Monolithically Integrated Optical Receiver with Spatially Modulated Optical Detector in CMOS Technology

设计了与标准CMOS工艺兼容的850 nM空间调制(SPATIAlly MOdulATEd,SM)结构光电探测器,在分析器件物理模型的基础上,建立了SPECTrE环境中等效电路的新模型。提出标准CMOS工艺下SM探测器与前置放大电路单片集成的电路设计。仿真结果表明,在850 nM光照下,SM探测器带宽达到400 MHz,并提供62 MA/W的响应度。整个集成芯片的工作速率为400 Mb/S,增益为0.81 kV/W,功耗为91 MW。A monolithically integrated optical receiver(λ=850 nm) with spatially modulated(SM) optical detector is designed in standard 0.5 μm CMOS technology,the equivalent circuit model of the SM light detector is built in the SPECTRE environment.Simulation results show that the SM optical detector researches a bandwidth of 420 MHz and a responsibility of 78 mA/W.OEIC has a bandwidth of 400 Mb/s and gain of 0.81 kV/W with the power dissipation of 91 mW.厦门市科技计划项目(3502Z20063002

Network performance isolation for virtual machines

Cloud computing is a new computing paradigm that aims to transform computing services into a utility, just as providing electricity in a “pay-as-you-go” manner. Data centers are increasingly adopting virtualization technology for the purpose of server consolidation, flexible resource management and better fault tolerance. Virtualization-based cloud services host networked applications in virtual machines (VMs), with each VM provided the desired amount of resources using resource isolation mechanisms. Effective network performance isolation is fundamental to data centers, which offers significant benefit of performance predictability for applications. This research is application-driven. We study how network performance isolation can be achieved for latency-sensitive cloud applications. For media streaming applications, network performance isolation means both predicable network bandwidth and low-jittered network latency. The current resource sharing methods for VMs mainly focus on resource proportional share, whereas ignore the fact that I/O latency in VM-hosted platforms is mostly related to resource provisioning rate. The resource isolation with only quantitative promise does not sufficiently guarantee performance isolation. Even the VM is allocated with adequate resources such as CPU time and network bandwidth, problems such as network jitter (variation in packet delays) can still happen if the resources are provisioned at inappropriate moments. So in order to achieve performance isolation, the problem is not only how many/much resources each VM gets, but more importantly whether the resources are provisioned in a timely manner. How to guarantee both requirements to be achieved in resource allocation is challenging. This thesis systematically analyzes the causes of unpredictable network latency in VM-hosted platforms, with both technical discussion and experimental illustration. We identify that the varied network latency is jointly caused by VMM CPU scheduler and network traffic shaper, and then address the problem in these two parts. In our solutions, we consider the design goals of resource provisioning rate and resource proportionality as two orthogonal dimensions. In the hypervisor, a proportional share CPU scheduler with soft real-time support is proposed to guarantee predictable scheduling delay; in network traffic shaper, we introduce the concept of smooth window to smooth packet delay and apply closed-loop feedback control to maintain network bandwidth consumption. The solutions are implemented in Xen 4.1.0 and Linux 2.6.32.13, which are both the latest versions when this research was conducted. Extensive experiments have been carried out using both real-life applications and low-level benchmarks. Testing results show that the proposed solutions can effectively guarantee network performance isolation, by achieving both predefined network bandwidth and low-jittered network latency.published_or_final_versionComputer ScienceMasterMaster of Philosoph

Delay-aware network I/O virtualization for cloud computing

Cloud datacenters are largely adopting virtual machines (VMs) to provide elastic computing services. As many cloud applications are communication-intensive, such as distributed data processing and web services, satisfactory network performance is critical to guarantee the service quality. In virtualized environments, a major problem is that the end hosts are separated by a virtualization layer and subject to the intervention of the hypervisor’s scheduling. Since the scheduling delays due to CPU sharing are commonly from tens of milliseconds to over one hundred milliseconds, when they are added to packet processing, network performance can be seriously degraded. To tackle this problem, prior works focus dominantly on modifying the hypervisor scheduler to hide the virtualization reality by reducing the delays as much as possible. However, this type of approaches brings many other problems, such as increased VM context switches and more complicated CPU resource allocation. This thesis tries to look at the problem from a different but simpler angle: we let the guest operating system (OS) accept the reality that each virtual CPU (vCPU) can be suspended and resumed at any time, and then think about how to refactor the network I/O subsystem to automatically tolerate such scheduling delays. In general, network I/O processing in the kernel includes two layers: protocol layer and interrupt layer. Our study shows that both layers are very sensitive to VM scheduling delays, and therefore must be redesigned accordingly. First, in the protocol layer, we propose a paravirtualized approach to help TCP counteract the distortion of congestion control caused by the hypervisor scheduler. Second, in the interrupt layer, for SMP-VMs that have multiple vCPUs, we propose a method to dynamically migrate interrupts from a preempted vCPU to a running one whenever it is possible, so that the delays will not be propagated to the protocol layer. Experiments with our prototypes in Xen/Linux show that our approaches can significantly improve the network throughput and responsiveness.published_or_final_versionComputer ScienceDoctoralDoctor of Philosoph

Effects of Urbanization and Industrialization on Farmland System in Shandong Peninsula

[目的]对城市和工业化对山东半岛农田系统的影响进行研究。[方法]以山东半岛为研究区;通过遥感解译、数据空间分析、社会统计数据分析;了解城市和工业化对农田系统的影响。[结果]山东半岛的荒地面积在研究时段先减后增;耕地面积逐渐减少;而果园和林地的面积逐年增加。造成这种差异趋势的主要原因是政府政策和农民利益最大化等因素共同作用的结果。同时;工业和城市化发展使用于农业生产的化肥施用量和农业机械总动力逐渐增加。这种发展趋势对环境、工业和城市化带来了不同影响。[结论]为了社会经济和环境的和谐发展;政府应制定更多的政策来协调社会经济和环境的发展