Cyclic Prefix Adaptation with Constant Overall Symbol Time for DFT-spread-OFDM and OFDM

TL;DR

This paper proposes a method to adapt the cyclic prefix duration in DFT-spread-OFDM and OFDM systems to varying delay spreads, maintaining a constant overall symbol time and improving spectral efficiency.

Contribution

It introduces a cyclic prefix adaptation technique that preserves symbol duration, along with implementation strategies like clock rate adjustment and Farrow filters.

Findings

Improved spectral efficiency with CP adaptation

Maintained constant overall symbol time

Reduced computational complexity through proposed methods

Abstract

For DFT-spread-OFDM or OFDM, if the delay spread varies in a wide range and the symbol duration is relatively short, adapting the cyclic prefix (CP) duration rather than using a fixed one may significantly improve the spectral efficiency while preventing inter-symbol interference (ISI). In practice, it may be beneficial to have a constant overall DFT-spread-OFDM/OFDM symbol time, which is the sum of the duration of a CP and the duration of a data portion. We propose to adapt the CP duration to the delay spread without changing the overall symbol time for DFT-spread-OFDM or OFDM, and address implementation challenges. In particular, we propose changing the clocking rate of ADC and DAC or using a Farrow filter to reduce the computational complexity of arbitrary-size DFT/IDFT resulting from the adaptation.