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WLAN

Page history last edited by Nancy Proctor 15 years, 7 months ago

WLAN Software-based positioning

 

WLAN location-based services (LBS) were first trialled by Tate Modern in their first multimedia tour pilot in 2002, and subsequently by the Royal Sonesta Hotel in Boston, and the Renwick Gallery, Smithsonian American Art Museum in 2003 and the Royal Institution in London in 2004. A wireless location-based tour was also piloted at the Posti Museum in Helsinki in 2004 and the Singapore Science Center in 2005, and wireless positioning has also been tested at the Blanton Museum at the University of Texas in Austin, as part of the GettyGuide system at the J. Paul Getty Museum in Los Angeles, and at the Museon in Den Haag in the Netherlands. Several Smithsonian Museums in Washington, DC, including the National Postal Museum, the National Museum of American History, the National Air and Space Museum’s Udvar-Hazy Center, the National Museum of Natural History, and the Castle Building (Smithsonian Information Center) planned for wireless positioning systems as part of a large-scale Smithsonian-wide pilot programme called the SIguide, and future installation at the National Portrait Gallery, Smithsonian American Art Museum, and other locations were also under discussion; however, these projects were never fully realized, in part because sufficient stability in wireless positioning was never achieved.  Also in Washington, DC, a handheld tour with WiFi positioning was implemented at the US Botanic Gardens. All of these projects in DC were designed to work with the tour content stored locally on the PDAs.

  

Software running over a wireless network covering the exhibition space can be used to calculate visitors’ whereabouts in the museum and deliver content automatically on the basis of their location. The principal elements of this solution are the wireless network and the software that does the location identification and application management.

  

The wireless network is composed of four main elements: 

  1. The tour server, on which the server-side positioning software is installed and where the  location calculations are made. The server may be an existing part of the museum’s infrastructure, or a dedicated server can be installed to isolate the tour’s activities from the rest of the building’s network.
  2. The transponders or ‘access points’, which relay radio signals between the visitors and the server. 
  3. The mobile computers (PDAs or web tablets), including ‘WiFi’ antennae or wireless cards (built in or external) and the ‘client’ software for the positioning system, carried by the visitors.
  4. Standard Ethernet cabling and switch(es) as required, to connect the access points to the server. 

 

Typically the access points are hardwired to the server, and in all cases the components of the wireless network require power, so ironically the only ‘wireless’ part of a wireless network is the connection between the visitor’s tour device and nearby access points. As visitors move about the museum or outdoor site, their handheld devices send signals to the access points, which are relayed to the server via the switch. By comparing the signal strength readings from access points near the visitor to a radio map of the space covered by the wireless network, the positioning software on the server can calculate each visitor’s likely location with respect to each access point.

   

The exhibition space’s radio map is created at the time that the LBS is set-up. The LBS software includes a survey tool that allows operators to record the strength of the signals received by the network’s access points from a portable device. This ‘signal strength’ or radio map is then related to an architectural map of the exhibition area, so that given combinations of signal strength readings can be correlated with specific locations in the galleries. With signals from at least three access points, the server can triangulate each visitor’s location, but even with one or two access points, the software is able to make some educated guesses about the visitor’s location on the basis of the signal strength to their portable device. Some systems, such as that used at the US Botanic Gardens, do not in fact rely on triangulation but rather signal strength reading from a single access point in each triggering space. The pilot installation at Musée d'Orsay in 2006-7 by Espro-Acoustiguide, using a proprietary wireless technology from the German company, Lesswire (akin to a Bluetooth protocol, in fact), similarly used single area beacons to update maps on visitors' handhelds to indicate which gallery the visitor was currently located in. 

  

The resolution or ‘granularity’ of the triangulation-based positioning platforms today is from one to three meters, depending on conditions, and most providers claim a 90-98% accuracy rate for their positioning solutions. Because WLAN solutions are based on radio signal strength, their accuracy is dependent on the conditions in the galleries and how they impact the radio signal strengths. The number of simultaneous users may cause signal strength readings to fluctuate, resulting in inaccurate positions being detected for users. Atmospheric conditions and the humidity of the local environment, which can be impacted by the number of bodies in a given room, for example, can also cause changes in signal strength readings. 

 

Most LBS software systems take upwards of 60 readings per second in order to increase the probable accuracy of the location calculations, and adjust for variations that can be predicted. They will also use intelligence from the visitor’s previous movements to exclude calculations that are wildly inaccurate or impossible – i.e. the software will assume that a visitor cannot move from one end of a large museum to another in the space of a couple of seconds, so any calculations that imply this sort of a location change are discarded as erroneous. For finer or ‘pin-point’ positioning, WLAN technologies can usually be combined with Infrared, Bluetooth or Radio Triggers, so that the software-based system handles larger, room-level racking, while the local tags or triggers provide more precise and sometimes quicker and more reliable content delivery for individual exhibits within the room.

 

The LBS software usually includes applications that can do different things with the raw X, Y, Z coordinates of a visitor’s location, such as deliver content relevant to nearby exhibits, or allow site staff to track visitor movements in real-time by watching a map of the galleries on which icons representing the visitors move.

   

Experience with WLAN software-based solutions has shown that in addition to incorrect location readings, visitors are most frustrated by the latency that seems to be inherent in location-based content delivery. Some latency actually increases the accuracy of the location-based response, as it allows the LBS system to take more readings of the visitor’s location. Additional latency can be caused by other operations over the wireless network, such as content delivery, or the handheld device’s processor speed. In practice, it takes from 2-20 seconds for the visitor to receive content when they move into a new location, whether it is requested by the visitor or automatically pushed by the server once the visitor’s new location is detected (Tate Modern Multimedia Tour Pilot 2002; Renwick Gallery pilot, Smithsonian American Art Museum, 2003-4; Royal Institution Science Navigator pilot 2004; GettyGuide 2004-5; US Botanic Gardens 2005). Latency and accuracy can be improved by installing more access points; both the ScienceAlive project at the Singapore Science Centre (Exploratorium, 2005, p. 11) and the Blanton Museum (Glenda Sims, comments to author 24 August, 2005) increased the number of access points on their network by 50% to speed response times, while Museon in the Netherlands had to double the number of access points on their network in order to achieve 1.5-2m granularity because of difficulties posed by their museum’s architecture (Hub Kockelkorn, email to author 19 August 2005). With their ‘GettyGuide’, the J. Paul Getty Museum in Los Angeles encountered similar challenges to wireless positioning from the site’s complex architecture.

   

Few LBS technology providers make a policy of providing museum-specific applications as an integral part of their software suite, so it is often up to the museum or another provider to adapt the LBS software to the wireless tour installation, or to use tools provided with the LBS system to 

 

‘keep the network in tune’ – i.e. optimised for location-awareness. Achieving consistent performance from WLAN positioning systems remains a challenge: as Michael Edson, Chief IT Officer of the Smithsonian American Art Museum notes, “making WiFi-based locality resolution work all-the-time (!) means spending time and money designing and refining the core wireless network, and using a wireless network management suite to tune it on an ongoing basis. The underlying wireless network has to be thought of as an integral component of the handheld solution and it has a high cost of ownership.” (email to the author 23 August 2005)   

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