On the efficiency of directional antennas in MIMO communication systems

It is conventionally believed that directional antennas are not as efficient as omnidirectional antennas in MIMO communications since they limit the effective angular spread of the scattering environment. However, it is often neglected that the power gain provided by directional antennas can compensate for the deleterious effect of their limited beamwidth. In this paper, we analyze the efficiency of directional antennas to investigate whether these antennas can improve the capacity of MIMO communication systems versus commonly used omnidirectional antennas. Employing a realistic MIMO channel model, we show that the performance of directional antennas depends on the scattering environment, the signal to noise ratio and the array configuration. Our simulation results suggest that in certain conditions directional antennas can indeed improve the capacity of MIMO systems compared to the capacity achieved by using omnidirectional antennas.