摘要:

The paper describes the use of a prediction-error filter (realised in the form of an adaptive lattice filter) for enhancing the detection of a moving target (for example aircraft and migrating flocks of birds) in the presence of clutter. This process is well suited for use in a surveillance radar environment (for example air-traffic control). The clutter may arise owing to reflections from ground and weather disturbances. Experimental results are included in the paper, comparing the performance of the processor with that of a conventional moving-target indication (MTI) filter.

DOI:10.1049/ip-f-1.1983.0061

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper describes a near-maximum-likelihood detection process suitable for use in a synchronous serial digital data transmission system that operates at 9600 bit/s over an HF radio link. The data signal at the input and output of the HF radio link is here a 2400 baud 16-level QAM signal with a bandwidth (measured between the 6 dB points) from about 600 to 3000 Hz. The detector is a development of a technique that operates at 2400 bit/s with a four-level QAM signal and which itself originated from a reduced-state Viterbi-algorithm detector. Results of computer simulation tests are presented, showing the tolerance to additive white Gaussian noise of a 9600 bit/s data transmission system employing the new detector and operating over a model of an I-IF radio link. The latter has two independent Rayleigh fading sky waves that introduce frequency spreads of 0.5 or 2 Hz into the data signal and have a relative transmission delay of 1 or 3 ms. It is assumed that the correct estimation of the channel is achieved at the receiver.

DOI:10.1049/ip-f-1.1983.0062

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Field trials in London between an elevated base station and a mobile moving in the city streets have produced a propagation data base at frequencies between 168 and 900 MHz. Various important parameters such as range, frequency and relative height, together with quantitative measures of the extent of urbanisation, have been used in conjunction with the data base to produce signal strength prediction models. These models are easy to use and go some way towards eliminating the subjective element inherent in assessing the degreee of urbanisation embodied in some other propagation prediction models.

DOI:10.1049/ip-f-1.1983.0063

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Analysis of mobile radio propagation results in London at 168, 455 and 900 MHz has shown that over small areas the signal envelope is well described by Rayleigh statistics, the local mean over larger similar areas being lognormally distributed. A comparison of different statistical distributions has been undertaken to provide a bridge between the local and global statistics and it shows that the experimental data are best fitted by a Suzuki (Rayleigh plus log-normal) distribution, the lognormal part having a standard deviation of approximately 4 dB. Values near the tails of the distribution can thereby be described with good accuracy, and hence the propagation prediction model is useful for area coverage estimation and frequency reuse planning.

DOI:10.1049/ip-f-1.1983.0064

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Although coherent synthetic apertures are common in radar, coherent apertures in sonar are difficult to synthesise with a single moving element owing to positional uncertainty and the very imperfect nature of the sonar propagation medium. The two techniques described in the paper show how a pair of receivers coupled in a phase-difference or phase-comparison monopulse configuration can reduce the effect of random fluctuations on the image produced by a side-looking terrain mapping system. To test this technique experimentally, a two-channel air sonar was built, coupled in a phase-difference monopulse configuration, and used as a side-looking terrain-mapping sonar. Encouraging experimental results are reported.

DOI:10.1049/ip-f-1.1983.0065

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper is a review of the subject of analogue encryption. The rank correlation approach to the study of permutations is also reviewed. Some families of permutations that have been used in scrambling systems are described. The problems of analogue encryption, as well as its scope, are analysed.

DOI:10.1049/ip-f-1.1983.0066

出版商:IEE    

年代:1983

数据来源: IET

摘要:

An interference improvement factor (IIF) is derived for a generalised square-law detector utilised for a radar application. This factor, which is a ratio of two quadratic forms, incorporates the effects of antenna beam shape as the radar beam scans over the target, interference due to receiver noise plus clutter and the target Doppler frequency. The IIF can be maximised to improve target detectability via eigenvalue, eigenvector techniques so that the optimal weights to be applied by a weighted integrator following the square-law device can be determined for anN-pulse batch. Numerical results are presented for a sea surveillance application.

DOI:10.1049/ip-f-1.1983.0067

出版商:IEE    

年代:1983

数据来源: IET

摘要:

In the paper two parallel architectural structures are developed to compute one-dimensional cyclic convolutions. The first structure is based on the Chinese remainder theorem and Kung's pipelined array. The second structure is a direct mapping from the mathematical definition of a cyclic convolution to a computational architecture. To compute ad-point cyclic convolution the first structure needsd/2 inner product cells, while the second structure and Kung's linear array requiredcells. However, to compute a cyclic convolution, the second structure requires less time than both the first structure and Kung's linear array. Another application of the second structure is to multiply a Toeplitz matrix by a vector. A table is listed to compare these two structures and Kung's linear array. Both structures are simple and regular and are therefore suitable for VLSI implementation.

DOI:10.1049/ip-f-1.1983.0068

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper reports on theory, tests and design of a low-cost broadband radio-frequency device that combines signals from two antennas to selectively null interfering signals. The theory and analysis of limitations pertain to both manual and adaptive null control devices. Tests illustrate cases in which nulling works well and those where propagation features limit null effectiveness. An important result of the tests is recognition that much work remains to be done to determine optimum antenna pairs for particular types of interference. An analysis section provides equations of general use for designing alternative implementations.

DOI:10.1049/ip-f-1.1983.0069

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Many signal processing systems rely on the efficient calculation of the discrete Fourier transform. The basic equations are manipulated to yield architectures to suit differing technologies and performance requirements. Finally a prime-radix transform algorithm is described offering very high performance that is ideally suited to present-day technology.

DOI:10.1049/ip-f-1.1983.0070

出版商:IEE    

年代:1983

数据来源: IET