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Introduction

The terms mobile positioning and mobile location are sometimes used interchangeably in conversation, but they are really two different things. Mobile positioning refers to determining the position of the mobile device. Mobile location refers to the location estimate derived from the mobile positioning operation.

There are various means of mobile positioning, which can be divided into two major categories - network based and handset based positioning. The purpose of positioning the mobile is to provide location-based services (LBS), including wireless emergency services.

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Positioning & Location Mgt

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Network-based Mobile Positioning Technology

This category is referred to as "network based" because the mobile network, in conjunction with network-based position determination equipment (PDE) is used to position the mobile device.

SS7 and Mobile Positioning

One of the easiest means of positioning the mobile user is to leverage the SS7 network to derive location. When a user invokes a service that requires the MSC to launch a message to a LBS residing on a SCP, the MSC may launch a SS7 message contain the cell of origin (COO) or cell ID (of the corresponding cell site currently serving the user). While potentially covering a large area, the COO may be used by LBS to approximate the location of the user. This type of positioning therefore has a large degree of uncertainty that should be taken into account by the LBS application in term of required quality of service (QOS).

Network based PDE

COO is not always available (for example: via SS7 with non-GSM WAP based services) nor does it always meet the QOS requirements of the LBS application. Therefore, network-based (or handset based) PDE must be employed.

Angle of Arrival Method

This method involves analysis of the angle of arrival (AOA) of a signal between the mobile phone and the cellular antenna. AOA PDE is used to capture AOA information to make calculations to determine an estimate of the mobile device position.

Time of Arrival Method

This method uses the time of arrival (TOA) of signals between the mobile phone and the cellular antenna. TOA PDE is used to capture time difference of arrival (TDOA) information to make calculations to determine an estimate of the mobile device position.

Radio Propagation Techniques

These techniques utilize a previously determined mapping of the radio frequency (RF) characteristics to determine an estimate of the mobile device position.

Hybrid Methods

Some hybrid methods of AOA and TOA exist that use the best of both to provide improved positioning.

Handset-based Mobile Positioning Technology

This category is referred to as "handset based" because the handset itself is the primary means of positioning the user, although the network can be used to provide assistance in acquiring the mobile device and/or making position estimate determinations based on measurement data and handset based position determination algorithms.

SIM Toolkit

The SIM Toolkit (STK), as an API between the Subscriber Identity Module (SIM) of a GSM mobile phone and an application, provides the means of positioning a mobile unit. Positioning information may be as approximate as COO or more precise through additional means such as use of the mobile network operation called timing advance (TA) or a procedure called network measurement report (NMR). In all cases, the STK allows for communication between the SIM (which may contain additional algorithms for positioning) and a location server application (which may contain additional algorithms to assist in mobile positioning). STK is a good technique to obtain position information while the mobile device is in the idle state.

Enhanced Observed Time Difference (E-OTD)

This is what is also referred to as reversed TOA or handset based TOA. The basic method is employed as with TOA, only the handset is much more actively involved in the positioning process. Specially equipped handsets are required.

GPS

Perhaps the best known or recognized handset based PDE is based on the Global Positioning System (GPS). By itself, GPS can be the most accurate (when satellites are acquired/available), but this technology is often enhanced by the network. Assisted GPS (A-GPS) refers to a PDE system that makes use of additional network equipment that is deployed to help acquire the mobile device (much faster than non-assisted GPS) and provide positioning when the A-GPS system is unsuccessful in acquiring any/enough satellites.

Mobile IN Technologies for Positioning

Mobile IN can also be deployed to assist in the positioning process. GSM and ANSI-41 based networks may employ the use of the GSM MAP Any Time Interrogation (ATI) and Position Request (PosReq) messages respectively for positioning.

These mobile IN procedures entail a LBS application middle-ware as an Service Control Function (SCF) launching a message (MAP ATI or PosReq) to the HLR for position information. The HLR may respond with approximate information (such as the COO) or more precise information (such as TA or NMR as in the case with GSM).

The value of mobile IN is to leverage the SS7 and IN network to obtain location, especially for mid-call/session position updates. Mobile IN may also be quite valuable for idle call positioning, but requires integration on the mobile network side to ensure current position information is made available.

The Importance of LBS Middle-ware

LBS middle-ware can be best defined as the application that do not provide the services themselves, but rather enable location based services.

One of the best examples of LBS middle-ware, that is required for all robust LBS implementations, is the location manager function. Among other things, the location manager function may be employed to convert positioning information into useful location information and make it available for LBS applications. One of the key value aspects of the location manager function is to enable the use of various positioning technologies in conjunction with various LBS applications. This functional element thus acts as a gateway or hub for location.

Another important role of the location manager function is to perform the SCF function for mobile IN positioning technologies as discussed above.

New network entities called the Mobile Positioning Center (MPC) and the Gateway Mobile Location Center (GMLC) are being standardized to provide for the location management function for ANSI-41 and GSM networks respectively.

The Future of Mobile Positioning

There is a bright future for mobile positioning as the key technology for enabling LBS applications, which themselves will become increasingly important as a key enabler of value added services.

Mobile positioning technology are also crucial for wireless emergency services.