Re: [time-nuts] Cell timing error
Greg Troxel g...@ir.bbn.com writes: Date: Sat, 15 Dec 2012 13:51:45 -0500 In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. Thanks for all the comments. Following up from a real keyboard: The tracfrone was on the ATT network, per the code on the SIM. So I think this was just ATT. The timing error was resolved sometime later on Saturday. I realize the phone display time and GSM time are not well connected. Emerald Time (iPhone program) does NTP and shows the difference between the time on the unix computer in the phone and NTP peers. Typically I see values from -0.5s to about 4.5s. Right now it shows +4.348s (phone computer is 4.348s slow). The phone display switched to 1849 at about 184907, which I attribute to 4s slow and a slow update rate of the display. Based on observing Emerald Time's offset over long periods, I believe that there is some loose synchronization of the phone cpu to the cell network, and that the phone free runs until it gets too far off and then it is stepped to be closer. On Saturday, Emerald Time was reporting +60.580. The time on my phone was 1 minute slow and updated around minute boundaries, just one minute behind. A tracphone (LG featurephone) showed exactly the same one-minute slow behavior. So I suspect that something was off in the GSM time reference. I am not sure if more than one cell site was affected. pgpVJVKfnar1U.pgp Description: PGP signature ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
On 12/15/2012 9:38 PM, Hal Murray wrote: GSM cell sites in the US have GPS because it is required to support E911 positioning. I'm not sure if it is used for anything other than this, but it doesn't have to be. So it's cheaper to install and maintain GPS rather than make one measurement and tell the setup where it is? No. In addition to knowing where the GSM cell site is, you time stamp the time of arrival of a specific feature in the cellphone signalling system. If the cellphone is heard by three (or more) cell sites, then you can calculate the location of the cellphone within the cell site using the time-of-arrival and speed-of-light calculations. The CDMA systems inherently depend on knowing time to sub microseconds in order to function. You can extract similar information from the signalling systems in CDMA. Newer cellphones have a GPS receiver front end inside the phone, which allows greater accuracy than the time of arrival systems. Many times, cellular signals bounce off of things between the handset and the base station, introducing a path length change and therefore a time-of-flight delay in the signal which causes errors in the time of arrival calculations. --- Graham / KE9H == ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
On 12/16/2012 05:40 PM, Graham / KE9H wrote: In addition to knowing where the GSM cell site is, you time stamp the time of arrival of a specific feature in the cellphone signalling system. If the cellphone is heard by three (or more) cell sites, then you can calculate the location of the cellphone within the cell site using the time-of-arrival and speed-of-light calculations. Since GSM is a TDM system, the arrival time of the TDM slot is the typical feature to measure. The active base station already does this, and send trimming values to steer the hand-set to stay within it's time-slot. This way you have a range measure, but it isn't enough for triangulation, so you would need to have another station measuring it too, but GSM will not usually do that, so you need to have a secondary receiver, tuned to the neighbour frequency in that direction. The CDMA systems inherently depend on knowing time to sub microseconds in order to function. You can extract similar information from the signalling systems in CDMA. You inherently have the same knowledge in GSM, it's just that you don't care about absolute time, but relative timing between the hand-set and the base station is being measured and steered. GSM stations being phase-aligned have better hand-over properties, and thus releases the channel in the cell the phone is leaving quicker, and thus increases the capacity... and allows new customers in and thus more money. So, well-timed base-stations is good for GSM too. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
Greg: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. --- Graham / KE9H == On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
In a prior life we had a CDMA timing receiver for NTP which used VZ for its source Sent from my iPhone On Dec 15, 2012, at 12:18 PM, Graham / KE9H time...@austin.rr.com wrote: Greg: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. --- Graham / KE9H == On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
On 12/15/12 2:16 PM, Scott McGrath wrote: In a prior life we had a CDMA timing receiver for NTP which used VZ for its source On Dec 15, 2012, at 12:18 PM, Graham / KE9H time...@austin.rr.com wrote: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. The time *displayed* on the phone might not reflect the time from the network. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
ATT uses UMTS in most areas which is a self-synchronizing modulation scheme. Supposedly one of the selling points is no dependence on GPS. All the extra sync channels and sync messaging is a capacity hog, not a very spectrally efficient standard in my opinion. About 85 maximum simultaneous voice calls in a 5Mhz UL / 5 Mhz DL sector/carrier before it starts to fall apart. A big step backwards from good old CDMA2000 (also just my opinion). But hey, you can surf the web while you talk on the same device. -Joe W4WN - Original Message - From: Jim Lux jim...@earthlink.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, December 15, 2012 5:43 PM Subject: Re: [time-nuts] Cell timing error On 12/15/12 2:16 PM, Scott McGrath wrote: In a prior life we had a CDMA timing receiver for NTP which used VZ for its source On Dec 15, 2012, at 12:18 PM, Graham / KE9H time...@austin.rr.com wrote: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. The time *displayed* on the phone might not reflect the time from the network. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
Hi There are a *lot* of layers between the base station and the phone it's self when it comes to the time that's displayed. There also are a *lot* of opportunities for error as each layer is linked together. Often when you see Verizon you are actually connected to Bob's Cell Phone Tower. Bob may or (may not) be very careful about linking all the layers together. Best bet, use something like an NTP client, that goes *around* all the network stuff. Bob On Dec 15, 2012, at 5:43 PM, Jim Lux jim...@earthlink.net wrote: On 12/15/12 2:16 PM, Scott McGrath wrote: In a prior life we had a CDMA timing receiver for NTP which used VZ for its source On Dec 15, 2012, at 12:18 PM, Graham / KE9H time...@austin.rr.com wrote: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. The time *displayed* on the phone might not reflect the time from the network. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
I can assure you the GSM shacks have GPS timing in them. I can dig up the photos if you want. -Original Message- From: Joseph Orsak jor...@nc.rr.com Sender: time-nuts-boun...@febo.com Date: Sat, 15 Dec 2012 18:24:20 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Cell timing error ATT uses UMTS in most areas which is a self-synchronizing modulation scheme. Supposedly one of the selling points is no dependence on GPS. All the extra sync channels and sync messaging is a capacity hog, not a very spectrally efficient standard in my opinion. About 85 maximum simultaneous voice calls in a 5Mhz UL / 5 Mhz DL sector/carrier before it starts to fall apart. A big step backwards from good old CDMA2000 (also just my opinion). But hey, you can surf the web while you talk on the same device. -Joe W4WN - Original Message - From: Jim Lux jim...@earthlink.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, December 15, 2012 5:43 PM Subject: Re: [time-nuts] Cell timing error On 12/15/12 2:16 PM, Scott McGrath wrote: In a prior life we had a CDMA timing receiver for NTP which used VZ for its source On Dec 15, 2012, at 12:18 PM, Graham / KE9H time...@austin.rr.com wrote: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. The time *displayed* on the phone might not reflect the time from the network. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
On 12/16/2012 12:59 AM, li...@lazygranch.com wrote: I can assure you the GSM shacks have GPS timing in them. I can dig up the photos if you want. Depens on how the network was built. GSM does not need anything but +/- 50 ppb timing. The PDH backhaul will provide that usually. The time that the mobile get's comes from the controler, which could be slaved using NTP... or not. It may not even transfer time, since this is an option which many but not all operators have enabled. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
GSM cell sites in the US have GPS because it is required to support E911 positioning. I'm not sure if it is used for anything other than this, but it doesn't have to be. In some other parts of the world it has been considered bad taste to let the operation of telecommunications infrastructure become dependent on a facility owned by the US military, so the standards that are popular there often try to avoid that. Dennis Ferguson On 15 Dec, 2012, at 18:59 , li...@lazygranch.com wrote: I can assure you the GSM shacks have GPS timing in them. I can dig up the photos if you want. -Original Message- From: Joseph Orsak jor...@nc.rr.com Sender: time-nuts-boun...@febo.com Date: Sat, 15 Dec 2012 18:24:20 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Cell timing error ATT uses UMTS in most areas which is a self-synchronizing modulation scheme. Supposedly one of the selling points is no dependence on GPS. All the extra sync channels and sync messaging is a capacity hog, not a very spectrally efficient standard in my opinion. About 85 maximum simultaneous voice calls in a 5Mhz UL / 5 Mhz DL sector/carrier before it starts to fall apart. A big step backwards from good old CDMA2000 (also just my opinion). But hey, you can surf the web while you talk on the same device. -Joe W4WN - Original Message - From: Jim Lux jim...@earthlink.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, December 15, 2012 5:43 PM Subject: Re: [time-nuts] Cell timing error On 12/15/12 2:16 PM, Scott McGrath wrote: In a prior life we had a CDMA timing receiver for NTP which used VZ for its source On Dec 15, 2012, at 12:18 PM, Graham / KE9H time...@austin.rr.com wrote: You should switch to Verizon. They are inherently accurate to milliseconds. Sub micro-seconds inside the base stations. On 12/15/2012 12:51 PM, Greg Troxel wrote: In central mass, ATT and tracfone (? carrier) are showing phone times very close to 1 min slow. Virgin/sprint is ok. I've never seen this before - usually it's a few s slow. The time *displayed* on the phone might not reflect the time from the network. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
I thought the networks did that deliberately to frustrate automated time shifting. On Sat, 15 Dec 2012 19:04:05 -0500, Joe Leikhim jleik...@leikhim.com wrote: I have to wonder how seriously these network designers are with respect to timing. For example we have Brighthouse cable. The time on the cable box clock is correct to WWV, however the program material is consistently 30 seconds or so late meaning the end of the program is cut off. Since my wife tends to record everything on the air, it is not practical to extend the recorder by a minute or a conflict occurs with other recordings. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
GSM cell sites in the US have GPS because it is required to support E911 positioning. I'm not sure if it is used for anything other than this, but it doesn't have to be. So it's cheaper to install and maintain GPS rather than make one measurement and tell the setup where it is? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cell timing error
On 15 Dec, 2012, at 22:38 , Hal Murray hmur...@megapathdsl.net wrote: GSM cell sites in the US have GPS because it is required to support E911 positioning. I'm not sure if it is used for anything other than this, but it doesn't have to be. So it's cheaper to install and maintain GPS rather than make one measurement and tell the setup where it is? E911 requires the carrier to be able to figure out where the handsets are. I think GPS is used as a common timing reference so they can triangulate to locate the phone using time-of-arrival measurements of the handset's transmissions made at several cell towers. GSM/UMTS carriers do it this way, at least. CDMA2000 carriers instead rely on the handsets to make the time-of-arrival measurements, both of signals from cell towers and of GPS signals the handset can hear. Dennis Ferguson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
