Radio communication system, mobile relay station, mobile station, and radio communication method

1. A radio communication system comprising:

a plurality of base stations;

a mobile relay station configured to

select a base station from among the plurality of base stations,

relay radio communication between the selected base station and a mobile station, and

notify the mobile station of mobility state information of the mobile relay station determined based on a number of base stations selected within a specified time; and

the mobile station configured to select a base station based on the mobility state information when the mobile station switches a device to be communicated with from the mobile relay station.

2. The radio communication system according to claim 1 , wherein the mobile station is further configured to:

detect an abnormality of the mobile relay station, and

switch the device to be communicated with from the mobile relay station to the base station when the abnormality is detected, and

select the base station based on the mobility state information when the device to be communicated with is switched to the base station.

3. The radio communication system according to claim 2 , wherein the mobile station is further configured to:

receive a parameter included in a specified evaluation formula for evaluating a communication quality of a cell, and

detect an occurrence of an overload on the mobile relay station as the abnormality when an amount of change in the parameter exceeds a specified threshold value.

4. The radio communication system according to claim 2 , wherein

the mobile relay station is further configured to transmit to the mobile station a reference radio wave which is a radio wave used to determine a radio communication quality between the mobile relay station and the mobile station, and

the mobile station is further configured to measure a radio field strength of the reference radio wave transmitted from the mobile relay station, and detect an occurrence of a malfunction in the mobile relay station as the abnormality when the radio field strength falls below a specified threshold value.

5. The radio communication system according to claim 1 , wherein the mobile station is further configured to:

correct, in accordance with the mobility state information, a parameter included in a specified evaluation formula for evaluating a communication quality of a cell, and

select the base station by using the specified evaluation formula including the corrected parameter.

6. A mobile relay station to relay radio communication between a base station and a mobile station, the mobile relay station comprising:

a processor configured to

select a base station from among a plurality of base stations, and

determine mobility state information of the mobile relay station based on a number of base stations selected by the processer within a specified time; and

a transmitter to notify the mobile station of the mobility state information of the mobile relay station.

7. A mobile station that performs radio communication with a base station, which is relayed by a mobile relay station, the mobile station comprising:

a receiver configured to receive mobility state information determined based on a number of base stations selected by the mobile relay station within a specified time, the mobility state information indicating the mobility state of the mobile relay station; and

a selector to select a base station based on mobility state information when a device to be communicated with the mobile station is switched from the mobile relay station.

8. A radio communication method of a mobile station that performs radio communication with a base station, which is relayed by a mobile relay station, the method comprising:

receiving mobility state information determined based on a number of base stations selected by the mobile relay station within a specified time, the mobility state information indicating the mobility state of the mobile relay station; and

selecting a base station based on the mobility state information when a device to be communicated with the mobile station is switched from the mobile relay station.