Multi-Antenna Techniques in Fixed Wireless Links

We present a summary of results based on several years of measurements for urban fixed wireless (FW) channels. Our results are aimed at providing reference data for practical applications in FW services. We discuss temporal stability and fade dynamics of outdoor-outdoor single-input single-output (SISO) channels with and without spatial diversity, a relevant aspect when considering the types of modulations that such a channel can support. Our main findings are that nearby vehicular traffic is the main source of temporal variations, but that in most practical situations temporal fades are very shallow. Spatial fades are quite significant and are stable over time. Diversity has the twofold effect of mitigating these fades and increasing temporal stability. We also present practical results on outdoor- indoor multiple-Input multiple-output (MIMO) channels. Based on empirical data we contrast spectral efficiencies for diverse types of systems, ranging from those that only use multiple antennas for beamforming to those that take full advantage of channel state information. We find that for low signal to noise ratio (SNR), beamforming achieves in practice spectral efficiencies comparable to that of MIMO and that it retains a significant proportion of such spectral efficiency at higher SNR, with the benefit of considerably lower complexity.