in over co-polarized setup especially in line of sight, and this gain can be attributed to reduced antenna correlation. Condition number varies between subcarriers. The condition number shown is the average over system bandwidth and time. LTE Small Cell Optimization X-polarized antenna provide better peak v-pol 2rx throughput x-pol 2rx Verticalpolarized antenna provide better throughput in poor RF conditions Downlink throughput (Mbps) Figure 12.43 Downlink throughput distribution for the same drive test route with two different UE antenna setups When deploying 4x2 open-or closed-loop spatial multiplexing, antenna correlation impact can be minimized by proper connection of feeders to antenna ports. To improve diversity gain, the correlation between reference signals R0 and R2 (also R1 and R3) should be minimized by connecting the corresponding antenna branches to cross-polarized or spatially separated ports. Carrier frequency also has an impact on the antenna correlation: as the wavelength increases the antenna correlation also increases for a given physical antenna separation. Figure 12.44 shows a scanner measurement sample where a cluster of eNodeBs is measured simultaneously on two frequencies, 800 MHz and 2.6 GHz. Each cell has two cross-polarized transmit antennas and the antenna chassis and azimuth direction are the same on both the frequencies. The scanner has two omni-directional receive antennas placed on the rooftop of the measurement car at 10 cm spacing. The RSRP difference, shown in the right-hand side subfigure, between the two frequencies is in excess of 10 dB, although in measurement the 800 MHz cells have 3 dB higher reference signal transmit power. Regardless of the higher path loss, the condition number on 2.6 GHz, shown in the left-hand side subfigure, is lower indicating smaller power difference between the first and second MIMO substreams, and thus better multi-stream capability. Power imbalance between antenna branches results in similar degradation as correlation. A rule of thumb for a 2x2 