MANHASSET, N.Y. Researchers from the Nokia Research Center (Irving, Texas) have demonstrated how partial-response signaling can improve the peak-to-average power ratio in orthogonal, frequency-division multiplex (OFDM) systems by as much as 5 dB, allowing the use of power amps with more efficiency or range, or both.
The technique is applicable to OFDM applications across the board, ranging from wireless LANs to fixed wireless access to digital TV broadcasts over the DVB system in Europe.
OFDM is proving popular for a range of applications because of its multipath tolerance and high spectral efficiency. But the high peak-to-average power ratio (PAPR) has been a consistent drawback of OFDM systems, said Venkatesh Vadde, a researcher at Nokia and author of the paper that was presented at the recent Rawcon 2001 conference.
"Traditionally, designers will clip the signal below a certain value to cater to the PAPR, but that introduces non-linearities and distortion," he said. "Alternatively, you can back off the PA peak-to-average ratio and operate it inefficiently at a much lower output power. However, using the partial-response technique, you reduce the PAPR substantially so you can operate the OFDM radio closer to its maximum power."
The partial-response technique temporarily compresses the signal, allowing extra time to rearrange the signal such that Cartesian correction can be used to stabilize the envelope.