Introduction to GSM Technology – SS1 Computer Hardware & GSM Repair Lesson Note (Second Term)

GSM, or Global System for Mobile Communications, is the digital standard that lets mobile phones make calls and send text messages on networks around the world. Your identity is stored on a SIM card. Your phone talks to a nearby tower in a cell, and the network passes your call to the next tower as you move.

This lesson moves from the big computers on our desks to the tiny ones in our pockets.

Behavioural objectives

By the end of the lesson, students should be able to:

• state what GSM and SIM stand for;
• describe the generations of mobile phones from 1G to 5G;
• name the three main parts of the GSM architecture and say what each does;
• explain what a cell is and what a handover is;
• list problems a GSM technician may meet, other than a broken screen.

How did mobile phones evolve?

Think back to the “brick” phones your parents might have used. Mobile phones have not always been slim and smart. They evolved in “Generations” (the G you see next to your signal bar).

• 1G (The Analogue Era): These phones were huge. You could only make voice calls, and the sound was often “scratchy.”
• 2G (The Birth of GSM): This introduced digital signals, which meant we could finally send SMS (Text Messages). The phones became smaller (think of the classic Nokia 3310).
• 3G (The Internet Era): This allowed us to browse websites and send emails on our phones.
• 4G & 5G (The High-Speed Era): This is what we use today for YouTube, TikTok and video calls.

What is GSM?

GSM stands for Global System for Mobile Communications. Before GSM, if you bought a phone in one country, it might not work in another.

GSM created a “universal language” for phones. The most important part of GSM for you is the SIM Card (Subscriber Identity Module).

• In the old days, the phone number was tied to the phone itself.
• With GSM, your “identity” is on the SIM card. You can move your SIM from a broken Infinix to a new Samsung, and your contacts and number stay the same.

How does GSM work? (GSM architecture)

When you call your friend, your voice goes through a very organised system. Think of it like a post office for voices.

The three main parts

1. The Mobile Station (MS): This is your physical phone and your SIM card.
2. Base Station Subsystem (BSS): These are the big metal telecom masts (towers) you see in your neighbourhood. They “catch” the signal from your phone.
3. Network Switching Subsystem (NSS): This is the “Brain” of the network, usually located in a big building owned by MTN, Airtel or Glo. It decides where to send your call and checks if you have enough credit (airtime).

What is a cell?

Why is it called a “Cell” phone? Imagine your city is covered by a giant “honeycomb” grid. Each hexagon in the grid is called a Cell, and each cell has its own tower in the middle.

• When you are travelling in a car or bus, your phone “talks” to one tower.
• As you move out of range, that tower “hands” you over to the next tower in the next cell.
• If this “handover” does not happen fast enough, the call drops. This is why calls sometimes cut when you are travelling at high speeds.

Why should a GSM technician learn this?

As a GSM repairer or technician, you need to know this because a faulty phone does not always have a broken screen.

• Network Problems: Sometimes a phone will not make calls because the Antenna (part of the Mobile Station) is broken.
• SIM Problems: Sometimes the phone is fine, but the “gold pads” that read the SIM card are dirty or bent.
• Software Lock: Sometimes a phone is “Network Locked,” meaning it can only work with specific networks (like a phone that only works on MTN).

GSM connects phones across the whole world. Understanding the generations and the towers helps you find where a connection is breaking.

Class discussion

1. Identify the nearest telecom mast to your house. Do you know which network (MTN, Glo, etc.) it belongs to?
2. If you take your SIM card out of your phone, can the phone still talk to the “Base Station”? (Hint: Try dialling an emergency number like 112).
3. Why was the invention of the SIM card so important for people who change phones often?

Evaluation

1. Write out in full: GSM and SIM.
2. Which generation introduced digital signals and SMS?
3. Name the three main parts of the GSM architecture and state what each one does.
4. What is a handover, and why can a call drop when you travel at high speed?
5. Give two reasons why a phone may fail to make calls even when its screen is not broken.

Assignment

In your notebook, explain in your own words how a call from your phone reaches your friend’s phone. Name the three main parts of the GSM architecture in the order the call passes through them.