Performance analysis of MC-CDMA cellular systems employing MMSE multiuser detector in presence of own-cell and co-cell interference

In this work, it is analyzed the uplink performance of MC-CDMA cellular systems in order to show that a MMSE multiuser detector can mitigate not only the own-cell interference, but also the co-cell interference. For the analysis, it is also considered a linear antenna array at the base station. The channel includes additive white Gaussian noise, exponential path-loss and slow frequency-selective Rayleigh fading. First, the interference in the cellular system is analyzed. Then, approximate expressions to evaluate the signal-to-interference ratio (SIR) are derived. Also, expressions to evaluate the bit error rate (BER) both for BPSK and M-QAM modulations are obtained. Monte Carlo simulations verify the tightness of the expressions. The results show that when we include the co-cell interference statistics in the MMSE detector design, the effects of this interference can be mitigated. Also, it is observed that the system can be overloaded when the number of antennas in the array is increased while the mean BER maintains reasonable values. Finally, with an asymptotic analysis of the BER expressions, the BER reduction with the MMSE multiuser detector when compared with the zero-forcing multiuser detector is obtained. This BER reduction has not been previously obtained in the literature.     

Flexible rewritable organic memory devices using nitrogen-doped CNTs/PEDOT:PSS composites

Nonvolatile rewritable organic memory devices based on poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and nitrogen doped multi-walled carbon nanotube (NCNT) nanocomposites were fabricated on glass and PET substrates.Organic memory devices with bistable resistive switching were obtained using very low NCTN concentration (∼0.002 wt%) in the polymeric matrix. The memory devices exhibited a good ON/OFF ratio of approximately three orders of magnitude, a good retention time of 10⁴ s under operating voltages ≤ |4V| and a few hundredths of write-read-erase-read cycles. The bistable resistive switching is mainly attributed to the creation of oxygen vacancies. These defects are introduced into the thin native Al oxide (AlOx) layer on the bottom electrode during the first voltage sweep. The well-dispersed NCNTs immersed in PEDOT:PSS play a key role as conductive channels for the electronic transport, hindering the electron trapping at the AlOx-polymer interface and inducing a soft dielectric breakdown of the AlOx layer. These PEDOT:PSS + NCNTs memory devices are to easy to apply in flexible low-cost technology and provide the possibility of large-scale integration.     

单蜂窝多用户系统下行链路中一种基于虚用户的调度算法

提出一种应用于机会波束成形系统的基于虚用户的调度方案。在单蜂窝多用户系统下行链路中,将用户的服务质量按其所拥有的应用连接数量划分为若干级别,其中高级用户以多个普通用户的身份参与调度。将该调度方案与传统的PFS算法相结合,提出VU—PFS算法。数值分析表明,新算法在保证系统吞吐量和普通用户间公平性的同时,也为高级用户提供了一定的QoS保障。     

Miniaturization of microstrip loop antenna for wireless applications based on metamaterial metasurface

The metamaterial and fractal techniques are two main methods for antenna miniaturization and in this paper, we have modeled an especial shape of the antenna based on loop formation with metamaterial load for this aim. The metamaterial layer is made by multi parallel rings and the result shows that the final antenna size reduced drastically while the frequency shifts from 7 to 4 GHz. The antenna has Omni-directional pattern with the gain of 3.5 dBi, so the size is reduced around 40%for 4.5 GHz and another resonance is made at 2.5 GHz with a return lossless than −6 dB with more than 60% frequency shift. The reflection and transmission have been utilized for showing the left hand characteristic based on two port periodic simulations in HFSS full wave software. We show that how the metamaterial load can provide the circular polarization (CP) by controlling the current distribution. We also presented that by making slots we obtained the better Axial Ratio (AR) and miniaturized the antenna with reconfigurable qualification. As a result of fact, we show that by using metasurface we able to miniaturized the antenna and simultaneously achieved the circular polarization.     

图像分割技术用于印刷电路板检测的研究

图像分割在图像分析、图像识别、图像检测等方面占有非常重要的地位,是从图像处理到图像分析的重要步骤,图像分割的好坏直接影响到图像分析的结果。针对此就印刷电路板检测过程中的图像分割进行研究。阈值分割技术的运算效率高、计算简单等特点非常适应印刷电路板检测的快速性和稳定性要求,因此着重介绍了四种阈值分割技术,并借用软件将各算法分别应用于实际的印刷电路板图像,然后对各个阈值化算法的分割结果做了对比和简要分析。     

Reliability assessment of principal point estimates for forensic applications

Although quite recent as a forensic research domain, computer vision analysis of scenes is likely to become more and more important in the near future, thanks to its robustness to image alterations at the signal level, such as image compression and filtering. However, the experimental assessment of vision-based forensic algorithms is a particularly critical task, since they cannot be tested on massive amounts of data, and their performance can heavily depend on user skill. In this paper we investigate on the accuracy and reliability of a vision-based, user-supervised method for the estimation of the camera principal point, to be used in cropping and splicing detection. Results of an extensive experimental evaluation show how the estimation accuracy depends on perspective conditions as well as on the selected image features. Such evidence led us to define a novel visual feature, referred to as Minimum Vanishing Angle, which can be used to assess the reliability of the method.     

Design on a highly birefringent and highly nonlinear tellurite ellipse core photonic crystal fiber with two zero dispersion wavelengths

In this paper, a new photonic crystal fiber (PCF) with two zero dispersion wavelengths (ZDWs) based on the tellurite ellipse core is designed. The air holes in the cladding region have a V-shape distribution, which can increase the birefringence. By adjusting the size of tellurite ellipse core, different birefringence and nonlinearity coefficient can be obtained, and the dispersion can also be tailored. When the long axis of the tellurite ellipse core is 0.5 μm and the short axis is 0.25 μm, the birefringence of 7.66 × 10⁻² and nonlinearity of 3400 W⁻¹ km⁻¹ around 1550 nm are obtained. This PCF structure provides a way to get the high birefringence and nonlinearity at the same time, which can find extensive applications in the optical communication and sensor system.     

New Signature Waveforms for Multi-rate QS-CDMA System with QPSK Modulation

This paper presents a multi-rate quasi-synchronous CDMA (QS-CDMA) system with QPSK modulation based on the new signature waveforms, namely GPZ-chip waveforms which are constructed by the generalized pairwise Z-complementary (GPZ) codes and optimal chip waveforms. According to the properties of GPZ-chip waveforms, the multiple access interference of different users can be reduced or eliminated. The interferences among different streams of the same user are handled by an optimal (or suboptimal) multi-stream detector(s). The performance of the proposed system is simulated and analyzed in a cellular communication environment consisting of multipath fading. The result shows that the proposed system has similar performance as compared to the single-rate QS-CDMA system employing GPZ codes with one chip waveform due to the properties of multi-stream detection. Also, the proposed system can achieve a significant interference reduction as compared to the multi-rate system employing concatenated WH/m sequence sets with one chip waveform due to the zero correlation zone properties of the GPZ-chip waveforms, thus resulting better BER performance.     

Multipath recycling method for transconductance enhancement of folded cascade amplifier

A multipath recycling method to enhance transconductance of the folded cascode amplifier is presented in this paper. The proposed method utilizes two idle paths to conduct small signal current, which leads to significant enhancement of transconductance compared to conventional folded cascade structure. Moreover, the improved performance is almost at no expense of power dissipation. The proposed multipath recycling and the conventional amplifiers are all designed in UMC 0.18 μm CMOS technology. Simulation results demonstrate that the transconductance of the proposed amplifier is improved by 450% and dc gain enhances 16 dB when compared with the folded cascode counterpart.