What is GSM & how it works?


GSM can be abbreviated as Global System for Mobile communication. Today, GSM has been used by more than 800 million users spread in 190 countries. This data defines 70% of digital wireless consumption so its very important to cover this topic.

In GSM, geographic location is divided into hexagonal cells whose side depends upon the power of the transmitter and load on transmitte. At the center of a cell, a base station is present consists of a transceiver (combo of transmitters and receivers) and an antenna.

To better understand the concept of GSM, you have to understand the different components of the global system for mobile communication.

#1. A mobile station (MS) – Mobile station means the device on which communication will take place. It simply means a mobile phone.
#2. Base transceiver system (BTS) – It is used to maintain radio connectivity with the mobile station.
#3. Base station controller (BSC) – The main function of the base station controller is to allocate the necessary time between the base transceiver system and the mobile station.
#4. Home location register (HLR) – HLR is the reference database for subscriber parameter such as subscriber’s ID, location, authentication key, etc.,
#5. Visitor location register (VLR) – It consists of the copy of data present in the HLR. It is a temporary storage unit. It stores information until the user is active.
#6. Equipment identity register (EIR) – It is a database which contains a list of all the active users on the network.
#7. The authentication center (AuC) – This center provides authentication of the user.

Working of Global System of Mobile Communication

GSM is a collection of TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access) and Frequency hopping. In the starting, GSM used two frequencies; 890 to 915 MHz frequency band for uplink and 935 to 960 MHz frequency for downlink. However, later on, the frequency 75 MHz bands are added.

1710 to 1785 MHz for up-link and 1805 to 1880 MHz for downlink. up-link is the link from the ground station to a satellite and downlink is the link from a satellite down to one or more ground stations or receivers.

Control Channels

GSM has the following Control channels to regulate everything;

BCH (Broadcast Channel): This control channel is only for to manage downlinks such as;
BCCH  (Broadcast Control Channel) to broadcast information about the serving cell.
SCH (Synchronization channel) is used to carry information like frame number.
FCCH (Frequency Correction Channel) enables a mobile station to synch with frequencies.
CCCH (Common Control Channel): It has the following links related to its control;
RACH (Random Access Channel) is used by the mobile station to establish the first link. It is totally uplink.
AGCH (Access Grant Channel) is used as an acknowledgment of the access established by RACH. It is downlink.
PCH (Paging Channel) is downlink which used if there is an incoming call or a short message.
DCCH (Dedicated Control Channel): It is a collection of both down and uplinks. The links controlled in this channel are;
SDCCH (Stand-alone Dedicated Control Channel) is used for call setup, authentication, ciphering location update and SMS.
SACCH (Slow Associated Control Channel) is used to transmit signals when MS is busy.
FACCH (Fast Associated Control Channel) is used to send quick messages.

Well, this article had thrown some brief night on the GSM if you want to know more about this topic, then stay connected with us as we have some other information related to GSM which we will share in our upcoming posts. So, keep reading and increasing your technical knowledge with us.

About the author

Arpit Agarwal

I am a freelancer content writer, web developer and Video editor who loves to write technical stuff and on the other hand makes awesome videos as well. I like to make people happy with my writing and also try to make sure, you come back to read more.

By Arpit Agarwal

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