Radio terminal, radio communication system, and radio communication method

1. A radio terminal comprising:

a radio interface configured to enable radio communication with a radio base station by using a predetermined radio band;

a controller configured to control switching between a wake-up state in which the radio interface is turned on and a sleep state in which the radio interface is turned off; and

an acquiring unit configured to acquire a reference wake-up timing scheduled as a wake-up timing for switching from the sleep state to the wake-up state, wherein

the controller shifts the wake-up timing from the reference wake-up timing to a different reference wake-up timing, and

the controller shifts the wake-up timing from the different reference wake-up timing back to the reference wake-up timing, when the predetermined radio band at the different wake-up timing is occupied by a different radio terminal.

2. The radio terminal according to claim 1 , wherein

the acquiring unit acquires the reference wake-up timing from the radio base station.

3. The radio terminal according to claim 1 , wherein

the acquiring unit acquires the reference wake-up timing from another radio terminal.

4. The radio terminal according to claim 1 , wherein

the acquiring unit autonomously acquires the reference wake-up timing.

5. The radio terminal according to any one of claims 2 to 4 , wherein

the reference wake-up timing is determined based on a usage state of the predetermined radio band.

6. The radio terminal according to any one of claims 2 to 4 , wherein

the reference wake-up timing is determined based on a length of time used for radio communication.

7. The radio terminal according to claim 1 , further comprising a monitor configured to monitor a usage state of the predetermined radio band in the wake-up state, wherein

the controller shifts the wake-up timing from the reference wake-up timing, based on the usage state of the predetermined radio band.

8. The radio terminal according to claim 1 , wherein

the controller shifts the wake-up timing from the reference wake-up timing, based on QoS information set for the radio communication performed by the radio terminal.

9. The radio terminal according to claim 1 , wherein

the controller shifts the wake-up timing from the reference wake-up timing, based on an error rate of the radio communication performed by the radio terminal.

10. The radio terminal according to claim 1 , further comprising a battery configured to provide electric power to the radio interface, wherein

the controller shifts the wake-up timing from the reference wake-up timing, based on a remaining amount of electric power of the battery.

11. The radio terminal according to any one of claims 8 to 10 , wherein

an upper limit is defined for a shift amount by which the wake-up timing is shifted from the reference wake-up timing, and

the controller shifts the wake-up timing from the reference wake-up timing without exceeding the upper limit for the shift amount.

12. The radio terminal according to any one of claims 8 to 10 , wherein

the controller shifts the wake-up timing from the reference wake-up timing when a different radio terminal performs radio communication immediately before the radio terminal has shifted the wake-up timing from the reference wake-up timing.

13. The radio terminal according to claim 1 , wherein

the controller controls a current shift amount by which the wake-up timing is shifted from the reference wake-up timing in a current shift, and

the controller controls a shift amount of a next shift, based on the current shift amount of the current shift.

14. The radio terminal according to claim 1 , wherein

the controller shifts the wake-up timing from the reference wake-up timing to the different reference wake-up timing that identifies an earlier time slot relative to the reference wake-up timing, and

the controller shifts the wake-up timing from the different reference wake-up timing back to the reference wake-up timing, when the earlier time slot is occupied by the different radio terminal.

15. A radio communication system comprising:

a radio base station; and

a plurality of radio terminals each having a radio interface configured to allow radio communication with the radio base station by using a predetermined radio band;

a controller configured to control switching between a wake-up state in which the radio interface is turned on and a sleep-state in which the radio interface is turned off; and

a setter configured to set a reference wake-up timing scheduled as a wake-up timing for switching from the sleep state to the wake-up state, wherein

the controller shifts the wake-up timing from the reference wake-up timing to a different reference wake-up timing, and

the controller shifts the wake-up timing from the different reference wake-up timing back to the reference wake-up timing, when the predetermined radio band at the different wake-up timing is occupied by a different radio terminal.

16. A radio communication method for performing radio communication by using a predetermined radio band in a radio communication system including a radio base station and a plurality of radio terminals each having a radio interface configured to allow radio communication with the radio base station, the radio communication method comprising:

controlling switching between a wake-up state in which the radio interface is turned on and a sleep-state in which the radio interface is turned off;

setting a reference wake-up timing scheduled as a wake-up timing for switching from the sleep state to the wake-up state;

shifting the wake-up timing from the reference wake-up timing to a different reference wake-up timing, and

shifting the wake-up timing from the different reference wake-up timing back to the reference wake-up timing, when the predetermined radio band at the different wake-up timing is occupied by a different radio terminal.