Mobile Positioning

This is a term I came across today, which I was unfamiliar with. Positioning the Mobile for what purpose and how? These were some mind boggling questions which sprang up on my head. Simply put, Mobile Positioning is used to provide Location Based Services (LBS) to various parties, as well as wireless emergency services. 

So what is LBS? A location-based service or LBS is an information and entertainment service, which is accessible with mobile devices through the mobile network and utilizes the ability to make use of the geographical position of the mobile device. Some examples for such LBS would be, discovering the nearest bank ATM or the whereabouts of an employee, vehicle tracking services, personalized weather reports etc.

It should be implied by now that Mobile positioning refers to determining the position of the mobile device which in turn is used to provide LBS. Mobile Positioning should not be confused with Mobile Location as the terms are sometimes used interchangeably in conversation. However, they are really two different things. Mobile location actually refers to the location estimate, derived from the mobile positioning operation.

There are various means of mobile positioning. However it can be divided into two major categories 

1.            Network based positioning
2.          Handset based positioning

Network-based Mobile Positioning Technology

Here, the mobile network, in conjunction with network-based Position Determination Equipment (PDE) is used to position the mobile device. Consequently,this category is referred to as "network based". Examples for this technology would be, 


1. SS7 and Mobile Positioning
This is one of the easiest means of positioning the mobile user! 

It leverages the SS7 network to derive location. When a user invokes a service that requires the Mobile Switching Center (MSC) to launch a message to a LBS residing on a SCP(Service Control Point), the MSC may launch a SS7 message. This SS7 message contains the Cell of Origin (COO) or Cell ID (of the corresponding cell site currently serving the user). 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 as COO has the potential of covering a large area. Thus, it should be taken into account by the LBS application  when  maintaining the  quality of service.  

2. Network based PDE

COO is not always available.

E.g:- via SS7 with non-GSM WAP based services

In addition COO does not it always assure the quality of the LBS application. Hence in such situations,  network-based (or handset based) PDE must be employed.

3. Angel of Arrival Method

When using this method, the Angle Of Arrival (AOA) of a signal between the mobile phone and the cellular antenna is analyzed. AOA PDE is used to capture AOA information to make calculations in order to determine an estimate of the mobile device position.

4. Time of Arrival Method

The Time Of Arrival (TOA) of signals between the mobile phone and the cellular antenna is used in the calculations of this method. TOA PDE is used to capture the Time Difference Of Arrival (TDOA) information. Then this information is used to make calculations to determine an estimate of the mobile device position.

5. Radio Propagation Techniques

Such techniques make use of a previously determined mapping of the radio frequency (RF) characteristics in order to determine an estimate of the mobile device position.

6. Hybrid Methods

These hybrid method include a combination of AOA and TOA and use the best of both to provide a better positioning result.

Handset-based Mobile Positioning Technology

The handset itself is the primary means of positioning the user in this method. However, 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.

1. SIM ToolKIT

The SIM Toolkit (STK), acts as an API between the Subscriber Identity Module (SIM) of a GSM mobile phone and an application. It provides the means of positioning a mobile unit. The positioning information provided by this method may be as approximate as COO or  maybe better through the usage of  additional means such as using  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 when the mobile device is in the idle state.  

2. Enhanced Observed Time Difference (E-OTD)

The basic method is employed as with TOA, except the fact that the handset is far more actively involved in the positioning process of this method. Specially equipped handsets are required for this purpose.This method is also referred to as reversed TOA or handset based TOA.

3. GPS 

Well this is a popular name. Even I know it!!

GPS or Global Positioning System is perhaps the best known or recognized handset-based PDE. When satellites are available GPS can be the most accurate method by itself. However this technology is often enhanced by the network. Assisted GPS (A-GPS) refers to a PDE system that makes use of additional network equipment which are 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

This can be deployed to assist in the positioning process.

The value of mobile IN is in leveraging 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. However it requires integration on the mobile network side to ensure current position information is made available.

The Importance of LBS Middle-ware

LBS middle-ware are application that do not provide the services themselves, but rather enable location based services.

The location manager function of LBS Middle-ware may be employed to convert positioning information into useful location information and make it available for LBS applications. One of the major advantages of this location manager function is enabling the use of various positioning technologies in conjunction with various LBS applications. Hence it acts as a gateway or hub for location.