Small-scale statistics of fixed relay polarimetric links using narrow-beamwidth antennas at 3.5 GHz

The BuNGee project (Beyond Next Generation Mobile Broadband) aims to improve the overall infrastructure capacity density provided by cellular networks to an ambitious goal of 1Gbps/km². Its innovative architecture relies on a Hub Base Station (HBS) connected to the operator back-haul on one side and to a large number of distributed Access Base Stations (ABSs) or fixed relays on the other side (self-backhaul links), the HBS-ABS links being implemented by means of narrow-beamwidth dual-polarized antennas. ABSs are then connected to Mobile Subscribers (MSs), forming access links. In this contribution, the small-scale statistics of the HBS-ABS relay links are characterized by means of an advanced ray-tracing tool to reflect the peculiarities of such architecture. In particular, the dependency of small-scale statistics upon the antenna beamwidth is critically investigated. Results are simultaneously compared with the reported parameters of existing models in the literature, e.g. WINNER II and IEEE 802.16 channel models. We focus on the spatial K-factor, spatial correlation coefficients, Cross Polarization and Co-Polar Ratios (XPR, CPR), in a dense urban deployment scenario. Furthermore, a tapped delay line model for fixed relay links with 20 MHz bandwidth is developed and analyzed.