User equipment, small cell and operation method thereof

A small cell for use in a communication system, comprising:

• a processor, being configured to generate a maintaining downlink signal according to a common cell identity or an adjacent cell identity of an adjacent small cell received from a backhaul network when it is determined that the small cell is in an off-state, the maintaining downlink signal utilizing fewer radio resources compared to a normal downlink signal which is generated when the small cell is in an on-state, the adjacent small cell being in the on-state;
• and
• a transceiver electrically connected to the processor, being configured to continuously transmit the maintaining downlink signal when the small cell is in the off-state and receive an uplink signal from a user equipment (UE);
• wherein the processor further switches the small cell from the off-state to the on-state according to the uplink signal, and generates the normal downlink signal according to a dedicated cell identity after the small cell is switched to the on-state, and
• wherein the uplink signal has a physical random access channel (PRACH), and the processor further determines whether a received signal strength of the PRACH is larger than a threshold value, and switches the small cell from the off-state to the on-state when the received signal strength is larger than the threshold value.