STANDARDS REPORT Standardization of Mobile Phone Positioning for 3G Systems Yilin Zhao Motorola Inc ABSTRACT Finding the location of the mobile phone is one of the important features of the 3G mobile communication system Many valuable locationbased services can be enabled by this new feature Telecommunication managers and engineers are often puzzled by location terminologies and techniques as well as how to implement them since location systems are not natural evolution from past generations of telecommunication systems In this paper we discuss briefly why locating mobile phone becomes a hot topic and what technologies are being studied We then describe and clarify the latest standards issues surrounding the positioning methods specified for 3G systems These include cell ID based assisted GPS and TDOAbased methods such as OTDOA E OTD and A FLT INTRODUCTION The U S Federal Communications Commission FCC has made Emergency 911 E911 a mandatory requirement for wireless communications services such as cellular telephone wideband broadband personal communications services PCS and geographic area specialized mobile radio SMR This ruling and upcoming service is called wireless E911 For Phase II implementation the FCC required that public safety answering point PSAP attendants of wireless communications networks must be able to know a 911 caller s phone number for return calls and the location of the caller so that calls can be routed to an appropriate PSAP and related emergency assistance attendants In 1999 the FCC decided to tighten the Phase II location accuracy requirement from 125 m in 67 percent of all cases to new numbers for handset based solutions 50 m in 67 percent of calls and 150 m in 95 percent of calls for networkbased solutions 100 m in 67 percent of calls and 300 m in 95 percent of calls Handset based solutions are for nonlegacy phones Networkbased solutions are for legacy phones In 2000 the FCC required wireless communications operators to offer operational location capable 108 0163 6804 02 17 00 2002 IEEE phones by October 1 2001 On September 8 2000 the FCC granted a limited waiver to VoiceStream with relaxed accuracy for an extended period Right after the October deadline of 2001 waivers were granted to Alltel AT T Wireless Cingular NEXTEL Sprint PCS and Verizon permitting them to postpone selling and activating location capable phones that satisfy the new numbers until 2002 or later The executive body of the European Union EU the European Commission EC has similar initiatives for their wireless emergency calls E112 Coordination groups within EC have been organizing meetings to specify similar requirements as their counterpart in the United States On March 26 2002 EU transport ministers approved 482 4 million in funding for the development of the European satellite system called Galileo This new system will rival the U S developed global positioning system GPS which has already been adopted as one of the technologies for positioning as discussed later In the United States a recent survey by Harris Interactive indicated that consumers were more interested in E911 than other new mobile phone features Out of 1006 adults 59 percent selected E911 service At a distant second 7 percent selected e mail service Besides emergency assistance wireless E911 and its positioning capability will certainly trigger and enhance many location based services For instance the telematics system 1 currently offered by automotive manufacturers such as GM s OnStar and Mercedes Benz s TeleAid can be improved significantly Future systems may no longer need to have separated location and communication devices attached permanently to the vehicle Therefore it is not difficult to understand why telecommunications manufacturers and operators have been actively pursuing the technologies to locate the mobile phone In this article we discuss location technologies specified by the 3rd Generation Partnership Project 3GPP and 3GPP2 respectively 3GPP has been concentrating on wideband code division multiple access W CDMA and Global System for Mobile Communications GSM systems while 3GPP2 has been focusing on cdma2000 and cdmaOne systems IEEE Communications Magazine July 2002 BASIC LOCATION TECHNOLOGIES There are three most commonly used location technologies standalone satellite based and terrestrial radio based 2 As examples a typical standalone technology is dead reckoning a typical satellite based technology is GPS and a typical terrestrial radio based technology is the C configuration of the Long Range Navigation LORAN C system For wireless E911 E112 and many other applications radio based satellite and terrestrial technologies are most popular Cellular networks are terrestrial based communications systems It is natural to utilize the signals of the network to determine the mobile phone location or assist in location determination Research in this area has been very active recently as evidenced by the latest round of publications and conferences The principles behind them are discussed below Radio based technology typically uses base stations satellites or other devices emitting radio signals to the mobile receiver to determine the position of its user Signals can also be emitted from the mobile device to the base Commonly studied techniques are angle of arrival AOA positioning time of arrival TOA positioning and time difference of arrival TDOA positioning All these methods require radio transmitters receivers or transceivers In other words they depend on emitting and receiving radio signals to determine the location of an object on which a radio receiver or transceiver is attached To make the position determination these methods generally work under the assumption that one end of the positioning system is fixed or known and the other movable e g a mobile phone However the location determination capability can be at either the fixed or the mobile end Generally it is up to the system designer to decide where the final location determination capability should reside For performance improvement hybrid methods various combinations of the techniques discussed or with additional techniques are possible To simplify our discussion in the following we use twodimensional 2D cases as application examples Readers should be able to expand the principles presented to 3D cases The AOA system determines the mobile phone position based on triangulation as shown in Fig 1a It is also called direction of arrival in some