CSCI 8715 PP6: Indoor Positioning Systems Group8 Nuosang Du, Sara Abouelella An indoor positioning system is a system to locate objects or people inside a building using sensory information collected by mobile devices. We know that GPS can t perform well for indoor positioning as signal cannot penetrate walls and are subject to multi-path distortion. Wi-Fi which is freely available in the building can penetrate walls and the signal is potent enough for Indoor Positioning. Other technologies like ibeacon, RFID tags, VLC, and ultrasound can be used for indoor positioning, but require infrastructure changes which are costly. It can be applied to many cases, such as find facilities in stadium or World Expo instead of paper map, or find lost people in Mall or Nursing Home. Chronological Taxonomy 1. Well-Developed WIFI 2. Newly-Developed but not so popularized Bluetooth 4.0(iBeacon) Visible Light Communication(VLC) Radio Frequency Identification(RFID) 3. Future Search Ultra-Wideband(UWB) Wi-Fi Approach Wi-Fi is the most popular indoor positioning technology now. Wireless access points detect devices and triangulate distance or location. Trilateration and angulation are two triangulation techniques. Trilateration estimates the position of an object by measuring its distance from multiple reference points. So it is also called range measurement techniques. Instead of measuring the distance directly using received signal strengths (RSS), time of arrival (TOA) or time difference of arrival (TDOA) is usually measured and the distance is derived by computing the attenuation of the emitted signal strength or by multiplying the radio signal velocity and the travel time. Angulation techniques are based on using angle and distance measurements to locate the target. The angles are measured with relative to a reference vector. Similar to the trilateration techniques, the dimension of location information determines minimum number of measuring units required and the geometric relationship between them. For example, angle information from two different measuring units and the distance information between both are required to estimate the target location in two dimensions. Now the most widely used method is RSS, it is a function of the location of the receiver in the building based on radio-map and fingerprinting. Signal strength depends on:
1. Distance between the transmitter and the receiver 2. Number of wall crossings between the transmitter and the receiver Radio Map is a map of signal strength values from a Wi-Fi transmitter created by recording signal strength at all discrete cells which make up the building floor space. The left image shows the radio map of one Wi-Fi transmitter with varying signal strength received. Given the signal strength vector from different Wi-Fi transmitters at the user's location we can do reverse radio signal mapping to find the user's location. User can be located with an estimation accuracy of 2 meters. Fingerprinting based on RSS values is the prevalent method of using WLAN for positioning. Depending on the density of calibration points, fingerprinting reaches accuracies of 2-50 m. The fingerprinting method is particularly of commercial interest, since off the shelf devices can be used. Experiments on WLAN time of arrival distance measurements have proven to be of poor quality due to multipath and low resolution of the clocks. Using RSS for distance estimation in indoor environments has also proved unreliable due to an irregular dependency between attenuation and distance in indoor environments. Works without GPS; Existing WIFI infrastructure are many; Large range(up to 150m); Fast enough in general and cheap; Can detects floor level; Relatively inaccurate(5-15m) compared to ibeacon/rfid; Application required; Privacy Problem; ibeacon Approach Many retailers as well as customers like to have instore tracking which approached until recently through hanged-on books on the entry door, posters and kiosks by most of retailers. Retailers tried to attack the problem with Bluetooth technology in mobiles but fast to learn that it is pain and there are technological limitations in pairing the devices. Wi-Fi is also tried out but not effective. Bluetooth low energy(ble) ibeacon send a signal, device detects signal and acts based on data service rules. During the last couple of years, there was a lot going on the Bluetooth market. The technology itself is not new, the functionality of Bluetooth
has been well-known since the 1990s. But it was only in recent years that whole new application scenarios have occurred, originating from the energy saving Bluetooth version BLE. Apple with its ibeacon and just recently Google with its Eddystone ibeacon have got the market moving furthermore. GPS will tell you how to get to the nearest Apple store. But with ibeacon, Apple hopes to guide you around once you re inside, whether it s to pick up an order or shop for a pair of headphones. Since GPS does not work indoors, ibeacon is a good alternative for indoor positioning and indoor navigation. ibeacon are able to send out signals, but they can t receive them. They are relatively cheap, can run on button cells up to two years and have a maximum range of 30 meters indoors. Accuracy is up to one meter. On the one hand they are used in client based solutions, that is to say, positioning via app on the smartphone itself. In this case, Bluetooth must be activated on the device. On the other hand, server based tracking solutions using ibeacon are possible as well. For positioning in client based applications, several ibeacon are required. They send out unique signals with which the application determines the position by means of fingerprinting. For ibeacon, it is possible to trigger an action, for example displaying a coupon or information on the smartphone. The key function of ibeacon is region monitoring. It s limited to 20 regions and can function in the background and has different delegates to notify the listening app of entry/exit in the region, even if the app is in the background or the phone is locked. As opposed to monitoring, which enables users to detect movement in-and-out of range of the beacons, ranging provides a list of beacons detected in a given region, along with the estimated distance from the user's device to each beacon. Ranging works only in the foreground but will return an array of all ibeacon found along with their properties such UIUD. An ibeacon broadcast has the ability to approximate when a user has entered, exited, or lingered in region. Depending on a customer's proximity(distance) to a ibeacon, they are able to receive different levels of interaction at each of different ranges. The implications of ibeacon is that commuters might get information on subway delays as they stand on the platform. Retailers will be also able to offer deals or track which aisles shoppers linger in the longest, can also give instore specialties, events and news for the day for that particular store. Cost-effective, unremarkable hardware; Low energy consumption; Flexible integration into the existing infrastructure; Works where other positioning techniques do not have a signal; High accuracy compared to WIFI(up to 1m); Additional hardware;
App is required for client based solutions; Relatively small range(up to 30m); VLC approach VLC is a data communications medium which uses visible light between 400 and 800 THz(fluorescent lamps/leds), belongs to optical wireless communications technology. Transmit signals at 10 Kb/s speed for fluorescent lamps or up to 500 Mb/s for LEDs. Specially designed electronic devices generally contain a photodiode receive signals from light sources. The image sensor used in these devices is in fact an array of photodiodes. VLC sensor may provide a spatial awareness of multiple light sources, since light-producing devices are used everywhere, and using visible light is also less dangerous for high-power applications. Recently, VLC-based indoor positioning system has become an attractive topic, it could be a key solution to unlocking the indoor location market. An imagination is that VLC system consists of several LED shields each attached to an USB interface which is programmed to transmit the global position relevant to the indoor position of the LED lamp. When a person is indoors, his global position will be given by the LEDs and ultrasound sensors. The location data can be transmitted via GSM to a monitoring system or to an individual smartphone. LEDs are so efficient and reliable that conventional lighting is expected to be replaced by solid-state illuminating devices in a decade. The way includes boundary mapping and last position mapping. Special LED and fluorescent lamps send out indiscernibly flickering light which can be detected by a smartphone camera or a separate photo detector, which is for example attached to a shopping basket. Technically it works like that: Each lamp has its own ID which it compiles into pulsing light and sends to smartphones in the reception range. The app can access a map in which the lamps and their IDs are located. The incidence angle helps refine the position. Then customers of supermarkets are being navigated to the required products as the crow flies. Additional hardware such as ibeacon can fill in, where light doesn t advance. A smartphone can determine its position via VLC, therefore and for having a back channel, an app is necessary. Thus, notifications can be transmitted to the user. Server based tracking, which includes devices without app, only works with additional hardware in the lamp. In the future, VLC could also be used for Wi-Fi connection, meaning a mature network of position-emitting white LEDs that will be applicable in eldercare homes, hospitals, and large offices. VLC has some inherent problems, including the need for line-of-sight and a complex value chain. But as part of a hybrid solution, offering ubiquitous sub-meter levels of accuracy, it is very potential.
Lamps are extensively available in buildings; Modern LED are energy efficient, not dependent on batteries; VLC is precise(less than 1 meter) and has a high range(up to 8 meters); No disturbing, eye-catching, costly hardware; The reserves of the smartphone battery(receiver); Low flexibility when installing lamps, high costs when modern lamps are already installed; Back channel and tracking only possible with special hardware/application; RFID Approach RFID uses electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically stored information. Unlike a barcode, the tag need not be within the line of sight of the reader, so it may be embedded in the tracked object. There are two approaches on RFID. Passive RFID systems use tags with no internal power source and instead are powered by the electromagnetic energy transmitted from an RFID reader. Passive RFID tags are used for applications such as access control, file tracking, race timing, supply chain management, smart labels, and more. The lower price point per tag makes employing passive RFID systems economical for many industries. Active RFID systems use battery-powered RFID tags that continuously broadcast their own signal. Active RFID tags are commonly used as ibeacon to accurately track the real-time location of assets or in high-speed environments such as tolling. Active tags provide a much longer read range than passive tags, but they are also much more expensive. Most RFID systems rely on proximity detection of permanently mount tags to locate mobile readers. Therefore the accuracy of an RFID system is directly related to the density of tag deployment and reading ranges. Some long range active RFID systems can also use signal strength information to improve the localization accuracy. The main application of RFID location systems is route guidance for pedestrians. The figure above shows how RFID works. RFID tags are used in many industries, for example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly
line; RFID-tagged pharmaceuticals can be tracked through warehouses. Active: can generate own signal, wider range of uses(aircraft transponder); Passive: no battery or maintenance needed, cheap(labels); Active: more expensive, limited battery life; Passive: few uses, still too expensive for some uses; UWB Approach UWB is a transmission from an antenna emitted signal bandwidth exceeds the lesser of 500 MHz or 20 % of the center frequency. Indoor Positioning uses the passive UWB systems, it have the potential for localization of people and objects from signal reflection, using the principle of radar. The advantage of passive UWB is that neither an active nor a passive tag needs to be worn by the user nor attached to the localized object. A typical passive localization setup includes one or more omni-directional emitter antennas and multiple listener antennas. In order to detect a moving person, time-invariant direct waves and strong static signals reflected from furniture need to be subtracted. Given that the locations of the emitter and receiver antennas are known, estimated ranges from the reflected waves can be used for any range-based algorithm such as TOA or TDOA multilateration to determine the object position. Follow the so called background subtraction approach, it is possible to observe extremely small movements such as cardiac or respiratory activity. Since achievable accuracy of TOA measurements is directly correlated to the signal bandwidth, Ultra-Wideband is well suited for precise ranging. At bandwidths of several hundred MHz and appropriate time resolution in the order of nanoseconds, ranging and positioning at cm-level are possible. It s especially useful for indoor environments where multipath is severe, since the wide bandwidth facilitates the detection of multiple time-delayed versions of a signal sequence. The reason why UWB has not entered the mass market is the requirement for a dedicated transmitter-receiver infrastructure. A valuable aspect of UWB technology is the ability for a UWB radio system to determine the "time of flight" of the transmission at various frequencies. This helps overcome multipath propagation, as at least some of the frequencies have a line-ofsight trajectory. With a cooperative symmetric two-way metering technique, distances can be measured to high resolution and accuracy by compensating for local clock drift and stochastic inaccuracy. Due to low emission levels permitted by regulatory agencies, UWB systems tend to be short-range indoor applications. For example: Fans can receive tickets information and seats tracking for designated games in stadium by UWB system. Passengers can easily find their car in an airport parking garage with the help of UWB. The figure below
shows how the UWB works. UWB transmits a radio signal over ultra-wide band of frequencies; UWB signals are transmitted for a much shorter duration with very low-power spectral density; UWB can be used in close proximity to other RF signals without causing or suffering from interference; UWB short duration pulses are easy to filter in order to determine which signals are correct and which are reflection and diffraction; UWB can achieve very high indoor location accuracy(20 cm) with the precise time of arrival(toa) measurement; Needs special transmitter and receiver, it limits the general applications of UWB on some degree; References: 1. Dmitry Namiot, International Journal of Open Information Technologies, Feb 2015, On Indoor positioning. 2. Patrick Lazik, Niranjini Rajagopal, CMU, 2015, ALPS: A Bluetooth and Ultrasound Platform for Mapping and Localization. 3. Privacy-Preserving Indoor Localization on Smartphones. Konstantinidis, A., +, TKDE Nov. 2015 3042-3055. 4. Shi, G., & Ming, Y. (2016). Survey of Indoor Positioning Systems Based on Ultrawideband (UWB) Technology. In Wireless Communications, Networking and Applications (pp. 1269-1278). Springer India. 5. Cypriani, M., Lassabe, F., Canalda, P., & Spies, F. (2010, September). Wi-Fi-based indoor positioning: Basic techniques, hybrid algorithms and open software platform. In Indoor Positioning and Indoor Navigation (IPIN), 2010 International Conference on (pp. 1-10). IEEE. 6. Bahl, P., & Padmanabhan, V. N. (2000). RADAR: An in-building RF-based user location and tracking system. In INFOCOM 2000. Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings. IEEE (Vol. 2, pp. 775-784).
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