Digital communication system using telephone line and initializing method thereof

1. An initializing method of a digital communication system using a telephone line, the method comprising the steps of:

(a) setting to a predetermined maximum value a gain of an amplifier for amplifying a signal received through the telephone line;

(b) transmitting a signal for requesting to establish a communications channel;

(c) reducing the gain of the amplifier to a predetermined level when a peak value of the received signal outputted from the amplifier during a predetermined time period is larger than a reference value;

(d) converting the received signal in a time-domain to signals in a frequency-domain;

(e) detecting a frequency of a signal that has the greatest intensity among the signals in the frequency-domain; and

(f) repeating the steps (b) to (e) until the signals of detected frequencies within a desired frequency band are inputted by a predetermined number.

2. The initializing method of claim 1 , wherein the amplifier is a programmable gain amplifier.

3. The initializing method of claim 1 , wherein the signal received through the telephone line is an analog signal.

4. The initializing method of claim 3 , after performing the step (a), further comprising the step (a- 1 ) converting the received signal outputted from the amplifier to a digital signal.

5. The initializing method of claim 1 , wherein the step (f) comprises the steps of:

determining whether the detected frequencies are within the desired frequency band;

returning to the step of transmitting the signal when each of the detected frequencies is not within the desired frequency band; and

returning to the step of transmitting the signal until a predetermined number of signals within the desired frequency band are inputted when the detected frequencies are within the desired frequency band.

6. The initializing method of claim 1 , wherein the digital communication system employs a data modulation method of discrete multi-tone (DMT).

7. The initializing method of claim 6 , wherein the desired frequency band is a frequency band corresponding to a desired tone among a plurality of tones.

8. A method of initializing a digital communication system using a telephone line, the method comprising the steps of:

(a) setting to a predetermined maximum value a gain of an amplifier for amplifying an analog signal received through the telephone line;

(b) transmitting a signal for requesting to establish a communication channel;

(c) converting the analog signal to a digital signal;

(d) detecting a peak value of digital signals during a predetermined time;

(e) comparing a detected peak value with a reference value;

(f) reducing the gain of the amplifier to a predetermined level when the detected peak value is larger than the reference value;

(g) converting the digital signals in a time-domain to signals in a frequency-domain;

(h) detecting a frequency of a signal that has the greatest intensity among the signals in the frequency-domain;

(i) determining whether a detected frequency is within a desired frequency band;

(j) returning to the step of transmitting the signal when the detected frequency is within the desired frequency band; and

(k) repeating the steps (b) to (j) until a predetermined number of signals in the detected frequency band are inputted when the detected frequency is within the desired frequency band.

9. The initializing method of claim 8 , wherein the amplifier is a programmable gain amplifier.

10. The initializing method of claim 8 , wherein the digital communication system employs a data modulation method of discrete multi-tone (DMT).

11. A digital communication system using a telephone line, the system comprising:

a controller for outputting a signal requesting to establish a communication channel;

an amplifier for controlling an amplitude of an analog signal received through the telephone line according to a gain of the amplifier; and

an analog-to-digital converter for converting an amplitude-controlled analog signal to a digital signal,

wherein the controller comprises:

a gain controller for receiving the digital signal and decreasing the gain of the amplifier when a peak value of the digital signals is larger than a reference value; and

a fast Fourier transformer for transforming the digital signals in a time-domain to signals in a frequency-domain, and

wherein the controller outputs the signal for requesting to establish the communication channel until a predetermined number of signals having detected frequencies in a desired frequency band are inputted.

12. The digital communication system of claim 11 , wherein the amplifier is a programmable gain amplifier.

13. The digital communication system of claim 8 , wherein the digital communication system employs a data modulation method of discrete multi-tone (DMT).