The analysis of coverage probability,ASE and EE in heterogeneous ultra-dense networks with power control

The ultra-dense network is a promising technology to increase the network capacity in the forthcoming fifthgeneration(5G)mobile communication networks by deploying lots of low power Small Base Stations(SBSs)which overlap with Macro Base Stations(MBSs).The interference and energy consumption increase rapidly with the number of SBSs although each SBS transmits with small power.In this paper,we model a downlink heterogeneous ultra-dense network where a lot of SBSs are randomly deployed with MBSs based on the Poisson point process.We derive the coverage probability and its variance,and analyze the area spectral efficiency and energy efficiency of the network considering three Fractional Power Control(FPC)strategies.The numerical results and Monte Carlo simulation results show that power control can mitigate the interference and balance the performances of inner-user and edge-user equipments.Especially,a great improvement of energy efficiency is archived with a little loss of area spectral efficiency when FPC is adopted.Finally,we analyze the effect of base stations’(BSs’)sleeping on the performance of the network when it is partially loaded.

Peak shrinking and interpolating for PAPR reduction in M-IFoF-based mobile fronthaul

We apply a Peak Shrinking and Interpolating(PSI)scheme to improve the Peak-to-Average Power Ratio(PAPR)performance in Multiple Intermediate-Frequency-over-Fiber(M-IFoF)based mobile fronthaul.The key idea is to detect the high peaks of the signal and shrink them,and then the shrunk peak values are interpolated into the original signal to reduce the PAPR.We also compare the PSI technique with the previous Tone-Reservation(TR)technique and Phase Pre-Distortion(PPD)technique in terms of PAPR reduction effect and computational complexity.The simulation results indicate that the PSI scheme can reduce the PAPR by more than 4.3 dB at 0.1%CCDF,which outperforms the two previous schemes with lower computational complexity.Furthermore,we find that altering M-IFoF system parameters has little effect on the performance of the PSI technique.

Distributed privacy protection strategy for MEC enhanced wireless body area networks

With the rapid development and widespread application of Wireless Body Area Networks(WBANs),the traditional centralized system architecture cannot handle the massive data generated by the edge devices.Meanwhile,in order to ensure the security of physiological privacy data and the identity privacy of patients,this paper presents a privacy protection strategy for Mobile Edge Computing(MEC)enhanced WBANs,which leverages the blockchain-based decentralized MEC paradigm to support efficient transmission of privacy information with low latency,high reliability within a high-demand data security scenario.On this basis,the Merkle tree optimization model is designed to authenticate nodes and to verify the source of physiological data.Furthermore,a hybrid signature algorithm is devised to guarantee the node anonymity with unforgeability,data integrity and reduced delay.The security performance analysis and simulation results show that our proposed strategy not only reduces the delay,but also secures the privacy and transmission of sensitive WBANs data.

Theoretical and Experimental Investigation on a 40Gb/s FSK transmission Link

A novel Frequency Shift Keying (FSK) transmitter that can operate at 40Gb/s and above is proposed. The transmission characteristics of a FSK signal at 40Gb/s are investigated under varying dispersion management. The resilience of compensation ratio and power level is obtained. We also experimentally demonstrate transmission over 100km SMF and transparent wavelength conversion based on a semiconductor optical amplifier.

Frontier research of ultra-high-speed ultra-large-capacity and ultra-long-haul optical transmission

Ultra-high-speed, ultra-large-capacity and ultra-long-haul （3U） are the forever pursuit of optical communication. As a new mode of optical communication, 3U transmission can greatly promote next generation optical internet and broadband mobile communication network development and technological progress, therefore it has become the focus of international high-tech intellectual property competition ground. This paper introduces the scientific problems, key technologies and important achievements in 3U transmission research.

A novel construction method of QC-LDPC codes based on CRT for optical communications

A novel construction method of quasi-cyclic low-density parity-check(QC-LDPC) codes is proposed based on Chinese remainder theory(CRT). The method can not only increase the code length without reducing the girth, but also greatly enhance the code rate, so it is easy to construct a high-rate code. The simulation results show that at the bit error rate(BER) of 10^(-7), the net coding gain(NCG) of the regular QC-LDPC(4 851, 4 546) code is respectively 2.06 dB, 1.36 dB, 0.53 dB and 0.31 dB more than those of the classic RS(255, 239) code in ITU-T G.975, the LDPC(32 640, 30 592) code in ITU-T G.975.1, the QC-LDPC(3 664, 3 436) code constructed by the improved combining construction method based on CRT and the irregular QC-LDPC(3 843, 3 603) code constructed by the construction method based on the Galois field(GF(q)) multiplicative group. Furthermore, all these five codes have the same code rate of 0.937. Therefore, the regular QC-LDPC(4 851, 4 546) code constructed by the proposed construction method has excellent error-correction performance, and can be more suitable for optical transmission systems.

Polarization rotator-splitter covering full optical communication bands based on L-shaped cross-section waveguide

We propose an ultra-broadband and fabrication-tolerant polarization rotator-splitter （PRS） based on a waveguide with an L-shaped cross section and a Y-junction. The proposed PRS is based on the 220 nm silicon- on-insulator platform, and it shows less than 0.27 dB insertion losses and larger than 14 dB polarization extinction ratios over a wavelength range from 1200 to 1700 nm. To the best of our knowledge, the PRS working in th~ whale nntie^l enmmunien,tinn hand is nrnnased far the first time.

A novel construction method of QC-LDPC codes based on the subgroup of the finite field multiplicative group for optical transmission systems

According to the requirements of the increasing development for optical transmission systems,a novel construction method of quasi-cyclic low-density parity-check(QC-LDPC) codes based on the subgroup of the finite field multiplicative group is proposed.Furthermore,this construction method can effectively avoid the girth-4 phenomena and has the advantages such as simpler construction,easier implementation,lower encoding/decoding complexity,better girth properties and more flexible adjustment for the code length and code rate.The simulation results show that the error correction performance of the QC-LDPC(3 780,3 540) code with the code rate of 93.7% constructed by this proposed method is excellent,its net coding gain is respectively 0.3dB,0.55dB,1.4dB and 1.98dB higher than those of the QC-LDPC(5 334,4 962) code constructed by the method based on the inverse element characteristics in the finite field multiplicative group,the SCG-LDPC(3 969,3 720) code constructed by the systematically constructed Gallager(SCG) random construction method,the LDPC(32 640,30 592) code in ITU-T G.975.1 and the classic RS(255,239) code which is widely used in optical transmission systems in ITU-T G.975 at the bit error rate(BER) of 10-7.Therefore,the constructed QC-LDPC(3 780,3 540) code is more suitable for optical transmission systems.

63-Tb/s(368×183.3-Gb/s) C- and L-band all-Raman transmission over 160-km SSMF using PDM-OFDM-16QAM modulation

By using PDM-OFDM-16QAM modulation, all-Raman amplification, coherent detection, and 7% forward error correction （FEC） threshold, we successfully demonstrate 63-Tb/s （368× 183.3-Gb/s） signal over 160- km standard single mode fiber （SSMF） transmission in the C- and L-bands with 25-GHz channel spacing. 368 optical channels with bandwidth spacing of 25 GHz are generated from 16 external cavity laser sources. After 160-km SSMF transmission, all tested bit error rate （BER） are under 3.8×10^-3, which can be recovered by 7% FEC threshold. Within each channel, we achieve the spectral efficiency of 6.85 bit/s/Hz in C/L band.

UTM:A trajectory privacy evaluating model for online health monitoring

A huge amount of sensitive personal data is being collected by various online health monitoring applications.Although the data is anonymous,the personal trajectories(e.g.,the chronological access records of small cells)could become the anchor of linkage attacks to re-identify the users.Focusing on trajectory privacy in online health monitoring,we propose the User Trajectory Model(UTM),a generic trajectory re-identification risk predicting model to reveal the underlying relationship between trajectory uniqueness and aggregated data(e.g.,number of individuals covered by each small cell),and using the parameter combination of aggregated data to further mathematically derive the statistical characteristics of uniqueness(i.e.,the expectation and the variance).Eventually,exhaustive simulations validate the effectiveness of the UTM in privacy risk evaluation,confirm our theoretical deductions and present counter-intuitive insights.

Full-space Cloud of Random Points with a Scrambling Metasurface

With the rapid progress in computer science,including artificial intelligence,big data and cloud computing,full-space spot generation can be pivotal to many practical applications,such as facial recognition,motion detection,augmented reality,etc.These opportunities may be achieved by using diffractive optical elements(DOEs)or light detection and ranging(LIDAR).However,DOEs suffer from intrinsic limitations,such as demanding depth-controlled fabrication techniques,large thicknesses(more than the wavelength),Lambertian operation only in half space,etc.LIDAR nevertheless relies on complex and bulky scanning systems,which hinders the miniaturization of the spot generator.Here,inspired by a Lambertian scatterer,we report a Hermitian-conjugate metasurface scrambling the incident light to a cloud of random points in full space with compressed information density,functioning in both transmission and reflection spaces.Over 4044 random spots are experimentally observed in the entire space,covering angles at nearly 90°.Our scrambling metasurface is made of amorphous silicon with a uniform subwavelength height,a nearly continuous phase coverage,a lightweight,flexible design,and low-heat dissipation.Thus,it may be mass produced by and integrated into existing semiconductor foundry designs.Our work opens important directions for emerging 3D recognition sensors,such as motion sensing,facial recognition,and other applications.

Deep space multi-file delivery protocol based on LT codes

A deep space multi-file delivery protocol（DSMDP） based on LT codes is proposed to reduce the influence of long delay and a high bit error rate（BER） in deep space communication. The protocol increases sending redundancy by LT codes to improve the success rate of file delivery, and adopts different protective strategies for different situations of packet loss. At the same time, the multi-file united delivery strategy is adopted to make full use of the retransmission time to reduce the end-toend transmission delay. Furthermore, the protocol determines the quantity of encoded packets according to the feedback for controlling redundancy. The simulation results show that the proposed protocol can significantly reduce the transmission delay of files, which would be effectively suitable for deep space communication environment of high BER and long delay.

A novel TS-EIA-PTS PAPR reduction algorithm for optical OFDM systems

Because the partial transmit sequence(PTS) peak-to-average power ratio(PAPR) reduction technology for optical orthogonal frequency division multiplexing(O-OFDM) systems has higher computational complexity, a novel two-stage enhanced-iterative-algorithm PTS(TS-EIA-PTS) PAPR reduction algorithm with lower computational complexity is proposed in this paper. The simulation results show that the proposed TS-EIA-PTS PAPR reduction algorithm can reduce the computational complexity by 18.47% in the condition of the original signal sequence partitioned into 4 sub-blocks at the remaining stage of n-d=5. Furthermore, it has almost the same PAPR reduction performance and the same bit error rate(BER) performance as the EIA-PTS algorithm, and with the increase of the subcarrier number, the computational complexity can be further reduced. As a result, the proposed TS-EIA-PTS PAPR reduction algorithm is more suitable for the practical O-OFDM systems.

Experimental demonstration of indoor interfered visible light communication system employing successive interference cancellation

Multipath interference induced power fading occurs when the transmission path lengths from the light emitting diodes to a single receiver are different in a visible light communication system. To solve this problem, we apply a QR-decomposition-based channel equalizer （QR-CE） to achieve successive interference cancellation for a discrete Fourier transform spreading （DFT-S） orthogonal frequency division multiplexing （OFDM） signal. We experimentally demonstrate a 200 Mb/s DFT-S OFDM over a 2 m free-space transmission. The experimental results show that a DFT-S OFDM with QR-CE attains much better bit error rate performance than a DFT-S OFDM with conventional CEs. The impacts of several parameters on a QR-CE are also investigated.

Resource-efficient quantum key distribution with integrated silicon photonics

Integrated photonics provides a promising platform for quantum key distribution(QKD)system in terms of miniaturization,robustness,and scalability.Tremendous QKD works based on integrated photonics have been reported.Nonetheless,most current chip-based QKD implementations require additional off-chip hardware to demodulate quantum states or perform auxiliary tasks such as time synchronization and polarization basis tracking.Here,we report a demonstration of resource-efficient chip-based BB84 QKD with a silicon-based encoder and a decoder.In our scheme,the time synchronization and polarization compensation are implemented relying on the preparation and measurement of the quantum states generated by on-chip devices;thus,we need no additional hardware.The experimental tests show that our scheme is highly stable with a low intrinsic quantum bit error rate of 0.50%±0.02%in a 6 h continuous run.Furthermore,over a commercial fiber channel up to150 km,the system enables the realization of secure key distribution at a rate of 866 bit/s.Our demonstration paves the way for a low-cost,wafer-scale manufactured QKD system.

Silicon-based decoder for polarization-encoding quantum key distribution

Silicon-based polarization-encoding quantum key distribution(QKD)has been extensively studied due to its advantageous characteris-tics of its low cost and robustness.However,given the difficulty of fabricating polarized independent components on the chip,previ-ous studies have only adopted off-chip devices to demodulate the quantum states or perform polarization compensation.In the cur-rent work,a fully chip-based decoder for polarization-encoding QKD was proposed.The chip realized a polarization state analyzer and compensated for the BB84 protocol without the requirement of additional hardware,which was based on a polarization-to-path conversion method utilizing a polarization splitter-rotator.The chip was fabricated adopting a standard silicon photonics foundry,which was of a compact design and suitable for mass production.In the experimental stability test,an average quantum bit error rate of 0.59%was achieved through continuous operation for 10 h with-out any polarization feedback.Furthermore,the chip enabled the automatic compensation of the fiber polarization drift when utiliz-ing the developed feedback algorithm,which was emulated by a ran-dom fiber polarization scrambler.Moreover,a finite-key secret rate of 240 bps over a fiber spool of 100 km was achieved in the case of the QKD demonstration.This study marks an important step to-ward the integrated,practical,and large-scale deployment of QKD systems.

A novel construction scheme of QC-LDPC codes based on the RU algorithm for optical transmission systems

A novel lower-complexity construction scheme of quasi-cyclic low-density parity-check(QC-LDPC) codes for optical transmission systems is proposed based on the structure of the parity-check matrix for the Richardson-Urbanke(RU) algorithm. Furthermore, a novel irregular QC-LDPC(4 288, 4 020) code with high code-rate of 0.937 is constructed by this novel construction scheme. The simulation analyses show that the net coding gain(NCG) of the novel irregular QC-LDPC(4 288,4 020) code is respectively 2.08 d B, 1.25 d B and 0.29 d B more than those of the classic RS(255, 239) code, the LDPC(32 640, 30 592) code and the irregular QC-LDPC(3 843, 3 603) code at the bit error rate(BER) of 10^(-6). The irregular QC-LDPC(4 288, 4 020) code has the lower encoding/decoding complexity compared with the LDPC(32 640, 30 592) code and the irregular QC-LDPC(3 843, 3 603) code. The proposed novel QC-LDPC(4 288, 4 020) code can be more suitable for the increasing development requirements of high-speed optical transmission systems.

Single-celled metasurface for labeled vortex beam generator

Vortex light is a unique beam characterized by a spiral phase as it propagates. A fundamental parameter of vortex light is the topological charge, which determines the amount of angular momentum and plays a crucial role in tailoring its behavior. However, conventional measurement methods for determining the topological charge, such as those based on interference and phase modulation, tend to be intricate and complex. In this regard, a labeled vortex beam generator is proposed, composed of a metasurface with a single-celled configuration. When the metasurface is illuminated by light of the designed wavelength, the outgoing light exhibits a vortex structure. Furthermore, the topological charge numbers can be directly observed with distinct labeled patterns when the metasurface is placed in an orthogonal-polarized optical path. With advantages such as ultra-compactness, high robustness, and exceptional precision, the proposed metasurface exhibits significant potential for applications in optical communication, light manipulation, optical sensing, etc.

Zero-order-free meta-holograms in a broadband visible range

The unwanted zero-order light accompanied by the birth of diffractive optical elements and caused mainly by fabrication errors and wavelength variations is a key factor that deteriorates the performance of diffraction-related optical devices such as holograms,gratings,beam shapers,beam splitters,optical diffusers,and diffractive microlenses.Here,inspired by the unique characteristic of nano-polarizer-based metasurfaces for both positive and negative amplitude modulation of incident light,we propose a general design paradigm to eliminate zero-order diffraction without burdening the metasurface design and fabrication.The experimentally demonstrated metahologram,which projects a holographic image with a wide angle of 70°×70°in the for field,presents a very low zero-order intensity(only 0.7%of the total energy of the reconstructed image).More importantly,the zero-orderfree meta-hologram has a large tolerance limit for wavelength variations(under a broadband illumination from520 to 660 nm),which brings important technical advances.The strategy proposed could significantly relieve the fabrication difficulty of metasurfaces and be viable for various diffractive-optics-related applications includingholography,laser beam shaping,optical data storage,vortex beam generation,and so on.