Methods for scheduling channel activities for multiple radio access technologies in a communications apparatus and communications apparatuses utilizing the same

An communications apparatus with multiple radio access technologies (RATs) is provided. A first RAT module transceives radio frequency (RF) signals in a first cellular network through the antenna. A second RAT module transceives RF signals in a second cellular network through the antenna. An arbiter receives a first and a second request from the first and second RAT module requesting permission to use the antenna for a first and a second channel activity, obtains a priority configuration for the first channel activity versus the second channel activity when the second channel activity collides with the first channel activity, and responds to one of the first and second RAT modules with an acknowledgement message and to the other of the first and second RAT modules with a rejection message based on the obtained priority configuration.