电光调制通信实验的改进

介绍了用光纤扩充电光调制通信教学实验的方法和特点,将光纤用于电光调制通信实验中,改善了实验装置的性能,拓宽了实验范围。     

一种多通道混沌调相扩频方式及其在水声通信中的应用

直接序列扩频通信是一种低检测概率通信方式,在保密通信中得到了广泛的应用。但该通信方式仍存在缺陷,其采用伪随机序列作为扩频码,而伪随机序列具有周期性和二值性等较为明显的特征,在敌对环境下这些特征可能被利用,使得直扩信号重要的特征参数被估计出来,进而引发信息泄露。针对这个问题,本文提出采用混沌调相序列代替伪随机序列,混沌调相序列是恒包络的复数值序列,可用数量多,相关特性好,而且克服了伪随机序列周期性和二值性的不足,具有更高的保密性。为了提高通信速率,将混沌调相序列与多通道技术相结合,数值仿真结果显示了该通信方式优异的误码率性能,表明该通信方式在水声通信中应用的可行性。     

Analysis of modulation format in the 40 Gbit/s optical communication system

Three different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CS-RZ) and the differential phase keying (DPSK) modulation format of each code are introduced in the article. A method of their modulated signal generation with computer is described, and a comparison of their spectra and waveforms is made. The 40 Gbps signal transmitted in 200 km G.652 fiber by way of single channel with erbium-doped-fiber-amplifier (EDFA) is simulated for these three formats. The ability of anti-dispersion and anti-PMD is analyzed. It is shown that RZ and CS-RZ formats are more tolerant than NRZ format in the same conditions.     

长波红外无线激光通信脉冲宽度调制实验研究

为实现长波红外无线激光通信,建立了基于脉宽调制的长波红外无线激光通信系统模型,对系统性能进行了分析,给出了系统误码率的计算公式.搭建了实验系统,对CO_2激光器的平均输出光功率随占空比的变化情况进行了分析,对不同占空比条件下接收端对应的激光平均脉冲宽度以及脉冲宽度受噪声影响的随机变化情况进行了分析,得到了激光输出平均光功率、平均脉冲宽度与占空比之间的关系,以及脉宽的分布规律,并将实验结果与理论分析结果进行了对比,在此基础上得到了脉宽最佳判决门限和系统各类工作参数同误码率之间的关系.结果表明,基于CO_2激光器的脉冲宽度调制能够实现长波红外无线激光通信.     

Power and rate control in wireless communication systems with energy harvesting and rateless codes

In this paper, for a wireless communication system with energy harvesting and rateless error correction codes, the joint optimization of transmit power, modulation scheme and code rate to maximize the long-term average achievable transmission rate under the constraint of available energy is studied. The method is given first to determine the codeword length (or code rate) for a signal-to-noise ratio (SNR) under the constraint of a pre-defined decoding error probability. Then the formula of the actual transmission rate is deduced with a specific modulation and code rate, and the optimization problem to maximize the long-term average actual transmission rate is constructed under the constraints of available harvested energy and the decoding complexity of the rateless code. Since energy harvesting and channel fading are both stochastic processes, the optimization problem is difficult to solve. By using the Lyapunov optimization framework, the original long-term optimization problem is transformed into a per time slot one. Then an efficient numerical method is proposed to obtain the solution to the problem. The proposed algorithm is verified by simulation, and the results show that the proposed algorithm can achieve a higher average actual transmission rate than the comparison algorithms aiming at optimizing the channel capacity.     

Dynamic routing,modulation level and spectrum allocation (RMLSA) in FWDM with modulation format conversion

This paper proposes a dynamic routing, modulation level and spectrum allocation (RMLSA) scheme in the flexible optical wavelength-division multiplexing (FWDM) networks with modulation format conversion ability. The scheme considers the modulation format conversion at the intermediate nodes and addresses the fragmentation problem by avoiding appearance of them. The influence of routing to the emergence of the fragmentation is quantified, which is referenced to decide which one route of k-paths to use. Simulation results demonstrate efficient reductions in blocking rates and improvements in failure recovery rates for the scheme in the network.     

用射线法计算柱形金属壁腔中光线传输的带宽与损耗

提出了一种适合在一些特定环境下做为光波传输手段的新颖光信道——利用金属壁腔传输信息。该信道适合于需要在两个不同实体间传输信息的特定结构中,首先提出了信道模型,然后讨论了不同结构参数对信道吸收损耗和带宽的影响,对所设计的具体信道的带宽和损耗进行了计算,并比较了不同金属镀层对损耗的影响。说明了合理选择信道参数信道可达到宽带宽低损耗的要求,因此该信道可运用于需在环型腔体中传输信息的结构中。     

光通信技术在物联网中的应用

介绍了物联网的定义及结构;从感知层和网络层角度,探讨了光通信技术(光纤通信和无线通信)在物联网中的应用现状和前景.光纤通信、近距离无线通信、移动通信是物联网开发的基础,制定物联网各个层面上统一的、标准化协议和技术标准是物联网未来发展必须解决的关键和难点.     

Generation of higher degree chaos by controlling harmonics of the modulating signal in EDFRL

Erbium doped fiber ring lasers (EDFRL) are being used to generate optical chaos for secure communication by modulating the cavity loss/pump power or exploiting nonlinearities. The security level in chaotic communication depends on degree of chaos quantified by the Lyapunov exponent and its variability which is determined by the number of tuneable system parameters which were limited to five main parameters, i.e. modulation index, modulation frequency, pump power, cavity gain and loss. In this study we have increased the number of tuneable parameters using square, triangular and sum of harmonics waveforms. We have analysed the effect on degree of chaos of phase and duty cycle of square modulating signal with gradual addition of harmonics. For the given cavity parameters, the Lyapunov exponents can be increased by more than fifteen times using square wave modulating signal and a duty cycle of 60%. The electrical parameters identified make generation of new chaotic sequences more flexible in a field deployed EDFRL chaotic system.     

混沌与湍流大气中的光通信

目前, 光无线通信的质量主要受到大气信道环境的制约, 大气信道中混沌介质与湍流的强烈扰动使得通信质量很差, 甚至通信中断. 提出了一种面到点的光无线通信机理: 利用面阵各单元的光信号在混沌介质中传输通道的空间非相干性, 通过桶探测器收集通过混沌介质的光信号的能量和, 平均各传输通道的交叉干扰, 降低混沌介质对光无线通信的影响; 利用随机噪声与随机编码的空间非相干性, 经过二阶相关运算, 构建新的信号传输方程, 减弱大气湍流及背景光对信号解码的干扰, 使得接收端并不需要窄带光学滤波器. 数值仿真和演示实验表明, 该光无线通信机理在混沌与湍流大气中的误码率为10^-4-10^-2, 能够实现复杂大气环境中的光通信, 在军事、抢险救援等方面具有重要应用价值.     

飞秒激光脉冲在非线性光纤中的传播

研究了非线性光纤中自相位调制导致光脉冲频谱展宽的详细物理过程,以此为光纤中光孤子产生的物理过程作准备。     

A survey on UAV placement optimization for UAV-assisted communication in 5G and beyond networks

With the increase in capacity demands and the requirement of ubiquitous coverage in the fifth generation and beyond wireless communications networks, unmanned aerial vehicles (UAVs) have acquired a great attention owing to their outstanding characteristics over traditional base stations and relays. UAVs can be deployed faster and with much lower expenditure than ground base stations. In addition, UAVs can enhance the network performance thanks to their strong line-of-sight link conditions with their associated users and their dynamic nature that adapts to varying network conditions. Optimization of the UAV 3D locations in a UAV-assisted wireless communication network was considered in a large body of research as it is a critical design issue that greatly affects communication performance. Although the topic of UAV placement optimization was considered in few surveys, these surveys reviewed only a small part of the growing literature. In addition, the surveys were brief and did not discuss many important design issues such as the objectives of the optimization problem, the adopted solution techniques, the air-to-ground channel models, the transmission media for access and backhaul links, the limited energy nature of the UAV on-board batteries, co-channel interference and spectrum sharing, the interference management, etc. Motivated by the importance of the topic of UAV placement optimization as well as the need for a detailed review of its recent literature, we survey 100 of the recent research papers and provide in-depth discussion to fill the gaps found in the previous survey papers. The considered research papers are summarized and categorized to highlight the differences in the deployment scenario and system model, the optimization objectives and parameters, the proposed solution techniques, and the decision-making strategies and many other points. We also point to some of the existing challenges and potential research directions that have been considered in the surveyed literature and that requires to be considered     

Generalized projective synchronization via the state observer and its application in secure communication

Based on the improved state observer and the pole placement technique,by adding a constant which extends the scope of use of the original system,a new design method of generalized projective synchronization is proposed.With this method,by changing the projective synchronization scale factor,one can achieve not only complete synchronization,but also anti-synchronization,as well as arbitrary percentage of projective synchronization,so that the system may attain arbitrary synchronization in a relatively short period of time,which makes this study more meaningful.By numerical simulation,and choosing appropriate scale factor,the results of repeated experiments verify that this method is highly effective and satisfactory.Finally,based on this method and the relevant feedback concept,a novel secure communication project is designed.Numerical simulation verifies that this secure communication project is very valid,and moreover,the experimental result has been greatly improved in decryption time.     

Linear and nonlinear distortion effects in direct detection 40 Gb/s MSK modulation formats multi-span optically amplified transmission

The generation of minimum shift keying (MSK) requires a linear variation of the phase, hence a constant frequency of the optical carrier. However, the generation of the optical phase may be preferred by driving an optical modulator using sinusoidal signal for practical implementation. Thus a nonlinear variation of the carrier phase, hence some distortion effects are produced. In this paper, we investigate the use of linear and nonlinear phase shaping filtering and their impacts on MSK modulated optical signals transmission over optically amplified long haul communications system. The evolution of the phasor of the in-phase and quadrature components is illustrated for lightwave-modulated signal transmission. The distinct features of three different MSK modulation formats: linear MSK, weakly nonlinear MSK and strongly nonlinear MSK and their transmission are simulated. Transmission performance obtained indicates the resilience of the MSK signals in transmission over multi-optically amplified multi-spans.     

Study on the DOP of Output Pulse in Optical Fiber Transmission Systems

In this paper the expression of the output pulse Stokes vector is derived based on the Jones matrix model proposed by A.Orlandini et al. The basic properties of degree of polarization (DOP) for output pulse are investigated.     

Decode-and-forward with quadrature spatial modulation in the presence of imperfect channel estimation

The performance of quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system with cooperative decode and forward (DF) relays is analyzed in this paper. QSM is a new MIMO transmission technique that enhances the overall performance of conventional spatial modulation through exploiting quadrature spatial dimension. A practical scenario is considered where the channel is estimated at the relays and the destination and the impact of channel estimation error is investigated. Two cooperative systems are considered in the study. In the first system, multiple single-antenna DF relays are assumed, whereas, in the second system, single multiple-antennas DF relay is considered. For both systems, an analytical expression for the pair wise error probability (PEP) is obtained. As well, an asymptotic expression for the PEP at high and pragmatic signal to noise ratio is derived. Derived expressions are used to provide an upper bound on the average bit error ratio. The derived analysis is corroborated through Monte Carlo simulations and results demonstrate a close-match for a wide range of SNR values.     

Enhanced chaotic communication in VCSELs with variable-polarization optical feedback and polarization-preserved optical injection

The communication performance and security enhancement in vertical-cavity surface-emitting lasers (VCSELs) subject to variable-polarization optical feedback (VPOF) are investigated numerically. Unidirectional polarization-preserved optical injection (PPOI) scheme is adopted, chaos modulation is utilized for message encryption, and two decoding methods are discussed and compared. The influences of VPOF on the performances of two decoding methods are focused on, and the effects of injection strength and frequency detuning are also considered. The security enhancement is further discussed by analyzing the robustness to mismatched feedback configuration and polarizer angle, as well as the intrinsic parameters. It is shown that, successful message encoding and decoding with Q-factors greater than 6 can be achieved by using unpredictability-enhanced chaotic carrier. In particular, the Q-factors are quite sensitive to the feedback configuration and laser parameters. When an attacker with open-loop is considered, Q-factors are smaller than 3 (6) for division (subtraction) decoding method. Specifically, even when an attacker with close-loop is considered, the Q-factors are lower than 6 when mismatched polarizer angles or intrinsic parameters exceed ±20% for subtraction method, and are more sensitive to parameter mismatch for division method, which enhances significantly the security, and thus is extremely useful for the security-enhanced chaotic communication system.     

卫星光通信中恒星背景噪声分析及抑制方法研究

建立了以恒星目视星等、等效温度为参数的恒星辐射谱模型,使利用恒星数据库进行背景噪声分析变得更加简捷。在此基础之上,分析了恒星自身特点及卫星光通信终端参数对背景噪声的抑制能力,提出并定义了抑制参数Ψ,以评价卫星光通信系统的抗噪性能;同时考虑背景噪声光功率对卫星光通信的影响,给出了补偿方法;分析结果表明,通过提高CCD采样频率、降低光学系统带宽等方法,可以有效地减少恒星噪点,降低恒星背景光对卫星光通信系统的影响。该项工作为进一步优化卫星光通信系统参数,提高其空间运行的稳定性打下了基础。     

Beam reception and data transmission performance analysis of optical taper used in a mobile wireless optical communication

Mobile wireless optical communication system was demonstrated experimentally by using a special solid coupling optical taper. The performance of special solid coupling optical taper and the data transmission performance with 240 Mbit/s were investigated on the rectilinear orbit between the mobile terminal and the fixed terminal. The experimental results shown that the scheme used in the mobile wireless optical communication system is reliable and quite simple, which could be widely used in future.     

Several optimization problems in satellite optical communications: Models and solutions

In this paper, we address several optimization problems in satellite optical communications. We show that the inter-satellite links with swaying transmitters can be described as an equivalent fading model. We further indicate that the instantaneous signal-to-noise ratio follows the reciprocal Pareto distribution. Then we conduct the analysis on several performance metrics such as the first and second moments of signal-to-noise ratio, the amount of fading, as well as the outage probability. Based on these metrics, we establish optimization models and provide the corresponding solutions.