A Novel Approach in Determination of the Appropriate Spatial Averaging Signal Length
Information about the spatial mean signal values is used as the control information in many practical aspects of digital communications (e.g. handoff, adaptive coding/modulation). That raises the question: How long the appropriate averaging length \({2L}\) should be in order to enable us to accurately estimate these spatial mean signal values? Lee was the first who gave analytical recommendations for the choice of the averaging length (\({2L}\) should be between \({20 \lambda }\) and \({40 \lambda }\)) and to date, his recommendations are being used as a reference for the averaging process. Although Lees recommendations give accurate mean signal estimations in some outdoor environments, the results obtained using Lees methodology are not applicable for indoor averaging, due to lack of their consistence with empirically obtained results (\(2L \le 10\lambda \)). Moreover, Lees recommendations cannot be used to explain much larger \({2L}\) values adopted in the processes of averaging in suburban/rural outdoor environments (\(2L \approx 100 \lambda \)). In contrast to Lee, who treated multipath variations as a dominant factor that affects the choice of the appropriate averaging length, in this paper it is shown that shadowing variations, beside multipath, play a crucial role in the process of \({2L}\) determination. Thus, considering also shadowing variability, a novel approach in determination of the appropriate mean signals averaging length is proposed in this paper. According to herein proposed approach, the appropriate averaging length should be determinated not just as a length at which the multipath is smoothed sufficiently, but also as a length at which shadowing can be considered as a highly correlated process. In contrast to existing analytical results, the results obtained following herein proposed methodology coincide well with all above mentioned empirical results and enable us to unambiguously determine the appropriate values of \({2L}\) for all types of wireless environments (both indoor and outdoor).
averaging length local mean signal value lognormal shadowing decorrelation distance shadowing spatial correlation