Energy Aware Signal Processing for Software Defined Radio Baseband Implementation

The fast pacing diversity and evolution of wireless communications require a wide variety of baseband implementations within a short time-to-market. Besides, the exponentially increased design complexity and design cost of deep sub-micron silicon highly desire the designs to be reused as much as possible. This yields an increasing demand for reconfigurable/ programmable baseband solutions. Implementing all baseband functionalities on programmable architectures, as foreseen in the tier-2 SDR, will become necessary in the future. However, the energy efficiency of SDR baseband platforms is a major concern. This brings a challenging gap that is continuously broadened by the exploding baseband complexity. We advocate a system level approach to bridge the gap. Specifically, we fully leverage the advantages (programmability) of SDR platforms to compensate its disadvantages (energy efficiency). Highly flexible and dynamic baseband signal processing algorithms are designed and implemented to exploit the abundant dynamics in the environment and the user requirement. Instead of always performing the best effort, the baseband can dynamically and autonomously adjust its work load to optimize the average energy consumption. In this paper, we will introduce such baseband signal processing techniques optimized for SDR implementations. The methodology and design steps will be presented together with 3 representative case studies in HSDPA, WiMAX and 3GPP LTE.     

Low Complexity Antenna Selection Scheme for Multicarrier MIMO Broadcast Communication

A low complexity antenna selection scheme for multicarrier MIMO (Multiple Input Multiple Output) broadcast systems is proposed in this paper. Under special condition of single user in the system or when the number of subcarrier is only one, the system reduces to conventional MIMO-OFDM (Orthogonal Frequency Division Multiplexing) system or MIMO-BC (Broadcast Channel) system respectively. By analysing sub-optimal antenna selection schemes developed earlier for single user MIMO-OFDM systems and single carrier MIMO-BC systems, one can see many similarities which can be extended to multicarrier MIMO broadcast systems. The proposed method exploits these similarities to obtain a low complexity system design with acceptable performance. The performance of the proposed scheme is studied via extensive simulation, and the computational complexity involved is compared to the conventional scheme. A selection gain of approximately 0.5 b/s/Hz is shown to be achievable using only two out of three antennas, and the proposed scheme is able to achieve up to 90% of the gain. This is achieved at a complexity that is significantly lower than the conventional methods, hence the practical implementation of the proposed scheme can be justified.     

强短脉冲激光冲击薄板高速变形的实验研究

强短脉冲激光冲击材料成形是一种高应变率的过程。很多已有测试手段由于响应带宽不够而无法进行有效测量。常用的任意面速度干涉仪(VISAR)价格昂贵、测试方法复杂,且存在条纹缺失。采用一种简单的光电测试系统探测出铝薄板在强短脉冲激光冲击下的高速变形过程。通过标定输出电压与变形量的关系,分析出薄板被冲击中心点的位移和速度,与文献仿真结果规律一致,计算出在8 J激光能量冲击时间内平均变形速度为8.49×104m/s。并由阻尼振动和弹性形变叠加的模型拟合出激光冲击薄板的形变过程,根据拟合系数计算出薄板的振动速度和塑性变形值,为分析和控制激光冲击变形工艺提供了依据。     

Performance analysis of bit error rate of data link system under pulse LFM interference in time-varying rayleigh channel

Wireless Networks - In such mobile platforms as ships and aircraft, the detection and reconnaissance devices are near to the communication facilities. When working at the same time, they will...     

An Investigation of the Electrical Degradation of GaN High-Electron-Mobility Transistors by Numerical Simulations of DC Characteristics and Scattering Parameters

The effects of direct-current (DC) stress on GaN high-electron-mobility transistors (HEMTs) are investigated by means of numerical simulations, by which the creation of an acceptor trap in the AlGaN barrier layer was correlated to the observed experimental degradation. An increase in the trap concentration induces a worsening of the saturated current I _DSS, transconductance g _m, and output conductance g _O. An increase in the length of the trapping region induces a degradation of I _DSS and g _m, but can reduce g _O. Analysis of scattering parameters in the saturation region shows that the cutoff frequency f _T matches the trend of g _m.     

Quantum Oscillations of Thermoelectric Effects in a Pseudo-one-dimensional Electron Gas With a Spin–Orbit Interaction

We consider thermoelectric effects in a pseudo-one-dimensional electron gas (P1DEG) with a spin–orbit interaction (SOI). The SOI splits the dispersion relation of the P1DEG into subbands with an energy gap. We find quantum oscillations in transport coefficients, which coincide with the locations of the subband edges, as a function of the electrochemical potential.     

Effect of Composition on Thermoelectric Properties in PbTe-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Composites

The solidification of alloys in the Bi₂Te₃-PbTe pseudobinary system at off- and near-eutectic compositions was investigated for their microstructure and thermoelectric properties. Dendritic and lamellar structures were clearly observed due to the phase separation and the existence of a metastable ternary phase. In this system, three phases with different compositions were observed: binary Bi₂Te₃, PbTe, and metastable PbBi₂Te₄. The Seebeck coefficient, electrical resistivity, and thermal conductivity of ternary alloys as well as binary compounds were measured. The phonon thermal conductivities of Pb-Bi-Te alloys were lower than those in binary PbTe and Bi₂Te₃, which could have resulted from the increased interfacial area between phases due to the existence of the metastable ternary phase and the resultant phase separation.     

Effect of Isothermal Aging and Thermal Cycling on Interfacial IMC Growth and Fracture Behavior of SnAgCu/Cu Joints

The growth behavior of interfacial intermetallic compounds (IMCs) of SnAgCu/Cu soldered joints was investigated during the reflow process, isothermal aging, and thermal cycling with a focus on the influence of these parameters on growth kinetics. The SnAgCu/Cu soldered joints were isothermally aged at 125°C, 150°C, and 175°C while the thermal cycling was performed within the temperature ranges from −25°C to 125°C and −40°C to 125°C. It was observed that a Cu₆Sn₅ layer formed, followed by rapid coarsening at the solder/Cu interface during reflowing. The grain size of the interfacial Cu₆Sn₅ was found to increase with aging time, and the morphology evolved from scallop-like to needle-like to rod-like and finally to particles. The rod-like Ag₃Sn phase was formed on the solder side in front of the previously formed Cu₆Sn₅ layer. However, when subject to an increase of the aging time, the Cu₃Sn phase was formed at the interface of the Cu₆Sn₅ layer and Cu substrate. The IMC growth rate increased with aging temperature for isothermally aged joints. During thermal cycling, the thickness of the IMC layer was found to increase with the number of thermal cycles, although the growth rate was slower than that for isothermal aging. The dwell time at the high-temperature end of the thermal cycles was found to significantly influence the growth rate of the IMCs. The growth of the IMCs, for both isothermal aging and thermal cycling, was found to be Arrhenius with aging temperature, and the corresponding diffusion factor and activation energy were obtained by data fitting. The tensile strength of the soldered joints decreased with increasing aging time. Consequently, the fracture site of the soldered joints migrated from the solder matrix to the interfacial Cu₆Sn₅ layer. Finally, the shear strength of the joints was found to decrease with both an increase in the number of thermal cycles and a decrease in the dwell temperature at the low end of the thermal cycle.     

深亚微米nMOSFET器件的总剂量电离辐射效应

选取了采用0.25μm工艺的两组器件进行研究.通过对这两种器件关态泄漏电流、跨导和栅电流等电学参数进行分析,得出当器件发展到深亚微米阶段时,影响其辐射效应的主要原因是场氧化层中的陷阱电荷.并对相关机理进行了分析和仿真验证.     

Thermosonic bonding of lead-free solder with metal bump for flip-chip bonding

While extensive research on the lead-free solder has been conducted, the high melting temperature of the lead-free solder has detrimental effects on the packages. Thermosonic bonding between metal bumps and lead-free solder using the longitudinal ultrasonic is investigated through numerical analysis and experiments for low-temperature soldering. The results of numerical calculation and measured viscoelastic properties show that a substantial amount of heat is generated in the solder bump due to viscoelastic heating. When the Au bump is thermosonically bonded to the lead-free solder bump (Sn-3%Ag-0.5%Cu), the entire Au bump is dissolved rapidly into the solder within 1 sec, which is caused by the scrubbing action of the ultrasonic. More reliable solder joints are obtained using the Cu/Ni/Au bump, which can be applied to flip-chip bonding.