Wireless Sensor Networks

Outline

• 4.1 Introduction
• 4.2 Hardware and Operating System
• 4.3 Communication Protocol
• 4.4 Important issue
• 4.5 Applications

4.1 Introduction

要背的基本概念

• Sensor node: sensing, data processing, and communicating capacity
  传感器节点: 感知、数据处理和通信能力
• Sensor network: a large number of sensor nodes that are densely deployed either inside the phenomenon or very close to it
  传感器网络: 大量的传感器节点密集部署在现象内部或非常接近现象内部
• A wireless sensor network (WSN) consists of spatially distributed autonomous sensors.
  无线传感器网络(WSN)由空间分布的自主传感器组成

Applications 应用

Application	解释
Wildlife Monitor	野生动物监测
Ecosystem record	生态系统记录
Traffic Monitor	交通监控
Building Monitor	构建监测
Healthy	健康
Military	军事
Home	家居
Commercial	商业

New Design Themes 新设计主题

• Long-lived systems that can be unattended
  可以无人值守的长寿命系统
  ① Low-duty cycle operation with bounded latency
  低占空比操作，延迟有限
  ② Exploit redundancy
  利用冗余
  ③ Tiered architectures (mix of form/energy factors)
  分层架构(形式/能量因素的混合)
• Self-configuring systems that can be deployed ad hoc
  可以临时部署的自配置系统
  ① Measure and adapt to unpredictable environment
  可以临时部署的自配置系统
  ② Exploit spatial diversity and density of sensor/actuator nodes
  开发传感器/执行器节点的空间多样性和密度

方法

• Leverage data processing inside the network
  利用网络内部的数据处理
• Achieve desired global behavior with adaptive localized algorithms.
  通过自适应局部化算法

Communication Architecture 通信体系结构

Factors	解释
Fault tolerance	容错
Scalability	可扩展性
Production costs	生产成本
Hardware constraints	硬件限制
Network topology	网络拓补结构
Transmission media	传播媒体
Environment	环境
Power consumption	功耗

• Fault Tolerance: The ability to sustain sensor network functionalities without any interruption due to sensor node failures.
  容错：支持传感器网络功能而不因传感器节点故障而中断的能力。
• Scalability: The number of sensor nodes
  可扩展性:传感器节点的数量
• Production Costs: The cost of a single node is very important to justify the overall cost of the network
  生产成本:单个节点的成本是非常重要的，以证明整个网络的成本

• Hardware's 4 basic unit:

basic unit	解释
sensing unit	传感单元
processing unit	处理单元
transceiver unit	收发单元
power unit	电源单元
Additional application-dependent units	更多的依赖于应用程序的单位

• Hardware Constraints

Constraints	解释
size	大小
Power	电量
Operate in high density	高集成度
Low cost	低成本
Autonomous	自动
Adaptive to environment	适应环境

• Sensor Network Topology
  Topology maintenance and change in 3 phases:
  拓扑维护和变更分3个阶段

phase	解释
Predeployment and deployment phase	预部署和部署阶段
Post-deployment phase	部署后阶段
Redeployment of additional nodes phase	额外节点的重新部署阶段

• Transmission Media 传播介质

media	解释
wireless medium	无线媒体
Radio	广播
Infrared	红外线
Optical	光学

4.2 Hardware and Operating System

Name	具体名称
Hardware	Berkeley Motes
	System of MICA Motes
	MICA Motes
	MICAz
	TelosB
Operating System	TinyOS
	Contiki
	LiteOS

• LiteOS is a real-time operating system (RTOS) for use in sensor networks.
  LiteOS是一个实时操作系统(RTOS)，用于传感器网络。
• memory-constrained 内存受限的

4.3 Communication Protocols

• Design Issues According to Protocol Stack 根据协议栈设计问题

Name	解释
Physical layer	物理层
Data link layer	数据链路层
Network layer	网络层
Transport layer	传输层

• Three Management Planes 三个管理方面

plane	解释
The power management plane	电源管理层面
The mobility management plane	移动管理层面
The task management plane	任务管理层面

4.4 Important Issues 重要问题

Issues	解释
Routing Protocols	路由协议
Topology Control	拓扑控制
Coverage Problems	覆盖问题
Time Synchronization	时间同步
Localization	本地化

4.4.1 Routing Protocols 路由协议

• Classified based on the underlying network structure:

categories	解释	翻译
Flat	Nodes are assigned equal roles	平面：节点被分配相等的角色
Hierarchical	Nodes will play different roles	分级：节点将扮演不同的角色
Location-based	Nodes’ positions are exploited to route data	基于位置的：节点的位置被用来路由数据

Flat Routing 平面路由协议

protocol	翻译
Sensor Protocols for Information via Negotiation(SPIN)	信息协商传感器协议
Directed diffusion (DD)	定向扩散

SPIN

• DD

feature	翻译
establish path	建立路径
Localized interactions	局部的相互作用

elements	翻译
Interest	感兴趣
Gradient	梯度
Data message	数据信息
Reinforcement	强化

DD

Hierarchical Routing 分级路由协议

• Advantages

advantages	翻译
scalability	可伸缩性
efficient communication	有效沟通

• Mainly two-layer routing

Name	翻译
Select cluster heads	选择集群头
Routing	路由

4.4.2 Topology Control 拓扑控制

• 定义
  Topology control is a technique used in distributed computing to alter the underlying network (modeled as a graph) in order to reduce the cost of distributed algorithms if ran over the new resulting graphs.
  拓扑控制是一种用于分布式计算的技术，用于改变底层网络(建模为一个图)，以便在运行新的结果图时降低分布式算法的成本。

• Subproblem of Topology control

Name	翻译	解释
topology construction	拓扑结构
topology maintenance	拓扑维护	connectivity and coverage are preserved

• Topology construction
  increase the number of message collisions
  将增加消息冲突的数量
• Topology maintenance
  nodes that are closer to the sink spend higher amounts of energy.
  距离接收器越近的节点消耗的能量越高

4.4.3 Coverage Problems 覆盖问题

• Goal
  each location in the targeted physical space should be within sensing range of at least one sensor.
  目标物理空间中的每个位置应在至少一个传感器的传感范围内。

• Simple Coverage Problem: entire area covered. 全覆盖

• K-Coverage Problem: entire region k-covered. 全被k次覆盖

• Types
  Area Coverage: cover/monitor an area/region.
  区域覆盖:覆盖/监测一个区域/区域。

  
  
  Area Coverage

Point Coverage: cover a set of points.
点覆盖:覆盖一组点。

Point Coverage

Barrier Coverage:minimize the probability of undetected penetration through the barrier (sensor network).
屏障覆盖:最小化未检测到的穿透屏障(传感器网络)的概率。

Barrier Coverage

4.4.4 Time Synchronization 时间同步

• Several issues in synchronization 同步上的一些问题

1. Master-slave v.s. peer-to-peer synchronization

   • Master-slave 主从
     attempt to synchronize with the master. 子节点与主节点同步
   • Peer-to-peer 点对点
     estimates the local time based on the clocks of other nodes
     通过通信估计出时间

2. Internal synchronization v.s. external synchronization

   • Internal synchronization
     minimize the maximum difference between the readings of local clocks of the sensors
     最小化传感器的本地时钟读数之间的最大差异

   • External synchronization
     A standard external source of time
     标准的外部时间源

4.4.5 Localization 本地化

• To determine the physical coordinates of a group of sensor nodes in a wireless sensor network (WSN).
  确定无线传感器网络(WSN)中一组传感器节点的物理坐标。
• Due to application context and massive scale, use of GPS is unrealistic, therefore, sensors need to self-organize a coordinate system.
  由于应用环境和大规模，使用GPS是不现实的，因此，传感器需要自组织一个坐标系统。
• To report data that is geographically meaningful
  报告具有地理意义的数据
• Services such as routing rely on location information; geographic routing protocols; context-based routing protocols, location-aware services
  路由等服务依赖于位置信息;地理路由协议;基于上下文的路由协议，位置感知服务

DV-hop Phase 1 DV-hop阶段1:

Euclidean Phase 1: 欧几里得阶段1:

研究一下