On the use of Padding Sequences for Post-DFT Insertion of Reference Signals in DFT-s-OFDM

When facing the challenges of wireless communications beyond 5G, single-carrier waveforms appear as a promising enabler for energy-efficient communications thanks to their low PAPR. Among the single-carrier waveforms, DFT-s-OFDM plays a privileged role because of its commonalities with CP-OFDM, albeit its flexibility to allocate control signals in the frequency domain is much more limited. This paper describes a technique for insertion of Reference Signals in the frequency domain based on the use of padding sequences appended to the data before the Transform Precoding stage, followed by direct reference signal insertion after DFT. We prove that the use of padding sequences can trade off PAPR vs. performance through proper sequence design, and that a dynamic framework for sequence selection based on feedback from the receiver can be advantageous. Simulations confirm the suitability of the proposed technique as an enabler for flexibly allocating distributed reference signals with a reduced overhead compared to other standard approaches.