摘要:

For Dick Tracy of comic-strip fame and Captain Kirk of ‘Star Trek’, voice communication from tiny equipment over vast distances posed no problem, but in the real world of 1986 the situation is much more difficult. Historically, mobile telephone systems using HF, VHF and UHF radio have been developed since the Second World War with military and commercial systems evolving in parallel. Although often the military needs have led the technological developments, more recently civil systems have been taking the lead in many areas. Initially voice communication by mobile radio operated in closed groups of users on an ‘all-informed’ basis, but, more recently, connection to the world's telephone network has been possible and incoming calls are automatically routed to mobile subscribers wherever they may be in the system—a real breakthrough in the concept of personal communication. But can this be extended ultimately to a worldwide system? And can the hardware really approach the convenience available to Dick Tracy and Captain Kirk? The paper considers some of the technical problems to be overcome in terrestial radio systems and touches on the prospects for satellites to play a role in this, but concludes that it will be some time before we can match the facilities available to our fictional heroes.

DOI:10.1049/ip-f-1.1987.0001

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The paper applies the Gram-Charlier series method to the calculation of the probability of errorPeof partial response (PR) systems. This method allows the exact calculation of error probability including the effects of sampling off-set and additive Gaussian noise. Five classes of precoded PR systems are considered. The results obtained in the method are compared with those obtained with Chernoff bounds.

DOI:10.1049/ip-f-1.1987.0002

出版商:IEE    

年代:1987

数据来源: IET

摘要:

We show how to compute the error probability of frequency-shift keying with limiter-discriminator-integrator detection in the presence of narrowband filters in the transmitter and receiver when the symbols are pseudoternary, i.e. they are generated from binary symbols using duobinary, modified duobinary and dicode rules. We show numerical results assuming a Butterworth filter in the receiver with 2, 3 and 4 poles. We optimise the sampling time, frequency deviation, filter bandwidth and threshold setting, and the conclusion is that the duobinary is the best partial response system. However, when compared with an uncoded, binary system the duobinary system is better only when the bandwidth is very small.

DOI:10.1049/ip-f-1.1987.0003

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Error performance analysis for the VHF digital mobile radio system is presented. The binary frequency-shift keying (FSK) system using noncoherent (NC) demodulation, with a limiter/discriminator receiver, is considered. All major error-causing factors, such as signal fading, Gaussian and impulsive noise, are taken into account and the corresponding general expression for the error probability is derived. This expression is then applied to the bit error rate (BER) evaluations for the three adequate receivers, described by the different mathematical models of their impulse responses. The calculated BER values are compared to the results obtained by measurements on the real laboratory models simulating the mobile radio systems considered. In conclusion, the mathematical model for the receiver impulse response yielding the best prediction results, when using the derived expression for the BER calculation, is proposed.

DOI:10.1049/ip-f-1.1987.0005

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A postdetection diversity system using a phase-correction loop modified by the inclusion of a differential demodulator (DD) or a frequency demodulator (FD) is described. Binary and quaternary digital modulation for DPSK and digital FM are considered. An analysis considering additive Gaussian noise shows that, although the diversity combiner proposed is inherently the postdetection type, the well known predetection equal-gain combining (EGC) or maximal-ratio combining (MRC) action can be approximately achieved. A unified analysis of bit error rate (BER) is presented for a Rayleigh fading environment, and fairly simple results are obtained. It is shown that the diversity gain of postdetection EGC is about 0.62 dB inferior to that of postdetection MRC when two-branch diversity is employed.

DOI:10.1049/ip-f-1.1987.0006

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The problem of clutter cancellation in a non-Gaussian environment is becoming more and more important in modern high-resolution radars, owing to uncertain clutter statistics. To evaluate the MTI canceller performances, in the paper we examine an intermediate frequency model which gives, in the video frequency, a signal with log-normal (LN) probability density function (PDF). The improvement factor needed to obtain optimum detection performances in a multiclutter environment will be evaluated.

DOI:10.1049/ip-f-1.1987.0007

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The paper describes the design of eight new rotationally invariant rate-2/3 and rate-3/4 convolutional codes. The rate-2/3 codes are suitable for 8PSK (8-level PSK) coded signals and are transparent to phase rotations in the received signal carrier phase, that are multiples of π/2 radians, whereas the rate-3/4 codes are suitable for 16PSK (16-level PSK) coded signals and are transparent to phase rotations that are multiples of π/4 radians. The new codes are bandwidth-efficient and, when combined with a simple carrier-phase correction system described in the paper, they are able to tolerate the likely carrier-phase changes in the reference carrier of the coherent demodulation process. Thus they avoid the prolonged error bursts that are otherwise caused in the detected data symbols by such phase shifts. Among these codes, two rotationally invariant rate-3/4 codes have been found with minimum free distances equal to those of the optimum but not rotationally invariant codes, having the same rates and constraint lengths. The majority of the codes designed here have asymptotic coding gains which are only up to about 0.5 dB inferior to those of the corresponding optimum but not rotationally invariant codes. Extensive computer simulation tests have been carried out on the various codes studied, and these have confirmed the optimum or near-optimum performances that have been theoretically predicted for these codes.

DOI:10.1049/ip-f-1.1987.0009

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A number of methods have been suggested to improve spectral or angular resolution. These methods have arisen from quite different fields of application, and are difficult to compare. The paper collects aspects for the application of such methods to the case of angular resolution with a phased array radar. We list the main methods and their properties, and point out constraints for a real radar application.

DOI:10.1049/ip-f-1.1987.0010

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Power spectral density (PSD) analysis is often undertaken assuming equally likely signalling input levels, and hence the different criteria of performance are evaluated with this condition in mind. In practice, however, cases of unequal probabilities of signalling input do arise due to choice of coder, and the study of these conditions is important. Power spectral densities are sensitive to variations in the probability density functions (PDFs), and both these curves and the fractional out-of-band spectra for multilevel FSK are treated in the paper. Different signalling inputs are used forM-ary CPFSK and the newly defined multi-hpartial response (MHPR) scheme. The influence of PDFs on creating spectral lines (for timing extraction) is also discussed.

DOI:10.1049/ip-f-1.1987.0012

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A linear prediction method for accurately estimating the parameters of a rational model of transient-type data is presented. This method makes use of the singular value decomposition of an extended-order autocorrelation-like matrix estimate associated with the time series being analysed. The method is first tested on simulated data consisting of three exponentially damped sinusoids of closely spaced frequencies in additive white Gaussian noise. Next, the method is used to analyse nuclear magnetic resonance (NMR) data.

DOI:10.1049/ip-f-1.1987.0013

出版商:IEE    

年代:1987

数据来源: IET