摘要:

Optimum detection of binary signals in impulsive, atmospheric radio noise has been considered. It has been show that an optimum, and a locally optimum receiver (weak signal), consist of a nonlinear device followed by a linear filter, the output of which is compared with a fixed threshold for making a decision. The receiver operating characteristics and the performance of a locally optimum receiver have been obtained. The channel capacity in impulsive, atmospheric radio noise has also been determined for low-signal/noise-ratio signals.

DOI:10.1049/ip-f-1.1981.0032

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The variation of HF interference spectra with distance on the surface of the earth has been studied by computer simulation and a field experiment. A computer model of the earth and the ionosphere over Europe has been constructed with randomly positioned transmitting stations. The received sky-wave-signal spectrum was then monitored as the receiving location was moved by up to 500km. In the field experiment, voice-channel interference was recorded at five receiving stations with separations up to 430km. The recordings were analysed spectrally and compared. Generally, good correlation of spectra at different receiving sites were observed in both the simulation and the field experiments. In both cases, the results were obtained using receiving aerials appropriate for high-angle sky-wave communication.

DOI:10.1049/ip-f-1.1981.0033

出版商:IEE    

年代:1981

数据来源: IET

摘要:

Planning rules for installing PCM systems on symmetric-pair cable have traditionally been based on cable crosstalk measurements taken on a pair-to-pair basis, and statistical methods have been used to predict the upper points, 99 or 99.9%, of a cumulative probability distribution of total interference power. Recently, more sophisticated measuring equipment has allowed cable measurements to be taken on a ‘barrage’ basis, necessitating considerably fewer measurements being taken to characterise the cable. Interest in these methods has been shown by several PTT administrations and the use of barrage cable test equipment is likely to become widespread. Statistical methods are required to translate these barrage measurements into useful ‘planning rules’, and the aim of this paper is to show how the statistical part of this process can be done, given some simplifying assumptions. The statistical techniques used here may well have applications in other areas of technology.

DOI:10.1049/ip-f-1.1981.0034

出版商:IEE    

年代:1981

数据来源: IET

摘要:

In PN spread-spectrum communication systems, a PN-code generator at the receiver has to track the PN code contained in the received signal. In practical applications, the time necessary for the initial synchronisation (acquisition) of the tracking ioop should be as short as possible. In the paper, formulas are set up for the calculation of the mean acquisition time for two important acquisition procedures, namely the serial-search active-correlation procedure and the matched-filter passive-correlation procedure. Further-more, the application of the formulas is illustrated by calculating the minimum realisable mean acquisition time and the optimum search rate of a serial acquisition system, and the minimum realisable mean acquisition time of a passive-correlation acquisition system.

DOI:10.1049/ip-f-1.1981.0035

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The analysis and presentation of ruby-laser-radar signatures in a particular application is examined. A complete system has been developed for this purpose, from acquisition of the return signal to contour presentation of target structures. In this case the target considered is an industrial plume emanating from a coal-fired power station.

DOI:10.1049/ip-f-1.1981.0036

出版商:IEE    

年代:1981

数据来源: IET

摘要:

Powerful connections exist between Steiner systems and error-correcting codes. Some of these relations are investigated with a view to majority-logic decoding of block codes. Later, the concept of Steiner systems is generalised and a few simple construction techniques for such designs are given. These yield a family of majority-logic decodable codes, some of which are also unequal-error-protection (UEP) codes. Only binary codes are considered.

DOI:10.1049/ip-f-1.1981.0038

出版商:IEE    

年代:1981

数据来源: IET

摘要:

Simulation results demonstrate the potential of some new distortion measures in assessing the maximum-likelihood performance of an unknown channel at a practical error rate. Comparison is made with distortion measures currently employed in equaliser design.

DOI:10.1049/ip-f-1.1981.0039

出版商:IEE    

年代:1981

数据来源: IET

摘要:

In the paper a new technique for the implementation of digital adaptive filters is presented, based on the use of a so-called distributed-arithmetic filter architecture which uses no multipliers in its realisation of the filtering function. Two adaptive algorithms suitable for this type of filter structure are developed and computer simulations show the viability of both approaches. A simplified-hardware prototype module has also been constructed which realises an 8-point transversal adaptive filter. Results from this prototype are presented to demonstrate the basic feasibility of the distributed-arithmetic adaptive-filter structure.

DOI:10.1049/ip-f-1.1981.0040

出版商:IEE    

年代:1981

数据来源: IET

摘要:

An investigation has been made of the subjective impairment introduced into PAL colour television by random noise of flat or triangular spectrum. Results are given in terms of a logistic surface model relating mean opinion score to noise power measured separately through luminance- and chrominance-weighting networks. The parameters given by the surface model (embracing all noise spectra) and by a simpler logistic model (applied to each spectrum in turn) are compared with those found in a closely similar study conducted some 14 years earlier. Although some parameters are significantly different at the 5% level, differences do not approach 1% and are, for all practical purposes, quite small. In general, a slightly increased sensitivity of observers to noise like impairments is apparent, particularly in the presence of triangular noise, and probable reasons are given for such changes. The results reported here are considered together with results from several earlier studies and indicate that the subjective assessment methodology of CCIR Recommendation 500–1, taken in conjunction with Pt. 1, Annex IV of CCIR Report 405–3, is well able to provide consistent results for experiments repeated at intervals ranging from a few weeks to many years.

DOI:10.1049/ip-f-1.1981.0041

出版商:IEE    

年代:1981

数据来源: IET

摘要:

In recent years, it has been demonstrated that partial-response continuous-phase modulation (sometimes also referred to as partial-response digital FM) is a spectrally efficient constant-envelope digital-modulation method. If maximum-likelihood sequence detection (e.g. the Viterbi detector) is used, these schemes can also be made power efficient. System complexity grows exponentially with the length of the baseband pulse that introduces the memory in the partial-response scheme. The smoothness and the length of this pulse determines the spectral properties. The paper considers binary systems based on short pulses of length ≤2 symbol intervals. New spectrum formulas are given for modulation schemes based on pulses with an increasing number of continuous derivatives. It is demonstrated how the spectral mainlobe and the spectral tails are affected by the shape of the pulse. Comparisons are made with binary full-response systems. The tradeoff between error probability and bandwidth is demonstrated.

DOI:10.1049/ip-f-1.1981.0042

出版商:IEE    

年代:1981

数据来源: IET