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Symbol synchronization and sampling frequency synchronization techniques in real-time DDO-OFDM systems

Authors
Journal
Optics Communications
0030-4018
Publisher
Elsevier
Publication Date
Volume
326
Identifiers
DOI: 10.1016/j.optcom.2014.04.011
Keywords
  • Symbol Synchronization
  • Sampling Frequency Synchronization
  • Orthogonal Frequency-Division Multiplexing (Ofdm)
  • Real-Time Signal Processing

Abstract

Abstract In this paper, we propose and experimentally demonstrate a symbol synchronization and sampling frequency synchronization techniques in real-time direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) system, over 100-km standard single mode fiber (SSMF) using a cost-effective directly modulated distributed feedback (DFB) laser. The experiment results show that the proposed symbol synchronization based on training sequence (TS) has a low complexity and high accuracy even at a sampling frequency offset (SFO) of 5000-ppm. Meanwhile, the proposed pilot-assisted sampling frequency synchronization between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) is capable of estimating SFOs with an accuracy of <±5-ppm for initial SFOs as large as 1000-ppm. Moreover, the sampling frequency synchronization technique can also compensate SFO effects within a small residual SFO caused by deviation of SFO estimation and low-precision or unstable clock source. The two synchronization techniques are suitable for high-speed DDO-OFDM transmission systems.

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