Adaptive gossip protocols: Managing security and redundancy in dense ad hoc networks

Many ad hoc routing algorithms rely on broadcast flooding for location discovery or, more generally, for secure routing applications. Flooding is a robust algorithm but because of its extreme redundancy, it is impractical in dense networks. Indeed in large wireless networks, the use of flooding algorithms may lead to broadcast storms where the number of collisions is so large that it causes system failure. To prevent broadcast storms, many mechanisms that reduce redundant transmissions have been proposed that reduce retransmission overhead either deterministically or probabilistically.Gossip is a probabilistic algorithm in which packet retransmission is based on the outcome of coin tosses. The retransmission probability can be fixed, dynamic or adaptive. With dynamic gossip, local information is used to determine the retransmission probability. With adaptive gossip, the decision to relay is adjusted adaptively based on the outcome of coin tosses, the local network structure, and the local response to the flooding call. The goal of gossip is to minimize the number of retransmissions, while retaining the main benefits of flooding, e.g., universal coverage, minimal state retention, and path length preservation.In this paper we consider ways to reduce the number of redundant transmissions in flooding while guaranteeing security. We present several new gossip protocols that exploit local connectivity to adaptively correct propagation failures and protect against Byzantine attacks. A main contribution of this work is that we introduce a cell-grid approach that allows us to analytically prove performance and security protocol properties. The last two gossip protocols that we give are fully adaptive, i.e., they automatically correct all faults and guarantee delivery, the first such protocols to the best of our knowledge.     

大容量广电网的P圈启发式算法研究

结合广电网大容量的发展要求,考虑较为复杂的网状网结构,网络生存性问题日益凸显。对经典的预置圈(P圈)容量算法进行了改进,并选用COST239网络拓扑对改进算法进行编程仿真。结果证明,改进算法在减少预置圈数量的同时能够提高资源利用率,性能有所提高,可以较好地解决广电网的生存性问题。     

含山台两个频道播控系统数字化改造方案

全面介绍了含山广播电视台两个频道播控系统数字化改造方案。从播控系统数字化改造的必要性入手,详细阐述了含山台改造后的数字化播控系统的结构与组成,同时深入浅出地分析了播控系统的整体技术架构、核心设备的备份措施以及局域网中播控部分的安全应急措施、技术特点和改造中应注意的问题。     

小型高清卫星直播车的设计与调试

首先介绍了小型高清卫星直播车的设计思路,接着介绍卫星、视音频、通话、电源等系统的功能及组成,最后重点介绍了各系统中设备选型基本要求,绘制各分系统内设备的信号关系框图,并对各系统安装调试做了较详细的阐述.深化了对卫星转播车的认识,也为今后设计类似系统和进行实践教学积累了经验.     

国家应急广播社区网站的技术系统架构

从国家应急广播社区网站的平台技术架构、应用系统架构设计、业务流程设计、系统架构设计、平台安全保障、系统接口技术实现等方面详细介绍了国家应急广播社区网站的技术系统架构。通过对当前互联网媒体建设采用的先进技术和国家应急广播社区网站技术系统架构的优点分析,论述了国家应急广播社区网站先进、成熟、安全可靠的性能和强大的应急功能。     

广播电台核心播控系统平台建设

核心播控系统平台作为广播电台采、编、录、播、发、监流程中的核心环节,承担广播信号的调度、交换、分配、传输、监测等功能,是全台安全播出的核心.本文主要对核心播控系统平台的建设情况进行介绍,建成后的核心播控系统平台能满足北京电台传统播出需求和新媒体融合发展需求,是一个汇集了全面应急、全面监测、信号调度控制等诸多功能的大型集...     

Broadcasting with Controlled Redundancy and Improved Localization in Wireless Sensor Networks

Wireless sensor networks （WSNs） consist of sensor nodes that broadcast a message within a network. Efficient broadcasting is a key requirement in sensor networks and has been a focal point of research over the last few years. There are many challenging tasks in the network, including redundancy control and sensor node localization that mainly depend on broadcasting. In this paper, we propose a broadcasting algorithm to control redundancy and improve localization （BACRIL） in WSNs. The proposed algorithm incorporates the benefits of the gossip protocol for optimizing message broadcasting within the network. Simulation results show a controlled level of redundancy, which is up to 57.6% if the number of sensor nodes deployed in a 500 m×500 m area are increased from 50 to 500.     

Maximum lifetime broadcast communications in cooperative multihop wireless ad hoc networks: Centralized and distributed approaches

We investigate the problem of broadcast routing in energy constrained stationary wireless ad hoc networks with an aim to maximizing the network lifetime measured as the number of successive broadcast sessions that can be supported. We propose an energy-aware spanning tree construction scheme supporting a broadcast request, considering three different signal transmission schemes in the physical layer: (a) point-to-point, (b) point-to-multipoint, and (c) multipoint-to-point. First we present a centralized algorithm that requires global topology information. Next, we extend this to design an approximate distributed algorithm, assuming the availability of k-hop neighborhood information at each node, with k as a parameter. We prove that the centralized scheme has time complexity polynomial in the number of nodes and the distributed scheme has a message complexity that is linear in the number of nodes. Results of numerical experiments demonstrate significant improvement in network lifetime following our centralized scheme compared to existing prominent non-cooperative broadcasting schemes proposed to solve the same lifetime maximization problem in wireless ad hoc networks. Due to lack of global topology information, the distributed solution does not produce as much advantage as the centralized solution. However, we demonstrate that with increasing value of k, the performance of the distributed scheme also improves significantly.     

Multimedia Broadcast Multicast Service Performance and its Enhancements in WCDMA Networks

Multimedia Broadcast Multicast Service (MBMS) in Wideband Code Division Multiple Access (WCDMA) networks is used to transmit information from one source to vast amount of recipients. The MBMS technique eases the load of the network and therefore allows network to serve more subscribers. The very aim of this study is to evaluate the performance of Release 6 MBMS and its performance enhancements in WCDMA networks. Special attention will be focused on macro and receive diversity which are considered in addition to time diversity provided by long interleaving as enhancements on MBMS performance. 3GPP Release 6 specifications for MBMS introduce two macro diversity schemes: soft and selective combining. The effect of those combining scheme concepts together with and without receive diversity provided by multiple receive antennas are examined. Also, a concept closely related to the receive diversity called Rx-switching i.e., turning the another receive antenna off in good channel situations for power saving purposes is studied. The system level performance of MBMS point-to-multipoint (p-t-m) mode is evaluated with dynamic system level tool in which e.g., mobility of users and interactions of the radio resource management functionalities are explicitly taken into account. Our studies indicate that macro diversity brings significant gains to the MBMS performance. Receive diversity together with macro diversity schemes improves the performance even more and therefore enhances the cell throughput that MBMS can offer. Furthermore, based on the findings of this study it seems that 2Rx Rake receiver can operate with a single antenna significant amount of time without sacrificing desired coverage and thus provide clear power saving opportunities.

广电网络呼叫中心的建设及知识库的建立

阐述了广电网络运营商呼叫中心系统建设的必要性、硬件配置及软件功能、管理和相关经验,同时具体论述了知识库的建立及相关应用。