QoS enhancement in OFDM based systems under transceiver impairments

Broadband wireless systems generally use orthogonal frequency division multiplexing (OFDM) with link adaptation (LA) to achieve high throughput while meeting bit error rate (BER) constraint. OFDM systems are known to be affected by non-linearity of high power amplifier (HPA) at transmitter, carrier frequency offset (CFO), symbol timing offset (STO) and channel estimation error at the receiver. The delay in feedback of channel state information (CSI) further affects the performance of LA procedures. The focus of this work is on performance analysis in presence of simultaneous affect of all these impairments on LA based OFDM systems. The results are found to be useful for threshold readjustment which is essential for successful implementation of LA scheme to counter the effects of change in operating conditions from ideal to as listed above.     

Investigation of laterally single-diffused metal oxide semiconductor (LSMOS) field effect transistor

We propose a distinct approach to implement a laterally single diffused metal-oxide-semiconductor (LSMOS) FET with only one impurity doped p-n junction. In the LSMOS, a single p-n junction is first created using lateral dopant diffusion. The channel is formed in the p region of the p-n junction and the n region acts as the drift region. Two distinct metals of different work function are used to form the “n⁺” source/drain regions and “p⁺” body contact using the charge plasma concept. We demonstrate that the LSMOS is similar in performance to a laterally double diffused metal-oxide-semiconductor (LDMOS) although it has only one impurity doped p-n junction. The LSMOS exhibits a breakdown voltage of ∼50.0 V, an average ON-resistance of 48.7 mΩ-mm² and a peak transconductance of 53.6 μS/μm similar to that of a comparable LDMOS.     

用CdSe/ZnS量子点提高体异质结有机太阳电池的效率

通过掺杂吸收光谱在可见光波段的量子点可提高聚合物对可见光的吸收,因此掺杂CdSe/ZnS核-壳结构量子点(CQDs)能提高聚(3-己基噻吩):[6,6]-苯基-C61-丁酸甲酯(P3HT:PCBM)体异质结太阳电池的能量转换效率.本文研究了CdSe/ZnS量子点在P3HT:PCBM中的不同掺杂比例及其表面配体对太阳电池光伏性能的影响,优化器件ITO(氧化铟锡)/PEDOT:PSS(聚(3,4-乙撑二氧噻吩:聚苯乙烯磺酸)/P3HT:PCBM:(CdSe/ZnS)/Al的能量转换效率达到了3.99%,与相同条件下没有掺杂量子点的参考器件ITO/PEDOT:PSS/P3HT:PCBM/Al相比,其能量转换效率提高了45.1%.     

选择性合成不同形貌的Sb2S3纳米结构应用于高性能的染料敏化太阳能电池（英文）

近几十年来,随着全球变暖和能源危机的日益严重,对取之不尽、用之不竭的清洁能源技术的需求越来越迫切.1991年Gratzel首次报道了染料敏化太阳能电池(DSSCs),它以低廉的价格、优异的理论功率转换效率(PCE)、环保、多色透明等优点而引起了研究者的关注.Sb2S3因其1.5-2.2 eV的间隙宽度被认为是最有前途的对电极材料之一.此外,Sb2S3是地球中含量丰富的无毒锑矿物的主要成分,还被广泛应用于太阳能转换材料、催化剂、光导探测器等领域.众所周知,石墨烯具有巨大的比表面积、显著的载流子迁移率和优异的热/化学稳定性,这使得提高电子转移效率和电催化活性成为可能.首先,采用改进的Hummers方法制备了氧化石墨烯纳米片;然后采用水热法通过改变Sb源以及实验pH值,合成了Sb2S3和Sb2S3@RGO样品.对样品进行X射线粉末衍射(XRD)、扫描电子显微镜镜(SEM)、投射电子显微镜(TEM)以及比表面积表征.结果表明,在Sb源不变的情况下,Sb2S3样品的形貌随pH值的变化而变化.以三乙酸锑为Sb源,在pH=3时,Sb2S3的形貌类似于一个完整的纳米棒结构;在pH值为6时,样品为不规则球体;当pH值为8时,纳米片结构开始出现;但当p H=10时,纳米片结构并不均匀.根据XRD分析,只有当pH值为3时,样品的衍射峰才与标准卡(JCPDS42-1393)的衍射峰一致.当以氯化锑作为锑源,样品的形貌由不规则的杆状(pH=3)转变为纳米球(pH=6),然后出现纳米片结构(pH=8).不同的是,当p H值为10时,纳米薄片形成均一的花状结构.XRD结果表明,除pH值为3外,样品的衍射峰与标准卡(JCPDS42-1393)的值吻合较好.结果表明,合成条件所需的Sb源和碱性环境是合成具有均匀花状结构的纳米片状Sb2S3所必不可少的.测得Sb2S3的比表面积约为41.72 m^2g^-1,平均孔径为31.08nm,Sb2S3@RGO的分别为44.53 m^2g^-1和22.65 nm.Sb2S3和Sb2S3@RGO复合材料均具有介孔结构,为内部电催化剂提供了广阔的通道,从而提高了对电极的催化能力,促进了电化学反应.将Sb2S3纳米花球和Sb2S3@RGO纳米薄片作为染料敏化太阳能电池的对电极进行了测试,由于石墨烯的引入,后者比前者具有更好的电催化性能.电化学实验结果表明,与Sb2S3,RGO,Pt作为对电极相比,制备的Sb2S3@RGO纳米薄片具有更好的催化活性、电荷转移能力和电化学稳定性,Sb2S3@RGO的功率转换效率达到8.17%,优于标准Pt对电极(7.75%).     

Research progress on transition metal oxide based electrode materials for asymmetric hybrid capacitors

In the past few years, the increasing energy consumption of traditional fossil fuels has posed a huge threat to human health. It is very imperious to develop the sustainable and renewable energy storage and conversion devices with low cost and environment friendly features. Hybrid supercapacitors are emerging as one of the promising energy devices with high power density, fast charge-discharge process and excellent cycle stability. However, morphology and structure of the electrode materials exert serious effect on their electrochemical performances. In this review, we summarized recent progresses in transition metal oxide based electrode materials for supercapacitors. Different synthesis routes and electrochemical performances of electrode materials and storage mechanisms of supercapacitor devices have been presented in details. The future developing trends of supercapacitor based on metal oxide electrode materials are also proposed.     

中低速磁浮列车悬浮供电系统测试与分析

作为中低速磁浮列车的关键设备,悬浮供电系统是决定悬浮控制系统能否稳定可靠工作的前提。通过介绍电磁型中低速磁浮列车的悬浮供电系统基本结构和工作原理,以某型样车为研究对象,制定了多工况测试方案,对悬浮供电系统的主电源、蓄电池和超级电容组等的性能开展了详细测试。为进一步开展中低速磁浮列车各主要功能模组的多工况性能测试提供了参...     

多用户多速率OFDM中的子载波分配和功率控制

该文基于对多用户多速率正交频分复用(OFDM)系统性能的分析,提出了子载波分配和功率控制方案。在采用P-QAM调制的下行链路中,如已知所有子信道的信息状态(CSI),在满足每一个用户的服务质量的前提下,先给固定速率的用户分配最优子信道,再给变速率的用户按照子信道链路增益最大化分配剩余的子信道;每一个用户分配的子信道数目,由链路增益的取值区间决定。信号发射功率则按照注水法则分配:链路增益大的子信道分配的功率大,链路增益小的子信道分配的功率小,则系统的总传输速率可达最大。仿真结果证明了该文提出的分配方案优于Jang的分配方案。     

数字超宽带信号的功率谱密度

该文根据各种超宽带(UWB)信号的调制特点,给出了统一的随机脉冲信号模型,并应用随机理论计算得出相应的功率谱密度(PSD)函数表达式,此PSD表达式应用范围广,适用于各种调制方式、多址方式、进制下的UWB信号。该文举例分析比较了几种典型调制下带有均匀分布的随机时间抖动(timing jitter)及理想情况下的信号PSD,结果表明,时抖动的存在平滑了信号功率谱,降低了对其他窄带通信系统的干扰。而且,文中给出的PSD函数表达式可以用来估计信号各参量的变化对PSD函数的影响,而不需要考虑脉冲序列的详细设计过程。     

修正Gram-Schmidt正交化构建电源分配网络时域宏模型

有理函数逼近法方程组病态条件数为构建电源分配网络时域宏模型带来了数值问题。该文提出利用修正Gram-Schmidt正交化处理对超定方程组系数矩阵进行正交三角分解,结合Bernoulli多项式求根方法及稳定、无源性准则可以精确构建无源时域宏模型。计算实例精确构建了自DC至1GHz频带内的宽带无源时域宏模型,从而验证了该方法的有效性。     

低功耗高性能限流比较器的设计与仿真

为了进一步改善DC-DC开关电源的效率、功耗和精度,以其中最关键的电路:限流电路为突破口,对传统CPM控制结构进行了改进,并引入了动态偏置的思想,采用0.6μmBICMOS工艺模型,设计了一种高性能、低功耗的限流比较器.分析了电路的设计原理和过程,并给出了仿真结果.