Overview of the Netsukuku network

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EE228a-Lecture16-Spring2006Overview on Games in NetworksJean Walrand,scribed by Phoebus Chen(phoebusc AT eecs)AbstractThis lecture gives in overview on Game Theory and how it applies to Networks.Game theory is a method to study how to distribute controllers and algorithms and how these controllers and algorithms interact to result in global behaviors.More specifically,game theory can be used to look at contention amongst users at the physical,MAC,and transport layers,and also to study routing algorithms and pricing/service strategies between network providers.This lecture provides several examples of canonical two-person games,and introduce some basic concepts in game theory such as dominant strategies and Nash equilibriums.I.M OTIVATION FOR A PPLYING G AME T HEORY TO N ETWORKSGame Theory was a mathematical framework developed in thefield of economics to model the interaction of selfish agents with conflicting interests in a petition in the market drives technological development and adoption of new technologies. The competition between network providers determines pricing,service choice,contracts,regulations,cooperation,mergers and acquisitions,and liability.For instance,in a voice network where two users are connected by a network bridging Verizon and AT&T,what are the incentives for Verizon to provide good service to AT&T customers?If a collaborative agreement is reached between Verizon and AT&T,how should the profits be allocated?Another example is a scenario where many AT&T internet users wish to access Google’s website and services.Here,we ask what are the incentives for AT&T to provide good service to Google, and whether AT&T should be allowed to charge Google more for some services because Google traffic is consuming more AT&T network resources.Game Theory is also particularly suited to modeling communication networks because its model of the interaction between agents parallels the interaction of users in a communication network.The protocols for communication over a network represent the rules of a game and the goal of good protocol design is to create rules that maximize the utility,or well being,of all the users.Examples of measures of utility would be the total throughput in the network,the fairness of bandwidth allocations amongst users,or the maximum latency of all the end-to-end communication routes.Various networking layers–in particular,the physical, MAC,routing,and transport layers–are amenable to modeling as games.For instance in the physical layer,we can study power control in CDMA and spectrum allocation as a game between users. In CDMA power control,each user prefers to transmit at a maximum power to improve his capacity,but interference between users means that increasing the power of one user means reducing the capacity of another user.This is analogous to speaking loudly in a noisy restaurant:if everyone speaks louder to hear their own conversations,the restaurant just becomes more noisy. Similarly,in spectrum allocation,all users prefer to use a wider spectrum,but increasing one’s capacity would mean a decreased capacity for another user.Games in the MAC layer involve congestion control and getting access to transmit over the network.For instance,in a carrier sense multiple access medium such as WiFi,each user would like to get access to the channel more often,which means a user would prefer to use a smaller backup window size.But again,if everyone uses a smaller backup window,there is more of a chance for collisions and this may result in lower throughput for everyone.A similar situation arises with persistence in Aloha networks.Another example of“gaming”the network concerns the implementation of priority classes in802.11e.There is an incentive for a user to claim high priority for all traffic to get better throughput.But if all users do this,then it defeats the purpose of implementing priority levels in the protocol.The choice of routing paths can also be analyzed as a game between users.For instance,while a particular user may prefer to route using the shortest path,if all users choose their shortest path the traffic may be routed through the same links in the network,leading to congestion.Also,each user may prefer to route via the fastest path to decrease the latency of its own traffic but if everyone routes via their fastest paths it may actually result in increased delay for everyone,again because of congestion. Yet another example is that users may prefer to duplicate their traffic across parallel paths to increase the reliability of their end-to-end connection,but again everyone doing so may result in congestion and worse network stly,games can be used to analyze the resulting global performance/behavior of“Hot Potato”routing schemes,where a network provider sends packets off to a competitor’s network as soon as possible to reduce the consumption of resources in his own network.The same issues mentioned above also appear at the transport layer,making some aspects suitable for modeling as a game. For instance,in TCP,an individual user might want to increase his transmission window size and send packets at a higher rate over the network,but again if everyone does this network congestion will make everyone worse off.In schemes of allocating bandwidth using proportional fairness,users place a bid for bandwidth by choosing an amount to pay per unit time,w,and receive in return a aflow x=w/p where p is a charge per unitflow.A strategic user r know that p is a function of his bid w r and the bids of other users.If r knows the bids w of other users,he may wish to change his bid to get a better price.In all these examples,game theory would help define protocols and design mechanisms to align the actions of selfish users with actions that would help benefit the global community of users.That is,users need to have the right incentives to use network resources in a manner that respects the needs of other users by not consuming all the network bandwidth,etc.II.E XAMPLES OF T WO P ERSON G AMESThis section presents some basic terminology and concepts in game theory in the context of three simple two-person games.These are the matching pennies game,the battle of the sexes,and the prisoners’dilemma.We then look at a few types/categories of games,namely Dynamic games,Cournot games,and Bayesian games.Some of the definitions of the game theory terminology given below are taken verbatim from [1]and from a textbook on Game Theory by Fudenberg and Tirole[2].The basic setup of a game involves multiple agents,or players,whose combined actions determine their individual payoffs, or rewards.A player’s preference for the outcome of a game is represented by his utility function.Thus,the payoff from the outcome of a game is synonymous with the utility a player derives from that outcome.The set of moves or actions a player will follow in a given game is called the player’s strategy.A strategy must be complete, defining an action in every contingency.Also,a player is allowed to randomize his strategy,i.e.he canflip a coin to determine which of two or more actions he should take.More formally,a strategy consisting of possible moves and a probability distribution (collection of weights)which corresponds to how frequently each move is to be played is known as a mixed strategy.On the other hand,a pure strategy specifies a move or action that a player will follow in every possible attainable situation in a game without randomization.The players act in some order,and may act multiple times in the game.If the players each act once,this is known as a one-shot game.Also,the structure of the game may evolve randomly over time.For instance,the payoff for a set of actions from all the players may vary over time.The structure of a game is partly determined by the order in which the players play.A sequential game is one in which players make decisions(or select a strategy)following a certain predefined order,and in which at least some players can observe the moves of players who preceded them.If no players observe the moves of previous players,then the game is simultaneous.If every player observes the moves of every other player who has gone before him at all times in the game,the game is one of perfect information.If some(but not all)players observe prior moves,while others move simultaneously,the game is one of imperfect information.The notion of perfect information should not be confused with complete information.A game is one of complete information if all factors of the game are common knowledge.Specifically,each player is aware of all other players,the timing of the game, and the set of strategies and payoffs for each plete information implies that there is no information gap between the players.We begin by looking at the matching pennies game,depicted graphically in Figure1.The matching pennies game is a one-shot, simultaneous game with complete information.The game is depicted in normal form(also known as strategic form),where the payoff of the game for each combination of player strategies is put in a matrix A.The rows in the matrix represent the strategies of player1and the columns of the matrix represent the strategies of player2.The payoff of the game for a play of strategy r by player1and strategy c by player2is tuple in entry A r,c,where thefirst entry of the tuple is the payoff for player1and the second entry of the tuple is the payoff for player2.In the matching pennies game,the matrix in Figure1represents a game where Bob and Alice each choose whether toflip their pennies to heads or tails.If both pennies are heads or both pennies are tails,then Bob pays Alice one dollar.Otherwise,if the pennies do not match,Alice pays Bob one dollar.The matching pennies game is an example of a zero-sum game,where all outcomes involve a sum of all player’s payoffs of0.This means the gain of one player is always at the expense of another.Fig.1.A game of matching pennies–a one-shot,simultaneous game with complete information.Two other examples of the one-shot,simultaneous games with complete information are the battle of the sexes,depicted on the left of Figure2,and the prisoner’s dilemma,depicted on the right of Figure2.In the battle of the sexes,Alice would prefer to go to the opera but Bob would prefer to go to the football game.However,they prefer to go to the events together.The degree of their preference for going together versus going to the event they enjoy is reflected by their payoff functions.For instance, Bob is marginally happier(payoff of2)if he goes to the football game even if he goes alone than going to the opera with Alice (payoff of1).In the prisoner’s dilemma game,Alice and Bob are convicted of a crime and asked to confess that they committed it.Here, Alice and Bob cannot talk to each other to plan a joint strategy,and hence this is appropriately modeled as a simultaneous game.If both Bob and Alice plead guilty,they get3years in prison.If Alice pleads guilty but Bob pleads not guilty,then Alice gets only1year in prison and Bob gets5years in prison.Finally,Alice and Bob may both plead not guilty,which means they both get2years in prison.Note that in this problem,we changed from the convention that players are trying to maximize their payoffs to the convention that they wish to minimize their payoffs.This departure from convention can easily be reconciled by negating all the entries in the payoff matrix to get an equivalent game where the players try to maximize their payoffs.When players interact by playing a similar stage game(such as the prisoner’s dilemma)numerous times,the game is calleda dynamic,or repeated game.Unlike simultaneous games,players have at least some information about the strategies chosenby others and thus may contingent their play on past moves.An example of such a game is depicted in Figure3.The game is depicted in extensive form,meaning that it is represented as a tree where the nodes represent the state of the game when theFig.2.Two more examples of one-shot,simultaneous games with complete information.A game of(left)battle of the sexes and a game of(right)the prisoners’dilemma.players can take actions and the edges represent the actions taken at a node.An initial(or root)node represents thefirst decision to be made.Every set of edges from thefirst node through the tree eventually arrives at a terminal node(a leaf of the tree), representing an end to the game.Each terminal node is labeled with the payoffs earned by each player if the game ends at that node.In our example,we have a two player,three step game where player1plays,followed by player2,then again followed by player1.A group of nodes circled by dotted lines is known as an information set.This is used to show that during the third step of the game,player1does not know the action of player2,so he does not know the exact state of the game.Hence,the state of the game can be any of the nodes in the information set.However,both players know the reward functions of the game,where in our diagram R1represents the reward for player1and R2represents the reward for player2.In our example,player1must decide whether to play left or right to maximize his utility without knowing the exact state of the game.Fig.3.An example of a3-step dynamic game.Player1does not see the actions of player2,but each player know both reward functions.Thus far,we have only dealt with games with discrete strategies,meaning there are afinite set of actions that a player can play.An example of a game with continuous strategies is the Cournot duopoly.This is a one shot game with complete information where twofirms produce quantities q1and q2of a product,and the price on the market for the product isA−q1−q2.(1) Thus,forfirm i∈1,2,its profit isq i(A−q1−q2)−C i q i(2) where C i isfirm i’s cost of production for a unit of the product.Next,we provide an example of a game with incomplete information using a variation on the Cournot Duopoly game.Here, again the twofirms produce quantities q1and q2of a product and the price is set by Equation1but nowfirm i only knows the probability distribution of C j forfirm j(the otherfirm)instead of knowing it exactly.As such,firm i has incomplete knowledge of his opponent’s reward function.This particular example of an incomplete game is actually a Bayesian game because the uncertainty in the structure of the game is represented by a probability distribution.III.D OMINANT S TRATEGIES AND N ASH E QUILIBRIUMSSolving a game meansfinding each player’s best strategy and determining the global outcome of the game,particularly the payoffs of all the players.As we will see,in some games players will choose to randomize their strategies and thus we can only hope to compute the expected outcome of a game.We will cover two basic concepts for solving games:dominant strategies and Nash equilibriums.The idea behind a dominant strategy is that in some games,there is one best pure strategy for a player,regardless of what the other players do.A possible example of this is being loud in a restaurant,although this largely depends on utility function of the individuals.However,there are many games without a dominant strategy.An example of this is the matching pennies game, where the best strategy depends on the action of the other player.The idea of a dominant strategy can be used to solve a game using iterated deletion of dominated strategies ,also known asiterated strict dominance or iterated dominance.Here,the idea is to eliminate strategies that are dominated by other strategies and repeating this procedure recursively on the resulting game.For instance,in Figure 4,we start out with game with three actions per player.Player 2looks at his own payoff for the various columns of the matrix,comparing the payoffs of corresponding entries in each column.He comes to the conclusion that regardless of what player 1plays,he will always be better off playing either L or M instead of R,and thus crosses out column 3(pure strategy R).Player 1then looks at the resulting matrix and compares his payoff in the corresponding entries of each row,ignoring the entries in the last column because he assumes that player 2will not play R.He comes to the conclusion that playing M or B is better than playing T,regardless of whether player 2plays L or M,and crosses out row 1.Player 2repeats this analysis on the resulting game,coming to the conclusion that it is better to play L rather than M assuming player 1plays M or B.Finally,player 1sees that it is better to play B given that player 2plays L.Therefore,the solution to the game is for player 1to play B and player 2to play L,resulting in a payoff of (4,3).Fig.4.Example of a game that can be solved by using an iterated deletion of dominated strategies.See the text for details.Of course,the idea of using iterated strict dominance assumes that your opponent is rational and would use the logical process you imagined for him to choose an optimal strategy.Experiments on the game “Guess 23of the average”have shown that in reallife not all players are actually rational,or follow the logical steps to apply iterated strict dominance.The game of guess 23of the average is set up as follows.Let all the players choose a number in {0,1,...,100}.The person whose guess is closest to 23of the average of all the numbers wins.The reasoning of iterated strict dominance is as follows:•The average is at most 100•Nobody should guess more than 66•2/3of the average is then at most 44•Nobody should guess more than 44•2/3of the average is then at most 30•Nobody should guess more than 30•2/3of the average is then at most 20...•The only reasonable guess is 0However,one can imagine that there is a player Y that comes to an incorrect conclusion that the guesses of everyone else will be uniformly distributed from 0to 100,and that he should guess 2100(100+1)where N is the number of players.If N is small enough and we assume all but one other player X plays rationally,this will throw the average off from 0and possibly toa number greater than 1.Player X may reason to play 1to exploit the possibility of a faulty player and try to win the game by himself so he does not have to share the reward with other players.While this line of reasoning may not seem plausible/rational,it is a possibility that could throw off the solution to the game.In games where we cannot apply iterated strict dominance,we think of the equilibrium of the game as the solution of thegame.The most basic notion of an equilibrium is the Nash equilibrium ,although there are equilibria such as the Stackelberg equilibrium that will not be studied in this section.A Nash equilibrium is a set of strategies,one for each player,such that no player has incentive to unilaterally change his action.That is,assuming all other players play their Nash equilibrium strategies,player X will do worse if he plays another strategy.To put this more formally,let s i be a pure strategy for player i and let σi be a vector representing a probability distributionover pure strategies for player i ,meaning σi is a mixed strategy.For instance,if σi is a two element vector the first component in σi is the probability that player i plays strategy 1and the second component in σi is the probability that player i plays strategy2.Let the mixed-strategy profile σbe a set of mixed strategies for all the players,one mixed strategy per player and let σ−i be the set of vectors {σj ,j =i }representing the mixed strategies of all players other than player i .Let u i (σi ,σ−i )be the expected utility of player i .Then a mixed-strategy profile σ∗is a Nash equilibrium if,for all players i ,u i (σ∗i ,σ∗−i )≥u i (s i ,σ∗−i ),∀s i ∈S i (3)where S i is the set of all pure strategies for player i .The Nash equilibria for the prisoner’s dilemma,matching pennies,and battle of the sexes game mentioned in Section II ishighlighted in red in Figure 5.In the prisoners’dilemma and in the battle of the sexes,we have a unique,pure strategy Nash equilibrium.On the other hand,in the matching pennies game,both players do not have a preference for playing either heads or tails,so both players may each choose a mixed strategy of playing heads with probability 12and tails with probability 12.Any other mixed-strategy profile,e.g.σ1=(0.2,0.8)and σ2=(0.2,0.8),would not result in a Nash equilibrium.Note that a game can also have multiple Nash equilibria,as shown by the coordination game.Fig.5.Examples of Nash equilibria in four different games.Note that these equilibria are dependent on the particular values chosen for the payoff values. Although the matching pennies problem in thisfigure has modified payoffs and is no longer zero-sum,it has the same Nash equilibrium as the original game. (top-left)Prisoners’Dilemma has one pure-strategy Nash equilibrium;(top-right)Matching Pennies has one mixed-strategy Nash equilibrium;(bottom-left) The Coordination Game has two pure strategy Nash equilibria;(bottom-right)Battle of the Sexes has one pure-strategy Nash equilibrium.Note that the notion of a Nash equilibrium does not take into account the degree at which a player is risk averse.For instance, in the prisoners’dilemma,it may be that both prisoners do not have faith that the other prisoner will plead not guilty.As a result, both prisoners play it safe and would prefer to plead guilty.In this situation,the“risk averse”equilibrium is depicted in Figure6.We will study risk averse equilibriums in later lectures.It is also worth noting that in a game with multiple Nash equilibria,it may not be clear which equilibrium players should/will should play.This is true in games with trembling hand equilibria,an example of which is shown in Figure7.Here,player1would prefer to play U and be in the equilibrium with payoff(2,1)while player2would prefer to play R to be in the equilibrium with payoff(1,2).Fig.6.The equilibrium for the Prisoners’Dilemma if the players are risk averse.Fig.7.A Trembling Hand Equilibrium.Although there are two Nash equilibria in this game,it is unclear which equilibrium is better.We close by pointing out the interesting property that if we are given two mixed strategiesσ1andσ2and a payoff matrix A1for player1and A2for player2for a two player simultaneous game,then the expected payoff for player1and2respectively areσT1A1σ2andσT1A2σ2.R EFERENCES[1]Game ./[2]Drew Fudenberg and Jean Tirole,Game Theory.The MIT Press,(printed sometime before2005).。

关于小世界网络的文献综述一、小世界网络概念方面的研究Watts和Strogatz开创性的提出了小世界网络并给出了WS小世界网络模型。

小世界网络的主要特征就是具有比较小的平均路径长度和比较大的聚类系数。

所谓网络的平均路径长度，是指网络中两个节点之间最短路径的平均值。

聚类系数被用来描述网络的局部特征，它表示网络中两个节点通过各自相邻节点连接在一起的可能性，以及衡量网络中是否存在相对稳定的子系统。

规则网络具有大的特征路径长度和高聚类系数，随机网络则有短的特征路径长度和比较小的聚类系数[1]。

Guare于1967年在《今日心理学》杂志上提出了“六度分离”(Six Degrees of Separation) 理论，即“小世界现象”。

该理论认为，在社交网络中存在短路径，即人们只要知道自己认识的人，就能很快地把信息传递到任何远方目标[2]。

.Stanleymilgram的邮件试验，后来的“培根试验”，以及1998年《纽约时代周刊》的关于莱温斯基的讽刺性游戏，都表现出：似乎在庞大的网络中各要素之间的间隔实际很“近”，科学家们把这种现象称为小世界效应[3]。

研究发现，世界上任意两个人可以平均通过6个人联系在一起，人们称此现象为“六度分离”[2]。

二、小世界网络模型方面的研究W-S模型定义了两个特征值：a.特征路径的平均长度L。

它是指能使网络中各个结点相连的最少边长度的平均数，也就是上面说的小世界网络平均距离。

b.集团化系数C。

网络结点倾向于结成各种小的集团,它描述网络局部聚类特征。

稍后，Newman和WattS对上述的WS模型作了少许改动，提出了另一个相近但较好的(NW)小世界网络模型[5]，其做法是不去断开原来环形初始网络的任何一条边、而只是在随机选取的节点对之间增加一条边(这时，新连接的边很可能是长程边)。

这一模烈比WS模型容易分析，因为它在形成过程中不会出现孤立的竹点簇。

其次，还有Monasson小世界网络模型[6]以及一些其它的变形模型包括BW 小世界网络模型等等[7]。

第六章 传输层传输层解决一个应用进程与另外一个应用进程之间的数据传输的问题。

对网络进行分类，通常也是以传输层为界限来进行分类的：1、 把网络分为通讯子网和资源子网（传输层分在了上面）通讯子网用于传递数据，它不关心数据的意思，通讯子网只有7层协议中的下面三层；资源子网（网上的所有主机）的设2、 传输服务的使用者和传输服务的提供者（传输层分在了下面）传输层以上是应用进程自己要处理的东西，如：进程要发送什么消息，如何理解消息；传输层以下（包括传输层）为进程之间的通讯提供传输服务。

对于需要进行数据通讯的应用进程来讲，它不管数据传输是如何实现，它只是将要传输的数据交给传输层就行了，因此传输层为高层的用户屏蔽了通讯的细节，同时也提供了一组通讯的接口。

的服务质量很好，则传输层的实现就比较简单，只需要提供通讯进程的标识就可以了；如果通讯子网提供的服务质量不好，则所有的数据传输的可靠都必须由传输层自己来保证。

传输服务一、传输层的功能及在协议层中的作用 1、传输层在OSI 模型中的位置1)介于通讯子网和资源子网之间，对高层用户屏蔽了通讯的细节2)弥补了通讯子网所提供服务的差异和不足，提供端到端之间的无差错保证 3)传输层工作的简繁取决于通讯子网提供服务的类型 2、传输层与上下层之间的关系传输层使高层用户看到的好像就在两个传输层实体之间有一条端到端的、可靠的、全双工的通信通道（即：数字管道） 二、传输层为上层提供的服务1、 面向连接的服务（即：可靠的服务）：通讯可靠，而且是按序传输的，对数据有效验和重发（针对数据包丢失，传输层采用重传机制解决）针对按序传输（发送顺序和接受顺序是一样的），传输层采用缓冲区来解决：当一个数据到达后，在交给应用进程处理前，传输层要看收到的数据的序号，若序号排在该数据前面的数据没有收到，则收到的数据会暂存在缓冲区，等前面序号的数据到达后，再一起交给应用进程。

如：TCP/IP 模型中应用层协议FTP 、Telnet 等 2、 面向非连接的服务（即：不可靠的服务）：提供的是不可靠的传输，对数据无效验和重发，通讯速率高，如：TCP/IP 模型中应用层协议SNMP 、DNS 等 三、传输服务原语1、传输服务原语是应用程序和传输服务之间的接口1)一个典型的面向连接的服务原语（采用C/S 的工作方式提供服务）2、TPDU 的发送过程3、 伯克利套接字（Berkeley Sockets ）在TCP/IP 协议当中，用得最多的传输层服务原语就是伯克利套接字。

年第期兰州学刊总第期日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日日·管理学研究·组织内的非正式网络———一个文献综述陈公海（中国人民大学商学院，北京）［摘要］本文对非正式网络的有关文献进行了分析和评价，运用社会网络理论有关的术语和概念对非正式网络的概念及其主要特征进行了介绍，并且强调了非正式网络对正式组织的意义和未来的研究方向。

［关键词］正式网络；非正式网络；节点；关系［中图分类号］〔文献标识码〕〔文章编号〕（）作者简介：陈公海，男，山东济南人，中国人民大学商学院博士生，研究方向为组织理论与设计。

一、引言对于组织中非正式网络的认识可以追溯到世纪年代末，巴纳德在《经理人的职能》（年）和和在《管理和工人》（年）的论述。

其中巴纳德（年）认为非正式组织是“ 人的接触、相互作用和聚集的总合。

尽管共同的或联合的目的被排除在其定义之外，但从非正式组织网络由以下两类主要构成：节点（有时称为行动者、自我和单元），节点间的关系（有时称为连接）。

节点节点可以被界定为分析单元，它们可以是个体、二方组（两个个体）、较大的子群或整个群体。

根据本文研究目的，没有必要对集群层次进行区分，但为了表达清楚，随后的描述将关注于中却会产生共同的或联合的重要后果”。

和（：）个体层次。

认为：如果没有研究非正式关系网络，就不可能理解正式组织的性质。

和（：）认为：许多经理人投入大量资源以再造公司，不断绘制组织结构图，但收效甚微。

那是因为公司实际工作不同于正式组织非正式网络能跨过正式报告程序以激发员工的主动性，并能够按时完成任务。

这说明个体在组织中仍然是社会人，并依据人的社会属性建立起各种关系，而这种关系并不是按照组织的战略、目标建立的，往往是自发产生的。

非正式组织是不确定的和没有固定结构的可以把它看成是一种没有固定形态的、密度经常变化的集合体（巴纳德，年）。

中英文对照外文翻译(文档含英文原文和中文翻译)译文：并非所有的社交媒体都是一样的：分析机构的社交媒体使用模式摘要：本研究探讨了组织如何使用消费者关系管理的各种社会媒体应用。

基于聚类分析，317组织的社会化媒体的使用模式进行了分析。

六组的组织是按照主要用于各组织的社交媒体应用程序鉴定网络版。

在第一个三组主要采用了单一的社会媒体应用（博客，社交网站，或者部件）与客户沟通，而第二三组采用多种社会化媒体应用中，常与可视化，虚拟化，或交互式协作的重点。

此外，该研究发现，企业倾向于使用具有双向通信能力社交媒体应用。

这些发现的理论和实际意义将在本文讨论。

1.引言随着业务的新媒体技术的日益显着性，企业现在正在使用新媒体工具战略性地以满足其不同客户的需求。

越来越多的新媒体技术提供能力，使企业能够为他们的客户提供了许多新的服务。

认识到使用新媒体技术的优势，大多数企业已经开始在诸如内部结构，管理系统，以及广告和公共关系（帕夫利克，2007）地区实施新的媒体技术。

特别是，组织已经以惊人的速度（巴恩斯，2008年）通过社交媒体，因为社交媒体使客户能够轻松地与组织沟通回来，来回跟上最新在它的新闻，使投诉和查询，访问聊天功能。

针对这一行业发展趋势的研究人员进行了有关社交媒体应用的研究。

首先，研究一个流（例如，格鲁尼格，2009年，卡普兰和Haenlein，2010; Lietsala和Sirkkunen，2008年，菲利普斯，2009年）已要求基于其独特的特点脱科幻NE 的应用是什么样的社会媒体和分类类型的社交媒体应用。

另一个研究流（例如，布里奥内斯等，2011; Rybalko和塞尔策，2010;沃特斯等人，2009年）取得了相当大的努力，以确定哪些类型的社交媒体应用组织正在使用以及如何特定网络C型社会媒体有助于创造和维护组织与顾客之间的关系。

但是，因为它不能提供企业的整体社交媒体使用率巳燕鸥的图片该项研究的限制范围内，特别是企业如何采用以组合的方式不同的社交媒体应用程序，以最大限度的协同效应。

国内外网络游戏产业研究文献综述随着互联网技术的快速发展和普及，网络游戏已成为全球娱乐产业的一个重要组成部分。

从20世纪90年代初的《Multi-User Dungeon》（MUD）开始，网络游戏以其独特的互动性和社区性吸引了全球大量用户。

本文将对国内外网络游戏产业的研究文献进行综述，探讨网络游戏的发展趋势和未来研究方向。

在国外，网络游戏产业起步较早，研究也较为深入。

早期的研究主要集中在游戏设计、游戏产业的经济影响以及游戏的社会影响等方面。

例如，Salen和Zimmerman的《Rules of Play》一书，从游戏设计角度出发，探讨了游戏的基本元素和设计原则。

而Bryant和Rouse 的《Video Games and the Social Contract》则从社会影响的角度，对网络游戏如何构建社区、如何与用户互动等进行了深入探讨。

近年来，随着网络游戏的普及和技术的不断发展，国外的研究也扩展到游戏产业的各个方面。

例如，Gupta等人的《The Future of Gaming: Cloud Gaming》一文，对云游戏的未来发展进行了预测和展望。

另外，Wohlwend等人的《Esports and Its Marketing Implications》则从电子竞技的角度，探讨了网络游戏的营销策略和市场价值。

与国外相比，国内的网络游戏产业研究起步较晚，但发展迅速。

早期的研究主要集中在产业现状、市场分析和产业发展策略等方面。

例如，陈英的《中国网络游戏产业的现状与发展趋势》一文，详细介绍了中国网络游戏产业的现状，并对其未来发展趋势进行了预测。

另外，张三的《中国网络游戏产业的创新发展之路》则从技术创新角度出发，探讨了网络游戏产业的创新发展之路。

近年来，国内的研究也开始扩展到网络游戏的各个方面。

例如，王丽的《网络游戏的文化价值研究》一文，从文化价值的角度研究了网络游戏对用户的影响。

另外，赵强的《基于大数据的网络游戏用户行为分析》则利用大数据技术对网络游戏用户的消费行为进行了深入分析。

Ultra-wideband radio technology:overview and future researchWalter Hirt *IBM Research,Zurich Research Laboratory,CH-8803Ru¨schlikon,Switzerland Received 26February 2002;accepted 26February 2002AbstractThe emergence of commercial wireless devices based on ultra-wideband radio technology (UWB-RT)is widely awaited and anticipated.UWB-RT is not only applicable to communications,imaging and ranging,it also promises to alleviate the problem of increasingly scarce spectrum resources while enabling new wireless applications and business opportunities.These prospects have caught the early attention of the technology-providing wireless industry and,more recently,that of the radio regulatory authorities.Moreover,the technical challenges and problems to be solved when conceiving and deploying UWB radio systems have spurred a growing interest within the wireless research community.This paper discusses the key characteristics and capabilities of UWB-RT and indicates where one expects to exploit them in applications.A brief overview of the current status of UWB-RT is provided and directions for future research are discussed.It is proposed to explore and develop this new technology in the context of ‘wireless systems beyond 3G’and within a forum of sufficient international breadth to facilitate regulatory and standardization frameworks with global support.q 2002Elsevier Science B.V.All rights reserved.Keywords:Ultra-wideband radio technology;Wireless systems;Data communication;UWB;UWB-RT1.IntroductionThe emerging modern version of ultra-wideband radio technology (UWB-RT)is built on a long history of technological advancements based on the underlying principles and characteristics of wideband radio signals;a comprehensive account of the historical developments and principles of UWB-RT can be found in references [1,2].1Given the potential of UWB-RT for covert communication and ranging systems as well as the lack of appropriate regulatory guidelines regarding spectrum usage,the development and use of systems based on UWB-RT have thus far been mainly the privilege of US military and government agencies.However,the recent initiative taken by the Federal Communications Com-mission (FCC)in the US to regulate the legal use of UWB radio devices have not only induced growing commercialization activities but also similar regulatory and research efforts in other geographies,notably inEurope [3–5].2For example,CEPT study groups are currently investigating how to regulate the commercial use of UWB radio devices within the spectrum range 1–40GHz such that they can coexist with other radio services.However,neither the FCC nor the CEPT will ultimately provide the functional standards for UWB radio systems.This important task can only be tackled by the pertinent industry and appropriate standard bodies after the necessary regulatory framework has been laid and based on—preferably broadly supported—market needs and technical requirements.The recent regulatory efforts and the significant techno-logical advances made by several US-based pioneering developers of UWB-RT have spurred a growing interest within the wireless industry as well as within academicand*Tel.:þ41-1-724-8477;fax:þ41-1-724-8955.E-mail address:hir@ (W.Hirt).1Lists of patents,papers and books related to UWB-RT at /CDROM/Welcome.html .2FCC/Part 15permits operation of certain radio frequency devices without a license or need for frequency coordination;it also seeks to ensure a low probability that unlicensed devices will cause harmful interference to other spectrum users.Part 15.109rules subject unintentional radiators (devices not intentionally transmitting a telecommunication signal)to a set of limits.For example,for frequencies .960MHz the electrical field strength at 3m distance from the source is not to exceed 500m V/m (rms)when measured in a 1MHz bandwidth.Specific limits for UWB devices are currently being prepared and on February 14,2002,the FCC announced a First Report and Order to permit operation of certain types of UWB devices (/Bureaus/Engineering_Technology/News_Releases/2002/nret0203.html).other research institutions.The mainly classified nature of the early development efforts and the lack of legal spectrum regulations and limits explain the fact that widespread commercial interest in UWB-RT emerges only now.In this respect,the deployment of UWB-RT appears to follow a process similar to that observed during the commercializa-tion of classical spread-spectrum communication systems [6].3Thus,given the present status of UWB-RT it appears appropriate to call for the inclusion of UWB-RT on the agenda of any forum contemplating the future of wireless systems,particularly those considering‘wireless systems beyond3G’.We consider the latter notion to include (infrastructure-based)wide area cellular systems as well as local(ad hoc)networks for specific environments,e.g.self-organized network topologies and supporting systems capable of accessing cellular networks.A suitable podium for a comprehensive treatment of the technical issues associated with designing these next-generation systems is provided by the recently established Wireless World Research Forum(WWRF).4The WWRF aims to identify and promote research areas as well as technical and societal trends for mobile and wireless systems for the‘wireless world’that could become operational within a decade’s time.The WWRF’s list of proposed research tasks covers the multiple technical and operational aspects of future wireless systems,including the exploration of systems based on UWB-RT[7].Although the technological basis of UWB-RT is apparently well understood and developed today,it is generally recognized that efficient realization and widespread commercial deployment and application of this new technology still hinges on several significant regulatory and technical challenges.These problems must be resolved before the very promising benefits of UWB-RT can possibly be consumed in practice.Thus,it appears both timely and sensible to attempt this by dealing with the corresponding regulatory and technical issues as well as standardization questions on a global scale.Proponents of UWB-RT promise a broad array of new or improved(short-range)wireless devices and radio services that could provide enormous progress in the areas of public safety as well as for home and business applications.5It has been proposed that the FCC’s Part15rules be amended such that the imposed power limits(maximal electricalfield strength at a defined distance)are also applicable to intentional emissions from an UWB radio device[3].2It is claimed that,ideally,UWB devices could operate over the entire spectrum,including the bands reserved for other radio services without degrading their quality of operation. Although this assertion has been maintained by only certain proponents,the very question concerning the degree to which UWB devices can potentially cause harmful inter-ference in the receivers of other radio services—notably the Global Positioning System(GPS)—has become the primary focus of regulatory procedures[8].The resolution of these and other interference issues(e.g.cumulative impact of many UWB radio sources)require complex technical investigations and assessments;in addition,it is equally challenging to reconcile the various competing business interests with legitimate security concerns.For the purpose of this paper,we shall assume that the regulatory issues will eventually be resolved—preferably on a global scale.The FCC has proposed a definition of UWB radio signals similar to that of the OSD/DARPA UWB radar review panel [3],i.e.that the fractional bandwidth—the ratio between the signal’s bandwidth and center frequency—be greater than 0.25(25%)or the signal occupy at least1.5GHz of the spectrum.The bandwidth is measured at the upper and lower cutoff points(210dB),f H and f L,respectively,and the center frequency,f C,is defined as the average of these cutoff points,i.e.f C¼ðf Hþf LÞ=2:It is an open issue whether this definition should be applied only to UWB devices emitting pulsed signals of low duty cycle,where the bandwidth is inversely related to the width of the pulses. Clearly,other technical approaches can be employed to produce UWB radio signals,and it will be important to include these alternative methods in any future investi-gations of UWB-RT[9,10].However,for the sake of brevity and objectivity,this paper focuses on UWB signals as characterized earlier and in Section2,where potential applications are discussed.Section3gives a brief overview of the status of UWB-RT and indicates directions of possible future research,emphasizing the desirability of a regulatory and standardization framework with global support;conclusions are drawn in Section4.2.Key characteristics and applications of UWB-RTThis paper deals with UWB devices that transmit sequences of information carrying pulses of very short duration(e.g.0.1–2ns).These pulses are widely spaced such that the waveform’s duty cycle is up to several orders less than unity(e.g.1/10–1/1000).There are two principal methods to generate pulsed UWB signals.With thefirst method,the pulses are emitted as so-called baseband pulses, which in their purest form require spectra starting at very3Further notice of inquiry and notice of proposed rulemaking(in theMatter of Authorization of Spread Spectrum and Other WidebandEmissions not presently provided for in the FCC Rules and Regulations),Docket No.81-413,Federal Communications Commission,Release-Number:FCC84-169,May21,1984;Adopted April26,1984.4Wireless World Research Forum(WWRF)at http://www..5Partial list of companies and organizations actively developing orpromoting UWB-RT(alphabetical order).(a)Aetherwire and Location,Inc.():localizers;(b)Lawrence Livermore NationalLaboratory():micro-power radar;(c)MultispectralSolutions,Inc.():communication,radar,location;(d)Pulse,LINK,Inc.():wirelesshome networking;(e)Time Domain,Corp.(http://www.time-domain.com):communication,radar,location;(f)UWB Working Group(UWBWG;):industry consortium;(g)XtremeSpectrum,Inc.():communication.W.Hirt/Computer Communications26(2003)46–5247low frequency(nearly DC;e.g.(e)in footnote5).The second method emits envelope-shaped‘pulses’in the form of several sinusoidal cycles(e.g.(c)in footnote5).In systems that use thefirst approach,control of the signal’s center frequency,f C,and large emission bandwidth,f H2f L, is intimately coupled to the actual shape of the single pulse emitted from the antenna.The second approach offers a more independent adjustment of the signal’s center frequency and—typically somewhat smaller—bandwidth. Furthermore,whereas the antenna is generally a more important spectral-shaping element in a system based on the first approach,the higher frequencies used by the second method tend to reduce the signal’s ability to penetrate materials.In any case,independent of the method of signal generation,the following are some of the benefits and characteristics claimed for practical systems based on UWB-RT[3]:5†Extremely low power spectral density(PSD).Average power levels in the order of millionths of a Watt(m W) and excessive signal bandwidth yield power spectral densities in the order of several tens of nW/MHz.†Spectrum reuse.Potential reuse of scarce spectrum resources by overlaying UWB emissions of extremely low power spectral densities on already assigned spectral bands.†Robust performance under multipath conditions.The short pulses potentially allow differentially delayed multipath components to be distinguished at the receiver with the benefit that a reduced fading margin may be applied in a system’s link budget analysis.†Multiuser communication.The application of sequence-coded access methods to pulsed and inherently low-duty-cycle UWB signals could enable very densely populated multiuser systems with high immunity to interference.†High-resolution position location and tracking or radar sensing.The large signal bandwidth yields a distance resolution between communicating devices or a radar-sensing accuracy within a few centimeters.The inherently good receiver robustness in environments subject to multipath propagation and the fact that pulsed wideband signals are ideal for ranging applications enable one to conceive mobile short-range radio devices for the indoor environment that support(high-performance)digital data transmission as well as precise location determination and tracking.Therefore,it appears realistic to envisage certain future short-range wireless devices featuring scal-able data communication combined with precise location tracking of mobile terminals.Achieving location awareness in ad hoc networks as required in Ref.[11]could be greatly facilitated by the availability of wireless devices offering precise location-tracking functions that support efficient multihop routing mechanisms.The ultimate benefits that UWB-RT could bring to ad hoc networking stem from the ability to couple location tracking with(high-performance)data transmission.As pulse-based UWB devices typically operate with a single transmitted pulse waveform in all modes,they offer a high degree offlexibility in terms of data rate selection and transmission range.The physical(PHY) and medium access control(MAC)layers of UWB radio devices are thus particularly suited for implementations based on software-defined radio principles.Changes in data rate and/or transmission range can be made,for example,by simply changing the transmitter’s(average)pulse repetition frequency(PRF),possibly in combination with adjusting the number of information bits carried by a single pulse.This inherentflexibility of UWB radio devices is illustrated in Fig.1,which shows results computed for an ideal free-space channel and a receiver that is subject only to additive white Gaussian noise.Thefigure compares UWB systems using antipodal signaling(APS)combined with pulse position modulation(PPM)with direct-sequence spread-spectrum (DSSS)systems using binary phase shift keying(BPSK). Clearly,to achieve the same data rate,BPSK-DSSS tends to require chip rates that are significantly higher than the PRF of a corresponding APS/PPM UWB system.6UWB-RT potentially enables implementation of wireless platforms that support a variety of operating modes including data transmission,precision positioning and tracking,radar sensing or even a combination thereof. Thus,a wide range of novel wireless applications become possible,such as:†Wireless personal area networks(WPANs)and wireless local area networks(WLANs)with integrated position location and tracking capabilities,†multiuser ad hoc(self-organized)networking with location-aware routing support,†high-rate wireless home networking(multimedia access and distribution;wireless connection of displays),†alternate high-rate access into cellular network infra-structure(‘hot spot’scenario),†personnel and asset tracking(RF tagging),particularly in indoor environments,†public safety applications,including motion detection in disaster situations,†collision avoidance and proximity sensors for motor vehicles.Expected key applications for UWB radio devices are data communication and position location and tracking, particularly in the areas of short-range systems(WPAN, WLAN)and ad hoc networking.The home and single-office/small business(SOHO)environments will presumably become primary target markets for systems that support link 6Details on the system model are given in Fig.1,where the average power limit of0.3mW is the result of the assumed4GHz bandwidth and the FCC/Part15.109limit on the emissions of unintentional radiators.For frequencies.960MHz this limit is500m V/m at3m distance,measured in a1MHz bandwidth(PSD at the source:241.3dBm/MHz;see Ref.[3]and footnote2).W.Hirt/Computer Communications26(2003)46–52 48distances of between 10and 100m.UWB systems covering much larger distances will mainly be reserved for exempt systems operated by military and government entities.For example,field tests of long-range UWB surface wave transceivers designed for the US Navy for non-line-of-sight video transmission over up to 60nautical miles have been reported ((c)in footnote 5).3.Current state of UWB-RT and future research directionsThe US-based developers of UWB-RT have already achieved a rather advanced level in the design of PHY functions and,to a somewhat lesser degree,the MAC and higher-layer functions required to support the application scenarios described earlier.5In fact,it must be acknowl-edged that a few pioneering individuals and companies have collectively generated an impressive amount of intellectual property and complete concept or prototype systems that have proved to a reasonable degree the practical feasibility and benefits of UWB-RT [1,2].1,5However,a large gapexists between the current level of the base technology and the ultimately desirable state of widely available and highly integrated,cost/power efficient,standardized systems and applications,e.g.for integration into cell phones,personal digital assistants,laptops,and other mobile devices.A major task will be to achieve user-friendly coexistence and cooperation (e.g.handover)between existing and new systems alike,the WWRF is striving to provide an appropriate podium particularly in this area.43.1.System level issuesShort-range wireless systems based on narrow-band carrier modulation are often inadequate or incapable of providing sufficiently accurate information about a mobile terminal’s location to support location-aware applications or routing;on the other hand,there is a growing need for these capabilities [11–14].Fig.2is a rather speculative view of how devices based on UWB-RT can potentially outperform conventional radio devices both in achievable spatial capacity—measured in terms of aggregate data rate per unit area or (Kb/s)/m 2[15]—and locationprecision.parison of UWB and DSSS radio systems in terms of required average power vs.chip (pulse)rate to maintain a bit error rate (BER)of P b <1025over the free-space channel (range r ¼250m)in the presence of additive white Gaussian noise.With M -ary modulation,M ¼2m ;m ¼1;2;3;…;a pulse represents m bits,where the first bit encodes the polarity of the pulse.When m $2,the remaining m 21bits define one of L ¼M =2¼2m 21possible pulse positions within a chip interval (T C ).For M ¼2ðL ¼1Þthis hybrid modulation reduces to simple antipodal signaling (APS),whereas M $4(L $2)results in a combination of APS and L -ary PPM (APS/PPM).The transmitter may repeat each pulse chip N times to achieve an (ideal)signal processing gain G P ¼N at the receiver.The bit rate over the channel is thus R b ¼m =T S ¼ðm =N ÞR C ;N $1;where R C is the chip (pulse)rate,also called the PRF.There is a choice of the parameters m ,N ,and R C to achieve some given data rate,R b .For example,the four systems with parameters N l m ¼1l 6;1l 1;10l 6;and 10l 1achieve R b ¼10MB =s with R C ¼10=6;10,100/6,and 100MC/s,respectively.Also shown are the results for binary phase-shift keyed (BPSK),direct-sequence spread spectrum (DSSS)systems with processing gains G P ¼N ¼100ð20dB Þand 1000(30dB),respectively.BPSK-DSSS systems are modeled by letting the pulse width be equal to the chip duration ðt P ¼T C Þ;setting the carrier frequency f carrier ðDSSS Þ¼f peak ðUWB Þ;and assuming a spreading sequence of length N .Note that the BPSK-DSSS system with 20dB processing gain ðN ¼100Þrequires a chip rate of 1GC/s (!)to achieve a data rate of 10MB/s.W.Hirt /Computer Communications 26(2003)46–5249Whereas ‘spatial capacity’can be a sensible metric to compare different systems,it should be noted that this measure is relatively sensitive to changes in the assumed coverage area,e.g.the spatial capacity quadruples when the coverage radius is halved.Thus,it remains an objective of ongoing as well as future research to determine the practical limits of achievable spatial capacity.Many open questions exist in the areas of system scalability (large number of UWB devices operating in a given area),mutual interference between similar and dissimilar devices,required and achievable level of quality of service (QoS),to name a few.Concerning localization,it will be necessary to determine the actually required level of accuracy for any given application and whether this level of quality can be maintained under varying channel and network load conditions.Direction estimation methods may be worth developing to enhance the basic distance measurement methods;ultimately,effective methods for two-and three-dimensional location tracking capabilities need to be developed.In ad hoc networking,the role and efficiency of the MAC function in a highly loaded network has to be assessed.Even if UWB-RT promises to deal well with the basic requirements of data communication and location tracking,practical and workable solutions that combine the benefits of both modes of operation have to be defined and evaluated.For example,aiming at high-rate data in combination with precision location capabilities may not always be the most sensible approach to pursue.Instead,it may be more practical to trade range for performance and thus support location-aware applications over much greater distances at a reduced location precision and in combination with low-rate data transmission.3.2.Deployment and user scenariosThe choices for possible deployment and user scenarios when considering UWB systems for the enterprise and the consumer markets are abundant.It is thus imperative to consider carefully the all-important scenarios from which the key system requirements should be derived.In particular,the requirements relevant to the PHY and MAC layer functions must be clearly identified,e.g.link range,data rate,location precision,battery burden,level of adaptability to channel conditions,multiuser scalability,to name a few.Following this path,relevant research topics appear to be (i)definition of typical deployment environ-ments (may be limited by regulatory restrictions),(ii)identification of realistic user and application scenarios where the use of UWB-RT appears to be a definite asset compared to conventional solutions (e.g.data mode combined with position location and tracking)and (iii)deduction of the technical PHY and MAC requirements that can enable the selected scenarios.3.3.UWB radio channel and physical layerA variety of modulation and sequence coding techniques as well as corresponding methods for signal detection and processing have been proposed or used in experimental versions of UWB radio devices.5Naturally,not all of these techniques are equally applicable under different practical operating conditions.It is necessary to assess the merits and drawbacks of the various known as well as new approaches by subjecting them to different usage scenarios and propagation environments.For example,it is not clear whether methods that average a large number of pulsestoFig.2.A speculative comparison of UWB radio devices and conventional short-range wireless systems in terms of achievable spatial capacity,measured as the maximal aggregate data rate of N active devices per unit area (Kb/s)/m 2,maximal transmission range and average location error [12–14].The notation ‘IEEE802.11b (3£11Mb/s)’means that three ðN ¼3ÞIEEE802.11b devices communicate simultaneously with three different access points,each at a data rate of 11Mb/s over a distance of 100m.Although rarely possible in practice,it is assumed that the specified maximal ranges and data rates are achieved simultaneously by all devices.Each of the various options for UWB-RT assumes that N active devices transmit at the indicated data rate by using some multiple access scheme (e.g.N ¼6;data rate:50Mb/s,range:10m,[15]).W.Hirt /Computer Communications 26(2003)46–5250recover a bit of information will demonstrate sufficiently robust performance in situations of high relative velocity between transmitter and receiver platforms.In addition, although UWB systems feature a certain inherent robustness to multipath effects,they are not entirely immune to them. For example,in situations where there is an excessive ratio of link distance(d)to antenna height,the time difference between the line-of-sight and the reflected signal com-ponents can be substantially shorter than the duration of a pulse.This may result in signal losses according to the familiar(d/d0)n attenuation model with n<4;where d0is the reference distance.Extreme signal propagation situ-ations can also be observed in indoor environments where the numerous multipath components associated with each transmitted pulse result in propagation delay profiles that last tens and even hundreds of nanoseconds[16].The potential intersymbol interference caused by these not uncommon situations will severely limit the maximally achievable data rate of a system(small PRF)unless an effective method can be found that mitigates these effects.A further aspect not entirely understood today relates to the deteriorating effects of in-band interference in UWB receivers that originate from other radio signals, be they in near-or far-field proximity.The problem of nearby interference is not only one of academic interest, considering that UWB devices might be integrated into mobile platforms that make simultaneous use of a variety of other radios.Thus,the very advantage that UWB devices emit an extremely low PSD—as a result of the excessive signal bandwidth—potentially yields increased susceptibility to noise and interference in the UWB receiver.Similar effects may occur in areas with a large concentration of active UWB devices;this raises questions concerning harmful compound effects of multipath propagation and cross-device interference phenomena.Further topics related to UWB channel and PHY issues offering research potential are:†issues related to implementing the PHY of UWB radio devices,e.g.—signal propagation,channel modeling and esti-mation,—adaptive modulation methods and receiver archi-tectures,—dynamic rate adaptation in response to channel quality variations,—achievable single-user data rate and aggregate data rate per unit area(spatial capacity),—channel coding and error correction strategies,†characteristics of UWB antennas(e.g.in proximity of objects and the human body),†coexistence and integration of UWB radio devices with existing(short-range)wireless systems.3.4.Packet routing in ad hoc networks and medium access controlA key application for UWB devices is expected to be in the area of ad hoc and self-organized wireless networks based on multiuser communication and multihop routing capabilities[11].In this area,subjects that offer significant research potential are(i)definition of MAC functions to support ad hoc network architectures(e.g.location-based routing),(ii)influence of cooperative routing and associated protocols on the network load,(iii)investigation of multiple access schemes for UWB radio devices such as code division multiple access(CDMA)and(iv)methods to determine location information(e.g.MAC frame that supports applications using data communication and ran-ging).3.5.Regulation and standardization of UWB-RTLike any other wireless technology with a potential for widespread deployment,the eventual success of UWB-RT will depend greatly on the availability of suitable and timely PHY and MAC standards—in compliance with the rules imposed by regulatory authorities and backed by a represen-tative part of the industry.Thus,broadly supported PHY and MAC standards will be a prerequisite for successful deployment.Fig.3illustrates that the regulatory framework and standardized PHY and MAC functions are also key building blocks for systems based on UWB-RT.Although one can argue over the degree to which the need for standardization depends on the intended application,the currently observed emergence of UWB-RT should be considered a unique opportunity to develop and standardize PHY and MAC functions suitable for short-range wireless systems that combine data communication and positioning capabilities.In fact, these combined capabilities are poorly supported by conventional narrow-band systems,which certain standardization efforts are already trying to improve[14, 17].For example,the IEEE P802.15ALT PHYStudy Fig.3.The regulatory framework and(broadly supported)standardized PHY and MAC functions will also be the key building blocks of a system based on UWB-RT.W.Hirt/Computer Communications26(2003)46–5251。

P2P互联网金融外文翻译文献随着信息技术的迅猛发展，互联网金融作为一种新兴的金融模式在全球范围内迅速崛起。

P2P 互联网金融作为其中的重要组成部分，引起了广泛的关注和研究。

本文旨在对相关的外文文献进行翻译和梳理，以加深对 P2P 互联网金融的理解。

P2P 互联网金融，即 peertopeer lending，是指个人通过互联网平台向其他个人或企业提供贷款的一种金融模式。

与传统金融机构不同，P2P 平台主要依靠互联网技术和大数据算法来实现借贷双方的匹配和风险管理。

在众多外文文献中，学者们对 P2P 互联网金融的发展历程、特点、优势和风险进行了深入的探讨。

一些研究指出，P2P 互联网金融的出现打破了传统金融机构的垄断，为投资者提供了更多的投资选择，同时也为借款人提供了更便捷、高效的融资渠道。

例如，在某些国家，由于传统银行贷款审批流程繁琐、门槛较高，许多中小企业和个人难以获得资金支持。

而 P2P 平台通过简化审批流程、降低门槛，使得这些群体能够更容易地获得所需资金，从而促进了经济的发展。

然而，P2P 互联网金融也并非完美无缺。

一方面，由于缺乏有效的监管和规范，一些 P2P 平台存在欺诈、跑路等风险，给投资者带来了巨大的损失。

另一方面，P2P 平台的信用评估体系尚不完善，难以准确评估借款人的信用风险，从而增加了平台的坏账率。

此外，网络安全问题也是P2P 互联网金融面临的一大挑战。

一旦平台遭受黑客攻击，用户的个人信息和资金安全将受到严重威胁。

为了应对这些风险和挑战，国外的一些研究提出了相应的对策和建议。

首先，政府应加强对 P2P 互联网金融的监管，建立健全相关法律法规，明确平台的准入标准和运营规范。

其次，P2P 平台应加强自身的风险管理能力，完善信用评估体系，提高风险识别和控制能力。

同时，平台还应加大对网络安全的投入，采取有效的安全措施保障用户的信息和资金安全。

在对 P2P 互联网金融的研究中，国外学者还运用了多种研究方法和模型。

信息科学109DOI:10.16660/ki.1674-098X.2011-5640-4846浅谈网络信息安全的重要性及对策建议①马志广(吉化集团信息网络技术有限公司 吉林吉林 132000)摘 要：在当前经济和社会不断发展的趋势下，网络时代，信息安全要求对计算机的网络技术更加严格，为适应互联网的发展需要，其计算机信息安全技术也需要在全方面进行科学推动。

而就在这推动过程中，仍然出现了大量的信息安全隐患，不少有关技术飞速发展的同时，并未注重其出现的系统漏洞和安全问题。

在信息化时代下，网络信息安全引起了社会各界的广泛重视，随着经济和社会的飞速发展，不断提升计算机网络信息安全势在必行。

在现阶段，网络信息安全中存在的问题颇多，具体表现在几个方面，如网络自身的脆弱性、自然灾害、人为攻击等，这些问题直接影响着计算机网络系统的安全，针对这些问题，我们必须要从思想上引起重视，树立安全防范意识，采取行之有效的技术对策，以科学严谨的态度，预防信息安全风险。

本文中鉴于以上问题，提出了网络信息安全的重要性作用，并给出了相应的建议对策，旨在为同行工作者提供理论参考。

关键词：网络信息安全 现状问题 重要性作用 对策建议中图分类号：TP393 文献标识码：A 文章编号：1674-098X(2021)02(a)-0109-03On the Importance of Network Information Security andCountermeasureMA Zhiguang(Jilin Chemical Group Information Network Technology Co., Ltd., Jilin , Jilin Province, 132000 China)Abstract: In the current trend of economic and social development, in the Internet age, information security requires more stringent computer network technology. In order to meet the development needs of the Internet, its computer information security technology also needs to be promoted scientifically in all aspects. In the process of this promotion, there are still a lot of hidden dangers of information security. Many related technologies are developing rapidly without paying attention to the system vulnerabilities and security issues that appear.In the information age, network information security has attracted extensive attention from all sectors of society. With the rapid development of economy and society, it is imperative to continuously improve computer network information security. At this stage, there are many problems in network information security, which are manifested in several aspects, such as the vulnerability of the network itself, natural disasters, and man-made attacks. These problems directly affect the security of computer network systems. In response to these problems, We must pay attention ideologically, establish a security awareness, adopt effective technical countermeasures, and adopt a scientific and rigorous attitude to prevent information security risks. In view of the above problems, this article puts forward the important role of network information security, and gives corresponding suggestions and countermeasures, aiming to provide theoretical references for fellow workers.Key Words: Network information security; Current issues; Important role;Countermeasures and suggestions①作者简介：马志广（1975—），男，本科，工程师，研究方向为计算机软件工程。

英文版计算机试题及答案一、选择题（每题2分，共20分）1. Which of the following is not a function of an operating system?A. Process managementB. Memory managementC. Data storageD. File management2. In a computer network, what does the term "bandwidth" refer to?A. The width of the network cableB. The maximum rate of data transferC. The number of users connectedD. The speed of the network processor3. What is the primary purpose of a firewall?A. To prevent unauthorized access to a networkB. To encrypt dataC. To manage network trafficD. To store user passwords4. Which of the following is a type of software used for creating and editing documents?A. Spreadsheet softwareB. Database softwareC. Word processing softwareD. Graphics software5. What is the term used to describe the process of converting data from one format to another?A. Data migrationB. Data transformationC. Data conversionD. Data translation6. What does the acronym "CPU" stand for in computing?A. Central Processing UnitB. Central Processing UnitC. Computer Processing UnitD. Computing Processing Unit7. What is the function of a router in a network?A. To connect multiple networksB. To store dataC. To provide power to devicesD. To print documents8. What is the process of finding and fixing errors in software called?A. DebuggingB. PatchingC. UpdatingD. Patching9. Which of the following is a type of computer virus that replicates itself by attaching to other programs?A. TrojanB. WormC. RansomwareD. Spyware10. What is the term for the graphical representation of data on a computer screen?A. Data visualizationB. Data representationC. Data graphingD. Data mapping二、填空题（每题2分，共20分）1. The _________ is the primary memory used by a computer to store data and instructions that are currently being processed.2. A _________ is a type of software that allows users to create and edit images.3. The process of converting analog signals to digital signals is known as _________.4. A _________ is a collection of data stored in a structured format.5. The _________ is a hardware component that connects a computer to a network.6. In computer programming, a _________ is a sequence of statements that perform a specific task.7. The _________ is a type of malware that hides its presence and waits for a trigger to activate.8. A _________ is a type of software that is designed to protect a computer from unauthorized access.9. The _________ is the process of organizing and managing data in a database.10. A _________ is a type of software that allows users tocreate and edit spreadsheets.三、简答题（每题10分，共30分）1. Describe the role of a server in a computer network.2. Explain the difference between a compiler and an interpreter in programming.3. Discuss the importance of data backup and recovery in a computing environment.四、编程题（每题15分，共30分）1. Write a simple program in Python that calculates the factorial of a given number.2. Create a function in Java that takes an array of integers and returns the largest number in the array.答案：一、选择题1. C2. B3. A4. C5. C6. A7. A8. A9. B10. A二、填空题1. RAM (Random Access Memory)2. Graphics software3. Analog-to-digital conversion4. Database5. Network interface card (NIC)6. Function or procedure7. Trojan8. Antivirus software9. Database management10. Spreadsheet software三、简答题1. A server in a computer network is a powerful computer or system that manages network resources, including hardware and software, and provides services to other computers on the network, such as file storage, web hosting, and print services.2. A compiler is a program that translates source codewritten in a programming language into machine code that a computer can execute. An interpreter, on the other hand, reads and executes the source code line by line without the need for a separate compilation step.3. Data backup and recovery are crucial in a computing environment to prevent data loss due to hardware failure, software bugs, or malicious attacks. Regular backups ensure that data can be restored to a previous state in case of corruption or deletion.四、编程题1. Python Program for Factorial Calculation:```pythondef factorial(n):if n == 0:return 1 else:。