摘要:

The paper presents a comprehensive analysis of frame alignment strategies for time division multiplexed digital signals. Comparisons are made between algorthims recommended by CCITT and others requiring slightly more sophisticated terminal processing. The principal transition times (misalignment detection, false exit, acquisition and false entry times) form the basis for comparison. The enhanced algorithms are shown to be better able to handle the conflicting requirements of rapid misalignment detection and the need to maintain an aligned condition in the presence of transmission errors. They also result in a significant reduction in acquisition time at high error probabilities, the condition under which alignment equipment is often required to act.

DOI:10.1049/ip-f-1.1985.0100

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A system for extracting Doppler signals from the HRPT data stream transmitted by NOAA satellites is described. These signals are used to improve the accuracy of tracking in a system which relies on satellite ephemeris to predict antenna pointing angles.

DOI:10.1049/ip-f-1.1985.0101

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Partial-response continuous phase modulation (CPM) signals can in many cases yield power spectra with narrow mainlobe and also low sidelobes. The optimum receiver for these signals is sometimes complex. In the paper the idea of using a smaller signal set in the receiver than used by the transmitter is considered. This is done by means of using a generalised average matched filter (AMF) receiver. Only coherent detection of signals transmitted over an additive white Gaussian noise channel is considered. The multiple-symbol AMF receiver can be implemented with fewer filters than the optimum receiver. These receivers are analysed for various partial-response CPM signals. The analysis is done under the assumption of error-free filter and phase updating. A Euclidean distance for mismatched signal sets is used to give the symbol error probability for large signal/noise ratios conditioned on error-free updating. Under the above assumptions, it is shown that the multiple-symbol AMF receiver performs equally well as the optimum receiver for schemes with low modulation indices and also for large modulation indices for some schemes. This is the case both for binary and quarternary schemes. A simple updatiing method is also simulated.

DOI:10.1049/ip-f-1.1985.0102

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The paper gives measurements of spectral occupancy for each ITU-defined user allocation, across the whole HF spectrum. Such measurements are being made currently during stable ionospheric conditions about midday and midnight, at the times of the winter and summer solstice, over a range of sunspot numbers. An application is given in which the occupancy results for a particular service (fixed in this case), are plotted as contours for direct comparison with the conventional OWF predictions. Thus it is possible to choose a frequency based on expected occupancy, as well as on predicted signal/atmospheric noise. The frequency choice for a particular 1500 km link is considered, when it appears beneficial to operate below the predicted OWF during daytime.

DOI:10.1049/ip-f-1.1985.0103

出版商:IEE    

年代:1985

数据来源: IET

摘要:

In the paper a novel class of spread-spectrum waveforms is proposed which is based on spreading operations in the frequency domain. As a main advantage over conventional spread-spectrum waveforms, the proposed waveforms are especially well suited for transform domain correlation at low expense, because their Fourier spectra may be constructed from simple binary pseudonoise sequences. It will be shown that SNR degradation due to time and amplitude limiting requirements in practical spread-spectrum communication systems can be limited to about 1.2 dB by properly choosing the system parameters. The paper is primarily intended to initiate the development of new techniques for obtaining spread-spectrum waveforms in the frequency domain, and does not purport to give a complete recipe for design.

DOI:10.1049/ip-f-1.1985.0105

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The problem of assessing error propagation in decision-directed feedback receivers is considered. It is shown that useful bounds on error statistics can be obtained by modelling the error mechanism using stochastic state-transition diagrams and then employing state reduction techniques to enable the complexity of the problem to be contained. This provides a more widely applicable approach to obtaining bounds on performance measures for such receivers than was previously available. The techniques are illustrated for representative error burst statistics of interest in practical applications.

DOI:10.1049/ip-f-1.1985.0106

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A new metric, termed ‘recovery distance’, is introduced for decision feedback receivsers, and is shown to provide the basis for a simple technique for obtaining bounds on a wide range of error statistics. The error propagation process is modelled using stochastic state transition diagrams with merging of states having the same recovery distance, providing the simplification required to render tractable the derivation of probability generating functions for error random variables of interest. The new technique is illustrated by deriving bounds on error statistics for various signal formats of interest for practical applications.

DOI:10.1049/ip-f-1.1985.0107

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A new class of binary sequences called here ‘m-like cipher sequences’ are introduced which have rather interesting properties for use as cipher sequences. These are derived by interleaving the so-called ‘elementarym-sequences’ along with some null sequences in a particular order. The resulting composite sequences are notm-sequences, but require deciphering and storage of a much larger number of bits for their complete prediction from the observed cipher text than that needed for predictingm-sequences of the same length. At the same time, the method of construction of these sequences ensures that their autocorrelation function is identical to that of anm-sequence of the same length.

DOI:10.1049/ip-f-1.1985.0108

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The concept of a finite-state machine (FSM) is used in an attempt to cover the deficiencies of the conventional digital filter design procedure with respect to finite-word-length effects. The problem of synthesis is considered in detail and a procedure whereby the FSM mappings are designed to best model a given difference equation is presented. This procedure is based on a well known graph theory algorithm. The FSM digital filter design procedure is evaluated by computer simulation of various small-word-length filters. Several examples are presented to demonstrate the improved performance of the FSM filters with respect to conventional fixed-point designs. The design procedure also allows the construction of limit-cycle-free high-order direct-form filters. This form is compared to the more conventional cascade structure.

DOI:10.1049/ip-f-1.1985.0109

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Asymptotic results are presented for the MUSIC and Kumaresan and Tufts spectral estimators. The paper makes use of results obtained by Sugiura, which are more accurate than those of Anderson. It is shown that the predictions are in good agreement with simulated results.

DOI:10.1049/ip-f-1.1985.0110

出版商:IEE    

年代:1985

数据来源: IET