All-Digital Timing Recovery for Free Space Optical Communication Signals With a Large Dynamic Range and Low OSNR

Yunfeng Gu,Sheng Cui,Changjian Ke,Keji Zhou,Deming Liu

doi:10.1109/jphot.2019.2956086

Yunfeng Gu, Sheng Cui + Show 3 more

Open Access

https://doi.org/10.1109/jphot.2019.2956086

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Abstract

The free space optical communication (FSOC) signals often exhibit a much larger dynamic range and much lower OSNR than optical fiber communication signals, due to the large-scale relative motion of the terminals, change of atmospheric channel conditions and large transmission loss. For this reason flexible digital coherent receivers (DCR) capable of adapting to different channel conditions have attracted much attention in the FSOC field. As timing recovery is indispensable for DCRs, the development of a timing recovery algorithm (TRA) capable of processing such FSOC signals is of particular interest in FSOC field. In this paper we evaluate the performance of Gardner's timing error detector (TED) and propose a new blind TED with a lower computation complexity and more stable output characteristics. Based on the proposed TED, we design a feedback parallel TRA suitable for the FSOC signals and implement it in a FPGA to evaluate its real-time performance. Numerical simulations and experiments illustrate the merits of the proposed TRA based on new TED with respect to the TRA based on Gardner's TED.

Highlights

Free space optical communication (FSOC) can exploit the unregulated and nearly unlimited bandwidth in the near-infrared band and provide higher data rate, lower size, weight and power (SWaP) profile lasercom terminals compared with microwave communication [1]–[3]
As timing recovery is indispensable for digital coherent receivers (DCR), the development of a timing recovery algorithm (TRA) capable of processing such FSOC signals is of particular interest in FSOC field
Experiments have shown that DCRs in combination with digital coherent combining (DCC) algorithms can handling FSOC signals with extremely low OSNR and very wide dynamic range [5]–[7]

Summary

Introduction

Free space optical communication (FSOC) can exploit the unregulated and nearly unlimited bandwidth in the near-infrared band and provide higher data rate, lower size, weight and power (SWaP) profile lasercom terminals compared with microwave communication [1]–[3]. Experiments have shown that DCRs in combination with digital coherent combining (DCC) algorithms can handling FSOC signals with extremely low OSNR (much lower than 0dB) and very wide dynamic range (much large than 30 dB) [5]–[7]. In this paper we first analyze and evaluate the performance of the Gardner’s TED and the feedback TRA based it for the FSOC signals, and propose a multiplication-free blind TED algorithm with a lower computation complexity and more stable output characteristics. Based on the proposed TED we design a parallel TRA suitable for FSOC signals with a large dynamic range and very low OSNR. To evaluate its real-time processing performance, the parallel TRA is implemented in a FPGA It is demonstrated in simulation and experiment that the proposed TED and TRA outperform the Gardner technique for the FSOC signals

A Multiplication-Free TED With Stable Output Characteristics

Design of the Feedback Parallel TRA

Real-Time Platform Implementation and Tests

Conclusions