Method and apparatus for optimizing dynamic range in DMT modems

1. A digital subscriber line communication system, the communication system comprising:

a digital subscriber line access multiplexer (DSLAM) for distributing a near end crosstalk (NEXT) model of anticipated disturbance from neighboring disturber subscriber lines; and

at least one modem having a transmit path and a receive path and coupled to the DSLAM, the modem using the distributed NEXT model to adjust a dynamic range of an analog portion of the receive path.

2. The communication system of claim 1 , wherein the modem adjusts the dynamic range of the analog portion of the receive path to accommodate the anticipated disturbance modeled in the distributed NEXT model.

3. The communication system of claim 1 , wherein the adjusted range is large enough to substantially avoid clipping of a received signal and at the same time not so large as to result in significant excess dynamic range.

4. The communication system of claim 1 , wherein the receive path comprises:

an analog-to-digital converter (ADC) with an output coupled to remaining components of the receive path, and an input, and the ADC digitizing a received analog signal; and

an analog gain control (AGC) with an input coupled to the received signal and an output coupled to the input of the ADC, wherein a level of the AGC is utilized to adjust the dynamic range of the analog portion of the receive path.

5. The communication system of claim 1 , wherein the at least one modem further comprises:

an analog-to-digital converter (ADC) receive path component with an output coupled to remaining components of the receive path, and an input, wherein the ADC digitizes a received analog signal;

an analog gain control (AGC) receive path component with an input coupled to the received signal and an output coupled to the input of the ADC, wherein a level of the AGC is utilized to adjust the dynamic range of the analog portion of the receive path; and

a range optimizer component coupled to the receive path, and responsive to the NEXT model to adjust the dynamic range of the analog portion of the receive path by injecting a disturber signal into the receive path during a training phase of operation and by adjusting the AGC to substantially avoid clipping thereof.

6. The communication system of claim 1 , wherein the at least one modem further comprises:

an analog-to-digital converter (ADC) receive path component with an output coupled to remaining components of the receive path, and an input, wherein the ADC digitizes a received analog signal;

an analog gain control (AGC) receive path component with an input coupled to the received signal and an output coupled to the input of the ADC, wherein a level of the AGC is utilized to adjust the dynamic range of the analog portion of the receive path; and

a range optimizer component coupled to the receive path, and responsive to the NEXT model to adjust the dynamic range of the analog portion of the receive path by calculating the anticipated disturbance modeled in the distributed NEXT model during a training phase of operation and by adjusting the AGC to substantially avoid clipping thereof.

7. The communication system of claim 1 , wherein the subscriber lines carry xDSL multi-tone modulated communications.

8. A modem comprising:

a transmit path and a receive path for respectively modulating and demodulating a communication channel;

a near end crosstalk (NEXT) model of anticipated disturbance from neighboring disturber subscriber lines; and

a range optimizer component coupled to the receive path, the range optimizer component using the NEXT model to adjust a dynamic range of an analog portion of the receive path.

9. The modem of claim 8 , wherein the range optimizer component adjusts the dynamic range of the analog portion of the receive path to accommodate the anticipated disturbance modeled in the distributed NEXT model.

10. The modem of claim 8 , wherein the adjusted range is large enough to substantially avoid clipping of a received signal and at the same time not so large as to result in significant excess dynamic range.

11. The modem of claim 8 , wherein the receive path of the at least one modem further comprises:

an analog-to-digital converter (ADC) with an output coupled to remaining components of the receive path, and an input, wherein the ADC digitizes a received analog signal; and

an analog gain control (AGC) with an input coupled to the received signal and an output coupled to the input of the ADC, wherein a level of the AGC is utilized to adjust the dynamic range of the analog portion of the receive path.

12. The modem of claim 8 , further comprising:

an analog-to-digital converter (ADC) receive path component with an output coupled to remaining components of the receive path, and an input, wherein the ADC digitizes a received analog signal;

an analog gain control (AGC) receive path component with an input coupled to the received signal and an output coupled to the input of the ADC, wherein a level of the AGC is utilized to adjust the dynamic range of the analog portion of the receive path,

wherein the range optimizer component adjusts the dynamic range of the analog portion of the receive path by injecting a disturber signal into the receive path during a training phase of operation and by adjusting the AGC to substantially avoid clipping thereof.

13. The modem of claim 8 , further comprising:

an analog-to-digital converter (ADC) receive path component with an output coupled to remaining components of the receive path, and an input, wherein the ADC digitizes a received analog signal; and

an analog gain control (AGC) receive path component with an input coupled to the received signal and an output coupled to the input of the ADC, and a level of the AGC utilized to adjust the dynamic range of the analog portion of the receive path,

wherein the range optimizer component adjusts the dynamic range of the analog portion of the receive path by calculating the anticipated disturbance modeled in the distributed NEXT model during a training phase of operation and by adjusting the AGC to substantially avoid clipping thereof.

14. The modem of claim 8 , wherein the communication channel carries xDSL multi-tone modulated communications.

15. A method for operating a modem having a transmit path and a receive path, the method comprising:

obtaining a near end crosstalk (NEXT) model of anticipated disturbance from neighboring disturber subscriber lines; and

adjusting a dynamic range of an analog portion of the receive path to accommodate the anticipated disturbance modeled in the distributed NEXT model.

16. The method of claim 15 , wherein the adjusted range is large enough to substantially avoid clipping of a received signal and at the same time not so large as to result in significant excess dynamic range.

17. The method of claim 15 , further comprising:

adjusting a gain of the received signal to substantially avoid clipping of the received signal including the anticipated disturbance thereto resulting from neighboring disturber subscriber lines.

18. The method of claim 15 , further comprising:

injecting a disturber signal into the receive path during a training phase of operation; and

adjusting a gain of the received signal to substantially avoid clipping thereof.

19. The method of claim 15 , further comprising:

calculating the anticipated disturbance modeled in the distributed NEXT model during a training phase of operation; and

adjusting a gain of the received signal to substantially avoid clipping thereof.