| 摘要 |
A Digital-Subscriber Line (DSL) modem reduces signal peaks by digital processing. The peak-to-average ratio (PAR) is effectively reduced by the PAR reduction when the signal peaks are reduced before transmission. The DSL transmitter uses discrete multi-tone (DMT) signaling in which multiple carrier waves in different frequency bins simultaneously carry multiple data bits. After symbol encoding, the data in the multiple frequency bins are converted from the frequency domain to the time domain by an inverse fast-Fourier transform (IFFT). The IFFT is accomplished by two IFFT stages. The first stage produces an intermediate array that is input to the second stage, which produces the final time-domain output. The time-domain output is searched for peaks that exceed a clipping threshold of the transmitter's digital-to-analog converter. When an over-threshold peak is found, the intermediate-array inputs that contributed to the peak are examined. One or more subsets of these intermediate inputs is sign-inverted, and the effect of the sign inversion on the peak is examined. When the adjusted peak is below threshold, the subsets that include these intermediate inputs are chosen for sign-inversion. All intermediate inputs within the chosen subset are sign inverted, and the difference due to the sign inversion on each output samples is calculated and added to the outputs of the second stage to adjust the time-domain output. The subsets of the intermediate array correspond to input-array subsets since the first IFFT stage is aligned with the input subsets.
|
