Question: What uniquely identifies a resource element in the resource grid for an antenna port?
Option 1: The complex value of the resource element
Option 2: The index pair (k,l) in the frequency and time domains, respectively
Option 3: The antenna port number
Option 4: The slot number
Explanation: A resource element is uniquely identified by its position in the resource grid, which is defined by the index pair (k,l) representing the frequency and time domains. This allows for precise identification and mapping of resource elements within the grid.