A direct-conversion mixer with DC-offset cancellation for IEEE 802.11a WLAN receiver

A DC-offset cancellation scheme in the 5GHz direct-conversion receiver compliant with IEEE 802.11a wireless LAN standard is described in this paper. It uses the analog feedback loop to eliminate the DC-offset at the output of the double-balanced mixer. The mixer has a simulation voltage conversion gain of IMB at 5.2GHz, noise figure of 9.67dB, IIP3 of 7.6dBm. The solution provides 39.1dB reduction according to the leakage value at LO and mixer load resistors, the additional noise figure added to mixer is less than 0.9dB, the added power dissipation is 0.1mW and was fabricated in 60GHz 0.35 mu m SiGe BiCMOS technology.

A power-saving scheme for IEEE 802.11 Ad hoc networks

In the Wireless Local Area Networks (WLANs), the terminals are often powered by battery, so the power-saving performance of the wireless network card is a very important issue. For IEEE 802.11 Ad hoc networks, a power-saving scheme is presented in Medium Access Control (MAC) layer to reduce the power consumption by allowing the nodes enter into the sleep mode, but the scheme is based on Time-Drive Scheme (TDS) whose power-saving efficiency becomes lower and lower with the network load increasing. This paper presented a novel energy-saving mechanism, called as Hybrid-Drive Scheme (HDS), which introduces into a Message.-Drive Scheme (MDS) and combines MDS with the conventional TDS. The MDS, could obtain high efficiency when the load is heavy; meanwhile the TDS has high efficiency when the network load is small. The analysis shows that the proposed HDS could obtain high energy-efficiency whether the network load is light or heavy and have higher energy-saving efficiency than conventional scheme in the IEEE 802.11 standard.

A two-step backoff scheme for improving the performance of the IEEE 802.11 distributed coordination function

This paper describes the binary exponential backoff mechanism of 802.11 distributed coordination function (DCF), and introduces some methods of modifying the backoff scheme. Then a novel backoff scheme, called Two-step Backoff scheme, is presented and illustrated. The simulation process in OPNET environment has been described also. At last, the analysis and simulation results show that the Two-step backoff scheme can enhance the performance of the IEEE 802.11 DCF.

5.2 GHz variable-gain amplifier and power amplifier driver for WLAN IEEE 802.11a transmitter front-end

A 5.2 GHz variable-gain amplifier (VGA) and a power amplifier (PA) driver are designed for WLAN IEEE 802.11a monolithic RFIC. The VGA and the PA driver are implemented in a 50 GHz 0.35 μm SiGe BiCMOS technology and occupy 1.12×1.25 mm~2 die area. The VGA with effective temperature compensation is controlled by 5 bits and has a gain range of 34 dB. The PA driver with tuned loads utilizes a differential input, single-ended output topology, and the tuned loads resonate at 5.2 GHz. The maximum overall gain of the VGA and the PA driver is 29 dB with the output third-order intercept point (OIP3) of 11 dBm. The gain drift over the temperature varying from -30 to 85℃ converges within±3 dB. The total current consumption is 45 mA under a 2.85 V power supply.

A direct-conversion mixer with a DC-offset cancellation for WLAN

This paper presents a 5GHz double-balanced mixer with DC-offset cancellation circuit for direct-conversion receiver compliant with IEEE 802.11a wireless LAN standard. The analog feedback loop is used, to eliminate the DC-offset at the output of the double-balanced mixer. The test results show that the mixer with DC-offset cancellation circuit has voltage conversion gain of 9.5dB at 5.15GHz, noise figure of 13.5dB, IIP3 of 7.6 dBm, 1.73mV DC-offset voltage and 67mW power with 3.3-V power supply. The DC-offset cancellation circuit has less than 0.1mm(2) additional area and 0.3mW added power dissipation. The direct conversion WLAN receiver has been implemented in a 0.35 mu m SiGe BiCMOS technology.

Design of Low Power Multi-Standard Active-RC Filter for WLAN and DVB-H

In this paper, a low-power, highly linear, integrated, active-RC filter exhibiting a multi-standard (IEEE 802.11a/b/g and DVB-H) application and bandwidth (3MHz, 4MHz, 9.5MHz) is present. The filter exploits digitally-controlled polysilicon resister banks and an accurate automatic tuning scheme to account for process and temperature variations. The automatic frequency calibration scheme provides better than 3% corner frequency accuracy. The Butterworth filter is design for receiver (WLAN and DVB-H mode) and transmitter (WLAN mode). The filter dissipation is 3.4 mA in RX mode and 2.3 mA (only for one path) in TX mode from 2.85-V supply. The dissipation of calibration consumes 2mA. The circuit has been fabricated in a 0.35um 47-GHz SiGe BiCMOS technology, the receiver and transmitter occupy 0.28-mm(2) and 0.16-mm(2) (calibration circuit excluded), respectively.

细辛精油和4种化学药剂对黄瓜灰霉病菌的抑制作用

采用菌丝生长速率法及孢子萌发法分别测定了细辛精油和4种化学药剂(30%嘧霉胺EC、50%双福生WP、75%百菌清WP、70%正品甲津托WP)对引起黄瓜灰霉病的灰葡萄孢菌菌丝生长和孢子萌发的抑制作用。结果表明,供试药剂对灰葡萄孢菌的菌丝生长和孢子萌发均有抑制作用,且对孢子萌发的抑制效果明显好于对菌丝生长的抑制效果;百菌清对灰葡萄孢菌菌丝生长的抑菌效果最好,EC50为1.6231mg/L;双福生对灰葡萄孢菌孢子萌发的抑制效果最好,EC50为0.0042mg/L;细辛精油对黄瓜灰葡萄孢菌的抑菌效果与其他4种化学药剂相比效果较差,对菌丝生长的EC50为159.580mg/L,对孢子萌发的EC50为71.1840mg/L,虽然其EC50偏高,但作为纯植物提取物,其抑菌中浓度低于160mg/L。

工业无线网络化控制系统结构及调度问题研究

无线通信技术在工业网络化控制系统中的应用已成为当今工业领域中的研究热点。然而无线通信技术在恶劣的工业环境中通信质量严重下降，使得现有无线通信技术在工业网络化控制系统中的应用受阻。为此在不断提高和改进无线信号传输性能的同时，更要在控制系统级层面上充分考虑无线通信技术的特点，进行相关系统结构和实时调度机制等方面的改进，以达到使系统产生的通信任务在应用层上得到可靠、实时调度的目的。同时也要从无线网络技术层面上入手，解决上层下达的通信任务在数据链路层中的实时调度问题。要设计适合工业无线网络化控制系统应用特点的MAC协议来有效调度网络所有节点的信息收发，减少高层下达的通信任务在网络中的平均时延，提高吞吐量，进而保证工业无线网络化控制系统的实时性。 因此，本文从工业无线网络化控制系统中的通信任务在数据链路层和应用层上的调度角度出发，以解决、改善工业无线网络化控制系统的实时性和可靠性等性能指标为目的。对工业无线网络化控制系统的结构、应用层调度策略和优化以及数据链路层中的MAC协议进行了系统的研究。主要工作和贡献有以下几点： （1）对工业网络化控制系统的基本问题和引入无线通信技术后产生的问题进行了探讨。在定性分析了工业环境对无线通信的影响及要求的同时，又推导出了无线通信的链路预算模型，并利用Matlab对该预算模型进行了建模，计算出了在工业级噪声指数和工业要求的误码率下，IEEE802.11b和IEEE802.15.4两大主流无线通信技术的链路预算情况及具体的量化数据。 （2）提出了工业无线网络化控制系统的双频二级拓扑结构和多路径传输机制。利用了无线信道特点和路径冗余优势，在系统级上改进了目前无线通信技术在工业网络化控制系统中的应用模式，部分缓解了无线通信技术在工业恶劣环境中的实时性和可靠性问题。为工业无线网络化控制系统结构的设计做了有益的尝试。同时，首次将DS-UWB技术应用于工业网络化控制系统中，设计出了基于该结构的UWB和FF及PROFIBUS的集成方案，为该结构的快速应用提供了有效的途径。 （3）提出了极大容忍无线通信时延的调度算法(GTD)。有效解决了工业无线网络化控制系统中周期性通信任务的实时性问题,部分弥补了因无线网络时延而导致周期性通信任务超时的缺陷。并针对GTD调度算法产生的通信窗口碎片问题进行了优化处理，又提出了面向非周期信息吞吐量最大化的优化调度算法，该算法提高了非周期性通信任务的吞吐量。同时，给出了基于这两种调度算法的非线性规划模型的调度时间表求解方法。 （4）提出了根据通信任务调度时间表进行分配无竞争期的混合CAP和CFP的MAC协议（HAF-MAC）。解决了工业无线网络化控制系统上层下达的周期性通信任务和非周期性通信任务在数据链路层中的实时调度问题，并有效解决了本文提出的应用层调度算法生成的预留时间可能存在浪费的问题。同时，在理论分析了HAF-MAC协议时隙利用率的基础上，提出了基于时隙的HAF-MAC（TSHAF-MAC）协议。TSHAF-MAC协议比HAF-MAC协议提高了时隙利用率，使吞吐量和平均延时得到了进一步改善，进而提高了非周期性通信任务的实时性。最后，对这两个协议进行了仿真建模与验证，进而较系统地解决了工业无线网络化控制系统中的通信任务的实时调度问题。 （5）分别将论文中的第三章和第四章的部分研究成果,在本人博士研究阶段研发的无线智能照明控制系统这一物理实验平台上进行了一定的验证。

数值模拟二元喷管的三维可压粘性流场

发展了一种用扫描有限元素法求解二元喷管内部湍流流场的数值模拟方法，并提出了N-S方程中二阶导数项新的离散方法，推导了更完善、更简洁的扫描有限元方程的表达式。用发展的方法对二维平面收扩喷管、两个大宽高比的二元喷管(宽高比分别为7和4)及其圆转方转接段的三维粘流场等算例的计算结果表明，该方法具有较宽广的适用范围，有较高的应用和研究价值。

Effective elastic moduli of inhomogeneous solids by embedded cell model

An embedded cell model is presented to obtain the effective elastic moduli for three-dimensional two-phase composites which is an exact analytic formula without any simplified approximation and can be expressed in an explicit form. For the different cells such as spherical inclusions and cracks surrounded by sphere and oblate ellipsoidal matrix, the effective elastic moduli are evaluated and the results are compared with those from various micromechanics models. These results show that the present model is direct, simple and efficient to deal with three-dimensional tyro-phase composites.

On properties of hyperchaos: Case study

Some properties of hyperchaos are exploited by studying both uncoupled and coupled CML. In addition to usual properties of chaotic strange attractors, there are other interesting properties, such as: the number of unstable periodic points embedded in the strange attractor increases dramatically increasing and a large number of low-dimensional chaotic invariant sets are contained in the strange attractor. These properties may be useful for regarding the edge of chaos as. the origin of complexity of dynamical systems.

10°尖锥标模高超声速动导数的实验测量

在中科院力学所JF-4B高超声速脉冲风洞中，用模型自由飞方法对10~。尖锥开展动态实验测量，并用参数微分法辨识得到了该模型的俯仰阻尼导数。实验结果表明，脉冲风洞中模型自由飞方法得到的10~。尖锥标模高超声速动态气动特性测量值与国外可比数据一致，重复测量精度与弹道靶试验相当。

饱和软基爆炸排水机理的初步研究

在现场实验研究的基础上，提出了饱和两相介质在爆炸动载下排水固结机理的一维简化模型。数值计算结果表明在强动载作用下，土层中两相介质由于运动惯性不同，两者会出现分离运动，土体的排水速度与两相介质的运动有关。动载作用后两相介质仍具有较大的惯性，继续排水，这与静载下是不同的。土中孔隙压力的变化与两相介质运动有关，计算值与实测值在量级上有可比性。

高层建筑结构之非线性地震响应分析

将高层建筑结构近似地等效成非线性弹性支承梁，以悬臂梁、柱之本征函数作为Ritz矢量，用能量法推导出结构的运动方程，其自由度数及计算量均比用有限元法时大为减小。用该文方法可以计算具弹塑性铰或弹塑性耗能器之剪切墙及框架式高层建筑结构。计算结果表明，采用非线性耗能器并引进高阻尼，可以显著地降低结构之地震响应。