Re: [Starlink] Time Synchronization in Satellite Networks

[Christian von der Ropp <cvdr@vdr.net>]

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Hi Hesham,

You do not acquire the time from a LEO satellite but directly from the GPS satellites which carry an atomic clock on board.
I'd not be aware of any LEO providing a GNSS signal but Xona plan such system (although not carrying proper atomic clocks but probably chip-sized atomic clocks that require frequent syncing with proper atomic clocks):
https://twitter.com/Megaconstellati/status/1708091536439673323

There are efforts to build trapped-ion quantum clocks that are expected to become significantly smaller and cheaper than traditional atomic clocks while as accurate which would make it viable to put an atomic clock-equivalent on small LEO satellites. Once that happens you would have an independent alternative to the big GNSS birds in MEO but with stronger signals. I'm told that we are 5-10 years away from such trapped-ion quantum clocks.

But for NTP clients, the described method (running a local NTP server in the satellite terminal synced to GPS) should be good enough.

Christian


Am 2. März 2024 18:02:47 OEZ schrieb Hesham ElBakoury <helbakoury@gmail.com>:
>Hi Christian,
>How you synchronize the time of the satellites in the network? Are you
>saying each satellite has a master clock?
>
>Hesham
>
>On Sat, Mar 2, 2024, 7:38 AM Christian von der Ropp <cvdr@vdr.net> wrote:
>
>> Why not acquire the time directly from by the satellite terminal and run
>> local NTP servers instead of syncing via the Internet? LEO satellite
>> terminals always have onboard GNSS antennas for geolocation which is
>> necessary to find the satellites, so integrating a local GNSS-disciplined
>> Stratum-1 NTP server seems trivial to me.
>>
>>
>> Am 2. März 2024 17:25:59 OEZ schrieb Hesham ElBakoury via Starlink <
>> starlink@lists.bufferbloat.net>:
>>
>>> Hi Sebastian,
>>> Can we still use PTP and NTP for time synchronization in  Satellite
>>> networks or we need new protocols? If we need new protocols, do such
>>> protocols exist?
>>>
>>> Thanks
>>> Hesham
>>>
>>> On Sat, Mar 2, 2024, 7:18 AM Sebastian Moeller <moeller0@gmx.de> wrote:
>>>
>>>> Hi Hesham
>>>>
>>>> > On 2. Mar 2024, at 16:03, Hesham ElBakoury via Starlink <
>>>> starlink@lists.bufferbloat.net> wrote:
>>>> >
>>>> > Time synchronization, for satellite networks, faces several challenges:
>>>> > 1. Signal Propagation Delays: Unlike terrestrial networks where
>>>> signals travel through cables at the speed of light,
>>>>
>>>> [SM] The speed of light in your typical glas fibers (and accidentally
>>>> the information propagation speed in metallic conductors) comes in roughly
>>>> at 2/3 of the speed of light in vacuum, while the speed of light in air at
>>>> see level is a mere 90 KM/s slower than in vacuum.
>>>>
>>>> > satellite communication involves signals traveling vast distances
>>>> through space. This creates significant delays.
>>>>
>>>> [SM] Sure distances might be larger, but propagation speed is around
>>>> 100000Km/s faster... my main point is speed of light is a) dependent on the
>>>> medium b) not the things that differentiates space from the earth's surface
>>>> here, but mere geometry and larger distances on larger spheres...
>>>>
>>>> > 2. Clock Drift: Even highly precise atomic clocks, used in satellites,
>>>> are susceptible to "drift" - gradually losing or gaining time. This drift,
>>>> caused by factors like temperature variations, radiation exposure, and
>>>> power fluctuations, can lead to inconsistencies in timekeeping across the
>>>> network.
>>>> > 3. Signal Degradation: As signals travel through space, they can
>>>> degrade due to factors like atmospheric interference, ionospheric
>>>> disturbances, and solar activity. This degradation can introduce noise and
>>>> errors, impacting the accuracy of time synchronization messages.
>>>> > 4. Limited Resources: Satellites have limited power and processing
>>>> capabilities. Implementing complex synchronization protocols can be
>>>> resource-intensive, requiring careful optimization to minimize their impact
>>>> on other functionalities.
>>>> > 5. Evolving Technologies: As satellite technologies and applications
>>>> continue to evolve, new challenges related to synchronization might emerge.
>>>> For example, the integration of constellations with thousands of satellites
>>>> poses unique synchronization challenges due to the sheer scale and
>>>> complexity of the network.
>>>> > These challenges necessitate the development of robust and efficient
>>>> time synchronization protocols for satellite networks and an integrated
>>>> satellite and  terrestrial networks
>>>> > Are you aware of such time synchronization protocols?
>>>> > I would think that using Satellite simulators is the most viable way
>>>> to develop and test these protocols given that using satellites is not that
>>>> easy.
>>>> > Thanks
>>>> > Hesham
>>>> >
>>>> >
>>>> >
>>>> > _______________________________________________
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>>>> > https://lists.bufferbloat.net/listinfo/starlink
>>>>
>>>> --
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>>

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