How Mobile Phones Make Calls and Evolve Through Generations

Mobile communication relies on a combination of wireless and wired technologies. When a user speaks into a phone, the voice is captured, transformed into digital data, and sent through a network of cell towers and central switching equipment to reach the intended recipient.

How a Mobile Phone Makes a Call

Voice to Digital Signal

A microphone picks up the speaker’s voice. Inside the handset, a MEMS sensor and an integrated circuit (IC) convert the acoustic waveform into a digital signal composed of zeros and ones.

Transmission via Electromagnetic Waves

The phone’s antenna then radiates this digital signal as electromagnetic waves. The transmission alters wave characteristics such as amplitude, frequency, or phase to represent the binary data.

Limitations of Electromagnetic Waves

Electromagnetic waves lose strength when they encounter physical objects, electrical equipment, environmental conditions, or the curvature of the Earth. These factors limit how far the waves can travel without assistance from network infrastructure.

Cellular Technology

Concept of Cells and Towers

Geographic areas are divided into hexagonal cells, each served by a cell tower that holds a specific frequency slot.

Wired Connectivity (Optical Fiber)

Cell towers are linked together primarily by optical fiber cables, which may be laid underground or underwater to provide national and international connectivity.

Signal Processing and Routing

When a phone transmits, the local tower receives the electromagnetic waves, converts them into high‑frequency light pulses, and sends them to a base transceiver box for processing. The processed voice signal is then routed to the destination tower, which re‑radiates the waves to the recipient’s phone. As a result, mobile communication uses both wireless and wired mediums.

“So, it's true that mobile communications are not entirely wireless, they do use a wired medium too.”

Mobile Switching Center (MSC)

Role and Function

The Mobile Switching Center (MSC) is the central point for a group of cell towers. It stores subscription information—including service plans, current location, and activity status—and manages call routing.

Home MSC vs. Foreign MSC

When a SIM card is purchased, its subscription data is registered in a “home MSC.” If the user moves outside the home MSC’s coverage, a “foreign MSC” takes over and communicates with the home MSC to keep track of the user’s location.

Location Tracking Techniques

MSCs track subscriber location through periodic updates, updates triggered when a phone crosses a predefined number of towers, and updates when the phone is turned on.

Call Routing Example (Emma and John)

Emma dials John’s number. The request first reaches Emma’s home MSC, which forwards it to John’s home MSC. John’s home MSC checks whether John is currently in his home MSC or a foreign MSC. If John is in his home MSC, the request is sent to his local cell tower to verify availability. If John is in a foreign MSC, the home MSC forwards the request to the foreign MSC, which then locates John’s phone and completes the call.

“The home MSC always knows which MSC area you are in.”

Frequency Spectrum Management

Importance of Frequency

Each subscriber is allocated a specific frequency range to transfer digital data.

Limited Spectrum and Subscriber Count

The available frequency spectrum is limited, yet billions of subscribers rely on it.

Solutions: Frequency Slot Distribution and Multiple Access Techniques

Frequency slot distribution assigns different frequency slots to different cell towers. Multiple access techniques—such as TDMA, CDMA, OFDMA, and MIMO—efficiently share these slots among active users within a cell area.

“However, the frequency spectrum available for cellular communications is quite limited, and there are billions of subscribers.”

Evolution of Mobile Generations

1G (First Generation)

1G introduced the first mobile phones that could be carried without a cable. It used analog transmission, resulting in poor voice quality, limited security, and inefficient frequency usage (Frequency Division Multiple Access).

2G (Second Generation)

2G adopted digital multiple access technologies like TDMA and CDMA, enabling SMS messaging and basic internet browsing.

3G (Third Generation)

3G focused on higher data transfer speeds—up to 2 Mbps—using WCDMA and expanded bandwidth for GPS, video, and voice calls, turning phones into smartphones.

4G (Fourth Generation)

4G achieved speeds of 20‑100 Mbps through OFDMA and MIMO technology, supporting high‑resolution movies and TV. MIMO employs multiple transmitter and receiver antennas to improve throughput.

5G (Fifth Generation)

5G, soon to be rolled out, will use enhanced MIMO and millimeter‑wave frequencies. It aims to support the Internet of Things (IoT), including driverless cars and smart homes.

“5G, to be rolled out soon, will use enhanced MIMO technology and millimeter waves.”