Using RFID-Capable Cell Phones for Creating an Extended Navigation Assistance

Transcription

1 Using RFID-Capable Cell Phones for Creating an Extended Navigation Assistance Andreas Loeffler and Dina Kuznetsova Chair of Information Technologies Departement of Electrical, Electronic and Communication Engineering Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany {lfr, Uwe Wissendheit Fraunhofer Institute for Integrated Circuits IIS Erlangen, Germany Abstract This paper offers an RFID-based indoor navigation application which utilizes cell phones with an RFID extension and distributed RFID tags fixed to interior equipment. This combination creates a special navigation environment which helps pedestrians to orient oneself in new respectively unknown environments. Therefore, each RFID tag contains information about the current position, location or an unknown environment. Thus, the current position can be determined, which is the basic for navigation. A further advantage of this application is the availability of additional graphical data stored on the RFID tags. This additional graphical data contains global information about the indoor environment and also local graphical information about the near environment of the RFID tag. This yields to an RFID-based navigation system, that not only shows the current position but also the near environment surrounding that specific location. Therefore, this systems grants navigation assistance by leading the user step-by-step or rather tag-by-tag to the final destination. I. INTRODUCTION Radio frequency IDentification (RFID) affects more and more our everyday life [1]. This starts with simple RFIDsystems such as EAS 1 -Systems or ski passes and ends with more complex RFID-systems, e.g. passport control or automatic toll systems. A simple RFID system as briefly described in Fig. 1 consists of one RFID reader (interrogator) and one or more RFID tags. The reader is able to read the data stored on the RFID tags, or to write data into the tags. This ability to read and write data distinguishes RFID from bar code. Also, there is no need for a line of sight as the communication between the reader and the tags is based on electromagnetic principles. In general, RFID tags have no own energy supplies, therefore they are supplied by the reader s energy field. The two principles RFID is based on, is first, the principle of backscatter, and second, the principle of inductive coupling. However, the RFID-based navigation system described in this paper is based on inductive coupling, thus only this principle is discussed furthermore. The frequencies of inductive operating RFID systems are at LF (about khz) and HF (13.56 MHz) frequencies. The two commonly used HFstandards are ISO and ISO This work is based 1 Electronic Article Surveillance. RFID-reader / interrogator Fig. 1. Antenna Energy & Data Data Antenna Simple RFID system RFID tag on the ISO standard (including the MIFARE extension) at MHz [2]. Using this standard, the range of the RFID system is limited to a few centimeters [3]. One important part concerning RFID systems and particularly tags is the available memory size of the applied tags. The current size of MIFARE tags is limited to a maximum of 4096 bytes (4k). Dealing with RFID inevitably leads to a technology called near field communication (NFC). The NFC technology is based on RFID (ISO 14443/MIFARE) at MHz and describes a peer-to-peer communication standard. The NFC standard [4] is used to connect two devices (e.g. a cell phone and a notebook) or is used to read ISO 14443/MIFARE based RFID tags. Nowadays, there exist a whole range of devices which implement the NFC technology, among these also cell phones. One of these NFC-capable cell phones is the Nokia 6131 NFC which is used in this work as a mobile RFID reader. Expanding on this idea of combining RFID and cell phones lead to the idea of creating an RFID-based navigation system. If we discuss navigation for pedestrians, we would think of satellite navigation systems as GPS and in future Galileo and GLONASS. The disadvantage of such systems is, that the satellite signals are hard to detect in buildings or other shielded areas. This in turn leads to alternative navigation systems, e.g. the fusion of WLAN navigation (with reference points) and inertial navigation systems [5] to get a very accurate position. Of course, WLAN access points (APs) must be installed and the map of the building must be available, too. Also, the WLAN reference map (with the reference points) must be available to the person/vehicle, which wants to navigate in a building. As positions of APs or interior equipment changes with time, the WLAN reference map must be updated frequently. One solution to avoid these drawbacks is the exclusive or additional /09/$ IEEE 471

2 usage of an RFID-based navigation system described in the following sections. Start Fig Operating principle of RFID-based navigation system Final destination II. MOBILE NAVIGATION WITH DISTRIBUTED RFID TAGS Briefly, the navigation system works as described in the following, referring to Fig. 2: The user starts the java-based mobile application RFID on the cell phone. After that, the application asks the user to choose between loading a previously available map or generating a new map. Assuming there is no previously defined map available, the user generates a new map and is prompted to enter the coordinates of the final destination in latitude and longitude. In general, these coordinates could also be local defined, instead of being global coordinates. Subsequently, the application asks for the first RFID tag. According to Fig. 2 this would be RFID tag #1. Reading out the data of the tag will give the user the current position (in latitude and longitude coordinates) and an overview of the surrounding environment of the RFID tag. In that case the cell phone would show the map with the rectangular area of map #1 (seen at the bottom of Fig. 2). In addition to the current position the tag also provides (if desired) local information about the object or spot it is attached to, e.g. a room number. The cell phone draws a red dot, which shows the current position (respectively the position of the RFID tag) of the user. Furthermore, a green dot shows the final destination and a orange line links the red and the green dot. However, the user walks along the floor and reads out #2. 4 Therefore, the current position changes (red dot) and the map is expanded (by map #2) through the additional data, stored on tag #2. The cell phone shows the extended map and the new current position and if available an additional description. Following this procedure the user reads out tag #3 and #4, until the final destination is reached (red and green dot are very together). III. RFID-BASED NAVIGATION SYSTEM The RFID-based navigation system (Fig. 2 shows the operating principle) splits into two main parts. The first part of the system consists of an RFID-capable cell phone 2, whereas the second part consists of various distributed RFID tags 3. These tags are fixed on objects in particular locations, e.g. office plates, walls, etc. The data stored on the tags include, among other data, the position of the fixed tag. Position data covers latitude, longitude and elevation. Additionally, a description of the location is also stored on the tag (e.g. the room number). Reading such a tag would offer the user only the position and a description of it, whereas the environment (e.g. the surrounding area and/or map) is still not considered. Beyond that, our proposed RFID-based navigation system extents the location data, by additionally storing data on the RFID tag, including graphical data like an extract of the map or the surrounding area of the tag. Featuring such additional graphical information enables users of these RFID-based navigation systems to orient themselves in the near environment of the RFID tag or current position, provided that the graphical data on the tag represents the near environment. Getting back to the first part of the system, consisting of the RFID-capable cell phone. The user of the system requires the cell phone to read out the RFID tags and also to show the position of the tag and the graphical information of the tag along the way to the final destination. Every newly read out RFID tag provides the user with a new current position (location data) and a new current environment (graphical data). This principle is shown in Fig. 2 walking along tag #1 to #4. The extract of the whole map, which is partly stored on the RFID tag, the current position and the final destination is showed on the cell phone, which gives the user the chance to navigate from Start to Final destination. An NFC-based cell phone is used for this navigation application as it might be possible that more and more new cell phones will inherit the capability to communicate via NFC [6]. IV. PREPARING THE RFID-BASED NAVIGATION SYSTEM This section shows briefly the basics of the navigation system, e.g. the used data formats, and the steps to take to prepare the navigation system for the usage with the RFIDcapable cell phone. Hence, the next subsection IV-A will introduce the GIDS-format, which describes how the data (location and graphical) is stored on the RFID tags. Subsequently, subsection IV-B describes the software application 2 Nokia 6131 NFC, Firmware Version MIFARE RFID tags, based on MF1ICs50 from NXP Semiconductors, 1024 bytes of memory 2009 SBMO/IEEE MTT-S International Microwave & Optoelectronics Conference (IMOC 2009) 472

3 DesktopApplication which is necessary to divert a complete map (picture, building plan, etc.) into smaller map extracts fitting on the RFID tags, whereas the mobile application MobileApplication running on the RFID-capable cell phone puts these map extracts physically into the memory of the RFID tags. A. GIDS format The GIDS format is a fairly arbitrarily chosen format, defined in [7]. This format was originally introduced to store location data on RFID tags. As not only the pure location data is of interest to a user, an attempt was made to extend the formerly GIDS format by adding graphical data, i.e. the local environment around the RFID tag. In that case the user has not only knowledge about the current location, but also about the near environment. How near the near environment really is, depends very much on the available memory capacity of the applied RFID tag. Our approach uses RFID tags with a memory size of 1024 bytes, but only 752 bytes are available to the user. The rest is used for security issues according to the MIFARE standard. Table I shows the basic structure of the extended GIDS format. The text string GIDS ushers the start of a GIDS tag. Location data describes the location data as latitude, longitude, elevation and description of the position. All but description are fixed in byte length (4 bytes). That means, the longer the description of the position, the less memory will be available on the tag for the storage of the subsequent graphical data. The text string ENDG ends the Location data. Up till this point the mentioned format equals the former GIDS format. The text string PICG describes the start of the extended GIDS format. Global graphical data contains data of the complete (global) map, not the extract. This data includes the size of the complete picture/map in pixels and factors to convert xy-coordinates given in pixels to latitude/longitude coordinates and vice versa. Using this data enables the user to generate a new map (see section II). The number of bytes for the block Global graphical data is fixed to 32 bytes. The block Local graphical data (PNG-file) contains picture data given as PNG data [8]. Depending on the length of the description, the block Local graphical data (PNG-file) can be longer or shorter, therefore carrying more or less graphical information for the user of the RFID-based navigation system. B. Mapping location and graphical data on RFID tags This subsection shows the procedure on how to store the location data and the surrounding environmental data (graphical data) into an RFID tag. This procedure is split into two parts. Part one uses a java-based tool called DesktopApplication which runs on a PC. This tool divides a given map, picture or building plan into smaller pictures (graphical data) and also extracts the position of the extracted smaller picture (location data), in reference to the whole map. The DesktopApplication exports this extracted data as ordinary files (special datasets). After uploading the exported files to the cell phone 4, the mobile application called MobileApplication is started on the cell phone (part two). This tool just writes the formerly exported data into the RFID tags. 1) DesktopApplication: Fig. 3 shows the operating principle of the DesktopApplication. After loading the tool the user is prompted to choose a basic map for the environment. This can be any map, picture etc. Up to date only PNG 5 -files are supported. After choosing the map the user must enter two coordinate pairs (Step 1). Both pairs define an xy-position in pixels and the appropriate longitude/latitude-position on the map. These coordinates definitions are necessary to convert x- and y-positions in pixels of the map to a longitude and latitude position and vice versa. Of course, the user is given the possibility to choose an arbitrarily longitude/latitude pattern. In Step 2 the map is divided into small picture extracts. Each map extract (graphical data), including the location data, will later be stored on an RFID tag. The size of the small map extracts depends mainly on two reasons, if it is assumed that the tag s memory is fixed, e.g. to 752 bytes. The first reason is the length of the description of the location data. The longer the description, the less memory is available for the graphical data. The second reason is the color depth of the picture. For instance, the usage of only black and white colors will lead to 1 bit per pixel, whereas a colored map with 256 colors will lead to 8 bit per pixel. The application described in this paper continuously uses black and white maps. In Step 2 of the DesktopApplication the user is given the possibility to choose as many picture extracts of the map as RFID tags are available. The user defines the position of the RFID tag and marks it on the map. After providing the location data (i.e. elevation and description, latitude and longitude are set automatically) to the DesktopApplication, the computer calculates the size of the surrounding quadratic pixel area, which represents the environmental data around the RFID tag. In Step 3 the computer automatically creates special datasets including location and graphical data for the RFID tags. These final datasets must be loaded on the NFC-capable cell phone in order to correctly write the information on the RFID tags. 2) MobileApplication: After uploading the datasets into the cell phone, the java-based mobile Application MobileApplication is started on the cell phone. The working principle of the MobileApplication is described in Fig. 4. In Step 1 the tool extracts the information from the special datasets for each RFID tag, i.e. all location data (latitude, longitude, elevation, description, etc.) and graphical data are put in a correct order so that the information is correctly written on the RFID tags. The writing process is done in Step 2, while the user chooses 4 This can be done by using either a USB or a Bluetooth connection. 5 Portable Network Graphics SBMO/IEEE MTT-S International Microwave & Optoelectronics Conference (IMOC 2009) 473

4 Memory of RFID tag GIDS Location data ENDG PICG Global graphical data Local graphical data (PNG-file) TABLE I EXTENDED GIDS FORMAT (SIMPLE DESCRIPTION) the map extract to store on the RFID tag. Subsequently the user is prompted to hold the RFID tag to the cell phone, so that the cell phone is able to write the information into the RFID tag. This writing process has to be done for every RFID tag. After writing the information to all RFID tags, the tags are placed at their final destinations according to the location data stored on the RFID tag. After this step, the preparation of the environment is finished and the RFID-based navigation system is ready to be of service. Start RFID Load new map? no yes Enter final destination Read first RFID tag Step 1 Step 2 Step 3 Step 1 Step 2 Location data: - Latitude - Longitude - Elevation - Description special datasets with information on location data and graphical environment Fig. 3. RFID-Transponder with location data (latitude, longitude, etc.) and graphical map information Operating principle of the DesktopApplication Special datasets with information on location data and graphical environment Fig. 4. Extract information for every RFID tag Tag-1 Tag-2 Tag-3 Operating principle of the MobileApplication V. VERIFICATION OF THE NAVIGATION SYSTEM IN OFFICE-ENVIRONMENT Once the system has been simulated successfully, the system s functionality must be proved by verifying the operation in the local office environment. Therefore, this section Fig. 5. Create/update current map Read next RFID tag Work flow of the mobile navigation application RFID describes the experiments carried out at the local office environment. The minimal setup consists of four RFID tags fixed at various positions in the building. The information (i.e. location data and graphical environment) existent on the tags was previously put on the RFID tags by using the software applications described in section IV-B. Fig. 2 shows the locations of the applied tags. The procedure carried out is shown in Fig. 6. The figure shows the location of the RFID tags and the enlarged and reworked displays of the cell phone. The verification begins by starting the cell phone application software RFID (the simple work flow is described in Fig. 5). The user selects load new map and inputs the desired coordinates of the final destination (see first picture in Fig. 6. Subsequently, tag #1 is read out. The result of the reading operation is first, the reception of the complete floor plan data and second, the first graphical data, showing the map environment around tag #1 (see second picture in Fig. 6). Third, the cell phone shows the current user position (red dot) and the final destination (green dot). These two positions are linked by a direct line (orange) helping the user finding the way through the office maze. In the following steps the user brachiates from tag to tag, updating the current map by reading out the corresponding location and graphical information stored on the corresponding tag (see following pictures of Fig. 6). After grabbing the information of the last tag, the user reaches the final destination (see picture four in Fig. 6) SBMO/IEEE MTT-S International Microwave & Optoelectronics Conference (IMOC 2009) 474

5 (1a) (1b) (2) (4) (3) red dot orange line green dot Fig. 6. RFID-based navigation system in operation VI. CONCLUSION & PERSPECTIVES An RFID-based navigation system was introduced. The purpose of the system is the creation of an extended navigation environment featuring the user with positions (location data) and graphical data of the near environment. The system is based on RFID tags distributed at fixed positions. These RFID tags contain an extended GIDS format, thus providing location data (latitude, longitude, elevation) and graphical data (map extract) to the user. As RFID reader an NFC-capable cell phone is used. By using the RFID-based navigation system, the cell phone not only shows the current position but also the near environment and a direct line to the final destination. Preparation of the navigation system is done through the usage of two java-based applications. The DesktopApplication divides the basic map into small map extracts, which are uploaded, including the appropriate map coordinates and description, to the cell phone. Subsequently, the mobile tool MobileApplication writes these data into the RFID tags, which are later on put to their final destinations. The RFID-based navigation system was installed and successfully verified in a local office environment. However, improving the system could be achieved by evaluating the orientation between the cell phone and the RFID tag, providing a special kind of a compass. Additionally, the system performance may be improved by using colored maps along with high memory RFID tags. ACKNOWLEDGMENT The authors would like to thank Simon Heisler for his support on this project. REFERENCES [1] J. Landt, The history of rfid, IEEE Potentials, vol. 24, no. 4, pp. 8 11, [2] NXP Semiconductors, Mifare Standards. [3] K. Finkenzeller, RFID-Handbuch: Grundlagen und praktische Anwendungen induktiver Funkanlagen, Transponder und kontaktloser Chipkarten. Hanser, [4] Near Field Communications. [5] J. Seitz, L. Patino-Studencka, B. Schindler, S. Haimerl, J. G. Boronat, S. Meyer, and J. Thielecke, Sensor Data Fusion for Pedestrian Navigation using WLAN and INS, Symposium Gyro Technology 2007, Karlsruhe, Germany, [6] J. Gozalvez, Long-term evolution fdd and tdd demonstration [mobile radio], Vehicular Technology Magazine, IEEE, vol. 3, no. 1, pp. 3 9, March [7] A. Loeffler, U. Wissendheit, H. Gerhaeuser, and D. Kuznetsova, GIDS - a system for combining RFID-based site information and web-based data for virtually displaying the location on handheld devices, in Proc. IEEE International Conference on RFID, 2008, pp [8] Portable Network Graphics SBMO/IEEE MTT-S International Microwave & Optoelectronics Conference (IMOC 2009) 475