GSM: What is it and how does it work?

The first GSM-based mobile services were started in 1991 in Finland and the acronym changed to Global System for Mobile Communications. Its main objective was to provide a uniform international standard for wireless mobile communications.  At the same time the first digital mobile system based on GSM recommendations was created, which later became known as GSM-1800.

At JSC Ingenium, network infrastructure solutions for MNOs and MVNOS, we explain exactly what they consist of and how they work.

What is GSM?

GSM or Global System for Mobile Communications is the most popular wireless mobile communication technique used for public communication. The GSM standard was developed to establish protocols for second-generation digital mobile networks (2G).

Initially it began as a circuit-switched network, but later, following the integration of General Packet Radio Service (GPRS) technology, it was implemented packet switching. The most commonly used GSM frequency bands are 900 MHz and 1800 MHz.

In Europe and Asia GSM operates in the frequency range of 900 to 1800 MHz, while in the United States and other countries of America it operates in the frequency range of 850 to 1900 MHz. Uses a digital air interface which converts analog signals into digital signals before transmission. Transmission speed is 270 Kbps.

Today, approximately 80% of mobile phones worldwide use the Global System for Mobile Communications (GSM). There are more than three billion users of this technology.

How does it work?

The Global System for Mobile Communications (GSM) uses a combination of time division multiple access (TDMA) and frequency division multiple access (FDMA).

Frequency Division Multiple Access:

It involves dividing a frequency band into multiple bands, so that each subdivided frequency band is assigned to a single subscriber. FDMA in GSM divides the 25 MHz bandwidth into 124 carrier frequencies, each with a separation of 200 KHz. Each base station is assigned one or more carrier frequencies.

Time Division Multiple Access:

It involves assigning the same frequency channel to different subscribers by dividing the frequency band into multiple time intervals. Each user gets its own time interval, allowing multiple stations to share the same transmission space.

In GSM, each subdivided carrier frequency is divided into different time intervals using the TDMA technique. Each TDMA frame has duration of 4.164 milliseconds (ms) and contains 8 time intervals. Each time interval, or physical channel within this framework, has duration of 577 microseconds and data is transmitted in that time interval in the form of bursts.

Evolving technologies

Although the GSM or 2G communications network is still the preferred network for many subscribers, especially in developing countries such as India, due to its availability and economy, there are different communication technologies, such as the Universal Mobile Telecommunications System (UMTS) and the Long Term Evolution (LTE). While UMTS provides third-generation wireless communication standards, LTE provides fourth-generation wireless communication standards.