摘要:

The paper shows that all ‘cyclic’ convolutional self orthogonal codes (CSOCs) generated by cyclic sets of even order have effective constraint lengths which meet the lower bound developed recently, and that the lower bound is a limiting bound for all CSOCs. Also, new upper bounds on the effective constraint length are developed for non-‘cyclic’ and ‘cyclic’ CSOCs.

DOI:10.1049/ip-f-1.1981.0010

出版商:IEE    

年代:1981

数据来源: IET

摘要:

A situation often encountered in a communication system, in which a digital interpolation filter is followed by a sinusoidal modulator, is considered. A mathematical model of the system is developed and some useful properties derived. These properties lead to an equivalent realisation of the interpolation filter and the subsequent commutation of the filter with the modulator. Applications to digital SSB generator designs are described, and it is shown that these properties explain why the complexity of the designs can be reduced.

DOI:10.1049/ip-f-1.1981.0011

出版商:IEE    

年代:1981

数据来源: IET

摘要:

Conventionally, radar trackers use fast or ‘instantaneous’ automatic gain control (AGC) loops for control of IF gain. The paper indicates that this practice may result in unnecessarily large errors when the tracking accuracy is limited by target ‘glint’ effects. The analysis considers a conical scan radar which is tracking a target consisting of two, point reflectors. Two limiting cases of AGC response time are considered: ‘fast’ AGC, when the response is much faster than fluctuations of the received signal, and ‘slow’ AGC, when the reverse is true. It is shown that fast AGC tends to track the larger of the two sources, whereas slow AGC tracks the radar ‘centre of gravity’ or centroid. The effects of an angle tracking error, such as might occur in tracking a fast, crossing target are also examined. The glint error probability distributions for the two AGC responses are considered and shown to be different. Fast AGC results in a small error most of the time but can result in occasional very large glint errors or ‘spikes’ slow AGC has a somewhat larger tracking error than fast AGC some of the time but never suffers from large amplitude spikes. The analyses indicate lower probabilities of glint errors than seem to be found in practice. It is conjectured that this may arise from angle-tracking loop saturation and slow recovery, either from large glint spikes or from movement of the major target source (bright spot wander). Slow AGC may give more accurate tracking than fast AGC under these circumstances.

DOI:10.1049/ip-f-1.1981.0013

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The paper considers the problem of the detection of a quaternary phase-shift-keyed signal which has been transmitted along with noise through a direct phase regenerator (DPR) corrupted by additional noise and coherently demodulated and sampled at the receiver. An expression is obtained for the symbol error probability (SEP), which includes the parameters that characterise the imperfections of a practical DPR. Equivalent signal/noise ratio degradations due to these imperfections are evaluated at the 10-6SEP point.

DOI:10.1049/ip-f-1.1981.0014

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The paper considers the problem of evaluating the performance of binary and quaternary coherent phase-shift-keyed (CPSK) signals which have been transmitted through an arbitrary bandpass nönlinearity (BPNL) and in the presence of additive gaussian noise (AGN) and cochannel interference (CCI). Both AGN and CCI are introduced before and after the BPNL. Exact expressions are derived for the symbol error probabilities (SEPs) of binary and quarternary CPSK transmissions. A power-series expansion is employed to describe the joint characteristic function of the pair of random variables defining each CCI. The recurrence method of Shimbo and Fang is used to determine the coefficients in each series, and the resulting expressions of SEPs are evaluated using Gaussian-Hermite quadrature techniques. Some results are presented for illustrative purposes.

DOI:10.1049/ip-f-1.1981.0015

出版商:IEE    

年代:1981

数据来源: IET

摘要:

The paper considers the correlation properties of sets of sequences in which each sequence is constructed by taking the Kronecker product (or tensor product) of two short sequences. It is shown that if the short sequences are carefully chosen then the correlation properties of such sets are nearly as good as those of sequences of comparable length that have been obtained by other means. Furthermore, it is much easier to optimise the phases of these sequences because of the structure that they inherit from the Kronecker product operation. This structure also enhances the ease of synchronisation for such sequences. If the signal/noise ratio is large, the time required to synchronise to Kronecker sequences is significantly less than the time required to synchronise to other sequences of comparable lengths. Thus, the Kronecker sequences allow one to achieve rapid acquisition at the expense of a very small deterioration in some of the correlation properties.

DOI:10.1049/ip-f-1.1981.0016

出版商:IEE    

年代:1981

数据来源: IET

摘要:

Feedback automatic gain control (FBAGC) is used to maintain the mean level of one or more signals throughout a signal processing system at a fixed value. The paper is particularly concerned with the application of FBAGC to receiver design and discusses the problem of attempting to suppress large unwanted envelope variations of an incoming signal without distorting any wanted modulation. A simple feedforward model of FBAGC systems predicts their effect on deep sinusoidal variations of the input signal's envelope. Experimental results confirming the predictions are presented, and a method of determining the parameters of an undefined AGC system given. Finally, the fundamental problems of FBAGC dynamics are discussed, and a technique is suggested for greatly improving them.

DOI:10.1049/ip-f-1.1981.0018

出版商:IEE    

年代:1981

数据来源: IET