Estimation of 2 × 2 MIMO capacity with dual-polarized antennas under received power imbalance through propagation measurements

MIMO (Multiple-Input Multiple-Output) is a promising technology for increasing the transmission capacity of cellular mobile systems in proportion to the number of antennas in both transmitter and receiver. Due to their physical size, dual-polarized antennas are superior in this system to single-polarized antennas on the transmitter sides. This paper examines a 2×2 MIMO with dual-polarized antennas on both transmitter and receiver. It is important to estimate MIMO capacity accurately in cellular mobile systems because optimization of cell coverage planning is advantageous in the deployment of service areas. The authors have proposed a MIMO capacity estimation method in terms of a 2×2 MIMO with dual-polarized antennas, whose capacity can be estimated using only the average SNR (signal to noise ratio) because the eigenvalue ratio, which is a key factor for estimating MIMO capacity, is large and its dependency on the propagation environment is small. This paper focuses on the received power imbalance, which might for example be caused by different antenna gains due to the side lobe patterns of transmitter antennas. Measured results verify that the eigenvalue ratio is strongly dependent on the received power imbalance, decreasing in proportion to that imbalance. It is important to consider the received power imbalance to estimate the 2×2 MIMO capacity accurately.