January 8, 2013
Outdoor positioning has proved to be very functional during the years, recently indoor positioning systems which I will be referred to as IPSs have been designed to provide location information of persons and devices. Numerous IPSs are being developed using diﬀerent infrastructure so the best solution for every situation can be found. This paper gives information and talks about the diﬀerent IPSs, some comparing occurs, what can be improved and aims to review current development and future scope of this technology.
Traditionally location aware applications have been used to outdoor environments, using mostly GPS. However very large and complex buildings exist these days, people have diﬃculties ﬁnding what they are looking for in the stated buildings (museums, hospitals, shopping centers, etc). Knowing where you are and navigating faster in such environments can increase the productivity and the quality of service provided by those services. IPSs haven’t had as much research as Outdoor Positioning Systems. Reasons of these are two technical problems. First GPS signals cannot reach indoor environments and second the complexity of indoor environments makes triangulation based approaches (which are used for GPS) less eﬀective. Some early systems using infrared, laser and ultrasonic range ﬁnders got good system performance in ﬁeld tests but such an approach isn’t appropriate because of its size, complexity and cost. Some researchers have been working on using WiFi even though it was not designed for this purpose. Most of these systems use a ﬁngerprinting approach due to the infeasibility of indoor triangulation. Fingerprinting 1
is based on the Received Signal Strength (RSS) transmitted by nearby WiFi access points. Although RSS may be of low cost and low complexity due to the large signal variance, insuﬃcient data and changing infrastructure such an approach may deliver inaccurate and unreliable results.
In the rest of the paper we will talk about the various IPSs their advantages and disadvantages, their eﬃciency and how easy it is to implement them.
Indoor Positioning Systems
IPSs are to be used in computer systems so a number of wireless technologies have been developed to enable location-awareness for indoor location uses. Technologies such as IR, ultra-sound, RFID, WLAN, Bluetooth, magnetic technology, etc. Each one of them has unique advantages but at the same time they have some limitations. A solution would be combining some of these technologies to make an ISP.
Active Badge system was one of the ﬁrst IPS designed at ATT Cambridge in 1990s, which covers the area inside a building and provides symbolic location information of each active badge such as the room where the active badge is. Although the price of active badges and networked sensors are cheap, the cables connecting sensors raise the cost of the Active Badge system. It provides room level accuracy. Because of the coverage range of infrared, several networked sensors are needed in a large environment.
IPS using Infrared (IR)
An IPS using infrared determines the position of an object based on its presence. Each object must contain a proprietary emitter that periodically transmits an infrared (IR) beacon containing a unique code for each object. IR receivers placed throughout the environment detect the beacons and determine the approximate position of the object because of the known location of the IR receiver.
An IPS using infrared is practically immune to interference because largely all other wireless communication systems operate in the RF spectrum which is far below the frequencies of light. Having no interference is very practical and helpful on most applications of an IPS. Infrared signals dont penetrate opaque materials such as walls and ceilings. An IR system must have numerous of receivers in each room...