Lower bounds on the Hamming auto- and cross correlations of frequency-hopping sequences

Frequency hopping (FH) sequences have found wide applications in various modern FH spread-spectrum communications and radar systems. In FH spread-spectrum communications, the interference occurs when two distinct transmitters use the same frequency simultaneously. In order to evaluate the goodness of FH sequence design, the Hamming correlation function is used as an important measure. In this correspondence, by considering separately the maximum Hamming autocorrelation sidelobe H/sub a/, and the maximum Hamming cross correlation H/sub c/, several new lower bounds on the size p of the frequency slot set F, the sequence length L, the family size M, and correlation properties are established. The new periodic bounds include the known Lempel-Greenberger bounds as special case when M=2, and are tighter than the Seay bounds under certain conditions when M>2. Furthermore, the new bounds disclose more information on the relationship between the maximum autocorrelation sidelobe and the maximum cross correlation compared with the Lempel-Greenberger bounds and Seay bounds. Besides, the aperiodic FH bounds which have not yet been previously reported are also presented and discussed in this correspondence.     

LTE系统一种高效率准动态部分频率复用方案

部分频率复用(FFR)是下一代移动通信系统中提升系统容量与边缘用户性能的核心技术之一.准动态FFR在增益与额外开销的平衡上具有明显优势,成为优化静态FFR技术的主要研究方向.本文提出了一种新的准动态FFR方案,以很低的额外开销,同时达到提高系统容量和改善边缘用户性能的目的.通过在LTE系统级仿真平台上的仿真,论文对算法的适用场景、增益和代价进行了深入分析.     

基于PAD图的牵引供电系统保护图形化平台研究

针对牵引供电系统微机保护软件开发存在的问题,提出基于问题分析图(PAD图)的图形化保护设计新思想。以Delphi7为开发工具,设计开发了基于PAD图的牵引供电系统保护图形化平台。在该平台上成功的实现了根据牵引供电系统保护方案定制对应的PAD图,然后从元件库中调用保护模块在保护平台上搭建图形程序,编译得到可执行程序,有效...     

Geosynthetic-reinforced pile-supported embankments with caps in a triangular pattern over soft clay

Given the limit studies on the behavior of GRPS embankments with different numbers of geosynthetic layers and pile caps in a triangular pattern, this paper conducted a series of three-dimensional (3-D) numerical analyses. The numerical model was verified based on a well-instrumented large-scale test. A 3-D soil arch model was proposed for pile caps in a triangular pattern, in which the crown of the upper boundary was approximately 1.4 times the clear spacing of pile caps. Inclusion of geosynthetic reinforcement reduced the soil arching effect but increased the total load carried by the piles. For the case with three geosynthetic layers, the lower layer had a significant effect on load transfer than the middle and upper layers, but each layer had an almost proportional effect on mitigating the differential settlement on the top of the gravel cushion. The maximum strains in the reinforcement concentrated on the geosynthetic strips bridging over two adjacent square cap corners.     

Compression behavior of porous NiTi shape memory alloy

Porous NiTi alloy with several different porosities was processed by spark plasma sintering. The compression behavior of the porous NiTi was examined with the aim of using it possibly as a high energy absorbing material. A model for the macroscopic compression behavior of porous shape memory alloy (SMA) is presented in this work, where Eshelby’s inhomogeneous inclusion method is used to predict the effective elastic and superelastic behavior of a porous SMA based on the assumption of stress–strain curve. The analytical results are compared with experimental data for porous NiTi with 13% porosity, resulting in a reasonably good agreement.     

二阶伏特拉滤波器RLS算法改进

分析了二阶伏特拉滤波器的一种快速RLS算法,针对其存在的收敛速度与收敛精度之间的矛盾,构造了遗忘因子函数并取代该算法中的固定遗忘因子,得到改进的RLS算法。提出了遗忘因子函数的构造原则并分析了相关参数的选取方法。算例表明:改进的RLS算法能解决收敛速度与收敛精度之间的矛盾,有效地加快了收敛速度。     

Facade staining arising from design features

The rain run-off flow pattern over some main facade design features of impermeable materials was investigated by conducting simulations over them. The relationship between run-off flow pattern and the observed staining patterns were evaluated. Four main design features namely ledges, joints misalignment, protruding fixtures, and louver units were identified. The formation of stains was observed to be irregular and was determinable by the run-off flow and the dirt build-up on the facade.     

Quasi-maximum-likelihood multiple-symbol differential detection for time-varying Rayleigh fading channel

The maximum-likelihood multiple-symbol differential detector (ML-MSDD) has better bit-error-rate performance than many other detectors for differential modulation. Unfortunately, the computational complexity of ML-MSDD quickly becomes prohibitive as the observation window size grows. While low-complexity MSDD algorithms for the time-invariant Rayleigh fading channel have been considered before, there is a need for low-complexity MSDD algorithms for general time-varying Rayleigh fading channels. A polynomial-time complexity approach called semi-definite relaxation (SDR) is employed to achieve differential detection with near maximum-likelihood (ML) performance. The proposed SDR quasi-maximum-likelihood (QML) multiple-symbol differential detection (SDR-QML-MSDD) is efficient in that its complexity is polynomial in the observation window size, even in the worst case, while it exhibits almost the same performance as ML-MSDD does.     

A new Co-ZIF derived nanoporous cobalt-rich carbons with high-potential-window as high-performance electrodes for supercapacitors

In this work, a Co-ZIF material and the derived nanoporous cobalt-rich carbons by direct carbonization of this Co-ZIF material were synthesized and used as electrode materials for supercapacitors. This ZIF material exhibited a high specific capacitance of 160.3 F g⁻¹ at 0.5 A g⁻¹, an excellent rate capability (73.72 F g⁻¹ at 10 A g⁻¹), and a good cycling stability with 100% of its initials specific capacitance after 8000 cycles. In addition, the obtained derived nanoporous carbons displayed ideal capacitor behaviors and were promising electroactive materials for supercapacitors at low current density. The nanoporous carbon obtained at 650 °C possessed a highest specific capacitance of 393 F g⁻¹ at 0.5 A g⁻¹ and a wide potential application range of −1.0–0.33 V. In addition, a symmetric supercapacitor device consisting of Z-C-650 and activated carbon exhibited a maximum energy density of 61.23 Wh Kg⁻¹ at a power density of 700 W kg⁻¹ and predicted that Z-C-650 could be used as a potential energy storage material.