内蒙古草原植被最大光能利用率取值优化研究

针对目前CASA (carnegie-ames-stanford approach)模型等植被生产力模型植被最大光能利用率的取值未对草原进行区分的问题,以内蒙古草甸草原、典型草原和荒漠草原为研究对象,结合野外实测NPP(net primary productivity)数据和CASA模型的建模思路优化了三大草原类型植被最大光能利用率,并以此为基础模拟分析了其植被光能利用率和NPP时空格局。结果表明,基于99个地面采样点所建立的一元二次方程模拟的草甸草原、典型草原和荒漠草原最大光能利用率分别为0.654,0.553和0.511 gC·MJ-1,平均为0.573 gC·MJ-1。与未对草原类型进行区分而统一取值为0.541 gC·MJ-1的结果相比,实测NPP与模拟NPP之间的决定系数和和均方根误差分别提高了0.024和2.62 gC·(m2·month-1)-1。受水热组合和草原类型的空间格局的影响,内蒙古草原植被光能利用率和NPP总体上由东北向西南逐渐下降趋势,呈明显的单峰季节变化特征。但光能利用率和NPP的最大值出现的月份有所不同,分别出现在8月份和7月份,这可能与植被吸收的光合有效辐射和光能利用率的最高值出现的月份不同有关。光能利用率和NPP平均值按草甸草原>典型草原>荒漠草原的顺序依次降低。     

基于伪对称序列的OFDM-PON系统载波间干扰抑制算法EI北大核心CSCD

受多种光纤非线性因素的影响,基于正交频分复用(OFDM)技术的无源光网络(PON)会受到较为严重的载波间干扰(ICI)。为了抑制OFDM-PON系统中的上述问题,构造了一种新的伪对称序列(PST),并提出将该问题转化为求解两个Toeplitz子系统,然后对其中一个子系统的解进行预处理,将其转化为另一子系统的输入,之后利用最小二乘准则对子系统求解,从而达到抑制载波间干扰的目的。在算法实现过程中,利用所构造序列的伪对称特性和快速傅里叶变换(FFT),避免了高阶矩阵直接求逆,从而提升了算法实时性。仿真结果表明,该方法不仅能够有效抑制OFDM-PON系统的载波间干扰,而且能有效提升该算法的实时性能。     

通过量子噪声信道之后Werner态的纠缠特性研究

利用并发度作为纠缠的度量研究了Werner态通过量子噪声信道(包括振幅和相位阻尼信道)之后的纠缠动力学性质,给出了Werner态通过量子噪声信道之后并发度的解析表达式,获得了纠缠突然死亡的参数条件。     

Novel wavelength-accurate InP-based arrayed waveguide grating

A 13-channel, InP-based arrayed waveguide grating （AWG） is designed and fabricated in which the on-chip loss of the central channel is about -5 dB and the crosstalk is less than -23 dB in the center of the spectrum response. However, the central wavelength and channel spacing are deviated from the design values. To improve their accuracy, an optimized design is adopted to compensate the process error. As a result, the central wavelength 1549.9 nm and channel spacing 1.59 nm are obtained in the experiment, while their design values are 1549.32 nm and 1.6 nm, respectively. The route capability and thermo-optic characteristic of the AWG are also discussed in detail.     

Signal processing for noncoherent underwater acoustic communication approaching channel capacity

Noncoherent underwater acoustic communication channel in adverse conditions is modeled as a phase-random Rayleigh fading channel,and its capacity curve is derived.To approach the channel capacity curve,the concatenated code of the nonbinary LDPC code and the constant weight code is proposed for noncoherent communication which can late be iteratively decoded in the probability domain.Without information of channel amplitude or phase in the receiver,statistic parameters of the respective signal and noise bins were estimated based on the moment estimation method,the posterior probabilities of the constant weight code words were further calculated,and the nonbinary LDPC code was decoded with the nonbinary factor graph algorithm.It is verified by simulations that by utilizing the proposed concatenated code and its processing algorithm,gap to channel capacity curve is reduced by 3 dB when compared to the existing method.Underwater communication experiments were carried out in both deep ocean（vertical communication,5 km）and shallow lake（horizontal communication,near 3 km,delay spread larger than 50 ms）,in which the signal frequency band was 6 kHz to10 kHz,and the data transmission rate Was 357 bps.The proposed scheme can work properly in both experiments with a signal-to-noise ratio threshold of 2 dB.The performance of the proposed algorithm Was well verified by the experiments.     

Protecting Distribution Entanglement by Weak Measurement and Reversal under Various Decoherence Sources

Protection of entanglement from disturbance of the environment is an essential task marion processing. We examine the validity and limitation of the weak measurement and reversal in quantum infor- （WMR） operation in the protection of distributed entanglement from various decoherence sources. Since the entanglement variation can be investigated analytically for an arbitrarily entangled bipartite pure state under three kinds of typical noisy quantum channels, we show explicitly that the WMR operation indeed helps for protecting distributed entanglement from ampli- tude damping and phase damping, but not for depolarizing. Bxperimental feasibility for testing our results is discussed using current laboratory techniques.     

基于功率谱收敛的低压电力载波信道中的噪声检测与建模

在低压电力线载波信道中,复杂的噪声特性是阻碍低电压电力线载波通信广泛应用的主要原因之一。因此,准确的噪声模型对于设计和优化电力线通信系统具有重要意义。为了得到更加准确噪声模型,给出一种等效背景噪声和功率谱收敛算法。通过对多组拟合参数的求解,并以归一化理论和噪声特性为基础,实现功率谱收敛算法对准确噪声模型的搭建。通过低压电力线信道噪声分析,验证了功率谱收敛算法在噪声模型中应用的可行性。     

340GHz太赫兹室内信道测量及仿真研究

太赫兹波的衰减性及高可用带宽使其在局域网环境中拥有广阔的应用前景.而太赫兹波的窄波束问题需要借助波束成形技术来解决.作为波束成形技术的关键内容,非直视情况下太赫兹频段的室内信道建模成为了当前亟待开展的工作.本文在340 GHz频段对多种常见室内装饰材料的太赫兹波反射特性和室内多径反射信道特性进行了实验研究,并基于射线追踪法对太赫兹室内信道进行仿真,仿真结果与测量结果符合较好,为进一步太赫兹室内信道建模提供了基础.     

LED显示屏高光效高画面填充比光学设计与研究

针对传统LED显示屏光能利用率和图像画面填充比低的缺点,基于非成像光学理论,提出了一种提高光能利用率和画面填充比的全彩LED显示模块结构系统和设计方法。利用复合抛物面集光器CPC对LED管芯发出光线的发散角进行变换压缩,从而避免了外表面全反射损耗,大幅度提高了系统的光能利用率。利用积分方腔匀光原理和散射元件对光能的二次分配,提高了显示屏的画面填充比、单位像素均匀度及基色复用面积。作为实例,根据上述方法设计了一个P10 mm全彩LED显示模块,利用光学设计软件LIGHTTOOLS对该显示模块系统进行了仿真建模和光线追迹,并对设计结果进行了分析。结果表明,系统光能利用率大于70%,画面填充比接近100%,单位像素区域内均匀度好于85%。显示模块具有能量利用率高、高画面填充比、显示效果均匀柔和、易于生产和装调的优点。     

改进的时序多重稀疏贝叶斯学习冰下水声信道估计方法

针对时序多重稀疏贝叶斯学习信道估计方法计算复杂度高且在低信噪比时估计精度低的问题,本文提出了一种改进的时序多重稀疏贝叶斯学习正交频分复用冰下水声信道估计方法。首先,采用奇异值分解方法对接收导频矩阵进行去噪;随后利用去噪后的接收导频矩阵结合最小二乘信道估计方法获得时序多重稀疏贝叶斯信道估计的超参数矩阵、感知矩阵等先验知识;最后,利用冰下水声信道的稀疏特性和多途结构较为稳定的特点,采用时序多重稀疏贝叶斯信道估计对不同符号的冰下水声信道进行联合重建。仿真结果显示,在能量系数为0.03时,改进方法信道估计均方误差相比较于原始方法至少降低了约2.87×10-5,运算时间至少下降了约为90%。第11次北极科学考察冰下试验结果显示,改进方法的平均原始误码率略微低于原始方法,平均运算时间降低约75%。研究结果表明,利用冰下水声信道的特点,改进方法可以实现高精度冰下水声信道估计,并且有效降低系统计算复杂度。