TABLE OF CONTENTS In recent years the importance of location services for mobile phone/cellular telecommunications has risen significantly. One of the major reasons for this is the requirement to locate mobile phones in the case of an emergency. For landlines it is a simple matter to trace the location of the call, because by their very nature they are fixed. For mobile phones the matter is quite different, and on many occasions the emergency services have had great difficulty in locating mobiles with any degree of accuracy. With rulings such as the E911 directive in the USA requiring operators to be able to locate mobile phones accurately, the concept of phone position location has become more important.
A number of techniques are made available by cell phone operators, including cell identity (Cell ID), Time Difference of Arrival (TDOA), Enhanced Observed Time Difference (EOTD), Advanced Forward Link Trilateration (AFLT) and Assisted GPS (A-GPS). Of these, Cell ID, TDOA and A-GPS are being widely used, with A-GPS emerging as the front runner. The other schemes have not gained any real acceptance and commercial usage.
Cell identity is the most basic positioning system used in GSM, and for many years was the only method of locating a mobile. It is a network-based method, and utilizes the fact that once the mobile has registered with the network, the network has to know where the mobile is so that it can be paged when there are incoming calls or text messages, etc. This information is available...
