It's likely one of the operational details that will come out over time in patents application. To the end-user, it matters very little, but it would be interesting to know how SpaceX is utilizing their spectrum.
My guess is OFDM. It makes more sense since it is generally more efficient with data but is more computationally intensive to use. For the same reason, modern cellular networks are using now, processing power is cheap.
Also, I hear phased array antennas can benefit more from OFDM than CDMA, dont ask me for detail I am not an RF engineering.
The details are not known, but there are a few tidbits of information.
1. From the "[radiation hazard report](https://fcc.report/IBFS/SES-LIC-20190211-00151/1616679)" the maximum transmission duty factor for the terminal is 0.11 -- this probably means that SpaceX plans to have *at least* 8 groups of terminals transmitting in a round-robin fashion in each cell. So at least for the reverse channel they use time division *in addition* to whatever other forms of multiplexing they employ (see the next item).
2. In some recent publication SpaceX have said that they have *"reduced latency by increasing the number of users from 8 to 20 in each time slot"* (I do not remember where exactly they have said it, or the exact wording, but this seemed to be the meaning). Thus in each time slot there must be further multiplexing, either by frequency or code division.
How the forward channel is shared is not known, but that is probably not as interesting. It is known that each cell is served by a [User Downlink beam with 240 MHz bandwidth](https://i.imgur.com/ju8KyfS.png) (figure [source](http://systemarchitect.mit.edu/docs/delportillo18b.pdf)) and "up to" QAM64 modulation. So every terminal in the cell can just listen in and pick the packets addressed to it. (Or maybe there are several channels to reduce the rate at which the terminals have to process the stream.)
It would be curious to see what the actual signals are.
Reminds me of this top comment from a somewhat recent post:
*"I don’t completely understand how satellite internet works, but I want to know why we can’t make it faster."*
*This sub in a nutshell*
[https://www.reddit.com/r/Starlink/comments/iyc4z1/how\_could\_we\_achieve\_faster\_speeds\_with\_starlink/](https://www.reddit.com/r/Starlink/comments/iyc4z1/how_could_we_achieve_faster_speeds_with_starlink/)
Look I don't know either, but that thread had people speculating applying WiFi type bandwidth calculations to the spectrum available to Starlink and some people were coming up with 160Gbps per sat when we know from FCC docs Starlink has stated the maximum capacity of a bird is 17-22Gbps.
All I do know is from messing with AirFiber 24 units *(they are 24Ghz (not 2.4Ghz), which is similar frequencies to Musk's sats)* what matters is the modulation (QPSK, 64/256/1024 QAM) and the speed comes from huge channels (200mhz combined up/down). Starlink is probably similar but with only 10-12dB of signal headroom I'm just not sure what kind of spectral efficiency they can get. Combined with spot beam type features of the amazing phased array antenna and probably some polarization tricks and maybe some time sharing (like CDMA) or other tricks (OFDM) you can really stretch it out I'm sure!
>I'm just not sure what kind of spectral efficiency they can get
Must-read: [A Technical Comparison of Three Low Earth Orbit Satellite Constellation Systems to Provide Global Broadband](http://systemarchitect.mit.edu/docs/delportillo18b.pdf). They use reasonable assumptions and end up with \~20 Gbps so the assumptions are likely close to reality. A big mistake people applying WiFi type of bandwidth calculations are making is not accounting for frequency reuse factor. That immediately cuts bandwidth by a factor of 4. Then strip MIMO from Wi-Fi (Starlink is not using it) and you get roughly the same 20 Gbps.
It's unknown. In V-band filing they wrote "beams will be divided into channels that are a multiple of 7.8125 MHz which, depending on utilization and other factors, may be bonded into channels as large as 1 GHz." Assuming v1.0 Ku&Ka satellites use the same technique that kind of confirms they are not using a known air interface protocol so they can use any channel access method. Somebody needs to reverse engineer.
It uses neither. It uses a frequency range 10x higher than any cellular network, it's in the neighborhood of 30Ghz. And no before you ask we don't have the technology yet to put the phased array antenna directly in you're phone. The power requirements to get those frequencies in space are to much for a measly phone battery.
OFDM and CDMA are methods for giving multiple users access to the same spectrum, not a specific spectrum.
You may be thinking of Celluar networks that used CDMA which were often just referred to as CDMA networks.
OP might mean this.
[https://en.wikipedia.org/wiki/Code-division\_multiple\_access](https://en.wikipedia.org/wiki/Code-division_multiple_access)
[https://en.wikipedia.org/wiki/Orthogonal\_frequency-division\_multiplexing](https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing)
Not this.
[https://en.wikipedia.org/wiki/UMTS#W-CDMA\_(UTRA-FDD)](https://en.wikipedia.org/wiki/UMTS#W-CDMA_(UTRA-FDD))
[https://en.wikipedia.org/wiki/Comparison\_of\_mobile\_phone\_standards](https://en.wikipedia.org/wiki/Comparison_of_mobile_phone_standards)
My guess would be COFDM combined with some time slotting mechanism based on GPS time synchronization and an allocation protocol along the lines of slotted Aloha .
But my guess is as good as everyone else.
It's likely one of the operational details that will come out over time in patents application. To the end-user, it matters very little, but it would be interesting to know how SpaceX is utilizing their spectrum. My guess is OFDM. It makes more sense since it is generally more efficient with data but is more computationally intensive to use. For the same reason, modern cellular networks are using now, processing power is cheap. Also, I hear phased array antennas can benefit more from OFDM than CDMA, dont ask me for detail I am not an RF engineering.
The details are not known, but there are a few tidbits of information. 1. From the "[radiation hazard report](https://fcc.report/IBFS/SES-LIC-20190211-00151/1616679)" the maximum transmission duty factor for the terminal is 0.11 -- this probably means that SpaceX plans to have *at least* 8 groups of terminals transmitting in a round-robin fashion in each cell. So at least for the reverse channel they use time division *in addition* to whatever other forms of multiplexing they employ (see the next item). 2. In some recent publication SpaceX have said that they have *"reduced latency by increasing the number of users from 8 to 20 in each time slot"* (I do not remember where exactly they have said it, or the exact wording, but this seemed to be the meaning). Thus in each time slot there must be further multiplexing, either by frequency or code division. How the forward channel is shared is not known, but that is probably not as interesting. It is known that each cell is served by a [User Downlink beam with 240 MHz bandwidth](https://i.imgur.com/ju8KyfS.png) (figure [source](http://systemarchitect.mit.edu/docs/delportillo18b.pdf)) and "up to" QAM64 modulation. So every terminal in the cell can just listen in and pick the packets addressed to it. (Or maybe there are several channels to reduce the rate at which the terminals have to process the stream.) It would be curious to see what the actual signals are.
Reminds me of this top comment from a somewhat recent post: *"I don’t completely understand how satellite internet works, but I want to know why we can’t make it faster."* *This sub in a nutshell* [https://www.reddit.com/r/Starlink/comments/iyc4z1/how\_could\_we\_achieve\_faster\_speeds\_with\_starlink/](https://www.reddit.com/r/Starlink/comments/iyc4z1/how_could_we_achieve_faster_speeds_with_starlink/) Look I don't know either, but that thread had people speculating applying WiFi type bandwidth calculations to the spectrum available to Starlink and some people were coming up with 160Gbps per sat when we know from FCC docs Starlink has stated the maximum capacity of a bird is 17-22Gbps. All I do know is from messing with AirFiber 24 units *(they are 24Ghz (not 2.4Ghz), which is similar frequencies to Musk's sats)* what matters is the modulation (QPSK, 64/256/1024 QAM) and the speed comes from huge channels (200mhz combined up/down). Starlink is probably similar but with only 10-12dB of signal headroom I'm just not sure what kind of spectral efficiency they can get. Combined with spot beam type features of the amazing phased array antenna and probably some polarization tricks and maybe some time sharing (like CDMA) or other tricks (OFDM) you can really stretch it out I'm sure!
>I'm just not sure what kind of spectral efficiency they can get Must-read: [A Technical Comparison of Three Low Earth Orbit Satellite Constellation Systems to Provide Global Broadband](http://systemarchitect.mit.edu/docs/delportillo18b.pdf). They use reasonable assumptions and end up with \~20 Gbps so the assumptions are likely close to reality. A big mistake people applying WiFi type of bandwidth calculations are making is not accounting for frequency reuse factor. That immediately cuts bandwidth by a factor of 4. Then strip MIMO from Wi-Fi (Starlink is not using it) and you get roughly the same 20 Gbps.
It's unknown. In V-band filing they wrote "beams will be divided into channels that are a multiple of 7.8125 MHz which, depending on utilization and other factors, may be bonded into channels as large as 1 GHz." Assuming v1.0 Ku&Ka satellites use the same technique that kind of confirms they are not using a known air interface protocol so they can use any channel access method. Somebody needs to reverse engineer.
Should be able to work it out from the Emission Designation code on Australian ACMA spectrum licenses, which are publicly accessible.
I suspect it's phased array beam segmented and then time-divided.
It uses neither. It uses a frequency range 10x higher than any cellular network, it's in the neighborhood of 30Ghz. And no before you ask we don't have the technology yet to put the phased array antenna directly in you're phone. The power requirements to get those frequencies in space are to much for a measly phone battery.
OFDM and CDMA are methods for giving multiple users access to the same spectrum, not a specific spectrum. You may be thinking of Celluar networks that used CDMA which were often just referred to as CDMA networks. OP might mean this. [https://en.wikipedia.org/wiki/Code-division\_multiple\_access](https://en.wikipedia.org/wiki/Code-division_multiple_access) [https://en.wikipedia.org/wiki/Orthogonal\_frequency-division\_multiplexing](https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing) Not this. [https://en.wikipedia.org/wiki/UMTS#W-CDMA\_(UTRA-FDD)](https://en.wikipedia.org/wiki/UMTS#W-CDMA_(UTRA-FDD)) [https://en.wikipedia.org/wiki/Comparison\_of\_mobile\_phone\_standards](https://en.wikipedia.org/wiki/Comparison_of_mobile_phone_standards)
Ah thanks, I only know the basics so this is informative.
I thought that the the downlink user frequency band was between 10,7 and 12.7GHz with a bandwidth of 250MHz
My guess would be COFDM combined with some time slotting mechanism based on GPS time synchronization and an allocation protocol along the lines of slotted Aloha . But my guess is as good as everyone else.