Iridium satellite phone query

Submitted: Thursday, Jan 17, 2008 at 14:01
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All these recent posts about satellite phones has motivated me to add another one...

I own an Iridium satellite phone (9505A) with it's own satellite number/SIM (so I'm not just using the SIM out of my GSM mobile on roam).

When I've used this phone (and other 9505's) outback, there is a noticeable delay in the transmission. I've read that this is due to the fact that Iridium's satellites are high orbit, and that the signal is being relayed via ground stations in the U.S.A.

Now, my normal, beaten up old GSM mobile stopped working this week, so I have used my satellite phone to make a few calls in the Sydney suburban area. I noticed that there is no delay when talking to other non satellite phones (GSM, fixed line etc...). Can anyone explain why?
I would expect that as an exclusive satellite phone (unlike other phones which will use GSM if in range, and satellites if out of range), it's signal would still be going up to the high orbit satellite and then back to the good ol' U.S. of A for processing.

I could of course ask my provider these questions but I've found from past experience that any question more challenging than "How much does it cost?" is met with silence before I'm transferred around the office until finally the cleaner is given a go .
I'm sure someone here who's in the Telco business can explain.

Tim
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Reply By: Member - John (Vic) - Thursday, Jan 17, 2008 at 14:29

Thursday, Jan 17, 2008 at 14:29
I have noticed the same from time to time.
I was coming south down the Birdsville Track awhile ago and was speaking to someone in Melbourne and it was as good as my mobile phone.
Other times it can have a small delay.

I just put it down to Sat position relative to me at the time, maybe atmospheric conditions and the possible number of users on the system at the time possibly causing a little congestion???

Still is has never failed to get a Sat Signal within 30 seconds or so of turning on and hold it for as long as I was holding a conversation.
Excellent technology in my book.
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Follow Up By: Member - JohnR (Vic)&Kath - Thursday, Jan 17, 2008 at 22:02

Thursday, Jan 17, 2008 at 22:02
Shuffling of data through the systems possibly John, with the congestion or otherwise? It is all digital data after all.
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Reply By: prado-wolf - Thursday, Jan 17, 2008 at 14:46

Thursday, Jan 17, 2008 at 14:46
I have the 9500 Motorola sat phone and i have the same delay in the outback but over x-mas i was up the high country and run the family in germany and it was crystal clear , same or better then the mobile sometimes.

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Follow Up By: Psi - Thursday, Jan 17, 2008 at 15:04

Thursday, Jan 17, 2008 at 15:04
Maybe you were closer to the satellites.....lol
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Follow Up By: prado-wolf - Thursday, Jan 17, 2008 at 15:08

Thursday, Jan 17, 2008 at 15:08
May be i had a DIRECT connection to God that day.
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Follow Up By: Love The Outback - Thursday, Jan 17, 2008 at 17:56

Thursday, Jan 17, 2008 at 17:56
Did your God answered hahaha....
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Follow Up By: prado-wolf - Thursday, Jan 17, 2008 at 21:36

Thursday, Jan 17, 2008 at 21:36
yes, loud and clear and he said , this would be a good place for information exchange if all the shmacks would disapear.
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Reply By: SoloGirl - Thursday, Jan 17, 2008 at 15:24

Thursday, Jan 17, 2008 at 15:24
I have the 9500 and called Perth from between Menzies and Bull Finch and there was no delay and quality was good.
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Reply By: Member - Graham H (QLD) - Thursday, Jan 17, 2008 at 15:45

Thursday, Jan 17, 2008 at 15:45
Possibly due to the bandwith of the satellites I noticed over the holidays that the internet slows down a lot. Probably due to all the kids using it. Think of it like a water pipe You can only pour so much down it and its full or the flows slows.
Probably uses packet swirtching which can cause delays like that similar on VOIP phones
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Reply By: Member - Dunworkin (WA) - Thursday, Jan 17, 2008 at 15:48

Thursday, Jan 17, 2008 at 15:48
Chalk one up for the old useless Globalstar, when... it was working it worked like any normal mobile, no delays, no interfernce it was good no matter where we were, same as when it was on CDMA which is still working but not for much longer.

Cheers

D


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Follow Up By: TimS - Thursday, Jan 17, 2008 at 15:58

Thursday, Jan 17, 2008 at 15:58
Well that may be so, but give me an Iridium phone anyday, delay or no delay ;)

Anyway, the delay is not a problem for me. I expected it anyway based on Iridium documentation and the fact they use high orbit satellites.
I've also experienced no delays in the bush, I'm just curious as to how this comes about.

Cheers,
Tim
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Follow Up By: Member - Mike DID - Thursday, Jan 17, 2008 at 22:36

Thursday, Jan 17, 2008 at 22:36
Globalstar phones send to a satellite in a 1400 km orbit and link the signal down to an earthstation in Australia.

That's the strength and weakness of Globalstar.
+ There is minimal delay in the signal.
- It's harder to get a link because the satellite must simultaneously be line-of-sight with the Satphone and the earthstation.
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Reply By: stocky - Thursday, Jan 17, 2008 at 17:14

Thursday, Jan 17, 2008 at 17:14
Because of the way Iridium works:
Signal goes up to a sat - then hops from sat to sat till it gets around to ground station in the US - then back to who your calling via l_a_n_d_l_i_n_e_s - compression of signal is high as inter-sat bandwidth is limited - more calls on the system = bigger delays. There is always a *little* delay due to sat height and the fact it gets relayed half way round the world :-)

GSTAR - signal goes up to sat and straight back to one of 3 grounds stations in oz then onto the phone network - hence shorter to NIL delay

hope that helps

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Follow Up By: stocky - Thursday, Jan 17, 2008 at 17:15

Thursday, Jan 17, 2008 at 17:15
weird - post was rejected as it contained the word "land-l-i-n-e" ???? WTH??
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Follow Up By: TimS - Thursday, Jan 17, 2008 at 19:03

Thursday, Jan 17, 2008 at 19:03
Thanks Stocky,

But I'm not convinced ... :)
I'm well aware that the "delay" in the Iridium system is due to the network topology described. So logically, if you added more calls (congestion), the "delay" should get worse.
What I find though, is that there is NO delay AT ALL when making calls within the 'burbs' (and other assorted places), regardless of when I'm making the calls. Just coincidence? Maybe, but I think the signal is not taking the route described, it is simply too quick and clear, indiscernible from a home phone or garden variety mobile.

Does anyone else using these phones experience a delay when using it within a suburban area or an area covered by GSM signals?

Cheers,
Tim

P.S. my posting was rejected too because of the word you mentioned. Seems that ExploreOz has some argument with a business with that name ....
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Follow Up By: stocky - Thursday, Jan 17, 2008 at 19:10

Thursday, Jan 17, 2008 at 19:10
Must be just luck of the draw - AFAIK the Iridium phones can only talk via their birds and they are constantly moving as well so its not like its a sat covering a particular area that gives it the better performance.

I have never had my Iridium sound anywhere near as good as my GSTAR so I can comment having never experienced what your explaining

:-)
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Follow Up By: Member - Mike DID - Thursday, Jan 17, 2008 at 22:43

Thursday, Jan 17, 2008 at 22:43
A satphone-to-satphone call would instead go SatA-SatB-SatC- USearthstation-SatD-SatE-SatF.
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Reply By: Bruce M - Thursday, Jan 17, 2008 at 19:45

Thursday, Jan 17, 2008 at 19:45
Permit me (a retired satellite consultant) to offer a few numbers to this discussion.

First, communications signals travel at the speed of light, ie 299,792km/sec. Satellites in the geostationary orbit are 35,786km above sea level, directly above the Equator. A simple calculation suggests that a radio signal takes around 0.24 seconds for the round trip up to the satellite and back to earth. So the latency (delay) in a conversation using a GEO satellite is around one quarter second.

Secondly, Iridium satellites operate at an orbital altitude of 780km; essentially they represent something like a set of mobile phone towers in the sky, with two essential differences. One is that they are moving. The other is that, unlike GEO satellites (and Globalstar satellites), Iridium satellites do not link directly back to earth; instead, they have inter-satellite links allowing the uplinked signal to be "hopped" from satellite to satellite until the it reaches a satellite that can see a ground station. Ignoring the US military station in Hawaii, Iridium has two ground stations, both in the US - in Tempe, Arizona and Leesburg, Virginia. Google Earth indicates that Leesburg is around 15,650km from Sydney, so a signal that started from an Iridium satellite above Sydney would take around 0.1 seconds to get to Leesburg and back to Sydney. That would only be if it came back via terrestrial cable; if the signal came back to Sydney via a GEO satellite, add another 0.24 seconds.

I hope this helps a little.

Bruce M
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Follow Up By: Member - bungarra (WA) - Thursday, Jan 17, 2008 at 23:02

Thursday, Jan 17, 2008 at 23:02
concise and well put Bruce M

in my past experience of the Global 'bleep" sh*t and my current few years of Telstar Iridium I am more than happy with a few parts of a second delay (on occasions) with the Iridium

the delay with the Global "bleep" sh*t can be so long as for a bloke to do a perish...and we always carry plenty of food and water !

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Reply By: Dean - Friday, Jan 18, 2008 at 10:16

Friday, Jan 18, 2008 at 10:16
Who knows Tim.
Ive made and received many calls, some with delay some with out, and always crystal clear, impressive technology.
Dean
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Reply By: TimS - Friday, Jan 18, 2008 at 10:50

Friday, Jan 18, 2008 at 10:50
I'm not concerned about the delay/latency factor when using the phone. The point I'm getting at is that the lack of delay and clarity of call when making calls within a suburban area indicates that the call is being intercepted and routed through Telstra's terrestrial GSM network.

This would benefit Telstra because they wouldn't be paying Iridium to use their satellites to route your phone call (via the USA), BUT they still charge the customer the satellite call rates!

Is it GStar who advertises that their phones use the GSM network if in range and only uses satellites (and hence satellite call charges) if out of GSM range?
I know Telstra says that the Motorola 9505s can't do that but they would wouldn't they?!
It's beneficial to Telstra to keep this capability quiet and reap the extra money from charging every poor sap who uses the 9505 on their network the satellite rates.

Can anyone prove this either way?

Does anyone who has one of these Motorola 9505A phones with it's own satellite SIM (NOT your GSM SIM) and hooked up via Telstra, experience any form of delay/latency when making a call from within a known GSM /CDMA covered area?

Tim
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Follow Up By: Member - Mike DID - Friday, Jan 18, 2008 at 11:16

Friday, Jan 18, 2008 at 11:16
There is a rare and expensive GSM adapter made that clips on the back of the 9505 - only because the 9505 simply does not have the capability to communicate on anything but the Iridium Satellite bands.
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Follow Up By: Member - John (Vic) - Friday, Jan 18, 2008 at 13:18

Friday, Jan 18, 2008 at 13:18
Never use it within known GSM coverage.
Why would you when a GSM call on your GSM phone is so much cheaper.

Besides Mike DID has provided the answer to your GSM query with the adapter answer.
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Follow Up By: TimS - Friday, Jan 18, 2008 at 14:39

Friday, Jan 18, 2008 at 14:39
Well you might want to use it if your GSM phone is broken, like mine is...

Anyway, I've been scouring the web and think I've found the answer to my own question.

It seems that the satellite that initially picks up the signal from your Sat phone, can determine that the call is coming from a GSM covered area and simply "drops" the call back into the local GSM network.
If this is correct then it means that your call is routed via the nearest satellite but is not being bounced around the globe between satellites to a ground station in the USA and back to OZ via some other route as is done when you're standing on Thring Rock, Vokes Hill or floating around in the middle of the Pacific.

This explains the lack of delay/latency when calling from within a GSM covered area. The call is simply bounced up and down between the ground and the overhead satellite.

None of this is a problem of course, I'm just interested in the explanation.

In fact, having compared call costs between my GSM phone and my Sat phone from the last trip, I might be better off throwing the broken GSM phone in the bin as I was paying $1.00 minute to use it in various country towns whereas the satellite phone calls were all flat rate of 0.99 cpm.... :)

Cheers,
Tim
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Follow Up By: Member - Mike DID - Friday, Jan 18, 2008 at 15:23

Friday, Jan 18, 2008 at 15:23
"It seems that the satellite that initially picks up the signal from your Sat phone, can determine that the call is coming from a GSM covered area"
- that's impossible for a single satellite to do.

" and simply "drops" the call back into the local GSM network. "
- Iridium satellites can only link to earth via earthstations in the USA.


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Follow Up By: Member - John (Vic) - Friday, Jan 18, 2008 at 16:03

Friday, Jan 18, 2008 at 16:03
Tim those Global$hit handsets that are duel Sat & CDMA first look for a CDMA signal before going Sat.

Iridium is simply a Sat system only no GSM or CDMA ability without the attachment mentioned above.

Your theory does not make sense when users like myself have experienced the no delay phenomenon in areas with no mobile coverage, IE Birdsville Track or Vic High Country.

I would also suggest that you double check the call cost as its 99 cents per 30 seconds plus connection charge on a $30.00 Telstra Plan.
Look here for current plans and costs Iridium Sat Plans
If you use the service without a plan its a lot more than 99 cents per 30 seconds.
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Follow Up By: Member - John (Vic) - Friday, Jan 18, 2008 at 16:43

Friday, Jan 18, 2008 at 16:43
Tim have a look here for a good overview of the Iridium System and the freqencies used.
Iridium System and how it works.
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