scholarly journals OCT-Precoding Combined with LDPC-Coding Scheme for 128 QAM MB-OFDM UWBoF System

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Changqing Xiang ◽  
Xi Yang ◽  
Xiaojun Zhu ◽  
Qiong He ◽  
Renmin Zhang ◽  
...  
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Signal To Noise Ratio ◽  
Ldpc Code ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Practical Application ◽  
Coding Scheme ◽  
Traditional Scheme ◽  
Receiver Performance ◽  
The Difference

In this paper, we proposed a coding scheme based on orthogonal cyclic transpose (OCT) precoding combined with low-density parity check (LDPC) code to improve the transmission performance of 128-quadrature amplitude modulation multiband orthogonal-frequency-division-multiplexing ultrawide band over fiber (128 QAM MB-OFDM UWBoF) system. The proposed scheme could not only improve the performance of the system but also average the signal-to-noise ratio (SNR) of subcarriers and reduce the difference among subchannels in practical application. The simulation results showed that compared with the traditional scheme, the receiver performance of this scheme was improved by 2.7 dB when the LDPC-coding rate was 87.5% through 70 km standard single mode fiber (SSMF) transmission and the bit error rate (BER) was 3.8 × 10−3. Besides, the constellation distribution was more convergent and uniform.

Efficient Blind Adaptive CSE to Reduce Cyclic Prefix Length in Direct Detection Optical OFDM Systems

2019 ◽  
Vol 0 (0) ◽  
Author(s):  
Asmaa Benieddi ◽  
Sid Ahmed Elahmar
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Direct Detection ◽  
Group Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Single Mode ◽  
Optical Signal ◽  
Single Mode Fiber ◽  
Cyclic Prefix ◽  
Ofdm Systems ◽  
Blind Adaptive

AbstractDirect detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems for a long-reach of standard single mode fiber (SSMF) require a large length of cyclic prefix (CP) to avoid the inter-symbol interference (ISI) effect caused by group velocity dispersion (GVD). Unfortunately, this method is inefficient due to the energy wasted in CP samples. In order to reduce the CP length and to mitigate the residual ISI, a novel blind adaptive channel shortening equalizer (CSE) is proposed in this paper. Based on the orthogonality between subcarriers in the fast Fourier transform (FFT) property, the proposed algorithm attempts to minimize the sum-squared correlation (SSCM) between each sample located in a well-defined window to update the CSE coefficients. Thus, the combined channel-CSE response is shortened. Therefore, it can cancel the residual ISI effect due to the GVD and the short CP length. The performance of the system is evaluated on basis of bit error rate (BER) versus optical signal to noise ratio (OSNR) for different CP lengths. The simulation results validate the new algorithm SSCM and show that it can reduce the CP length with a much better system improvement than existing algorithms.

scholarly journals Microdrilled tapers to enhance optical fiber lasers for sensing

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. A. Perez-Herrera ◽  
M. Bravo ◽  
P. Roldan-Varona ◽  
D. Leandro ◽  
L. Rodriguez-Cobo ◽  
...  
Keyword(s):  
Optical Fiber ◽  
Optical Fibers ◽  
Fiber Lasers ◽  
Signal To Noise Ratio ◽  
Power Level ◽  
Single Mode ◽  
Optical Signal ◽  
Single Mode Fiber ◽  
Output Power Level ◽  
Linear Cavity

AbstractIn this work, an experimental analysis of the performance of different types of quasi-randomly distributed reflectors inscribed into a single-mode fiber as a sensing mirror is presented. These artificially-controlled backscattering fiber reflectors are used in short linear cavity fiber lasers. In particular, laser emission and sensor application features are analyzed when employing optical tapered fibers, micro-drilled optical fibers and 50 μm-waist or 100 μm-waist micro-drilled tapered fibers (MDTF). Single-wavelength laser with an output power level of about 8.2 dBm and an optical signal-to-noise ratio of 45 dB were measured when employing a 50 μm-waist micro-drilled tapered optical fiber. The achieved temperature sensitivities were similar to those of FBGs; however, the strain sensitivity improved more than one order of magnitude in comparison with FBG sensors, attaining slope sensitivities as good as 18.1 pm/με when using a 50 μm-waist MDTF as distributed reflector.

scholarly journals Improved Training Sequence Channel Estimation Scheme in 16QAM MB-OFDM UWBoF System

2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Changqing Xiang ◽  
Xi Yang ◽  
Xuan Zhou ◽  
Xiaojun Zhu ◽  
Jincan Xu ◽  
...  
Keyword(s):  
Channel Estimation ◽  
Time Domain ◽  
Orthogonal Frequency Division Multiplexing ◽  
Single Mode ◽  
Training Sequence ◽  
Single Mode Fiber ◽  
Frequency Division ◽  
Training Sequences ◽  
Estimation Scheme ◽  
Simulation Results

In this paper, an improved channel estimation scheme based on time-domain orthogonal gray complementary training sequence (Golay TS) is proposed to resist subcarrier mutual beat interference in 16-quadrature amplitude modulation multiband orthogonal-frequency-division-multiplexing ultrawide band over fiber (16QAM MB-OFDM UWBoF) systems. The simulation results showed that the performance of system with the improved Golay TS channel estimation scheme was improved by about 1 dB compared with the traditional Golay TS channel estimation scheme, at a bit error rate (BER) of 3.8 × 10−3 after 70 km standard single mode fiber (SSMF) transmission. At the same time, the synchronization and channel estimation performance of Golay TS and the selected frequency-domain orthogonal training sequences (TSs) were compared. The simulation results showed that the performance of system with the TSs channel estimation was improved by about 2.7 dB compared with the improved Golay TS channel estimation.

scholarly journals Carrier-Assisted Phase Retrieval

2021 ◽  
Author(s):  
Qi Wu
Keyword(s):  
Phase Retrieval ◽  
Forward Error Correction ◽  
Signal To Noise Ratio ◽  
Single Mode ◽  
Local Oscillator ◽  
Optical Signal ◽  
Single Mode Fiber ◽  
Critical Parameters ◽  
Hardware Complexity ◽  
Full Field

Phase-retrieval (PR) schemes based on the modified Gerchberg-Saxton (GS) algorithm capture the full-field employing a dispersive element and intensity-only measurements to eliminate the use of a local oscillator. In this work, we propose two carrier-assisted PR schemes, namely central carrier-assisted PR (CCA-PR) and edge carrier-assisted PR (ECA-PR), to improve the comprehensive performance of PR receiver in terms of convergence speed, redundancy, and computational complexity. The proposed CCA-PR recovers the electrical field employing a reference carrier at 0 GHz with several iterations between two projection planes. It avoids pilot symbols and digital backpropagation to the transmitter and offers a flexible electrical bandwidth requirement compared with conventional PR schemes. To lower the carrier-to-signal power ratio (CSPR) requirement and enable faster convergence for the carrier-assisted PR schemes, the ECA-PR is proposed to obtain the initial phase for the GS algorithm. We numerically characterize the performance of the two schemes and experimentally demonstrate them for 30 GBaud 16-quadrature amplitude modulation (16-QAM) transmission over 80 km single-mode fiber with a bit error rate (BER) below the threshold of 7% hard-decision forward error correction (HD-FEC). Several critical parameters are analyzed, including the applied dispersion value, CSPR, and electrical bandwidth. Moreover, we compare the hardware complexity and optical signal-to-noise ratio (OSNR) sensitivity of proposed PR schemes with mainstream field recovery schemes.

Analysis of secured Optical Orthogonal Frequency Division Multiplexed System

2017 ◽  
Vol 38 (2) ◽  
Author(s):  
Harsimranjit Singh Gill ◽  
Kamaljit Singh Bhatia ◽  
Sandeep Singh Gill
Keyword(s):  
Signal To Noise Ratio ◽  
Average Power ◽  
Single Mode ◽  
Optical Signal ◽  
Data Encryption ◽  
Single Mode Fiber ◽  
Frequency Division ◽  
Ofdm Systems ◽  
Ofdm Signal ◽  
Coded Ofdm

AbstractIn this paper, security issues for optical orthogonal frequency division multiplexed (OFDM) systems are emphasized. The encryption has been done on the data of coded OFDM symbols using data encryption standard (DES) algorithm before transmitting through the fiber. The results obtained justify that the DES provides better security to the input data without further bandwidth requirement. The data is transmitted to a distance of 1,000 km in a single-mode fiber with 16-quadrature amplitude modulation. The peak-to-average power ratio and optical signal-to-noise ratio of secure coded OFDM signal is fairly better than the conventional OFDM signal.

scholarly journals Joint Encryption Scheme Based on the Chaotic DCT Matrix and SLM Algorithm in an OFDM-PON System

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Shuai Zhang ◽  
Liqun Huang ◽  
Mingxu Zhu
Keyword(s):  
Data Transmission ◽  
Orthogonal Frequency Division Multiplexing ◽  
Optical Network ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Passive Optical Network ◽  
Encryption Scheme ◽  
Chaotic Mapping ◽  
Data Transmission Security ◽  
Selective Mapping

In order to effectively solve the problem of data transmission security and peak-to-average ratio (PAPR) in an orthogonal frequency division multiplexing passive optical network (OFDM-PON) transmission system, in this paper, a joint encryption scheme of discrete cosine transform (DCT) and selective mapping (SLM) based on chaotic mapping is proposed. In this scheme, the chaotic sequence of a 3D Lorenz chaotic system is used as the row and column index of the DCT matrix and the phase factor of SLM to resist selective plaintext attack, and the system encryption is realized while reducing PAPR. The theoretical analysis and numerical simulation show that the common OFDM-PON, the proposed algorithm, can obtain a PAPR suppression gain of ∼4.8 dB and improve the receiver sensitivity by ∼4 dB BER @ 10 − 3 . In addition, it shows that, with the increase of row/column index mismatch of the DCT matrix, the bit error rate of the system increases gradually. An encrypted data transmission of 8 GB/s 16-QAM optical OFDM signals is successfully simulated over a 20 km standard single-mode fiber, which proves the excellent confidentiality of the proposed secure transmission.

scholarly journals Faster-Than-Nyquist 400 G Implementation Using 126-GBaud QPSK-OFDM With 88-GSa/s Undersampling

2021 ◽  
Vol 9 ◽  
Author(s):  
Peng Liu ◽  
Hongxian Chen ◽  
Weihao Ni ◽  
Fan Li
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Forward Error Correction ◽  
Sampling Rate ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Mobile Internet ◽  
Optical Carrier ◽  
Low Frequencies ◽  
Ofdm Signal ◽  
Internet Of Things Technology

In this study, we demonstrated generation and transmission of 114 Gbaud and 126 Gbaud faster-than-Nyquist (FTN) discrete Fourier transform-spread (DFT-spread) quadrature phase shift keying orthogonal frequency division multiplexing (QPSK-OFDM) with 88-Gsa/s sampling rate digital-to-analog converters (DACs) experimentally. It is the first time to realize 400G FTN DFT-spread QPSK-OFDM signal per optical carrier for metro and regional applications, which will be a solution for network operators to address the issue of increasing bandwidth derived from the rapid popularization of mobile Internet and the wide application of IoT (Internet of Things technology). Delay-and-add filter (DAF) is adopted to realize frequency shaping at the transmitter to keep higher portions of energy of signal at low frequencies, which makes the OFDM much more robust to strong filtering effect. After pre-equalization, bit error rate (BER) performance of 114 GBaud and 126 GBaud FTN DFT-spread QPSK-OFDM has been significantly improved, and maximum-likelihood sequence estimation (MLSE) shows a better effect than binary decoding in the aspect of against the inter symbol interference (ISI) introduced by spectrum compression. The effective bit rate of dual polarization 126 Gbaud FTN DFT-spread QPSK-OFDM which is generated with 88 GSa/s sampling rate is 410.08 Gb/s, to the exclusion of all overhead including TSs, cyclic prefix (CP), and 20% forward error correction (FEC) coding. We successfully transmit 8 × 400 Gbit/s FTN DFT-spread QPSK-OFDM signal generated from 88 Gsa/s sampling rate DAC over 420 km single mode fiber (SMF) with the BER under 2.4 × 10−2.

scholarly journals An Off-Axis Differential Method for Improvement of a Femtosecond Laser Differential Chromatic Confocal Probe

2020 ◽  
Vol 10 (20) ◽  
pp. 7235
Author(s):  
Chong Chen ◽  
Yuki Shimizu ◽  
Ryo Sato ◽  
Hiraku Matsukuma ◽  
Wei Gao
Keyword(s):  
Femtosecond Laser ◽  
Focal Plane ◽  
Signal To Noise Ratio ◽  
Single Mode ◽  
Measurement Range ◽  
Single Mode Fiber ◽  
Differential Method ◽  
Laser Source ◽  
Dual Detector ◽  
Chromatic Confocal Probe

This paper presents an off-axis differential method for the improvement of a femtosecond laser differential chromatic confocal probe having a dual-detector configuration. In the proposed off-axis differential method employing a pair of single-mode fiber detectors, a major modification is made to the conventional differential setup in such a way that the fiber detector in the reference detector is located at the focal plane of a collecting lens but with a certain amount of off-axis detector shift, while the fiber detector in the measurement detector is located on the rear focal plane without the off-axis detector shift; this setup is different from the conventional one where the difference between the two confocal detectors is provided by giving a defocus to one of the fiber detectors. The newly proposed off-axis differential method enables the differential chromatic confocal setup to obtain the normalized chromatic confocal output with a better signal-to-noise ratio and approaches a Z-directional measurement range of approximately 46 μm, as well as a measurement resolution of 20 nm, while simplifying the optical alignments in the differential chromatic confocal setup, as well as the signal processing through eliminating the complicated arithmetic operations in the determination of the peak wavelength. Numerical calculations based on a theoretical equation and experiments are carried out to verify the feasibility of the proposed off-axis differential method for the differential chromatic confocal probe with a mode-locked femtosecond laser source.

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