Experimental Demonstration of a Low-Complexity Phase Noise Compensation for CO-OFDM Systems

In this letter, a low-complexity phase noise compensation scheme based on Kalman filtering theory is experimentally demonstrated for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) transmissions. The proposed scheme can operate in two modes, pilot-aided mode and blind mode, resulting in a variety of phase noise tracking configurations upon particular transmission scenario. At a bit error rate of 3.8×10^-3 and for 40 GBaud 16-QAM 64 subcarriers CO-OFDM systems, the proposed method operating in the pilot-aided mode reduces the pilot overhead by a factor of 2 in comparison with the conventional pilot-aided scheme, while in the blind mode, our scheme's complexity is far superior to one of the state-of-the-art computational efficient decision-direct-free blind approach by a factor of 20.

I. Introduction

Shortly after its introduction to optical communication, orthogonal frequency division multiplexing (OFDM) attracted a lot of attention because of the simple equalization and tolerance to chromatic dispersion (CD) [1]–[4]. OFDM with larger number of subcarriers makes the signal more robust against CD but at the same time, more vulnerable to phase noise (PN) which mainly originates from imperfect lasers at both transmitter and receiver. In addition, the impact of fiber nonlinearity is also proportional to the number of subcarriers as a concequence of higher peak-to-average power ratio phenomenon [5], [6]. Thanks to the fast development of digital signal processing (DSP), the impact of the static effect like CD can be effectively compensated by employing the overlapped frequency domain equalizers before OFDM demodulation [7]. As a result, OFDM with small-to-moderate number of subcarriers has become a great interest for optical communication systems.