Method and apparatus for peak to average power ratio reduction for orthogonal frequency division multiplex systems
View Patent ↗A multi-stage signal processing method is provided that reduces the Peak to Average Power Ratio (PAPR) of an Orthogonal Frequency Division Multiplexed (OFDM) signal without increasing the bit error rate of the system. The multi-stage processing system apportions the tones into a number of types, and processes the tones in an order and by a process consistent with their determined type. Advantageously, preprocessing of the time domain signal may be used to condition the data tones for optimal PAPR reduction during the multi-stage process.
1. A method for reducing a Peak to Average Power Ratio (PAPR) of a signal, the signal comprising a plurality of tones, the plurality of tones apportioned into a set of data tones and a set of reserved tones, the method comprising the steps of:
modifying a signal value of at least one of the reserved tones according to a first processing method;
after the modification of the signal value of the at least one of the reserved tones, modifying a signal value of at least one of the data tones according to a second processing method to provide a modified signal; and
transmitting the modified signal to a receiver.
2. The method according to claim 1 , wherein the first processing method is a Projection onto Convex Sets (POCS) processing method.
3. The method according to claim 1 wherein the first processing method is an Active Constellation Extension (ACE) processing method.
4. The method according to claim 1 , wherein the first processing method is a Gradient Project Active Constellation Extension (GP-ACE) processing method.
5. The method according to claim 1 wherein the second processing method is an Active Constellation Extension (ACE) processing method.
6. The method according to claim 1 wherein the second processing method is a Gradient Project Active Constellation Extension (GP-ACE) processing method.
7. The method according to claim 1 , further comprising the steps of:
applying an Inverse Discrete Fourier Transform (IDFT) to an input signal OFDM signal to provide a time domain signal;
clipping the time domain signal to provide a clipped time domain signal; and
applying a Discrete Fourier Transform (DFT) to the clipped time domain signal to provide a clipped frequency domain representation of the input signal.
8. The method according to claim 7 , further comprising the step of oversampling the input signal.
9. The method according to claim 7 , wherein the step of modifying the signal value of the at least one reserved tone replaces the signal value of the at least one reserved tone with the clipped frequency domain representation of the reserved tone.
10. The method according to claim 7 , wherein the at least one data tone is from a set of at least two constellation points, and wherein step of modifying the signal value of the at least one data tone modifies a position of at least one constellation point of the at least one data tone while retaining a minimum distance between the at least two constellation points.
11. The method according to claim 7 , wherein the plurality of tones further includes a set of restricted tones.
12. The method according to claim 11 further comprising the step of preserving the value of a restricted tone.
13. An Orthogonal Frequency Division Multiplexing (OFDM) transmitter comprising:
Peak to Average Power Ratio (PAPR) reduction circuitry comprising at least two stages, wherein a first stage of the PAPR reduction circuitry processes a first type of tones of an OFDM signal, a second stage of the PAPR reduction circuitry processes a second, different type of tones of the OFDM signal; and wherein the first stage of processing operates on the OFDM signal prior to the second stage operating on the OFDM signal.
14. The OFDM transmitter of claim 13 , wherein the first type of tones are reserved tones and the first stage of PAPR reduction circuitry includes circuitry for performing Projection onto Convex Sets (POCS).
15. The OFDM transmitter of claim 13 , wherein the first type of tones are reserved tones and the first stage of PAPR reduction circuitry includes circuitry for performing Active Constellation Extension (ACE).
16. The OFDM transmitter of claim 13 , wherein the first type of tones are reserved tones and the first stage of PAPR reduction circuitry includes circuitry for performing Gradient Project Active Constellation Extension (GP-ACE).
17. The OFDM transmitter of claim 13 wherein the second type of tones is data tones and the second stage of PAPR reduction circuitry include circuitry for performing Active Constellation Extension (ACE).
18. The OFDM transmitter of claim 13 , wherein the second type of tones is data tones and the second stage of PAPR reduction circuitry include circuitry for performing Gradient Project Active Constellation Extension (GP-ACE) processing method.
19. The OFDM transmitter of claim 13 wherein the OFDM signal further comprises restricted tones.
20. The OFDM transmitter of claim 13 further comprising:
IDFT circuitry for providing a time domain representation of the OFDM signal;
clipping circuitry for providing a clipped time domain representation of the OFDM signal;
DFT circuitry for providing a clipped frequency domain representation of the clipped time domain representation of the OFDM signal; and
wherein the first stage of PAPR reduction circuitry replaces the reserved tones of the OFDM signal with the clipped frequency domain representation of the OFDM signal.
21. The OFDM transmitter of claim 13 further comprising:
IDFT circuitry for providing a time domain representation of the OFDM signal;
clipping circuitry for providing a clipped time domain representation of the OFDM signal;
DFT circuitry for providing a clipped frequency domain representation of the clipped time domain representation of the OFDM signal; and
wherein the second stage of PAPR reduction circuitry modifies constellation points of the data tones of the OFDM signal.
22. The OFDM transmitter of claim 13 further comprising preprocessing circuitry for processing the OFDM circuitry prior to the PAPR reduction circuitry.
23. The OFDM transmitter of claim 22 wherein the preprocessing circuitry comprises circuitry for determining a set of phase rotation to apply to each one of the tones of the OFDM signal.
24. The OFDM transmitter of claim 22 wherein the preprocessing circuit includes circuitry to perform Partial Transmit Sequence (PTS) processing.
25. The OFDM transmitter of claim 22 wherein the preprocessing circuit includes circuitry to perform Selective Mapping (SLM) processing on the OFDM signal.
26. A method of allocating tones in a multicarrier communication system comprising the steps of:
designating a first set of tones as a reserved set of tones, the reserved set of tones being reserved for Peak to Average Power Ratio (PAPR) reduction;
designating a second set of tones as data tone;
reserving a third set of tones as restricted tones; and
processing each type of tone of a received input signal by an OFDM transmitter in a different manner to provide an output signal with a desirable PAPR characteristic.
27. The method according to claim 26 , wherein each reserved tone in the set of reserved tones is distributed randomly within the multicarrier signal.
28. The method according to claim 24 , wherein the step of processing includes the step of oversampling the received input signal.