On the cross-correlation properties of large-scale fading in distributed antenna systems

Spatially distributed transmission points connected to the same source, known as distributed antenna systems, is one of the promising communication techniques that is capable to improve system performance. The distribution of the transmission points over a large geographical area increases the chances for the receive mobile station (MS) to experience favorable channel conditions from one link or more, simultaneously. However, this anticipated gain depends heavily on the cross-correlation properties of the parameters of different links, especially the large scale parameters (LSP). In this contribution, propagation measurements were used in order to study the cross-correlation of the large-scale fading (LSF) of different links in a distributed antenna system. Multi-site fully-coherent wideband (40 MHz bandwidth) measurements for a semi-urban microcell environment at 2.6 GHz with four base stations (BSs) and one MS were performed. The study of the LSF cross-correlation properties was performed on the global scale (i.e., using the LSF values of the full measurement route at once), and on the local scale (i.e., over local areas of hundreds of wavelengths long). It was found that, for the investigated environment, analyzing the LSF cross-correlation properties on the local scale gives better insight compared to performing the analysis on the global scale; the variations of the LSF of the different links are caused mainly by independent interacting objects (IOs), which reduce the probability of having all the links degrade simultaneously; and a Gaussian distribution can be used to model the cross-correlation coefficients for each link pairs.