摘要:

The paper describes several methods of deriving minimum phase impulse response functions given only the amplitude frequency characteristics. The suitability of these methods for use in digital transmission system analysis is considered.

DOI:10.1049/ip-f-1.1984.0067

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The performance of an MTI canceller selection rule, which is solely based on clutter suppression, is analysed in terms of incorrect selection probability and average loss in signal-to-interference ratio (SIR). It is concluded that the variation in target signal power transfer, as a function of the target radial velocity, is responsible for most incorrect canceller choices. The resulting loss in SIR is typically around 3 dB, with peaks to 6–9 dB in worst-case situations.

DOI:10.1049/ip-f-1.1984.0068

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The paper describes the results of a simulation of a coupled phase-locked AFC/feedforward AGC system with a two tone fading input. The theoretical predictions agree closely with those obtained under laboratory conditions, and show that considerable care should be exercised in the selection of the phase-locked loop bandwidth, normalised to twice maximum Doppler (ωn/2ωd). Failure to do so can result in nonoptimum feedforward AGC performance.

DOI:10.1049/ip-f-1.1984.0069

出版商:IEE    

年代:1984

数据来源: IET

摘要:

This paper describes the design, implementation and performance of an experimental 14/11 GHz, 120 Mbit/s regenerative satellite transponder for possible use in the European communications satellite (ECS) system. Quarternary DPSK and CPSK are applied on the uplink and downlink, respectively. Demodulation and modulation are performed directly at RF. Specific components of the regenerative transponder, which are the pulse shaping filter, the differential demodulator, the baseband regenerator, the modulator and the output filter, were developed. Using the developed components, a laboratory model of the transponder was completed and evaluated. Bit-error-rate measurements were carried out with a test equipment simulating the earth terminals.

DOI:10.1049/ip-f-1.1984.0070

出版商:IEE    

年代:1984

数据来源: IET

摘要:

With current technology, the real-time implementation of a multinotch logic-product (MLP) polarisation suppression filter which covers only a moderate area in polarisation space can only be realised as a rather bulky piece of hardware (typically with more than 61 notches). This has led to the development of the concept of nonlinear polarisation-vector translation (PVT), which allows the number of notches in the MLP filter to be drastically reduced without seriously degrading the effectiveness of the overall process. The mathematical representation of the nonlinear PVT process is described in the paper, and a limited theoretical assessment is given of its performance when used in conjunction with a single-notch filter in a target-plus-clutter environment. By way of illustration, some results are included on the suppression capability obtained when using experimentally derived rain data.

DOI:10.1049/ip-f-1.1984.0071

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A method of coding images based on interleaved blocks is proposed. These block have irregular outlines with both holes and islands. It is shown that if they are designed by the application of ‘n-cycles’ to a rectangular array, the resulting block shapes interleave perfectly without overlap. Used in transform coding, they substantially reduce the visiblity of block structure at low data rates. Experimental investigations are reported which identified desirable properties of interleaved blocks, in terms of their degree of overlap and interior distribution of pels. The pre-and post-transformations associated with the use of such blocks are easily accomplished by a simple modification of pel addressing routines, this being the only processing overhead incurred. Limited experiments on another form of overlapping block, which merged rather than interleaved with its neighbours, are also reported. These were computationally more involved and tended to magnify interblock contrasts.

DOI:10.1049/ip-f-1.1984.0072

出版商:IEE    

年代:1984

数据来源: IET

摘要:

In this paper, the potential application of adaptive lattice equalisers based on gradient search adaptive algorithms, is examined. The assessment is based on simulations of equaliser performance in data communications systems which provides a comparison of the relative performance of these adaptive lattice equalisers with transversal equalisers. It highlights the critical balance between rapid convergence and degradation due to algorithm noise, which is involved when selecting the algorithm stepsize. Two new adaptive equaliser approaches are suggested, one based on a timed lattice structure feeding a linear combiner. The other is a short timed lattice structure in cascade with a transversal equaliser. Both approaches are shown to offer fast converging adaptive equalisers for data communications applications, which have a converged error performance superior to that of the direct application of a gradient adaptive lattice equaliser.

DOI:10.1049/ip-f-1.1984.0073

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Power efficient schemes with excellent power spectra are contained among the continuous phase modulation (CPM) schemes. This is a constant envelope digital modulation technique, which in general requires a maximum-likelihood sequence detector (Viterbi detector) for efficient detection. This optimum receiver is sometimes complex. In this paper a parallel MSK-type receiver is studied. It is useful for binary schemes with modulation indexh= 1/2. We consider coherent detection of signals transmitted over an additive white Gaussian noise channel and also over a Rayleigh fading channel. The MSK-type receiver can be implemented with only two filters and simple decision logic. Error probability formulas are given both for the nonfading and the fading channel. A simple algorithm giving the optimum filter for the Gaussian channel for high signal/noise ratios is presented. The optimum filter for low signal/noise ratios is also derived. For intermediate signal/noise ratios numerical optimisations are presented, both for the Gaussian and the Rayleigh fading channels. We have also considered diversity schems with ideal two-branch maximal ratio combining and selection combining. The optimum receiver filters are given for some selected schemes. It is shown that also, for the more complex CPM schemes, the loss compared to the optimum receiver is moderate.

DOI:10.1049/ip-f-1.1984.0074

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The paper presents some general principles related to the performance of a space-based radar (SBR) using pulse Doppler to suppress the earth clutter. These principles are developed using a heuristic description of clutter as seen from a space-based radar, and illustrated by means of a case study. It is demonstrated that SBR performance varies with look direction and that clear areas exist in the clutter spectrum, where targets can be easily detected. Also, velocity compensation techniques can be employed to enhance detection for certain look directions.

DOI:10.1049/ip-f-1.1984.0075

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Site diversity is one method for reducing rain outages on earth-satellite communications links. A previously proposed prediction model for dual-site diversity, based on simple meteorological concepts that relate diversity performance to single-path rain attenuation, is evaluated against a compilation of 23 measured data sets. Prediction errors for the model are established and then discussed in terms of path elevation angle and rain convectivity. Possible refinements to the model are also mentioned.

DOI:10.1049/ip-f-1.1984.0076

出版商:IEE    

年代:1984

数据来源: IET