Location-based services with positioning are one of the most interesting areas in the new world of mobile telephony. Key to these services is that the system knows the user’s location. The technology is available now, and all the new services being developed will immediately reach a mass market consisting of everyone who already has a GSM phone. There are practical services that provide information about the nearest restaurant, etc., as well as business-oriented services that increase efficiency by providing a navigation aid or helping to manage a fleet of vehicles. There are also security services for tracking or searching for items in transport. Advertising, entertainment and games will be included, too.

Mobile positioning services were launched at an early stage. The first version of the Mobile Positioning System (MPS 1.0) was already available in 1997. This provided the foundation for the GSM positioning standard released in 1999. In the autumn of 2000, the Location Interoperability Forum was established, which has since grown to 200 members. This group’s mission is to ensure interoperability between positioning systems and services from different manufacturers.

Energy Programming, with a market share of slightly more than 15 percent and commercial systems in operation since May 2000, can offer a complete package for launching new services. Included in the package are MPS and the positioning functions that are required in the network, terminals that support they new applications and positioning services and service platforms that help operators to roll out new services quickly. Today’s services are for GSM, but they will work equally well in 3G networks for which the technical implementation is only slightly different. 

Three different methods  

There are currently three different methods for positioning. The primary difference is how accurately a mobile terminal’s position can be determined. One method is based on intelligence in the network, while the other two use the terminal. Network-based services allow an ordinary GSM phone to be used, while the terminal-based systems require a special telephone but also provide better accuracy.

For 2G networks, the network-based service is CGI + TA (Cell Global Identity + Timing Advance). This system is based on the fact that the system can identify the cell or cell sector surrounding a base station in which the user is located and can use TA to determine the distance between the user and the radio mast. The precision depends on the cell size and is typically 200 or 300 meters in urban environments and several kilometers in rural areas. CGI, which is the simplest method, is always available as a fall-back, if the more advanced methods do not work.

The terminal-based E-OTD (Enhanced Observed Time Difference) system requires new software in the phone that calculates the user’s position using signals from three base stations. The phone compares the time it takes for a signal to be received from each of the three base stations and uses measurement equipment called a Location Management Unit (LMU) consisting of the GSM radio, a GPS (Global Positioning System) receiver and the mobile phone and a reference time transmitted by a GPS satellite to calculate the position. The system, which is commercially available in the US, has an accuracy of 50 to 250 meters.

The greatest accuracy, 10 to 30 meters, is obtained with the terminal-based A-GPR (Assistant GPS) system, which requires both software and a GPS chip in the phone. One or more GPS reference receivers in the network provide assisting data to the phone, such as which GPS satellite is closest. A-GPS provides better coverage and more rapid positioning and uses less battery power than traditional GPS. The system will be available next year.

3G systems Development for 3G systems includes a network-based solution called Cell ID + RTT (Round Trip Time) and the terminal-based systems OTDOA (Observed Time Difference of Arrival) and A-GPS. Cell ID + RTT is the 3G equivalent of CGI + TA, while OTDOA works in the same manner as E-OTD.

Energy Programming can shortly offer CGI + TA in its MPS-G 3.0 system, where G stands for GSM. This autumn, a standardized MPS-G 5.0 system will be released that will also support E-OTD and A-GPS. A system for 3G called MPS.U 1.0 will also be available.

MPS consists of positioning software in the mobile network plus a Server Mobile Positioning Center (SMPC) that calculates longitude and latitude and a service gateway called GMPC.

With the 5.0 release, the SMPC will be taken out of the GMPC and moved further out in the network. In 3G systems, the GMPC is re-used, while the SMPC is integrated in the RNC (Radio Network Controller).

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