GSM (Global System for
Global System for
GSM-900 and GSM-1800 are used in most parts of the world.
GSM-1800 is also called PCS in Hong Kong and the United Kingdom. Most of the GSM operators in India use the 900 MHz band. Operators like Hutch, Airtel, Idea, and some others, use 900MHz in rural areas and 1800MHz in urban areas.
GSM-850 and GSM-1900 are used in the United
and many other countries in the
Cellular is the term used to describe the 850 MHz band, as the original analog cellular mobile communication system was allocated in this spectrum. Providers commonly operate in one or both frequency ranges.
European Telecommunications Standards Institute (ETSI), original GSM standardization body.
Constellation used by GSM: QPSK, 8PSK, 16-QAM.
The method chosen by GSM is a combination of Time- and Frequency-Division Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the (maximum) 25 MHz bandwidth into 124 carrier frequencies spaced 200 kHz apart. One or more carrier frequencies are assigned to each base station. Each of these carrier frequencies is then divided in time, using a TDMA scheme. The fundamental unit of time in this TDMA scheme is called a burst period and it lasts 15/26 ms (or approx. 0.577 ms). Eight burst periods are grouped into a TDMA frame (120/26 ms, or approx. 4.615 ms), which forms the basic unit for the definition of logical channels. One physical channel is one burst period per TDMA frame.
Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. It allows several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his own timeslot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only the part of its bandwidth they require. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, and combat-net radio systems.
TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.
Applications for GSM:
-Digital Communication such GPS, Cell Phones, Laptops.
1.) Mobile Station
The mobile station (MS) consists of the mobile equipment (the terminal) and a smart card called the Subscriber Identity Module (SIM). The SIM provides personal mobility, so that the user can have access to subscribed services irrespective of a specific terminal. By inserting the SIM card into another GSM terminal, the user is able to receive calls at that terminal, make calls from that terminal, and receive other subscribed services.
The mobile equipment is uniquely identified by the International Mobile Equipment Identity (IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key for authentication, and other information. The IMEI and the IMSI are independent, thereby allowing personal mobility. The SIM card may be protected against unauthorized use by a password or personal identity number.
The central component
of the Network Subsystem is the
The Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC, provide the call-routing and roaming capabilities of GSM. The HLR contains all the administrative information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile. The location of the mobile is typically in the form of the signalling address of the VLR associated with the mobile station. The actual routing procedure will be described later. There is logically one HLR per GSM network, although it may be implemented as a distributed database.
The Visitor Location Register (VLR) contains selected administrative information from the HLR, necessary for call control and provision of the subscribed services, for each mobile currently located in the geographical area controlled by the VLR. Although each functional entity can be implemented as an independent unit, all manufacturers of switching equipment to date implement the VLR together with the MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR, thus simplifying the signalling required. Note that the MSC contains no information about particular mobile stations --- this information is stored in the location registers.
The other two registers are used for authentication and security purposes.
The Equipment Identity Register (EIR) is a database that contains a list of all
valid mobile equipment on the network, where each mobile station is identified
by its International Mobile Equipment Identity (IMEI). An IMEI is marked as
invalid if it has been reported stolen or is not type approved. The
3.) Base Station Subsystem (BSS)
The Base Station Subsystem is composed of two parts, the Base Transceiver Station (BTS) and the Base Station Controller (BSC). These communicate across the standardized Abis interface, allowing (as in the rest of the system) operation between components made by different suppliers.
The Base Transceiver Station houses the radio tranceivers that define a cell and handles the radio-link protocols with the Mobile Station. In a large urban area, there will potentially be a large number of BTSs deployed, thus the requirements for a BTS are ruggedness, reliability, portability, and minimum cost.
The Base Station Controller manages the radio resources for one or more BTSs. It handles radio-channel setup, frequency hopping,
and handovers, as described below. The BSC is the connection between the mobile
station and the
Gaussian Pulse Shape for GSM.
physical layers document:
-Pulse Coded Modulation (PCM)
-Regular Pulse Excited - Linear Predictive Coder (RPE--LPC)
-Enhanced Full-Rate (EFR)
Channel coding and modulation:
-Gaussian-filtered Minimum Shift Keying (GMSK).
Standardizations for GSM found in: