Introduction to Smart Phone Positioning

Introduction

It is hard to image a life without the Internet, as it becomes a very important part of our life from the aspects of working and free time activities. People typically access to the Internet via a PC (Personal Computer) in office or at home with a fixed Internet connection, and via a smart phone while they are in moving with a wireless Internet connection. As the number of smart phone users is increasing all the time, the world is now spinning to a new direction that consumers are accessing to the Internet more and more with their smart phones. The experience of accessing to the Internet via a smart phone is different from that using a PC. The most significant difference is the size of the screen. Although the screen size of a smart phone is much smaller than that of a PC, the touch screen technology and the intelligent web browser in smart phones aid the users to surf in the Internet with a very comfortable and interesting experience. You don’t feel that you are “limited” by the small screen. The mobility offered by the smart phones makes it possible to access the Internet anytime and anywhere with much lower power consumption.

The location information of the connected mobile users becomes important while they are in moving. Location-based service is therefore becoming one of the key application categories in smart phones. For example, navigation is now becoming a well-known application in smart phones. The enable technology for this unique mobile application is the positioning technology.

Most smart phones are embedded with low-cost navigation sensors such as GNSS (Global Navigation Satellite System) receiver, accelerometer, digital compass, and gyroscope. In addition to these low cost sensors, RF (Radio Frequency) signals from networks of WLAN (Wireless Local Area Network), Bluetooth and RAN (Radio Access Network) are also available in smart phones. All these sensors and signals are vital sources for locating mobile users.

Different positioning systems, sensors and signals of opportunity are used for locating smart phones in different environments. For outdoors, the most common positioning solution is the GNSS-based solution. GNSS works properly whenever an open view to the sky is available. However, there are circumstances that an open sky is not visible, e.g. in urban areas or in forests with dense foliage. In these cases, motion sensors such as accelerometer and orientation sensors such as gyroscopes and digital compasses have to be adopted for augmenting the GNSS solution. For indoors, the most common positioning solution is the fingerprinting solution using the RF signals from WLAN, Bluetooth and RFID (Radio Frequency Identification) networks. Motion and orientation sensors can also be used for indoor positioning. There are four types of positioning solutions that are applicable to smart phones: the GNSS-based positioning solution, the RAN-based positioning solution, the positioning solution based on the signals of opportunity, and the hybrid multi-sensor multi-network positioning solution.

The GNSS-based solution is a well known technology. Its operational principles can be found from a large number of text books, e.g. Kaplan and Hegarty (2006). For a low cost receiver, the positioning accuracy of 2-5 meters is achievable easily when an open view to the sky is available. However, the GNSS signals are attenuated significantly or even blocked totally indoors. High sensitivity receiver can be used for such indoor environments to which weak GNSS signals can penetrate through. The positioning accuracy, however, ranges from tens of meters to hundreds of meters depending on the building types (Lachapelle, 2007; Kuusiniemi, Wieser, Lachapelle & Takala, 2007). New GPS signals made on L2C and L5 and signals in the new GNSS systems such as Galileo and COMPASS will offer a better opportunity for signal acquisition and tracking indoors and will improve the positioning performance for these environments.