A distributed coordination scheme to improve the performance of IEEE 802.11 in multi-hop networks

This paper investigates the performance of IEEE 802.11 in multi-hop scenarios and shows how its aggressive behavior can throttle the spatial reuse and reduce bandwidth efficiency. An adaptive, layer-2, distributed coordination scheme for 802.11 using explicit medium access control (MAC) feedback is then proposed to pace the transmissions on adjacent nodes, thereby assisting the MAC protocol to operate around its saturation state while minimizing resource contention. Simulation results show that the proposed scheme outperforms the original 802.11 MAC.     

Power adaptation for BPSK signaling with average and peak power constraints in Rayleigh fading channels

We consider power adaptation strategies for binary phase-shift keying signals in Rayleigh fading channels under the assumption that channel state information is provided at both the transmitter and the receiver. We first derive a closed-form expression for the optimal power adaptation that minimizes average bit-error rate (BER) subject to average and peak transmission power constraints. Then, we analyze the average BER for channel inversion power adaptation with the same constraints. Our results show that the performance difference between the optimal power adaptation and the channel inversion becomes negligibly small as available average transmission power increases and/or peak-to-average power ratio decreases. We also find that an optimal peak-to-average power ratio exists that minimizes the average BER in the channel inversion scheme.     

通信设备的电磁兼容性设计

本文介绍了通信产品的电磁兼容性要求、国内外标准、电磁兼容设计。     

3-D NONLINEAR SUPERCAVITATING FLOW IN A GRAVITY FIELD

In this paper,perturbation method and Fourier-cosine-expansion method are used to solve a 3-D nonlinear problem of a supercavitating flow in an inclined field of gravity at large Froude numbers.By expanding the velocity potential into a power series of a small parameter,the original 3-D nonlinear problem is reduced to a number of 2-D ones. The solutions of the first three orders are derived in detail and expressed in terms of the complete elliptic integrals of the first and second kinds.Then the boundary integral equation method is applied to get the numerical solutions for each order.Computational results are provided for supercavitating flows past cones under various flow conditions.     

三峡工程基础帷幕灌浆试验

根据三峡工程坝基岩石地质特点,采用“孔口封闭、高压灌浆”法和ＧＩＮ法以及使用没灌浆材料,在现场进行灌浆试验,以便对三峡工程主体建筑物基础灌浆设计技术参数进行验证并寻求合适的交流 材料、施工方法与工艺措施。此次帷幕灌浆试验结果表明：“孔口封闭、高压灌浆”法灌浆效果明显,能达到设计源防渗标准;ＧＩＮ灌浆法,其抗生及耐久性达不到设计要求。湿磨普通水泥浆液和改性灌浆水泥,均能满足三峡帷幕灌浆对浆材的要求。     

Composite derivative and edge detection

This paper proposes a new concept of composite derivative, which is realized by the combination of fractional-order differentiation and fractional-order integration. Then, the composite derivative is applied to edge detection and a novel edge detection algorithm is formulated. The experimental results verify the effectiveness of the proposed operator. Finally, qualitative and quantitative comparisons with classic integer-order operators (Roberts, Prewitt and Sobel et al.) are performed. The comparisons show the promising feature of the proposed algorithm, which is reflected in the compromise between detection accuracy and noise suppression.     

Design of oversampled nonuniform filter banks with arbitrary rational frequency partitioning

Among the theory and design of oversampled nonuniform filter banks (NUFBs), most of the existing works only consider the cases with integer decimators, and up to now the issue with rational sampling factors has not been discussed yet. In this paper, we generalize the partial modulation technique to realize arbitrary rational frequency partitioning of oversampled NUFBs with highly desired linear-phase (LP) property. Further for the subbands with sampling factors violating the guard band restriction, a phase-modification scheme is derived to avoid uneliminable large aliasing and meanwhile preserving the LP characteristics of shifted analysis/synthesis filters. By using the proposed method, the design issue of LP oversampled NUFBs can be reduced to that of several prototypes, decreasing the design complexity largely. As illustrated by examples, the proposed algorithm is more general in terms of arbitrary rational decimation and thus has broad application prospects.     

基于PNNI递阶拓扑结构的VP网络规划

ＡＴＭ网络中的ＶＰ层网络规划在大规模网络情形下求解会发生困难,文章借鉴了ＰＮＮＩ网络递阶结构,设计了一种分级规划方法,有效地解决了大规模ＡＴＭ网络ＶＰ层规划问题,并用进化规划对规划问题进行了求解。文中给出了数值算例。     

直接扩频通信同步系统的FPGA设计与实现

对直接扩频通信同步系统进行了研究,使用PN码作为扩频序列,利用其良好的自相关性,提出一种新式的滑动相关法使收发端同步,并给出该系统的FPGA实现方法。利用ISE10．1开发软件仿真验证,证明此方法可以提高运算速度,减少捕获时间。     

Phase estimation characteristics of ultra-wideband quasi-radio signal

Synthesis and analysis of the maximum likelihood algorithm for estimating the phase of ultra-wideband quasi-radio signal with unknown amplitude and phase are performed. Duration of the specified signal may amount to several periods or a fraction of the period of harmonic oscillation. Characteristics of the classical maximum likelihood phase estimate of a narrow-band radio signal are found when receiving an ultra-wideband quasi-radio signal. Applicability conditions of narrow-band radio signal model are defined for solving the problem of phase estimation with the specified accuracy.