Proceedings of the 2009 IEEE 9th Malaysia International Conference on Communications
15 -17 December 2009 Kuala Lumpur Malaysia

GPS Based Child Care System using RSSI Technique
Kok Sun Wong, Wei Lun Ng, Jin Hui Chong, Chee Kyun Ng, Aduwati Sali, Nor Kamariah Noordin
Department of Computer and Communication Systems Engineering,
Faculty of Engineering, University Putra Malaysia,
UPM Serdang, 43400 Selangor, Malaysia.
{k_sun85, william_2909}@hotmail.com, {jinhui, mpnck, aduwati, nknordin}@eng.upm.edu.my
Abstract— In today's society, missing child cases increases rapidly. Child care is a critical issue in solving this epidemic.
Various systems and methods have been implemented in solving this crisis. In this paper, the global position system (GPS) based child care system is proposed to solve this problem. This system consists of two nodes; child and parent nodes, each carried by the child and parent respectively. The child node consists of a simple circuit that has a Bluetooth module and a GPS receiver. The parent node is a mobile device that has Bluetooth connection.
The GPS technology helps to determine the exact position of the child. The parent node receives the location of the child and displays the information on a designed map using a GUI program that is embedded into the mobile device. Besides the location, the distance between parent and child can also be determined using Bluetooth connection. A data from received signal strength indicator (RSSI) is extracted out from the
Bluetooth connection and is used as vital information in determining the distance between parent and child. An alert is triggered when the distance between the parent and child is far apart for a certain range. The proposed system proves to be useful as a locator that could locate missing and wandering child for the parents.
Keywords—

GPS, Bluetooth, RSSI, child care system.

I. INTRODUCTION
Globalization has resulted in increased employment opportunities. With urbanization, the employment rate is further increased for both men and women. A key issue that is raised year after year is the necessary trade-off between devotion to family versus to career. In effect, the complex and long working hours result in the compromise of the quality of child care among the employees. This is understated, yet an increasing psychological concern in the minds of many employees. This affects the overall performance of many employees as they worried on their well being of their child rather than work [1, 2].
There are a variety of child monitor gadgets available in commercial market space that provide child care system. The advantage of having child monitors are their capability to detect intelligently more than what care-takers or nannies can detect by intuition; that is monitoring the location of the child and their condition. However, gadgets have their own limitations and scope of application.
According to police statistics for the year 2003 to 2008, four children go missing every day in Malaysia, and three of

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them are girls. These startling figures also show that almost one-third of the 8,000 missing children or 2,500 children are yet to be found. While police have a list of reasons for a child's disappearance, there are no known causes for more than 1,700 children, one-fifth of the total. Between January and May 2008, more than 550 missing children reports were filed. The fear of child abduction is very real. It is something we understandably do not feel very able to cope with. Many parents feel better when they are able to see where their kids are. Hence, a system is required to help parents or guardians to keep track of their children and prevent this kind of tragedy
[3].
A child-safety group came up with the "Missing Children
Screensaver" project in the United States. This application draws on idle computer power to display updated news, information and photos of missing or abducted children. Each time the screensaver kicks in; it updates the contents providing the latest information available. Another child care program, the "AMBER Alert Program", named after 9-yearold kidnap and murder victim Amber Hagerman, is a partnership between law enforcement agencies, broadcasters and transportation agencies to activate an urgent bulletin in the most serious child-abduction cases, much like how information is spread during severe weather emergencies.
Descriptions of the abducted child and suspected abductor will be broadcast to the community. This approach uses a device to capture and digitize each child’s finger print electronically, store this information and provide encoding of this data for a transmit/receive device via global position system (GPS) locating. This design differs from other approaches in that it links to the America’s Missing Broadcast Emergency
Response (AMBER) database, and has onboard memory that provides a history of target movement, altitude, temperature, and speed direction. Since its inception 12 years ago, it has registered 421 successful recoveries [4].
In this paper, the development of a system named GPS based child care system is proposed using the combination of
GPS and Bluetooth technology. This system could provide parents the accessibility to locate their child. The system is compromised of two devices, each hold by parent and the child. The device carried by the child is known as the child node while for the parent is parent node. The child node consists of a GPS receiver module that connects to a
Bluetooth module with a microcontroller. The GPS receiver

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has the capability to calculate the position of the child using data received from GPS satellites. These data are collected by the microcontroller (MCU) and transmitted out to the detector device using wireless Bluetooth transceiver. The child node has the capability to transmit out data at a radius range of ten meters. The parent node is a server based application that analyzes the data received from the child node. It can be a
Bluetooth embedded laptop, a computer that connected with a
USB Bluetooth Dongle or personal digital assistant (PDA).
Parent can monitor and control the proposed system with the program user interface (or GUI) embedded in the parent node.
The parent node will alert the parent through received signal strength indicator (RSSI) from Bluetooth connection if the child is away from them five meters.
II. SYSTEM DEVELOPMENT
The proposed system is a system that detects the location of the child and the distance of child from the parent. The system consists of two devices as shown in Fig. 1, which are child node device and parent node device. The child node device is a Bluetooth GPS receiver that will be carried by the child while the parent node device is a mobile apparatus carried by the child’s parent. The child node is connected to the parent node via Bluetooth to form a piconet. In the Bluetooth transceiver, child node is the slave while the parent node is the master to be monitored by parent. When the child node is activated, the GPS receiver at the slave device determines the position of child from GPS satellites. The location determined by the GPS receiver is then sent to parent node via Bluetooth.
The developed program in the parent node will interpret the data received from child node and display the location data of the child. At the same time, the parent node will determine the
RSSI of the Bluetooth signal strength between child node and parent node. If child node is away from parent node for certain distance, for example five meters, the parent node will be alerted to aware the parent about the safety of their child.

Fig. 1. System devices.

A. Child Node Device
The child node is a device used to provide the information of the location of the child to the parent. The main components in this device are the GPS receiver and Bluetooth enabled. The GPS receiver is used to determine the location of the child by providing the data such as longitude and latitude of the location of the child to the parent. The data format of the Child Node is the NMEA0183 sentence format. The data

is sent to the parent via Bluetooth. The Bluetooth in the child node not only plays the role as a transmitter, but also contribute in the determination of distance between child and parent. The child node design consists of three main components embedded on it, which are Parallax GPS receiver, PIC16F84A as microcontroller and Bluetooth module KC-11. Each component has its own functions and responsibility. Figure 2 shows the process flow of child node development. The GPS receiver will calculate the position of child by calculating its position from at least four satellites. The necessary information is extracted out by the PIC16F84A. The encoded information is transmitted to the parent node via Bluetooth transceiver. Fig. 2. Process flow of child node development.

B. Parent Node Device
Parent node is a mobile device with the GPS based child care system program installed. The parent node is monitored by the parents. There are two basic requirements for a mobile phone to be used as a parent node. First and foremost, the mobile phone must be run under the operating system of
Microsoft Windows Mobile version 5.0 and above. The second requirement is the mobile phone must be Bluetooth enabled. A program is designed to be installed and run in the parent node. The software consists of the graphic user interface (GUI) for parents to connect the parent node to the child node, thereafter monitor the location of the child and also determine the distance of the child from them. Figure 3 shows the hierarchy of the designing process of the parent node. There are two types of application that has been designed which are
Windows Application and Mobile Application. The Mobile
Application is debugged in the emulator and also in the mobile phone with the operating system Window Mobile 6.
Since the emulator of Visual Studio 2005 does not consists of
Bluetooth function, therefore FreeBT USB Driver and
Bluetooth Mobile Device Emulator are required to solve the problem. Microsoft ActiveSync is required for the mobile phone to be connected to the Visual Studio 2005 in order to debug and install the application to the mobile phone.

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III. SYSTEM OPERATION
The process flow of the GPS based child care system is shown in Fig. 5. First of all the child node and the Bluetooth of parent node are turned on. When the child node is turned on, the GPS receiver is started to calculate its location by the received signal from satellites. The child node is ready to send the data via Bluetooth and waiting to transmit the data via
Bluetooth once it is connected to the parent node. When the mobile application at the parent node is run, the parent is required to select the Bluetooth device which is the Child
Node to be connected. Thereafter parent is required to select the communication port for the communication between child node and parent node. Once the two devices are connected, the Bluetooth GPS receiver sends the data of the location of the child to the parent node. The parent node retrieve the required data and display the location and RSSI value at the
GUI. If the child node is away from the parent node more than five meters or the connection between the child node and parent node is lost, parent will receive alert from the parent node. Fig. 3. Hierarchy of the designing process of the parent node.

C. RSSI Calculation
Distance between child and parent is an important issue in the GPS based child care system. Therefore, the required calculations of the distance between child node and parent node are estimated by an approximation of the RSSI. The relationship between distance and RSSI can be derived as y = - 13.3 ln (x) - 47
(1)
where y is the measured signal strength and x is distance. The value of RSSI calculated from the equation above is the theoretical result. The result is compared to the practical result which is the RSSI value measured.
Since the Bluetooth device do not provide any interface to extract the real received signal strength, the distance measurement in the proposed system is using the RSSI value retrieved by the designed program in order to derive the range of estimation between the child node and parent node. The
RSSI value is obtained with the coding as shown in the Fig. 4.
For precise position estimation, the dependence between the distance and the received signal strength is determined by carried out few experiments under different conditions. The measurement of RSSI is obtained by placing the child node in indoor, outdoor, inside a box, and in the bag. The obtained results are compared in order to determine the impact of the location of the child node to the RSSI value.

Fig. 4. The coding for retrieving RSSI value.

Fig. 5. Process flow of the GPS based child care system.

The signal transmitted by the child node is retrieved and interpreted by the parent node. The parent node consists of three pages in order to display the retrieved and interpreted data. The three pages are main page, data page and map page.
A. Main Page
Figure 6 shows the layout of the main page designed. The search button is used to search the available Bluetooth device.
After the parent node found available Bluetooth device, the name of the available devices are shown at the first
ComboBox. After the Bluetooth device to be connected is selected, parent is required to select the communication port for thereafter click the Start button to connect to the Bluetooth device selected.

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If device.Rssi < -13 Or device.Rssi > 125 Then
MessageBox.Show("Alert!! Child is far away!!")
End If
If myGPSToolKit.IsGPSConnected = False Then
MessageBox.Show("Bluetooth not connected!!")
End If

Fig. 9. The coding for checking the status of the child node.

Fig. 6. The main page of parent node.

B. Data Page
The data page as shown in Fig. 7 is used to display the data of the location of the child. The data displayed includes latitude, longitude, altitude and RSSI. Besides, the status of the connection is shown at the bottom of data page.

IV. RESULTS AND DISCUSSION
The child node and parent node are tested and the results are recorded. The results from RSSI, Child Node and Parent
Node are compared and discussed. Some experiments are handled in order to test and check the functionality of GPS
Child Care System. The RSSI value determined from the connection of two Bluetooth devices can be used to determine the distance between them. The RSSI is obtained by calculation and measurement of the signal strength between two Bluetooth devices. The result calculated from equation (1) is used to plot the graph of RSSI versus distance as shown in
Fig. 10.

Fig. 10. Graph of calculated RSSI versus distance.
Fig. 7. The data page of parent node.

C. Map Page
The location of the child is interpreted thereafter displayed on the map. Figure 8 shows the layout of the map page designed. Parent will receive alert when the child is away more than five meters from them or when the child node is disconnected from the parent node. Figure 9 shows the coding used to check the status of the child node.

The graph plotted shows the RSSI value is inversely proportional to the distance between two devices. The retrieved values of RSSI are recorded in Table 1 based on different conditions such as indoor, outdoor, in a bag, and inside a box. These retrieved values are based on the code shown in Fig. 4. The retrieved value is unitless because different companies define their measurement in different manner [5]. From the data measured shown in the Table 1, the
RSSI retrieved at indoor, outdoor, and inside a closed bag or box is almost the same. Therefore, the effect of the location of the child node in obtaining the RSSI value is not a concern.
Table 1. The retrieved RSSI values at various conditions.

Fig. 8. The layout of the map page in parent node.

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These retrieved values shown in Table 1 are plotted as shown in Fig. 11. The plotted graph is almost similar to calculated graph that shown in Fig. 10. If the RSSI is within the Golden Receiver Range, the retrieved RSSI is zero. If the
RSSI is below the Golden Receiver Range limit, the retrieved
RSSI is a negative value. If the RSSI is above the Golden
Receiver Range limit, the RSSI retrieved is a positive value.
The retrieved RSSI value is varied within the margin of ± 3 at certain distance. For example, at the distance of five meters, the RSSI value is at average of -13. By referring the graph in
Fig. 10, the RSSI value is approximately at - 70 dBm for five meters distance. Hence, when the RSSI value is lower than this value, meaning that the distance between Child Node and the Parent Node is more than five meters, hence an alert message is sent to parent. The distance of five meters is chosen as a threshold value because the selected Bluetooth transceiver could only support within ten meters range.
Figures 12 to 16 show the snapshot of the tested GPS based child care system. When the parent clicked the search button at the main page, the designed program is start to search for the available Bluetooth device in range as shown in Fig. 12.
After the searching process is finished, parent is required to select Bluetooth device to be connected and the communication port as shown in Figs. 13 and 14. When the parent node is successfully connected to the child node, the data of the location of child will be displayed as shown in the
Fig. 15. If the child is away from parent more than five meter or the child node is disconnected from the Parent Node, parent will receive alert message as shown in Fig. 16.

Fig. 11. The graph of retrieved RSSI values at various conditions.

Fig. 13. Select Bluetooth device to be connected.

Fig. 14. Select communication port.

Fig. 15. Data of the location of child.

Fig. 16. Alerting message.

Fig. 12. Searching available Bluetooth device.

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V. EXPERIMENTAL AT TOWER BLOCK CAR PARK
The designed GPS based child care system is tested at
Engineering Tower Block car park. The child node is placed at different places while the location of the parent node is fixed, as shown in the Fig. 17. This figure is sketched without any scaling. The obtained results are recorded in the Table 2.
By referring to Table 2, the location of child can be obtained when the child node is away from parent node less than ten meters, which are at points 1, 2 and 7. The location of child at point 3, 4, 5 and 6 cannot be determined since the child node is apart from parent node more than ten meters.

VI. CONCLUSION
The GPS based child care system has been successfully designed and implemented. The suitable Bluetooth tranceivers are used to represent the child node and parent node in the proposed system. As conclusion, the system is able to protect the child safety by monitoring the location of the child.
Overall, the basic prototype was developed and tested with successful workability. However, the current proposed system could not save the location of child. Therefore, the addition of database is recommended for future implementation. The database can be used to store the history of child location and also the map. The parent node in the system can only monitor one child node. Hence, it is recommended to modify the parent node in order to monitor more child nodes.
Additionally, this is recommended to used a transceiver that can cover wider range so that the child’s location can be detected. REFERENCES
[1]

[2]
Fig. 17. Map of the Engineering Tower Block car park.
Table 2. Data retrieved by the parent node.

[3]
[4]

[5]

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D. Sampath and S. Sundaram, "Telecommunication System for Remote
Monitoring and Access in Child Care," IET International Conference on Wireless, Mobile and Multimedia Networks, pp. 81 - 84, 11 - 12 Jan.
2008.
D. J. Bendz and K. A. Bendz, "Balancing Work Life Issues: A Two
Dimensional/Two Generation Perspective," International Symposium on Technology and Society, Women and Technology: Historical,
Societal, and Professional Perspectives Proceedings, pp. 223, 29 - 31
July 1999.
S. Suparmaniam, L. Dhanangunan and I. L. Mokhtar, "STRESSED
OUT: Wrong Priorities Harming Children," Malaysia's New Straits
Times Newspaper, Frontpage, 17 Nov. 2008.
A. B. Russell, H. G. Nik, R. Kangarloo and S. Nooristany, "AMBER
Child
Protection
System,"
http://mason.gmu.edu/~hghaffar/AMBER_Project_files/FinalPresentati on.pdf. Wild Packets, “Converting Signal Strength Percentage to dBm
Values,” Nov. 2002.