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

Multiple-input multiple-output (MIMO) wireless systems employ spatialmultiplexingto increase spectral efficiency or transmit diversity (space-time coding)techniques to improve link reliability.The performance of these signaling techniques is highly dependent on channelcharacteristics whichin turn depend on antenna height and spacing and richness of scattering. Theuse ofdual-polarized antennas is a cost- and space-effective alternative where twospatially separated uni-polarized antennas can be replaced by a singledual-polarizedantenna element. In this paper, we use fixed-wireless experimental datacollected in atypical suburban environment at 2.5 GHz to investigate the performance ofspatialmultiplexing and transmit diversity (Alamouti scheme) for a dual-polarizedantennasetup. Channel measurements were conducted over a cell of radius 7 km andchannel statistics such as K-factor, cross-polarizationdiscrimination (XPD), and fading signal correlation were extracted fromthe gathered data. At each location, differentcombinations of these parametersyield different performance (measured in terms of average uncoded bit errorrate)of spatial multiplexing and the Alamouti scheme.The results indicate that proper selection of the transmissionmode through feedback, if possible, can reduce thebit error rate by several orders of magnitude. Furthermore, the resultshint at the existence of a preferred-mode switching distance within a cell– above/below which one mode of transmission exhibits generally superiorperformance.

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