Multipath Angle Spread and Performance in Indoor Measured Tri-Polarized Massive MIMO Channels

In this letter, a tri-polarized multiple-input multipleoutput (MIMO) system is proposed, which consists of a practical uniform linear array (ULA) with 20 tri-polarized antennas as the transmitting end (Tx) and a ULA with 8 tri-polarized antennas as the receiving end (Rx). The polarimetric channel characteristics are measured and analyzed in two typical indoor scenarios: line-ofsight (LoS) and obstructed LOS (OLoS) scenarios at 3.55 GHz. The angular power spectrum (APS), root mean square angle spread (AS), correlation coefficient, and channel capacity are investigated based on measured data. Results show that channel characteristics and MIMO performance are heavily dependent on antenna polarizations. Compared with the co-polarized patch-like radiation pattern, the ASs of the co-polarized monopole-like radiation pattern and their cross-polarizations are larger, resulting in smaller correlation coefficients and higher channel capacities. The capacity of the tri-polarized MIMO system can reach at least 2.75 times that of the single-polarized and 1.39 times that of the dualpolarized system for one antenna at Rx and 20 antennas at Tx. Thus, communication channels with different polarizations can be considered independent, and the number of independent parallel channels in MIMO systems can be effectively increased through the tri-polarized antenna.