DOI:10.1049/ip-f-1.1980.0025

出版商:IEE    

年代:1980

数据来源: IET

摘要:

This paper extends a simple mathematical treatment of the problem of cochannel interference in land mobile radio presented earlier, in which the interdependence between frequency reuse distance and required protection ratio was developed. By considering realistic patterns of frequency assignment, it is demonstrated that, for a given grade of service, spectrum economy is a discontinuous function of protection ratio, thus the precise value of protection ratio may not be as important as it first appears. Properties of different modulation systems are compared from this standpoint and the superiority of s.s.b. over f.m. tentatively indicated in the earlier communication, is confirmed.

DOI:10.1049/ip-f-1.1980.0026

出版商:IEE    

年代:1980

数据来源: IET

摘要:

In this paper an analogue c.c.d./m.o.s. implementation of an adaptive filter having high bandwidth and a large time-bandwidth product is described. The system demonstrates greatly improved performance characteristics in terms of size, power consumption, ease of use and increased bandwidth over previously published designs. Such a processor has many potential applications in communications signal processing, for the performance of tasks such as noise, echo and multipath cancellation and adaptive equalisation over both voice-band communications links (satellite, radio or 2– and 4-wire links) and high-bit-rate digital communication links. Possible applications in many other areas also exist. The main objective of the paper is to show that the prototype adaptive filter, which was based on a monolithic 256-point programmable transversal filter, behaves experimentally in a manner very close to that expected from theoretical models of an ideal adaptive filter, rather than to establish its efficacy for specific applications.

DOI:10.1049/ip-f-1.1980.0027

出版商:IEE    

年代:1980

数据来源: IET

摘要:

This paper presents results on error probability as related to ciphertext length for masking ciphers. It also estimates minimum ciphertext length for unique decipherment. Two decipherment techniques have been presented. Our analysis indicates that masking ciphers are generally less effective than block ciphers.

DOI:10.1049/ip-f-1.1980.0028

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The application of data-filtering techniques for air-traffic-control and surveillance systems is re-reviewed. Operational requirements of these systems are primarily described. They are typically composed of radars (mechanical scanning and phased array), data-processing devices (digital computers) and displays. The environment is determined by the number and characteristics of targets and by the density and characteristics of the unintentional (weather, etc.) and intentional interferences. The effect of the environment on the filtering techniques used is also considered. In the case of air traffic control,a(α, β) filtering algorithm, which is used for primary radars, secondary radars and d.a.b.s. (discrete address beacon systems) is described. Collision-avoidance techniques and their implementation are also mentioned. In the case of air defence and surveillance systems, the algorithms are more sophisticated because of unpredictable target motion, high acceleration and intentional interferences. The types of algorithms which may be employed are the Kalman filter (also with variable data rate for phased-array radar), adaptive filters for manoeuvring targets, filters for target tracking in clutter and jamming environment, a filter for tracking of targets formations and, finally, nonlinear filters using radial velocity information. Moreover, the above mentioned techniques affect fire-control and interceptor-guidance methods. The filtering methods are extended to the multiradar case. Some specific problems, which are herein emphasised, concern the ways of combining the information coming from the different radars, the measurement time alignment and co-ordinate conversion over large areas. The methods of filter implementation, being affected by the technology available, are also described. Finally, a comprehensive list of references, refering to the different topics, has been included.

DOI:10.1049/ip-f-1.1980.0030

出版商:IEE    

年代:1980

数据来源: IET

摘要:

A predictor based on three previous ‘pels’ along a scan line is examined for d.p.c.m. encoding of composite Pal signals. The predictor coefficients are described in terms of the ratio of sampling frequencyfsto colour subcarrierfsc. Predictions based on p.e.l.s on the second previous and previous lines are derived for the case offs/fsc= 2.5. Simple 2-dimensional predictors are then formed and used in the d.p.c.m. encoding of a Pal colour-bar signal.

DOI:10.1049/ip-f-1.1980.0031

出版商:IEE    

年代:1980

数据来源: IET

摘要:

At sea and in fair weather, the choice of operating wavelength for search radars for the detection of surface targets is largely influenced by the required angular resolution and maximum aerial aperture allowed. However, in considering maximum detection ranges in excess of 15 n miles, attenuation through very heavy precipitation favours a lower wavelength of the order of 10 cm, although angular resolution requirements are more easily and cheaply met by going to a wavelength of 3 cm or less. When aerial height is limited to 5 or 10 m only, the resultant low transition range demands the use of the shorter wavelength for surface targets, but in the case of large vessels able to carry scanners 40 to 50 m above sea level, the choice is more open. The paper presents data, analysis and some conclusions on the use of two radars on wavelengths of 3 and 10 cm colocated some 45 m above sea level, under precipitation-free conditions and outside the sea clutter region for either set under the conditions prevailing for the period of the trial. Attention is drawn to the wide variation of differential performance experienced in the trials, believed to be due to anomolous propagation even over the relatively short ranges considered.

DOI:10.1049/ip-f-1.1980.0032

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Sea clutter was measured using and L-band long-range air-route surveillance radar (a.r.s.r.) at very low grazing angles between 0.13° and 0.25°. From the stored data of six scans, it is shown that the sea-clutter amplitude statistics obey a log-Weibull distribution.

DOI:10.1049/ip-f-1.1980.0033

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Numerical results on the nonperiodic autocorrelation parameter important in phase-coded direct-sequence spread-spectrum communication is given. Optimal phases with respect to autocorrelation for all maximal-length sequences of periods 31, 63, 127, 255, 511, 1023, 2047 and 4095 are obtained.

DOI:10.1049/ip-f-1.1980.0034

出版商:IEE    

年代:1980

数据来源: IET