MIMO Systems: Principles, Iterative Techniques, and Advanced Polarization - Adaptive Signal Processing in Wireless Communications - page 120

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FIgure 4.16 Difference between the triple-polarized and single-polarized channel capacities
of 3 × 3 MIMO systems employing dipole antennas.

the urban case by χ θ and χ ϕ ~ N (0, 9). As shown in Figure 4.15a , the MIMO channel
capacity increases as the angle spread increases at Tx and Rx for the same polarization
antennas. In contrast, dual polarization improves the channel capacity due to the lower
antenna correlation, as shown in Figure 4.15b. However, when the spatial correlation of
the single-polarized antennas is lower, the channel capacity is proportional until 6.7 dB
for AS > 80°. It should be noted that the MIMO channel capacity is significantly depen-
dent on the antenna correlation.
Figure 4.16 shows the difference between the triple-polarized and single-polarized
channel capacities (Δ C = C triple-polar - C single-polar ) of the 3 × 3 MIMO system versus the
average XPD and AS. The propagation environment has the same conditions as the pre-
vious section. For the triple-polarization configuration, x -, y -, and z -oriented dipole
antennas are employed. This can represent a combination of angular and polarization
techniques. We found that for the triple-polarization case, the average power of the sub-
channel can be unfortunately lost when the angular spread is not large enough until
covering all antennas. As seen in Figure 4.16, the single-polarized channel capacity can
be superior to the triple-polarized channel capacity because single polarization has a low
spatial correlation and triple polarization loses the subchannel power due to insufficient
angular spread. However, generally speaking for most scenarios, triple polarizations can
maintain a higher capacity with respect to the single-polarization case.

4.5.6 Impact of Depolarization Effect on MIMO Configurations
In this section, we investigate the impact of the depolarization effect on 4 × 4 MIMO sys-
tems with single- and dual-polarization configurations. While pattern and polarization