Ericsson GSM products did lock their master oscillator to the 2.048 mbps
stream.
The master oscillator was 13 MHz, and I understand the RF was locked to
that. As well as lots of timing bibs and bobs..
John
Subject: [time-nuts] Re: Austron Oscillator Products
To: "'Discussion of precise time and frequency measurement'"
time-nuts@lists.febo.com
Message-ID: 011201da6afe$e7bea780$b73bf680$@haine-online.net
Content-Type: text/plain; charset="utf-8"
GSM standards development started in 1982 though there was prior work in several labs. Basic phy layer parameters were probably fixed by 1985 as the development cycle was quite long drawn out (especially for handsets as the "long pole" went through the tester!). Networks were launched in 1991 so devices must have been in procurement several years before then. When were these devices made? I think they might have locked BTS clocks to the incoming PCM 2.048 Mbit/s links, not sure about the RF, though given the way all the numbers are interrelated they might have had to.
TVB in an email was asking about the numerology of GSM.
The channel spacing in GSM is 200kHz = 13MHz/65, and all subsequent
standards have channel centre frequencies that are on the same 200kHz raster
though the channels are now much wider. 200kHz can also be divided by 25 to
8kHz and locked to 2048kHz divided by 256 hence lock to the E1 rate.
The channel symbol rate is 13MHz/48 = 270.8333.. kbit/s.
From
https://www.rfcafe.com/references/electrical/gsm-specs.htm#:~:text=A%20GSM%2
0Multiframe%20is%20the,Bit%20being%203.69231%20%CE%BCs%20long.:
"A GSM Multiframe is the basic unit, and is 120 ms long. There are 26 Frames
in each Multiframe, with each Frame being 4.61538 ms long (120 ms/26).
Within each Frame are 8 Timeslots at 576.92 μs per Timeslot (577 μs in round
numbers). Finally, there are 156.25 Bits per Timeslot, each Bit being
3.69231 μs long."
So every handset needed a 13MHz oscillator that had to be within 1ppm before
lock and was then pulled in to lock using feedback from an "f burst" in each
downlink timeslot. VCTCXOs were used initially so low cost very small
components became available based on hundreds of millions of devices being
made. Eventually digitally locked oscillators took over I believe. The
specs for 4G and 5G are considerably tighter I think.
-----Original Message-----
From: John via time-nuts time-nuts@lists.febo.com
Sent: Saturday, March 2, 2024 7:27 AM
To: time-nuts@lists.febo.com
Cc: John reid.john@hotmail.com
Subject: [time-nuts] Re: Austron Oscillator Products - GSM
Ericsson GSM products did lock their master oscillator to the 2.048 mbps
stream.
The master oscillator was 13 MHz, and I understand the RF was locked to
that. As well as lots of timing bibs and bobs..
John
Subject: [time-nuts] Re: Austron Oscillator Products
To: "'Discussion of precise time and frequency measurement'"
time-nuts@lists.febo.com
Message-ID: 011201da6afe$e7bea780$b73bf680$@haine-online.net
Content-Type: text/plain; charset="utf-8"
GSM standards development started in 1982 though there was prior work in
several labs. Basic phy layer parameters were probably fixed by 1985 as the
development cycle was quite long drawn out (especially for handsets as the
"long pole" went through the tester!). Networks were launched in 1991 so
devices must have been in procurement several years before then. When were
these devices made? I think they might have locked BTS clocks to the
incoming PCM 2.048 Mbit/s links, not sure about the RF, though given the way
all the numbers are interrelated they might have had to.
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
email to time-nuts-leave@lists.febo.com
Hi,
To add to this, is GSM and some of the others one also uses Timing
Advance (TA) to steer the phase of the handset so that the TDM frame
arrives in the middle of the TDM slot, as experiences by the
basestation. As you realize, this is an indirect range indication. In
well functioning systems, the TA is set to reasonably close values as it
handsover to another cell, and by collecting the TA corrections needed
as it arrives, the recommendations set can be improved. Doing this
improve the hand-over times and frees capacity quicker in the old cell,
allowing more calls there. With 4G and 5G in TDD mode (for 5G it's
needed to deliver all promises) the phase is managed on network where as
2G, 3G, and 4G (FDD) avoids that, and only required frequencie to be
within +/- 50 ppb. Toss in a raising awareness that GNSS may not be
there all the time, there is a bit of a challenge, which is taken with
various degrees of seriousness depending on which country you're in.
Let's just say it keeps me busy on my daytime job.
Cheers,
Magnus
On 2024-03-02 12:27, john.haine--- via time-nuts wrote:
TVB in an email was asking about the numerology of GSM.
The channel spacing in GSM is 200kHz = 13MHz/65, and all subsequent
standards have channel centre frequencies that are on the same 200kHz raster
though the channels are now much wider. 200kHz can also be divided by 25 to
8kHz and locked to 2048kHz divided by 256 hence lock to the E1 rate.
The channel symbol rate is 13MHz/48 = 270.8333.. kbit/s.
From
https://www.rfcafe.com/references/electrical/gsm-specs.htm#:~:text=A%20GSM%2
0Multiframe%20is%20the,Bit%20being%203.69231%20%CE%BCs%20long.:
"A GSM Multiframe is the basic unit, and is 120 ms long. There are 26 Frames
in each Multiframe, with each Frame being 4.61538 ms long (120 ms/26).
Within each Frame are 8 Timeslots at 576.92 μs per Timeslot (577 μs in round
numbers). Finally, there are 156.25 Bits per Timeslot, each Bit being
3.69231 μs long."
So every handset needed a 13MHz oscillator that had to be within 1ppm before
lock and was then pulled in to lock using feedback from an "f burst" in each
downlink timeslot. VCTCXOs were used initially so low cost very small
components became available based on hundreds of millions of devices being
made. Eventually digitally locked oscillators took over I believe. The
specs for 4G and 5G are considerably tighter I think.
-----Original Message-----
From: John via time-nuts time-nuts@lists.febo.com
Sent: Saturday, March 2, 2024 7:27 AM
To: time-nuts@lists.febo.com
Cc: John reid.john@hotmail.com
Subject: [time-nuts] Re: Austron Oscillator Products - GSM
Ericsson GSM products did lock their master oscillator to the 2.048 mbps
stream.
The master oscillator was 13 MHz, and I understand the RF was locked to
that. As well as lots of timing bibs and bobs..
John
From: john.haine@haine-online.net
Subject: [time-nuts] Re: Austron Oscillator Products
To: "'Discussion of precise time and frequency measurement'"
time-nuts@lists.febo.com
Message-ID: 011201da6afe$e7bea780$b73bf680$@haine-online.net
Content-Type: text/plain; charset="utf-8"GSM standards development started in 1982 though there was prior work in
several labs. Basic phy layer parameters were probably fixed by 1985 as the
development cycle was quite long drawn out (especially for handsets as the
"long pole" went through the tester!). Networks were launched in 1991 so
devices must have been in procurement several years before then. When were
these devices made? I think they might have locked BTS clocks to the
incoming PCM 2.048 Mbit/s links, not sure about the RF, though given the way
all the numbers are interrelated they might have had to.
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
email to time-nuts-leave@lists.febo.com
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To unsubscribe send an email to time-nuts-leave@lists.febo.com