In this series of articles I will describe how mobile location enables many exciting new areas, including:
- Location Based Advertising,
- location Based Billing, and
- location Based Services.
First let’s look at how mobile location works. Mobile Location is the process of establishing the geographic position of a mobile phone or device. In North America, Mobile Location is often referred to as Cellular Location.
There are four principal ways that this can be done:
If the mobile phone has a GPS chip set inside it, the GPS receiver can be used to locate the phone. GPS is based on a constellation of 24 satellites that are orbiting the globe. If the GPS receiver can pick up four or more of the satellites, it is able to establish the location of the phone, based on the amount that the signal from each satellite is delayed. The advantage of GPS is that it is highly accurate, often down to tens of metres. The disadvantages are that it only works on devices that have an integrated GPS, it usually does not work indoors, and it drains device batteries very quickly.
The SIM card, used in the great majority of the world’s phones, is the means by which a subscriber is identified to the network. While the SIM card may be considered a secure data storage device, it is in fact a low-power computer. In SIM-based location, an application on the SIM card obtains the ID of the cell the mobile phone is currently listening to. When the location of a mobile needs to be obtained, the application sends the cell ID information to a location server via SMS. The location server then combines knowledge of the cell locations with the cell ID observations to estimate the phone’s location.
The advantage of SIM location is that it can be used for the great majority of mobile phones, and it works anywhere that there is mobile coverage. The disadvantage is that it is not as accurate as GPS. However, it can be much more accurate than Network Cell-ID (see below), because it is able to use historical information about the cell sites heard by the phone. On some handsets it is possible to access the signal strength information enabling accuracy to be improved my ip location.
Whenever a mobile phone makes a call, the Network Operator knows through which cell the phone is communicating. Based on the location of the cell, the Operator is able to estimate the location of the phone. Because it utilises the Cell Identifier (Cell-ID), as measured in the mobile Network, this method is known as Network Cell-ID or NCID. The advantage is that the method works on all phones in a network. The disadvantage is that it is not as accurate as SIM location, because it has to use a single Cell-ID measurement.
An improved version of NCID is known as Enhanced CID or E-CID. This uses additional information such as Timing Advance or signal strength measurements (from probes) to improve accuracy. NCID and E-CID, however, do not easily support the the longer integration times that can be used in handset and SIM based location to improve accuracy.
Handset-based Location is similar to SIM-based location, the difference being that the application resides in the phone, rather than in the SIM card. Unlike SIM location, which exploits an industry standard to which all mobile phones should comply, handset-based location depends very much on the degree to which the handset’s operating system provides cell-ID information and signal strength. The application that accesses the cell data may be pre-loaded onto the phone, as occurs with Singapore Press Holdings’ Rednano Locate, or downloaded and installed, as is the case with Google’s My Location.
If the handset supports Wi-Fi, then it is also possible to use the Wi-Fi access points to derive a location estimate. Wi-Fi-based location provides very accurate location in urban areas, but only works on a small proportion of the total number of mobile phones.
In summary, there are four major ways to locate a mobile, each with their own advantages and disadvantages. GPS is the most accurate method, but SIM Location can be used for many more handsets. More information on how to implement SIM and handset based location can be found here.