Performance of trellis coded-8PSK with cochannel interference

The performance of trellis coded-8PSK in the presence of cochannel interference is analyzed and compared with the performance of uncoded QPSK. The analytical expressions are derived and supported by simulating the bit error rate performance of different TC-8PSK systems. The analytical and simulation results show that TC-8PSK is slightly more robust to cochannel interference than uncoded QPSK     

YAG脉冲激光器快速连通保护系统

本文阐述了ＹＡＧ脉冲激光器的一种快速连通保护系统，利用大功率二极管作为连通故障信号检出的关键元件，采用了可控硅与继电器双重保护，使得整个保护系统既快速可靠，又简便适用。     

MNLS inverse discriminates between neuronal activity on oppositewalls of a simulated sulcus of the brain

The minimum-norm least-squares (MNLS) inverse for magnetic field measurements is applied to a representation of a sulcus of the human brain, where one or both walls have regions of neuronal activity. Simulations indicate that the magnetic source image (MSI) is largely confined to the appropriate wall of the sulcus, even for a depth of 4 cm where the distance between walls is only 3 mm. Two nearly oppositely oriented dipoles located 3 mm apart are found to be distinguished. Influences on the quality of the MSI by measurement noise and inaccuracy in determining the image surface are discussed in detail     

An FDTD/ray-tracing analysis method for wave penetration through inhomogeneous walls

A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic.     

两种自主开发的图形外延SiGe工艺

使用清华大学微电子学研究所研发的UHV/CVD系统深入研究了图形外延SiGe工艺,分别选用单一的SiO2介质层和SiO2/P0ly-Si复合介质层,作为图形外延SiGe单晶材料的窗口屏蔽介质,开发出了不同的实用化图形外延SiGe工艺.     

计算机网络信息安全技术分析

本文论述了计算机网络面临的威胁和常见的黑客入侵技术，然后从信息加密技术、防火墙技术、入侵检测技术、系统容灾技术、网络安全管理策略等方面，分析了计算机网络信息安全的基本对策。     

基于"替换法"的汉字加、解密实现技术

文章讨论的基于“替换法”的汉字信息加、解密实现技术,改变了传统的汉字加密结果,使加密后的密文仍是可以识别和再利用的汉字,发送者可以在任何可编辑汉字的通讯设备上发送和接收密文,确保中文信息传输过程中的安全性。加、解密算法实现的代码语言为VFP6.0。     

Photo-bleaching induced electro-optic polymer modulators with dual driving electrodes operating at 1.55 /spl mu/m wavelength

Electro-optic (EO) polymeric Mach-Zehnder (MZ) modulators with photo-bleaching (PB) induced waveguides and dual driving electrodes operating at 1.55 /spl mu/m wavelength have been demonstrated. The half-wave voltage of the integrated polymeric modulator was 4.5 V in a push-pull configuration with a 1.5 cm interaction length. The extinction ratio was greater than 20 dB, and the fibre-to-fibre insertion loss was 8 dB for the TM polarisation. The achieved fibre-to-fibre insertion loss and driving voltage are the best, to the authors knowledge, in the reported PB induced MZ EO polymeric modulators.     

Packet acquisition in upstream transmission of the DOCSIS standard

In upstream transmission of the DOCSIS (data over cable service interface specification) 1.0/1.1 and the TDMA mode of DOCSIS 2.0 standard, a packet begins with a preamble, the length and value of which are programmable by the headend. The acquisition process includes packet detection, symbol timing estimation, carrier frequency offset estimation and carrier phase estimation by means of the preamble so that the following information packet can be correctly demodulated. Methods to solve these tasks are not subject to standardization and are left to the system designer. However, they have a great impact on the system performance and thus are key elements for implementation. We present dedicated algorithms. A specific preamble is created and the corresponding scheme for packet acquisition is described in some detail. The packet detecting algorithm is independent of the carrier and symbol timing. The symbol timing estimate is obtained by using the minimum mean square algorithm regardless of the carrier frequency deviation and carrier phase. Algorithms for estimating the carrier frequency offset and carrier phase are proposed. Computer simulation results are given for all algorithms presented.     

Breakdown probabilities for thin heterostructure avalanche photodiodes

The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostructure APDs that may have multiple multiplication layers. The generalization addresses layer-boundary effects such as the initial energy of injected carriers as well as the layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication layer serves to both downshift and sharpen the breakdown probability curve as a function of the applied reverse-bias voltage. In structures where the injected carriers have an initial energy that is comparable to the ionization threshold energy, the transition from linear mode to Geiger-mode is more abrupt than in structures in which such initial energy is negligible. The theory is applied to two recently fabricated Al/sub 0.6/Ga/sub 0.4/As-GaAs heterostructure APDs and to other homostructure thin GaAs APDs and the predictions of the breakdown-voltage thresholds are verified.