We claim:
1. A communication system comprising a base station (72), an MME unit (73)
connecting the base station (72), and a mobile terminal (71) which can perform radio
communication with the base station (72),
wherein the base station (72) is configured to shift between an energy saving state and a normal state, the base station (72) reducing energy consumption in the energy saving state and performing a normal operation in the normal state,
the MME unit (73) is configured to inform the base station (72) of a predetermined period,
the base station (72) is configured to transmit, even in the energy saving state, a signal necessary for measurement for the predetermined period, and
the mobile terminal (71) is configured to check a presence of the base station (72) in the energy saving state based on the signal necessary for measurement.
2. A base station (72) used in a communication system comprising the base
station (72), an MME unit (73) connecting the base station (72), and a mobile
terminal (71) which can perform radio communication with the base station (72),
wherein the base station (72) is configured to shift between an energy saving state and a normal state, the base station (72) reducing energy consumption in the energy saving state and performing a normal operation in the normal state,
the base station (72) is configured to be informed of a predetermined period by the MME unit(73), and
the base station (72) is configured to transmit, even in the energy saving state, a signal necessary for measurement to the mobile terminal (71) for the predetermined period.
3. A mobile terminal (71) used in a communication system comprising a base
station (72) shifting between an energy saving state to reduce energy consumption
and a normal state to perform a normal operation, an MME unit (73) connecting the

base station (72), and the mobile terminal (71) which can perform radio communication with the base station (72),
wherein the mobile terminal (71) is configured to receive a signal necessary for measurement transmitted for a predetermined period by the base station (72) in the energy saving state, the predetermined period of which MME unit (73) notified the base station (72), and
the mobile terminal (71) is configured to check a presence of the base station (72) in the energy saving state based on the signal necessary for measurement.