A Simple Blind Sampling Frequency Offset Estimation Scheme for Short-Reach DD-OFDM Systems

Hong Wen,Rui Deng,Ming Chen,Fengnian Liu,Kunping Luo,Tiezhu Zong,Qinghui Chen,Kang Geng

doi:10.1109/jphot.2020.3027028

Abstract

In this paper, a simple and overhead-free sampling frequency offset (SFO) blind estimation and compensation scheme is proposed and experimentally demonstrated in a short-reach direct detection orthogonal frequency division multiplexing (DD-OFDM) transmission system. After extracting subcarriers of OFDM symbols from multiple OFDM frames, the phase shift is obtained by the fourth-power algorithm, and the obtained results are averaged to perform phase estimation. It can achieve high-precision SFO estimation while ensuring low computational complexity as well as high spectral efficiency. The experimental results show that the SFO estimation accuracy using the proposed scheme can be significantly reduced to as low as ±3 ppm when SFO ranges from -1000 ppm to +1000 ppm after 20-km standard single-mode fiber (SSMF) transmission. Moreover, for the QPSK/16QAM encoded DD-OFDM systems aided by the proposed scheme, up to ±200 ppm SFO can be compensated with slight error vector magnitude (EVM) penalties after 20-km SSMF transmission. Furthermore, the results demonstrate that despite the existence of severe SFO, our proposed SFO compensation scheme can offer nearly negligible power penalties in the DD-OFDM system with optical back-to-back (OBTB) and 20-km SSMF transmission as compared to the ideal case without SFO.

Highlights

Driven by the proliferation of bandwidth-hungry services, such as 4K/8K HD video, cloud computing, virtual reality (VR), and other emerging industries, enormous efforts are being made to explore high data-rate, low-cost, and low power dissipation in optical communication systems
The experimental results show that the sampling frequency offset (SFO) estimation accuracy using the proposed scheme can be significantly reduced to as low as ±3 ppm when SFO ranges from −1000 ppm to +1000 ppm after 20-km standard single-mode fiber (SSMF) transmission
The fourth power operation is imposed on selected subcarriers from multiple Orthogonal frequency-division multiplexing (OFDM) frames

Summary

Introduction

Driven by the proliferation of bandwidth-hungry services, such as 4K/8K HD video, cloud computing, virtual reality (VR), and other emerging industries, enormous efforts are being made to explore high data-rate, low-cost, and low power dissipation in optical communication systems. It is imperative to study the SFO estimation and compensation schemes for high data-rate optical OFDM transmission systems. The synchronization signal is employed to control the ADC clock frequency by the external voltage-controlled oscillator to compensate for the SFO effect, which requires high precision and stable voltage-controlled oscillator. A dedicated electrical clock signal is used to extract timing information at the receiver [10] It requires a precise clock signal, and will undoubtedly make the system complex. The training symbol (TS)-aided SFO estimation and compensation approach has attended Researchers’ attention [11]–[13]. These approaches have simplified computational complexity and improved spectral efficiency (SE), but require multiple training symbols and a strict OFDM structure, limiting estimation and compensation range of SFO (±200 ppm). Since pilots need to be transmitted in each symbol, the adoption of pilots is not suitable, especially for small size based fast Fourier transform (FFT) in OFDM systems in terms of spectral efficiency

Methods

Results

Conclusion