No abstract

This paper provides analyses of three types of diversity combining systems in practical use. These are: selection diversity, maximal-ratio diversity, and equal-gain diversity systems. Quantitative measures of the relative performance (under realistic conditions) of the three systems are provided. The effects of various departures from ideal conditions, such as non-Rayleigh fading and partially coherent signal or noise voltages, are considered. Some discussion is also included of the relative merits of predetection and postdetection combining and of the problems in determining and using long-term distributions. The principal results are given in graphs and tables, useful in system design. It is seen that the simplest possible combiner, the equal-gain system, will generally yield performance essentially equivalent to the maximum obtainable from any quasilinear system. The principal application of the results is to diversity communication systems and the discussion is set in that context, but many of the results are also applicable to certain radar and navigation systems.

The closed-form equations given are based on the results of finite element analyses of double-edge-notched plates subject to tension or in-plane bending. The notch dimensions were varied in a parametric survey from shallow, part-circular forms to deep, sharp, slits with semi-circular ends, giving stress concentration factors varying from 1.2 to 13 (net stress basis).The concept of a configuration factor for notches, similar to that used to calculate crack-tip stress field intensity factors, is introduced. It is shown in the first instance that the analogous crack configuration factor can be used directly to mod@ the elastic stress concentration factor for an elliptical hole, giving closed-form functions that do not involve empirical fitting constants and have acceptable practical accuracy. Reasons for the effectiveness of this form are given, together with an analysis of the points where the notch stress concentration factors diverge from the simple closed form. Further refinements that improve accuracy are given and comparisons are also made with stress concentration factors for hyperbolic edge notches.

Thirty adult subjects learned to associate nonsense names varying in word length with nonsense visual stimuli varying in visual complexity. Simple reaction times (SRTs), visual duration thresholds (VDTs), matching response latencies (MRLs), and naming response latencies (NRLs) were then obtained from these subjects. The data indicate that SRTs, VDTs, and NRLs are significantly related to word length and that VDTs and NRLs are significantly related to visual complexity. There is also a tendency for MRLs to increase with increases in word length, particularly for “no” responses. However, the effects of word length on VDTs, MRLs, and NRLs may be confounded with the number of trials needed to learn the paired associates or with the number of overlearning trials. The data are consistent with an interpretation that motor planning or some form of implicit speech process may be a part of the total time required for the naming response.