On the performance of hybrid carrier system with spectrum precoding based on WFRFT

Zhenduo Wang,Naitong Zhang,Xiaolu Wang,Lin Mei,Xuejun Sha

doi:10.1186/s13638-017-0890-7

Abstract

High out-of-band (OOB) power emission has become the main shortcoming of multicarrier scheme in regard to the requirements and challenges of 5G. In this paper, two effective OOB power reduction methods, previously applied to traditional orthogonal frequency division multiplexing (OFDM) system, are proposed in hybrid carrier (HC) scheme based on weighted-type fractional Fourier transform (WFRFT). Simulation results demonstrate that, due to the flexible selection of WFRFT order in the HC system, combined bit error rate (BER) and peak-to-average power ratio (PAPR) performance advantages are gained without sidelobe impact and significant complexity increase in comparison with the OFDM scheme with spectrum precoding. In projection precoding, a smaller error vector magnitude of precoder Gχ is obtained in the proposed hybrid carrier scheme. In SVD precoding with an orthogonal decoding at the receiver, better BER performance could also be acquired at WFRFT order over the fading channels. The proposed two WFRFT-based structures are complementary, and their potential scenarios are given. In addition, applying the feature of projection precoding to channel estimation, a novel pilot structure based on WFRFT is posed to reduce the introduced error of spectrum precoding and finally helps to improve the BER performance.

Highlights

The efficient utilization of idle spectrum becomes the main means to solve the shortage of limited spectrum resources in modern wireless communication system
A precoding scheme which focuses on suppressing out-of-subband emission of the discrete Fourier transform (DFT)-based orthogonal frequency division multiplexing (OFDM) system is proposed in [15], whose bit error rate (BER) performance is improved as a result of frequency diversity
As a trade-off of OFDM and single carrier (SC) schemes, the hybrid carrier (HC) scheme based on weighted-type fractional Fourier transform (WFRFT) adapts to diverse scenes due to its flexible and configurable parameters

Summary

Introduction

The efficient utilization of idle spectrum becomes the main means to solve the shortage of limited spectrum resources in modern wireless communication system. Existing methods for reducing sidelobe of multicarrier scheme are proposed, involving time domain windowing, subcarrier weighting, insertion of cancelation carriers (CCs), and precoding. N-continuous OFDM is proposed in [14] through precoding the information symbols and achieves obvious out-of-band power reduction with slight decline of reliability. A precoding scheme which focuses on suppressing out-of-subband emission of the DFT-based OFDM system is proposed in [15], whose BER performance is improved as a result of frequency diversity. Joint PAPR reduction and sidelobe suppression is achieved in [23] through dynamically extending part of the constellation points on the secondary user subcarriers and adding several signal cancelation symbols on the primary user subcarriers. A novel WFRFT-based pilot structure with smaller estimation error is posed according to the characteristics of spectrum precoders. The required precoder can be selected according to the applications, specific requirements, and potential scenarios

OOB power analysis

OFDM scheme

HC scheme with WFRFT-based pilot structure

BER results

Conclusions