Recent advances and future challenges for massive MIMO channel measurements and models大规模多输入多输出通信系统的信道测量与建模的最新进展及未来挑战

This paper considers a unicast multiuser multiple-input single-output (MISO) downlink system overheard by multiple single-antenna eavesdroppers. The objective is to jointly design the beamforming vectors and the artificial noise (AN) covariance matrix with imperfect channel state information (CSI) at the transmitter, such that the total transmit power is minimized while satisfying probabilistic quality of service (QoS) constraints at legitimate users and the eavesdroppers. Using Bernstein-type inequalities and the S-procedure, we recast the non-convex power minimization problem as two different convex semidefinite programs (SDPs) which can be solved using interior-point methods. Simulation results show that the proposed methods outperform a nonrobust method and the ones using the isotropic AN.     

The control of spontaneous emission from a three-level atom in an anisotropic photonic crystal with two asymmetric bands

We theoretically investigate the spontaneous emission light of an excited three-level atom embedded in an anisotropic photonic crystal with two asymmetric bands. The property of spontaneous emission relating to the atomic position in a unit cell of the crystal is described with a position-dependent phase difference. The atomic transition in free space can be manipulated by the other associated transition coupling to photonic crystal. The result shows that the spontaneous emission spectra are effectively shifted and tuned by the atomic position-dependent phase, which results in the asymmetric distribution of the photonic density of states between two bands, and the increasing band can push the emitted light towards the other band. The physical process can be further illuminated through analyzing the emitted field in photonic crystal. The result perhaps offers an interesting route towards tunable photonic devices.     

Energy efficiency and area spectral efficiency tradeoff for coexisting wireless body sensor networks共存无线体域网的能效和区域频效折中

The coexistence of wireless body sensor networks (WBSNs) is a very challenging problem, due to strong interference, which seriously affects energy consumption and spectral reuse. The energy efficiency and spectral efficiency are two key performance evaluation metrics for wireless communication networks. In this paper, the fundamental tradeoff between energy efficiency and area spectral efficiency of WBSNs is first investigated under the Poisson point process (PPP) model and Matern hard-core point process (HCPP) model using stochastic geometry. The circuit power consumption is taken into consideration in energy efficiency calculation. The tradeoff judgement coefficient is developed and is shown to serve as a promising complementary measure. In addition, this paper proposes a new nearest neighbour distance power control strategy to improve energy efficiency. We show that there exists an optimal transmit power highly dependant on the density of WBSNs and the nearest neighbour distance. Some important properties are also addressed in the analysis of coexisting WBSNs based on the IEEE 802.15.4 standard, such as the impact of intensity nodes distribution, optimal guard zone, and outage probability. Simulation results show that the proposed power control design can reduce the outage probability and enhance energy efficiency. Energy efficiency and area spectral efficiency of the HCPP model are better than those of the PPP model. In addition, the optimal density of WBSNs coexistence is obtained.     

Stability analysis of deep-buried hard rock underground laboratories based on stereophotogrammetry and discontinuity identification

Bulletin of Engineering Geology and the Environment - In a tunnel, instabilities in the surrounding rock mostly occur within the sidewalls and crown. After acquiring the rock mass structure, a...     

On the Sum Rate Capacity of MIMO Broadcast Channels in Cognitive Radio Networks with Interference Power Constraints

This paper investigates the sum rate capacity of MIMO broadcast channels (MIMO-BCs) in cognitive radio networks. A suboptimal user-selection algorithm is proposed to achieve a large sum rate capacity with reduced complexity. This algorithm consists of two steps. First, zero-forcing beamforming is utilized as a downlink precoding technique that precancels inter-user interference. Second, singular value decomposition is applied to the channel matrices of all the secondary users and only consider the singular vectors corresponding to the maximum singular values. The proposed user-selection algorithm chooses singular vectors which are nearly orthogonal to each other and nearly orthogonal to the vector of primary users. With this algorithm, the sum rate capacity of MIMO-BCs in CR networks with interference power constraints and transmit power constraints is derived. We formulate the sum rate capacity as a multi-constraint optimization problem and develop an algorithm to solve the problem in its equivalent form. Finally, numerical simulations are conducted to corroborate our theoretical results in flat Rayleigh fading environments. It is shown that the proposed algorithms are capable of achieving a large sum rate capacity with a very low complexity.     

Energy Efficiency Analysis of MISO-OFDM Communication Systems Considering Power and Capacity Constraints

In this paper, the energy efficiency of multi-input single-output and orthogonal frequency division multiplexing (MISO-OFDM) communication systems with power and capacity constraints is investigated. By formulating the power allocation problem of MISO-OFDM communication systems, the minimum subchannel transmission power is analyzed with power and capacity constraints. Simulation results indicate that there exists a specific minimum subchannel capacity threshold. Moreover, the energy efficiency of MISO-OFDM communication systems starts to increase only when the minimum subchannel capacity exceeds the specific threshold.     

空间光通信中应用于精密指向的面阵探测器的定位精度分析与验证

为了实现空间光通信中高精度的链路,本文重点研究了影响面阵探测器对于目标定位精度的关键因素。首先从机理上分析了质心算法的误差,并仿真验证了满足空间无损采样条件的必要性。我们定义了NU值并以此为指标来量化探测器的非均匀性,随着NU自0开始线性增长,质心的定位误差持续增长但是速度放缓。当NU值为0.005时,最大定位误差为0.043 像素。在目标入射到光学系统的光强不断改变的条件下,NU值越小,质心位置越接近光斑的真实位置。我们通过实验测试了某种典型的CMOS探测器在不同光照强度下的像元响应,建立了像元响应非均匀性的数理模型,计算出NU值于线性响应范围内在0.0045到0.0048范围内波动。光斑质心定位精度的实验结果表明,绝对定位误差小于0.05 像素,可以满足高精度链路的需求,验证了理论和仿真的有效性。     

A Study of MIMO Gaussian Channels Based on Synergetics

By interpolating between information theory and synergetics, we provide a bridge to connect the two kinds of subjects. As an application, the capacity formula of multiple-input multiple-output Gaussian channels based on the Fokker-Planck Equation of the synergetics is derived. It is in accordance with Telatar’s capacity formula in information theory and gives a physical explanation (order parameters) of the observed channel characteristics. Moreover, the master equation of the information theory is also derived to obtain error exponents. Error exponents provide a partial solution to how to get close to channel capacity by giving an upper bound to the probability of error. These results demonstrate that the notion of synergetics introduced here can serve as an intuitive tool in information theory.     

A no-tension elastic–plastic model and optimized back-analysis technique for modeling nonlinear mechanical behavior of rock mass in tunneling

In this paper, we present a no-tension elastic–plastic model and an optimized back-analysis technique for stability analysis of underground tunnels. A set of constitutive equations is presented to simulate the no-tension behavior and plastic yielding of jointed rock masses which yield according to the Drucker–Prager yield criterion and permits no-tension. A nonlinear 2-D finite element model is consequently formulated for the prediction of the behavior of the excavated rock mass. As for the model parameters, the genetic algorithm technique is employed to find the optimal rock mass properties by minimizing the discrepancy between the predicted results and field measurement. The nonlinear finite element model coupling with the genetic algorithm optimized back-analysis technique is then applied to a synthetic example of a deep tunnel in yielding rock. The results show that the forward and back-analysis system is capable of estimating the model parameters with stable and good convergence and give reasonable predictions. Numerical experiments are also carried out to check the influences of position and numbers of measurements to the reliability of the back-analysis results. Furthermore, the sensitivity analysis of the genetic algorithms optimization procedure is discussed in terms of identification of geo-material properties.     

基于Web Services架构的加工特征识别技术

提出了通过Web Services体系架构进行加工特征的网络化识别.整个系统由CAD文件特征识别功能服务模块,Web Services实现架构组成.在基于特征的CAD实体造型系统的基础上提出了一种继承式的特征识别方法.对于复杂的模型,利用这种方法并辅以交互式特征定义也可以取得良好的特征识别效果.通过WebServices实现了符合STEP标准的模型文件和加工特征文件在CAD系统、CAPP系统之间进行信息交换,从而实现了产品加工特征的网络化识别.