Starlink direct to cell (was SpaceX & T-mobile event 25 Aug 2022)

[raptorx2]

Loss rate is pretty high, this looks like UDP, so I would expect sustained throughput of TCP with retransmissions etc would be substantially lower.  QUIC would probably perform better than TCP here.  Still pretty cool.

LTE Stack development is still in it's infancy. A very steep learning curve. 

Remember, this is running on low-power constrained processing on the satellite.

However, learning Stack development should allow them to deploy other "custom" air interfaces for ultra secure government communications.  IMO

Not exactly "infancy". LTE is deployed on billions of devices and has been around for a decade, with roots going back at least three decades. Quite a few developers are familiar with it, and several stacks are available for purchase.

What I don't know is how it is being used for satellite. The lower layers are highly optimized for comms between a cell tower and a cell phone. I was very surprised to learn that the basic lower-layer packet error rate is 10%. I'm used to error rates below 0.1%. The LTE trick is fast NAK and retransmit between the phone and cell tower, and since the distance is so low the recovery is instantaneous. The other trick is that the receiver keeps the bad block. The retransmitted packet uses a different FEC than the first one, and is designed so the two packets together form a longer and more robust FEC block.  The problem I have is that this trick won't work nearly as well over a 300 km link, so they will be doing something else.

An advantage of Starlink over the other D2D potential providers is that the RAN is on the satellite and will be operating at very high look angles to the Terrestrial Device.  So the maximum delay is that amount between the Terrestrial Device at the edge of the Satellite Contour to the Satellite itself.   Current authorized 53 degree shell is at 525km.   However, just last week, SpaceX petitioned the FCC to authorize the VLEO shells that were deferred in the original Gen2 Grant.  Perhaps SpaceX will target D2D from these VLEO shells  340km 53degree shells for D2D satellites and perhaps 360km 96.9 degree shells for D2D.

SpaceX could launch the Group 8 satellites @ 53 degree using Exuma trajectory (D2D) Satellites and raise them to 340km for checkout until the FCC grants operational authority to keep them at 340km after authorization. I don't think there is any timeline requirement to raise the satellites.

[Asteroza]

There's additional long term implications regarding what Android 15 will bake into itself to assist D2D LTE efforts.

[RedLineTrain]

https://twitter.com/elonmusk/status/1764032892663906313

SpaceX just achieved peak download speed of 17Mb/s from satellite direct to unmodified Samsung Android phone

This is a good start in what appears to be ~5 Mhz of frequency.  Shows promise.  It will probably take a while for them to dial this in to make it a tight service.

[FutureSpaceTourist]

https://twitter.com/planet4589/status/1764547101969494427

The six test satellites for Starlink's direct-to-cell system were launched as part of Group 7-9 in Jan. The other sats on the launch (blue) have raised to 550 km but the DTC sats (magenta) are being operated at 360 km

[Darkseraph]

Given that Starlink satellites can connect to some unmodified android phones, is there not a potential security concern there, that it could serve as a gigantic electronic signals snooping network with global reach, but American owned? I can't imagine other countries liking an overhead persistent Stingray system...

[envy887]

Given that Starlink satellites can connect to some unmodified android phones, is there not a potential security concern there, that it could serve as a gigantic electronic signals snooping network with global reach, but American owned? I can't imagine other countries liking an overhead persistent Stingray system...

SpaceX won't operate without a license in most countries, so if they don't like it they just won't issue a license.

The countries where they will operate unlicensed (e.g. Iran) won't like it, but there's pretty much nothing they can do about it.

[raptorx2]

March 4, 2023 FCC filing

SpaceX continues to "hint" of their plan to operate D2D satellites in the VLEO Gen. 2 orbits.
*****************
"SpaceX’s direct-to-cell spacecraft have begun to raise from their initial deployment altitude. SpaceX anticipates continuing to test the performance of these satellites at lower altitudes, where atmospheric drag on the vehicle is at its highest and passive decay will take a matter of weeks. In addition to the benefits for space sustainability from operating at these lower altitudes, these operations also improve service for consumers by lowering latency and improving link budget while remaining within its authorized power flux-density (“PFD”) limits. SpaceX will continue to test at these lower altitudes to further validate its performance expectations at lower altitude shells within its ITU filing"

"Link Budget: SpaceX conducted tests up to its maximum authorized PFD of -80 dBW/m2 /MHz. Measured downlink and uplink link budgets fell within 1-2 dB of SpaceX’s modeled link budget, including realistic path losses, polarization losses, atmospheric losses, foliage losses, and human factors losses. This has enabled devices to communicate with the satellites through tree cover and indoors (although the direct-to-cell service is designed for outdoor use), and down to an elevation angle of 25 degrees. During the tests, SpaceX was able to demonstrate a peak download speed of over 17 Mbps."

[RedLineTrain]

Much better results than advertised at the announcement event.  The ability to go indoors and under foliage cover is a nice achievement, which could change the addressable market size.  It would be wonderful to get out from under the choices made by the original Iridium constellation.  As I understand it, those choices were a bit ad hoc, so it's great to see some solid testing to increase the operating envelope.

[raptorx2]

Elon noted at the TMUS Sept. 2022 event that "It should work, if it's in your pocket".

It would be interesting as to how long they had been working on these lab simulations before that event.

Once thing that appears has changed "Drastically" since the event, is the size of the array that was stated to be required by Elon..

= 27 sq meters and required Starship.

[RedLineTrain]

Yes, when in August 2022 Musk stated a 2-4 Mbps/cell download capacity, he appears to have been assuming the v2 satellite in Starship configuration (~25 square meter antenna in the speech, but 27 square meter in the FCC filing) using 1.4 MHz of frequency.

What has changed is that SpaceX was able to upgrade the v2 Mini to have more or less the same capacity with a ~20 square meter antenna.

The recent 17 Mbps/cell test was done with 5 MHz of frequency, so they appear to have hit their mark.

Here is a relevant post from Michael Sheetz in December 2022 with excerpts from the FCC filing.  This was quoted upthread.

https://twitter.com/thesheetztweetz/status/1600595289995345920

[raptorx2]

Given the photos supplied of the D2D satellites in integration in Vandenberg.  I don't think they are even 20 square meters anymore.  Maybe more like 12 square meters. See comparisons provided by CATdlr in photo below.

[RedLineTrain]

The final rule for supplement coverage from space has been issued...

https://docs.fcc.gov/public/attachments/FCC-24-28A1.pdf

[raptorx2]

Breaking:  Incoming changes to Direct 2 Cell Docket.

FCC updates Status Date of SpaceX's application to 3/23/14 indicating an incoming update to the docket.

[OceanCat]

Breaking:  Incoming changes to Direct 2 Cell Docket.

FCC updates Status Date of SpaceX's application to 3/23/14 indicating an incoming update to the docket.

The status was most likely updated due to the new amendment SAT-AMD-20240322-00061:

SpaceX seeks authority to operate its direct-to-cellular payloads in the lower altitude shells 340-360 km requested for its Gen2 system.

[raptorx2]

Couldn't find that filing on Friday??  Thank you for the direction. Reposted to X/Twitter with due citation applied.

https://twitter.com/FREESPEECH1017/status/1771960434469261594

[raptorx2]

As a note.   SAT-AMD-20240322-00061 will likely only provide SCS US PCS G-Block  service in the VLEO shells.  Not global Ka/Ku broadband service.  At least not initially until DISH's interference concerns with the VLEO shells are addressed from the Gen. 2 R&O

[raptorx2]

FCC approves Starlink's expanded D2D testing Experimental STA in only 3 days.

0519-EX-ST-2024  WW9XPI Filed on March 25, 2024
0519-EX-ST-2024  WW9XPI Approved on March 28, 2024

Beginning April 15th, 2024.  Starlink can now test D2D, Beam Forming Topology Software,etc in the entire States of California, Texas, Hawaii, and Washington State, along with 6 additional US test sites.

[FutureSpaceTourist]

https://twitter.com/michaelnicollsx/status/1776801323528122382

With tonight’s first Group 8 launch we kick off deployment of our commercial direct to cell constellation!  @Starlink

[catdlr]

https://twitter.com/SpaceX/status/1776826998360613348

SpaceX
@SpaceX
Falcon 9 launches 21
@Starlink satellites – including six with Direct to Cell capabilities – to orbit from California following the first successful demo of Direct to Cell texting in early 2024

[raptorx2]

SpaceX files for FCC Experimental authority to test Direct 2 Cell in New Zealand, Australia, Japan, and Canada.