摘要:

A review is made of radio paging receiver requirements and a new receiver architecture is described which uses a direct conversion (zero-IF) principle. This circuit is shown to have advantages over the conventional superheterodyne with high-frequency IF and in particular is shown to be suitable for monolithic realisation. A single chip which performs as a complete high-sensitivity VHF receiver is presented, and the resulting miniature pager is shown.

DOI:10.1049/ip-f-1.1982.0002

出版商:IEE    

年代:1982

数据来源: IET

摘要:

For PCM digital transmission systems, used on symmetrical pair cables, the performance is usually limited by near-end crosstalk (NEXT), introduced into the disturbed pair by crosstalk paths in the first few hundred metres of the main cable. There are, however, also NEXT crosstalk paths inside the repeater housing and in the (electrically short) tail cables. Such crosstalk is referred to as ‘repeater housing crosstalk’ or ‘apparatus case crosstalk’ and in some circumstances may be the source of interference which limits system performance. The difference between repeater housing crosstalk and near-end crosstalk from the main cable is discussed. A model of repeater housing crosstalk is developed, and its use in simulating real conditions is shown. Two Monte Carlo simulations are shown to be necessary: the first, to show the variation from housing to housing-the ‘outer loop’ the second, to calculate the magnitude of the 10−6peak total crosstalk-the - inner loop’. The methods of calculation are fully described and applied to a particular example. It is concluded for this example that, at the cumulative 99.9% point for repeater housings, the ‘10−6peak voltage’ level is approximately 4 dB less than that which would be obtained if the voltage were Gaussian distributed; the difference falls to about 3 dB at the 95% level and further reduces to about 1 dB at the median (50%) level. For the whole distribution of housings, the mean ‘peak factor’ was 12.5 dB (compared with 13.5 dB for a Gaussian distribution) and the standard deviation was 0.7 dB.

DOI:10.1049/ip-f-1.1982.0003

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The behaviour of the slotted ALOHA satellite channel with a finite buffer at each of the user terminals is studied. Approximate relationships between the queuing delay, overflow probabilities and buffer size are derived as functions of the system input parameters (i.e. the number of users, the traffic intensity, the transmission and the retransmission probabilities) for two cases found in the literature: the symmetric case (same transmission and retransmission probabilities), and the asymmetric case (transmission probability far greater than the retransmission probability). For comparison, the channel performance with an infinite buffer is also derived. Additionally, the stability condition for the system is defined in the latter case. The analysis carried out in the paper reveals that the queuing delays are quite significant, especially under high traffic conditions.

DOI:10.1049/ip-f-1.1982.0004

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The paper considers various aspects of obtaining the design availability requirements for long-haul toll fibre-optic transmission systems in Canada, i.e. an availability of 99.98% for a reference length of 6400 km. The paper looks into unavailabilities of various subsystems (e.g. fibre splices, fibre connectors, protection switches etc.) and estimates the mean time between failure (MTBF) requirement for field and office fibre-optic repeaters and its dependence on protection ratio, protection switching lengths, mean down time (MDT) etc. The effect of the degradation of laser lifetime due to environmental conditions is also considered. Both the short-and long-wavelength operation of long-haul toll fibre-optic transmission systems are discussed.

DOI:10.1049/ip-f-1.1982.0005

出版商:IEE    

年代:1982

数据来源: IET

摘要:

In the paper, five schemes for the adaptive transform coding of video signals are presented. Adaptation is based on adaptive quantisation and adaptive bit selection. A Max quantiser having a Laplacian density distribution is used to achieve adaptive quantisation, whereas classification according to the activity within the transform block and based on the human visual characteristics are used for adaptive bit selection. The discrete cosine transform and the Hadamard transform are used to transform three source pictures of different statistics, and results are compared to find the best scheme for each transform and picture. Photographic results are presented to see the effects of the distortions introduced by different transforms on different source pictures due to data compression. Owing to the limitations of the photographic process, the subjective quality of the pictures as perceived from the video monitor cannot be accurately represented. However they are useful for comparison purposes.

DOI:10.1049/ip-f-1.1982.0006

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The paper discusses the effects of Fresnel ripples on the suppression of peak time sidelobes in low time-bandwidth (TB) product linear-FM pulse compression systems employing internally Hamming weighted compression filters. Two methods for the reduction of these effects are investigated. The first, amplitude tapering of the rectangular FM pulse, yields significantly diminished sidelobes forTBproducts less than about 100 and is of particular interest for spectrum analysis. The second, applicable to short risetime high-power radar transmitters, is cubic phase predistortion of the rectangular transmitted pulse. This procedure is found to be very effective forTBproducts less than about 50 (e.g. about 10 dB improvement forTB=10 compared with usual chirp). Both techniques force the fall-off of far sidelobes. Computed results on the achievable sidelobe suppression are presented as a function of theTBproduct and compared with conventional Hamming weighting. Finally, it is shown that the superior Doppler performance of linear FM is not affected by the discussed waveform modifications.

DOI:10.1049/ip-f-1.1982.0007

出版商:IEE    

年代:1982

数据来源: IET

摘要:

Whereas time-domain approaches to one-dimensional inverse scattering can be said to be well understood, many conceptual difficulties remain for more than one dimension, except in situations where elementary echo-location ideas apply. Algorithms appropriate for inverse problems involving branched ducts and transmission lines are presented here; such problems can be thought of as being intermediate in difficulty between one-dimensional and many-dimensional problems. Data processing procedures that can handle noisy measurements are described. The effects of finite signal bandwidth are taken into account. Results are presented of the inversion of ideal data (generated in a computer) and data derived from actual measurements.

DOI:10.1049/ip-f-1.1982.0008

出版商:IEE    

年代:1982

数据来源: IET

摘要:

A sidelobe canceller (SLC) can be efficiently employed to reduce the effects of jammers on a radar system. The paper deals with the evaluation of SLC performance, taking into account the estimation errors of the weighting coefficients of the auxiliary antennas. An explicit formula for the cancellation is given as a function of the ratio of the closed-loop bandwidth of the adaptive circuits and the radar receiver bandwidth, for one (single-sidelobe canceller, SSLC) auxiliary antenna and two (double-sidelobe canceller, DSLC) auxiliary antennas of the adaptive array and for one jammer. Therefore a relationship between the system adaption speed and the accuracy in the estimation of the jamming signal is obtained. A comparison is made between the performance of the two systems. From this analysis, a suitable selection of circuit parameters is suggested. Extensions are also made for any number of auxiliary antennas and for more than one jammer.

DOI:10.1049/ip-f-1.1982.0009

出版商:IEE    

年代:1982

数据来源: IET

摘要:

An algorithm is described for realisation of the discrete cosine transform. The algorithm has been designed to allow implementation in hardware for 625-line pictures. It employs factorisation of the transform matrix into sparse matrices, some of which are sparse factors of a Hadamard matrix. Further attention is given to the sharing of hardware components so as to reduce circuit complexity.

DOI:10.1049/ip-f-1.1982.0010

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The dynamic frequency response of a recursive MTI filter is usually calculated by simulating the in-phase and quadrature channels and the improvement factor determined by using numerical integration. An equivalent nonrecursive filter is described which simplifies calculation for recursive filter characteristics, with and without initialisation.

DOI:10.1049/ip-f-1.1982.0011

出版商:IEE    

年代:1982

数据来源: IET