Location-Based Services
 E-OTD Method of Location Identification
(Updated Sept. 1, 2001)

Acknowledgement - Much of this content on this page  is based on CPS and Ericsson's websites. Go there for more complete info. 

Architectural View from Network Infrastructure Vendor's Perspective

Different network vendors have different ways of incorporating location identification information. We are showing Ericsson's Mobile Positioning System (MPS) as one such approach that supports multiple methods of location identification information.  Then we explain how E-OTD works.

E-OTD
Enhanced Observed Time Difference (E-OTD) is a technology for identifying the location of a cellular caller. This is in competition to GPS-based location identification. Main difference between the two methods is that GPS uses a constellation of satellites maintained by the US department of defense. On the other hand, E-OTD uses a mathematical algorithm to identify the location of the caller based on the time signal takes to reach a set of base stations and then through a triangulation scheme, determine the approximate area where the caller might be.

Major motivation for E-OTD came from E-911 regulatory requirement by FCC in USA for public-safety agencies. In Europe, the motivation was for location-based m-commerce applications. 

E-OTD is becoming the a de facto standard for E-911 Phase II implementation among U.S. GSM carriers. It started with VoiceStream, (www.voicestream.com) - a GSM carrier that has received FCC approval to implement E-OTD. Other current and future GSM carriers, including AT&T Wireless, (www.attws.com) Carolina PCS, (www.carolinaphone.com), Cingular (www.cingular.com), Conestoga Wireless ( www.callconestoga.com/cwc/) and PCS One (www.pcsone.com) intend to use E-OTD to meet Phase II accuracy requirements of E911and have made that known to FCC. 

How Does E-OTD Work?
Cambridge Position System provides a good explanation of how E-OTD determines the location. Go here for additional information. The diagram below gives an indication of how this is achieved.

Note : MobileInfo acknowledges CPS as the sources of the graphic.

What Network Operators Need To Do?

Both handsets and base stations need hardware upgrade. Handsets need to incorporate appropriate chips and base stations need to add hardware to support cursor technology.  

Handset Integration of E-OTD (Graphic courtesy of CPS)

MobileInfo Advisory: E-OTD has become the most affordable and popular method of position determination. Cambridge Position systems (http://www.cursor-system.com) is a major player.