In this survey we identified some measuring metrics to study the average noise power variations in typical outdoor power substations. Power substations generally have metallic structures and despite the insulation considerations have high electric fields. The physical size of a substation does not allow a complete controlled experiment. We arranged a setup plan to study the noise floor variation in a few substation yards in residential, industrial/isolated (sparsely populated) subdivisions, collected the empirical data sets and compared the achieved results with the known noise constituents that were cited in the literature. A two-weeks measuring window was chosen to control for any possible factors that might confound results. The analysis suggests that the noise floor variation (and hence the link quality) has an underlying dominant semi-deterministic time-dependent constituent in addition to the classical random distribution. Although it is of no surprise that the semi-deterministic component is associated with the location of the substation yard (e.g. residential or industrial), its dynamic range is significant. The methodology, which is adopted in this study, has applications in the analysis of Fixed Wireless Access (FWA), Local Multipoint Distribution Service (LMDS).
In array signal processing in general, we often wish to fuse the collected data at several sensor elements and implement a given estimation or detection task. This study is a selective treatment of the wideband array processing under some specific assumptions. Shannon Spatial Sampling Limit defines an upper bound for the frequency of transmission given certain element spacings in arrays. Beyond this bound, the exceeded ambiguity, due to spatial aliasing, avoids correct estimation of the signal parameters -e.g. the Direction Of Arrival (DOA), which is of our interest in this study. In another vein, decreasing the element spacing to meet a wider spectral support is difficult to implement due to the electromagnetic mutual coupling of the sensor elements in the array and the reduction of the resolution. This work is an attempt to develop a methodology for resolving this ambiguity or aliasing in the wideband scenario using statistical signal processing. Our approach is heuristic. We consider known implementations, adopt them to meet our scenario and then analyze the performance of our proposed method. Although the models and the formulations presented in this survey can be further generalized, we limit our discussion mainly to the Uniform Linear Arrays (ULA). Many of the topics discussed in this study have a potential for being useful in practical applications, since they would allow a realistic modeling and offer more flexibility than the conventional array processing framework, hence we believe that there are already sufficient interest in this study.
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