Empirical comparison of MIMO and beamforming schemes for outdoor-indoor scenarios

We present an empirically based comparative study of spectral efficiency for a variety of transmission systems applicable to a fixed or repositionable wireless environment, in the context of Wi-Fi, WiMAX or MuniNet systems. A narrowband 4times4 multiple input multiple output (MIMO) channel sounder was constructed and a series of outdoor to indoor measurements were carried out, in multiple locations and with different array configurations. The channel measurements were used to compute the efficiency of different systems that could be deployed in such scenarios, ranging from a full MIMO system with perfect channel state information (CSI) at both ends to simple diversity schemes such as classical beamforming. We show comparisons of efficiency for the different transmit/receive configurations operating in a representative variety of locations. Our results indicate that for low values of signal to noise ratio (SNR), in the range of 5 dB, such as found in strong interference scenarios, simple schemes can achieve median spectral efficiencies as high as 80% of that of MIMO with complete CSI.