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How It Works

Understanding the technology behind Apple's satellite communication system

Communication Principle

Apple's satellite communication system uses a "bent-pipe" architecture where satellites act as mirrors in space. When your iPhone connects to a satellite, the signal is relayed to a ground station (called an "anchor") which is connected to the internet, allowing communication with Apple's services.

This system enables emergency services, location sharing, and messaging even when you're outside of cellular and Wi-Fi coverage areas.

Satellite Communication Principle
Fig. 1: Communication principle for Find My location sharing

The Satellite Network

Apple partners with Globalstar, a company operating satellites in Low Earth Orbit (LEO) at approximately 1,414 km above Earth. These satellites orbit the planet multiple times per day, providing global coverage.

Satellite Constellation
The Globalstar constellation consists of 48 satellites with an additional 4 spare satellites. Apple currently uses 28 of these satellites for its service.
Ground Stations
Multiple ground stations around the world receive signals from the satellites and connect to Apple's servers via the internet, enabling global coverage.
Orbital Mechanics
Satellites orbit Earth every 2 hours, making approximately 12 turns around the planet per day, ensuring consistent coverage as they pass overhead.

Technical Implementation

Apple has developed a sophisticated system that combines hardware and software innovations to enable satellite communication on iPhones.

Hardware Components

Custom Modem: Apple partnered with Qualcomm to develop a custom modem supporting satellite communication.

Specialized Antenna: A customized antenna design boosts outgoing signals to reach satellites hundreds of kilometers away.

Baseband Processor: Handles the signal processing required for satellite communication.

Software Components

Satellite Tracking: The iPhone calculates satellite positions using Two-Line Element (TLE) data to guide users where to point their device.

Compression Algorithms: Special text compression reduces message size for efficient transmission over limited bandwidth.

Security Protocols: End-to-end encryption protects all communications sent via satellite.

User Experience

When using satellite features, the iPhone provides a specialized interface to help users establish and maintain a connection.

Connection Process

  1. The iPhone detects when cellular and Wi-Fi are unavailable
  2. User initiates a satellite feature (Emergency SOS, Find My, etc.)
  3. iPhone calculates positions of available satellites
  4. User is guided to point their iPhone toward a satellite
  5. Connection is established and maintained as needed
  6. Data is transmitted in compressed, encrypted format
Satellite Connection Interface

Signal Transmission

The iPhone transmits satellite signals over the L-Band (1,610 MHz to 1,626.5 MHz) and receives signals over the S-Band (2,483.5 MHz to 2,500 MHz).

The system uses Single Carrier Frequency Division Multiple Access (SC-FDMA) with a channel spacing of 200 kHz. Each transmission consists of multiple bursts, with each burst containing different data types.

Under optimal conditions, a complete transmission takes approximately 20 seconds, though challenging conditions may extend this time.

Signal Transmission Spectrogram
Fig. 2: Spectrogram of physical-layer uplink signal