Novel Tone Reservation Method for DFT-s-OFDM

Selahattin Gokceli,Mikko Valkama,Kari Pajukoski,Esa Tiirola,Taneli Riihonen,Ismael Peruga

doi:10.1109/lwc.2021.3094887

Abstract

In this letter, a novel guard-tone reservation (GTR) method is proposed to reduce the peak-to-average power ratio (PAPR) of discrete Fourier transform-spread-orthogonal frequency-division multiplexing (DFT-s-OFDM) waveform. Unlike existing PAPR reduction methods, the proposed GTR operates directly in the data symbol domain, estimating the peaks through the relations between the data symbols, while the corresponding peak-cancellation signal (PCS) is efficiently embedded into the waveform processing. Furthermore, the PCS is generated by exploiting only the guard-band tones, leaving thus the inband data tones undistorted. The performance of the method is evaluated in 5G New Radio (NR) uplink context including also realistic measured power amplifier (PA) characteristics. The obtained results show that significant PAPR reduction and corresponding PA output power gains can be obtained while the computational complexity is shown to be low.

Highlights

T HE BASELINE physical-layer waveform of 5G New Radio (NR) [1], [2] is cyclic-prefix (CP) orthogonal frequency-division multiplexing (OFDM), while discrete Fourier transformspread-OFDM (DFT-s-OFDM) is supported in uplink (UL) [1], [2], as it is known to have lower peak-to-average power ratio (PAPR)
While in general the length of the deployed peak detection filter is a trade-off between processing complexity and peak detection performance, we use the above configuration in the following numerical results, and show that very efficient PAPR reduction can be obtained with very low complexity compared to the existing reference methods
The ACLR is evaluated by following the 5G NR guidelines, while the corresponding UL spectrum emission mask (SEM) [9, Sec. 6] assessment is included in the results

Summary

INTRODUCTION

T HE BASELINE physical-layer waveform of 5G NR [1], [2] is cyclic-prefix (CP) orthogonal frequency-division multiplexing (OFDM), while discrete Fourier transformspread-OFDM (DFT-s-OFDM) is supported in uplink (UL) [1], [2], as it is known to have lower peak-to-average power ratio (PAPR). Most of the solutions involve iterative processing and come with substantial computational complexity and power consumption, making their application in mobile terminal transmitters challenging To this end, in [4], a time-domain kernel building on TR tones is used to create the peak-cancellation signal (PCS). This way, multiple peaks can be cancelled in each iteration, but the complexity increases with respect to [4]. Similar approach is considered in [7] but different from [6], the BER increase is more controlled In both studies, it is discovered that consecutive symbols on the outer constellation points and with opposite phases have the highest contribution to the resulting time-domain peaks. The provided numerical results illustrate the efficiency of the proposed method, while high-lighting the low computational complexity of the solution

DFT-s-OFDM Signal Model

Peak Detection Filter

Proposed GTR Method

Low-Complexity Implementation

NUMERICAL RESULTS AND ANALYSIS

Results and Discussion

CONCLUSION