Performance of amplify forward and decode forward cooperative strategies for body surface communications in UWB Body Area Networks

Body area networks (BAN) are being developed for telemonitoring of patients. Ultra wideband (UWB) is the most preferred choice for the physical layer of the BAN as it provides high data rate at low power consumption along with a simple transceiver structure. But because of high fading characteristics of the human body channel, the range of UWB will be limited, and a reliable communication cannot be guaranteed. In that case, cooperative communications may be applied to BAN for improving system performance and link quality. The paper proposes a novel approach by applying amplify and forward, and decode and forward cooperative relaying strategies with maximal ratio combining for BAN. The performance of single relay AF and DF relaying have been compared with direct transmission. Further, the efficacy of the proposed strategies has been validated by transmitting electrocardiogram signals and magnetic resonance imaging images. Simulations and validations have been carried out on Institute of Electrical and Electronics Engineers designated CM3 channel model for BAN designed from real time measurements data. A signal‐to‐noise ratio gain of at least 3 dB is clearly observed from simulation results. Thus, transmit power requirement can be minimized, which in turn improves the battery life of body sensor nodes. Copyright © 2015 John Wiley & Sons, Ltd.     

关于差分放大器的几点讨论

差分放大器在电子线路中有着广泛的应用,在模拟电子技术的教学中是重要内容之一。提出了差分放大器除了在直耦放大器中克服零点漂移外,其设置的目地是可以对2个输入端的差进行放大,同时对在非对称下情况如何减少失调电压及共模电压的范围做了详细的介绍,这些对于教学和电路设计及电路的合理应用却是非常重要的。     

快衰落信道条件下无线中继系统波束形成方案

随着设备小型化的发展趋势,天线间距较小,信道具有相关性;且假设发射端处于高速移动状态,无法获得完全信道状态信息,只能根据部分信道状态信息设计发射端波束形成方案。针对发射端和接收端配置多天线的固定增益放大转发无线中继系统,以最大化接收端信噪比为准则,设计了基于部分信道状态信息的波束形成方案,推导了系统中断概率和平均误符号率的闭合表达式,通过仿真验证了性能分析的有效性和所设计方案的优越性。在平均误符号率为10-2、相关系数为0.8时,所提方案比反馈信道状态信息的方案节约1.6 dB的信噪比。     

双向放大转发中继系统最优功率分配策略研究

为了提高双向中继系统总速率,针对双向放大转发中继系统提出了一种运用信噪比平衡技术进行各节点间功率分配的最优功率分配方案,并推导得出了最优功率分配方案表达式。理论分析和仿真结果表明,所提出的最优功率分配方案有效提高了系统可达总速率,改善了系统性能。     

An amplify‐and‐forward and decode‐and‐forward mixed relay communication system and its performance analysis

A kind of amplify‐and‐forward (AF) and decode‐and‐forward (DF) mixed relay communication system is proposed in this letter. The source broadcasts the signal to all the relays. Relays that can decode the signal adopt DF scheme to retransmit the signal, while the rest adopt AF scheme for retransmission. The destination employs maximum ratio combining technique to maximize the received signal‐to‐noise ratio. Another situation concerned in this letter is that when the relay cannot decode the source signal, it may retransmit the interference signal with AF scheme. Closed‐form expressions of outage probability are derived. Simulation results show that the analytical curves agree with the simulated ones very well, and the AF‐DF mixed relay system can improve the availability of the relays. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimal power‐aware relay placement for cooperative wireless sensor networks

We study the problem of optimizing the symbol error probability (SEP) performance of cluster‐based cooperative wireless sensor networks. Recent studies in literature show that an efficient relay selection protocol based on simple geographical information of the nodes to execute cooperative diversity can significantly improve the SEP performance at the destination of such networks. As well, similar line of research on optimal power allocation (for the source and relay nodes) can be found in literature. However, to achieve the best SEP performance at the destination of a cooperative wireless sensor network, joint optimization of power allocation and relay placement should be accomplished. To this aim, we reformulate the SEP of a multi‐hop cooperative communication in a general form and optimize transmitted power level and relay placement simultaneously. This analysis is developed for both amplify‐and‐forward and decode‐and‐forward relaying protocols. Simulation results demonstrate that the proposed joint optimization can effectively improve the SEP performance of the network. Copyright © 2013 John Wiley & Sons, Ltd.     

一起低压电容器谐波放大引发的10kV开关跳闸事故

某公司在后半夜其配变10kV开关发生频繁跳闸,原因是由于低压电容器引发谐波谐振放大。     

新型基于波形无线下载的任意波形功率电源

设计了一种基于SOPC技术(可编程片上系统)及Nios II嵌入式软核处理器的任意波形功率电源,其特点是电源的幅度、频率、相位可在线编程,输出波形无线网络下载,双路输出高精度、大功率的恒定电压和恒定电流。重点介绍了系统架构、任意波形发生器及功率放大器的设计。     

宽带放大电路自激振荡成因分析与抑制的研究

文中以OPA691芯片搭建的放大电路为样本,研究并实际测量了当驱动电缆长度与波长λ相比拟时引起的宽带放大电路的自激振荡,分析了成因并构建了解释模型,最后提出了消除此种自激振荡的简易有效方法,对宽带放大电路设计的消除自激振荡提供了一定参考。     

Joint optimization of source and relay precoding in non‐regenerative MIMO relay systems

We investigate the problem of precoding optimization in an amplify‐and‐forward multiple‐input‐multiple‐output relay system. Most reported works on this problem focus chiefly on the design of relay precoder without simultaneously optimizing the direct link. In this paper, we propose a method for joint source/relay precoder design, taking both direct and relay links into account. Our design is based on maximizing the mutual information (MI) under limited transmission power constraints at the source and relay, respectively. We first formulate a constrained optimization problem before relaxing the original cost function for tractability and derive a MI lower bound. This elaborate bound can asymptotically approach the exact expression of MI in an iterative fashion. In contrast to previous strategies, we then prove that the optimal structure of the source and relay precoders jointly convert the multiple‐input‐multiple‐output relay channel into a bank of single‐input‐single‐output relay channels without having to assume a beamforming structure to simplify the derivation. Specifically, the linear precoding design problem degenerates into power loading among multiple single‐input‐single‐output relay channels. Applying standard Lagrange technique results in a scalar convex optimization, and it can be readily solved by iterative water filling. Numerical examples demonstrate that the proposed scheme, either exploiting partial or full channel state information, significantly outperforms the existing methods. Copyright © 2012 John Wiley & Sons, Ltd.