Transmitter and method for reducing the peak-to-average power ratio of a digitally modulated communication signal
View Patent ↗A transmitter and method for processing a digitally modulated communication signal, which may reduce peak-to-average-power-ratio (PAPR) while maintaining acceptable error rates is disclosed. After subcarrier mapping, a first digital representation of the signal is upsampled into a second digital representation, which is transformed into a first time domain representation. Samples whose magnitudes exceed a magnitude limit are limited to that limit to produce a second time domain representation. The second time domain representation is transformed to a third frequency domain representation, which is downsampled into a fourth frequency domain representation. In addition to the in-band subcarriers, some out-of-band subcarriers adjacent to the frequency band are preserved while the remaining out-of-band subcarriers are eliminated to produce a fifth frequency domain representation. The fifth frequency domain representation is then transformed to a third time domain representation, which is converted to an analog signal to be transmitted.
1. A method for processing a digitally modulated communication signal comprising:
upsampling a first frequency domain representation of the digitally modulated communication signal by an upsampling factor to generate a second frequency domain representation;
transforming the second frequency domain representation into a first time domain representation;
limiting the magnitude of samples of the first time domain representation to a magnitude limit;
transforming the first time domain representation with the magnitude limit into a third frequency domain representation;
downsampling the third frequency domain representation by a downsampling factor to produce a fourth frequency domain representation; and
filtering the fourth frequency domain representation in a frequency domain filter circuit to produce a fifth frequency domain representation, wherein the fifth frequency domain representation is filtered to include in-band subcarriers and included out-of-band subcarriers but to exclude excluded out-of-band subcarriers.
2. The method of claim 1 wherein the upsampling factor is greater than the downsampling factor.
3. The method of claim 1 wherein the upsampling factor is in a range from twice to eight times, inclusive, the downsampling factor.
4. The method of claim 1 wherein the in-band subcarriers and the included out-of-band subcarriers are a subset of a plurality of available subcarriers.
5. The method of claim 1 wherein the excluded out-of-band subcarriers include all out-of-band subcarriers having frequencies lower than a low frequency limit of the included out-of-band subcarriers.
6. The method of claim 1 wherein the excluded out-of-band subcarriers include all out-of-band subcarriers having frequencies higher than a high frequency limit of the included out-of-band subcarriers.
7. The method of claim 1 wherein the fifth frequency domain representation conforms to a specified spectral emission mask, wherein the specified spectral emission mask describes limits in frequency and signal strength which the digitally modulated communication signal is permitted to occupy in an electromagnetic spectrum.
8. A transmitter for processing a digitally modulated communication signal comprising:
processing circuits; and
a digital-to-analog converter (DAC) coupled to the processor, the processing circuits configured to upsample a first frequency domain representation of the digitally modulated communication signal by an upsampling factor to produce a second frequency domain representation, to transform the second frequency domain representation into a first time domain representation, to limit the magnitude of samples of the first time domain representation to a magnitude limit to produce a second time domain representation, to transform the second time domain representation into a third frequency domain representation, to downsample the third frequency domain representation by a downsampling factor to produce a fourth frequency domain representation, to filter the fourth frequency domain representation to produce a fifth frequency domain representation, wherein the fifth frequency domain representation is filtered to include in-band subcarriers and included out-of-band subcarriers but to exclude excluded out-of-band subcarriers, to transform the fifth frequency domain representation into a third time domain representation; and to provide the third time domain representation to the DAC to produce an analog signal for transmission.
9. The transmitter of claim 8 wherein the upsampling factor is greater than the downsampling factor.
10. The transmitter of claim 8 wherein the upsampling factor is in a range from twice to eight times, inclusive, the downsampling factor.
11. The transmitter of claim 8 wherein the selected subcarriers are a subset of a plurality of available subcarriers.
12. The transmitter of claim 8 wherein the excluded out-of-band subcarriers include all out-of-band subcarriers having frequencies lower than a low frequency limit of the included out-of-band subcarriers.
13. The transmitter of claim 8 wherein the excluded out-of-band subcarriers include all out-of-band subcarriers having frequencies higher than a high frequency limit of the included out-of-band subcarriers.
14. The transmitter of claim 8 wherein the fifth frequency domain representation conforms to a specified spectral emission mask, wherein the specified spectral emission mask describes limits in frequency and signal strength which the digitally modulated communication signal is permitted to occupy in an electromagnetic spectrum.
15. A method for processing a digitally modulated communication signal comprising:
selecting an upsampling factor for upsampling;
selecting a downsampling factor for downsampling;
selecting selected subcarriers for frequency domain filtering;
upsampling a first frequency domain representation of the digitally modulated communication signal by the upsampling factor to produce a second frequency domain representation;
transforming the second frequency domain representation into a first time domain representation;
limiting the magnitude of samples of the first time domain representation to a magnitude limit to produce a second time domain representation;
transforming the second time domain representation into a third frequency domain representation;
downsampling the third frequency domain representation by the downsampling factor to produce a fourth frequency domain representation;
filtering the fourth frequency domain representation in a frequency domain filter circuit to produce a fifth frequency domain representation, wherein the fifth frequency domain representation is filtered, based on the selecting the selected subcarriers, to include in-band subcarriers and included out-of-band subcarriers in the fifth frequency domain representation but to exclude excluded out-of-band subcarriers from the fifth frequency domain representation;
transforming the fifth frequency domain representation into a third time domain representation;
determining an error rate resulting from selecting of the upsampling factor, the downsampling factor, and the selected subcarriers;
determining if the error rate is acceptable; and
if the error rate is unacceptable, selecting at least one new value for at least one parameter selected from a group consisting of the upsampling factor, the downsampling factor, and the selected subcarriers.
16. The method of claim 15 further comprising:
comparing the error rate to an error rate value, wherein the error rate value is a bit error rate (BER).
17. The method of claim 15 further comprising:
comparing the error rate to an error rate value, wherein the error rate value is a block error rate (BLER).
18. The method of claim 15 wherein the fifth frequency domain representation conforms to a specified spectral emission mask, wherein the specified spectral emission mask describes limits in frequency and signal strength which the digitally modulated communication signal is permitted to occupy in an electromagnetic spectrum.
19. The method of claim 15 wherein the upsampling factor is greater than the downsampling factor.
20. The method of claim 19 wherein the upsampling factor is in a range from twice to eight times, inclusive, the downsampling factor.