Radio communication system, network side device, small cell base station, and transmission power control method

A small cell base station which forms a small cell smaller than a large cell formed by a large cell base station and is installed within the large cell, comprising:

• a receiver configured to receive upper-limit value information from a network side device which is formed of at least one of the large cell base station and an upper-level device of the large cell base station;
• a maximum value determination unit configured to determine a maximum value of transmission power of a radio terminal based on the upper-limit value information received by the receiver and a propagation loss value indicating a propagation loss from the radio terminal connected to the small cell base station to the large cell base station;
• and
• a transmission power controller configured to control transmission power of the radio terminal so that the transmission power does not exceed the maximum value determined by the maximum value determination unit, wherein
• the upper-limit value information indicates an upper-limit value of an amount of interference which is received by the large cell base station from one radio terminal, and
• the upper-limit value is determined based on a permissible value of a total amount of interference which is received by the large cell base station from radio terminals connected to the small cell base station within the large cell and the number of small cell base stations within the large cell.

A transmission power control method of controlling transmission powers of radio terminals connected to small cell base stations in a radio communication system in which each of the small cell base stations forms a small cell smaller than a large cell formed by a large cell base station and the small cell base stations are installed within the large cell, comprising the steps of:

• determining, by a network side device which is formed of at least one of the large cell base station and an upper-level device of the large cell base station, an upper-level value of an amount of interference which is received by the large cell base station from each of the radio terminals based on a permissible value of a total amount of interference which is received by the large cell base station from the radio terminals and the number of the small cell base stations within the large cell;
• and
• transmitting upper-limit value information indicating the determined upper-limit value from the network side device to the small cell base stations, and
• receiving, by the small cell base stations, the upper-limit value information from the network side device;
• determining, by the small cell base stations, a maximum value of transmission powers of the respective radio terminals based on the received upper-limit value information and a propagation loss value indicating a propagation loss from the respective radio terminals to the large cell base station;
• and
• controlling, by the small cell base stations, transmission power of each of the radio terminals so that the transmission power does not exceed the determined maximum value.