Method and system for crest factor reduction
An apparatus and system are provided for crest factor reduction (CFR). Preferably, a peak from the wideband signal is detected. A gain from the magnitude of the peak and a threshold can then be calculated. Based on this information, each carrier's contribution to the peak can be approximated, and a cancellation pulse coefficient for each carrier from its contribution to the peak can be calculated. A base cancellation pulse can be calculated from the cancellation pulse coefficients for each carrier, and a cancellation pulse can be calculated from the base cancellation pulse and the gain, which can then be applied to the wideband signal.
1. An apparatus comprising:
an input section that receives an input signal and that generates an intermediate signal, wherein the input section includes:
an interface that receives the input signal and that generates a wideband signal;
a crest factor reduction (CFR) unit that reduces a peak-to-average ratio (PAR) of the wideband signal, wherein the CFR unit has a stage that includes:
a peak detector that detects a peak from the wideband signal; and
a cancellation pulse calculator that is coupled to the peak detector and that calculates a cancellation pulse having an envelop and phase information that are approximately the same as the peak, wherein the cancellation pulse calculator includes:
a gain calculator that is coupled to the peak detector and that that calculates a gain from the magnitude of the peak and a threshold;
a contribution calculator that is coupled to the peak detector and that approximates each carrier's contribution to the peak;
a coefficient calculator that is coupled to the contribution calculator and that calculates a cancellation pulse coefficient for each carrier from its contribution to the peak;
a first pulse calculator that is coupled to the coefficient calculator and that calculates a base cancellation pulse from the cancellation pulse coefficients for each carrier;
a second pulse calculator that is coupled to the gain calculator and to the first pulse calculator and that calculate a cancellation pulse from the base cancellation pulse and the gaiff, and
a peak canceller that is coupled to the peak detector and to the second pulse calculator and that applies the cancellation pulse to the wideband signal;
output logic that receives a signal the wideband signal from the CFR unit having a reduced PAR and that generates the intermediate signal; and
an output section that receives the intermediate signal and that generates a transmission signal.
2. The apparatus of claim 1 , wherein the interface further comprises:
interface logic that receives the input signal; and
a digital upconverter (DUC) that receives an output from the interface logic and that generates the wideband signal.
3. The apparatus of claim 1 , wherein the CFR unit further comprises a plurality of stages that each have the computer program produce embodied thereon.
4. The apparatus of claim 1 , wherein the output section further comprises:
an analog-to-digital converter (ADC) pipeline that receives a feedback signal; and
a digital-to-analog converter (DAC) pipeline that generates the transmission signal from an output from the ADC pipeline and the intermediate signal.
5. The apparatus of claim 1 , wherein the cancellation pulse calculator further comprises a lookup table that includes a plurality of prestored cancellation pulses.
6. A system for generating and transmitting a transmission signal, the system comprising:
an input section that receives an input signal and that generates an intermediate signal, wherein the input section includes:
an interface that receives the input signal and that generates a wideband signal;
a crest factor reduction (CFR) unit that that reduces a peak-to-average ratio (PAR) of the wideband signal, wherein the CFR unit has a stage that includes:
a peak detector that detects a peak from the wideband signal; and
a cancellation pulse calculator that is coupled to the peak detector and that calculates a cancellation pulse having an envelop and phase information that are approximately the same as the peak, wherein the cancellation pulse calculator includes:
a gain calculator that is coupled to the peak detector and that that calculates a gain from the magnitude of the peak and a threshold;
a contribution calculator that is coupled to the peak detector and that approximates each carrier's contribution to the peak;
a coefficient calculator that is coupled to the contribution calculator and that calculates a cancellation pulse coefficient for each carrier from its contribution to the peak;
a first pulse calculator that is coupled to the coefficient calculator and that calculates a base cancellation pulse from the cancellation pulse coefficients for each carrier;
a second pulse calculator that is coupled to the gain calculator and to the first pulse calculator and that calculate a cancellation pulse from the base cancellation pulse and the gain; and
a peak canceller that is coupled to the peak detector and to the second pulse calculator and that applies the cancellation pulse to the wideband signal;
output logic that receives a signal the wideband signal from the CFR unit having a reduced PAR and that generates the intermediate signal;
an output section that receives the intermediate signal and that generates a digital transmission signal;
transmission circuitry that receives the digital transmission signal and generates a radio frequency (RF) signal; and
an antenna that outputs the RF signal.
7. The system of claim 6 , wherein the interface further comprises:
interface logic that receives the input signal; and
a DUC that receives an output from the interface logic and that generates the wideband signal.
8. The system of claim 6 , wherein the CFR unit further comprises a plurality of stages that each have the computer program produce embodied thereon.
9. The system of claim 6 , wherein the output section further comprises:
an analog-to-digital converter (ADC) pipeline that receives a feedback signal; and
a digital-to-analog converter (DAC) pipeline that generates the transmission signal from an output from the ADC pipeline and the intermediate signal.
10. The system of claim 6 , wherein the cancellation pulse calculator further comprises a lookup table that includes a plurality of prestored cancellation .pulses.
11. The system of claim 6 , wherein the transmission circuitry further comprises:
a digital-to-analog converter (DAC) that receives the digital transmission signal;
a quadrature modulator that receives an output from the DAC and generates the RF signal;
an amplifier that amplifies the RF signal; and
an analog-to-digital converter (ADC) feedback pipelines that generates a feedback signal for the output section from the RF signal.