Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA): A Tutorial Review

Orthogonal frequency division multiple access (OFDMA) has recently attracted vast research attention from both academia and industry and has become part of new emerging standards for broadband wireless access. Even though the OFDMA concept is simple in its basic principle, the design of a practical OFDMA system is far from being a trivial task. Synchronization represents one of the most challenging issues and plays a major role in the physical layer design. The goal of this paper is to provide a comprehensive survey of the latest results in the field of synchronization for OFDMA systems, with tutorial objectives foremost. After quantifying the effects of synchronization errors on the system performance, we review some common methods to achieve timing and frequency alignment in a downlink transmission. We then consider the uplink case, where synchronization is made particularly difficult by the fact that each user's signal is characterized by different timing and frequency errors, and the base station has thus to estimate a relatively large number of unknown parameters. A second difficulty is related to how the estimated parameters must be employed to correct the uplink timing and frequency errors. The paper concludes with a comparison of the reviewed synchronization schemes in an OFDMA scenario inspired by the IEEE 802.16 standard for wireless metropolitan area networks.     

Multi-echelon Multiple Criteria Spares Allocation

This paper presents an approach for allocating spares on three echelons to increase system reliability and decrease plant down-time in a cost-effective manner. The usual assumptions are made: a) the demands for spares have the Poisson distribution with known demand rates, b) all the failures of plant parts are s-independent, c) for the plant to be operating, all parts must be operating, thus forming 1-out-of-M:F configuration. To each echelon of the spatially distributed spare-support system is associated a relevant optimization criterion and a corresponding constraint. The algorithm for determining stock levels adapts the known `per-pound' procedure, applied in sequence from the first echelon to the third echelon. The sequential optimization is computationally efficient. The test examples have confirmed that the algorithms proposed can handle 3-echelon sparing problems with even thousands of part types.     

备件保障性的综合与分配模型

备件保障性是装备战备完好性的重要因素。首次给出了备件保障性的综合和分配模型。为系统备件保障性预计和设计创造了前提条件。同时为完善系统的战备完好性的工程设计奠定基础。     

Reliable Circuit Techniques for Low-Voltage Analog Design in Deep Submicron Standard CMOS: A Tutorial

We present in this paper an overview of circuit techniques dedicated to design reliable low-voltage (1-V and below) analog functions in deep submicron standard CMOS processes. The challenges of designing such low-voltage and reliable analog building blocks are addressed both at circuit and physical layout levels. State-of-the-art circuit topologies and techniques (input level shifting, bulk and current driven, DTMOS), used to build main analog modules (operational amplifier, analog CMOS switches) are covered with the implementation of MOS capacitors.     

Nash Bargaining in Resource Allocation for Cognitive Radio: A Review

Wireless Personal Communications - The technology is growing towards smart communication through smart devices. This smart communication leads to the development of Vehicular Ad Hoc Network...     

Clocking Analysis, Implementation and Measurement Techniques for High-Speed Data Links—A Tutorial

The performance of high-speed wireline data links depend crucially on the quality and precision of their clocking infrastructure. For future applications, such as microprocessor systems that require terabytes/s of aggregate bandwidth, signaling system designers will have to become even more aware of detailed clock design tradeoffs in order to jointly optimize I/O power, bandwidth, reliability, silicon area and testability. The goal of this tutorial is to assist I/O circuit and system designers in developing intuitive and practical understanding of I/O clocking tradeoffs at all levels of the link hierarchy from the circuit-level implementation to system-level architecture.      

Optimum Resource Allocation for Relay Networks with Differential Modulation

In this paper, we investigate the resource allocation in a differentially modulated relay network. In addition to the energy optimization, we also consider location optimization to minimize the average symbol error rate (SER). The closed- form solution is derived for the single-relay case, and formulas allowing numerical search are provided for multiple-relay cases. Analytical and simulated comparisons confirm that the optimized systems provide considerable improvement over the unoptimized systems, and that the minimum SER can be achieved via the joint energy-location optimization.     

A New Technique for Depot and Sub-Depot Spares

This paper presents work in analyzing the combined spares provisioning implementation for depot and sub-depots. A method was developed for obtaining the minimum number of depot plus sub-depot spares. Not only is the number of spares important, but their cost as well. In order for the sub-depot model to achieve the savings in spares, a large number of depots (depots plus sub-depots) will be required than is required by the depot model, but the total capacity of this larger number of depots will be less than the capacity of the depots using the simple depot model. Therefore, one must not only study the numbers of spares and their cost, but must also account for the cost of the depots and sub-depots in order to truly optimize the design.     

Optimum Power Allocation for Multiuser OFDM with Arbitrary Signal Constellations

This paper formulates power allocation policies that maximize the region of mutual informations achievable in multiuser downlink OFDM channels. Arbitrary partitioning of the available tones among users and arbitrary modulation formats, possibly different for every user, are considered. Two distinct policies are derived, respectively for slow fading channels tracked instantaneously by the transmitter and for fast fading channels known only statistically thereby. With instantaneous channel tracking, the solution adopts the form of a multiuser mercury/waterfilling procedure that generalizes the single-user mercury/waterfilling introduced in [1], [2]. With only statistical channel information, in contrast, the mercury/waterfllling interpretation is lost. For both policies, a number of limiting regimes are explored and illustrative examples are provided.     

脉冲雷达优化设计与资源分配问题

在介绍脉冲雷达优化设计与资源分配问题的基础上,讨论了运用价值工程原理和运筹学中匈牙利算法实现脉冲雷达优化设计与资源分配问题时的模型转化,并最终用通过VC＋＋6．0平台上实现了脉冲雷达优化设计资源分配过程。     

Optimum Allocation of Multibeam Communications Satellite Resources

Future communications satellites can be expected to employ multibeam antennas for both receiving (uplink) and transmitting (downlink). The use of multibeam satellite transmitting antennas raises the question of how to assign the transmitted power and antenna gain to each of theNbeams such that optimum use is made of satellite resources. We refer to this problem as the downlink allocation problem; it is part of the larger problem of allocating all satellite network variables. This concise paper deals with both problems. Specifically, we rigorously formulate and solve the downlink problem for an arbitrary number of beams using the Lagrange multiplier technique for constrained extremal problems. We then discuss procedures for incorporating the optimum downlink allocation results into a complete system allocation.     

Optimum Link Allocation of Fixed Topology Networks

An algorithm determines the optimum link allocation of fixed topology networks having perfectly reliable nodes. The link reliabilities are allocated iteratively using the sensitivities of the network reliability function with respect to each link. An example illustrates the algorithm.     

突防任务中组网雷达干扰资源分配研究

基于突防飞机的位置构建了干扰效果评估指标,综合考虑突防飞机在整个突防过程中的位置变化时的干扰效益,利用概率加权法确定最终的目标函数,采用蚁群算法求解出干扰分配决策。仿真结果表明,该文提出的干扰效果评估指标可以很好地解决干扰资源分配问题,对实际作战指挥有一定的指导意义。     

Design for Stability of High-Speed Integrated Photoreceivers: A Tutorial

We propose a Design for Stability (DFS) methodology dedicated to the design of reliable high-speed integrated photoreceiver front-ends. This methodology based on the stability factor, S-parameters and Z-parameters analysis is made of four rules that high-speed designers will apply during the stability check of their design. To demonstrate its effectiveness, the proposed DFS methodology was applied to build a transimpedance amplifier (TIA) compliant to Synchronous Optical Network (SONET) OC-192 (10-Gb/s) standard. Experimental results in agreement with initial design specifications show excellent performances such as: 11 GHz bandwidth, −20 dBm sensitivity measured at 10-Gb/s for a Bit Error Rate (BER) of 10^{− 9} and 10 ps peak-to-peak jitter.     

视频监控技术的发展与现状

视频监控技术为重要场所安全防护提供了可靠保障,随着视频监控系统应用领域的扩大,视频监控技术得到了迅速发展。首先对视频监控技术的发展历程分三个阶段进行了概括,其次对视频监控中的关键技术的现状和发展方向进行了分析,其中重点描述了运动检测中的主流方法———背景差方法,目标跟踪中用于解决遮挡问题的合并分裂方法和直接穿透方法,最后提出了视频监控技术在实际应用中所面临的问题。     

不对称放大转发双向中继功率分配及中继位置选择

该文研究基于放大转发中继的不对称双向中继系统容量问题。首先,在瑞利衰落信道环境下,从双向通信的角度,通过理论分析得出其中断概率精确表达式和渐进表达式。理论分析发现节点发射功率和源节点目标速率共同决定系统中断概率,并且在大多数业务下系统中断性能仅取决于单向链路,而与另一链路无关。基于此,以优化系统中断性能为目标,提出一种基于业务知识的节点功率分配算法和中继位置选择算法。数值仿真实验结果表明,通过功率分配和中继位置选择可以显著提高不对称放大转发双向中继系统的中断性能。     

Shield Techniques for Application Layer DDoS Attack in MANET: A Methodological Review

In today’s world of wireless networks the mobile ad-hoc networks are widely preferred as a communication medium as these are infrastructure less networks. The application layer of these networks is targeted by attackers because it is responsible for actual data exchange with end users. As human dependency on wireless networks is increasing the DDoS attacks i.e. distributed denial of service attack which becomes a nightmare for the researchers. This attack is one of the most devastating attacks that can be executed on web-servers and congest the network keys like socket connections, CPU cycles, and memory database. In this current mobile computing world the necessity of DDOS attack management is significantly increased because this attack can degrade the entire web experience. Further, this DDOS attack is commenced along with the legitimate requests so it is also important to differentiate DDoS attack from other similar Events. This review endeavors to explore with more emphasis on application layer DDoS attack and its management stages like prevention, detection, mitigation and Differentiation along with comparative statement of prominent techniques discovered in each stage. This methodological survey report shall lead the way to researchers and network designers to suit the specific management scheme to provide the complete protection of wireless networks from DDoS attack.