How Satellite Phones Work: A Comprehensive Explanation

This page explains how satellite phones work, covering communication with landline phones, mobile phones, and other satellite phones.

What are Satellite Phones?

Satellite phones provide global communication coverage, even in remote and isolated areas where traditional cellular networks and wired transmission technologies are unavailable. They use satellites orbiting the Earth for communication, hence the name “satellite phones” or “Sat phones.” They support both voice and data connections.

Different satellite constellations like Iridium, Thuraya, Globalstar, and Inmarsat are deployed to provide services to these phones. For example, Iridium uses 66 Low Earth Orbit (LEO) satellites to ensure reliable communication and emergency services worldwide.

Satellite phones are a lifeline during emergencies and critical situations when connectivity is crucial. Travelers, adventurers, and professionals working in remote regions under extreme conditions often rely on them when other communication methods are unavailable.

How Do Satellite Phones Work?

Satellite phones communicate with satellites orbiting the Earth to connect with other phone types. Different satellite technologies (Iridium, GlobalStar, Thuraya, etc.) utilize varying numbers of satellites in different orbits.

Iridium, for instance, has about 66 satellites in Low Earth Orbit (LEO).

Ground stations are vital for facilitating communication between satellite phones and terrestrial communication infrastructure. They interface with satellites on one end and traditional terrestrial networks on the other. These ground stations connect with landline networks (PSTN), cellular mobile networks, and PSDN (Public Switched Data Network) used for internet access.

The ground station acts as a gateway between the satellite phone system’s elements. It performs essential functions, including:

• Signal reception and transmission
• Handover management
• Call routing
• Data processing and management
• Satellite tracking and monitoring
• Network control and coordination
• Security and encryption

Let’s explore three scenarios of satellite phone calls: satellite phone to satellite phone, satellite phone to landline phone, and satellite phone to cellular mobile phone.

Satellite Phone Calling Another Satellite Phone

Here are the steps involved when both the calling and called parties are using satellite phones:

1. The user of satellite phone A (the calling party) dials the phone number of satellite phone B (the called party). Satellite phone A sends a radio signal to the nearest satellite, including the phone number of satellite phone B.
2. The satellite receives the radio signal and relays it to a ground station on Earth.
3. The ground station relays the call signal back to a satellite in orbit near satellite phone B. In this scenario, the receiver’s satellite phone should ideally support direct satellite-to-satellite communication to avoid using terrestrial networks during call setup.
4. If the receiver’s satellite phone doesn’t support direct satellite communication, the call signal is routed from the ground station to a satellite facilitating communication with satellite phone B.
5. When satellite phone B receives the call from the satellite and acknowledges the request, two-way communication is established between the calling and called parties.
6. Both satellite phones can now exchange data, text messages, and access basic internet services directly through the satellite network.
7. When either party ends the call, all resources are released and become available for the next call or session.

Satellite Phone Calling a Landline Phone

Here’s how a call works when the calling party uses a satellite phone, and the called party has a landline phone:

1. The satellite phone user initiates a call by dialing the landline phone number. The satellite phone’s transmitter sends a radio signal to the nearest satellite.
2. The satellite receives the signal from the satellite phone and relays it to a ground station on Earth.
3. The ground station transfers the call to the appropriate terrestrial communication network based on the dialed number. Because the recipient’s device is a landline phone, the call is routed through the PSTN to the appropriate landline exchange serving the recipient.
4. When the landline phone rings and the user answers, a two-way communication channel is established.
5. Both parties can now communicate with each other.
6. When the call ends, the communication channels are freed, and both phones return to their idle state, ready for the next call.

Satellite Phone Calling a Cellular Mobile Phone

Here’s the process when a satellite phone calls a mobile phone:

1. The satellite phone user dials the mobile phone number.
2. The satellite receives the signal from the satellite phone and relays it to the ground station on Earth.
3. The ground station transfers the call to the appropriate cellular network, as determined by the dialed number. Because the recipient uses a mobile phone, the call is routed through the cellular network to the cell tower serving the recipient’s phone number.
4. The mobile phone receives the call and rings.
5. Once the recipient answers, a two-way voice communication channel is established.
6. Both parties can now communicate with each other.
7. When either party ends the call, the resources are freed and available for the next call.

The Future of Satellite Phone Technology

As we know, ground stations are essential for satellite phone communication. Advances in satellite technology and constellations are continually evolving. New satellite constellations, planned for global broadband internet coverage, may incorporate inter-satellite links (ISLs).

These ISLs allow direct communication between satellites, enabling faster data transfer and more efficient satellite handovers.

Currently, ground stations act as gateways to route signals between satellites and to interface with terrestrial communication networks, ensuring global coverage and reliable communication for satellite phone users.