Achieving Near Maximum Ratio Combining Diversity Gains With Directive Antennas

We present an empirically based comparison of the effectiveness of spatial and angular diversity systems in outdoor-to-indoor fixed wireless links. We concentrate on the simple to implement, single RF-chain selection diversity systems. We find that for such systems, angular diversity very significantly outperforms spatial diversity using comparatively sized arrays. This occurs despite the fact that our test environment is characterized by the presence of strong multipath propagation. Our results show that for a diversity order 20, the advantage of angular over spatial-selection diversity is about 4 dB at the median level for non-line-of-sight (NLOS) links and close to 8 dB for the line-of-sight (LOS) case. When compared to the optimum maximum ratio combiner, the performance loss of angular selection diversity is 2 dB and 4 dB for LOS and NLOS, respectively. To provide a reference that explains the observed results we use a Ricean fading model that includes correlation, which is analyzed theoretically and via simulation. This model is found to match our measurement data very well and can, thus, be used to predict the performance of diversity systems for the type of settings we considered.