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1、物理层和链路层认知技术物理层和链路层认知技术物理层和链路层认知技术认知无线电, Pareto, 多目标规划, 遗传算法认知无线电技术学习三物理层和链路层认知技术by Thomas W. Rondeau and Charles W。 Bostian(Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA, USA)概念和观点理解:casebased theory - 案例理论;genetic algorithms (GAs) - 遗传算法(GA)It is not a pur
2、ely selfish adaptation where the radio seeks to maximize its own consumption of resources. CR不是只追求自身资源消耗最大化的自私自适应参数调整。“tragedy of the commons” - 共有悲剧。 2.4GHz ISM频段,IEEE 802。11设备和蓝牙设备相互干扰,前者有更高的发射功率,后者具有不断重发数据包直到传输成功的协议.This chapter addresses methods of how to find a local or global optimum for the c
3、urrent channel environment (当前信道环境下的全局或局部最优)。 最优的定义:a radio is optimized when it achieves a level of performance that satisfies its users needs while minimizing its consumption of resources such as occupied bandwidth and battery power。 满足用户需求的同时最小化其带宽和功率等资源消耗.Cognitive radios merge AI and wireless c
4、ommunications。 - CR是AI与无线通信相结合的产物。认知引擎是其智能核心。The cognitive engine takes in information from the user domain, the radio domain, the policy domain, and the radio itself. The user domain (用户域) passes information relevant to the users application and networking needs to help direct the cognitive engines
5、 optimization. The radio domain (无线电域) information consists of radio frequency (RF) and environmental data that could affect system performance such as propagation or interference sources. The policy engine (政策引擎) receives policy-related information from the policy domain (政策域). This information hel
6、ps the cognitive radio decide on allowable (and legal) solutions and blocks any solutions that break local regulations.In radio, we can think of the classical transmitters and receivers as having adjustable controlparameters (knobs) that control the radios operating parameters. Knob - 旋钮,文中用其代表无线电的可
7、调节参数。Radio performance metrics are referred to as meters. Meter - 文中用来作为衡量CR结果的指标.The knobs of a radio are any of the parameters that affect link performance and radio operation。 Knob:影响链路性能和无线电操作的任何参数。物理层中,中心频率、符号速率、发射功率、调制类型和调制阶数、PSF(脉冲成型滤波器)类型和阶数、扩频类型、扩频因子等;链路层中则为各种可以改进网络性能的变量,信道编码与交织的类型和速率、接入控制方
8、法(如流量控制、帧大小以及多址接入技术)等.物理层链路层MAC层知识-物理层的主要任务是实现通信双方的物理连接,以比特流(bits)的形式传送数据信息,并向数据链路层提供透明的传输服务.物理层是构成通信网络的基础,所有的通信设备、主机都需要通过物理线路互联。物理层建立在传输介质的基础上,与传输媒介密切相关,是系统和传输介质的物理接口,是OSI模型的最低层. 物理层有关的连接设备有:集线器、中继器、传输媒介连接器、调制解调器等。物理层主要解决的问题是:连接类型、物理拓扑结构、数字信号、位同步方式、带宽使用、多路复用等.数据链路层的功能就是利用物理层提供的比特流传输功能,实现在相邻节点(node)
9、间的透明、可靠的数据传输,具体要实现下列功能:链路管理、帧同步、差错控制(CRC,ARQ,信道编码,交织)、流量控制. 根据网络规模的不同,数据链路层的协议可分为两类:一类是针对广域网(WAN)的数据链路层协议,如HDLC、PPP、SLIP等;一类是局域网(LAN)中的数据链路层协议,如MAC子层协议和LLC子层协议。 MAC(子)层位于OSI七层协议中数据链路层的下半部分,主要负责控制与连接物理层的物理介质。在发送数据的时候,MAC协议可以事先判断是否可以发送数据,如果可以发送将给数据加上一些控制信息,最终将数据以及控制信息以规定的格式发送到物理层;在接收数据的时候,MAC协议首先判断输入的
10、信息并是否发生传输错误,如果没有错误,则去掉控制信息发送至LLC层。Performance is a measure of the systems operation based on the meter readings. In optimization theory (最优化理论), the meters represent utility and cost functions (效用或代价函数) that must be maximized or minimized for optimum radio operation。 All of these performance analysi
11、s functions constitute objective functions (目标函数)。Modeling Outcome as a Primary Objective - 将结果建模为主要目标The basic process followed by a cognitive radio is that it adjusts its knobs to achieve some desired (optimum) combination of meter readings。 Rather than randomly trying all possible combinations of
12、 knob settings and observing what happens, it makes intelligent decisions about which settings to try and observes the results of these trials。BER与SINR的观测例子The radio observes the BER and SINR value。 If these are consistent according to the above formulas, the radio can assume that the channel is beh
13、aving predictably。 It can then turn knobs that directly affect SINR, for example starting with the easiest, transmitter power。 If the transmitter power is already at the allowable limit, the radio may lower the data rate to change the occupied bandwidth and therefore increase the average energy per
14、bit. If the BER and SINR arenot consistent with the known formulas, the radio might assume, for example, that the channel is dispersive and opt to change the carrier frequency rather than the transmitter power。MODM (MultiObjectives Decision Making, 多目标决策) 理路或称MOP (Multi-Objective Programming, 多目标规划;
15、Multi-objective Optimization Problem, 多目标最优化问题)理论In an MODM problem space, a set of solutions optimizes the overall system, if there is no one solution that exhibits a best performance in all dimensions. - 此话怎讲,貌似不通?理解Pareto前沿最重要的概念是所有的解都是各个目标函数的折中.只有很小一部分多目标问题可以使其解同时优化所有目标,这个概念称为乌托邦点。多目标规划中,由于存在目标之
16、间的冲突和无法比较的现象,一个解在某个目标上是最好的,在其他的目标上可能比较差。Pareto 在1986 年提出多目标的不受支配解(Nondominated set)的概念.其定义为:假设任何二解S1 及S2 对所有目标而言,S1均优于S2,则我们称S1 支配S2,若S1 的解没有被其他解所支配,则S1 称为非支配解(不受支配解),也称Pareto解。这些非支配解的集合即所谓的Pareto Front。所以座落在Pareto front 中的所有解皆不受Pareto Front 以外的解(以及Pareto Front 以内的其它解)所支配,因此这些非支配解较其他解而言亦拥有最少的目标冲突,所以提供决策者一个较佳的选择空间。在某个非支配解的基础上改进任何目标函数的同时,必然会削弱至少一个其他目标函数。不同的目标对不同的用户需求和信道条件有