摘要:

After briefly tracing transmission system development to the present day, the paper goes on to consider the likely progression of both services and technology in the near and far future. To provide a clear focus for the discussion, a number of ‘end point’ developments and targets are postulated as the ultimate objectives of the transmission engineer. The latest technology developments are then cited as being capable of providing the means to achieve these objectives, which would then lead to a continuing exponential growth in both traffic and services. It is concluded that future traffic and service demands will ultimately rely upon optical fibre systems as the major point-to-point carrier, with radio and satellite devoted to mobile, broadcast, rapid-response and ‘outback’ applications.

DOI:10.1049/ip-f-1.1984.0102

出版商:IEE    

年代:1984

数据来源: IET

摘要:

In the paper some of the cryptographic techniques, algorithms and applications in computer networks are reviewed. Symmetric and asymmetric cryptosystems, possible cryptanalytical attacks, cryptosecurity and the relevance of complexity theory to the security of ciphers are described. The major threats and counter-measures in computer-network communications are outlined. Finally, cryptographic applications and limitations in computer networks are examined.

DOI:10.1049/ip-f-1.1984.0103

出版商:IEE    

年代:1984

数据来源: IET

摘要:

An experimental investigation is described of the scattering effect responsible for large errors in the azimuth bearing measurements obtained with a 1 GHz monopulse receiver on a particular site when the signal source occupied positions near the top of a distant hill. The received field distribution on a horizontal line directly in front of the monopulse aperture was sampled by means of a travelling probe antenna and recorded holographically. Computer processing of the holograms formed images that revealed the scattering mechanism. A simulation was used to study the effects of different components of the multipath field on the monopulse measurement.

DOI:10.1049/ip-f-1.1984.0105

出版商:IEE    

年代:1984

数据来源: IET

摘要:

In a transform coding system, a large number of bits have to be allocated to high-energy DC coefficients for both fine quantisation and good channel error immunity. Three schemes are proposed, in which the DC coefficients are not transmitted, but estimated at the receiver. This allows a reduction in bit rate, as well as the possibility of eliminating the serious effect of channel errors on those coefficients.

DOI:10.1049/ip-f-1.1984.0106

出版商:IEE    

年代:1984

数据来源: IET

摘要:

It is demonstrated that the maximum entropy method is closely related to a general likelihood ratio detector which tests for the equality of two covariance matrices. These results may be used to indicate which (if any) maximum entropy spectral estimate contains significant information.

DOI:10.1049/ip-f-1.1984.0107

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Sequences are often used as a basis for code division multiplexing. In order that minimum interference from other users should occur, it is important that the sequences used should have good cross-correlation properties. Various sets of sequences have been derived with appropriate properties, but the sources have been well dispersed within the literature. In the paper are collected six of the most important of these sequence sets, and examples are given of the way in which they are constructed.

DOI:10.1049/ip-f-1.1984.0108

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The paper presents a new and general description of a class of one-coincidence sequence sets. The set leaders of this class are derived from the combination ofNlinearly independent phases of a binarym-sequence of lengthS= 2N−1. This class will be referred to in this paper as them-sequence class of one-coincidence sequences. The total number of one-coincidence sets of this class is derived. It is shown that the total number of them-sequence class of one-coincidence sets is much larger than the number previously described in the literature. A general proof of the one-coincidence property of these sets is presented, and four equivalent conditions for the existence of one-coincidence sequence sets is derived.

DOI:10.1049/ip-f-1.1984.0109

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The class of carrier recovery which is often employed in PSK-TDMA systems is ‘frequency multiplier/narrow-band filter/frequency divider’. Cycle slips occur when a signal extracted from the narrow-band filter is embedded in some noise. In the PSK-TDMA systems, a transmitted signalSis of the burst form while received noiseNis in the steady state. A preceding burst signalIis often allocated immediately before the burst signalS. In this paper, the transient occurrence probability of the cycle slips is analytically derived, assuming that the products of the multiplier, which are a burst signal (S × S) and a preceding burst signal (I × I) as well as a steady-state noise (N × N), a burst noise (S × N) and a preceding burst noise (I × N), are coexistent at the narrow-band filter output. Also the transient cycle slip occurrence probability is numerically calculated using the results of the analysis.

DOI:10.1049/ip-f-1.1984.0110

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A hybrid direct-sequence/frequency-hopping spread-spectrum communication modem for burst format transmission of digital data has been developed. A burst consists of a short synchronisation preamble and the data packet. Data modulation is accomplished by assignment of pairs of pseudonoise sequences with low crosscorrelation for message ones and zeros. The spreading code chip pattern is changed from bit to bit in both the preamble and the message portion of a burst. Receiver signal processing is based on the application of surface-acoustic-wave (SAW) elastic convolvers to programmable matched filtering. The performance of the system in an additive white Gaussian noise channel is analysed, measures of performance being the probability of burst loss and the bit error probability in the case of ideal synchronisation. Evaluations for a particular design are presented, and some experimental results obtained with a test system are shown for comparison.

DOI:10.1049/ip-f-1.1984.0111

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Sliding correlators are frequently used in the acquisition of pseudonoise sequences in spread-spectrum and ranging systems. High-speed acquisition is often required. The paper examines the decorrelation between the received and locally generated codes and the increase in self-generated noise at the output of the correlator as the search rate is increased. A numerical approach enables the analysis to be carried out for search rates well in excess of 1 bit per sequence period. It is found that decorrelation and self-noise place an upper bound on the search rate of the synchroniser, which has been ignored previously. The analysis has been carried out for a range of code lengths, and analytic expressions are obtained for both decorrelation and self-noise terms, which enable the effects to be estimated by extrapolation for other, longer, codes, where the effects are more pronounced. The results enable a correction factor to be incorporated into the expression for the maximum search rate of a sliding correlator under external noise conditions.

DOI:10.1049/ip-f-1.1984.0112

出版商:IEE    

年代:1984

数据来源: IET