Communication terminal

1. A communication terminal that calculates the communication quality of a signal transmitted from a radio base station, for each of multiple subbands into which a system bandwidth is divided, comprising:

a determining unit that determines, based on the number of resource blocks, as the unit of radio resource, in the entire system band, and based on the number of resource blocks for each of the subbands, designated in accordance with the number of resource blocks in the entire system band in advance, whether a small band or a subband formed of a lower number of resource blocks than the number of resource blocks for each of the subbands is present;

a noise power calculator that calculates noise power of the signal for each of the subbands, using reference signals included in the signal transmitted from the radio base station;

a signal power calculator that calculates signal power of the signal for each of subbands, using the reference signals and the noise power calculated by the noise power calculator;

a channel capacity calculator that calculates channel capacity for each of the subbands, based on the noise power and the signal power; and,

a CQI transmitter that transmits CQI (Channel Quality Information) to the radio base station, based on the channel capacity, wherein

the noise power calculator, when the determining unit determines that the small subband is present, calculates the noise power as combined noise power, using the reference signals included in the small subband and the adjacent subband next to the small subband,

the signal power calculator, when the determining unit determines that the small subband is present, calculates the signal power as combined signal power, using the reference signals included in the small subband and the adjacent subband next to the small subband and the combined noise power, and

the channel capacity calculator calculates combined channel capacity based on the combined noise power and the combined signal power, and calculates channel capacity in the small subband based on the combined channel capacity and the channel capacity calculated in the adjacent subband.

2. The communication terminal according to claim 1 , wherein the channel capacity calculator calculates a SNR (Signal to Noise Ratio) based on the noise power and the signal power, calculates the channel capacity based on the SNR, calculates a combined SNR based on the combined noise power and the combined signal power and calculates the combined channel capacity based on the combined SNR.

3. The communication terminal according to claim 1 , wherein the noise power calculator calculates the noise power and the combined noise power using the ZF (Zero Forcing) value of the reference signal, and

the signal power calculator calculates the signal power using the ZF value of the reference signal and the noise power and calculates the combined signal power using the ZF value of the reference signal and the combined noise power.

4. The communication terminal according to claim 1 , characterized by operating on the LTE (Long Term Evolution) standard.

5. A communication quality calculation method for calculating the communication quality of a signal transmitted from a radio base station to a communication terminal, for each of multiple subbands into which a system bandwidth is divided, comprising:

a process of determining, based on the number of resource blocks, as the unit of radio resource, in the entire system band, and based on the number of resource blocks for each of the subbands, designated in accordance with the number of resource blocks in the entire system band, whether a small band or a subband formed of a lower number of resource blocks than the number of resource blocks for each of the subbands is present;

a process of calculating noise power of the signal for each of the subbands, using reference signals included in the signal transmitted from the radio base station to the communication terminal;

a process of calculating signal power of the signal for each of subbands, using the reference signals and the noise power;

a process of calculating channel capacity for each of the subbands, based on the noise power and the signal power;

a process of calculating the noise power as combined noise power, using the reference signals included in the small subband and the adjacent subband next to the small subband when it is determined that the small subband is present;

a process of calculating the signal power as combined signal power, using the reference signals included in the small subband and the adjacent subband next to the small subband and the combined noise power, when it is determined that the small subband is present;

a process of calculating combined channel capacity based on the combined noise power and the combined signal power;

a process of calculating channel capacity in the small subband, based on the combined channel capacity and the channel capacity calculated in the adjacent subband; and,

a process of transmitting CQI (Channel Quality Information) from the communication terminal to the radio base station, based on the channel capacity.

6. The communication quality method according to claim 5 , further comprising:

a process of calculating a SNR (Signal to Noise Ratio) based on the noise power and the signal power;

a process of calculating the channel capacity based on the SNR;

a process of calculating a combined SNR based on the combined noise power and the combined signal power; and,

a process of calculating the combined channel capacity based on the combined SNR.

7. The communication quality method according to claim 5 , further comprising:

a process of calculating the noise power and the combined noise power using the ZF (Zero Forcing) value of the reference signal;

a process of calculating the signal power using the ZF value of the reference signal and the noise power; and,

a process of calculating the combined signal power using the ZF value of the reference signal and the combined noise power.