Effect of antenna polarization on the capacity of a multiple element system in an indoor environment

We analyze the behavior of a multiple element antenna system in an indoor environment based on the measurements taken in the Lucent Bell Labs building in Crawford Hill, NJ, with a system of 12 transmitters and 15 receivers. In particular, we investigate the capacity behavior with respect to the polarization of the transmitting/receiving elements and the distance between the transmitting and the receiving arrays. The analysis of the power rolloff versus distance clearly demonstrates the different propagation characteristics of the horizontally versus the vertically polarized electric fields. Under strong line-of-sight (LOS) conditions (hallway environment), the power of the horizontally polarized waves falls off faster with distance than that of the vertically polarized fields. Also, the cross-polarization coupling is about -15 dB. Under nonline-of-sight (NLOS) conditions (labs), both polarizations display similar rolloff behavior with distance and the cross-polarization coupling is about 0 dB. There is a power loss of at least 15 dB under NLOS conditions relative to LOS conditions. The average received signal power affects the system capacity. In the hallway, horizontally polarized systems achieve lower capacities than their vertically polarized counterparts. Also the achievable capacity in the labs is much lower than that in the hallway, because of the lower average received power. The comparison of single polarization systems to hybrid polarization systems shows that combined polarization systems perform better in terms of achievable capacity. Therefore, there lies an advantage in using both electric field polarizations. However, under strong LOS conditions the channel itself inherently limits the capacity behavior of the system.