Design of Streetlight Monitoring and Control System Based on Wireless Sensor Networks

Chunguo Jing, Dongmei Shu and Deying Gu Automation Engineering Department

Northeastern University at Qinhuangdao 066004 Qinhuangdao, China

Abstract- The remote streetlight monitoring and control system has been applied in urban streetlight. In general, this system monitoring and control scope only reaches the streetlight transformer station. In this work, an experimental system of wireless sensor network was developed to study the feasibility for streetlight monitoring and control system. This system consists of the sensor node, the remote terminal unit and the control center. The sensor node was installed at each lamp pole and used to detect and control lamp. The remote terminal unit serves as relay station between the control center and the sensor nodes. The control center monitor and control all streetlight real time. The hardware of sensor node and remote terminal unit was design. The software was developed for sensor node, remote terminal unit and the control center. The multi-hop used in nodes. The test results show that the system can be used for the streetlight control. The system application in streetlight can extend control scope to each lamp, reduce in streetlight electricity and maintenance cost, and increase availability of streetlight.

I. INTRODUCTION

Streetlight is an indispensable part of a city’s infrastructure, the main function of which is to illuminate the city’s streets during the dark hours of the day. It also has a function to decorate street and even has some effects to reduce traffic accident and street crime [1, 2]. So it is important for the public and city governor to guarantee street lighting normal on and off. In the beginning, street lighting was switched on at dusk and switched off at dawn by manual operation, and then the smart controller was used to switch street lighting on and off automatically based on sunrise/sunset times light intensity of controller surroundings [3] at each transformer station. Although the smart controller can automatically turn streetlight on and off, the cases of street lighting on at daytime and off at night often occur because the smart controller time is wrong or the light sensor is covered with dust or whatever. These increase the public dissatisfaction with improper streetlights and will lead to some potential danger for street vehicle and pedestrian. In order to find out failure streetlight and reduce wasted energy, the maintenance man needs to patrol street by street at night and day. This increases the maintenance and management cost. Since above reasons and streetlight function diversification, the streetlight control by smart controller can’t meet with the requirements of streetlight control.

Now the remote streetlight monitoring and control system was widely used for street lighting monitoring and operation.

The system is consists of the control center, remote terminal unit (RTU) and communication devices [4]. The control center is responsible to control and monitor the whole streetlight system. The RTU installed at each of the streetlight transformer station and uses to control and monitor each of the remote sites. The radio and general packet radio service (GPRS) are two main technologies for communication between the control center and RTU. The remote streetlight monitoring and control system realizes real-time centralized management and control for all RTUs, but the system control scope only reaches the streetlight transformer station, the individual lamp status could not be detected by this system. In order to control, monitoring and diagnosing hundreds of thousands of lamps from the control center, the wireless sensor network was used in the remote streetlight monitoring and control system. An experimental system was built to study the feasibility of streetlight control using wireless sensor network.

II. WIRELESS SENSOR NETWORKS

Some existing technology such as Power Line Carrier (PLC) can also be used for the purpose of the individual lamp control and monitoring. But PCL technology has some problems such as noise, the changing of lines input impedance, carrier signal attenuation that often lead to communication failure. So wireless sensor network was chosen for streetlight control in this work.

Sensor Node

Sink Node

IP Net work

User Computer

Fig. 1 A schematic of wireless sensor network systemWireless sensor network (WSN) is a new technology in

recent years. Many researchers have put their effort to study wireless sensor network. It is considered as a technology to connect information world with physical world together. A wireless sensor network system consists of sensor nodes, sink nodes, Internet or information transport network and user computers [5]. Sensor nodes communicate with each other using wireless mode and operating at ISM band. The node

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sending power is restricted, so it forces the node using multi hop network to deliver data. Figure 1 is a common wireless sensor network schematic.

In wireless sensor network, the sensor nodes are organized into a set of node clusters; each node belongs to at least one cluster. Every cluster has a sink node that acts as a local controller for the nodes in that cluster or connect to the remote user computer through IP network.

Fig. 2 Architecture of sensor node in wireless sensor networkThe node architecture of wireless sensor network often

consists of three layers: a physical layer, a medium access control (MAC) layer and an application layer [6]. Each layer provides services for the above layers using well-defined interfaces. Figure 2 shows the layer architecture of a sensor node and the functions of each layer. In different application, the physical layer will have some distinction, these includes senor type, actuator and the number of sensors.

The main features of wireless sensor networks are low cost and distribution in large numbers. To achieve the economies of scale needed to reach a large market at low cost, certain features of wireless sensor networks need to be standardized, so that the products from different manufacturers may inter-operate. There are two standards about wireless sensor network that published by IEEE. They are the IEEE 802.15.4 Low Rate Wireless Personal Area Network (WPAN) standard [7] and the IEEE 1451.5 Wireless Smart Transducer Interface standard [8]. So it needs to follow these standards in study and design wireless sensor network.

The potential applications of wireless sensor network include industrial control and monitoring, home automation and consumer electronics such as wireless keyboards and personal computer (PC)-enhanced toys, security and military sensing, asset tracking and supply chain management, intelligent agriculture, and health monitoring [9]. In this study, an experimental wireless sensor network system was designed to control, monitor and diagnose the streetlight.

Streetlight system control and maintenance is a labor-intensive high-cost task for the streetlight department. Using wireless sensor network on streetlight has following advantages. First, the flexible control methods of streetlight can greatly save the energy consumption. For example, the system could permit every second or third lamp to be lit at a very late hour when few people are out. The system also has dimming control function, Individual or a bank of street lights can be dimmed up to 60 percent of the rated light intensity levels during low traffic periods. A study by Echelon Corporation shows that using street lighting monitoring

system could cut streetlight energy costs by 30 percent while increasing roadway safety [10]. Secondly, the sensor node that mounted on individual lamp pole can monitor every lamp status; it replaces physical patrol maintenance along the street. Therefore it reduces the maintenance and management cost significantly. Thirdly, real time remote monitoring ensures immediately detection and quick recovery of RTU or streetlight failure, it improves the public satisfaction to streetlight, reduces calls of service.

III. SYSTEM ARCHITECTURE

The remote streetlight monitoring and control system based on wireless sensor network technology is consists of the control center, RTUs, GPRS module and wireless sensor nodes. Figure 3 shows a structure of the remote streetlight monitoring and control system using wireless sensor network. The sensor nodes were installed at each street lamp pole. Due to the restriction of the sensor node power, the sensor node uses multi-hope routing transmitting data. All sensor nodes that power by same transformer station make up of a cluster. RTU performs sink node function in this cluster. In order to simplify the routing from RTU to the control center, the information transmits between RTU and the control center using GPRS network.

Control Center

Transformer Station

Streetlight Pole

Sensor Node

GPRS

Fig. 3 The structure of streetlight power cable monitoring system based on wireless sensor networks

The application which running on the central computer is used to control and monitor the streetlight system. It includes many features such as displaying system topology and geographical maps, updating RTUs and lamps with the relevant information, setting lighting schedules, sending control commands to RTU, audible and visual alerts upon failures, forwarding SMS alerts messages to personnel cell phones, producing report sheet. Figure 4 illustrates a screen shot taken from a streetlight application.

The RTU serves as the sink node at each streetlight transformer station, and as such is responsible to control and monitor sensor nodes within it’s coverage area, communicate with the control center using GPRS module, and store the relevant data. RTU also gathers information about the single lamp status, power line voltage and current, processes these data and sends them to the control center or acts accordingly.

The sensor node is responsible to control and monitor pole lamp. It switches lamp on and off according received commands from RTU. The sensor node also has dimming

Senor, actuator, transmitter, receiver, local data storage, A/D and D/A converters

Routine protocol, multiple access control, packet data format

Software, Internet, interface, application Application layer

MAC layer

Physical layer

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street lighting function. The data transmission between the sensor node and RTU is using multi-hop protocol.

Fig 4. A screen shot taken from a streetlight application The GPRS module serves as a gateway between the control

center application and the remote RTUs via the GSM network. It is a connectivity solution based on Internet protocols. It is available with almost every GSM network. The GPRS throughput rates can reach up to 115kbit/s. So it is particularly suited for sending and receiving small bursts of data.

IV. SYSTEM DESIGN

System design includes the following items: RTU hardware design, sensor node hardware design, RTU software development, sensor node software development and central application development.

A. Hardware DesignSince there are hundreds of thousands of street lamps and

hundreds of the streetlight transformer stations in a big city, the individual node and RTU have to be inexpensive so that the investment on the streetlight monitoring and control system could be returned within the next several years. Low cost and high-integrated devices need to be considered in hardware design.

Sensor Node Design: The WSN sensor node has both sensing and communication capabilities and can work as a transmitter node, a receiver node, or a relay node. There are hundreds of thousands of lamp poles in a city, so the WSN sensor node hardware design is the key for low-cost wireless sensor network. The single chip microcomputer unit (MCU) type, radio transceiver should be carefully selected to meet the low cost, high capability in designing node hardware. There are many MCUs and radio transceivers can be chosen in commercial market. The available MCU includes ATmega 128, PIC16F8X and ARM 7/9 etc. The available single chip radio transceiver includes nRF903, nRF2401, CC1000, CC2420 etc. The determination of chips should be considered features, price, peripheral extend capability and so on. Figure 5 illustrates a WSN sensor node hardware designed according to MICA2 [11] and used in this work.

The AVR 8 bit microcontroller ATmega 128 was chosen in this design because it offers a 16 MIPS performance, 128K bytes in-system programmable flash, sufficient peripherals

like 8 channels 10 bit ADC, UARTS, SPI serial interface, I/O ports, two 8-bit timer/counters, six sleep modes can running at a very low energy consumption [12].

MCUATmega128

SignalRegulat ion

CurrentTransformer

PowerAmplifier

Actuators(Relay)

RadioTransceiver

CC1000

Fig. 5 Block diagram for sensor node hardware architectureThe radio transceiver CC1000 uses a FSK modulation

scheme in the 315/433/868 and 915MHz ISM band. The frequency can be changed by program. The power consumption is very low, the maximal transmitting current is 7.4mA and supply voltage is between 2.1V to 3.6V. It requires very few external components. The data rate is up to 76.8kBaud [13]. So it fits for short-range wireless communication applications and used in this design. In this work, the frequency was chosen at 433MHz and its range up to 200 meters.

The sensor node turns street lamp on and off according to receiving commands from RTU. The sensor node determines lamp status through detecting power line current. The lamp status sends to RTU only when lamp status changes. If it is lamp on time and the sensor node reports lamp off status, it should be think that the lamp occurs failure and needs to send lamp current status to the control center. Since vary sensor nodes have different identities, the control center can identify fault lamp and display it on geographical map. The maintenance man can quickly arrive fault lamp place and repair it.

RTU Design: The remote terminal unit is an embedded system. Figure 6 is a block diagram for RTU hardware architecture. The MCU and radio transceiver chosen in RTU design are same as the sensor node hardware for simplifying RTU hardware and software design.

MCUATmega128

SignalRegulation

Keyborad and LCD

Volt ageTransformer

CurrentTransformer

Light IntensitySensor

PowerAmplifier

Actuators(Relay)

Meter ReadingModule

GPRS Module

RadioTransceiver

CC1000

RS-232

Fig. 6 Block diagram for RTU hardware architectureIn order to simplify the RTU routing and improve the

reliability of system, all messages transmit between RTUs and the control center using GPRS protocol. In this design, the GPRS module is chosen the G18 wireless modem that comes from Motorola Communications Ltd. The interface between the MCU and G18 module is RS-232 at 9600bps. The G18 module is controlled via AT commands and allows connecting any embedded system or devices to the Internet

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using the GPRS protocol over GSM network. This module is compatible with 900MHz/1800MHz/1900Mhz frequencies of cellular networks across the world [14]. In this application, the TCP/IP packet was transmitted through G18 module.

RTU mainly serves as sink node, it also has control and data acquisition functions. The sensor nodes may not be installed on the lamp pole in some less importance and far from the center streets for shorting capital reason. In this case, the RTU directly turns streetlight on and off by means of controlling relay to switch power supply on and off at transformer station. The current street lighting status was determined by detecting power line current. If the sensor node was mounted at each lamp pole, the RTU sends control commands to every sensor nodes and receives lamp status from the sensor node. The meter-reading module is used to sum total energy consumption in transformer station range. The light intensity can be used to switch lamp on and off when it occurs abnormal weather such as rainy, snowy or foggy. The RTU can independently run without the control center management. The lighting on/off schedules reside in each RTU. This feature enhances the system reliability.

B. Software DevelopmentThe software development of remote streetlight monitoring

and control system includes the sensor node software development, RTU software development and the central application development.

Sensor node software development: The best way to develop software for the sensor node is to use the operating system TinyOS [15, 16] along with the programming language nesC [17, 18]. TinyOS is an event-driven operating system designed for sensor network nodes that have very limited resources. TinyOS supports modularity and event-based programming by the concept of components. A component contains semantically related functionality, for example, for handling a radio interface or for computing routes. Such a component comprises the required state information in a frame, the program code for normal tasks, and handlers for events and commands.

The nesC language is an extension to the C programming language designed to embody the structuring concepts and execution model of TinyOS. It allows a programmer to define interface types that define commands and events that belong together. This allows to easily expressing split-phase programming style by putting commands and their corresponding completion events into the same interface. Components then provide certain interfaces to their users and in turn use other interfaces from underlying components.

In this study, using nesC language under TinyOS developed the sensor node software. The following is an example of nesC program.

configuration TimerC { provides {

interface StdControl; interface Timer; }

}implementation {

components TimerM, HWClock; StdControl = TimerM.StdControl;

Timer = TimerM.Timer; TimerM.Clk -> HWClock.Clock;

}The multi-hop is basic feature of WSN route protocol

because the sensor node energy is limited. Sensor networks are dense wireless networks of heterogeneous nodes collecting and disseminating environmental data. There are many scenarios in which such networks might be used. Wireless sensor networks consist of hundreds or thousands of small, cheap, battery-driven, spread-out nodes bearing a wireless modem to accomplish a monitoring or control task jointly. Because above feature of WSN, many route protocols were presented such as energy-aware routing, directed diffusion, geographical and energy aware routing. In this application, the battery of sensor node can be recharged every night, the energy isn’t main problem. The numbers of the sensor node in a transformer station scope is limited and the position of each sensor nodes is also fixed. So the sensor node routing is designation route. To avoid routing broken caused by node failure, every node assigns two relay nodes, one is running and another is backup.

RTU software development: Because the MCU and radio transceiver of RTU are same with the sensor node, the RTU software development is also used nesC language under TinyOS. The partial codes used in sensor code can be reused in RTU software development. The primary difference is that RTU needs to communicate with the control center using GPRS protocol. The G18 module is a GSM900/1800/1900 device with GPRS capabilities, but it is not directly support TCP/IP application. In order to transmit TCP/IP packet through G18 module, it needs to develop GPRS API to sending and receiving TCP/IP packet over Internet. These APIs manage input and output streams exactly as the Socket API do. To maintain this modularity, these streams must be kept very similar to the Socket API but with extra functionality added. Therefore, three classes were defined to manage G18 module.

thrMonitor: Thread that checks the signal strength. When the thrMonitor detects low signal strength, it will send an Exception describing the problem.

GPRSSocket: Class uses to initialize and set up the G18 device.

Server: Server that receives the I/O streams once the socket session has been established.

The GPRSSocket class initializes and configures the device using AT commands. Every command calling the G18 device generates a reply. Depending of the type of command is the type of the reply. Every reply ends either with an OK or with an ERROR message. If the command was issued to obtain information then the information is received and is ended with an OK message. For example: to know the signal strength, the following command is issued:

AT+CPIN And the reply would be: +CPIN:20,1 OK If using AT commands initialize G18 device. It must

perform the following steps: 1) Define the GPRS connection.

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For example: AT+CGCONT=1,“IP”,“APN”,“0.0.0.0”,0,0 //APN should be replaced with the provider name

2) Define Quality of Service. For example: At+CGQREQ=1,0,0,0,0,0 3) Define minimum acceptable Quality of Service. For example: At+CGQMIN=1,0,0,0,0 4) Activate PDP context using the AT+CGACT=1 command.The algorithm for calculating the sunrise/sunset times

according to the RTUs location and the current date is implemented in RTU. When the power lines do not install the sensor node, the RTU directly turns on and off based on sunrise/sunset time.

The Control Center Software development: The control center software is the core of the remote streetlight monitoring and control system. The central application should have following features: First, the software should be easy to use and interface must be friendly. Secondly, the application should be configurable and extendable. When the new RTU was mounted, it can be easy to add in system. Thirdly, the geographic information system (GIS) should be used for displaying RTUs and sensor nodes position and status. In order to meet all these requirements, the software was developed using Borland C++ Builder 5.0 and MapInfo MapX 5.0. The software runs on Windows 2000 operate system.

Borland C++ builder (BCB) is a RAD program tool. It allows programmer changing the program visually, rather than program code. The core of this technology is component. BCB programming is surprisingly easy. Programmer only puts some VCL can implement a simple program. So BCB was selected to write the control center codes in this application.

Mapx is an ActiveX, it developed by MapInfo Corporation. It easy integrates MapX into new and existing applications with Visual Basic, Visual C++, and Delphi. So it is easiest, most cost-effective way to embed mapping function into application [19]. In this application the MapX was used to implement GIS function.

Fig. 7 Map of Streetlight power cable monitoring The red flags indicate the position of fault lamps and RTUs

Figure 7 shows the partial map of the remote streetlight monitoring and control system screen shot. All sensor nodes and RTUs display on the map. Once sensor node detects the lamp state changing, it sends status information to the control center through RTU and its state immediately display on the

map. The user can find fault RTU or lamp and decide to repair it.

The database functions were implement by Microsoft Access 2000. All sensor node and RTU names and parameters saved in database. The acquisition data and alarm information also saved in it. All data can be produced as a report and also can be print out.

V. CONCLUSIONS

In this paper, a design of the remote streetlight monitoring and control system based on wireless sensor network architecture was presented. The sensor node and RTU hardware were designed using ATmega 128 MCU, CC1000 radio transceiver and G18 wireless modem. The sensor node and RTU software were developed using nesC language under TinyOS operate system. The control center software with GIS functions also were developed using BCB and MapX. The results show that wireless sensor network can be used to monitor and control each street lamp. This system applied in streetlight department will reduce energy consumption, lower management and maintenance cost, and improve public satisfaction to streetlight. The design can also serve as a platform for many other applications and researches in wireless sensor network. The future work include that lower the sensor node cost, test the sensor nodes communication reliability and the control methods in abnormal weather etc.

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