基于基站协作的5G与NGSO星座系统间干扰规避方法研究

针对Q/V频段5G基站与非静止轨道(NGSO)卫星星座系统地球站之间的同频干扰问题,提出了一种基于5G基站协作的干扰规避方法。由多个5G基站组成基站簇,通过簇内基站间协作设置空间隔离来减缓5G基站对地球站的有害干扰。以OneWeb星座系统作为受扰系统,验证了所提方法的干扰减缓效果。结果表明,当干噪比门限值为-12.2 dB时,所提方法能够将OneWeb地球站的干扰发生概率减小30%。     

Doppler as a new dimension for multiple access in LEO satellite systems

The problem of flow control for little LEO satellite communications systems is studied. In these systems the satellite functions as a ‘bent pipe’ transponder for messaging between small terminals and a command and data acquisition (CDA) earth station. A novel scheme for averting traffic overflow on the inbound channel (from terminal to CDA), which we call ‘Doppler-based multiple access’ (DBMA), is introduced. In DBMA the CDA specifies a subset of the visibility footprint as a region of eligibility (ROE). Only terminals located in the ROE are permitted to transmit. By varying the size and location of the ROE, effective flow control on the inbound channel is achieved. The ROEs are specified in terms of parameters of the Doppler frequency shift versus time curve observed at terminals on the outbound downlink channel (from satellite to terminal). The effectiveness and elegance of the DBMA protocol are illustrated through computer simulation. © 1997 John Wiley & Sons, Ltd.     

A new fault-management method using congestion-avoidance routing for optical burst-switched networks

Optical burst switching (OBS) has been proposed as a promising technique to support high-bandwidth, bursty data traffic in the next-generation optical Internet. This study investigates a new fault-management framework for an OBS network. In an OBS network, burst-loss performance is a critical concern. In OBS, the data-burst transmission is delayed by an offset time (relative to its burst control packet (BCP), or header), and the burst follows its header without waiting for an acknowledgment for resource reservation. Thus, a burst may be lost at an intermediate node due to contention, which is generally resolved according to the local routing and bandwidth information. The routing table maintained in each OBS node is generally pre-computed and fixed to forward the data bursts. Such a static forwarding feature might have limited efficiency to resolve contentions. Moreover, a burst may be lost and the network may be congested when a network element (e.g., fiber link) fails. Therefore, for reliable burst transport, we develop dynamic routing approaches for preplanned congestion avoidance. Our goal is to proactively avoid congestion during the route-computation process, and our approach employs wavelength-channel utilization, traffic distribution, and link-distance information in the proposed objective functions for routing. Two update mechanisms for maintaining a dynamic routing table are presented to accommodate bursty data traffic. Based on our routing mechanisms, we also propose a new congestion-avoidance-and-protection (CAP) approach, which employs a primary route and a group of backup routes for each node pair against failures and congestion. The performance of the proposed protection strategy using congestion-avoidance routing is demonstrated to be promising through illustrative numerical examples.

A Hybrid Collision Avoidance Scheme for Ad Hoc Networks

A novel hybrid collision avoidance scheme that combines both sender-initiated and receiver-initiated collision-avoidance handshake is proposed for multi-hop ad hoc networks. The new scheme is compatible with the popular IEEE 802.11 MAC protocol and involves only some additional queue management and book-keeping work. Simulations of both UDP- and TCP-based applications are conducted with the IEEE 802.11 MAC protocol, a measurement-based fair scheme and the new scheme. It is shown that the new scheme can alleviate the fairness problem with almost no degradation in throughput. More importantly, it is shown that without explicit information exchange among nodes, the fairness problem cannot be solved conclusively if reasonable throughput is to be maintained. Hence it calls for further work to integrate the new collision avoidance scheme with other schemes that approximate fair queueing and use more contention information in channel access to achieve some QoS assurances in ad hoc networks.     

A full-scale solution to the rectilinear obstacle-avoiding Steiner problem

Routing is one of the important steps in very/ultra large-scale integration (VLSI/ULSI) physical design. Rectilinear Steiner minimal tree (RSMT) construction is an essential part of routing. Macro cells, IP blocks, and pre-routed nets are often regarded as obstacles in the routing phase. Obstacle-avoiding RSMT (OARSMT) algorithms are useful for practical routing applications. However, OARSMT algorithms for multi-terminal net routing still cannot meet the requirements of practical applications. This paper focuses on the OARSMT problem and gives a solution to full-scale nets based on two algorithms, namely An-OARSMan and FORSTer. (1) Based on ant colony optimization (ACO), An-OARSMan can be used for common scale nets with less than 100 terminals in a circuit. An heuristic, greedy obstacle penalty distance (OP-distance), is used in the algorithm and performed on the track graph. (2) FORSTer is a three-step heuristic used for large-scale nets with more than 100 terminals in a circuit. In Step 1, it first partitions all terminals into some subsets in the presence of obstacles. In Step 2, it then connects terminals in each connected graph with one or more trees, respectively. In Step 3, it finally connects the forest consisting of trees constructed in Step 2 into a complete Steiner tree spanning all terminals while avoiding all obstacles. (3) These two graph-based algorithms have been implemented and tested on different kinds of cases. Experimental results show that An-OARSMan can handle both convex and concave polygon obstacles with short wire length. It achieves the optimal solution in the cases with no more than seven terminals. The experimental results also show that FORSTer has short running time, which is suitable for routing large-scale nets among obstacles, even for routing a net with one thousand terminals in the presence of 100 rectangular obstacles.     

Understanding publics’ post-crisis social media engagement behaviors: An examination of antecedents and mediators

This study examines the psychological mechanisms underlying the process that enables publics’ individual differences (e.g., the levels of uncertainty avoidance and social media usage) to give rise to varying post-crisis social media engagement intentions (e.g., information seeking, support seeking, and negative word-of-mouth). The study confirms that this process is serially mediated by perceived threat severity, perceived susceptibility, and negative emotions. These psychological mediators, however, function differently between uncertainty avoidance and social media usage. For uncertainty avoidance, a high arousal negative emotion (e.g., anger, fear) is a more essential step to influence engagement intentions than a low arousal emotion (e.g., shame, guilt). For social media usage, however, the type of aroused negative emotions does not matter. Rather, the relationship social media usage has with information seeking is different from that with support seeking and negative word-of-mouth intentions. Social media usage induces information seeking intentions only through publics’ cognitive appraisals of the situation without the activation of negative emotions, while it induces supporting seeking and negative word-of-mouth intentions through both cognitive appraisals and negative emotion arousals.     

微型扑翼飞行器控制系统设计

微型扑翼飞行器的控制是一个难点问题,不仅对体积和重量有一定限制,还需要使飞行器能够有一定的鲁棒性和自主飞行能力。本文设计的控制系统通过遥控和自主飞行相结合的方式,很好的实现了对微型扑翼飞行器的控制。并进一步通过飞行实验验证了控制系统的可行性,飞行效果良好。     

常见的无线电干扰及其规避措施探讨

无线电干扰查处工作,是无线电管理工作中的一项重要的任务,作为无线电管理工作者对监测设备的工作原理、功能、技术性能、指标要深刻领会理解,要求掌握电磁环境随地形、频率、天气、距离等外部条件的变化规律。掌握各类干扰的成因及其规避措施,是有效降低无线电干扰发生率的主要途径。如何科学有效地规避频率间的干扰,介绍常见的无线电干扰类型、特征、危害性及其抑制干扰采取的措施。     

Fast solution of the obstacle problem

The purpose of this paper is to present a fast algorithm for the numerical solution of the one-dimensional obstacle problem. It is proven that the algorithm converges in a finite number of steps; application examples showing its efficiency are presented.This work was supported by the National Research Council of Argentina, Grant No. PID-3091000.     

Augmented Lagrangian Active Set Methods for Obstacle Problems

Active set strategies for two-dimensional and three-dimensional, unilateral and bilateral obstacle problems are described. Emphasis is given to algorithms resulting from the augmented Lagrangian (i.e., primal-dual formulation of the discretized obstacle problems), for which convergence and rate of convergence are considered. For the bilateral case, modifications of the basic primal-dual algorithm are also introduced and analyzed. Finally, efficient computer realizations that are based on multigrid and multilevel methods are suggested and different aspects of the proposed techniques are investigated through numerical experiments.