Dynamically selecting methods to reduce distortion in multi-carrier modulated signals resulting from high peak-to-average power ratios
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. A computer-implemented method for reducing peak-to-average power ratio (PAPR) of a transmitter's multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) one or more reserved tones reserved a priori for PAPR reduction, the method comprising:
(a) assigning one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it;
(b) assigning one or more PAPR-reduction symbols to one or more free tones, and assigning one or more PAPR-reduction symbols to the one or more reserved tones; and
(c) applying multi-carrier modulation to the one or more data symbols, the one or more free-tone PAPR-reduction symbols, and the one or more reserved-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal, wherein:
one or more of steps (a), (b), and (c) is implemented by the computer.
2. The invention of claim 1 , wherein the multi-carrier modulated signal is an orthogonal frequency division multiplexed (OFDM) signal and the multi-carrier modulation is OFDM modulation.
3. A computer-implemented method for reducing peak-to-average power ratio (PAPR) of a transmitter's multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) zero, one, or more reserved tones reserved a priori for PAPR reduction, the method comprising:
(a) assigning one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it;
(b) assigning one or more PAPR-reduction symbols to one or more free tones;
(c) applying multi-carrier modulation to the one or more data symbols and the one or more free-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal;
(d) determining whether a tone having a free-tone PAPR-reduction symbol is used by an adjacent transmitter; and
(e) causing an interference-reduction method to be implemented if the tone is determined to be used by an adjacent transmitter, wherein:
one or more of steps (a), (b), and (c) is implemented by the computer.
4. A computer-implemented method for reducing peak-to-average power ratio (PAPR) of a transmitter's multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) zero, one, or more reserved tones reserved a priori for PAPR reduction, the method comprising:
(a) assigning one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it;
(b) assigning one or more PAPR-reduction symbols to one or more free tones;
(c) applying multi-carrier modulation to the one or more data symbols and the one or more free-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal, wherein:
one or more of steps (a), (b), and (c) is implemented by the computer;
for a first multi-carrier modulated symbol in the multi-carrier modulated signal, at least one tone is assigned a free-tone PAPR-reduction symbol; and
for a second multi-carrier modulated symbol in the multi-carrier modulated signal, the at least one tone is assigned a data symbol.
5. A computer-implemented method for reducing peak-to-average power ratio (PAPR) of a transmitter's multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) zero, one, or more reserved tones reserved a priori for PAPR reduction, the method comprising:
(a) assigning one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it;
(b) assigning one or more PAPR-reduction symbols to one or more free tones;
(c) applying multi-carrier modulation to the one or more data symbols and the one or more free-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal, wherein:
one or more of steps (a), (b), and (c) is implemented by the computer; and
the one or more data symbols are generated using a higher-order of modulation than is used to generate the one or more data symbols data symbols when no PAPR-reduction symbols are applied to the free tones, the reserved tones, or both the free tones and the reserved tones.
6. A transmitter for reducing peak-to-average power ratio (PAPR) of a multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) one or more reserved tones reserved a priori for PAPR reduction, the transmitter comprising:
a subcarrier mapper adapted to (a) assign one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it, (b) assign one or more PAPR-reduction symbols to one or more free tones, and (c) assign one or more PAPR-reduction symbols to the one or more reserved tones; and
an inverse fast Fourier transform (IFFT) processor adapted to apply multi-carrier modulation to the one or more data symbols, the one or more free-tone PAPR-reduction symbols, and the one or more reserved-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal.
7. The invention of claim 6 , wherein the multi-carrier modulated signal is an orthogonal frequency division multiplexed (OFDM) signal and the multi-carrier modulation is OFDM modulation.
8. The invention of claim 6 , further comprising a PAPR-reduction symbol generator adapted to generate the one or more PAPR-reduction symbols for the one or more free tones.
9. A transmitter for reducing peak-to-average power ratio (PAPR) of a multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) zero, one, or more reserved tones reserved a priori for PAPR reduction, the transmitter comprising:
a subcarrier mapper adapted to (a) assign one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it, and (b) assign one or more PAPR-reduction symbols to one or more free tones;
an inverse fast Fourier transform (IFFT) processor adapted to apply multi-carrier modulation to the one or more data symbols and the one or more free-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal; and
a controller adapted to:
determine whether a tone having a free-tone PAPR-reduction symbol is used by an adjacent transmitter; and
cause an interference-reduction method to be implemented if the tone is determined to be used by an adjacent transmitter.
10. A transmitter for reducing peak-to-average power ratio (PAPR) of a multi-carrier modulated signal having (i) a plurality of unreserved tones and (ii) zero, one, or more reserved tones reserved a priori for PAPR reduction, the transmitter comprising:
a subcarrier mapper adapted to (a) assign one or more data symbols to one or more unreserved tones, such that at least one other unreserved tone is a free tone having no data symbol assigned to it, and (b) assign one or more PAPR-reduction symbols to one or more free tones; and
an inverse fast Fourier transform (IFFT) processor adapted to apply multi-carrier modulation to the one or more data symbols and the one or more free-tone PAPR-reduction symbols based on the tone assignments to generate the multi-carrier modulated signal, wherein:
for a first multi-carrier modulated symbol in the multi-carrier modulated signal, the subcarrier mapper assigns a free-tone PAPR-reduction symbol to at least one tone; and
for a second multi-carrier modulated symbol in the multi-carrier modulated signal, the subcarrier mapper assigns a data symbol to the at least one tone.
11. A computer-implemented method for reducing peak-to-average power ratio (PAPR) of a transmitter's multi-carrier modulated signal, the method comprising:
(a) determining whether the transmitter has one or more tones available for PAPR reduction, wherein step (a) determines whether at least one tone available for PAPR reduction is an unreserved tone having no data symbol assigned to it; 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, wherein at one or more of steps (a), (b1), and (b2) is implemented by the computer.
12. The invention of claim 11 , wherein the multi-carrier modulated signal is an orthogonal frequency division multiplexed (OFDM) signal.
13. The invention of claim 11 , wherein step (a) determines whether at least one tone available for PAPR reduction is reserved a priori for PAPR reduction.
14. The invention of claim 11 , 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.
15. A computer-implemented method for reducing peak-to-average power ratio PAPR of a transmitter's multi-carrier modulated signal, the method comprising:
(a) determining whether 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, wherein:
one or more of steps (a), (b1), and (b2) is implemented by the computer;
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.
16. The invention of claim 15 , 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.
17. 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 the controller is adapted to:
(a) determine whether the multi-carrier modulator has one or more tones available for PAPR reduction, wherein the controller determines whether at least one tone available for PAPR reduction is an unreserved tone having no data symbol assigned to it; 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.
18. The invention of claim 17 , wherein the multi-carrier modulator is an orthogonal frequency division multiplexing (OFDM) modulator and the multi-carrier modulated signal is an OFDM signal.
19. The invention of claim 17 , wherein the apparatus further comprises the multi-carrier modulator.
20. The invention of claim 17 , wherein the controller determines whether at least one tone available for PAPR reduction is reserved a priori for PAPR reduction.
21. 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 the controller is adapted to:
(a) determine whether 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, 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.