Quasi-distributed sensing network based on coherence multiplexing and spatial division multiplexing for coal mine security monitoring

A low-cost fiber Bragg grating(FBG) sensing system for coal-mine security monitoring is proposed in this paper.Based on the coherence multiplexing(CM) and spatial division multiplexing(SDM) techniques,this hybrid sensing network can support more than 40 sensors for quasi-distributed detection.It is demonstrated experimentally that the multiplexed sensing signal of each sensor can be clearly distinguished by an optical low-coherence reflectometry(OLCR).Methane concentration is detected with maximum sensitivities of an intensity variation of 10.92% and a concentration variation of 1%,using a well-designed sensor structure.Strain and temperature are also detected by this system,which also exhibits good results in the experiment.

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.

From first fibers to mode-division multiplexing(Invited Paper)

This Review focuses on optical transmission fibers and the high-capacity systems operating thereon. It attempts to combine key lessons learned from the 50-year history of low-loss optical fibers with views on future fiber and systems requirements, discussing likely evolution paths and potential pitfalls in resolving the optical network capacity crunch.

2 Tbit/s based coherent wavelength division multiplexing passive optical network for 5G transport

Future high-speed mobile communication systems require low latency and high capacity networks.Coherent wavelength division multiplexing(WDM)passive optical network(PON)scheme is expected to play a vital role in these systems.In this paper,coherent WDM-PON scheme based on dual-polarization 16-quadrature amplitude modulation(DP-16 QAM)transceiver has been investigated.The aim of this scheme is to build a 2 Tbit/s(125 Gbit/s/λ×16 wavelengths)network that will be used in the construction of the transport architecture of fifth generation(5 G)and beyond 5 G(B5 G)cellular networks either in mobile front haul(MFH)or mobile back haul(MBH).The results indicate that the proposed scheme is very adequate for both 5 G and B5 G cellular networks requirements.

Improved pilot data aided feed forward based on maximum likelihood for carrier phase jitter recovery in coherent optical orthogonal frequency division multiplexing

Pilot data aided feed forward （PAFF） carrier recovery is essential for phase noise tracking in coherent optical receivers. This paper describes a new PAFF system based on new pilot arrangement and maximum likelihood （ML） to estimate the phase jitter in coherent receiver- induced by local oscillator＇s lasers and sampling clock errors. Square M-ary quadrature amplitude modulation （M-QAM） （4, 16, 64, and 256） schemes were used. A detailed mathematical description of the method was presented. The system performance was evaluated through numerical simulations and compared to those with noisefree receiver （ideal receiver） and feed forward without ML. The simulation results show that PAFF performs near the expected ideal phase recovery. Results clearly suggest that ML significantly improves the tolerance of phase error variance. From bit error rate （BER） sensibility evaluation, it was clearly observed that the new estimation method performs better with a 4-QAM （or quadrature phase shift keying （QPSK）） format compared to three others square QAM schemes. Analog to digital converter （ADC） resolution effect on the system performance was analyzed in terms of Q-factor. Finite resolution effect on 4-QAM is negligible while it negatively affects the system performance when M increases.

Carrier recovery in coherent receiver of optical orthogonal frequency division multiplexing system

In this paper, we reviewed our common phase error （CPE） and intercarrier interference （ICI） compensation methods for coherent optical orthogonal frequency division multiplexing （CO-OFDM） system. We first presented a unified CPE estimation framework combining decision-aided （DA）, pilot-aided （PA） and decision feed- back （DF） algorithms. The DA method is used to estimate the CPE of the current OFDM symbol based on the decision statistics of the previous symbol. DA ＋ PA helps increase the phase noise tolerance of DA and reduce the overhead of PA, while DA ＋ DF reduces the overhead to zero, achieving best performance with one more step of estimation, compensation and demodulation. We also described a modified time-domain blind intercarrier interference （BL-ICI） mitigation algorithm over non- constant amplitude formats. The new algorithm is derived from the BL-ICI algorithm over constant amplitude format for wireless networks. A new power estimation scheme was proposed for the BL-ICI algorithm to adapt to non- constant amplitude format. It has the same order of complexity with frequency domain decision-aided ICI （DA-ICI） compensation method and does not suffer from symbol decision errors. The effectiveness of both CPE and ICI compensation algorithms were demonstrated in a simulated 56-Gbit/s CO-OFDM system with various modulation formats.

A novel improved SLM scheme of the PAPR reduction technology in CO-OFDM systems

The higher peak-to-average power ratio(PAPR) is a major shortcoming of coherent optical orthogonal frequency division multiplexing(CO-OFDM) systems. Selective mapping(SLM) technology can effectively reduce the probability of high PAPR, but it has higher computational complexity, and requires additional bandwidth to transmit the side information, which will affect the transmission efficiency of the system. In response to these shortcomings, a novel improved SLM(NI-SLM) scheme with low complexity and without side information is proposed. Simulation results show that the proposed scheme can exponentially reduce the computational complexity, and the bit error rate(BER) performance can greatly approach the original signal. What's more, it shows the better PAPR reduction performance.

Recent progress in an ‘ultra-high speed, ultra-large capacity, ultra-long distance' optical transmission system(Invited Paper)

From 2010 to 2015, the Wuhan Institute of Posts and Telecommunications（WRI） had undertaken the national key basic research development program project ‘ultra-high speed, ultra-large capacity, ultra-long distance（3U）optical transmission based research＇ as the leading agency. Under the support of the project, we have obtained a series of achievements in scientific research and engineering. Some of the results have been widely used in commercial systems. This Review will make a preliminary summary of the achievements during the past 5 years.

Transmission of 200 Tb/s （375 × 3 × 178.125 Gb/s） PDM-DFTS-OFDM-32QAM super channel over lkm FMF

A few-mode fiber （FMF） is designed to support three spatial modes （LP01, LP 11a, and LP 11 b） and fabricated through plasma chemical vapor deposition （PCVD）and rod-in-tube （RIT） method. Using PDM-DFTS-OFDM- 32QAM modulation, wavelength division multiplexing, mode multiplexing, and coherent detection, we successfully demonstrated 200Tb/s （375× 3 × 178.125Gb/s） signal over 1 km FMF using C and L bands with 25 GHz channel spacing. After 1 km FMF transmission, all the tested bit error rates （BERs） are below 20% forward error correction （FEC） threshold （2.0 × 10-2）. Within each sub-channel, we achieved a spectral efficiency of 21.375 bits/Hz in the C and L bands.

A novel timing synchronization for CO-OFDM systems using CAZAC sequences

A novel symbol timing synchronization algorithm based on constant amplitude zero auto correlation(CAZAC) sequences is proposed for coherent optical orthogonal frequency division multiplexing(CO-OFDM) systems. The training symbol of the proposed algorithm is comprised of four different parts, utilizing even symmetry property of each part to accomplish timing synchronization. The performance of the proposed algorithm is demonstrated by means of simulations in OFDM and CO-OFDM systems. The proposed algorithm is shown to eliminate the timing sidelobes of Park's algorithm and has a more accurate timing estimation. In the condition of chromatic dispersion(CD), the timing metric of the proposed method still maintains its peak value at the correct timing point, while the values are almost 0 at all the other positions. Meanwhile, the timing mean square error(MSE) of the proposed algorithm remains around 10^(-6).

A code-aided carrier synchronization algorithm based on improved nonbinary low-density parity-check codes

In order to further improve the carrier synchronization estimation range and accuracy at low signal-to-noise ratio(SNR), this paper proposes a code-aided carrier synchronization algorithm based on improved nonbinary low-density parity-check(NB-LDPC) codes to study the polarization-division-multiplexing coherent optical orthogonal frequency division multiplexing(PDM-CO-OFDM) system performance in the cases of quadrature phase shift keying(QPSK) and 16 quadrature amplitude modulation(16-QAM) modes. The simulation results indicate that this algorithm can enlarge frequency and phase offset estimation ranges and enhance accuracy of the system greatly, and the bit error rate(BER) performance of the system is improved effectively compared with that of the system employing traditional NB-LDPC code-aided carrier synchronization algorithm.