Holographic Diffusers for Indoor Infrared Communication Systems

Diffused infrared transmission is one of thepreferred techniques used in indoor wirelesscommunications. Tolerance to shadowing and a lack ofalignment requirements are among the many advantagesoffered by this technique compared to the line-of-sighttechniques. However, it has its disadvantages, namelyhigh path loss and multipath dispersion. The limitationimposed by eye-safety requirements restricts the transmitted power. Therefore, efficient useof transmitted optical power is the key for practicalbroadband infrared systems. In this paper, we report onusing a holographic diffuser for shaping of infrared radiation pattern in an indoorinfrared transmission system. The holographic diffusershave the advantage of light weight and added flexibilityin the system design. The reported measurements show that employing a properly designed holographicdiffuser can reduce the path loss of a nondirectedoptical link. The results also show another advantage ofusing the proposed holographic diffuser, which is additional tolerance of the transmission toshadowing.     

BER Performance of NRZ-OOK and Manchester Modulation in Indoor Wireless Infrared Links

This paper describes a novel approach to theevaluation of the bit error rate (BER) performance ofoptical wireless links that takes into account shotnoise, fluorescent light interference, and intersymbol interference (ISI) from both multipathdispersion and high-pass filtering (HPF) at thereceiver. The calculation of the BER is achieved withthe use of an efficient numerical technique based onnonclassical Gauss Quadrature Rules. Fluorescent lightinterference is modeled as a Fourier series expansionwith coefficients taken from measurements, whilemultipath-induced ISI is calculated by using previouslyreported IR channel models. Application of the techniquepresented here allows for the calculation of the optimumHPF cutoff frequency that minimizes the overallperformance penalty. Finally, as an application of this method, the BER performance of NRZ-OOK andManchester (2-PPM) modulation is evaluated and numericalresults are presented for different linkscenarios.     

Channel Estimation for Realistic Indoor Optical Wireless Communication in ACO-OFDM Systems

Terahertz wave has attracted wide attention for its great transparency, low photon energy and high imaging resolution. Experiments were performed to explore the basic application of continuous terahertz wave. Some articles for daily use were chosen and sealed as samples and detected by the continuous-wave terahertz imaging system. Then a foam specimen was made with inclusions placed in it and detected by the system. The experimental results demonstrate that the system can detect and image the shapes and locations of the samples and inclusions correctly, though the air hole defect in the foam specimen is difficult to identify. The different colors indicating the strength of the reflected signal help to distinguish the different materials. The work paves the way for our future research and application of continuous terahertz wave.     

无线通信系统中发射分集技术研究

在无线通信系统中,不同场景下有不同的传播模型。为了研究发射分集技术对抗多径效应的性能,文中总结了无线通讯系统中室外场景下的传播模型。针对传统的Okumura-Hata传播模型来研究不同环境下发射信号的功率损耗,在接收端计算各信号副本的接收功率,通过与预设的接收功率门限作比较,得出每个信号副本以及各副本等增益合并后的信号可用性,从而研究发射分集对于信号可用性的提升作用。仿真结果表明,分集技术能明显提升接收机接收信号的可用性。     

异构无线通信系统的协同分集性能研究

提出了一种基于协同机理的异构无线通信机制,研究了影响该异构协同通信系统分集传输性能的关键因素,从理论上给出了第二跳链路采用和不采用时间分集方案时中断概率和协同中继节点数量、第一跳和第二跳链路的信道增益、标称功率等的关系.数值分析结果表明异构协同分集性能主要受分集机制、协同中继节点数、第二跳链路小尺度衰落、标称功率等因素影响.     

光纤通信接收机放大器的等效噪声模型

许多光纤通信文献给出了如图1所示的光接收放大器的等效噪声模型。本文证明了这个等效噪声模型与原始噪声模型不等价，并且也不具有可测性。所以，这个等效噪声模型是不正确的，因而不宜采用。作者认为，在光纤通信接收机的设计中，噪声计算只是为了分析接收机的灵敏度，而不是用来确定最佳信号源电阻，因而可以不用等效噪声模型，直接用原始的噪声模型反而更简单和更精确。     

Estimation of Channel Impulse Response Using Modified Ceiling Bounce Model in Non-Directed Indoor Optical Wireless Systems

In this paper a modification to the traditional Ceiling bounce model is proposed for use with non-directed indoor optical wireless systems which takes into account the transceiver separation distances as well as their actual positions while computing the impulse response. This modification is done by combining the results of DC gain computation and the statistical model along with the traditional Ceiling bounce approach. We show that the results of the proposed modification agree better than the traditional Ceiling bounce model with the reported experimental results of Barry et al. (1993. IEEE Journal on Selected Areas in Communications, 11, 367–379). The modified Ceiling bounce model is used to study the effect of transceiver positions on the rms delay spread and channel impulse response.

水下无线光通信接收光功率的计算研究

在水下无线光通信中,以往计算接收光功率的方法大多没有考虑水体散射对光束发散角和光功率分布的影响。采用汉克尔变换的光束传输函数研究了在水下三维空间的光功率分布,在此分布基础上考虑接收机尺寸、空间位置、接收平面角度等因素产生的几何损耗,求得接收光功率,并进行了实验,结果表明本方法比以往方法更接近实验数据。     

级联光放大器通信系统中的信噪比变化

我们从计算掺光纤放大器输出的光子数的起伏入手，得到了适用于各种工作状态的单个ＥＤＦＡ输出信噪比表达式，由此分析了级联光放大器通信系统中的信噪比变化，并与前人的工作进行了比较。     

激光器相位噪声对高速IM／DD光纤通信系统特性影响的研究

光源的光谱特性对高速光纤通信系统的传输特性有很大的影响，本文分析了半导体激光器的相位噪声（线宽）对高速光纤通信系统特性的影响，分析结果指出，在高速长距离ＩＭ／ＤＤ系统的设计与分析中必须考虑激光器线宽的影响，由于光纤的色散特性，激光器的相位噪声在接收端将转化为强度噪声，使光接收机的接收灵敏度产生恶化，并在ＢＥＲ－Ｐｒ曲线上表现出“饱和”现象（ｆｌｏｏｒ）。本文的实验结果验证了这一点     

水下激光通信系统接收机倾角及位置对接收光功率的影响研究

采用蒙特卡洛方法建立了水下高斯光束传输仿真模型,基于该模型重点研究了接收机倾角和接收机位置对接收光功率的影响规律。仿真结果表明:在水下信道中,当接收机探测器阵面与激光出射角垂直时,接收光功率最大,随着接收机探测器阵面倾斜角度的增加,接收光功率逐渐减小;当接收机沿着Y轴方向正向移动时,且接收机在激光束的直径范围内时,接收光功率不变;当接收机在激光束的直径范围外时,接收光功率随着接收机偏离原点距离的增加而减小。仿真结果可为水下激光通信工程实践提供参考依据。     

OFDM技术在海上无线通信系统的应用分析

本文通过对OFDM技术性能的分析,阐述了OFDM技术的无线系统结构和OFDM技术的优势,结合海上无线系统的实际应用情况,论述了OFDM宽带无线通信系统在海上无线系统的应用,通过分析和研究得出基于OFDM技术的无线宽带通信系统是海上无线通信系统发展的必然趋势.     

通信系统仿真中关于噪声的分析与研究

仿真通信系统时,由系统频带Eb/n0到离散噪声序列方差的推算是正确建模的关键。而频带Eb/n0、基带Eb/n0、频带SNR、基带SNR等相互间的关系难以精确把握;从频带到基带,从连续到离散的变换又容易让人模糊。该文阐明了这些概念间的相互关系,给出了从频带Eb/n0到离散噪声序列方差的详细推演过程。     

极化分集时MIMO系统的信道容量

论文给出了MIMO系统采用极化分集时的信道模型,对接收信号空间相关性和信道容量进行了研究,并对其随接收天线极化夹角的变化情况进行了分析。研究表明,采用极化分集技术的MIMO系统具有良好的非相关衰落特性,信道容量得到显著提高。     

可靠性理论在光纤通信系统设计中的应用

主要研究了可靠性理论在波分复用光纤通信系统中的应用，并依据可靠性理论对光纤传输系统进行了初步设计。通过对光纤通信系统的可靠性理论模型的理论分析和计算得出的相关结论，以期对光通信系统及其设备的设计提供参考。     

无线光通信中RCPT/ARQ自适应 差错控制机制的研究

为了克服无线光通信中的光强闪烁、大气衰减等信道干扰,本文结合无线光信道下Turbo码迭代译码算法,分析了RCPT码的穿孔图案特性,在此基础上完整给出了无线光通信系统RCPT/ARQ自适应差错控制方案,仿真表明RCPT/ARQ自适应差错控制方案显著提高了链路的吞吐量和稳定性.同时结合无线光信道的特性,提出了RCPT/ARQ机制下的排序重发策略,进一步优化系统在恶劣信道条件下的链路吞吐量.     

光纤通信系统中偏振损耗对偏振态的影响

推导出具有偏振相关损耗(PDL)器件的Stokes模型,研究了光纤通信系统中PDL对光信号偏振态(SOP)的影响。数值模拟结果表明,入射信号光偏振度(DOP)小于1时,PDL对出射信号光的DOP和强度有直接影响;当入射光DOP等于1时,PDL对出射信号光的DOP没有影响,但随PDL的增加,出射光强度迅速减小,且信号光的SOP变化加剧。     

光纤偏振模散随波长变化特性的研究

目前,偏振模散已经成为高速光纤通信系统发展的主要障碍,本文用琼斯传输矩阵法研究了偏振模散,通过数值模拟给出其统计特性,差分群时延服从麦克斯韦分布;PMD各阶项随波长随机变化;偏振主态在邦加球上的变化走向说明出现了PMD高阶项。     

基于最小均方自适应滤波器的无线光通信接收性能分析

无线光通信(OWC)系统采用大气通道作为传输媒介,而大气湍流效应引入了与信号强度有关的乘性噪声。为了消除乘性噪声所引起的信号衰落,分析并给出了基于最小均方(LMS)自适应滤波器的判决门限更新算法和稳态的抽头权系数相关矩阵算法。通过理论分析和计算机仿真,讨论了最小均方滤波器及其参数对无线光通信接收性能的影响。结果表明,采用非因果滤波器的无线光通信系统对湍流噪声具有明显的抑制作用。在弱湍流情况下,基于自适应最小均方滤波器的系统误码率(BER)低于10-8,可以满足网络通信的要求。通过分析不同滤波器阶数对误码率的影响表明,所采用的255阶的非因果结构的最小均方滤波器是最优的结构。     

Research on the Handover of a Novel Cellular Architecture in Wireless Personal Communication Systems

1　IntroductionHandoverbetweencellsisplayinganimportantroleincellularcommunicationsystems[1～ 1 2 ] .Thehandoverprocedureanditseffectivenessareseriouslylimitedbythecellulararchitectureasaresultofmar ketplanning .Basedonthehexagonalcellulararchi tecture,manyhandoverprocedureshavebeendis cussedandevaluated ,andmostoftheimprovementproposedonthemleadstotheintroductionofsector ingcellularorlayeredcellularmodel.Otherwise ,abetterhandoverprocedureisessentialinmaintainingacallinprogressbutitreflectshi…