Moving Object Counting with an Infrared Sensor Network
By Chi-Keung Ki

ABSTRACT Wireless Sensor Network (WSN) has become a hot research topic recently.Great benefit can be gained through the deployment of the WSN over a wide range of applications,covering the domains of commercial, military as well as residential. In this project, we design a counting system which tracks people who pass through a detecting zone as well as the corresponding moving directions.Such a system can be deployed in traffic control, resource management, and human flow control. Our design is based on our self-made cost-effective Infrared Sensing Module board which co-operates with a WSN.The design of our system includes Infrared Sensing Module design, sensor clustering, node communication, system architecture and deployment.We conduct a series of experiments to evaluate the system performance which demonstrates the efficiency of our Moving Object Counting system. KEYWORDS Infrared radiation;Wireless Sensor Node

1 Wireless Sensor Network
1.1 Introduction to Infrared
Infrared radiation is a part of the electromagnetic radiation with a wavelength lying between visible light and radio waves.Infrared have be widely used nowadays including data communications,night vision,object tracking and so on.People commonly use infrared in data communication,since it is easily generated and only suffers little from electromagnetic interference.Take the TV remote control as an example,which can be found in everyone's home.The infrared remote control systems use infrared light-emitting diodes (LEDs) to send out an IR (infrared) signal when the button is pushed.A different pattern of pulses indicates the corresponding button being pushed. To allow the control of multiple appliances such as a TV,VCR,and cable box,without interference,systems generally have a preamble and an address to synchronize the receiver and identify the source and location of the infrared signal.To encode the data, systems generally vary the


width of the pulses (pulse-width modulation) or the width of the spaces between the pulses (pulse space modulation).Another popular system,bi-phase encoding,uses signal transitions to convey information.Each pulse is actually a burst of IR at the carrier frequency. A 'high' means a burst of IR energy at the carrier frequency and a 'low' represents an absence of IR energy.There is no encoding standard. However, while a great many home entertainment devices use their own proprietary encoding schemes, some quasi-standards do exist. These include RC-5, RC-6, and REC-80.In addition,many manufacturers,such as NEC,have also established their own standards.

1.2 Wireless sensor network
Wireless sensor network (WSN) is a wireless network which consists of a vast number of autonomous sensor nodes using sensors to monitor physical or environmental conditions, such as temperature,acoustics,vibration,pressure,motion or pollutants,at different locations.Each node in a sensor network is typically equipped with a wireless communications device,a small microcontroller, one or more sensors,and an energy source, usually a battery.The size of a single sensor node can be as large as a shoebox and can be as small as the size of a grain of dust,depending on different applications.The cost of sensor nodes is similarly variable,ranging from hundreds of dollars to a few cents, depending on the size of the sensor network and the complexity requirement of the individual sensor nodes.The size and cost are constrained by sensor nodes,therefore,have result in corresponding limitations on available inputs such as energy,memory, computational speed and bandwidth.The development of wireless sensor networks (WSN) was originally motivated by military applications such as battlefield surveillance.Due to the advancement in micro-electronic mechanical system technology (MEMS),embedded microprocessors,and wireless networking,the WSN can be benefited in many civilian application automation. areas,including habitat monitoring,healthcare applications,and home

1.3 Types of Wireless Sensor Networks
Wireless sensor network nodes are typically less complex than general-purpose operating systems both because of the special requirements of sensor network applications


and the resource constraints in sensor network hardware platforms.The operating system does not need to include support for user interfaces. Furthermore,the resource constraints in terms of memory and memory mapping hardware support make mechanisms such as virtual memory either unnecessary or impossible to implement.Tiny OS is possibly the first operating system specifically designed for wireless sensor networks.Unlike most other operating systems,Tiny OS is based on an event-driven programming model instead of multithreading.Tiny OS programs are composed into event handlers and tasks with run to completion-semantics.When an external event occurs,such as an incoming data packet or a sensor reading,TinyOS calls the appropriate event handler to handle the event.The TinyOS and programs are both written in a special programming language called NesC which is an extension to the C programming language.NesC is designed to detect race conditions between tasks and event handlers. There are also operating systems that allow programming in C. Examples of such operating systems include Contiki ,and MANTIS. Contiki is designed to support loading modules over the network and run-time loading of standard ELF files.The Contiki kernel is event-driven,like TinyOS, but the system supports multithreading on a per-application basis. Unlike the event-driven Contiki kernel,the MANTIS kernel is based on preemptive multithreading.With preemptive multithreading, applications do not need to explicitly yield the microprocessor to other processes.

1.4 Introduction to Wireless Sensor Node
A sensor node, also known as a mote, is a node in a wireless sensor network that is capable of performing processing, gathering sensory information and communicating with other connected nodes in the network.Sensor node should be in small size,consuming extremely low energy,autonomous and operating unattended,and adaptive to the environment.As wireless sensor nodes are micro-electronic sensor device, they can only be equipped with a limited power source.The main components of a sensor node include sensors,microcontroller,transceiver,and power source.Sensors are hardware devices that can produce measurable response to a change in a physical condition such as light density and sound density.The continuous analog signal collected by the sensors is digitized by Analog-to-Digital converter.The digitized signal is then passed to controllers for further



processing.Most of the theoretical work on WSNs considers Passive and Omni directional sensors.Passive and Omni directional sensors sense the data without actually manipulating the environment with active probing,while no notion of “direction”is involved in these measurements.Commonly people deploy sensor for detecting heat (e.g. thermal sensor), light (e.g. infrared sensor), ultra sound (e.g. ultrasonic sensor), or electromagnetism (e.g. magnetic sensor).In practice,a sensor node can equip with more than one sensor. Micro-controller performs tasks,processes data and controls the operations of other components in the sensor node.The sensor node is responsible for the signal processing upon the detection of the physical events as needed or on demand.It handles the interruption from the transceiver.In addition, it deals with the internal behavior, such as application-specific computation. The function of both transmitter and receiver are combined into a single device known as transceivers that are used in sensor nodes.Transceivers allow a sensor node to exchange information between the neighboring sensors and the sink node (a central receiver).The operational states of a transceiver are Transmit,Receive,Idle and Sleep. Power is stored either in the batteries or the capacitors.Batteries are the main source of power supplying for the sensor nodes.Two types of batteries used are chargeable and non-rechargeable. They are also classified according to electrochemical material used for electrode such as Nickel-cadmium,Nickel-zinc,Nickel metal hydride,and Lithium-Ion. Current sensors are developed which are able to renew their energy from solar to vibration energy.Two major power saving policies used are Dynamic Power Management and Dynamic Voltage Scaling. DPM takes care of shutting down parts of sensor node which are not currently used or active.DVS scheme varies the power levels depending on the non-deterministic workload. By varying the voltage along with the frequency, it is possible to obtain quadratic reduction in power consumption.

1.5 Challenges
The major challenges in the design and implementation of the wireless sensor network are mainly the energy limitation, hardware limitation and the area of coverage.Energy is the scarcest resource of WSN nodes, and it determines the lifetime of WSN nodes.WSN



nodes are meant to be deployed in large numbers in various environments, including remote and hostile regions,with ad-hoc communications as key.For this reason, algorithms and protocols need to be lifetime maximization,robustness and fault tolerance and self-configuration.The challenge in hardware is to produce low cost and tiny sensor nodes. With respect to these objectives,current sensor nodes usually have limited computational capability and memory space. Consequently,the application software and algorithms in WSN should be well-optimized and condensed.In order to maximize the coverage area with a high stability and robustness of each signal node, multi-hop communication with low power consumption is preferred.Furthermore,to deal with the large network size, the designed protocol for a large scale WSN must be distributed.

1.6 Research Issues
Researchers are interested in various areas of wireless sensor network, which include the design, implementation and operation.These include hardware,software and middle-ware,which means primitives between the software and the hardware.As the WSNs are generally deployed in the resources-constrained environments with battery operated nodes,the researchers are mainly focus on the issues of energy optimization, coverage areas improvement,errors reduction,sensor network application,data security,sensor node mobility, and data packet routing algorithm among the sensors.In literature, a large group of researchers devoted a great amount of effort in the WSN.They focused in various areas, including physical property,sensor training,security through intelligent node cooperation, medium access,sensor coverage with random and deterministic placement, object locating and tracking, sensor location determination,addressing,energy efficient broadcasting and active scheduling,energy conserved routing,connectivity,data dissemination and

gathering,sensor centric quality of routing, topology control and maintenance, etc.



[1] G . 5 . Cheung , J . Y . M , Azzi , 0 . Intelligenc in building : the prtential advanced modelling Loveday . D . L . Virk . Automation in Construction . 1997:447-461. [2] Kirill Yelizarov v . home security System . Microchip Technology InC .1998:44-48. [3] B.D.Moore. Tradeoffs in selecting IC temperature sensors. Microprocessors and Microsystems, 1999, 23:181-184. [4] AT89C51 DATA SHEEP Philips Semiconductors 1999:55-58. [5]Yang. Y., Yi. J., Woo, Y.Y., and Kim. B· Optimum design for linearity and efficiency of microwave Doherty amplifier using a new load matching technique, Microw. J., 2001, 44:20–36.



作者 Chi-Keung Ki

摘要 近来,无线传感器网络(WSN)已经成为一个热点的研究方向。在涉及商业、军事和住宅的广 泛应用领域中,通过无线传感器网络的部署,人们可获得巨大的收益。在这个项目中,我们设计了 一个计数系统,此系统追踪经过检测区域及其相应移动方向上的人。在交通管理、资源管理和人 流量控制方面,我们也可以部署这样的系统。本设计是基于自制低成本的红外传感模块板,而且 它与无线传感器网络相联系。系统的设计包括红外传感模块设计、传感器集群、节点通讯、系统 架构和部署。通过一系列实验,我们可以评估系统的性能,进而论证采用红外传感器网络对移动 目标计数的系统效率。 关键词 红外辐射;无线传感器节点

1 无线传感器网络
1.1 红外的介绍
红外辐射,是电磁辐射的一部分——介于可见光与无线电波之间的波长。现如今, 红外已经被广泛应用,包括数据通讯、夜视装置、目标追踪等。由于红外线易产生且 只受较少的电磁干扰,人们在数据通讯中通常使用红外。以电视遥控器的控制为例, 我们知道每个人的家里都有电视遥控器。当按下按钮时,红外遥控器系统利用红外发 光二极管(LEDS)来发出红外(红外线)讯号。 而脉冲的不同模式表示相应的按钮正被按 下。为使多种电器的控制不受相互的干扰,例如电视机、录像机、有线电视盒,为与 接收机同步且识别来源和红外信号的位置,通常系统都有前导码和地址。为对数据进 行编码,系统通常改变不同脉冲的宽度(脉宽调制)或脉冲间的间隔宽度(脉冲间隔调 制)。另一种受欢迎的系统—双相编码,它利用信号转换来传递信息,这是因为每个 脉冲实际上是在载波频率中的红外突发。 “高”的含义是在载波频率中的红外能量的释 放,而“低”代表红外能量的消失。虽然没有编码标准,但当许许多多的家庭娱乐设备 使用自身所有的编码方案时,一些精确的标准确实存在。这些编码的标准包括 RC-5、 RC -6和 REC-80。此外,许多如 NEC 的制造商也确立了他们自己的标准。



1.2 无线传感器网络
无线传感器网络(WSN)是一种由大量自主的传感器节点组成的无线网络, 在不同 的地点,它利用传感器监测物理条件或环境条件,如温度、音质、振动、压力、移动 或污染物。在传感器网络中,每个节点都专门配备了一个无线通信设备,包括一个小 型的单片机、一个或多个传感器、一种能源,而能源通常是一块电池。单一的传感器 节点的大小可以像鞋盒一样大,也可以像一粒尘埃一样小,这取决于不同的应用程序。 而传感器节点的成本同样是不定的,从几美分到几百美元,这要根据传感器网络的大小 以及个别传感器节点的复杂性的要求。由于大小和成本受传感器节点的限制,导致了 在可利用的的输入方面有了相应的限制,例如能量,记忆力,计算速度和带宽。无线传感 器网络的发展(WSN)起初是由于军事应用,例如战场上的监视。但随着在微电子机械 系统技术(MEMS)、 嵌入式处理器和无线网络方面的进步, WSN 也能够受益于许多民 用的应用领域,包括生态监督、医疗应用以及家庭自动化。

1.3 无线传感器网络的类型
由于传感器网络应用的特殊要求以及在传感器网络硬件平台的资源限制, 通常无 线传感器网络节点并没有通用的操作系统的复杂。 这个操作系统确实不需要涵括用户 界面的支持。 而且在内存方面和内存映射的硬件支持方面的资源约束使得类似虚拟内 存一样的机制变得没有必要或无法实现。 微型操作系统可能是第一个专门为无线传感 器网络而设计的操作系统。不像其它大多数的操作系统,微型操作系统是一个基于代 替多线程的驱动事件的编程模型。 微型操作系统的程序都是由趋向语义完成的事件处 理程序和任务而组成的。当一个外部事件发生时,例如一个传入的数据包或一个传感 器读数,微型操作系统的传感器会调用匹配的事件处理程序来处理这个事件。这个微 型操作系统和程序都是用一种名为 NesC 特殊的编程语言来编写的,而 NesC 是一种 C 程序设计语言的扩展。NesC 是用来侦测在任务和事件处理器之间的竞争条件。同 样也有操作系统允许用 C 语言进行编程。类似操作系统的例子包含 Contiki 和 MANTIS。Contiki 是为在网络上支持模块加载和运行时标准精灵的文件下载而设计 的。 这个 Contiki 的内核是驱动事件型的,就像微型操作系统,但在每个应用基础上系统 支持多线程。 不像驱动事件型的 Contiki 内核,MANTIS 内核是基于先发制人的多线程。 由于先发制人的多线程,应用程序不需要明确地使微处理器顺从其他的过程。

1.4 无线传感器节点的介绍


一个传感器节点像众所周知的一粒尘埃一样,它是一个能够执行并处理的无线传 感网络中的节点,它收集感官信息且与其他网络中的连接节点有关联。传感器节点一 般都是体积小、极低能源消耗、自治的、操作无人值守以及适应环境的。随着无线传 感器节点变成微电子传感器装置,它们可以只配备有限电源。传感器节点的主要部件 包括传感器、单片机、收发器和电源。传感器是随类似光密度和声音密度的物理条件 的变化而产生可测量响应的硬件设备。 由传感器采集的连续模拟信号经过模拟数字转 换器而数字化。然后,数字信号通过控制器进行了进一步的加工。大部分有关无线传 感器网络的理论著作都涉及被动和全方位的传感器。尽管没有“方向”的概念涉及这 些测量,被动和全方位的传感器实际上并未积极地通过探索操作环境来检测数据。通 常人们部署传感器来探测热度(例如热传感器),光(例如红外传感器)、 超声波(例如超声 波传感器)或电磁超声传感器(例如磁传感器)。实际上,一个传感节点可以配备不止一 个传感器。在传感器的接节点上,微控制器执行任务、处理数据以及控制其他元件的 运行。传感器节点负责在有需要的或要求的物理事件的检测方面进行信号处理。它处 理来自收发器的中断。此外,它也处理内部动作,就如专有的应用计算。 将发射机和接收机的功能都并入到一个单一的设备是收发器, 它应用于传感器节 点。收发器允许一个传感节点在相邻的传感器和汇集点(一个中央接收器)之间交换 信息。一个无线电收发器的工作状态是传送、接收、闲置和休眠。它的能量是储存在 电池或电容器中。电池是为传感器节点提供能量的主要来源。使用的电池分为可充电 和不可再充电两种类型。它们也可根据用于电极的电化学材料来进行分类,如镍镉、 镍锌、镍氢金属化合物和锂离子。由于电流传感器得到了进一步研发,使得可以更新 从太阳能到机械振动的能量。 它们两个主要采用的节约能源政策是动态电源管理和动 态电压缩放。动态电源管理负责关闭部分目前还不使用或不活跃的传感器节点。动态 电压缩放方案则根据非确定性工作量来改变功率水平。 通过频率的变化而不断改变电 压,这种方案在功率消耗方面的二次还原是有希望的。

1.5 挑战
在无线传感器网络的设计与实现中,最关键的挑战主要是能源的局限性、硬件限 制和覆盖面积。能源是无线传感器网络节点的最紧缺的资源,它决定了无线传感器网 络节点的使用寿命。随着及时通信日益成为重点,无线传感器网络节点就意味着要大 量的被部署在各种环境条件下,包括远程的和敌对的地区。由于这个原因,算法和协议



就需要生命周期最大化、稳健性、故障容错和自我配置。而在硬件方面的挑战是要生 产成本低和微小的传感器节点。关于这些目标,通常电流传感器节点具有有限的计算 能力和内存空间。因此,在无线传感器网络中应用软件和算法应该优化并且浓缩。为 用一个高稳定性和稳健性的不同信号节点来最大限度地覆盖范围,而低功耗多跳通信 会优先考虑。而且,要处理大型网络规模,对大规模的无线传感器网络所设计的协议 必须得以分布。

1.6 研究性问题
研究人员对无线传感器网络的各功能区都很感兴趣,其中包括设计、执行和操作。 这些功能区域包括硬件、软件、中间件,而中间件是在软件和硬件之间的基本物体。 由于配备电池供电操作节点的无线传感器网络通常都部署在资源有限的网络环境下, 研究者主要关注能量优化、覆盖区域的改善、错误减少、传感器网络应用程序、数据 安全、传感器节点的移动以及在传感器中路由算法的数据包问题。在理论方面,一大 群研究人员在无线传感器网络方面投入了大量的精力。他们关注各个领域,包括物理 性质、传感器训练、与智能节点协作的安全、介质存取、伴有随机的和确定性放置的 传感器覆盖、物体的定位与跟踪、传感器位置的确定、寻址、节能的播送和活跃性的 调度、路由能量转换、连接、数据收发、路由传感器的核心质量、拓扑控制和维护等。




[1] G . 5 . Cheung , J . Y . M , Azzi , 0 . Intelligenc in building : the prtential advanced modelling Loveday . D . L . Virk . Automation in Construction . 1997:447-461. [2] Kirill Yelizarov v . home security System . Microchip Technology InC .1998:44-48. [3] B.D.Moore. Tradeoffs in selecting IC temperature sensors. Microprocessors and Microsystems, 1999, 23:181-184. [4] AT89C51 DATA SHEEP Philips Semiconductors 1999:55-58. [5] Yang. Y., Yi. J., Woo, Y.Y., and Kim. B· Optimum design for linearity and efficiency of microwave Doherty amplifier using a new load matching technique, Microw. J., 2001, 44:20–36.






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