$ASTS satellite #BlueWalker3 in orbit testing is ongoing.
It is the cutting edge of 5g Non-Terrestrial-Network NTN, Direct-To-Handset, DTH, technology.
It has a lot of interesting design choices.
Selected, in tech, standard and regulatory terms as it was purpose built.
1/n
Previous schematic of the transparent satellite AST uses is one of two NTN DTH architectures supported by the global 3GPP 5g standard.
The alternative AST opted out of has parts, or all, of the base-station placed onboard the satellite, whereas ASTs is on earth.
2/n
Starlink DTH is an add-on functionality to an existing architecture built for another purpose. It uses the other architecture.
This has several implications.
For handoff and multi connectivity.
But importantly ..
3/n
Having the eNodeB or base-station on the ground like AST does allows access to it and it allows use of COTS cutting edge hardware like Nokia single-RAN Airscale.
AST has been working with Nokia Bell Labs for two years to integrate assuring best possible technology. 4/n
Satellite communications payload is another choice where AST stands out. It is typical GEO (high altitude) satellite specs, but placed in LEO (low altitude).
A bit like putting an ocean-liner in a pond it might seem.
5/n
That allows for more narrow beams using less power, yet creating high sihnal strengths.
The win is three fold. Good mapping/resolution. High spectrum reuse and high modulation.
Resulting in good coverage and high throughput.
6/n
Low Earth Orbit has these benefits. Low RTT latency is one. Essential to work with 5g.
But also problems. Latency is still higher than terrestrial towers. Doppler shift needs to be handled and Farraday rotation of the polarization.
AST BlueBird servicelinks are 20 degrees above horizon.
8/n
That is another extreme design choice made possible by the huge 20 meter square array. As you need all of it to make a so narrow and strong beam.
The BlueWalker3 test satellite will generate such smsll cells 30-35 degrees above horizon as its phased array is smaller.
9/n
$AST uses fixed cell sites and steerable beams. Beams that are made more narrow and elliptical near the edge of the satellite firld of view in order to cast circular beamcells of uniform size onto the surface of the earth. It does not use moving cells.
10/n
The backhaul, or feeder link, field of view is even wider. It works down to 10 degrees above horizon as its antenna is a steerable 70 cm dish connecting to huge steerable dishes at the gateways.
11/n
There is much more, to tell, about the design choices made.
One is that the satellite is FPGA, or software defined. It means they can patch and tweak a lot during in orbit tests.
I will just summarize, for now, that the choices made are very wise as you scrutinize them.
12/12
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The objective of BlueWalker3 is to test many things. It is a novel form-factor satellite. Q/V backhaul dishes and cellular fronthaul phased array all new.
But if the RF loop is closed on 4g/5g protocols I would call that a success.
If broadband speeds are achieved, even better.
The $ASTS BlueWalker3 5g coverage lowband servicelink in band5 of 892MHz is being picked up in central Europe and North America, along with FirstNet servicelink frequencies. These are downlink frequencies, sat to handset used at / near Midland, Tx.
The mode QPSK stated by the hobby astronomers for FirstNet DL is used for Physical Broadcast Channel, PBCH, in the DL, and is broadcast from the eNB (basest.) to all UEs(users)
After initial cell synchronization completed, UE reads MIB (Master information block) on PBCH.
2/n
The mode stated on band5, is so far just ”FM”.
However it is interesting that these signals are also being picked up in Czechia and Slovenia of central Europe. Testing is to be on 6 continents, but the European state(-s) was not disclosed on recent update.
The proponent of this particular Bear narrative, James Dunstan, did so under the name of ”Tech Freedom”. He is also a registered agent of competitor Lynk, which he failed to mention in that article.
”unless .. AST & Science seeks a license from a country willing to abide by international space norms, the FCC should not grant the market access request.”
BlueBird block 1, BBb1, are same size as BlueWalker3, BW3, that is currently in orbit.
Size is 1288x1288x~1650 mm shape is like a cube, and BW3 was packed inside an even larger barrel shaped ”LVA”, Launch Vehicle Adptor.
Weight assumed to be approx 1500 kg each.
2/n
Falcon 9 and Falcon Heavy fairings comes in two sizes. The extended version has room for a central pillar of LVA diameter (~1900) that is some ~ 15.5 meters high.
Plenty of space for 5 LVAs on top of eachother. Close to 3 meters vertical space each. 2–2.5 needed.
Size Matters. A thread that takes a look at the latest $ASTS filing regarding Maui / Hana, the 830-835 MHz lowband used there. And touches on the subject of phased arrays.
1/n
It is known that $ASTS Bluebirds has 2800 km wide Field of view. Which translates to 58 degrees of boresight or 116 degree wide or 20 degree above horizon. This is for Bluebird Block 2. Full size.
It is very wide.
2/n
A phased array is a lot of antennas that often are spaced half a wavelength apart. By timing the transmission phase shift you can steer the beam electronically.
There is this timeline on one slide 5.
I interpret this as a timeline of milestones reached / completed.
In essence ”Not Later Than” dates.
Of some importance not to get things wrong. Launch + 6 months is when testing should be _completed_. Not when it is supposed to start.
2/n
We see the civilian Kennedy Space Center logo which is to be expected.
Also a SpaceForce logo. That is a US military branch.
It may imply that in the years after the 6 months tests BW3 has defence mission.
Mat also imply that a SpaceForce asset will be used to look at BW3. 3/n