GSM Global System for Mobile communications is an open, digital cellular technology used for transmitting mobile voice and data services. GSM is a circuit-switched system that divides each kHz channel into eight 25kHz time-slots. GSM operates in the MHz and 1.
GSM supports data transfer speeds of up to 9. Another major benefit is its international roaming capability, allowing users to access the same services when travelling abroad as at home. This gives consumers seamless and same number connectivity in more than countries.
GSM satellite roaming has also extended service access to areas where terrestrial coverage is not available. Global System for Mobile Communications.
The first European digital standard, developed to establish cellular compatibility throughout Europe. It's success has spread to all parts of the world and over 80 GSM networks are now operational. It operates at MHz. The NextG Network is a step up from the 3G Network and is availible at faster speeds Australia wide compared to the 3G Network which is limited to only major population centres.
Cellular is the term used to describe the MHz band, as the original analog cellular mobile communication system was allocated in this spectrum.
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Providers commonly operate in one or both frequency ranges. 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. 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. 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. 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 SIM card may be protected against unauthorized use by a password or personal identity number. Mobile Switching Centre.
It acts like a normal switching node of the PSTN or ISDN, and additionally provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. These services are provided in conjuction with several functional entities, which together form the Network Subsystem. 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. 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. An IMEI is marked as invalid if it has been reported stolen or is not type approved.
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The Authentication Center AuC is a protected database that stores a copy of the secret key stored in each subscriber's SIM card, which is used for authentication and encryption over the radio channel. 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. It handles radio-channel setup, frequency hopping, and handovers, as described below. Duplex spacing of 45 MHz is used.
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In some countries the GSM band has been extended to cover a larger frequency range. Channel numbers to GSM-R provides additional channels and specialized services for use by railway personnel. All these variants are included in the GSM specification. GSM uses - MHz to send information from the Mobile Station to the Base Transceiver Station uplink and - MHz for the other direction downlink , providing channels channel numbers to Duplex spacing is 95 MHz.