Cell reselection control method

1. A cell reselection control method comprising:

transmitting, by a base station configured to manage a cell having a first coverage and a second coverage as a portion enhanced more than the first coverage, to a radio terminal under the cell, a reselection instruction which instructs to reselect a neighboring cell different from the cell;

determining, by the radio terminal, whether the radio terminal is in the first coverage or the second coverage based on one or more cell signal thresholds associated with the second coverage;

receiving, by the radio terminal in RRC idle mode, the reselection instruction when the radio terminal is in the second coverage;

reselecting, by the radio terminal in the RRC idle mode, the neighboring cell according to the reselection instruction when the radio terminal is in the second coverage; and

ignoring, by the radio terminal in the RRC idle mode, the reselection instruction when the reselection instruction is received by the radio terminal in the first coverage.

2. The cell reselection control method according to claim 1 , wherein

in the transmitting the reselection instruction, the base station transmits the reselection instruction to the radio terminal in the RRC idle mode which is in the second coverage, and

in the reselecting the neighboring cell, the radio terminal which is in the second coverage reselects the neighboring cell according to reception of the reselection instruction.

3. The cell reselection control method according to claim 1 , wherein

if the radio terminal receives the reselection instruction when the radio terminal is in the first coverage, in the reselecting the neighboring cell, the radio terminal reselects the neighboring cell according to the reselection instruction when the radio terminal moves from the first coverage to the second coverage.

4. The cell reselection control method according to claim 1 , wherein

the reselecting the neighboring cell includes reselecting, by the radio terminal, the neighboring cell belonging to a same frequency as a frequency to which the cell belongs.

5. The cell reselection control method according to claim 4 , wherein

the transmitting the information indicating the allowable reception level difference includes transmitting, by the base station, information indicating a first allowable reception level difference used for the reselection of the neighboring cell belonging to the same frequency as the frequency to which the cell belongs and information indicating a second allowable reception level difference used for the reselection of the neighboring cell belonging to a frequency different from the frequency to which the cell belongs.

6. The cell reselection control method according to claim 1 , wherein

the second coverage is associated with a plurality of coverage enhancement levels having different degrees of coverage enhancement, and

the transmitting the reselection instruction includes transmitting, by the base station, the reselection instruction to the radio terminal of a specific coverage enhancement level among the plurality of coverage enhancement levels.

7. The cell reselection control method according to claim 1 , wherein

the transmitting the reselection instruction includes transmitting, by the base station, information indicating an allowable reception level difference between the cell and the neighboring cell to the radio terminal, and

the reselecting the neighboring cell includes reselecting, by the radio terminal, the neighboring cell when a reception level difference between the cell and the neighboring cell is within the allowable reception level difference.

8. The cell reselection control method according to claim 1 , further comprising:

transmitting, by the base station, to the radio terminal, a timer value indicating a period during which the cell is excluded from a reselection candidate after the neighboring cell is reselected; and

excluding, by the radio terminal, the cell from the reselection candidate during the period indicated by the timer value after the neighboring cell is reselected according to the reception of the reselection instruction.

9. A cell reselection control method comprising:

transmitting, by a base station configured to manage a cell having a first coverage and a second coverage as a portion enhanced more than the first coverage, intra-frequency reselection information indicating that a reselection of a neighboring cell belonging to a same frequency as a frequency of the cell is not allowed to be performed during an access restriction when the access restriction to the cell is set;

determining, by the radio terminal, whether the radio terminal is in the first coverage or the second coverage based on one or more cell signal thresholds associated with the second coverage;

reselecting, by the radio terminal in an RRC idle mode which is in the second coverage, the neighboring cell belonging to the same frequency as the frequency of the cell regardless of the intra-frequency reselection information, even when the radio terminal which is in the second coverage and in the RRC idle mode receives the intra-frequency reselection information; and

performing a control to not reselect the neighboring cell belonging to the same frequency as the frequency of the cell, by the radio terminal in the RRC idle mode which is in the first coverage, when the radio terminal which is in the first coverage receives the intra-frequency reselection information.

10. The cell reselection control method according to claim 9 , further comprising:

transmitting, by the base station, to the radio terminal, a timer value indicating a period during which the cell is excluded from a reselection candidate after the neighboring cell is reselected; and

excluding, by the radio terminal, the cell from the reselection candidate during the period indicated by the timer value after the neighboring cell is reselected.