分布式无标度LT码

LT码是喷泉码的一种,在删除信道中性能优越,分布式喷泉码多信源多中继的特性适合用于深空通信中。无标度网络（SF network）具有平均路径（APL）长最小的特性,非常适合喷泉码的度分布设计需求。首先介绍了LT码的编译码算法,然后对无标度网络和基于无标度网络的SF-LT码度分布设计进行了详细分析和优化,最后在删除信道条件下,选取码长较短、删除概率较小的情形对分布式二信源SF-LT码进行仿真分析,仿真结果表明,与LT码相比,分布式SF-LT码具有更好的性能。     

基于网络利用率最大化来提高无线Mesh网络中TCP协议的传输性能

In Wireless Mesh Networks (WMNs), the performance of conventional TCP significantly deteriorates due to the unreliable wireless channel. To enhance TCP performance in WMNs, TCP/LT is proposed in this paper. It introduces fountain codes into packet reorganization in the protocol stack of mesh gateways and mesh clients. Furthermore, it is compatible with conventional TCP. Regarded as a Performance Enhancement Proxies (PEP), a mesh gateway buffers TCP packets into several blocks. It simultaneously processes them by using fountain encoders and then sends them to mesh clients. Apart from the improvement of the throughput of a unitary TCP flow, the entire network utility maximization can also be ensured by adjusting the scale of coding blocks for each TCP flow adaptively. Simulations show that TCP/LT presents high throughput gains over single TCP in lossy links of WMNs while preserving the fairness for multiple TCPs. As losses increase, the transmission delay of TCP/LT experiences a slow linear growth in contrast to the exponential growth of TCP.     

A novel approach of limited-randomness fountain codes in deep space communication

Digital fountain is applied into deep space communication for its rateless and non-feedback forward error correction. However, the long code length and encoding overhead are confined factors to guarantee a considerable recovery probability as power and buffer-limited equipment in deep space environment. At the same time, the typical fountain decoding is sub-optimum decoding algorithm. We propose a new approach, Dependent Sequences Compensation Algorithm (DSCA), to improve the encoding efficiency by restricting the randomness in fountain encoding. While decoding algorithm is also optimized by redundant information in stopping set. The results show that the optimized method can obtain a 10⁻⁴ decoding failure rate with overhead under 0.20 for code length 500, which indicates the usefulness of the proposed approach in deep space communication.     

LT码的性能分析及仿真

LT码（Luby Transform Codes）属于喷泉码的其中一种,它是一类基于图的线性纠删码,其应用的信道环境是删除信道（BEC,Binary Erasure Channel）。这里主要介绍在二元删除信道模型下,LT码的4种度分布设计方法及,分析了短码长和长码长情况下的LT码在不同信道删除概率情况下的性能及比较。研究结果表明：在删除概率非常大的情况下,只要译码端接收到足够多的包都能以高概率译出原始数据包,只是产生的冗余度大,这里的结果将为系统选择不同参数的LT码提供参考。     

LT1778应用电路设计

随着电子技术的迅猛发展,单板电路正常工作所要求的电源种类越来越多,功耗越来越大,这就向产品电源系统的设计师提出了新的挑战。目前,开关电源已越来越多的用于单板电路供电。文中介绍了Linear公司的开关管控制器LT1778的工作原理、设计方法及PCB布线要点,并给出实例供有关的设计人员参考。     

LT码新型度分布及其在电力线通信中的应用

Luby变换(Luby Transform,LT)码作为信道编码应用于电力线通信(Power Line Communication,PLC),可实现电信号的可靠传输。度分布对LT码编译码性能的影响至关重要。为了得到更优的度分布,首先调整二进制指数分布(Binary Exponential Distribution,BED)中的度数比例,获得一种译码性能更优的改进的二进制指数分布(Improved BED,IBED)。然后,根据IBED在冗余度较小时译码成功率高,而冗余度增大后鲁棒孤子分布(Robust Soliton Distribution,RSD)的译码性能表现更佳的特点,通过求和归一化的方式将IBED与RSD两种度分布的优势进行有机结合,提出一种新型二进制鲁棒孤子分布(Binary RSD,BRSD)。仿真结果表明,与其他方法及传统的RSD相比,采用新度分布进行LT编码,可明显降低译码开销,并节约编译码耗时。将新型度分布应用于基于LT码的PLC系统中,能有效地抑制PLC信道中各种噪声对电信号的干扰,并提高通信效率。     

多媒体手持通信终端降压稳压器设计

文中设计采用LT1940单片双降压型稳压器,提供双路1.4A输出和双相开关,其开关频率达到1.1MHz,足够满足大功率、体积小、连续供电的要求,而且可以检测输出电压状态并单独控制其通断,满足其系统高效节能工作。     

小型化宽带钽酸锂晶体滤波器

介绍比较了钽酸锂(LiTaO3,简称LT)晶体和其他几种常用压电体波材料的物理特性,并从电路结构设计、寄生和谐波抑制及温度性能等方面详细介绍了单片钽酸锂晶体滤波器的设计方法并根据该方案设计了一种11.2 MHz单片式晶体滤波器.结果表明,钽酸锂晶体能方便地实现相对带宽0.8%～4.0%、频率温度稳定性好、体积小的宽带晶体滤波器,具有广泛的应用价值.     

Cypress：为系统提供更多解决方案

正在电气系统中,配线和电缆中的电压降会引起相当大的负载调节误差。当负载电流增加时,配线中的电压降(IR损耗)将增加(由于线路阻抗的原因),而输送至系统的电压将下降。解决这一问题的传统方法是利用一对连接在稳压器反馈网络和负载之间     

Effect of cyclodextrins on the viability of endothelial cells

Natural cyclodextrins (CD) and some of their derivatives have been tested in order to evaluate their cytotoxicity on LT2 endothelial cells. After 1 h of treatment with concentrations not higher than 10 mM, the number of cells was quantified by measuring DNA content. No significative decrease in the DNA amount was observed except for the dimethyl-β-CD at the highest tested concentration.