Method and apparatus for reducing peak-to-average power ratio in a discrete multi-tone signal

• US 6,674,810 B1
• Filed: 05/27/1999
• Issued: 01/06/2004
• Est. Priority Date: 05/27/1999
• Status: Expired due to Fees

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Cheng, Yaqi
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/321,523
• Time in Patent Office: 1,685 Days
• Field of Search: 375/316, 375/296, 375/260, 375/285, 370/69.1, 370/110.2, 370/110.3, 370/317, 370/525
• US Class Current: 375/296
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04L 27/2618 Reduction thereof using auxiliary subcarriers

Abstract

A method and apparatus for reducing peak-to-average power ratio in a discrete multi-tone signal. A shaping signal is generated and added to a discrete multi-tone signal to be transmitted. The shaping signal includes tones that are outside a transmission band assigned to the discrete multi-tone signal to be transmitted. One or more filters may be used to suppress the shaping function after digital-to-analog conversion has been performed. Alternatively, echo cancellation may be performed to cancel feedback tones associated with the transmit signal and shaping signal that may occur on the receive path of a discrete multi-tone transceiver. The peak-to-average power ratio reduction method and apparatus may be used in an ADSL modem in one embodiment.

Claims

1. In a discrete multi-tone transceiver, a method for reducing peak-to-average power ratio in a transmit signal, comprising the steps of:

interpolating a discrete multi-tone signal to produce an interpolated discrete multi-tone signal;

determining whether a peak magnitude exceeds a pre-determined magnitude parameter, wherein the peak magnitude is associated with either of the discrete multi-tone signal or the interpolated discrete multi-tone signal;

adding a shaping signal to the interpolated discrete multi-tone signal to produce a modified signal, in response to determining that the peak magnitude exceeds the pre-determined magnitude parameter, wherein the shaping signal consists entirely of tones located outside a transmission band allocated to the discrete multi-tone signal;

converting the modified signal to an analog transmit signal; and

canceling feedback tones introduced to a receive signal within the discrete multi-tone transceiver, wherein the feedback tones are associated with the shaping signal.

2. A computer readable medium having stored therein instructions for causing a processing unit to execute the method of claim 1.

3. The method of claim 1, wherein the discrete multi-tone transceiver is an asymmetric digital subscriber line modem.

4. The method of claim 1, wherein the step of adding a shaping signal to the interpolated discrete multi-tone signal includes:

generating the shaping signal from a pre-determined shaping function, wherein the shaping signal is centered on a peak in the interpolated discrete multi-tone signal, and wherein the shaping signal consists entirely of tones located outside the transmission band allocated to the discrete multi-tone signal; and

adding the shaping signal to the interpolated discrete multi-tone signal to produce a reduced peak magnitude.

5. The method of claim 1, wherein the step of canceling feedback tones comprises:

determining whether the canceling of feedback tones is effective in removing a shaping component associated with the shaping signal; and

filtering the analog transmit signal to suppress a shaping component associated with the shaping signal in response to determining that the canceling of feedback tones is not effective in removing the shaping component associated with the shaping signal.

6. The method of claim 1, wherein the step of canceling feedback tones is performed by subtracting an echo cancellation parameter from the receive signal, wherein the echo cancellation parameter is derived at least in part from the modified signal.

7. The method of claim 1, wherein the pre-determined magnitude parameter is derived from a specified peak-to-average ratio parameter.

8. A discrete multi-tone transmitter, comprising in combination:

an Inverse Fast Fourier Transform that transforms transmit signals from a frequency domain to a time domain;

an interpolation unit that interpolates the transmit signals to produce tones located outside a transmission band allocated to the transmit signals;

a shaping signal generator that generates a shaping signal from tones located outside the transmission band allocated to the transmit signals in response to a transmit signal exceeding a pre-determined magnitude parameter;

an adder that adds the shaping signal to the transmit signal exceeding the pre-determined magnitude parameter;

a digital-to-analog converter that converts the transmit signals in the time domain to analog transmit signals;

a filter that suppresses a shaping component from one or more of the analog transmit signals, wherein the shaping component is associated with the shaping signal; and

an interface for interfacing the transmitter to a communications medium.

9. The discrete multi-tone transmitter of claim 8, further comprising in combination:

an analog-to-digital converter that converts analog receive signals to receive signals in the time domain; and

an echo cancellation unit that cancels feedback tones from the receive signals, wherein the feedback tones are derived at least in part from either of the modified signal or the shaping signal.

10. The discrete multi-tone transmitter of claim 9, wherein the echo cancellation unit subtracts an echo cancellation parameter from the receive signal, wherein the echo cancellation parameter is derived at least in part from the modified signal or the shaping signal.

11. The discrete multi-tone transmitter of claim 8, wherein the shaping signal generator generates the shaping signal from tones located exclusively outside a transmission band allocated to the transmit signals.

12. The discrete multi-tone transmitter of claim 8, wherein the transmission band allocated to the transmit signals is an upstream transmission band in an asymmetric digital subscriber line.

13. The discrete multi-tone transmitter of claim 8, wherein the transmission band allocated to the transmit signals is an downstream transmission band in an asymmetric digital subscriber line.

14. The discrete multi-tone transmitter of claim 8, wherein the pre-determined magnitude parameter is derived from resolution characteristics of the digital-to-analog converter.