How does Starlink Satellite Internet Work?š”āš„
Summary
TLDRThis script delves into the revolutionary technology of Starlink, a satellite internet system. It explains how a pizza-sized dish transmits data to satellites orbiting 550 km above Earth, using phased array antennas and beamforming to maintain a focused beam for high-speed data transfer. The video explores the inner workings of the satellite dish, the communication process between the dish and the satellite using 64QAM, and the challenges of sending and receiving signals in a rapidly moving environment. It offers a detailed look at the engineering marvels that make satellite internet both feasible and efficient.
Takeaways
- š°ļø Starlink uses a phased array satellite dish that both sends and receives internet data from low Earth orbit satellites, unlike traditional TV satellite dishes that only receive signals.
- š The Starlink satellites orbit at a much lower altitude of 550 kilometers compared to TV satellites at 35,000 kilometers, requiring precise and continuous beam steering to maintain connection.
- š The dish switches between different satellites every few minutes due to the fast movement of the satellites across the sky.
- š” Inside the Starlink dish, there's a sophisticated setup including motors, a PCB with microchips, and a massive array of 1280 antennas arranged in a hexagonal pattern for phased array communication.
- š¶ Each antenna in the array is controlled by microchips to generate and steer electromagnetic waves, creating a focused beam to communicate with the satellite.
- š The phased array uses beamforming to combine the signals from all antennas, resulting in a powerful beam capable of reaching the satellite in space.
- š§ Phased array beam steering is achieved by adjusting the phase of the signals sent to each antenna, allowing the beam to be directed towards the fast-moving satellite.
- š The system uses GPS and software to calculate the precise angles and phase shifts needed for the antennas to maintain a lock on the satellite.
- š Data transmission between the dish and satellite utilizes 64QAM modulation, encoding 6-bit binary values with different amplitude and phase permutations, enabling high-speed data transfer.
- š„ The video codec h.264 is used to compress and transmit high-quality video data, allowing users to stream content smoothly.
- šØāš« The script highlights the multidisciplinary nature of the technology, touching on fields like electromagnetics, signal processing, and antenna design.
Q & A
What is the primary function of the Starlink satellite dish compared to a traditional TV satellite dish?
-The Starlink satellite dish, also known as Dishy McFlatface, both sends and receives internet data from a Starlink satellite orbiting 550 kilometers away, unlike traditional TV satellite dishes which only receive TV signals from broadcast satellites orbiting at an altitude of 35,000 kilometers.
How fast do the Starlink satellites move and what is the significance of their speed?
-Starlink satellites move at an incredible speed of around 27,000 kilometers per hour. This speed is significant as it allows for the rapid transmission of data at hundreds of megabits per second, despite the continuous need to angle or steer the data beam between the moving dish and satellite.
Why do Starlink satellites need to be in low Earth orbit?
-Starlink satellites are in low Earth orbit to provide low latencies of around 20 milliseconds, which is critical for activities such as online gaming or web browsing without noticeable delays.
What is the purpose of the phased array in the Starlink ground dish?
-The phased array in the Starlink ground dish is used to send and receive electromagnetic waves that are angled to and from a Starlink satellite. It consists of 1280 antennas arranged in a hexagonal honeycomb pattern, working together to focus the signal into a tight, powerful beam.
How does the phased array beam steering work in the Starlink dish?
-Phased array beam steering works by continuously changing the phase of the signals sent to the antennas, which alters the timing of the peaks and troughs emitted from each antenna. This creates a sweeping zone of constructive interference that can be directed towards the satellite.
What is the role of the motors in the Starlink dish during its operation?
-The motors in the Starlink dish are used only for initial setup to get the dish pointed in the proper general direction. They do not continuously move the dish to point directly at the Starlink satellite during operation.
How does the Starlink dish ensure it is communicating with the correct satellite?
-The Starlink dish uses its GPS coordinates and the known orbital position of the Starlink satellite. The software in the dish computes the exact set of 3D angles and required phase shift for each of the antennas to perfectly aim the beam at the satellite.
What is the maximum data transfer rate achievable with the Starlink system?
-The Starlink system can achieve a data transfer rate of up to 540 million bits per second using 64QAM (Quadrature Amplitude Modulation), which allows for the transmission of 6-bit binary values through different combinations of amplitude and phase.
How does the Starlink dish handle the transition between different satellites as they move out of its field of view?
-The Starlink dish switches between different satellites every 4 or so minutes as they move out of its field of view. This is managed by the dish's software, which constantly computes and updates the phase shifts required for communication with the next satellite in view.
What is the significance of the 100-degree field of view for the Starlink dish?
-The 100-degree field of view allows the Starlink dish to steer the beam in any direction within that range, ensuring continuous communication with the rapidly moving satellites without the need for physical movement of the dish.
How does the Starlink system minimize latency in data transmission?
-The Starlink system minimizes latency by distributing the time slots for data transmission throughout a single second, rather than grouping them all together. This ensures that the data is sent and received with minimal delay.
Outlines
š°ļø Starlink Satellite Internet Technology
This paragraph introduces the Starlink satellite internet system, highlighting its impressive technological feats. The system uses a large satellite dish, capable of transmitting data to satellites orbiting at 550 kilometers above Earth. The Starlink satellites move at an astonishing speed of 27,000 kilometers per hour, facilitating high-speed data transfer with minimal latency. The dish dynamically adjusts to maintain a direct connection with the rapidly moving satellites, switching between them every few minutes. The video promises an in-depth exploration of the technologies enabling this system, including the inner workings of the satellite dish, its ability to steer the data beam, and the data transmission capabilities that allow for simultaneous streaming of multiple HD movies.
š Dissecting Dishy McFlatface and Its Antennas
The second paragraph delves into the technical differences between traditional TV satellite dishes and the Starlink ground dish, humorously named 'Dishy McFlatface.' Unlike TV dishes that only receive signals, Dishy sends and receives internet data. The Starlink satellite's lower orbit of 550 kilometers allows for faster data transmission but requires precise beam steering. The paragraph describes the internal components of Dishy, including its motors, ethernet cable, and the intricate printed circuit board (PCB) with microchips and GPS module. It also explains the phased array of 1280 antennas that work together to send and receive signals to the satellite, emphasizing the complexity and precision of the technology.
š” Understanding Antenna Function and Beamforming
This paragraph explains the function of a single antenna within Dishy's phased array, focusing on the aperture-coupled patch antenna. It describes the process of generating an electromagnetic wave through the antenna's layers, including the microstrip transmission line feed and the antenna patch. The paragraph simplifies the complex process by illustrating how high-frequency signals create oscillating electric fields, leading to the formation of electromagnetic waves. It also touches on the antenna's ability to transmit and receive signals, the importance of phase shifting, and the concept of beamforming, which combines the power of multiple antennas to create a focused beam capable of reaching outer space.
š Steering the Beam with Phased Array Technology
The fourth paragraph discusses the advanced technique of phased array beam steering, which is essential for maintaining a connection with the fast-moving Starlink satellite. It explains how phase shifting the signals sent to the antennas can angle the beam without physically moving the dish. The paragraph uses a simplified two-antenna example to demonstrate how constructive and destructive interference patterns can be manipulated to steer the beam. It also explains how Dishy uses GPS coordinates and software to calculate the necessary phase shifts for each antenna, allowing for precise beam direction and the ability to track satellites across a 100-degree field of view.
š Data Transmission via 64QAM Modulation
The fifth paragraph explores how data is transmitted between Dishy and the Starlink satellite using 64QAM (Quadrature Amplitude Modulation). It describes the process of encoding binary data into variations of amplitude and phase, creating a constellation diagram with 64 different permutations. The paragraph explains how these symbols, each containing 6 bits of data, are transmitted in rapid succession, resulting in a high data transfer rate. It also discusses the division of transmission time between upload and download, and the distribution of these time slots to reduce latency.
š Conclusion and Further Exploration
The final paragraph wraps up the video script by acknowledging the complexity of the technology and the effort put into creating the video. It invites viewers to engage with the content through subscriptions, likes, and comments, and provides a link for further learning through Brilliant.org. The paragraph also clarifies some of the video's visual representations, emphasizing the actual scale of Dishy and the satellite, and the speed at which electromagnetic waves travel. It concludes by thanking sponsors and collaborators, and encourages viewers to explore more of Branch Education's content.
Mindmap
Keywords
š”Starlink
š”Satellite Dish
š”Phased Array
š”Beamforming
š”Parabolic Reflector
š”Orbital Position
š”Microchips
š”Quadrature Amplitude Modulation (64QAM)
š”Electromagnetic Waves
š”Constellation Diagram
Highlights
Beaming internet from the woods using a large satellite dish to a satellite 550 km away is a technological marvel.
Starlink satellites move at 27,000 km/h, with data speeds of hundreds of megabits per second.
The dish and satellite continuously angle to maintain a direct data beam connection.
The dish switches between different satellites every 4 minutes to maintain connectivity as they move out of view.
The video explores key technologies enabling satellite internet, including the satellite dish's inner workings.
Dishy McFlatface, the Starlink ground dish, both sends and receives internet data from orbiting satellites.
Starlink satellites are in low earth orbit for lower latency, requiring thousands for global coverage.
Dishy McFlatface contains 1280 antennas arranged in a hexagonal honeycomb pattern for phased array communication.
Each antenna in Dishy is controlled by microchips to generate and steer electromagnetic waves to the satellite.
Phased array beam steering uses phase shifting to angle the beam without physically moving the dish.
64QAM is used to encode 6-bit binary values into variations of amplitude and phase for data transmission.
The video provides a detailed explanation of how Dishy and the Starlink satellite communicate using electromagnetic waves.
The video explains advanced concepts in an accessible way, including the use of Brilliant for further learning.
The video clarifies misconceptions about the scale of Dishy and the satellite, and the speed of electromagnetic wave transmission.
The video script underwent extensive revisions to ensure accuracy and depth of information.
The video concludes with an invitation to support the creators and explore more technology through their animations.
Transcripts
Beaming internet from the middle of theĀ woods using an extra-large pizza-sized
satellite dish placed on top of your house upĀ to a satellite orbiting 550 kilometers outside
Earthās atmosphere, well letās be honest, isĀ technologically mind-blowing. Whatās even crazier
is that the Starlink satellites move incrediblyĀ fast, around 27,000 kilometers per hour,
and data is being sent back and forth between themĀ at hundreds of megabits per second, all while the
dish and satellite are continuously anglingĀ or steering the beam of data pointed directly
between them. On top of that, the dish switchesĀ between different satellites every 4 or so minutes
because they move out of the dishesā field ofĀ view rather quickly. If you have no clue as to
how this is possible, stick around because weāreĀ going to dive into the multiple key technologies
which enable satellite internet to magically work. First, weāll explore inside the satellite dish and
see how it generates a beam of data that is ableĀ to reach space. Second, weāll see how this dish
continuously steers the beam so that it pointsĀ directly at a satellite moving across the sky. And
third, weāll dive into what exactly the dish andĀ satellite are sending inside the beam that results
in your ability to stream five HD movies or showsĀ simultaneously. This video is quite long as itās
full of in-depth details. We recommend watchingĀ it first at one point two five times speed,
and then a second time at one and a half speedĀ to understand it as a complete technology. So,
stick around, and letās jump right in. First, letās start by clarifying the
difference between a television satellite dishĀ such as this one, and the Starlink ground dish,
which Elon Musk dubbed Dishy McFlatface or DishyĀ for short. TV dishes use a parabolic reflector
to focus the electromagnetic waves which areĀ the TV signals sent from broadcast satellites
orbiting the Earth at an altitude of 35 thousandĀ kilometers. TV satellite dishes only receive
TV signals from space, they canāt send data. Dishy, however, both sends and receives internet
data from a Starlink satellite orbiting 550Ā kilometers away. While the Starlink satellite is
60 times closer than TV satellites, itās still anĀ incredible distance to wirelessly send a signal,
and thus the beams between Dishy and the StarlinkĀ satellite need to be focused into tight powerful
beams that are continuously angled or steered toĀ point at one another. Compare this to TV broadcast
signals which come from a satellite the size ofĀ a van, and whose signals propagate in a wide fan
that covers land masses larger than NorthĀ America. Table size Starlink satellites,
however, need to be in a low earth orbitĀ to provide for 20-millisecond latencies,
which is critical for smoothly playing internetĀ games or surfing the web, and as a result, their
coverage is much smaller. Thus 10,000 or moreĀ Starlink satellites, all orbiting at incredibly
fast speeds in a low earth orbit, are required toĀ provide satellite internet to the entire earth.
Letās now open up Dishy McFlatface. At the back,Ā we have a pair of motors and an ethernet cable
that connects to the router. Note that theseĀ motors donāt continuously move Dishy to point
directly at the Starlink satellite; theyāre usedĀ only for initial setup to get the dish pointed in
the proper general direction. Opening up Dishy,Ā we find an aluminum structural back-plate and on
the other side, we find a massive printed circuitĀ board or PCB. One side has 640 small microchips
and 20 larger microchips organized inĀ a pattern with very intricate traces
fanning out from the larger to smaller microchips,Ā along with additional chips including the main CPU
and GPS module on the edge of the PCB. On theĀ other side are 1,400ish copper circles with a grid
of squares between the circles. On the next layer,Ā thereās a rubber honeycomb pattern with small,
notched cop-per circles, and behind that, we findĀ another honeycomb pattern and then the front side
of Dishy. So, what are we looking at? Well, inĀ essence, we have 1280 antennas arranged in a
hexagonal honeycomb pattern, with each stack ofĀ copper circles being a single antenna controlled
by the microchips on the PCB. This massive arrayĀ works together in whatās called a phased array
in order to send and receive electromagneticĀ waves that are angled to and from a Starlink
satellite orbiting 550 kilometers above. LetāsĀ zoom in and see how a single antenna operates.
Here we have an aperture coupled patch antennaĀ composed of 6 layers, most of which are inside
the PCB. It looks very different from theĀ antenna of an old-school radio, and is honestly,
incredibly complicated, so letās simplifyĀ it. Weāll remove a few of the layers for now,
and step through the basic principles ofĀ how we generate an electromagnetic wave
that propagates out from this antenna. To start, at the bottom we have a microstrip
transmission line feed coming from one of theĀ small microchips. This transmission line feed is
just a copper PCB trace or wire that abruptly endsĀ under the antenna stack. We send a 12 Gigahertz
high-frequency voltage or signal to the feedĀ wire which is a voltage that goes up and down
in a sinusoidal fashion, going from positiveĀ to negative and back to positive once every 83
pico-seconds, 12 billion times a second, or 12Ā Gigahertz. Note that high-frequency electricity
works differently from direct current or lowĀ frequency 50 or 60-hertz household electricity.
For example, above the copper feed wire, weĀ have a copper circle with notches cut into it
called an antenna patch. With DC orĀ low-frequency alternating current,
there wouldnāt be much happening because the patchĀ is isolated, but with a high-frequency signal,
the power sent to the feed wire is coupled or sentĀ to the patch. How exactly does this happen? Well,
as mentioned earlier, a 12 Gigahertz signal isĀ applied to the copper feed wire. When the voltage
is at the bottom of its sinusoidal, or trough,Ā we have a concentration of electrons pushed to
the end of the feed wire thus creating a zone ofĀ negative charge which corresponds to the maximum
negative voltage. This concentration of electronsĀ on the tip of the wire repels all electrons away,
including the electrons on the top of the patch,Ā and as a result, these electrons are pushed to
the other side of the circular patch. Thus, oneĀ side of the patch becomes positively charged,
while the other becomes negativelyĀ charged, thereby creating electric
fields between the patch and feed wire like so. However, when we reverse the voltage to the
copper feed wire 42 picoseconds later, we have aĀ concentration of positive charges, or a lack of
electrons at the end of the wire, and thus theĀ electrons in the patch flow to the other side,
the voltage in the patch is flipped, and theĀ direction of the electric fields are also flipped.
Because the feed wire voltage oscillates back andĀ forth, 42 picoseconds between one peak and trough,
the electric fields in the patch will alsoĀ oscillate as the electrons, or current,
flows back and forth. If we pause the oscillation
we can see some of these electric field vectors,Ā or arrows, from the patch, are vertical, and
because they are equal and opposite, they cancelĀ out. However, other electric fields are horizontal
in the same plane of the patch and are calledĀ fringing fields. These fringing fields are in the
same direction and thus they add to each other,Ā resulting in a combined electric field pointing
in this direction. At the same time, electronsĀ flowing from one side of the disk to the other,
which is an electric current, generate aĀ magnetic field with a strength and direction,
or vector, perpendicular to the fringingĀ electric field vector. As a result,
we have an electric field pointing one way, andĀ a magnetic field pointing perpendicular to that.
Letās move forward in time to where theĀ voltage on the feedline becomes positive,
and now, weāre at the peak of the sinusoid, 42Ā picoseconds later. The charge concentrations,
or voltage, as well as the current, is allĀ flipped, and thus the electric and magnetic
fields point in the opposite directions. ElectricĀ and magnetic fields propagate in all directions,
and by creating these oscillating fields,Ā weāve generated an electromagnetic wave
which travels in the direction perpendicular toĀ both the electric and magnetic field vectors.
Because the two sets of field vectors are notĀ all in the same plane, but rather are curved, the
propagating electromagnetic wave travels outwardsĀ in an expanding shell or balloon-like fashion,
kind of like a light bulb on the ceiling. LetāsĀ simplify the visual so we only see the peak and
trough or top and bottom of each wave and noteĀ that the trough is just a vector pointed in the
opposite direction. Additionally, the strengthsĀ of these field vectors directly relate back to
the voltage and signal that we originally sentĀ to the copper microstrip feed wire at the bottom
of the stack. Which means, if we want to makeĀ these electric and magnetic fields stronger,
we just have to increase the voltage sent to theĀ feedline. Itās like a dimmer on a light switch:
more power equals a brighter light. Thus far weāve been talking about this
aperture-coupled patch-antenna as transmitting;Ā however, it can also be used for receiving a
signal. In this microchip, called a front-endĀ module, we switch the antenna from transmit to
receive and turn off the 12 Gigahertz signal.Ā When an electromagnetic wave from the satellite
is directed towards Dishy, the electric fieldsĀ from this incoming signal will influence the
electrons in the copper patch, thus generatingĀ an oscillating flow of electrons. This received
high-frequency signal is then coupled to theĀ feedline where itās sent to the front-end module
chip which amplifies the signal. Thus, theseĀ antennas can be used to both transmit and receive
electromagnetic waves, but, not at the same time. Two quick things to note. First, as seen earlier,
this antenna has many more layers and is moreĀ complicated than weāve discussed. For example,
here are two circular patches. The bottom isĀ used to transmit at 13 Gigahertz while the top
to receive at 11.7 Gigahertz. Additionally,Ā there are two H slots and two feed wires to
support circular polarization, a reflective planeĀ in the back, and also, there are multiple features
for isolating the operation of one antenna fromĀ the adjacent antennas. Weāve included these and
many more details in the creatorās comments whichĀ you can find in the English Canadian subtitles.
The second note is that there are electromagneticĀ waves of all different frequencies from
thousands of different sources passing throughĀ every point on Earth, whether it be visible
light from the sun, radio waves from radio orĀ cell towers, or TV signals from satellites or
towers. Therefore in order to block out allĀ other frequencies of electromagnetic waves,
these antenna patches are designed withĀ very exact dimensions so that they receive
and transmit only a very narrow range ofĀ frequencies, and all the other frequencies
outside this range are essentially ignoredĀ by the antenna. Letās move on and see how
a single antenna can be combined with others inĀ order to amplify the beam to reach outer space.
This single antenna is only a centimeter orĀ so in diameter and using only it would be
like turning on and off one light bulb and tryingĀ to see it from the international space station.
What we need is a way to make the light a fewĀ thousand times brighter, and then focus all the
electromagnetic waves into a single powerfulĀ beam. Enter the massive Mr. McFlatface PCB,
55 centimeters wide with a total of 1280Ā identical antennas in a hexagonal array. The
technique of combining all the antennasāĀ power together is called beamforming.
So how does it work? Well, letās first see whatĀ happens when we have two simplified antennas
spaced a short distance away. As mentioned before,Ā one antenna generates an electromagnetic wave that
propagates outwards in a balloon shape. At everyĀ single point in space, thereās only one electric
field vector with a strength and direction andĀ thus the two antennasā oscillating electric
field vectors combine together at all points inĀ space. In some areas, the electric fields from
the antennas are pointing in the same directionĀ with overlapping peaks, and thus add together via
constructive interference, and in other locations,Ā theyāre oppo-site with one peak and one trough,
and thus they cancel each other via destructiveĀ interference. We can now see that the zone where
they add together constructively is far tighter,Ā or more focused, than a single antenna alone.
When we add even more antennas, the zone ofĀ constructive interference becomes even more
focused in what is called a beam front.Ā Thus, by adding 1280 antennas together
we can form a beam with so much intensity andĀ directionality that it can reach outer space.
Now you might be thinking that the strength of 1Ā antenna duplicated 1280 times over would result in
a combined power of, well, 1280 times a singleĀ antenna, but youād be mistaken. The effective
power and range of the main beam from all theseĀ antennas combined is actually closer to 3500 times
that of a single antenna. The quick explanationĀ is that by having these patterns of constructive
and destructive interference, itās as if weĀ took a single antenna, multiplied it by 1280,
and then placed a whole bunch of mirrors aroundĀ it and left only a single hole for the main beam
to exit through. The long explanation requiresĀ a ton of math and physics, so letās move on.
Dishy McFlatface and the Starlink SatellitesĀ undoubtedly have some rather complicated science
and engineering inside and to fully comprehend itĀ all you have to be a multidisciplinary student.
To help you do that, check out Brilliant, whichĀ is sponsoring this video. Brilliant is an amazing
tool for learning. They teach a wide rangeĀ of STEM topics in hands-on, interactive ways,
many of which directly relate to StarlinkĀ and other cutting-edge technologies such as
electric cars, quantum computers,Ā rocketry, or neural networks. For example,
they have an entire course dedicatedĀ to Waves and Light, and another one on
gravitational physics which will greatly helpĀ in understanding Starlink and SpaceX rockets.
Brilliant is nothing like a boring textbook,Ā but rather all the courses use interactive
modules to make the lessons entertainingĀ and to help the concepts stick in your head.
To really understand todayās frontier technologiesĀ and to help you become a revolutionary engineer
and entrepreneur like Elon Musk, you haveĀ to be versed in a wide range of fields in
science and engineering. We recommend you signĀ up, try out some of the lessons for free and,
if you like them, which weāre sure you will, signĀ up for an annual subscription. To the viewers of
this channel, Brilliant is offering 20% off anĀ annual subscription to the first 200 people who
sign up. Just go to brilliant.org/brancheducation.Ā You can find that link in the description below.
Now letās continue exploring how a powerfulĀ beam can be continuously swept across the sky,
and then how we fill it with hundredsĀ of megabits of data every second.
As a quick refresher from before, hereāsĀ an array of 1280 antennas and we fed them
all with the same 12 Gigahertz signal in order toĀ create a laser-like beam propagating perpendicular
to Dishy. However, as mentioned earlier, we needĀ to be able to angle this beam so that it points
directly at the Starlink satellite zoomingĀ across the sky at 27,000 kilometers per hour.
Using the motors isnāt feasible because they wouldĀ break within a month and arenāt accurate enough.
So, the solution is to use whatāsĀ called phased array beam steering.
Letās go back to our two-antennaĀ example. Before we were feeding
the same signal to the two antennas, and thusĀ the antennas were in phase with one another.
Understanding phase is critical, so quickly:Ā changing the height or amplitude of the signal
is done by changing the power sent to theĀ antenna, thus making the signal stronger
or weaker. The frequency is how many peaks andĀ troughs, or wavelengths there are in one second,
and changing the phase is shifting the signal leftĀ or right. Phase shifting is measured in degrees
between 0 and 359, because, if we shift the signalĀ 360 degrees, or one full wavelength, then weāre
back at the beginning, exactly as if we were toĀ loop around a circle. For example, hereās a signal
with a 45-degree phase shift, hereās anotherĀ with a 180-degree shift, and then another with a
315-degree shift. Your eyes canāt see differencesĀ in phase shifted visible light, however, high-tech
circuitry such as whatās inside Dishy is reallyĀ good at detecting and working with phase shifts.
So then, how do we use phase shifting to angle theĀ beam and have it point directly at the satellite?
The solution is to phase shift the signal sent toĀ one antenna with respect to the other antenna and,
as a result, the timing of the peaks and troughsĀ emitted from one antenna is different from
the other. These peaks and troughs propagateĀ outwards, and the location of the constructive
interference is now angled to the left withĀ destructive interference everywhere else.
If we change the phase of the antennas again, theĀ zone of constructive interference is angled to
the right. Therefore, by continuously changingĀ the phase of the signals sent to the antennas,
we can create a sweeping zone ofĀ the constructive interference.
Let's bring in six more antennas and simplifyĀ the visual so that we only see a section of the
peaks from each wave. Far away from theĀ antennas, the waves join to form a wave
front that is a planar wave. Kind of like oceanĀ waves crashing on a shoreline. Just as before,
by continuously changing the timing of whenĀ each wave peak is emitted by each antenna,
we can change the angle at which the wave frontĀ is formed, essentially steering the beam in one
direction or another. And, if we bring inĀ more antennas in a two-dimensional array,
we can now steer the beam in any directionĀ within a one-hundred-degree field of view.
Letās move back to view all 1280 antennas inĀ Dishy. In order to know the exact angle the beam
needs to be pointed or steered, we use the GPSĀ coordinates of Dishy from this chip over here,
along with the orbital position of the StarlinkĀ satellite which is known in Dishyās software. The
software computes the exact set of 3D angles andĀ the required phase shift for each of the antennas.
These phase shift results are then sentĀ to the 20 larger chips called beamformers,
and each beamformer coordinates between 32 smallerĀ chips called front end modules, each of which
controls 2 antennas. Every few microseconds, theseĀ computations are recalculated and disseminated to
all the microchips in order to perfectly aim theĀ beam at the satellite. As a result, the beam can
be steered anywhere in a 100-degree field of view. There are a few quick notes. First, the main beam,
also called the main lobe looks like this.Ā However, constructive and destructive
interference isnāt perfect, and as a resultĀ there are additional side lobes of lesser power.
Third, Mr. McFlatface holds is a single phasedĀ array, however, on the Starlink satellite,
there are in fact 4 phased array antennas. TwoĀ are used to communicate with multiple Dishys,
and 2 are used to communicate with the groundĀ stations to relay the internet traffic.
And fourth, phased arrays are used in manyĀ applications, and interestingly theyāre used
on commercial airlines to allow for mid-flightĀ internet. So this video also tangentially
explains how mid-flight internet works. Before we explore how actual data is sent,
we want to mention that this video took a monthĀ to research, two dozen script revisions, and two
months to model and animate. If your mind is blownĀ by the complexity of this technology and the depth
of this video click the subscribe button, likeĀ this video, write a comment below, and weāll
be sure to create more videos like this one. The third topic weāre going to dive into is how
information gets sent between Dishy andĀ the Starlink satellite. For example,
weāve talked about high-frequencyĀ sinusoid-shaped electromagnetic waves,
but that doesnāt look anything like binaryĀ and even less like your favorite TV show.
So, whatās happening? Well, Dishy and theĀ satellite indeed send a signal that looks like
this; however, they vary the amplitude and theĀ phase of the transmitted signal and then assign
or encode 6-bit binary values to each differentĀ combination or permutation of amplitude and phase.
With 6 bits, there are 64 differentĀ values, and thus we need 64 different
permutations of amplitude and phase. However,Ā instead of listing all the permutations,
itās more easily visualized by arranging the 64Ā different values in a graph called a constellation
diagram as shown. Letās look at the point 011 101Ā and draw a line from the origin to this point.
The distance from the origin is the amplitudeĀ of the signal, and the angle from the positive-X
axis is the phase. Itās a bit like using polarĀ coordinates. Thus, for Dishy to send these 6-bits,
it transmits a signal with an amplitudeĀ of 59% and a phase shift of 121 degrees.
Then, if the next value being sent is 101 000, theĀ signal switches to an 87% amplitude or brightness,
and a 305-degree phase shift. After that it sendsĀ the next value with a different amplitude and
phase shift. Each of these 6-bit groupings areĀ called symbols and they last for only 10 or so
nanoseconds before the next symbol is sent. Lots of times you see the signal scrunched
up like this however, because the frequency ofĀ the signal is just once every 83 picoseconds,
or 12 Gigahertz, and since a symbol lasts 10Ā nanoseconds, itās more accurate to have around
120 wavelengths per symbol before the next symbolĀ is sent. Because weāre dealing on the order of
pico and nanoseconds, that means that weĀ can fit 90 million 6-bit groups or symbols,
resulting in 540 million bits per second. However,Ā note that this data transfer is shared between
download and upload. Since this particular antennaĀ canāt transmit and receive data at the same time,
about 74 milliseconds of every second isĀ used to send data from Dishy to the Starlink
satellite and 926 milliseconds is used to sendĀ data from the satellite down to Dishy. And,
for the sake of reducing latency, these timeĀ slots get distributed throughout a single second
instead of grouping them all together. This technique of sending 6-bit values
using different variations of amplitude andĀ phase is called 64QAM or Quadrature Amplitude
Modulation and is more complicated than weĀ discussed but letās not get sidetracked.
Now that we have a stream of millions of 6-bitĀ symbols yielding hundreds of megabits of data per
second, in order to turn it into your favoriteĀ TV show we use the advanced video codec, or
h.264 format. You can learn more about that in ourĀ video that explores image compression shown here.
Iām sure you have many questions, and byĀ all means put them in the comments below,
but before we finish letās clarify two things. First, the scale of practically everything in this
video is off. Hereās the correct scale of DishyĀ and the Starlink Satellite, however Dishy is 550
kilometers away which we canāt correctly show. InĀ stark contrast, the emitted electromagnetic waves
are only around 2.5 centimeters apart, and thusĀ between Dishy and the satellite there are around
22 million wavelengths which is many more than theĀ few waves that you see here. Additionally, in this
animation weāre showing the wavelengths slowlyĀ making their way up and down, when in reality
it only takes around 2 milliseconds for anĀ electromagnetic wave emitted from Dishy or
the Starlink satellite to reach the other. The second clarification is that we
disproportionately show Dishy emittingĀ electromagnetic waves and sending them
to the satellite. In reality the satellite dishĀ is more frequently in receive mode and the steps
and physics of receiving an electromagnetic waveĀ are similar to emitting one, just in reverse.
Thatās pretty much it for how Starlink and DishyĀ send data to each other. The original script for
this video was over 45 minutes long, so all theĀ details that were cut got thrown in the creatorās
comments found in the English Canada subtitles. Thank you to all of our Patreon and YouTube
Membership Sponsors for helping to makeĀ this video. Also, thank you to Colin
OāFlynn at NewAE Technology for lending us aĀ Starlink Dishy PCB for imaging and research.
This is Branch Education, and weĀ create 3D animations that dive
deep into the technology that drives ourĀ modern world. Watch another Branch video
by clicking one of these cards or click hereĀ to subscribe. Thanks for watching to the end!
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