Global System For Mobile Communications (GSM): Explained

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Did you know that GSM history goes back to 1975 and it is the most popular wireless cellular communication technique? If you want to learn more about GSM and how it works, you are in the right place. We are going to go over everything there is to know about it. 

Keep reading to learn all the ins and outs of GSM networks. 

What Does GSM Mean? 

Global System for Mobile Communication is an international standard term. There are many parts of the world like Europe, where GSM is the only type of cellular service available. GSM was developed as a digital system. 

In Europe and in Asia, GSM operates in the 900 MHz band, and in the United States, it operates in the 1900 MHz band. 

Companies like Mobile Versterkers help with making sure that you are getting the most out of your signal with a special GSM amplifier. 

How Does GSM Work? 

There is a combination of Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) that is used for GSM to work. FDMA is a frequency band that is divided into multiple bands where each sub-divided frequency band is given to a single subscriber. 

TDMA is where the same frequency channel is given to different subscribers. This is done by dividing the frequency band into different time slots. Every user gets his or her own timeslot. This allows multiple stations to share the same transmission space. 

Originally GSM used two frequency bands of 25 MHz width, 890 to 915 MHz frequency band for up-link, and 935 to 960 MHz frequency for down-link. After some time, two 75 MHz bands were added. This included 1710 to 1785 MHz for up-link and 1805 to 1880 MHz for down-link. 

The up-link is the link from the ground station to a satellite and the down-link is the link from a satellite down to one or more receivers or ground stations. GSM divides the 25 MHz band into 124 channels where each one has 200 KHz width and the 200 KHz that is not used serves as a guard band to help avoid any interference. 

GSM Network 

The GSM network has four parts that work together to function as one. You have the mobile device, the BSS (base station subsystem), the NSS (network switching subsystem), and the OSS (operation and support subsystem). 

First, the mobile device connects to the network with its hardware, and then the SIM card provides the network with identifying information about the mobile user. Next, the BSS will handle the traffic between the NSS and the cell phone device. 

This is made up of the base transceiver (BTS) and the base station controller (BSC). The BTS has the equipment that communicates with the mobile phones, and the BSC communicates with a group of BTS stations and controls them. 

The NSS helps with routing the calls, authenticating and storing caller information via the SIM cards, and helps with SMS (short message service). 

Main Controls 

There are a few main controls in GSM and each control has three different types included. 

Common Control Channel 

This is also known as the CCCH and it has a few types available. There is the RACH (Random Access Channel) which is used by MS when it's first making access to the network. The RAHC is only for up-link. 

The second type is the PCH (Paging Channel). This is only for down-link. PCH is the network page for the MS when there is a short message incoming, or an incoming call. 

AGCH (Access Grant Channel) is the third type of CCCH. This is only for down-link and it is used for acknowledgment of the access attempt that is sent on RACH. 

Broadcast Channel 

The BCH or Broadcast Channel is only for down-link and it has three different types as well. The first type is the FCCH (Frequency Correction Channel). This is what enables MS to synchronize to frequency. 

The second type is the BCCH (Broadcast Control Channel). This is what broadcasts information about the serving cell. The last type is the SCH (Synchronization Channel). This is what carries information for frame synchronization, such as the base station identity code and the frame number. 

Dedicated Control Channel 

The DCCH is for down-link and for up-link and also has three different types. There is the FACCH (Fast Associated Control Channel) which is used to send fast messages. Another type is the SDCCH (Stand-Alone Dedicated Control Channel), which is used to set up calls, authenticate the calls, and to cipher location update and SMS. 

The third type of DCCH is SACCH (Slow Associated Control Channel). This is used to transfer signals while MS is having an ongoing conversation on topic or while the SDCCH is being used. 

Technology Growth 

Even though GSM is the preferred network for many subscribers because it is economic and available everywhere, there are different communication technologies being developed and others that have already been developed. You might be familiar with Universal Mobile Telecommunications System (UMTS) or Long Term Evolution (LTE) technologies. 

UMTS provides users with 3rd generation wireless communications, giving them faster data speeds. LTE provides 4th generation technology. 

Feeling Like A GSM Expert? 

As you can see there is a lot to know about GSM. You might have never realized how much was behind making a simple phone call on a mobile device. We have seen the mobile phone revolution unfold right before our eyes and it will continue to grow and expand over time. 

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