Characterising an In-Room MIMO System Employing Elevation-Directional Access Point Antennas

The performance of an in-room MIMO system is investigated with the use of elevation-directional access point (AP) antennas which emphasize wall-reflected NLOS components instead of non-directional antennas. Simulation results suggest that the mean MIMO capacity throughout an idealised in-room environment can be improved on the order of 14% coupled with a 3% increase in mean relative MIMO gain if the appropriate main-lobe elevation direction is selected. The associated antennas are omnidirectional in azimuth and exhibit directivities and elevation half-power beamwidths on the order of 6 dBi and 28°, respectively. Experimental results obtained via channel measurements reveal more modest improvements due to the increased multipath richness exhibited by the real environment; a mean capacity improvement of approximately 5% is achieved, but this is accompanied by a minor reduction in relative MIMO gain. This level of performance may not be significant enough to warrant switching to elevation-directional AP antennas; however, the measured results provide qualitative verification of the simulation model. In any case, the results quantify the modest in-room MIMO performance gains one should expect when considering only wall reflections in the design of elevation-directional AP antennas at microwave frequencies.