Blind symbol synchronization for direct detection optical OFDM using a reduced number of virtual subcarriers.

R Bouziane,R I Killey

doi:10.1364/oe.23.006444

Abstract

Symbol synchronization constitutes a major component in optical OFDM transceivers. In this paper, we propose reducing the complexity of a blind symbol synchronization technique for direct detection OFDM receivers based on virtual subcarriers by optimizing the number and location of the virtual subcarriers. Compared to the system design in our previous study, this new technique offers a reduction of 92% in the number of virtual subcarriers (from 26 to 2 in a system with 50 data carrying subchannels) resulting in significant savings in complexity with a minimal penalty. Moreover, it offers an increase in the system capacity as more subcarriers can be used to transmit data. The technique was assessed experimentally using a transmission system of direct detection 16-QAM optical OFDM operating at a data rate of 30.65 Gb/s over 23.3 km SSMF with BER of 10(-3). Negligible penalty was observed at high received powers. However, at low received powers, the number of averaging symbols had to be increased in order to improve the robustness of the method.

Highlights

Direct detection optical orthogonal frequency division multiplexing (OFDM) has been proposed as a promising technique for future passive optical networks (PON) and data-centre applications [1, 2]
Symbol synchronization constitutes a major component in optical OFDM transceivers
We propose reducing the complexity of a blind symbol synchronization technique for direct detection OFDM receivers based on virtual subcarriers by optimizing the number and location of the virtual subcarriers

Summary

Introduction

Direct detection optical orthogonal frequency division multiplexing (OFDM) has been proposed as a promising technique for future passive optical networks (PON) and data-centre applications [1, 2]. Its implementation in high speed optical communications is computationally expensive because of the high sampling frequency required in such systems (multiple Giga samples per second) compared to the digital signal processing (DSP) clock frequency which is in the range of a few hundreds of MHz. In addition, most OFDM synchronization methods require training symbols which increase the overhead of the system. Bouziane et al presented a frequencydomain cross-correlation method that uses special training symbols in [5] and another technique based on the standard deviation of the FFT output symbols in [6]. We demonstrate the technique experimentally with a 30.65 Gb/s OFDM signal transmission, using just two VSCs for synchronization, and we compare its performance with systems using blind symbol synchronization with 26 VSCs, and with the conventional Schmidl & Cox algorithm

System concept

Complexity evaluation of the proposed method

Findings

Conclusion