A multilayer recognition model for twitter user geolocation

Wireless Networks - Geolocation is important for many emerging applications such as disaster management and recommendation system. In this paper, we propose a multilayer recognition model (MRM) to...     

Resource allocation for OFDM relay systems with statistical QoS guarantees

By integrating the concept of effective capacity, we propose the resource allocation schemes for subcarrier‐pair based OFDM decode‐and‐forward and amplify‐and‐forward relay systems for quality‐of‐service (QoS) guarantees. The objective is to maximize the system throughput subject to a given statistical delay QoS constraint. First, we pair the subcarriers over the source‐relay channel and the relay‐destination channel by the descending order of the subcarriers' channel gains. Second, by making use of the derived equivalent end‐to‐end channel gains of the subcarrier pairs, we apply joint water‐filling power allocation over the subcarrier pairs and then partition the power of the subcarrier pairs between the source and the relay. We prove that as the equivalent end‐to‐end channel gains of the subcarrier pairs are given, the combination of sorted subcarrier pairing and joint water‐filling power allocation is jointly optimal to maximize the effective capacity. The simulation results show that our proposed schemes achieve the highest effective capacity for OFDM decode‐and‐forward and amplify‐and‐forward relay systems as compared with other existing schemes. The results also verify that our proposed schemes can efficiently provide different levels of delay QoS guarantees, even if under the stringent delay QoS constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

Trust establishment in cooperative wireless relaying networks

In cooperative wireless networks, relay nodes are employed to improve the performance of the network in terms of throughput and reliability. However, the presence of malicious relay nodes in the network may severely degrade the performance of the system. When a relay node behaves maliciously, there exists a possibility that such a node refuses to cooperate when it is selected for cooperation or deliberately drops the received packets. Trust establishment is a mechanism to detect misbehaving nodes in a network. In this paper, we propose a trust establishment method for cooperative wireless networks by using Bayesian framework. In contrast with the previous schemes proposed in wireless networks, this approach takes the channel state information and the relay selection decisions into account to derive a pure trust value for each relay node. The proposed method can be applied to any cooperative system with a general relay selection policy whose decisions in each cooperative transmission are independent of the previous ones. Moreover, it does not impose additional communication overhead on the system as it uses the available information in relay selection procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

不同氧化退火工艺下SiO2/SiC界面特性研究

The effect of the different re-oxidation annealing （ROA） processes on the SiO2/SiC interface charac- teristics has been investigated. With different annealing processes, the flat band voltage, effective dielectric charge density and interface trap density are obtained from the capacitance-voltage curves. It is found that the lowest interface trap density is obtained by the wet-oxidation annealing process at 1050 ℃ for 30 min, while a large num- ber of effective dielectric charges are generated. The components at the SiO2/SiC interface are analyzed by X-ray photoelectron spectroscopy （XPS） testing. It is found that the effective dielectric charges are generated due to the existence of the C and H atoms in the wet-oxidation annealing process.     

CIGS Thin Films for Cd-Free Solar Cells by One-Step Sputtering Process

Cu(In_1?x Ga _x )Se₂ (CIGS) thin films were deposited by a one-step radio frequency (RF) magnetron sputtering process using a quaternary CIGS target. The influence of substrate temperature on the composition, structure, and optical properties of the CIGS films was investigated. All the CIGS films exhibited the chalcopyrite structure with a preferential orientation along the (112) direction. The CIGS film deposited at 623 K showed significant improvement in film crystallinity and surface morphology compared to films deposited at 523 and 573 K. To simplify the manufacturing procedure of solar cells and avoid the use of the toxic element Cd, the properties of ZnS films prepared by RF sputtering were also investigated. The results revealed that the sputtered ZnS film exhibits good lattice matching with the sputtered CIGS film with significantly lower optical absorption loss. Finally, all-sputtered Cd-free CIGS-based heterojunction solar cells with the structure SLG/Mo/CIGS/ZnS/AZO/Al grids were fabricated without post-selenization. Furthermore, the results demonstrated the feasibility of using a full sputtering process for the fabrication of Cd-free CIGS-based solar cell.     

一种用于MEMS电容式加速度计的116dB动态范围CMOS读出电路

A high stability in-circuit reprogrammable technique control system for a capacitive MEMS accelerometer is presented. Modulation and demodulation are used to separate the signal from the low frequency noise. A low-noise low-offset charge integrator is employed in this circuit to implement a capacitance-to-voltage converter and minimize the noise and offset. The application-specific integrated circuit （ASIC） is fabricated in a 0.5 /μm one-ploy three-metal CMOS process. The measured results of the proposed circuit show that the noise floor of the ASIC is -116 dBV, the sensitivity of the accelerometer is 66 mV/g with a nonlinearity of 0.5%. The chip occupies 3.5×2.5 mm2 and the current is 3.5 mA.     

低功耗、高线性度的电流模可编程增益放大器

本文设计了一种电流模式下,带电流模直流失调消除（DCOC）电路的class-AB的可编程增益放大器。电路基于电流放大器,可以实现40dB的增益动态范围,增益步长为1dB。电流模可编程增益放大器由0.18-μm CMOS工艺实现,电路具有较宽的电流增益范围、较低的直流功耗和较小的芯片面积。放大器电路芯片面积为0.099μm2,在1.8V电压下静态电流为2.52mA。测试结果表明电路增益范围为10dB到50dB,增益误差为±0.40dB,OP1dB为11.80dBm到13.71dBm,3dB带宽为22.2MHz到34.7MHz。     

GaN基HEMT微加速度计的压阻系数测试

介绍了GaN基HEMT微加速度计结构的设计、加工及测试过程,并对结果做出了分析。通过喇曼测试与ANSYS仿真软件相结合的方式进行应力测试分析,利用安捷伦4156C测试仪对GaN基HEMT进行不同应力状态及不同温度下IDS-VDS特性测试,并通过相关测试数据计算分析GaN基HEMT的压阻系数及其变化规律。结果表明:常温下GaN基HEMT的等效压阻系数为(2.47±0.04)×10-9Pa-1,高于Si的压阻系数(7.23±3.62)×10-10Pa-1。同时测试了HEMT在-40~50℃的输出特性,实验结果表明,HEMT饱和源漏电流随着温度的升高而下降。压阻系数具有负温度系数,且压阻系数随着温度的升高以226TPa-1/℃的速率减小。     

广东省有线数字电视监管系统试点建设

本文主要介绍广东省有线数字电视监管系统第一期试点建设的架构,描述了广东省有线数字电视监管系统一些新的设计思路,结合职能部门对监管平台的技术需求,介绍了监管平台的主要功能及其在有线数字电视监管中发挥的作用.     

星/机双基地混合滑动聚束式SAR距离-多普勒成像算法

该文提出了星/机双基地混合滑动聚束式SAR的距离-多普勒成像算法。文中首先通过级数反演法得到了此双基构型下场景目标的2维频谱,并通过解析近似得到随距离空变的频谱表达。在此基础上,提出了先根据谱分析技术对回波信号进行方位去混叠处理,再进行2维频域处理得到全孔径聚焦的双基地SAR 距离-多普勒成像算法。该算法不需要进行子孔径分块和插值操作,运算量小,效率高。最后通过仿真实验验证了算法的有效性。