘要:

An analysis of two-level picture compression techniques applied to low-resolution moving images is reported. The object is to discover the most suitable technique for visual communication at low data rates using feature-extracted ‘cartoons’. Reversible facsimile compression techniques are reviewed, then results presented to demonstrate their relative performance. In general, three-dimensional techniques prove to be most efficient, since they exploit both spatial and temporal relationships in the picture. However, the lower compression of two-dimensional coding is balanced by its superior error recovery performance, and it is therefore recommended for very low-data-rate transmision over conventional telephone lines, where error rates are high. From the tested range of 2-D and 3-D techniques, ‘relative address coding’ is most successful, being about 10% more efficient than its nearest rival, except for high-resolution pictures with little movement, where ‘block location coding’ of diffence frames shows a small advantage. Application of irreversible preprocessing improves the compression performance, but the gain is small, and requires additional processing power.

DOI:10.1049/ip-f-1.1986.0041

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Ground and sea clutter were discriminated by using texture analysis in image processing. As a discriminator, a nonlinear transformation of a local pattern was defined to deal with high-order statistics. The discrimination using this method indicated good performance.

DOI:10.1049/ip-f-1.1986.0042

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Two new transforms which can be used as substitutes for the Walsh transform are generated using the theory of dyadic symmetry. The new transforms have virtually the same complexity and computational requirements as the Walsh transform, employing additions, subtractions and binary shifts only, but have an efficiency, defined in terms of their ability to decorrelate signal data, which lies between that of the Walsh transform and that of the discrete cosine transform.

DOI:10.1049/ip-f-1.1986.0043

出版商:IEE    

年代:1986

数据来源: IET

摘要:

In the paper a new go-back-Nscheme for communication systems using error-detecting codes is described. This scheme has a buffer at the receiver side in order to introduce a memory into the go-back-Nprotocol. This memory and a soft demodulation of each received symbol significantly increase the performance of classical go-back-Nschemes. It is also shown that, for mean and high error rate conditions, the scheme proposed has a higher throughput than the selective scheme and, at the same time, a lower implementation conplexity.

DOI:10.1049/ip-f-1.1986.0044

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The analysis postulates an algorithm for adaptively varying the target-track update rate as a function of target manoeuvring. The algorithm proposes to vary the target observation time interval by an amount that tends to maintain a constant residual error. As an example, the algorithm is shown to be implemented with a two-dimensional alpha-beta filter. Simulated results are calculated for a target manoeuvre consisting of a single 90° turn. The results show that when a manoeuvre is detected, the sampling time interval can be reduced rapidly to facilitate tracking with reduceed error. After the manoeuvre, the sampling interval is increased automatically so more time can be made available to the phased array radar for other activities.

DOI:10.1049/ip-f-1.1986.0045

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A new class of nonlinearly generated sequences containing several sets all equivalent to the ‘small set of Kasami sequences’, having optimal CCF and ACF properties, is introduced. The new class of sequences is obtained by interleavingm-sequences with the interleaving order governed by a set of sequences called the prime sequences introduced by Shaar and Davies. The construction procedure and the study of the CCF and ACF properties is presented in detail using the integer representation introduced by the present authors in an earlier paper.

DOI:10.1049/ip-f-1.1986.0046

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A new, general method is presented to determine the equivalent linear span (ELS) of binary sequences having an interleaved or related structure. The method is based on a polynomial representation of the interleaved sequences followed by the use of the Euclid algorithm for factorisation, to yield a minimal polynomial. The degree of this minimal polynomial can be identified as the required ELS value. The method is then used here to show that the ELS values of the so-calledm-like sequences and the prime and relative prime interleaved sequences, proposed recently by the authors, are quite large and compare favourably with those of the bent function sequences.

DOI:10.1049/ip-f-1.1986.0047

出版商:IEE    

年代:1986

数据来源: IET