摘要:

In the Viterbi-algorithm detection of a multilevel digital signal having a large alphabet (many levels), such as a 16-level QAM signal, very considerable equipment complexity is involved, even when the sampled impulse response of the channel has only a few components. A recent development of the Viterbi-algorithm detector, known as the pseudobinary Viterbi-algorithm detector, effectively recodes the received multilevel data signal into a binary signal and implements the conventional Viterbi-algorithm detection process for the corresponding binary signal, thus very greatly reducing the complexity of the detector. Since there is only a small loss in tolerance to noise as a result of the given modification, a potentially useful detection process is obtained. The paper describes two novel detection processes in which the given pseudobinary technique is applied to two different near-maximum-likelihood detectors. The particular application studied is that of a synchronous serial 9600 bit/s modem transmitting a 16-level QAM signal over a telephone circuit in the public switched telephone network. Results of computer simulation tests are presented, comparing the tolerances to additive white Gaussian noise of various arrangements of each detector, when operating over models of two different telephone circuits.

DOI:10.1049/ip-f-1.1982.0046

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The theoretical prediction of propagation in precipitation conditions has received much attention in the literature, but in some parts of the world sand and dust storms occur more frequently. In the paper, we attempt to place bounds on the likely effects of sand and dust storms, particularly attenuation and depolarisation in the 3–37 GHz frequency range covering most of the existing and planned operational radio and satellite links. We show that attenuation and crosspolarisation effects are quite small in modest dry sand and dust storms with visibilities around 100 m for linear polarisation up to 37 GHz. However, significant attenuation and crosspolarisation can result in humid areas for circular polarisation and for bad storms with visibilities around 20 m and less.

DOI:10.1049/ip-f-1.1982.0047

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The availability of MSI, LSI and now VLSI, in conjunction with the development of various new decoding and processing algorithms, has dramatically altered the feasibility of applying cost-effective error-correction coding to communication systems, particularly in the telecommunications area. Several of the new techniques now available and the advances which, together with VLSI implementation, they make possible are described. Reed-Solomon codes, either on their own, or in a concatenated arrangement with another block or convolutional code, emerge as possible candidates for a widely applicable ‘standard’ EDC code.

DOI:10.1049/ip-f-1.1982.0048

出版商:IEE    

年代:1982

数据来源: IET

摘要:

Formulas for the amplitudes in forward and backward scattering are derived for the scattering of electromagnetic waves by dielectric obstacles which are small compared with the wavelength. Both zero- and first-order scattering are considered. It is also shown that in the zero order it is always possible to arrange that a particle of real permittivity produces no crosspolarisation.

DOI:10.1049/ip-f-1.1982.0049

出版商:IEE    

年代:1982

数据来源: IET

摘要:

In the paper, an asymmetric maximum-likelihood receiver (based on the Gram-Schmidt ortho normalisation procedure) is described for handling the low-angle tracking-radar problem where the direct and specular multipath components of the received signal impinge on the array antenna from arbitrary directions. Also, by means of a simple test based on Fisher'sF-statistic, we are able to determine the most likely number of waves incident on the array. The processor is applicable to the situation where it is desired to track multiple targets present within the radar's scanning volume. Thus the estimator described in the paper is also applicable to the general problem of determining the frequencies of multiple sinusoids that are embedded in white Gaussian noise.

DOI:10.1049/ip-f-1.1982.0050

出版商:IEE    

年代:1982

数据来源: IET

摘要:

Methods for measuring the complex frequency response of linear and weakly nonlinear systems and for the determination of related functions are described, making use of the capabilities offered by digital signal-processing techniques.

DOI:10.1049/ip-f-1.1982.0051

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The optimal receiver for a given transmitter and both the optimal receiver and transmitter are derived for a digital communication system in which the desired signal is of the partial-response type. The optimality criterion is the minimisation of the mean square error between the actual output and the desired output at the sampling time.

DOI:10.1049/ip-f-1.1982.0052

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The conventional digital phase-locked loop (DPLL) has a number of problems which need to be solved: the pull-in and lock ranges are very restricted by the phase detector and are dependent on the noise bandwidth, and their operation is not linear. In the paper, DPLLs free from such disadvantages are proposed. These DPLLs are realised by a new method, i.e. by use of integrators in a pulse frequency-modulation system, and the higher-order DPLL is systematically designed by controlling the free-running frequency of one VCO with the error of the other DPLLs. The operation of the DPLL is similar to that of an analogue PLL (APLL). However, the former operates linearly in a wider region than does the latter; unlike the APLL, the pull-in and lock ranges of the first-order and imperfect second-order DPLL are the same as those of the perfect second- order APLL in the range from zero to almost the maximum frequency of the VCO and are independent of the noise bandwidth. Excellent agreement is obtained between theory and experiments.

DOI:10.1049/ip-f-1.1982.0053

出版商:IEE    

年代:1982

数据来源: IET

摘要:

At present, aircraft tracks for ATC purposes are formed by filtering SSR data measurements only, but the introduction of selectively addressed systems such as ASDEL and DABS will make it possible to transmit additional on-board measurements to the ground station. This information may be used to significantly improve the tracking performance, and Part 1 of the paper considered the question of the measurement accuracy required and the mechanism by which it may be incorporated into the tracking algorithm. Whereas Part 1 considered the extended Kalman filter as a reference against which to compare other sub-optimal filters, Part 2 considers practical filters, incorporating aircraft-derived data, which are considerably more economical than this reference, and which, in the typical ATC environment studied, gave almost identical results.

DOI:10.1049/ip-f-1.1982.0054

出版商:IEE    

年代:1982

数据来源: IET

摘要:

In the paper, phase noise and its effects on a quadrature-phase-modulated carrier is studied. The functions of the receiver carrier recovery loop when operated in a time-division multiple-access channel are explained. In this case, the bursts received from various earth stations via satellite need to be dealt with in a rather short time frame, so that the information required for carrier phase recovery can be extracted promptly. A procedure for obtaining the phase-noise spectral density is developed and examined by an example.

DOI:10.1049/ip-f-1.1982.0055

出版商:IEE    

年代:1982

数据来源: IET