Communications in a wireless network for carrier Selection and switching are provided. A terminal in the wireless network is simultaneously receiving data on at most m carriers. A base station in the wireless network sends an activation command associated with more than m carriers to the terminal. The terminal activates the more than m carriers. Then the base station selects a first subset from the activated carriers, and sends a first monitoring command associated with the first subset via a first physical-layer signaling to the terminal. When load and/or interference situations are changed, the base station selects a second subset from the activated carriers, and sends a second monitoring command associated with the second subset via a second physical-layer signaling to the terminal, wherein the first subset is different from the second subset.