Dynamically selecting methods to reduce distortion in multi-carrier modulated signals resulting from high peak-to-average power ratios
View Patent ↗In one embodiment, an algorithm dynamically selects a method for reducing distortion in a multi-carrier modulated signal, such as an orthogonal frequency division multiplexing (OFDM) signal. The algorithm directs a transmitter to transmit peak-to-average power ratio (PAPR)-reduction signals over reserved tones (i.e., frequencies) if reserved tones are available. If reserved tones are not available, then the algorithm directs the transmitter to transmit PAPR-reduction symbols over free tones if free tones are available. If the free tones for this transmitter are used by adjacent transmitters, then interference-reduction techniques may be used to reduce interference with the adjacent transmitters. If reserved tones and free tones are not available, then the transmitter may use an alternative method to reduce distortion, such as successive clipping and filtering. In another embodiment, the transmitter may transmit PAPR-reduction symbols over both free and reserved tones, if available.
1. An apparatus comprising a controller for a multi-carrier modulator having a PAPR-reduction symbol generator and an inverse fast Fourier transform (IFFT) processor, wherein:
(a) the controller is configured to determine whether or not the multi-carrier modulator has one or more tones available for PAPR reduction; and
(b) if the controller determines that the multi-carrier modulator has one or more tones available for PAPR reduction, then:
(b1) the PAPR-reduction symbol generator generates at least one PAPR-reduction symbol for at least one tone available for PAPR reduction; and
(b2) the IFFT processor generates the multi-carrier modulated signal using the at least one PAPR-reduction symbol; and
(c) if the controller determines that the multi-carrier modulator does not have one or more tones available for PAPR reduction, then the IFFT processor generates the multi-carrier modulated signal without using a PAPR-reduction symbol.
2. The invention of claim 1 , wherein the multi-carrier modulator is an orthogonal frequency division multiplexing (OFDM) modulator and the multi-carrier modulated signal is an OFDM signal.
3. The invention of claim 1 , wherein the apparatus further comprises the multi-carrier modulator.
4. The invention of claim 1 , wherein the controller determines whether at least one tone available for PAPR reduction is reserved a priori for PAPR reduction.
5. The invention of claim 1 , wherein the controller determines whether at least one tone available for PAPR reduction is an unreserved tone having no data symbol assigned to it.
6. The invention of claim 1 , wherein:
the controller is further adapted to determine whether the multi-carrier modulator has one or more reserved tones reserved a priori for PAPR reduction; and
if the controller determines that the multi-carrier modulator has one or more reserved tones, then:
the PAPR-reduction symbol generator further generates at least one other PAPR-reduction symbol for at least one reserved tone; and
the IFFT processor generates the multi-carrier modulated signal using the at least one PAPR-reduction symbol and the at least one other PAPR-reduction symbol.
7. A computer-implemented method for reducing peak-to-average power ratio (PAPR) of a transmitter's multi-carrier modulated signal, the method comprising:
(a) the computer determining whether or not the transmitter has one or more tones available for PAPR reduction; and
(b) if step (a) determines that the transmitter has one or more tones available for PAPR reduction, then:
(b1) assigning at least one PAPR-reduction symbol to at least one tone available for PAPR reduction; and
(b2) generating the multi-carrier modulated signal using the at least one PAPR-reduction symbol; and
(c) if step (a) determines that the multi-carrier modulator does not have one or more tones available for PAPR reduction, then generating the multi-carrier modulated signal without using a PAPR-reduction symbol.
8. The invention of claim 7 , wherein the multi-carrier modulated signal is an orthogonal frequency division multiplexed (OFDM) signal.
9. The invention of claim 7 , wherein step (a) determines whether at least one tone available for PAPR reduction is reserved a priori for PAPR reduction.
10. The invention of claim 7 , wherein step (a) determines whether at least one tone available for PAPR reduction is an unreserved tone having no data symbol assigned to it.
11. The invention of claim 10 , wherein:
if step (a) determines that at least one tone available for PAPR reduction is an unreserved tone having no data symbol assigned to it, then step (b) further comprises determining if the at least one unreserved tone is used by an adjacent transmitter; and
if step (b) determines that the at least one unreserved tone is used by an adjacent transmitter, then step (b) further comprises applying an interference-reduction method for the multi-carrier modulated signal.
12. The invention of claim 7 , wherein:
step (a) comprises determining whether the transmitter has one or more reserved tones reserved a priori for PAPR reduction; and
if step (a) determines that the transmitter has one or more reserved tones, then:
step (b1) further comprises generating at least one other PAPR-reduction symbol for at least one reserved tone; and
step (b2) comprises generating the multi-carrier modulated signal using the at least one PAPR-reduction symbol and the at least one other PAPR-reduction symbol.
13. The invention of claim 12 , wherein if step (a) determines that the multi-carrier modulation has no free tones and no reserved tones, then the multi-carrier modulated signal is generated using a technique that reduces distortion of the multi-carrier modulated signal by a downstream amplifier, wherein the technique does not use any free or reserved tones.