Overview
This lecture explains the core technologies behind Starlink’s satellite internet, focusing on how signals are transmitted, steered, and encoded between a ground dish and a fast-moving low-Earth orbit satellite.
Satellite Internet Basics
- Starlink internet uses a pizza-sized ground dish (“Dishy McFlatface”) to connect with satellites 550 km above Earth.
- Satellites move at ~27,000 km/h and each dish connects to a satellite for about 4 minutes before switching.
- Low Earth Orbit (LEO) satellites provide lower latency (~20 ms) compared to traditional TV satellites.
Dish vs. TV Satellite Dish
- TV dishes only receive signals from geostationary satellites at 35,000 km altitude, using parabolic reflectors.
- Starlink’s Dishy both sends and receives data and must target moving satellites in LEO.
Dishy McFlatface Hardware
- Dishy features 1280 small antennas in a hexagonal array on a large printed circuit board (PCB).
- Motors are used for initial alignment, not continuous movement.
- Each antenna is controlled by microchips for precise operation.
Phased Array Antenna & Beamforming
- A phased array combines signals from multiple antennas to form a focused, steerable beam.
- Beamforming enhances signal power—1280 antennas yield a signal roughly 3500x stronger than a single antenna.
- Phase shifting (adjusting signal timing) enables electronic steering of the beam to track satellites.
Beam Steering Technology
- The dish uses GPS and satellite position data to compute precise angles and phase shifts for beam steering.
- Main beam can be steered within a 100-degree field of view, recalculated every few microseconds.
- Starlink satellites use multiple phased arrays to connect with dishes and ground stations.
Modulation & Data Transmission
- Data is transmitted using 64QAM (Quadrature Amplitude Modulation), encoding 6 bits per symbol via amplitude and phase shifts.
- Symbols last about 10 nanoseconds, enabling transfer rates of hundreds of megabits per second.
- Time slots are divided between upload and download, as the dish can’t send and receive at the same time.
Signal Reception & Filtering
- Dish antennas are tuned for specific frequencies (11-13 GHz) to filter out interference from other signals.
- Patch antennas operate as both transmitters and receivers but not simultaneously.
Key Terms & Definitions
- Phased Array — antenna system where multiple elements’ signals combine to form a focused, steerable beam.
- Beamforming — technique of combining antennas’ outputs to reinforce signal in one direction.
- Phase Shift — altering the timing of a wave, changing constructive interference direction.
- 64QAM — modulation method encoding 6 bits per symbol by changing amplitude and phase.
Action Items / Next Steps
- Review key concepts of phased arrays and beamforming.
- Optional: Explore more about digital modulation (64QAM) and advanced video codecs (H.264).