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Journal ArticleDOI

Pilot-free common phase error estimation for CO-OFDM with improved spectral efficiency

TL;DR: An improved pilot free phase noise mitigation algorithm for CO-OFDM systems using weighted multi-level QPSK partitioning and Kalman filtering is proposed and an improvement in spectral efficiency is demonstrated.
Abstract: We propose an improved pilot free phase noise mitigation algorithm for CO-OFDM systems using weighted multi-level QPSK partitioning and Kalman filtering. Through extensive Monte Carlo simulations, we demonstrate an improvement in spectral efficiency of $>$ 6% in case of 200 Gbps single channel and 1 Tbps multi channel 16QAM CO-OFDM transmission with blind carrier phase estimation. We also experimentally demonstrate the performance of the proposed algorithm against the standard pilot aided algorithm for the transmission of 120 Gbps 16QAM CO-OFDM at different noise levels.

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Citations
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Journal ArticleDOI
TL;DR: In this article , the basic functioning of an optical amplifier and distortions of coherent signals when used as amplifiers are discussed, and optical signal processing techniques enabled by SOAs with an emphasis on all-optical wavelength conversion, optical phase conjugation, and phase quantization of coherent optical signals.
Abstract: Owing to advances in fabrication technology and device design, semiconductor optical amplifiers (SOAs) are evolving as a promising candidate for future optical coherent communication links. This review article focuses on the fundamentals and broad applications of SOAs, specifically for optical channels with advanced modulation formats, as an integrable broadband amplifier in commercial transponders and as a nonlinear medium for optical signal processing. We discuss the basic functioning of an SOA and distortions of coherent signals when SOAs are used as amplifiers. We first focus on the techniques used for low-distortion amplification of phase-modulated signals using SOAs. Then we discuss optical signal processing techniques enabled by SOAs with an emphasis on all-optical wavelength conversion, optical phase conjugation, and phase quantization of coherent optical signals.

5 citations

Journal ArticleDOI
15 Oct 2020
TL;DR: In this paper, the authors demonstrate superchannel transmission using CO-OFDM with higher cardinality QAM corresponding to total data rates up to 760 Gbps over 25 km fiber using optical carriers generated from an externally injection locked gain-switched comb source with linewidth ≈19 kHz.
Abstract: We experimentally demonstrate superchannel transmission using CO-OFDM with higher cardinality QAM corresponding to total data rates up to 760 Gbps over 25 km fiber using optical carriers generated from an externally injection locked gain-switched comb source with linewidth ≈19 kHz. Bandwidth re-configurability is demonstrated by operating the comb with different line spacing (20 GHz, 11 GHz) for the choice of (16-/32-/64-) QAM considered and we show the BER performance is within the SD-FEC limit. The system proposed can be used in any short reach application including DCIs and in access networks.

5 citations

Proceedings ArticleDOI
10 May 2020
TL;DR: In this article, a CO-OFDM superchannel transmission over 25 km using optical carrier generated from an externally injected gain-switched comb source with linewidth ≈ 19 kHz was demonstrated.
Abstract: We experimentally demonstrate 608 Gbps CO-OFDM superchannel transmission over 25 km using optical carrier generated from an externally injected gain-switched comb source with linewidth ≈19 kHz. We show the BER performance is within the HD-FEC limit.

2 citations

Journal ArticleDOI
TL;DR: The effectiveness of the SOA-based phase conjugator to improve the link budget with a 100 km standard single mode fiber link for 20 GHz coherent OFDM signals, with QPSK and 16QAM modulations and a corresponding net bit-rate of 40 Gbps and 80 Gbps respectively is experimentally demonstrated.
Abstract: We study the use of nonlinear semiconductor optical amplifier (SOA) for generating optical phase conjugate towards compensation of distortions in short distance optical fiber transmission due to Kerr nonlinearity and chromatic dispersion in coherent multi-carrier lightwave signals. We experimentally demonstrate the effectiveness of the SOA-based phase conjugator to improve the link budget with a 100 km standard single mode fiber link for 20 GHz coherent OFDM signals, with QPSK and 16QAM modulations and a corresponding net bit-rate of 40 Gbps and 80 Gbps respectively. Mid-span spectral inversion scheme is employed where the optical phase conjugate is generated through a partially degenerate four-wave mixing process in a nonlinear SOA. We demonstrate a bit error rate performance within $2\times 10^{-2}$ for an average launched power of up to 12 dBm (9 dBm) for QPSK (16QAM) coherent OFDM signals, in a 100 km fiber link. We also investigate the possible improvement in link budget using numerical simulation for 16QAM and 64QAM CO-OFDM signals with the proposed scheme.

2 citations


Cites methods from "Pilot-free common phase error estim..."

  • ...The received data is first conjugated, processed using the standard CO-OFDM DSP algorithms [33] and the performance of the same is evaluated as a function of the OSNR as shown in Fig....

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  • ...The digitized output is post-processed using off-line digital signal processing (DSP) algorithms, which includes (correlation-based) time and (blind) frequency synchronization, training symbols based channel estimation/ equalization and pilot subcarriers assisted phase noise correction [33]....

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Posted ContentDOI
TL;DR: A DWPT based CO-OFDM system with Wilcoxon Robust Extreme Learning Machine based pilot-free phase noise compensator using multi-level QPSK partitioning of 16-QAM has been proposed and the percentage improvement in performance and spectral efficiency over traditional pilot-aided techniques is 6 and 21 respectively.
Abstract: Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) system with Pilot-free phase noise compensator was introduced in order to accomplish the need of high spectral efficiency in the optical communication. In CO-OFDM system Discrete wavelet packet transforms (DWPTs) in place of Fast Fourier Transforms (FFTs) had attracted more attention since it has removed the need of cyclic prefix used to compensate fiber dispersion. In this paper, a DWPT based CO-OFDM system with Wilcoxon Robust Extreme Learning Machine based pilot-free phase noise compensator using multi-level QPSK partitioning of 16-QAM has been proposed. From the results of this work it has been seen that the percentage improvement in performance (in terms of Q-Factor) and spectral efficiency over traditional pilot-aided techniques is approximately 6 and 21 respectively. Moreover, this proposed work will comparatively reduce the overall system complexity.
References
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Journal ArticleDOI
TL;DR: An exact analysis of orthogonal frequency-division multiplexing (OFDM) performance in the presence of phase noise and a general phase-noise suppression scheme which, by analytical and numerical results, proves to be quite effective in practice.
Abstract: We provide an exact analysis of orthogonal frequency-division multiplexing (OFDM) performance in the presence of phase noise Unlike most methods which assume small phase noise, we examine the general case for any phase noise levels After deriving a closed-form expression for the signal-to-noise-plus-interference ratio (SINR), we exhibit the effects of phase noise by precisely expressing the OFDM system performance as a function of its critical parameters This helps in understanding the meaning of small phase noise and how it reflects on the proper parameters selection of a specific OFDM system In order to combat phase noise, we also provide in this paper a general phase-noise suppression scheme, which, by analytical and numerical results, proves to be quite effective in practice

355 citations


"Pilot-free common phase error estim..." refers background in this paper

  • ...However, due to the longer symbol duration (Ts), the CO-OFDM system is more susceptible to phase noise due to laser linewidth ( ν2 ) and hence suffers performance degradation due to common phase error (CPE) and inter carrier interference (ICI) [4]....

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  • ...N F F T and N F F T is the number of subcarriers; Ym (k), Xm (k), I C I m (k) and Wm (k) represent the received signal, transmitted signal, Inter Carrier Interference (ICI) and AWGN terms respectively in the kth sub-carrier of the mth OFDM symbol....

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  • ...This algorithm can be further extended by modifying and incorporating equalization for the effect of ICI and the state vector of the Kalman filter can also take additional parameter to estimate and correct the residual frequency offset, if any....

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  • ...However, due to the longer symbol duration (Ts), the CO-OFDM system is more susceptible to phase noise due to laser linewidth ( ν 2 ) and hence suffers performance degradation due to common phase error (CPE) and inter carrier interference (ICI) [4]....

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  • ...The ICI component due to phase noise is described as I C Im (k) = N F F T −1∑ l=0, l =k Xm (l)Im (l − k), (2) with Im (p ) = 1N F F T N F F T −1∑ n=0 e j [ 2πp n N F F T +φm (n) ] (3) where Im (0) is the common phase error (CPE) factor given as Im (0) ≈ exp (jφ(m)) and φ(m) is the CPE across the subcarriers of the mth OFDM symbol given as φ(m) = arg { 1 N F F T N F F T −1∑ n=0 e jφm (n) } ....

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Proceedings Article
01 Sep 2009
TL;DR: In this paper, the authors demonstrate the generation of a 1.2-Tb/s NGI-CO-OFDM superchannel comprising of 24 frequency-locked 12.5GHz spaced PDM-QPSK carriers, and transmit it over 72×100-km of ultra-large-area fiber, achieving 3.7b /s/Hz channel spectral efficiency.
Abstract: We demonstrate the generation of a novel 1.2-Tb/s NGI-CO-OFDM superchannel comprising of 24 frequency-locked 12.5-GHz spaced PDM-QPSK carriers, and transmit it over 72×100-km of ultra-large-area fiber, achieving 3.7-b/s/Hz channel spectral-efficiency (SE) and a record SE-distance product of 27,000-km·b/s/Hz.

264 citations


"Pilot-free common phase error estim..." refers background in this paper

  • ...Coherent optical OFDM (CO-OFDM) is one such multi-carrier scheme that is comprehensively investigated in optical communication systems as an alternate to Nyquist pulse shaped single carrier transmission for >Terabit/s transmission and inelastic optical networks [2]....

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Journal IssueDOI
TL;DR: In this paper, the optical OFDM architectures are reviewed, and their performance under various system conditions are compared and compared with alternative technologies, and the challenges in the implementation of optical ONDM are also discussed.
Abstract: Orthogonal frequency division multiplexing (OFDM) is a widely used modulation/multiplexing technology in wireless and data communications. Leveraging recent advances in high-speed complementary metal-oxide semiconductor (CMOS) technologies and optical modulation and detection technologies, optical OFDM at a 40Gb/s or even a 100Gb/s information rate becomes feasible. At the optical transmitter, OFDM is realized by a digital signal processor (DSP) using inverse fast Fourier transformation (iFFT) with subsequent digital-to-analog conversion and Cartesian electro-optic modulation. At the receiver, the signal optical field is first reconstructed, e.g., by coherent detection. Then reverse signal processing is applied to recover the original data. OFDM enables efficient compensation of transmission effects such as chromatic dispersion and polarization mode dispersion that often are prohibiting impairments to cost-effective realization of high-speed optical transport systems. In light of the emerging demand for a 100+ Gb/s data rate in future optical transport systems, optical OFDM is considered to be a promising enabling technology. In this paper, the optical OFDM architectures will be reviewed, and their performance under various system conditions will be discussed and compared with alternative technologies. The challenges in the implementation of optical OFDM will also be discussed.

58 citations


"Pilot-free common phase error estim..." refers background in this paper

  • ...CO-OFDM also has extreme tolerance to linear fiber impairments such as chromatic dispersion and polarization mode dispersion and hence enables simple equalization [3]....

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Journal ArticleDOI
TL;DR: The feasibility of zero-overhead laser phase noise compensation (PNC) for long-haul coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission systems, using the decision-directed phase equalizer (DDPE), and the complexity of DDPE versus CE is analyzed in terms of the number of required complex multiplications per bit.
Abstract: We report and investigate the feasibility of zero-overhead laser phase noise compensation (PNC) for long-haul coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission systems, using the decision-directed phase equalizer (DDPE). DDPE updates the equalization parameters on a symbol-by-symbol basis after an initial decision making stage and retrieves an estimation of the phase noise value by extracting and averaging the phase drift of all OFDM sub-channels. Subsequently, a second equalization is performed by using the estimated phase noise value which is followed by a final decision making stage. We numerically compare the performance of DDPE and the CO-OFDM conventional equalizer (CE) for different laser linewidth values after transmission over 2000 km of uncompensated single-mode fiber (SMF) at 40 Gb/s and investigate the effect of fiber nonlinearity and amplified spontaneous emission (ASE) noise on the received signal quality. Furthermore, we analytically analyze the complexity of DDPE versus CE in terms of the number of required complex multiplications per bit.

49 citations


"Pilot-free common phase error estim..." refers background or methods in this paper

  • ...Non-pilot aided zero-overhead CPE estimations were proposed in [7], [8] by using higher order statistics and decision directed (DD) iterative algorithms....

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  • ...For instance, [7] estimated the complexity of the DD algorithm to be almost 28% additional compared to the conventional pilot aided algorithm....

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  • ...The polarization is adjusted to have maximum power coupled in one of the polarization and is then fed to a phase diverse coherent receiver with a local oscillator tuned to 1550 nm and with ν ≈ 50 KHz....

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  • ...In this method these pilots are used at the receiver to estimate the CPE as [7], [8]...

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  • ...In addition, DD-CPE algorithms inherit error propagation when the initialization is erroneous or when the laser linewidth is large (>100 KHz) [7]....

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Journal ArticleDOI
TL;DR: The carrier phase recovery for 16-ary quadrature amplitude modulation (16-QAM) optical coherent systems using the quaternary phase-shift keying (QPSK) partitioning with sliding window averaging and differential decoding with the impact of analog-to-digital converter (ADC) resolution is investigated.
Abstract: This letter presents the carrier phase recovery for 16-ary quadrature amplitude modulation (16-QAM) optical coherent systems using the quaternary phase-shift keying (QPSK) partitioning with sliding window averaging and differential decoding. We assess the increase in linewidth tolerance achievable with sliding window averaging as opposed to block averaging. Simulation results demonstrate that combined linewidth symbol duration product, Δv · Ts, 10-4 is tolerable at the target bit error ratio (BER) of 10-2 and 10-3 for a penalty of 0.6 and 0.8 dB, respectively, compared with the theoretical limit with differential decoding. The impact of analog-to-digital converter (ADC) resolution on the performance of the QPSK partitioning algorithm is also investigated. Finally, the performance of the algorithm using the measured phase noise for a distributed feedback (DFB) laser is presented for different values of Δv · Ts. We show that for Δv · Ts > 10-4, the penalty of block averaging is > 0.5 dB with respect to sliding window averaging at the target BER of 10-3 with the measured phase noise. The degradation associated with block averaging at the target BER of 10-2 is shown to be less significant compared to sliding window averaging.

32 citations


"Pilot-free common phase error estim..." refers methods in this paper

  • ...In such square MQAM baseband modulated data, a multi-level QPSK partitioning [10] is performed to extract the outermost and the innermost QPSK points from the constellation....

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