Location-Based Services
(Updated on March 29,  2002 - Incorporating Content Provided By Mike Flom of Portable Internet)

Location Identification Methods 

In the initial implementation (during 2000 and 2001) of this application, the users were being prompted to provide his/her location by zip/postal code or nearest street intersection, city/town information or by other means depending on the implementation. As an example GeePS uses city/town information provided by users to find information on retailers in the user's town. In subsequent and more sophisticated implementations introduced during 2001and 2002, following software and hardware-based solutions were being proposed:

• GPS-A (Assisted GPS) - A GPS transceiver attached to or integrated into the handheld device or smart phone can provide very accurate location information to a wireless portal which could serve personalized content to the device. This option is kind of expensive from device perspective and network providers are not pushing this option. 

• Cell ID - The network operator uses cell id to identify in which cell the caller is at a given time. This is a very approximate method.

• E-OTD (Enhanced Observed Time Difference) - It is a hybrid technology that uses both the handset and the network to determine a caller’s location. The technology compares arrival times of wireless phone signals to find the caller. E-OTD requires minor software upgrades to the network and E-OTD chips are required in the device and a hardware component (LMU - location mobile unit) is added to the network's base stations. See more information on E-OTD on Cambridge Positioning System's site.

• TDOA - Time Difference On Arrival -  a technology patented by True Position, affords another way of deducing location, by timing signals between users and base stations. This is accurate and doesn't require handsets to be modified. However, in a typical network, equipment has to be added to tens of thousands of base stations - so the cost works out at $3 to $5 per subscriber, according to a company official, who asked not to be identified. >>More
  

• Agilent's acceSS7 - Uses a bunch of technologies to achieve its goals, but all of them are based on adding probes to the few hundred base-station controllers in a typical network. No modifications are necessary in handsets of base stations, which keeps the cost down. See more on this here.