Numerical analysis on an OOK-NRZ visible light communication system based on a single white LED

An OOK-NRZ visible light communication (VLC) system is designed by using a single white LED and a 550 nm visible photodetector. The emitting model of the single LED is established, and the general expression of the detector’s output signals under OOK modulation is deduced. With the selected LED, detector and other related parameters, the designed communication system is optimized and its performance is analyzed. The optimized communication distance between the LED and the detector is 0.54 m at the communication bit rate of 1 Mbit/s. With the best communication distance, when the signal-to-noise ratio (SNR) is larger than 6.5 dB, the bit error rate (BER) can drop to 10-4. The analytical model and theory presented in this paper can be of certain practical meanings in the design of similar communication systems.     

大气闪烁对无线激光通信效能的影响

由于大气湍流的存在,使激光信号在大气传输中产生振幅的随机起伏,称为大气闪烁。大气闪烁将引起激光通信误码率的增加。由光强起伏大小的统计规律和通信基本原理推导出了弱湍流条件下由光强闪烁引起的误码率计算公式,分别建立了地面水平链路和地-空斜向链路中的大气闪烁误码率模型,对模型进行了仿真,分析了湍流强弱、信号调制方式、链路距离、激光波长及地面发射仰角对闪烁误码率的影响,得到了闪烁误码率的变化规律。结果表明,通过合理选择信号调制方式、激光波长、站址位置及地面发射仰角等方式能够有效地降低大气闪烁误码率,提高通信可靠性。     

紫外分离双脉冲位置调制误码性能分析

基于紫外非视距(NLOS)单次散射信道传输模型,分析了用于无线紫外光通信的分离双脉冲位置调制(SDPPM)方案的误码性能.介绍了SDPPM调制方案的符号结构,将该调制方案与开关键控调制(OOK)、脉冲位置调制(PPM)和双脉冲位置调制(D-PPM)在带宽需求、功率需求方面进行比较.利用光子计数方法,研究了无背景辐射噪声条件下SDPPM的误符率(SER).对PPM、D-PPM和SDPPM紫外通信系统的误码性能进行仿真,分析路径损耗对其影响.结果表明,SDPPM在信源比特分组长度n为5和6 bit时获得了带宽需求与功率需求的较好平衡.当SER达到10-4时,有效通信距离比D-PPM长20 m左右.同时,SDPPM调制方案降低了紫外光散射通信中因多径色散造成的码间串扰(ISI).     

Optical Communication Using Subcarrier PSK Intensity Modulation Through Atmospheric Turbulence Channels

This paper studies optical communications using subcarrier phase shift keying (PSK) intensity modulation through atmospheric turbulence channels. The bit error rate (BER) is derived for optical communication systems employing either on/off key (OOK) or subcarrier PSK intensity modulation. It is shown that at BER = 10^-6 and a scintillation level of sigma = 0.1, an optical communication system employing subcarrier BPSK is 3 dB better than a comparable system using fixed-threshold OOK. When sigma = 0.2, an optical communication system employing subcarrier BPSK achieves a BER = 10^-6 at SNR = 13.7 dB, while the BER of a comparable system employing OOK can never be less than 10^-4. Convolutional codes are discussed for optical communication through atmospheric turbulence channels. Interleaving is employed to overcome memory effect in atmospheric turbulence channels. An upper bound on BER is derived for optical communication systems employing convolutional codes and subcarrier BPSK modulation.     

Performance study of an OFDM visible light communication system based on white LED array

By introducing orthogonal frequency division multiplexing (OFDM) technology, a visible light communication (VLC) system using a 5x5 white LED array is studied in this paper. The OFDM transmitter and receiver are modeled through MATLAB/Simulink tool. The electrical-optical-electrical (EOE) response of the VLC channel, which is also the response of the detector, is derived based on Lambert’s lighting model. Then the modeling on the overall OFDM/VLC system is established by combining the above three models together. The effects of the factors which include the digital modulation, Reed-Solomon (RS) coding, pilot form, pilot ratio (PR) and communication distance on the bit error rate (BER) of the system are discussed. The results show that through the use of RS coding, block pilot, quadrate phase shift keying (QPSK) modulation and a suitable pilot ratio about 1/3, under the communication rate about 550 kbit/s, the BER can be dropped to below 10-5, and the communication distance can reach 0.9 m.     

全双工逆向调制回复空间光通信系统性能评价

基于逆向调制反射器(MRR)的空间光通信系统因其结构紧凑、可免去链路一端的捕跟(APT)系统、功耗低等优点,是空间光通信系统研究热点之一。提出采用双波长激光发射实现全双工逆向调制回复空间光通信结构,并基于该结构对强度调制解调模式,通信距离为300 km,通信速率为1 GHz下的地面站对近地小卫星全双工通信链路进行了链路计算及通信误码率的分析。当MRR端口径为0.1 m时,通信链路余量大于5 dB,通信误码率优于10-15,满足通信链路的要求。并进一步分析了仿真结果存在的缺陷。结果表明所提出的空间光通信结构在小卫星对地面站全双工激光通信是可行的,是未来空间光通信系统发展趋势之一。     

Performance Analysis of Cooperative Communication System with Hierarchical Modulation over Rayleigh Fading Channel

Much attention had been devoted to study the bit error rate (BER) of hierarchical modulation on point-to-point transmissions in recent years. But few mention the error performance of hierarchical modulation on cooperative communication systems. Thus, in this paper, we derive the explicit closed-form expressions of the exact bit error rate computation for cooperative communication systems with hierarchical modulation over additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. To obtain the theoretical formulas of error rate performance, an analyzing model is proposed to clearly express all possibilities of each transmission. For error rate performance, the expression for BER is a function of distance parameters. Based on this relationship, a criterion is proposed to choose the optimal distance parameters for minimizing the BER of the refinement bits while guaranteeing the BER requirement of the base bits. Simulation results validate the correctness of the derived BERs of the base bits and the refinement bits. Also from simulation results, the performance with optimal distance parameters is greatly improved compared to the non-optimal distance parameters.     

水下复合信道对GMSK无线光通信系统性能的影响

The absorption and scattering of light in seawater channel cause signal attenuation, and the turbulence of seawater causes signal amplitude fluctuation, both of which will reduce the bit error rate (BER) performance of underwater wireless optical communication (UWOC) system. The effects of the two channel characteristics on the signal performance were considered comprehensively, and a method was proposed to equate the transmission distance and turbulence probability density function to the system signal-to-noise ratio (SNR) and turbulence noise, and then the signal attenuation and turbulence noise were combined into the signal waveform to establish the underwater composite channel signal transmission model. According to the experimental system parameters, the signal transmission waveforms of Gaussian minimum frequency shift keying (GMSK) modulation under composite channel were simulated, and the one-bit difference demodulation algorithm was used to compare the demodulated waveforms with the original waveform, and the influence relationships of composite channel on the system BER performance was analyzed. The simulation experiment results show that, compared with on-off keying modulation (OOK), pulse position modulation (PPM), GMSK system can obtain the SNR gain of 3.3 dB, 4.8 dB respectively only in the attenuation channel with seawater attenuation coefficient of 0.151 m?1. Under the composite channel, GMSK modulation performance is superior to OOK modulation and PPM modulation. When the water attenuation coefficient is 0.151 m?1, and turbulence intensity variance is smaller than 0.16, GMSK modulation system has no error rate limit, the system BER is decided by signal attenuation and turbulence noise and Gaussian noise together, GMSK modulation achieves SNR gain of 4.35 dB compared with PPM modulation. Furthermore, turbulence intensity variance is greater than 0.16, system BER arrives limit, which value is determined by the turbulence intensity, and the limit value of BER increases nonlinearly with the increase of turbulence intensity.     

逆向调制激光通信作用距离及误码率分析

为了分析逆向调制激光通信系统中OOK调制方式下的误码率特性,在分析回波功率模型和误码率性能的基础上,利用Optisystem仿真软件建立了逆向调制激光通信链路。链路采用NRZ码对不同通信距离、不同能见度下的100 Mbps和1 Gbps通信速率进行了仿真,根据所得信噪比值计算出不同条件下的误码率,并结合“眼图”特征得出不同条件下可实现的逆向通信距离。结果表明,误码率随着大气能见度的增大而减小,随着通信距离增大而增加。在大气能见度为10 km的条件下,系统可以实现通信速率为100 Mbps、距离为2 km的逆向通信。     

Performance enhancement of overall LEO/MEO intersatellite optical wireless communication systems

This paper has deeply investigated the performance signature of modulation techniques based low earth orbit (LEO)/medium earth orbit (MEO) intersatellite optical wireless communication systems for possible communication coverage distance of 20 000 km with possible transmission bit rate of 0.5 Tb/s. These modulation techniques that are namely multilevel quadrature amplitude modulation (M‐QAM), multilevel phase shift keying (N‐PSK), multilevel pulse amplitude modulation (H‐PAM), and finally multilevel differential phase shift keying (L‐DPSK) based on different electrical pulse generators for upgrading LEO/MEO intersatellite link operation efficiency. These pulse generators that are namely Gaussian pulse generator (GPG), hyperbolic secant pulse generator (HSPG), and raised cosine pulse generator (RCPG). The variations of maximum Q‐factor, minimum bit error rate (BER), and optical signal‐to‐noise ratio in relation to number of bits/symbol for different modulation techniques can be deeply studied in the presence of vertical cavity surface emitting laser (VCSEL). This study is done with using Optiwave system simulation version 7 for different modulation techniques, and all figures are sketched with using wizard Excel sheet set up. It is observed that maximum Q‐factor and minimum BER are optimized with using GPG and 8‐PAM, as well as 4‐DPSK with both HSPG and RCPG.     

Energy Efficient Lighting System for Indoor Parking with Ubiquitous Communication

This paper presents visible light communication (VLC) based energy efficient lighting system in indoor parking area for illumination and at the same time would offer ubiquitous data communication. Light emitting diodes (LEDs) based VLC is used for communication and illumination at the same time. We have optimized the position of LED emitters on the ceiling in the parking area to obtain the desired signal-to-noise ratio (SNR) and bit error rate (BER). Two lighting configurations in the parking area are discussed. We compared the power transmission from LED emitters, number of emitters, SNR distribution, BER and cost for both the configurations. Multi-level pulse modulations are used in this work along with simple on off keying (OOK) for modulation. We compared OOK with M-PAM, multi-level pulse position modulation and invert multi-level pulse position modulation to obtain the required SNR and power to achieve the same BER. Simulation results are presented and discussed. It is observed that the system allows uniform illumination in the parking area and at the same time high data rate communication.     

大气湍流中直升机助降紫外光引导调制研究

为了研究大气湍流中不同调制方式对无线紫外光通信系统的性能影响,基于紫外光非直视通信模型,理论推导了弱湍流条件下开关键控、脉冲位置调制的误比特率。采用紫外光引导直升机助降模型,在不同调制方式下仿真分析了发射功率、通信距离、发散角、接收视场角、收发仰角对误比特率的影响。结果表明,不同调制方式的误比特率随着发射功率、发散角、接收视场角的增大而不断减小,随着通信距离、收发仰角的增大而增大; 在相同条件下,脉冲位置调制比开关键控的误比特率更低,而且随着调制阶数的增加,误比特率会越来越小。这一结果对提高紫外光通信系统在大气湍流中的抗干扰能力具有一定的应用价值。     

非二进制LDPC码编码调制在光纤通信中的应用

为满足100Gb/s光纤通信的需求,提出了非二进制LDPC码编码调制(NB-LDPC-CM)方案.该方案通过使用频谱效率调制以及非二进制前向纠错LDPC码,提供了一种在高总比特率下实现可靠通信的前向纠错机制.与现有的BI-LDPC-CM方案相比,该方案在误比特率(BER)为10-7的情况下,采用16点、32点、和64点四维星座图时,额外提供的净编码增益分别为0.26dB、1.14dB和2.14dB.     

海洋大气湍流对激光通信系统性能的影响分析

大气湍流引起光波强度在光束截面内的闪烁,降低了激光通信系统的信噪比.应用基于Rytov近似的激光大气传输光强起伏理论模型,在局地均匀各向同性Kolmogolov湍流谱的假设条件下,对大气湍流引起的光强起伏进行了分析.并从信号检测理论出发,将大气湍流与激光通信系统误码率指标相结合.分析结果表明,在典型的海洋大气湍流环境下,以误码率指标衡量,随着C2n的增加,激光通信系统的有效作用距离大大缩短,当C2n达到5×10-15m-2/3时,通信的有效距离不足2 km,当C2n达到3×10-14m-2/3时,通信的有效距离降至1 km以下.     

A nonlinear equalization for a PAM4 IM/DD system using MZM

The nonlinear distortion caused by the Mach-Zehnder modulator(MZM) is one of the main limiting factors for the improvement of the transmission performance of the intensity modulation and direct detection(IM/DD) optical communication system. In order to solve the problem, an improved Volterra nonlinear equalization(VNLE) method is proposed. Compared with the traditional VNLE that uses the least mean square(LMS) to calculate the tap coefficients, the improved VNLE uses the least square(LS) method ...     

FTH-PPM多址接入技术在60 GHz脉冲无线通信系统中的性能

针对60 GHz脉冲无线通信系统中存在的多址接入干扰问题,研究了基于FTH-PPM多址接入方案的性能。在IEEE 802.15.3c信道模型下,分析了系统误码率性能与跳频码数量、信噪比、用户数之间的关系,研究了FTH-PPM多址调制系统特性,并与TH-PPM、TH-PAM方案进行比较。仿真结果表明,系统在多址条件下,可以通过改变信噪比、频率跳数、用户数来满足所需的误码率,同时在一定范围内,FTH-PPM的误码率性能优于TH-PAM和TH-PPM的误码率性能,并且可以根据脉冲占空比的值选择合适的多址调制方式,为60 GHz脉冲无线通信的应用提供技术参考。     

电磁脉冲串作用下的数字通信电台敏感判据研究

为研究电磁脉冲串对数字通信电台的阻塞效应机理,以某型数字通信电台为受试对象,通过电磁脉冲注入试验,研究了受试电台误码率随电磁脉冲串幅值、重复间隔时间的变化规律。结果表明,随着脉冲幅值的增大,误码率先单调上升再以不同规律变化;不同脉冲重复率下受试电台的敏感误码率相差较大,敏感误码率不能用固定数值作为敏感判据,但利用敏感误码率与脉冲重复率成正比作为判据则具有较高的准确度,据此给出了受试数字电台的误码率敏感判据及试验方法,以通过部分试验数据获取任意脉冲重复率下的误码率敏感判据。     

Improved NSGA-II optimizing coding-link cost trade-offs for multicast routing in WDM networks

The present study proposed a high-data-rate underwater optical wireless communication (UOWC) system to propagate the laser blue–green waves through water. The presented study not only focuses on analysis of challenges in UOWC link including attenuation, absorption, scattering and turbulence model, but also investigates the performance of the proposed system using two different methods of balanced modulation schemes. Spectrum efficiency of the system can be improved by using appropriate modulation formats. Return-to-zero differential phase shift keying (RZ-DPSK) and non-return-to-zero differential phase shift keying (NRZ-DPSK) schemes are two modulation formats that we investigate them to improve the characteristics of the proposed UOWC system. The paper explains a real model and exhaustive analysis for advanced UOWC works by using channel model and modulation formats for presented underwater link. Performance of the proposed system under different modulation schemes and physical aspects of UOWC is studied with several parameters like max quality factor, min bit error rate (BER) and eye diagram. For clear ocean, the performance of the proposed system is good and min BER less than 10^?90 for two modulation formats. Generally, results at different condition show that the operation of NRZ-DPSK modulation has better performance than RZ-DPSK scheme.     

Performance Enhancement of Gaussian Minimum Shift Keying Using Optimum Phase Sampling Technique for Turbulent Free-Space Optical Communication

In this paper, analytical performances of Gaussian minimum shift keying (GMSK) are studied for free space optical communication system. Authors propose an innovative sampling technique called, optimum phase sampling technique to investigate the bit error performance of GMSK modulation. Subsequently, performances of GMSK like, bit error rate (BER), power spectral density, and adjacent carrier interference (ACI) have also been investigated and compared with other modulation techniques. Furthermore, return to zero (RZ) coding input bit stream prior to GMSK technique improves the ACI performance of GMSK. To end with, we present the improvement of degradation parameter (γ) in a tabular form through phase sampling technique. Moreover, both optimum phase sampling and narrow pulse shaping of RZ-GMSK obtains near optimal result of BER. The numerical results show, that the proposed phase sampled RZ-GMSK of 70% duty cycle at BT?=?0.6 has a degradation value of 0.979, which is comparable to GMSK at BT?=?∞. Moreover, the proposed RZ-GMSK achieves lower ACI value and has an error rate of 7?×?10^?7, which is lower than the GMSK of 1?×?10^?6 BER value.

     

自适应调制STBC-OCT预编码在MIMO-OFDM VLC系统中的研究

为改善多入多出正交频分复用(MIMO-OFDM)的可见光通信(VLC)系统的性能,提出将自适应调制、空时分组码(STBC)及正交循环矩阵变换(OCT)相结合应用于该系统中,设计并建立了一个2×2 MIMO-OFDM系统,来评估所提出的自适应调制STBC-OCT预编码方案的性能。在不同的调制方式、不同的编码方案下研究其误码率（BER）性能、峰均功率比(PAPR)性能、不同的直流偏置（DC）与驱动电压峰值(V_PP)下的BER性能。结果表明:与其它预编码方法相比,采用自适应调制STBC-OCT预编码方案能获得相对均衡且高的信噪比（SNR）值及更低的PAPR。当传输距离为0.5 m,DC为2.7 V、V_PP为2.7~2.8 V时所提方案能获得最佳的BER性能,并始终低于前向纠错(pre-FEC)门限7%的阈值3.8×10?3。该方案能够有效地克服MIMO-OFDM VLC系统带宽限制的问题并提供最佳的可靠性。