Survey of software defined D2D and V2X communication

The related D2D (device-to-device) and V2X (vehicle-to-everything) are regarded as vital components of 5G communication system,which providing alternative network services and multiple application services for cellular network.In the meanwhile,SDN (software defined networking) can improve the compatibilities and flexibilities of D2D and V2X.SD-D2D (software defined D2D communication) and SD-V2X (software defined V2X communication) technologies were reviewed.Based on their similarities and respective characteristics,their state-of-arts and architectures were reviewed accordingly,and the key technologies such as D2D location/discovery management,D2D routing control,D2D flow table management,V2V path scheduling,and V2V path recovery were analyzed.Finally,it was pointed out that the SD-D2D architecture was approaching mature and the SD-V2X framework had been preliminarily determined,the existing problems of interference management,mobile management and routing management in D2D/V2X communication could be effectively solved.Furthermore,it was also pointed out that the disconnection between the existing SD-D2D/V2X studies and the actual application needed to be overcome.     

基于信干噪比的D2D通信功率控制与资源分配

为了优化长期演进(LTE)系统引入设备直传(D2D)通信后带来的同频干扰、系统边缘用户性能恶化问题,提出一种基于信干噪比(SINR)的多小区D2D通信资源分配方案,通过调整信干噪比阈值将部分蜂窝用户(CU)转化为D2D用户并释放频谱资源进而获得较佳的资源分配策略,同时提出一种基于小区间D2D竞争机制的配置算法有效降低小区间干扰.仿真表明,算法能够有效提升系统容量,并提升小区边缘D2D用户公平性.     

Bio-inspired power control and channel allocation for cellular networks with D2D communications

With the tremendous increment of traffic in the next generation mobile networks, device to device (D2D) communication is proposed to relieve the traffic burden of the base station and improve the overall network capacity. It supports direct communications between devices and could reuse the resources of cellular users (CUs). Despite the advantages, D2D communications bring great challenges in interference management. In this paper, we study the power control and channel allocation problems in three scenarios: (1) one CU and one D2D pair; (2) one CU and multiple D2D pairs; (3) multiple CUs and multiple D2D pairs. The goal is to coordinate the mutual interferences and maximize the overall network capacity. We derive sufficient conditions to guarantee the efficiency of D2D communications in scenarios with one CU and one D2D pair. We propose the bio-inspired PSO-P power control algorithm for the scenarios with one CU and multiple D2D pairs, and the PSO-CP algorithm for the scenarios with multiple CUs and multiple D2D pairs to jointly assign channels and powers. Simulation results show that the proposed algorithms are efficient in improving the overall network capacity.

     

D2D研究现状及发展前景

LTE Device to Device(D2D)Proximity Services(LTE终端直通近距离服务)即我们熟知的LTE-D2D(端到端)技术。2013年,D2D成为3GPP组织重点研讨技术之一,其标准化工作正在讨论完善之中。LTE-D2D是在LTE-A系统(辅助)控制或无网络基础设施的情况下,用户设备在授权频段上直接进行通信的技术。它的出现将在一定程度上缓解无线频谱资源匮乏的问题,并能够提升蜂窝系统频谱效率。文章对D2D通信的发展历程、场景和关键技术进行了介绍,最后展望D2D技术发展前景及在未来应用中的情况。     

D2D通信中联合链路共享与功率分配算法研究

针对D2D （Device-to-Device,D2D）通信过程中的资源分配问题,提出一种联合链路共享和功率分配算法.在保证系统内蜂窝用户服务质量（Quality of Service,QoS）需求的前提下,利用系统的信道状态信息,为D2D用户生成一个由蜂窝用户组成的通信链路的候选集合;在通信链路候选集合内使用凸优化方法得到D2D用户最优功率分配策略;最后利用（Kuhn-Munkres,KM）算法求解最大加权二部图匹配（Maximum Weight Bipartite Matching,MWBM）问题,为D2D用户选择最优的蜂窝用户进行资源共享.仿真结果表明该算法能有效的提升通信网络的吞吐量,可以为D2D用户选择最优的资源分配策略.     

Compositional and Dimensional Control of 2D and Quasi‐2D Lead Halide Perovskites in Water

Blue light emitting two dimensional (2D) and quasi‐2D layered halide perovskites (LHPs) are gaining attention in solid‐state lighting applications but their fragile stability in humid condition is one of the most pressing issues for their practical applications. Though water is much greener and cost effective, organic solvents must be used during synthesis as well as the device fabrication process for these LHPs due to their water‐sensitivity/instability and consequently, water‐stable blue‐light emitting 2D and quasi‐2D LHPs have not been documented yet. Here, water‐mediated facile and cost‐effective syntheses, characterizations, and optical properties of 16 organic–inorganic hybrid compounds are reported including 2D (A′)₂PbX₄ (A′ = butylammonium, X = Cl/Br/I) (8 compounds), 3D perovskites (4), and quasi‐2D (A′)_pA_x?1B_xX_3x+1 LHPs (A = methylammonium) (4) in water. Here, both composition and dimension of LHPs are tuned in water, which has never been explored yet. Furthermore, the dual emissive nature is observed in quasi‐2D perovskites, where the intensity of two photoluminescence (PL) peaks are governed by 2D and 3D inorganic layers. The Pb(OH)₂‐coated 2D and quasi‐2D perovskites are highly stable in water even after several months. In addition, single particle imaging is performed to correlate structural–optical property of these LHPs.     

D2D网络中信道选择与功率控制策略研究

针对D2D通信的资源分配问题,该文研究了D2D信道选择与功率控制策略。在保证蜂窝用户服务质量(QoS)的前提下,提出一种基于启发式的D2D信道选择算法,为系统内的D2D用户找到合适的信道复用资源。同时,利用拉格朗日对偶方法求解得到D2D用户最优传输功率。仿真结果表明当蜂窝用户与多对D2D用户共享信道资源时能够大幅度提升系统平均吞吐量。在相同条件下,该算法的性能要明显优于现有算法。     

5G网络中DR-OC型D2D通信收益模型及定价研究

Device-to-Device(D2D)通信是下一代(5G)移动网络的重要组成部分。D2D设备间在不依赖基站的情况下直接进行数据传输,并通过重复使用蜂窝小区的频率资源从而提高移动通信系统的容量。为了激励蜂窝网络用户参与到D2D通信,运营商对D2D通信的定价是一个很关键的问题。文中首先介绍了D2D的基本概念及其四种主要类型,并就其中DR-OC型D2D通信定价提出了运营商和D2D设备的收益模型,然后仿真分析了网络中谱单价和奖励带宽对双方收益的影响。仿真结果显示运营商可以通过调整奖励带宽来协调双方收益以激励更多的用户参与到D2D通信。     

2D Metallic Transition-Metal Dichalcogenides: Structures,Synthesis, Properties,and Applications

2D materials and the associated heterostructures define an ideal material platform for investigating physical and chemical properties, and exhibiting new functional applications in (opto)electronic devices, electrocatalysis, and energy storage. 2D transition metal dichalcogenides (2D TMDs), as a member of the 2D materials family including 2D semiconducting TMDs (s-TMDs) and 2D metallic/semimetallic TMDs (m-TMDs) have attracted considerable attention in the scientific community. Over the past decade, the 2D s-TMDs have been extensively researched and reviewed elsewhere. Because of their distinctive physical properties including intrinsic magnetism, charge-density-wave order and superconductivity, and potential applications, such as high-performance electronic devices, catalysis, and as metal electrode contacts, 2D m-TMDs have grabbed widespread attention in recent years. However, reviews demonstrating the m-TMDs systematically and comprehensively have been rarely reported. Here, the recent advances in 2D m-TMDs in the aspects of their unique structures, synthetic approaches, distinctive physical properties, and functional applications are highlighted. Finally, the current challenges and perspectives are discussed.     

基于加权二部图及贪婪策略的蜂窝网络D2D通信资源分配

D2D(Device-to-Device)通信是解决频谱资源稀缺问题的关键技术之一。该文研究蜂窝网络中“many-to-many”的复杂场景,即单个RB(Resource Block)可以分配给多对D2D用户重用,并且允许单个D2D用户对使用多个RB,其中D2D用户对数量远多于蜂窝用户设备(Cellular User Equipment, CUE)数量和RB数量。考虑CUE对资源使用具有更高优先级,将此优化问题分解为蜂窝用户资源分配和D2D用户资源重用两个阶段。在第1阶段,提出基于公平性的循环二部图匹配(Fairness-based Circular Bipartite Graph Matching, FCBGM)算法,将现有的RB分配给所有CUE,以最大化蜂窝用户和速率。在第2阶段,分别提出基于二部图的资源重用(Bipartite Graph-based Resource Reuse, BGRR)算法和基于贪婪策略的资源重用(Greedy-based Resource Reuse, GRR)算法,目标是将已经分配给CUE的RB再次分配给D2D用户重用,以最大化系统和速率,同时确保CUE的基本速率需求。仿真结果表明,在D2D用户对数量远大于CUE数量和RB数量的情况下,与现有典型算法相比,所提算法能够有效提高系统和速率,增加D2D接入率,同时兼顾用户公平性和服务质量需求。     

基于大规模MIMO和D2D技术的混合网络能量效率研究

文章研究了基于大规模多输入多输出（multiple-input multiple-output,MIMO）和端到端（device-to-device,D2D）技术的双层混合网络及其能量效率,面向D2D用户（D2D user,DU）提出了无线能量采集方案。在该混合网络模型中,宏蜂窝基站由大规模MIMO天线阵列构成,D2D网络覆盖在宏蜂窝之上,与蜂窝网共享频谱。为了保证D2D通信,系统配置了由小规模MIMO天线构成的专用能量发射基站（power beacon,PB）,其通过迫零预编码向能量约束的D2D发射机传送能量;同时,为了提高网络的能量效率,DU还可以从附近蜂窝网用户（cellular user,CU）的射频（radio frequency,RF）干扰信号中采集能量。对此混合网模型和能量采集方案,文章通过假设网络中CU、DU以及PB的位置服从独立泊松点过程和利用随机几何分析方法,基于反功率控制方案得到了网络中任一D2D发射机通过采集足够能量来建立通信链路的概率,其以简单的积分形式给出。分析和数值结果表明,文章提出的无线能量采集方案由于PB的配置保证了D2D通信的可靠性;同时又因为充分利用了附近CU的RF干扰信号,有效提高了D2D用户采集足够能量的概率,节约了PB的能量,改善了系统的能量效率。      

异构云无线接入网场景下D2D通信资源共享与分配

针对异构云无线接入网中的前向链路受限问题,提出了一种基于干扰阈值的设备到设备(Device-to-Device,D2D)多用户分簇方案,并对系统信道和功率资源的分配进行优化。首先根据D2D用户之间的干扰级别,利用着色图理论对多用户进行分簇;然后,在满足D2D用户和蜂窝用户服务质量约束下,建立了基于D2D用户和速率最大化的资源分配模型,并进一步采用二分法对已分簇的D2D用户进行功率优化分配。仿真实验结果验证了所提方案相比传统方案,系统频谱利用率提高了55%以上。     

基于资源分配和功率控制的D2D中继选择

为优化蜂窝用户通信与设备直传(D2D)中继通信共存下的同频干扰问题,满足蜂窝用户容量要求,提出了一种基于能效的联合资源分配和功率控制的D2 D中继选择算法.该算法首先对等效D2 D中继链路进行资源分配,减小算法复杂度的同时使得D2 D链路对蜂窝链路产生的干扰最小;然后以资源分配结果和功率控制算法为依据进行中继选择.该方案不仅考虑了D2 D中继链路的能效问题,而且还同时考虑到了对蜂窝链路的干扰问题.通过仿真验证,所提算法不仅能有效提升D2 D中继链路的能效值,同时降低了对蜂窝用户的干扰.     

Power allocation and relay selection for network-coded D2D communication underlay heterogeneous cellular networks

Underlay device-to-device (D2D) communication is an attractive technology enabling nearby cellular users to communicate with each other directly in order to increase data rate and spectral efficiency. The current cellular heterogeneous networks consist of macrocell base stations and small cell base stations with different transmit powers and coverage areas. Femtocell is the most popular small cell which is expected to be utilized in dense and ultra-dense scenarios in the future. Network coding in relay-assisted multi-hop communications improves achievable transmission rate and coverage of D2D communications. In this paper, two-hop random linear network coding network in cooperative D2D communication (RLNC-CDC) is considered. We propose to use femtocell base station (FBS) as a relay. We assume that the D2D pair and relay operate in the frequency band which is allocated to femtocell network. Therefore, there would be interference from the relay node and the D2D communication on the femtocell network users. To reduce the interference, the sum of transmit powers of the D2D pair and selected relay FBS should be minimized in a way that the highest transmission rate for the D2D pair is achieved. The constraints on the bounds of transmit powers of the D2D and relay node as well as the minimum required transmission rate for D2D communication are considered and the optimum solution is obtained. Simulation results indicate that the proposed RLNC-CDC achieves higher data rate and smaller outage probability than the direct D2D transmission.     

Cs(7DJ)+H2的反应与非反应碰撞转移截面的测定

利用激光泵浦-吸收技术,研究了在样品池中的Cs(7D_J)+H₂→CsH[X¹∑+(v″=0)]+H光化学反应过程。双光子激发Cs-H₂混合蒸气中Cs原子至7²D态,荧光中除有泵浦能级发生的直接荧光外,还包含由精细结构碰撞转移产生的敏化荧光,CsH分子是由7D原子与H₂间的三体碰撞反应产生的。利用780 nm激光测量了CsH X¹∑+(v″=0→v″=21)吸收带。△Ⅰ′和△Ⅰ″分别表示泵浦7D_3/2和7D_5/2时的吸收光强。解速率方程组,得到7D_3/2→7D_5/2和7D_5/2→7D_3/2精细结构转移截面分别为(1.3±0.3)×10^-14和(9.8±2.0)×10^-15cm²。从7D_J碰撞到7D以外态的截面分别为(4.0±1.0)×10^-15(对J=3/2)和(3.6+0.9)×10^-15cm²(对J=5/2)。Cs(7D_J)+H₂→CsH+H的反应截面分别是(1.4±0.5)×10^-16(J=3/2)和(1.1±0.4)×10^-16cm²(J=5/2),7D_3/2与H₂的反应活动...更多性大于7D_5/2。     

Motion and structure from feature correspondences: a review

We present a review of algorithms and their performance for determining three-dimensional (3D) motion and structure of rigid objects when their corresponding features are known at different times or are viewed by different cameras. Three categories of problems are considered, depending upon whether the features are two (2D) or three-dimensional (3D) and the type of correspondence: a) 3D to 3D (i.e., locations of corresponding features in 3D space are known at two different times), b) 2D to 3D (i.e., locations of features in 3D space and their projection on the camera plane are known, and c) 2D to 2D (i.e., projections of features on the camera plane are known at two different times). Features considered include points, straight lines, curved lines, and corners. Emphasis is on problem formulation, efficient algorithms for solution, existence and uniqueness of solutions, and sensitivity of solutions to noise in the observed data. Algorithms described have been used in a variety of applications. Some of these are: a) positioning and navigating 3D objects in a 3D world, b) camera calibration, i.e., determining location and orientation of a camera by observing 3D features whose location is known, c) estimating motion and structure of moving objects relative to a camera. We mention some of the mathematical techniques borrowed from algebraic geometry, projective geometry, and homotopy theory that are required to solve these problems, list unsolved problems, and give some directions for future research     

Outage performance analysis and resource allocation algorithm for energy harvesting D2D communication system

Wireless Networks - In this paper, we consider an energy harvesting device-to-device (D2D) communication system, where D2D transmitter can use mode A to directly communicate with D2D receiver or...     

2D and 3D Hybrid Systems for Enhancement of Chondrogenic Differentiation of Tonsil‐Derived Mesenchymal Stem Cells

2D/3D hybrid cell culture systems are constructed by increasing the temperature of the thermogelling poly(ethylene glycol)‐poly(l ‐alanine) diblock copolymer (PEG‐l ‐PA) aqueous solution in which tonsil tissue‐derived mesenchymal stem cells and graphene oxide (GO) or reduced graphene oxide (rGO) are suspended, to 37 °C. The cells exhibit spherical cell morphologies in 2D/3D hybrid culture systems of GO/PEG‐l ‐PA and rGO/PEG‐l ‐PA by using the growth medium. The cell proliferations are 30%–50% higher in the rGO/PEG‐l ‐PA hybrid system than in the GO/PEG‐l ‐PA hybrid system. When chondrogenic culture media enriched with TGF‐β3 is used in the 2D/3D hybrid systems, cells extensively aggregate, and the expression of chondrogenic biomarkers of SOX 9, COL II A1, COL II, and COL X significantly increases in the GO/PEG‐l ‐PA 2D/3D hybrid system as compared with the PEG‐l ‐PA 3D systems and rGO/PEG‐l ‐PA 2D/3D hybrid system, suggesting that the GO/PEG‐l ‐PA 2D/3D hybrid system can be an excellent candidate as a chondrogenic differentiation platform of the stem cell. This paper also suggests that a 2D/3D hybrid system prepared by incorporating 2D materials with various surface biofunctionalities in the in situ forming 3D hydrogel matrix can be a new cell culture system.     

基于用户中断概率的D2D通信干扰协调与资源分配

在LTE系统中引入设备直传(D2D)通信技术,会因为D2D用户复用蜂窝用户资源进行通信而产生同频干扰.在现有的干扰协调与资源分配研究中,都需要基站获取各个通信链路的信道状态信息(CSI),但这样无疑会增加基站的信令负担.为减小干扰与基站的信令负担,提出了一种基于用户中断概率的干扰协调与资源分配算法,首先在保证蜂窝用户正常通信的情况下,通过限制D2D用户到基站间的距离来降低干扰;其次通过遍历所有蜂窝用户的频谱资源,选择能使D2D用户的总中断概率最低的频谱资源进行复用.仿真结果表明,所提算法能够在保证蜂窝用户正常通信的情况下,明显降低D2D用户的平均中断概率,同时还能够降低基站信令负担.     

Self‐Crystallized Multifunctional 2D Perovskite for Efficient and Stable Perovskite Solar Cells

Recently, perovskite solar cells (PSC) with high power‐conversion efficiency (PCE) and long‐term stability have been achieved by employing 2D perovskite layers on 3D perovskite light absorbers. However, in‐depth studies on the material and the interface between the two perovskite layers are still required to understand the role of the 2D perovskite in PSCs. Self‐crystallization of 2D perovskite is successfully induced by deposition of benzyl ammonium iodide (BnAI) on top of a 3D perovskite light absorber. The self‐crystallized 2D perovskite can perform a multifunctional role in facilitating hole transfer, owing to its random crystalline orientation and passivating traps in the 3D perovskite. The use of the multifunctional 2D perovskite (M2P) leads to improvement in PCE and long‐term stability of PSCs both with and without organic hole transporting material (HTM), 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) compared to the devices without the M2P.