理性密钥共享的扩展博弈模型

理性密钥共享体制通过引入惩罚策略使得参与者不会偏离协议,常采用的惩罚是一旦发现有人偏离就立即终止协议.这种惩罚策略有时导致惩罚人自身利益严格受损,从而降低了对被惩罚人的威慑.为了克服这一弱点,本文以扩展博弈为模型分析了理性密钥共享体制.首先给出(2,2)门限的理性密钥共享体制,证明了所给的协议是该博弈的一个序贯均衡,即经过任何历史之后坚持原协议仍然是每一个参与者的最优选择.特别地,在发现有人偏离后,协议所给出的惩罚策略既可以有效惩罚偏离者又能够完全维护惩罚人的利益.这是本文对前人设计的理性密钥共享体制的一个重要改进.然后针对将协议扩展到(t,n)门限情形,实现密钥分发人离线,达到计算的均衡等相关问题给出了一般的解决方案.     

Pebble games for studying storage sharing

Pebble games are played on a directed acyclic graph (dag). Placing a pebble on a vertex may be thought of as entering the value of the subexpression represented by the vertex into accessible storage. In some applications, there are types associated with vertices e.g. some vertices may represent functions, others may represent function values. We are interested in determining if vertices of the same type can share storage. The problem considered is as follows. We are given a labelled dag to be pebbled. A pebble may be placed on a vertex if all sons of the vertex have pebbles—in fact it is legal to move a pebble from a son to a father. Pebbles may be picked up at any time. The objective is to pebble each vertex exactly once. We will be interested in ‘one pebblings of l vertices’ in which there is at most one pebble on vertices with label l, at all times; and ‘stack pebblings of l vertices’ in which the pebbled vertices with label l are along a path, at all times. Results about the existence of such pebblings are presented. The results have applications to testing serializability of database updates, and potential applications to semantics directed compiler generation.     

Rational secret sharing as extensive games

The threat that comes from previously used punishment strategies in rational secret sharing is weakened because the punishment somtimes also causes loss to the punisher himself.In this paper,we first model 2-out-of-2 rational secret sharing in an extensive game with imperfect information,and then provide a strategy for achieving secret recovery in this game.Moreover,we prove that the strategy is a sequential equilibrium which means after any history of the game no player can benefit from deviations so long as the other players stick to the strategy.In particular,when a deviation is detected,the punishment executed by the punisher is still his optimal option.Therefor,by considering rational secret sharing as an extensive game,we design punishment strategies that effectively punish the deviants and meanwhile guarantee punishers’ benefit.Hence,these punishments are more credible than previous ones.Except assuming the existence of simultaneous channels,our scheme can have dealer off-line and extend to the t-out-of-n setting,and also satisfies computational equilibria in some sense.     

基于分布式频谱图的混合频谱共享研究

在认知无线网络中,频谱制图是在空间上发现频谱空洞的新技术。针对目前集中式频谱制图不能适应无线网络结构变化的问题,提出一种次用户自组织的分布式制图方案。次用户根据Delaunay三角网生长法自组织生成三角网,然后进行本地插值生成频谱态势图。在获得分布式频谱态势图的基础上,提出一种次用户分布式混合频谱共享方案。次用户根据频谱态势信息判断自身所处环境,选择overlay或者underlay接入方案,以最大化容量为准则推导了最优功率分配方案理论,仿真分析表明,该方案性能明显优于传统的检测避让方法,有效提高了系统容量。     

基于频谱合约的协作频谱共享方法

针对授权频谱资源不足的问题,结合非对称网络信息的特点和通信双方自私性的需求,提出一种多用户协作频谱共享(CSS)合约机制的设计与实现方法。首先,通过将CSS映射成劳动力市场,研究对称网络信息条件下多用户频谱合约建模方法;在此基础上,针对合约签订后非授权用户(SU)行为隐匿性引起的道德风险问题,研究非对称网络信息条件下频谱合约建模方法,以激励双方协作行为和保证频谱共享的实现。实验结果表明,在授权用户(PU)直接传输速率低于0.2 b/s时,协作频谱共享时整个系统容量是双方不参与共享时的3倍以上。提出的多用户CSS合约机制能为无线频谱的高效利用和资源共享提供新思路。     

改进的协作频谱共享方案

针对认知无线电系统,提出一种改进的协作频谱共享方案,其中,次用户充当中继,协助主用户传输。改进方案采用解码-再生编码-转发中继协议,通过污纸编码有效地在发射端消除来自主用户信号的干扰,并且分配一部分功率协助传输主用户信号,保证主用户的中断性能。通过理论推导,得出次用户离主用户发射机的距离半径表达式。仿真结果表明,改进方案能有效扩大次用户的频谱共享范围,还提高了主用户和次用户的中断性能。     

On power allocation for a cognitive radio network with hybrid spectrum sharing

In this study we propose a hybrid spectrum sharing scheme based on power control by combining Overlay with Underlay schemes,to improve radio spectrum efficiency.In the scheme,the secondary users dynamically switch their operational states between Overlay and Underlay according to the spectrum occupancy.Thus the dynamics of the primary network is first modeled with a discrete-state Markov process to find the time fraction of secondary users in the Overlay state and that in the Underlay state,which leads to the capacity model of the hybrid spectrum sharing system.Under the criterion of maximizing capacity,the power allocation of the cognitive network is researched and the optimum power allocation for secondary users is deduced.As a result,the maximum achievable capacity of the cognitive network is obtained.Simulations are given to prove the analysis further.Theoretical and simulated results indicate that hybrid spectrum sharing based on power control provides a higher capacity than single Overlay and Underlay systems for the cognitive network,i.e.,hybrid spectrum sharing can further improve radio spectrum efficiency.     

When ignorance helps: Graphical multicast cost sharing games

In non-cooperative games played on highly decentralized networks the assumption that each player knows the strategy adopted by any other player may be too optimistic or even infeasible. In such situations, the set of players of which each player knows the chosen strategy can be modeled by means of a social knowledge graph in which nodes represent players and there is an edge from i to j if i knows j. Following the framework introduced in [7], we study the impact of social knowledge graphs on the fundamental multicast cost sharing game in which all the players want to receive the same communication from a given source in an undirected network. In the classical complete information case, such a game is known to be highly inefficient, since its price of anarchy can be as high as the total number of players ρ. We first show that, under our incomplete information setting, pure Nash equilibria always exist only if the social knowledge graph is directed acyclic (DAG). We then prove that the price of stability of any DAG is at least and provide a DAG lowering the classical price of anarchy to a value between and log²ρ. If specific instances of the game are concerned, that is if the social knowledge graph can be selected as a function of the instance, we show that the price of stability is at least , and that the same bound holds also for the price of anarchy of any social knowledge graph (not only DAGs). Moreover, we provide a nearly matching upper bound by proving that, for any fixed instance, there always exists a DAG yielding a price of anarchy less than 4. Our results open a new window on how the performances of non-cooperative systems may benefit from the lack of total knowledge among players.     

Extending available spectrum in cognitive radio: Hierarchical spectrum sharing network

Cognitive radio (CR) is an emerging communication paradigm to address spectrum insufficiency by opportunistically accessing inactive spectrum. Normally, there are several distinct wireless systems co-existing in the same area. Hence, how to efficiently share the available spectrum among these systems becomes a significant challenge in CR. In this paper, a spectrum-heterogeneity-based hierarchical spectrum sharing network (HSSN) is proposed for CR. In HSSN, available spectrum bands are classified into two categories. To enable the infrastructure, spectrum identification and classification are developed, and the strategies on how to effectively utilize these two types of spectrum are also discussed. In addition, the associated protocol is exploited for spectrum selection and route forwarding. Analysis and simulation results indicate that the HSSN can significantly improve spectrum utilization and provide a considerable extension to the available spectrum.     

基于频谱异构和用户移动的频谱共享算法研究

频谱共享允许多个认知节点以机会主义方式使用空闲频谱资源,而绝大多数的频谱共享研究没有考虑传输距离、错误率等方面的频谱异构特性。针对集中控制认知无线网络,提出一种基于频谱异构和用户移动的频谱共享算法。网络中不同类型的频谱信道具有不同的覆盖范围,认知用户可以静止或移动。认知用户的信道分配综合考虑了信道可使用时间、用户地理位置、接入公平性等因素,并在此基础上建立了一个信道分配效用函数,最终目的是最大化系统总效用。仿真结果表明,提出的频谱共享算法能够大大减少系统中的信道切换次数,同时系统其他方面的性能也能够得到保证。     

认知无线网络中基于价格的频谱共享模型

为了使用户可以根据信道质量的变化动态调整带宽价格,从而改变用户收益,提出考虑用户移动性的频谱共享模型。该模型中信道质量随着用户的位置变化,主用户提出的带宽价格综合考虑所有次用户请求的带宽和信道质量的影响;同时,请求的带宽又受到带宽价格的制约,从而用户收益也随着用户位置而变化。仿真结果表明,在用户运动过程中,可以选择最佳位置使用户收益最大。     

mzXML在质谱数据共享中的应用

要实现分析仪器数据的共享,首先应建立一套统一的数据交换标准,以规范数据格式;XML在共享性、开放性和扩展性等方面的诸多优点,因而更适用于质谱数据的存储与交换。本文解析MS文件的存储结构,介绍基于XML的mzXML标准,达到从MS到mzXML文件的转换目的,并以随机访问的形式解析mzXML文件,以提高mzXML文件的解析速度。     

基于智能分析的分布式频谱共享技术研究

次用户以跳频序列的方式共享动态的频谱是分布式认知无线电网络频谱共享技术的解决方法之一。在此类方法中,次用户跟随特定的跳频序列接入到它的所有可用信道中,并在此过程中实现与其他次用户的交会。根据分布式认知网络的组网特性,提出了一种针对交会操作的MAC层超帧结构,使得整个认知网络在此结构支撑下可以取得更好的系统性能。根据次用户的频谱感知和使用信道情况的积累与分析,建立次用户的智能频谱库,为次用户的信道接入提供策略支持。仿真结果表明,提出的MAC协议能在高网络负载情况下能获得较好的综合性能。     

On finite potential games

A linear system, called the potential equation (PE), is presented. It is proved that a finite game is potential if and only if its potential equation has solution. Some properties of the potential equation are obtained. Based on these properties, a closed form solution of the PE is obtained. Moreover, a formula based on the solution of the PE is obtained to calculate the potential function. Finally, it is proved that a networked evolutionary game is potential if and only if its fundamental network game is potential. Some interesting examples are presented to illustrate the theoretical results.     

On weighted balls-into-bins games

We consider the well-known problem of randomly allocating m$m$ balls into n$n$ bins. We investigate various properties of single-choice games as well as multiple-choice games in the context of weighted balls. We are particularly interested in questions that are concerned with the distribution of ball weights, and the order in which balls are allocated. Do any of these parameters influence the maximum expected load of any bin, and if yes, then how?     

QoS-aware distributed spectrum sharing for heterogeneous wireless cognitive networks

Ubiquitous wireless networking calls for efficient dynamic spectrum allocation (DSA) among heterogeneous users with diverse transmission types and bandwidth demands. To meet user-specific quality-of-service (QoS) requirements, the power and spectrum allocated to each user should lie inside a bounded region in order to be meaningful for the intended application. Most existing DSA methods aim at enhancing the total system utility. As such, spectrum wastage may arise when the system-wise optimal allocation falls outside individual users’ desired regions for QoS provisioning. The goal of this paper is to develop QoS-aware distributed DSA schemes using game-theoretic approach. We derive DSA solutions that respect QoS and avoid naively boosting or sacrificing some users’ utilities to maximize the network spectrum utilization. Specifically, we propose two game-based DSA algorithms: one resorts to proper scaling of the transmission power according to each user’s useful utility range, and the other embeds the QoS factor into the utility function used during gaming. To evaluate DSA schemes from a practical QoS perspective, we introduce two new metrics, namely “system useful utility” and “fraction of QoS-satisfied users”. Simulations confirm that the proposed DSA techniques outperform existing QoS-blind game models in terms of the spectrum sharing efficiency in heterogeneous networks. Convergence analysis of the proposed QoS-aware DSA algorithms is also provided.     

基于社交网络的认知无线电频谱共享模型*

综合考虑激励因子、用户优先级和用户信誉提出一种基于社交网络的认知无线电频谱共享模型,并据此提出新的频谱共享方案。提出的方案通过对因子排序和比较各非授权用户的因子值,确定共享频带的非授权用户。结果表明,与未考虑社会关系的频谱共享方案相比,提出的频谱共享方案对应的成功共享次数更多,更能适应个性化的频谱共享环境。     

一种动态频谱共享通信系统接入控制算法*

针对动态频谱共享通信系统的MAC设计,设计了集中式网络环境下的MAC帧结构,提出了一种基于接入点延时反馈竞争信道信息的时隙ALOHA访问控制算法。在分析时隙ALOHA算法的稳定性基础上,提出使用倍乘因子与伪贝叶斯算法相结合的方法以保证系统的稳定性。仿真结果表明,当发送概率与实际值相差较大时,该算法能达到快速调整的效果,获得稳定的吞吐量。     

Opportunistic sharing scheme for spectrum allocation in wireless virtualization

The past few decades have witnessed an increasing growth in mobile and wireless network, leading to a corresponding fast growth in mobile demands. However, the proliferating mobile demands compel wireless network to face several challenges, such as the conflict between spectrum crisis and low resource utilization ratio, and the poor quality of service and quality of experience. Wireless virtualization, enabling multiple concurrent virtual networks running on shared wireless substrate resource, has been proposed as a promising way to overcome the plights of the current mobile and wireless network. How to efficiently allocate the resource, especially the spectrum resource, of physical network to multiple virtual networks is one fundamental and important challenge in wireless virtualization. This paper rethinks the characteristics of virtual networks’ requirements, and then divides the requirement into a baseline part and a fluctuant part. Based on it, this paper introduces an opportunistic spectrum sharing approach, through which we formulate the spectrum resource allocation problem as an NP-Hard problem. Then, we propose our opportunistic spectrum resource allocation scheme for the wireless virtualization. Simulations validate the performance advantages of our approach and show that opportunistic spectrum sharing significantly improves the revenue, resource utilization and acceptance ratio of physical wireless network while decreasing the payments of virtual networks.