Band limiting method and wireless communication system

1. A band limiting method for limiting a bandwidth of a signal that is transmitted/received between a transmitter and a receiver, the method comprising:

said receiver estimating a channel quality;

said transmitter amplifying the signal by a gain proportional to a difference between a required signal-to-noise power ratio and channel quality information, which is an estimation result of the channel quality, and transmitting the signal so that said receiver can obtain said signal-to-noise power ratio;

said receiver determining a roll-off rate of an adaptive filter that causes the filtering of a signal by said transmitter and said receiver to have roll-off characteristics based on said channel quality information; and

said transmitter using said adaptive filter including the determined roll-off rate to filter and transmit the signal.

2. A band limiting method for limiting a bandwidth of signal that is transmitted/received between a transmitter and a receiver, the method comprising:

said receiver estimating a channel quality;

said transmitter amplifying the signal by a gain proportional to a difference between a required signal-to-noise power ratio and channel quality information, which is an estimation result of the channel quality, and transmitting the signal so that said receiver can obtain said signal-to-noise power ratio;

said transmitter determining a roll-off rate of an adaptive filter that causes the filtering of a signal by said transmitter and said receiver to have roll-off characteristics based on said channel quality information; and

said transmitter using said adaptive filter including the determined roll-off rate to filter and transmit the signal.

3. The band limiting method according to claim 1 , wherein

the larger the transmission power of said signal, the larger is the value of said roll-off rate that is set.

4. The band limiting method according to claim 1 , wherein

a total frequency band used for transmission/reception of a signal between the transmitter and the receiver is divided into a plurality of frequency blocks, and

the frequency blocks used for transmission/reception of a signal are respectively allocated in accordance with values of said determined roll-off rate.

5. The band limiting method according to claim 4 , wherein

a frequency block located at a band edge of a total frequency band used for transmission/reception of a signal between said transmitter and said receiver among said plurality of frequency blocks is used for transmission/reception of a signal whose value corresponds to the smallest value of said roll-off rate.

6. The band limiting method according to claim 4 , wherein

a bandwidth of a frequency block used for transmission/reception of a signal whose value corresponds to the largest value of said roll-off rate among said plurality of frequency blocks is made widest.

7. A wireless communication system for limiting the bandwidth of a signal that is transmitted/received between a transmitter and a receiver, said receiver comprising:

a channel quality estimator that estimates a channel quality; and

a roll-off rate determination section that determines a roll-off rate of an adaptive filter that causes the filtering of a signal by said transmitter and said receiver to have roll-off characteristics based on channel quality information that is an estimation result of said channel quality, and said transmitter comprising:

a variable gain amplifier that amplifies the signal by a gain proportional to a difference between a required signal-to-noise power ratio and said channel quality information and transmits the signal so that said receiver can obtain said signal-to-noise power ratio; and

an adaptive filter that filters the signal to be transmitted at the roll-off rate determined by said roll-off rate determination section.

8. A wireless communication system for limiting the bandwidth of a signal that is transmitted/received between a transmitter and a receiver, said receiver comprising:

a channel quality estimator that estimates a channel quality, and said transmitter comprising:

a roll-off rate determination section that determines a roll-off rate of an adaptive filter that causes the filtering of a signal by said transmitter and said receiver to have roll-off characteristics based on channel quality information that is an estimation result of said channel quality;

a variable gain amplifier that amplifies the signal by a gain proportional to a difference between a required signal-to-noise power ratio and said channel quality information and transmits the signal so that said receiver can obtain said signal-to-noise power ratio; and

an adaptive filter that filters the signal to be transmitted at the roll-off rate determined by said roll-off rate determination section.

9. The wireless communication system according to claim 7 , wherein

the larger the transmission power of said signal, the larger is the value of said roll-off rate that is set by said roll-off rate determination section.

10. The wireless communication system according to claim 7 , wherein

said transmitter and said receiver divide a total frequency band used for transmission/reception of a signal into a plurality of frequency blocks and

respectively allocate the frequency blocks used for transmission/reception of a signal in accordance with values of said determined roll-off rate.

11. The wireless communication system according to claim 10 , wherein

said transmitter and said receiver use a frequency block located at a band edge of a total frequency band used for transmission/reception of a signal among said plurality of frequency blocks for transmission/reception of a signal whose value corresponds to the smallest value of said roll-off rate.

12. The wireless communication system according to claim 10 , wherein

said transmitter and said receiver make a bandwidth of a frequency block used for transmission/reception of a signal whose value corresponds to said roll-off rate with the largest value among said plurality of frequency blocks widest.

13. A program for causing a computer to execute a process for limiting the bandwidth of a signal to be transmitted/received, the program causing a computer to execute processes of:

estimating a channel quality of a received signal;

amplifying the signal in a variable gain amplifier by a gain proportional to a difference between a required signal-to-noise power ratio and channel quality information, which is an estimation result of the channel quality, and transmitting the signal so that said signal-to-noise power ratio can be obtained by said received signal; and

filtering the signal to be transmitted/received by roll-off characteristics having a roll-off rate determined based on said channel quality information which is an estimation result of said channel quality.

14. The program according to claim 13 , wherein

the larger the transmission power of the signal, the larger is the value of said roll-off rate that must be set by process executed by a computer.

15. The program according to claim 13 , said program causing the computer to execute processes of:

dividing a total frequency band used for transmission/reception of a signal into a plurality of frequency blocks, and

respectively allocating said frequency blocks used for transmission/reception of a signal in accordance with values of said determined roll-off rate.

16. The program according to claim 15 , said program causing the computer to execute a process of using a frequency block located at a band edge of a total frequency band used for transmission/reception of a signal among said plurality of frequency blocks for transmission/reception of a signal whose value corresponds to the smallest value of said roll-off rate.

17. The program according to claim 15 , said program causing the computer to execute a process of making a bandwidth of a frequency block used for transmission/reception of a signal whose value corresponds to said roll-off rate with the largest value among said plurality of frequency blocks widest.