OFDM peak-to-average power ratio reduction method
The OFDM peak-to-average power ratio reduction apparatus and method provides a compressive sensing algorithm that estimates the sparsity pattern of a sparse vector by a limited number of measurements. When the positions of the clipped peaks are known beforehand by, e.g., a genie-augmented receiver, then the algorithm optimally performs amplitude estimation utilizing a least squares estimation technique. When the cardinality of the peak-reducing signal is known at the receiver at initialization, the receiver optimizes the estimated peak-reducing signal by using least squares.
1. A peak-to-average power ratio reduction method in an orthogonal frequency division multiplexing (OFDM) transmitter, the method comprising the steps of:
generating a baseband OFDM symbol while reserving a fixed subset of null tones in random distribution over an available transmission spectrum;
increasing the number of reserved tones, thereby improving the peak-to-average power ratio reduction while yielding an improved estimate of a peak-reducing signal at a receiver of an OFDM signal, wherein a Symbol Error Rate is improved;
generating a sparse time domain peak-reducing signal;
adding the peak-reducing signal to the OFDM signal, thereby annihilating peaks of the OFDM signal exceeding a predetermined clipping threshold; and
transmitting the OFDM signal, wherein reserved null tones are no longer null due to the addition of the peak-reducing signal.
2. The peak-to-average power ratio reduction method according to claim 1 , further comprising the step of:
utilizing the peak-reducing signal to directly operate on only the highest peaks of the OFDM signal.
3. The peak-to-average power ratio reduction method according to claim 1 , wherein the predetermined clipping threshold is consistent with sparsity of the peak-reducing signal.
4. The peak-to-average power ratio reduction method according to claim 1 , wherein the peak-reducing signal is a function of the number of reserved tones.
5. The peak-to-average power ratio reduction method according to claim 4 , wherein the reserved tones provide spectral support for the peak-reducing signal, thereby reducing computational complexity of the peak-to-average power ratio reduction method.
6. The peak-to-average power ratio reduction method according to claim 1 , wherein the peak-reducing signal is formulated based on a threshold level crossing of an original OFDM signal.
7. The peak-to-average power ratio reduction method according to claim 1 , wherein the peak-reducing signal is formulated based on order statistics of an original OFDM signal.
8. The peak-to-average power ratio reduction method according to claim 7 , wherein the transmitter sends a cardinality of the peak-reducing signal based on said order statistics of the original OFDM signal, the cardinality being sent by the transmitter as side information for use in a receiver's initialization process.
9. A peak-to-average power ratio (PAPR) reduction method in an orthogonal frequency division multiplexing (OFDM) receiver, the method comprising the steps of:
reserving null tones in random distribution over an available transmission spectrum;
increasing the number of reserved tones, thereby improving peak-to-average power ratio reduction while yielding an improved estimate of a peak-reducing signal at a receiver of an OFDM signal, wherein a Symbol Error Rate is improved;
receiving a reduced PAPR OFDM signal;
estimating a peak-reducing signal by observing spectral content of reserved null tones of the OFDM signal received by the receiver; and
subtracting the estimated peak-reducing signal from the received OFDM signal, thereby recovering an estimate of an original OFDM signal.
10. The peak-to-average power ratio reduction method according to claim 9 , further comprising the steps of:
estimating the peak-reducing signal by using partial measurements on the reserved tones induced at the receiver;
compressively sensing the reserved tones, thereby recovering the peak-reducing signal amplitudes and their positions at the receiver in order to reduce the complexity of the PAPR reduction method.
11. The peak-to-average power ratio reduction method according to claim 9 , wherein the step of estimating the peak-reducing signal by using the partial measurements on the reserved tones induced at the receiver is performed by a Candes-Randall-Tao SOCP Estimator.
12. The peak-to-average power ratio reduction method according to claim 9 , wherein the estimated peak-reducing signal is refined at the receiver by using Least Squares.
13. The peak-to-average power ratio reduction method according to claim 12 , wherein the refined peak-reducing signal is subtracted from the received peak-reduced OFDM signal, thereby recovering a refined estimate of the original OFDM signal.
14. An orthogonal frequency division multiplexing (OFDM) transceiver, comprising:
means for generating a baseband OFDM symbol while reserving a fixed subset of null tones;
means for generating a sparse time domain peak-reducing signal;
means for adding the peak-reducing signal to an OFDM signal, thereby annihilating peaks of the OFDM signal exceeding a predetermined clipping threshold;
means for reserving null tones in random distribution over an available transmission spectrum;
means for increasing the number of reserved tones, thereby improving the peak-to-average power ratio reduction while yielding an improved estimate of the peak-reducing signal at a receiver of the OFDM signal, wherein a Symbol Error Rate is improved;
means for transmitting the OFDM signal, wherein the reserved null tones are no longer null due to the addition of the peak-reducing signal;
means for receiving a reduced peak-average-power ratio OFDM signal;
means for estimating a peak-reducing signal by observing spectral content of reserved null tones of the OFDM signal received by the transceiver; and
means for subtracting the estimated peak-reducing signal from the received OFDM signal, thereby recovering an estimate of an original OFDM signal.
15. The OFDM transceiver according to claim 14 , further comprising:
means for estimating the peak-reducing signal by using partial measurements on the reserved tones induced at the receiver;
means for compressively sensing the reserved tones, thereby recovering the peak reducing signal amplitudes and their positions at the transceiver, thereby reducing complexity of peak-average-power ratio reduction.
16. The OFDM transceiver according to claim 15 , wherein said means for compressive sensing estimation comprises a Candes-Randall-Tao SOCP Estimator.