Question: In a 2D cross-polarized antenna array at an eNodeB (eNB), with N total antennas, M antennas in the first dimension (vertical) per polarization, K antennas in the second dimension (horizontal) per polarization, and P polarization groups, how are the antennas typically labelled for a specific element's index assignment?
Option 1: Increasing order of polarization group, then row (first dimension), and finally column (second dimension)
Option 2: Increasing order of the first dimension (vertical), then the second dimension (horizontal), and finally the polarization group
Option 3: Increasing order of the second dimension (horizontal), then the first dimension (vertical), and finally the polarization group
Option 4: Random assignment based on antenna performance characteristics
Explanation: According to MIMO channel correlation matrices definition for 2D cross-polarized antennas at eNodeB, the labelling of antennas follows a specific order: firstly by increasing order of the second dimension (horizontal), then by the first dimension (vertical), and finally by the polarization group. This structured approach ensures systematic indexing within the antenna array, facilitating clear identification and management of each antenna element across different dimensions and polarizations.