Cell Global Identity

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Cell Global Identity (CGI) is a globally unique identifier for a Base Transceiver Station in mobile phone networks [1] . It consists of four parts: Mobile Country Code (MCC), Mobile Network Code (MNC), Location Area Code (LAC) and Cell Identification (CI). It is an integral part of 3GPP specifications for mobile networks, for example, for identifying individual base stations to "handover" ongoing phone calls between separately controlled base stations, or between different mobile technologies [2] .

Base transceiver station

A base transceiver station (BTS) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets), WLL phones, computers with wireless Internet connectivity. The network can be that of any of the wireless communication technologies like GSM, CDMA, wireless local loop, Wi-Fi, WiMAX or other wide area network (WAN) technology.

The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC).

The 3rd Generation Partnership Project (3GPP) is a standards organization which develops protocols for mobile telephony. Its best known work is the development and maintenance of:

Contents

MCC and MNC make up a PLMN identifier, and PLMN and LAC make up a Location Area Identity (LAI), which uniquely identifies a Location Area of a given operator's network. So a CGI can be seen as a LAI with added Cell Identification, to further identify the individual base station of that Location Area.

In telecommunication, a Public Land Mobile Network (PLMN) is a combination of wireless communication services offered by a specific operator in a specific country. A PLMN typically consists of several cellular technologies like GSM/2G, UMTS/3G, LTE/4G, offered by a single operator within a given country, often referred to as a cellular network.

Each location area of a public land mobile network (PLMN) has its own unique identifier which is known as its location area identity (LAI). This internationally unique identifier is used for location updating of mobile subscribers. It is composed of a three decimal digit mobile country code (MCC), a two to three digit mobile network code (MNC) that identifies a Subscriber Module Public Land Mobile Network in that country, and a location area code (LAC) which is a 16 bit number with two special values, thereby allowing 65534 location areas within one GSM PLMN.

Overview

Examples

These are merely contrived examples and do not necessarily represent real cells (see the list of Mobile Country Codes and [3] ).

Note that an MNC can be of two-digit form and three-digit form with leading zeros, so that 01 and 001 are actually two distinct MNCs. Hence the CGIs 001-02-3-4 and 001-002-3-4 would be two completely unrelated cells, which would be in the same country, but belong to two completely distinct operators (02 and 002). From PLMN assignments, it is apparent that such dualities of two-digit and three-digit MNCs with the same number value are avoided. An example for an actual three-digit MNC with leading zeros is 750-001, of the operator Cable and Wireless South Atlantic Ltd (Falkland Islands).

Geographic location

A more specific application of the CGI is to roughly determine a mobile phone's geographical position. If a cell phone is connected to a GSM network then the position of that particular cell phone can be determined using CGI of the cell which is covering that cell phone. There is a series of related technologies that were developed based on CGI that enhances the location precision: Cell Global Identity with Timing Advance (CGI+TA), Enhanced CGI (E-CGI), Cell ID for WCDMA, Uplink Time Difference Of Arrival (U-TDOA) and Any Time Interrogation (ATI), and the high accuracy terminal based method Assisted Global Positioning System (A-GPS). [4]

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References

  1. ↑ 3GPP TS 23.003 §4.3.1 "Cell Identity (CI) and Cell Global Identification (CGI)" https://www.etsi.org/deliver/etsi_ts/123000_123099/123003/15.04.00_60/ts_123003v150400p.pdf
  2. ↑ 3GPP TS 48.008 §3.2.1.9 "HANDOVER REQUIRED" and §3.2.2.17 "Cell Identifier" https://www.etsi.org/deliver/etsi_ts/148000_148099/148008/15.00.00_60/ts_148008v150000p.pdf
  3. ↑ "Mobile Country Codes (MCC) and Mobile Network Codes (MNC)".
  4. ↑ "Location Based Services System overview". ERICSSON. 2009. Archived from the original on January 6, 2010. Retrieved 2009-05-25.
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