1. A mobile communication system comprising a first local base station
device (eNB), a serving cell, being either a normal base station device providing a
macro cell or a second local base station device and a user equipment device (UE)
configured to perform radio communication with the local base station device
(eNB) and the serving cell,
wherein upon predetermined shift conditions being satisfied, the first local base station device (eNB) is adapted to shift from a normal operation state to an energy saving operation state (ST1503, ST1504), the first local base station device (eNB) is adapted to perform a transmission operation for downlink transmission signals to be transmitted to the user equipment device (UE) and a reception operation for uplink transmission signals transmitted from the user equipment device (UE) in the normal operation state, and stop the transmission operation for at least part of the downlink transmission signals and perform the reception operation in the energy saving operation state,
characterized in that
the user equipment device (UE) is adapted to judge whether or not a reception quality of the serving cell falls below a threshold and, if the reception quality of the serving cell falls below the threshold, the user equipment device (UE) is adapted to transmit an uplink signal to cause the first local base station (eNB) to shift from the energy saving operation to the normal operation state.
2. The system according to claim 1,
wherein upon reception of the uplink transmission signals (RACH) in the energy saving operation state, the first local base station device (eNB) shifts from the energy saving operation state to the normal operation state.
3. The system according to claim 1,
comprising a communication device (901) configured to perform radio communication or wire communication,
wherein upon reception of a predetermined signal from the communication device (901) in the energy saving operation state, the first local base station device (eNB) shifts from the energy saving operation state to the normal operation state (ST1510, ST1511).
4. The system according to claim 3,
wherein the predetermined signal is a paging signal.

5. The system according to any of claims 1 to 4,
wherein the first local base station device (eNB) performs the reception operation at a predetermined timing in the energy saving operation state.
6. The system according to any of claims 1 to 4,
comprising a communication device (901) configured to perform radio communication or wire communication with the first local base station device (eNB),
wherein the shift condition includes at least one of the conditions that:
(a) the user equipment device (UE) being in a connected state with the first local base station device (eNB) does not exist for a predetermined period;
(b) an instruction to turn off the power for the transmission operation and the reception operation of the first local base station device (eNB) is provided; and
(c) an instruction to shift from the normal operation state to the energy saving operation state is provided by a base station device (902) other than the first local base station (eNB) device or a communication device (901).