Performance of Multi-Antenna Signaling Strategies Using Dual-Polarized Antennas: Measurement Results and Analysis

Multiple-input multiple-output (MIMO) wireless systems employ spatial multiplexing to increase spectral efficiency or transmit diversity (space-time coding) techniques to improve link reliability. The performance of these signaling techniques is highly dependent on channel characteristics which in turn depend on antenna height and spacing and richness of scattering. The use of dual-polarized antennas is a costand space-effective alternative where two spatially separated uni-polarized antennas can be replaced by a single dual-polarized antenna element. In this paper, we use fixed-wireless experimental data collected in a typical suburban environment at 2.5 GHz to investigate the performance of spatial multiplexing and transmit diversity (Alamouti scheme) for a dual-polarized antenna setup. Channel measurements were conducted over a cell of radius 7 km and channel statistics such as K-factor, cross-polarization discrimination (XPD), and fading signal correlation were extracted from the gathered data. At each location, different combinations of these parameters yield different performance (measured in terms of average uncoded bit error rate) of spatial multiplexing and the Alamouti scheme. The results indicate that proper selection of the transmission mode through feedback, if possible, can reduce the bit error rate by several orders of magnitude. Furthermore, the results hint at the existence of a preferred-mode switching distance within a cell – above/below which one mode of transmission exhibits generally superior performance.