MIMO信道相对路径延时校准技术的研究

应用模块化仪器平台组建多输入多输出(MIMO)信道路径参数校准装置,利用信道估计技术测量MIMO信道的频率响应,依据傅氏变换理论设计数据处理程序,并计算出相对路径延时,实现对MIMO信道模拟器中该参数的校准。使用延迟线制作两路径标准延时网络,解决量值溯源问题。经过实验验证,校准系统的相对路径延时测量范围最长可达到5000 ns,在500 MHz的频率点上,从291 ns到585 ns相对路径延时测量最大示值误差不超过56 ns的延时分辨力。     

MIMO水声通信中的空时分组扩展编码方案探讨

采用多输入多输出（MIMO）结构和空时编码可以使水声通信系统获得分集增益,改善系统性能。针对水声信道中的频率选择性衰落,研究了一种用于MIMO水声通信系统的空时分组扩展编码方案（STBSC）,利用正交扩频编码克服了水声信道中多径干扰对空时分组编码（STBC）信号正交性的破坏。给出了方案的系统模型和实现框图,采用MIMO水声模型对方案的性能进行了仿真。仿真结果表明,STBSC方案在多径水声信道中可以得到完全发射分集。最后介绍了方案的水库试验,试验结果表明了方案的有效性。     

基于凸集投影的水声信道辨识算法

研究了使用凸集投影方法进行水声信道辨识的可行性,给出了凸集投影常用的凸集约束的条件,并推导了在复数域中的凸集约束的表达式。计算机仿真和实验结果证明,在较高信噪比的情况下,使用凸集投影方法可以正确估计水声信道中的多途幅度衰减和相位变化,其分辨率优于传统最大似然估计器-匹配滤波器,可作为研究水声信道的有力工具。     

预编码室内MIMO可见光通信系统空间相关性分析

为了解决多用户MIMO(MU-MIMO)室内可见光通信中存在用户间干扰问题及对角化(BD)算法所产生的子信道强弱的问题,利用子流选择BD算法,对室内MU-MIMO可见光通信系统的误码率进行优化。建立了MU-MIMO室内可见光通信的信道模型,利用控制变量法并采用不同LED与PD距离的参数,对比了在4×4 MIMO与8×8 MIMO两种不同的室内系统布局方式下的信道空间相关性,分析对比子流选择BD算法及BD算法的系统容量及误码率性能。结果表明,随着空间相关的不断增强,误码率性能下降,子流选择BD算法相对于BD算法可以带来4 dB以上的增益。     

适用于OFDM系统的改进的信道估计算法

针对实际系统中的信道冲激响应(CIR)泄漏问题,提出了一种适用于梳状导频正交频分复用(OFDM)系统的改进的最小二乘(LS)信道估计算法.该算法基于分数抽头延时信道近似(FTCA)的参数化信道模型,此信道模型采用一个抽头间隔为分数倍采样间隔的抽头延时线结构的有限冲激响应(FIR)滤波器表示.此算法首先通过FTCA信道模型来近似实际信道,然后再估计该信道模型中的某些参数来获取实际的信道信息;该算法利用了FTCA信道模型中所有的延时抽头,从而很好地抑制了CIR泄漏.仿真与分析表明,FTCA信道模型能够有效地近似实际信道,同时降低信道自相关矩阵的维数,从而提高信道估计的性能.     

浅海水声信道盲估计方法比较

由于多途效应,水下声源和水听器之间的通道可以建模为一个多途时延衰减信道.通过水下信道特性的合理假设,盲解卷积技术可以用于浅海水下信道的估计.不需要源信号和信道的先验知识,利用单水听器的接收数据,采用频率域的自然梯度方法、等变化方法、信息最大化方法来估计水下仿真信道,仿真证明了它们对水下信道估计的性能,其中等变化和自然梯度方法明显由于信息最大化方法.     

水下报文通信抗干扰方法

针对水声通信中的衰减信道和多途效应对报文通信的影响,利用混沌编码方式以获取处理增益,并利用拷贝相关器对信道进行估值的基础上,提出了用相干重置的方法对多途效应加以利用,以降低误码率.仿真结果表明,相干重置的方法相对于直接相关解码方法具有更低的误码率.由此可见,以上的方法对减少多途干扰的影响是有明显的效果的.水声通信一般部...     

基于伪随机序列的多波束水声探测系统的信道估计技术

多波束水声探测系统不同方向回波信号的同时检测,可以理解为通信中的信道估计问题。在水下多径传播环境中,多径信道的时延参数和幅度衰减参数的估计是多波束探测系统实现目标探测、定位和识别的基础,而抑制来自其它波束的多址干扰(MAI)是信道估计算法的重要目标。将直接序列码分多址(Direct Sequence Code-Division Multiple Access,简称DS-CDMA)通信系统模型应用于水声多波束探测系统。建立了基于伪随机序列的水下多波束探测系统的信号模型,研究了基于子空间方法的超分辨率信道估计算法。并给出了数值仿真实现,分析了信噪比、多址干扰及发射波束数等对信道估计算法性能的影响。仿真结果表明,该算法具有抑制多址干扰的性能,信道参数的估计方差逼近Cramer-Rao下界。这种信道估计技术尤其适合应用于多波束参量阵探测系统。     

水溶性气溶胶对自由空间量子通信性能影响

为了研究水溶性气溶胶对量子通信的影响,本文根据水溶性有机碳(WSOC)的复折射率及Mie散射理论得到其消光效率因子,分析了水溶性气溶胶粒子质量浓度对量子通信链路衰减、信道容量、信道生存函数以及信道误码率的影响并进行了仿真实验。结果表明,当传输距离为8 km,水溶性气溶胶粒子质量浓度分别为1.5μg/m³和6.5μg/m³时,对应的链路衰减、信道容量和信道误码率分别为0.506 d B/km和2.193 dB/km、0.622 bit/s和0.314 bit/s、0.0055和0.0099;当水溶性气溶胶粒子浓度为4μg/m³,传输距离分别为4 km和10 km时,对应的信道容量保真度分别为0.82和0.45。实际进行量子通信时,应根据水溶性气溶胶粒子的浓度来调整各项性能参数以保证通信正常进行。     

浅海水声信道中的一种带循环均衡的Turbo译码结构

针对浅海水声信道长时延、强多途干扰的特点,建立了一种新的带自适应循环判决反馈均衡的Turbo译码结构,并对其性能进行了仿真研究.该结构对典型的Turbo译码器进行了改进,使之不但能输出信息比特,同时又能输出校验比特,这些比特经硬判决、符号映射及信道交织后反馈回判决反馈均衡器,构成带自适应循环判决反馈均衡的Turbo译码结构.厦门港实测5途浅海水声信道仿真结果显示,该结构具有优良的抗多途性能,信噪比大于4dB时,误比特率小于10-5,比联合判决反馈均衡的Turbo译码结构提高了约2.5dB.     

双通道衰减测量系统的串扰分析

通过对双平衡混频器的分析,推导出双通道衰减测量系统串扰的分析模型,并对双通道衰减测量系统进行了泄漏测试,验证了分析结果。基于分析结果,得出本振通道的隔离度应不小于120 dB的设计,以使在100 dB量程,串扰影响不大于0.01 dB。串扰分析模型对毫米波双通道衰减测量系统的设计以及不确定度评定具有一定的参考价值。     

Slow pulses in disordered photonic-crystal waveguides

Using a 3D fully-vectorial coupled Bloch-mode method, we present a systematic study of the transport of slow-light pulses in single-mode photonic-crystal waveguides (PhCW) with a realistic disorder model. For the intermediate regime corresponding to waveguide lengths of the order of the mean-free path (3 dB attenuation), we show that the group-velocity has a strong impact on the pulse broadening and distortion, limiting the practical use of PhCW to group indices below ≈50. For smaller group velocities, the pulse experiences an additional delay and the group-velocity is no longer a meaningful quantity.     

Electronically controlled agile lens-based broadband variable photonic delay line for photonic and radio frequency signal processing

To the best of our knowledge, proposed for the first time is the design of an optically broadband variable photonic delay line (VPDL) using an electronically controlled variable focus lens (ECVFL), mirror motion, and beam-conditioned free-space laser beam propagation. This loss-minimized fiber-coupled VPDL design using micro-optic components has the ability to simultaneously provide optical attenuation controls and analog-mode high-resolution (subpicoseconds) continuous delays over a moderate (e.g., <5 ns) range of time delays. An example VPDL design using a liquid-based ECVFL demonstrates up to a 1 ns time-delay range with >10 dB optical attenuation controls. The proposed VPDL is deployed to demonstrate a two-tap RF notch filter with tuned notches at 854.04 and 855.19 MHz with 22.6 dB notch depth control via VPDL attenuation control operations. The proposed VPDL is useful in signal conditioning applications requiring fiber-coupled broadband light time delay and attenuation controls.     

Rainfall measurements at Ku-band satellite link in Penang, Malaysia

The rainfall path attenuation at 12.255 GHz measured at Universiti Sains Malaysia for 5 years (2002-2006) is presented. The data obtained are useful to investigate the impairment because of rainfall attenuation in satellite links operating in tropical and equatorial climates. The path attenuation increases significantly with the rainfall rate measured on the ground, with rain fades exceeding 20 dB being measured at rainfall rates of 130 mm/h. Maximum exceeded time for rain rate and attenuation were observed during the wet months. The cumulative distributions of attenuation derived from the measured data are presented and compared with those obtained with existing prediction methods.     

Optical rib waveguides based on sol-gel derived silica-titania films

Rib channel waveguides were produced with the application of chemical wet etching of the sol-gel derived silica-titania (SiO₂-TiO₂) waveguide films. The silica-titania films were etched in water solutions of ammonia fluoride. In the etching process, the waveguide films were selectively masked with a photoresist. This paper presents the theoretical analysis of rib channel waveguides as well as the results of experimental research on slab and rib channel waveguides. For slab waveguides the attenuation of 0.15 dB/cm was obtained, and for the produced single mode rib channel waveguides, the attenuation of 1.7 dB/cm was obtained.     

Compact optical-fiber variable attenuator arrays with polymer-network liquid crystals

Electrically controlled fiber variable-optical-attenuator arrays with polymer-network liquid crystals are shown to be compact and to have a large attenuation range (30-40 dB) and low residual loss (0.55 dB) at wavelengths from 1.3 to 1.6 mum. Their estimated power consumption is very low (<30 nW/channel), and arrays with more than ten channels can be made. The manufacturing process is simple: Trenches 30-100 mum wide are cut across parallel conductive-layer-coated optical fibers and are filled with a polymer-network liquid crystal. The attenuation properties depend on UV-curing conditions and on trench width.     

Wideband radio channel measurement system at 2 GHz

This paper describes the wideband radio channel sounding techniques for mobile radio channel measurements. Implementation of the cross-correlation method using both a sliding correlator and a matched filter detector is presented. Limitations and accuracy of radio channel measurements are discussed. Typically, delay resolution of about 20 ns is achieved with 100 MHz bandwidth. With a sliding correlator, a dynamic range of 25 dB was obtained with maximum Doppler bandwidth of 25 Hz and maximum excess delay of 19 μs. Digital matched filtering with a maximum sampling rate of 125 MHz can be used in real-time measurements with Doppler shifts of several kilohertz and 30 dB dynamic range. Using matched filter deconvolution as a resolution enhancement technique is discussed. Examples of the time-variant complex impulse response measurements are given     

极化码在OFDM水声通信中的应用研究

极化码(Polar code)因其高可靠性、实用的线性编、译码复杂度和理论上唯一可达香农极限等特点,成为信道编码领域新的研究热点.其编、译码方法的研究扩展至多种信道类型和应用领域,但在水声信道中的理论证明和应用研究相对较少且滞后.针对具有显著多途、多普勒扩散和有限带宽等复杂特性的水声信道,文章提出了与之相匹配的极化码信...