[Starlink] SpaceX/Starlink says it's ready for a fall satellite-to-cell service with T-Mobile
Ulrich Speidel
u.speidel at auckland.ac.nz
Tue Jun 4 09:11:20 EDT 2024
Yep. Getting 17 Mb/s from a single satellite to a single cellphone is
one thing. But serving multiple/many users is a different story. Because
if that's what you want to do, you only have a few options:
* Share the beam capacity between them - everyone gets a slice.
* Have more (and smaller) beams, so the same frequency can be used in
parallel for multiple users. This requires more and larger antennas
on the satellite.
* Up EIRP to get more power down to Earth. This requires larger
antennas on the satellite.
As a general rule, when it comes to having sharp beams, both antenna
gain (for a fixed size antenna) and path loss between spacecraft and
ground increase with the square of the carrier frequency. Antenna gain
helps us to get a nice signal at the receiver, path loss works against
us in this sense. We have one antenna at each end - and gains multiply -
so that gives us a term that's proportional to frequency to the power of
4. Divide that by the frequency to the power of 2 from your path loss
and you end up with a signal at the receiver that is proportional to the
frequency squared. What does this mean in practice? Well, it means it's
easier to project sharp beams if your carrier frequency is higher.
Now for the D2D phone spectrum that SpaceX are using, we're between 1
and 2 GHz. The Ku and Ka spectrum band that Starlink is otherwise
licensed for is between 10 and 30 GHz. That's very much back foot
territory for the D2D beams compared to the Ku and Ka ones.
So low bit rate D2D services with few users are a much easier target to
hit than 4G data rates for the rural populus at large.
On 4/06/2024 11:54 pm, Frantisek Borsik via Starlink wrote:
> The whole article is worth reading, but tl;dr;
>
> "The promise of D2D is alluring – that we can be connected wherever we
> are – no more not-spots and the certainty of always being able to
> contact others. But the reality is some way from this. The only
> existing D2D service is Apple’s iPhone emergency communications which
> offers messaging to the emergency services and vehicle assistance in
> 16 countries. This does not appear to be a service Apple thinks it can
> charge for at present.
>
> Those offerings that have the greatest potential for ubiquity are
> within the MSS spectrum. But here bandwidths are too constrained to
> deliver full service capabilities. Other MSS operators such as Iridium
> have struggled to put together a commercial D2D proposition (although
> their core business remains strong).
>
> The other approach of using MS spectrum has strong backers in the form
> of SpaceX and T-Mobile as well as multiple promising start-ups. But it
> is beset with challenges of avoiding interference with existing
> terrestrial use, overcoming restrictions in border areas, ensuring
> compliance with hundreds of regulators, of which only one has a
> defined policy towards D2D at present, doing deals with hundreds of
> operators and managing other regulatory hurdles. Only US-based
> coverage looks likely any time soon and the true extent of that
> remains unclear.
>
> With limited offers, the consumer interest will be less. Quite how
> much less is very unclear, but it is clear that the business case will
> be challenging. Most consumers appear to have limited interest in
> paying more per month for better coverage.
>
> In summary, D2D’s alluring promise of ubiquitous fully-featured global
> connectivity is not likely to be realised any time soon, if ever, but
> a reduced service level in a few countries may be sufficient to
> justify launching suitable satellites."
>
>
>
> All the best,
>
> Frank
>
> Frantisek (Frank) Borsik
>
> https://www.linkedin.com/in/frantisekborsik
>
> Signal, Telegram, WhatsApp: +421919416714
>
> iMessage, mobile: +420775230885
>
> Skype: casioa5302ca
>
> frantisek.borsik at gmail.com
>
>
>
> On Tue, Jun 4, 2024 at 1:43 PM Alexandre Petrescu via Starlink
> <starlink at lists.bufferbloat.net> wrote:
>
> does it say whether it is text only, data only, or everything
> including voice?
>
> Le 04/06/2024 à 13:20, Frantisek Borsik via Starlink a écrit :
>> Some additional reading from William Webb:
>>
>> https://www.linkedin.com/pulse/satellite-direct-device-workable-william-webb-sonke/?trackingId=Sjha4DY8SqONFA9g%2Bb5b%2Bw%3D%3D
>>
>> All the best,
>>
>> Frank
>>
>> Frantisek (Frank) Borsik
>>
>> https://www.linkedin.com/in/frantisekborsik
>>
>> Signal, Telegram, WhatsApp: +421919416714
>>
>> iMessage, mobile: +420775230885
>>
>> Skype: casioa5302ca
>>
>> frantisek.borsik at gmail.com
>>
>>
>>
>> On Tue, Jun 4, 2024 at 2:54 AM David Lang <david at lang.hm> wrote:
>>
>> Eugene Y Chang wrote:
>>
>> >> On Jun 3, 2024, at 12:41 PM, David Lang <david at lang.hm> wrote:
>> >>
>> >> Eugene Y Chang wrote:
>> >>
>> >>> I expect low data rate because the distance will fall
>> back to a lower coding rate.
>> >>
>> >> I think it's going to be more a matter of very large
>> cells, so many people sharing the available bandwidth
>> >>
>> >>> I observe a difference in my phone’s batter life between
>> urban and rural usage. I expect the battery life to be
>> significantly reduced with Starlink.
>> >>> And yes… if the phone isn’t communicating then the
>> battery life isn’t drawn down much…
>> >>
>> >> In my experience, a phone that's trying to find a tower
>> uses more power than one that has a tower, but is otherwise idle
>> >
>> > When the phone is searching for a tower, it is transmitting
>> at maximum power.
>> > Then, the phone adjusts the transmit power according to the
>> distance to the tower,
>> > In an urban environment, the distance to the tower is
>> usually less (i.e. smaller cells due to subscriber density).
>> > In a rural environment, there is more distance to the
>> tower, and the phone is transmitting at higher power (i.e.,
>> towers are farther apart for larger cells due to fewer
>> subscribers per tower, up to the max tower separation.)
>> > When you are mobile, the power is proportionate to the mean
>> distance to the tower during your operations.
>>
>> and for direct-to-satellite, it's going to be a max power
>> situation, similar to
>> rural.
>>
>> But when a phone is not connected, how frequent are it's
>> searches for towers
>> (especially if it has multiple bands to check) compared to
>> the 'keepalive' pings
>> when it is connected? if it's doing more transmissions for
>> it's search and
>> attempts to connect than it does while connected and just
>> confirming the
>> connection, that could eat more power.
>>
>> David Lang
>>
>>
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--
****************************************************************
Dr. Ulrich Speidel
School of Computer Science
Room 303S.594 (City Campus)
Ph: (+64-9)-373-7599 ext. 85282
The University of Auckland
ulrich at cs.auckland.ac.nz
http://www.cs.auckland.ac.nz/~ulrich/
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