Base station apparatus

1. A base station apparatus installed in a small-cell base station of a small cell, the small-cell base station and the small cell being located in a macro cell, which communicates with a mobile station in a mobile communication network, the base station apparatus in the small-cell base station comprising:

a control section that acquires load information L1 of the small cell located in the macro cell and load information L2 of the macro cell including the small cell, increments a counter n when the difference (L1−L2) between the L1 and the L2 is larger than a preset threshold Lth within a predetermined time, adjusts a setting of an offset (Ocn) for the macro cell in a conditional expression for handover from the small cell to the macro cell to advance a hand-out from the small cell to the macro cell, including by increasing the setting of offset (Ocn) when the incremented value of the counter n within the predetermined time is larger than a predetermined number of times Ninc before a control of a downlink transmission power of the small-cell base station, and controls a decreasing of the downlink transmission power of the small-cell base station to decrease an interference from the small cell to the mobile station handovered from the small cell to the macro cell when the setting of offset (Ocn) is increased after the adjusted value of offset Ocn reaches a predetermined maximum value or minimum value.

2. The base station apparatus according to claim 1 , wherein the control section controls to decrement the counter n when the difference (L2−L1) between the L1 and the L2 is larger than the preset threshold Tdec or the difference (L2−L1) is equal to or larger than the threshold Tdec within a predetermined time, to decrease the setting of offset (Ocn) to delay the hand-out from the small cell to the macro cell when the incremented value of the counter n within the predetermined time is smaller than a predetermined number of times Ndec or the incremented value is equal to or smaller than the predetermined number of times Ndec, and controls to increase the downlink transmission power of the small-cell base station when the setting of offset (Ocn) is decreased.

3. The base station apparatus according to claim 2 , wherein the control section preferentially performs the setting change of the offset (Ocn) for handover and performs the control to increase the downlink transmission power after the offset (Ocn) become a predetermined maximum value or minimum value.

4. The base station apparatus according to claim 1 , wherein the counter n is incremented when the difference (L1−L2) is equal to or larger than the threshold Lth.

5. The base station apparatus according to claim 1 , wherein the offset (Ocn) is increased when the incremented value of the counter n within the predetermined time is equal to or larger than the predetermined number of times Ninc.

6. For a base station apparatus installed in a small-cell base station of a small cell, the small-cell base station and the small cell located in a macro cell and in communication with a mobile station in a mobile communication network, a method comprising:

acquiring load information L1 of the small cell and load information L2 of the macro cell;

if a difference (L1−L2) between the L1 and the L2 is larger than a first preset threshold within a predetermined time, incrementing a counter n;

performing a first adjustment of a value of an offset for the macro cell in a conditional expression for handover from the small cell to the macro cell, including increasing the value of the offset if the incremented value of the counter n within the predetermined time is larger than a predetermined value, Ninc; and

in response to the adjusted value of the offset reaching a predetermined maximum value or minimum value, controlling a decrease in a downlink transmission power of the small-cell base station.

7. The method according to claim 6 , wherein decreasing the downlink transmission power decreases an interference from the small cell to the mobile station handovered from the small cell to the macro cell when the value of the offset is adjusted.

8. The method according to claim 6 , wherein performing the first adjustment of the value of the offset advances a hand-out from the small cell to the macro cell.

9. The method according to claim 6 , wherein the first adjustment is an increase of the value of the offset.

10. The method according to claim 6 , further comprising:

if a difference (L2−L1) between the L1 and the L2 is larger than a second preset threshold within a predetermined time, decrementing the counter n;

if the incremented value of the counter n within the predetermined time is smaller than a predetermined value, Ninc, performing a second adjustment of the value of the offset; and

controlling an increase in the downlink transmission power of the small-cell base station if the second adjustment of the value of the offset is performed.

11. The method according to claim 10 , wherein performing the second adjustment of the value of the offset delays a hand-out from the small cell to the macro cell.

12. The method according to claim 11 , wherein the increase in the downlink transmission power is controlled after the value of the offset becomes a predetermined maximum value or predetermined minimum value.

13. The method according to claim 11 , wherein the second adjustment is a decrease of the value of the offset.