Enabling cost-effective high-performance vibration sensing in digital subcarrier multiplexing systems.

Enabling communication networks with sensing functionality has attracted significant interest lately. The digital subcarrier multiplexing (DSCM) technology is widely promoted in short-reach scenarios for its inherent flexibility of fine-tuning the spectrum. Its compatibility with large-scale as-deployed coherent architectures makes it particularly suited for cost-sensitive integrated sensing and communication applications. In this paper, we propose a scheme of spectrally integrating the digital linear frequency modulated sensing signal into DSCM signals to achieve simultaneous sensing and communication through shared transmitter. Consequently, this cost-effective scheme has been demonstrated to achieve 100-Gb/s dual-polarization quadrature phase-shift keying (DP-QPSK) and 200-Gb/s dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM) transmission with a distributed acoustic sensing sensitivity of 69 pε/Hz and 88 pε/Hz respectively, at a spatial resolution of 4 m.

Low-complexity amplitude-division irregular QAM formats for short-reach unamplified coherent optical systems.

A low-complexity scheme is proposed to realize irregular uniform quadrature amplitude modulation (QAM) formats with Gray mapping, which are named amplitude-division irregular QAM (AD-Ir-QAM) formats. Compared to conventional probabilistic shaping (PS) with the Maxwell-Boltzmann (MB) distribution (PS-MB), irregular QAM formats show a smaller peak-to-average power (PAPR) and achieve a better performance in systems with the peak-power constraint. Compared with irregular QAM formats realized by PS (PS-Ir-QAM), AD-Ir-QAM formats realize a more flexible rate adaptation and have a lower implementation complexity. Experimental results obtained in an unamplified coherent optical system show that, at a generalized mutual information (GMI) of 4.5 bits/2D-symbol, AD-Ir-100QAM achieves gains of 2.1 and 0.5 dB in the power budget over PS-MB-100QAM and PS-Ir-100QAM, respectively.

Digital pre-distortion using a Gauss-Newton-based direct learning architecture for coherent optical transmitters.

Digital pre-distortion (DPD) is a powerful technique to mitigate transmitter nonlinear distortion in optical transmissions. In this Letter, the identification of DPD coefficients based on the direct learning architecture (DLA) using the Gauss-Newton (GN) method is applied in optical communications for the first time. To the best of our knowledge, this is the first time that the DLA has been realized without training an auxiliary neural network to mitigate optical transmitter nonlinear distortion. We describe the principle of the DLA using the GN method and compare the DLA with the indirect learning architecture (ILA) that uses the least-square (LS) method. Extensive numerical and experimental results indicate that the GN-based DLA is superior to the LS-based ILA, especially in a low signal-to-noise ratio scenario.

Coherent digital-analog radio-over-fiber (DA-RoF) system with a CPRI-equivalent data rate beyond 1 Tb/s for fronthaul.

We propose and experimentally demonstrate a coherent digital-analog radio-over-fiber (DA-RoF) system and achieve the transmission of Tb/s common public radio interface (CPRI)-equivalent data rate for fronthaul. The proposed coherent DA-RoF system includes DA-RoF modulation, demodulation and DA-RoF compatible coherent digital signal processing (DSP) blocks. A theoretical analysis of the DA-RoF scheme together with parameter optimization is accomplished as well. In the experiment, a 25 Gbaud DA-RoF signal with 1 Tb/s CPRI-equivalent data rate is transmitted in the system, satisfying the error vector magnitude (EVM) requirement for 256-quadrature amplitude modulation (QAM) signal transmission. With the symbol rate reduced to 10 Gbaud, an EVM below 2.5% is achieved, which meets the requirement for 1024-QAM transmission. The experimental results show that the coherent DA-RoF system is a promising solution for future fronthaul.

Subcarrier-pairing entropy loading for digital subcarrier-multiplexing systems with colored-SNR distributions.

A subcarrier-pairing entropy loading (SubP-EL) scheme with fairly low complexity is proposed for digital subcarrier-multiplexing (SCM) systems with colored signal-to-noise ratio (SNR) distributions. With the constraint of the target entropy, SubP-EL iteratively optimizes the entropy of subcarriers in pair. After convergence, SubP-EL can approach the optimal performance which is evaluated in simulations and experiments by comparison with the brute-force search method. Meanwhile the complexity of SubP-EL is significantly reduced compared with the brute-force search. In particular, in an 8-subcarrier system with five different SNRs, the complexity of SubP-EL is reduced by approximately a factor of 764, 95 and 13 with the entropy granularities of 0.05 bits/2D-symbol, 0.1 bits/2D-symbol and 0.2 bits/2D-symbol, respectively. The performance of SubP-EL is evaluated in simulations and experiments. In the experiments with 345 km fiber transmissions, the average NGMI gain of SubP-EL over the system without entropy loading is 0.0286 for different optical filtering cases.

Frequency-offset-tolerant optical frequency comb-based coherent transmission for intra-datacenter interconnections.

In recent years, in order to increase the capacity and scalability of intra-datacenter (DC) transmission, the optical frequency comb (OFC) source has been considered promising to replace discrete lasers, aiming to reduce the cost of wavelength division multiplexing (WDM) transmission within DC. In this paper, an OFC based coherent architecture is proposed. An OFC, in the receiver side, is split by a splitter with a uniform power ratio and separately used as local oscillators (LOs) to detect the demultiplexed signals. The signal spectrum is copied onto every tone of the LO-OFC, and a large frequency offset (FO) tolerance is achieved. In addition, the required ADC sampling rate is the same as a system without FO. Extensive simulations are conducted. In the simulated coherent WDM transmission system, a 3-tone-OFC is used to provide 3 carriers, and an 11-tone-OFC is split and used to provide LO-OFCs. For a 64GBd polarization multiplexing 16 quadrature amplitude modulation (PM-16QAM) WDM transmission, the tolerances of FO are up to about ±0.3THz and ±0.374THz for the 1st/3rd signal, and the 2nd signal, respectively, below the pre-forward error correction (FEC) bit error rate (BER) level of 1.25×10-2. Moreover, the maximum tolerance of FO linearly increases with the number of effective tones in LO-OFC. Further, extensive experiments with back-to-back connection are conducted to verify the performance. The tolerance of FO is up to >36 GHz for 36GBd PM-16QAM transmission with a 3-tone-LO-OFC below the BER level of 1.25×10-2. The proposed OFC based coherent architecture is a promising solution for intra-DC interconnections with a large FO.

PMD estimation and its enabled feedforward adaptive equalization based on superimposed FrFT training sequences.

Fractional Fourier transform (FrFT) training sequences (TSs) have been proposed to superimpose with signals to achieve time synchronization and polarization mode dispersion (PMD) estimation simultaneously before equalization. The feasibility of the proposed scheme is verified by experiment of a 30 GBaud/s PDM quadrature phase shift keying (QPSK) system. Without sacrificing spectrum efficiency, the proposed PMD estimation is robust against amplifier spontaneous emission (ASE) noise and has steady performance in a wide PMD range from 0 ps to 108 ps. The root mean square error (RMSE) of PMD is 5.6 ps by experimental verification. Further, the PMD estimated before equalization is utilized to adjust the numbers of taps in a subsequently tap-varied equalizer, which achieves feedforward adaptive equalization (FFD-AEQ). The number of the AEQ taps is adjusted to an optimal value with the prior-PMD information estimated by FrFT TSs. The experimental results show that the tap-varied AEQ has 52.6% power consumption decrease compared to the tap-fixed AEQ with 13 taps.

Ultra-fast RSOP tracking via 3 pilot tones for short-distance coherent SCM systems.

We propose an algorithm to track the rotation of state of polarization (RSOP) for short-distance coherent subcarrier-multiplexing systems. 3 pilot tones are used to estimate RSOP matrices on a block-by-block basis and recover phase noise as well. An ultra-fast RSOP tracking ability using the proposed algorithm is demonstrated by experiment. Specifically, the bit error rate increases from 2.3×10-3 to 5.6×10-3 when the RSOP speed increases from 0 rad/s to 50 Mrad/s. We also demonstrate the robustness of the algorithm against polarization mode dispersion and polarization dependent loss.

[Short-term effectiveness of acetabular reconstruction with three-dimensional printed trabecular metal pads in hip revision].

OBJECTIVE: To investigate the short-term effectiveness of three-dimensional (3D) printed trabecular metal pads for Paprosky type Ⅲ acetabular defect in hip revision. METHODS: Between August 2014 and December 2015, the 3D printed trabecular metal pads were used to repair Paprosky type Ⅲ acetabular defects and reconstruct the annular structure of the acetabulums in 5 cases of primary hip revision. There were 3 males and 2 females, aged from 50 to 72 years, with an average age of 66 years. The time from initial replacement to revision was 10 to 18 years, with an average of 14.4 years. The types of prostheses in primary replacement were non-cemented in 3 cases and cemented in 2 cases. The types of acetabular bone defects were Paprosky type ⅢA in 3 cases and Paprosky type ⅢB in 2 cases. The preoperative Harris score was 34.23±11.67. The height of rotation center of affected hip was (38.17±8.87) mm and the horizontal position was (35.62±9.12) mm. RESULTS: The operation time was 120-180 minutes, with an average of 142 minutes. The intraoperative bleeding volume was 800-1 700 mL, with an average of 1 100 mL. Five patients were followed up 18-24 months (mean, 21 months). At last follow-up, the Harris score was 79.82±8.70, which was significantly higher than that before operation (t=16.991, P=0.000). At 1 week after operation, the abduction angle of acetabular cup was 38-42° (mean, 39.4 °) and the anteversion angle was 13-18 ° (mean, 14.6°). The height and horizontal position of rotation center of affected hip were (22.08±8.33) mm and (29.03±6.28) mm, respectively, showing significant differences when compared with those before operation (P<0.05); there was no significant difference when compared with those of healthy hip [(28.62±7.73), (27.29±4.22) mm] (P>0.05). During the follow-up, there was no complication such as prosthesis loosening, dislocation, or periprosthetic fracture. CONCLUSION: In hip revision, 3D printed trabecular metal pads can repair Paprosky type Ⅲ acetabular defect, reconstruct the structure of acetabulum, provide a stable supporting structure for the acetabular cup, reconstruct the relatively normal rotation center of the hip joint, avoid iatrogenic bone loss, and achieve satisfactory functional recovery of the hip. The long-term effectiveness needs further follow-up.

Effects of low-intensity and low-frequency ultrasound combined with tobramycin on biofilms of extended-spectrum beta-lactamases (ESBLs) Escherichia coli.

Low-intensity and low-frequency ultrasound (LILFU) can enhance the bactericidal action of antibiotics against various sensitive bacterial species. The current study investigated the effects of LILFU combined with tobramycin on extended-spectrum beta-lactamases (ESBLs) Escherichia coli biofilms (a multi-drug resistant bacteria). The biofilms of ESBLs E. coli were established and treated with ultrasound (42 kHz and ISATA of 0.66 W/cm2) continuously for 0.5 h with and without tobramycin. The bacterial viability, the morphology and the antibiotic penetration of ESBLs E. Coli biofilms were investigated. The results demonstrated that the bacterial viability of biofilms significantly declined and the diameter of the inhibition zone was significantly increased after treatment with ultrasound combined with tobramycin compared with the controls (P < 0.05). Confocal laser scanning microscopy showed that the bacterial viability was affected most in the outer layer of ESBLs E. coli biofilms after joint treatment. The morphological structure of the biofilms was altered remarkably after joint treatment based on scanning electron microscopy, especially in regard to reduced thickness and loosened structure. These results suggest that the combination of ultrasound and tobramycin can exert synergistic bactericidal effects against biofilms formed by ESBLs E. coli.

Modulation format identification enabled by the digital frequency-offset loading technique for hitless coherent transceiver.

We propose a blind and fast modulation format identification (MFI) enabled by the digital frequency-offset (FO) loading technique for hitless coherent transceiver. Since modulation format information is encoded to the FO distribution during digital signal processing (DSP) at the transmitter side (Tx), we can use the fast Fourier transformation based FO estimation (FFT-FOE) method to obtain the FO distribution of individual data block after constant modulus algorithm (CMA) pre-equalization at the receiver side, in order to realize non-data-aided (NDA) and fast MFI. The obtained FO can be also used for subsequent FO compensation (FOC), without additional complexity. We numerically investigate and experimentally verify the proposed MFI with high accuracy and fast format switching among 28 Gbaud dual-polarization (DP)-4/8/16/64QAM, time domain hybrid-4/16QAM, and set partitioning (SP)-128QAM. In particular, the proposed MFI brings no performance degradation, in term of tolerance of amplified spontaneous emission (ASE) noise, laser linewidth, and fiber nonlinearity. Finally, a hitless coherent transceiver enabled by the proposed MFI with switching-block of only 2048 symbols is demonstrated over 1500 km standard single mode fiber (SSMF) transmission.

Experimental study on the influence of low-frequency and low-intensity ultrasound on the permeability of the Mycobacterium smegmatis cytoderm and potentiation with levofloxacin.

Tuberculosis is an infectious disease caused by the bacterium M. tuberculosis. The aim of this study was to investigate the bactericidal effect and underlying mechanisms of low-frequency and low-intensity ultrasound combined with levofloxacin treatment against M. smegmatis (a surrogate of M. tuberculosis). As part of this study, M. smegmatis was continuously irradiated with low frequency ultrasound (42kHz) using several different doses whereby both intensity (0.138, 0.190 and 0.329W/cm2) and exposure time (5, 15 and 20min) were varied. Flow cytometric analyses revealed that the permeability of M. smegmatis increased following ultrasound exposure. The survival rate, structure and morphology of bacteria in the lower-dose (ISATA=0.138W/cm2 for 5min) ultrasound group displayed no significant differences upon comparison with the untreated group. However, the survival rate of bacteria was significantly reduced and the bacterial structure was damaged in the higher-dose (ISATA=0.329W/cm2 for 20min) ultrasound group. Ultrasound irradiation (0.138W/cm2) was subsequently applied to M. smegmatis in combination with levofloxacin treatment for 5min. The results demonstrated that the bactericidal effect of ultrasonic irradiation combined with levofloxacin is higher compared to ultrasound alone or levofloxacin alone.

Damage Effects on Bacille Calmette-Guérin by Low-Frequency, Low-Intensity Ultrasound: A Pilot Study.

OBJECTIVES: To perform an in vitro experimental study of the possible damage effects on Bacille Calmette-Guérin (BCG) by low-frequency (42-kHz) ultrasound (US) irradiation at low spatially and temporally averaged intensities and different exposure times. METHODS: A 2-mL BCG suspension was added to the wells of a 24-well cell culture plate. Then the samples were randomly divided into 4 groups, each group including 3 wells, with group 1 as a control group and groups 2, 3, and 4, as US treatment groups. The samples for groups 2, 3, and 4 were irradiated with US at 0.13 W/cm(2) for 5 minutes, 0.13 W/cm(2) for 15 minutes, and 1.53 W/cm(2) for 15 minutes, respectively. After irradiation, the temperature, ratio of damage, and structure of the bacteria were examined. The cavitation effect of the device was detected by the passive cavitation detection method. RESULTS: After US irradiation at the different doses (intensity and exposure time), no significant temperature change was found in all sample suspensions. The ratio of bacterial damage tested by flow cytometry and the optical density of the suspensions as assayed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric method showed that the US-irradiated groups were significantly different from the control group. The BCG damage ratio reached 28% at the intensity of 1.53 W/cm(2). Transmission electron microscopic results showed that the bacterial structure of BCG could be destroyed by low-frequency, low-intensity US. CONCLUSIONS: Low-frequency, low-intensity US can cause acute injury to BCG, and the degree of injury is closely correlated with the US dose applied.

[Clinical study on the early reconstruction of complex acetabular fractures].

OBJECTIVE: To explore the best opportunity of structure reconstruction for complex acetabular fracture in order to provide the accurate time for clinical operative treatment. METHODS: Complex acetabular fracture patients were divided into experimental group (93 cases, 96 hips) and control group (98 cases, 101 hips) randomly according to the operative time. The operation of patients were done respectively at the 7th, 10th day after injury in experimental group and control group. The operative time, the excellent and good rate of reduction,the postoperative complications,the joint function (ache to walk,joint activity),the SF-36 were evaluated. RESULTS: (1) The operative time of experimental group was obviously shorter than control group according to different fracture classification. (2) According to the standard of Matta' joint function and X-ray, the experimental group was better than control group. (3) The excellent and good rate of reduction in experimental group was obviously higher than control group, according to CT scan before operation and after operation. CONCLUSION: The early structure reconstruction of complex acetabular fracture can obviously decrease operative time and complications, increase the rate of operative reduction.