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140 posts

Master Geek


  Reply # 212834 6-May-2009 12:52
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Of course. Vodafone are not the defendants in this case. I mean that they have no defence for bringing the case.

478 posts

Ultimate Geek
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  Reply # 212836 6-May-2009 12:55
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damn, wish it was televised, streamed or reported on, better than a soap.

 
 
 
 


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  Reply # 212838 6-May-2009 13:06
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Old Grey Geek: From what I have read up on this particular problem it would appear that Telecoms TX has some spurious emissions in vodafone's RX band.

All Txs have spurious emissions to some extent; nothing new there.

Old Grey Geek: However, MED has said that those emissions are within accepted levels.

If that is indeed true, it isn't Telecom who are at fault.  I would like to see a copy of Telecom's statement of defence so we get their side of the story as well.

Old Grey Geek:  It would seem that Voda's mast head amps are raising these emissions to a problematic level.

Voda's mast head amps are supposed to amplify signals within their passband.  If the intefering signals from Telecom are In-Band, there is nothing any filter can do to solve the problem, as Alexx has already pointed out above.

Old Grey Geek:  So, what to do?. If vodafone reduces the gain on the mast head amps it could solve the problem of interference but degrade the operation of their network.

If indeed the problem turns out to be gain-related, it points to Dynamic Range limitations as being the root cause of the problem.

Most likely, what is happening here is that Telecom's In-Band emissions i.e. the signals they are permitted to transmit under the terms of their licence, are blasting through into Vodafone's Head Amplifiers at a very high level and thus they are causing Intermodulation or Blocking for two reasons:

1)  Geographical proximity of Telecom's base stations to Vodafone's base stations in many cases

2)  Lack of filtering on the inputs to Vodafone's Head Amplifiers

In that case, the best way to solve this problem is to use a two-pronged approach:

-  Better Head Amplifiers with larger Dynamic Range
-  Improved Input Filtering

Either option on its own may be sufficient, but it would be preferable to do both in order to give a greater degree of protection.

140 posts

Master Geek


  Reply # 212840 6-May-2009 13:25
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"All Txs have spurious emissions to some extent; nothing new there." True

"Voda's mast head amps are supposed to amplify signals within their passband."
Here, I think lies the problem. Rather than build more towers Vodafone relies on the, at the time, fact that there were no detremental signals in their passband and went the way of increasing RX gain instead. Unfortunately... Surely they knew ages ago what Telecom were doing?

"1) Use higher-gain antennae so the Head Amps could be left set to a lower gain" Surely this would cause the same problem? gain is gain.

"2) Use better Head Amplifiers with larger Dynamic Range"
This one always confuses me. Surely you want narrower dynamic range?

23 posts

Geek


  Reply # 212843 6-May-2009 13:34
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I for one have had all of the so called "interference" related issues, but have experienced them on the Vodafone 3G 2100 band. I was forced to switch to GSM 900 due to ongoing and escalating service degradation with Vodafone's 3G. Nearly all of my "interference" issues disappeared when using GSM 900

The symptoms of dropped calls, call setups failing, no forward to voicemail, delayed text messages all sound rather familiar. Clearly, Telecom XT has no part to play in the 3G 2100 issues that have been growing worse for some time, as they are in the 850 band only. It would be very interesting indeed to see if the increase in customer complaints are 2G (900) or 3G (2100) related. What have other G'Zoners experienced?

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Uber Geek
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  Reply # 212844 6-May-2009 13:36
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This is an interesting article about how vodafone are becoming more aggressive to competition in NZ, and doesn't appear to have much faith in NZs systems and regulations.

http://www.zdnet.com.au/blogs/techie-isles/soa/Vodafone-NZ-flexes-legal-muscle-But-why-/0,2001113776,339296260,00.htm

If telecom do have to delay the release of the XT network, considering they have probably done everything right, according to NZs regulation, I assume they could seek compensation from the MED or regulators. However even if they do delay the release, I think this is still bad PR for VF, as it shows how nasty they can get.

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  Reply # 212845 6-May-2009 13:40
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The real problem here is that the situation we have here in NZ doesn't exist anywhere else in the world.

Telecom are running a WCDMA network at the top end of their available 800MHz spectrum. Vodafone (and NZ Comms) are running networks at the low end of their 900MHz spectrum.

Australia is the only other country that has both 800 and 900 networks and Next G uses 800MHz spectrum at a far lower frequency than Telecom do. If their Ericsson kit had the same issues the AlcatelLucent appears to have then it would probably go unnoticed.

The guard band between the AMPS and TACS (now GSM) bands may have been fine in the analogue days but may possibly now be insufficient with a CDMA based air interface that has totally different characteristics to a TDMA based system.

At the end of the day Telecom may not be doing anything wrong and Vodafone may not be doing anything wrong. Telecom have publically however that their network is causing interference and that filters could be installed before the end of May to stop the interference.

The situation really is a matter of whether Telecom should be allowed to launch with a network that continues to cause interference - how important is the launch date really? Everybody was expecting June.

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  Reply # 212846 6-May-2009 13:41
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The only issues I have ever had have been 3G related.

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  Reply # 212847 6-May-2009 13:41
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Old Grey Geek: "1) Use higher-gain antennae so the Head Amps could be left set to a lower gain" Surely this would cause the same problem? gain is gain.

Yes, you're quite right.  While you were busy composing this post, I was editing mine because I realised that part didn't make sense Embarassed

Old Grey Geek: "2) Use better Head Amplifiers with larger Dynamic Range"

This one always confuses me. Surely you want narrower dynamic range?

Dynamic Range is measured in dB.  Simply put, it is the range of input signals that can be accommodated without causing non-linearity to occur.

If a receiver has a Dynamic Range of 100dB, it means that it can accommodate signals 100dB above the Noise Floor before a specified percentage of non-linearity occurs.

Whereas, if the DR is 80dB, it can only accommodate signals up to 80dB above the Noise Floor.

At least, that's my understanding of it.  Someone will no doubt correct me if I'm wrong Smile

600 posts

Ultimate Geek
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  Reply # 212858 6-May-2009 14:12
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I'm starting to get confused.  I'm seeing two different situations being discussed, and I'm personally getting lost in the details.

Let me see if I can draw some pictures....

First situation:  TNZ is leaking into VF's frequency range...


TNZ:
          *
          *
          *                                  *
         ------------------------------
         TNZ                               VF
         Freq                              Freq

Second situation:  TNZ is broadcasting a strong signal close to VF's frequency and VFs amps are doing something goofy:
          *                                                                                        *                                                  *
          *                                                                                        *                                                  *
          *                                *                                                      *                   *                              *
         -----------------------------    So, post amplification, we have    ------------------ instead of ------------
         TNZ                            VF
         Freq                           Freq

So, after amplification, the TNZ signal effectively prevents the VF signal from being brought into a usable range?

Do we know if it's one or the other?  Is it both?

I would think that the  first situation is handled by a filter on TNZ's equipment, and the second by one on VF's?

Hmm I hope the formatting works!




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  Reply # 212862 6-May-2009 14:34
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jpollock: I'm starting to get confused.  I'm seeing two different situations being discussed, and I'm personally getting lost in the details.

First situation:  TNZ is leaking into VF's frequency range...

Yes, you have hit the nail on the head with this one.  It is pretty simple, thus easily dealt with at Telecom's end, so no need to cover it further.

jpollock: So, after amplification, the TNZ signal effectively prevents the VF signal from being brought into a usable range?

What is happening here are by-products of non-linearity in Vodafone's Head Amps.  There are two main mechanisms by which this can occur:

1)  Blocking.  This is where the sensitivity of the receiver to In-Band signals is reduced by the presence of a strong Out-of-Band signal.

2)  Intermodulation.  This where two or more Out-of-Band signals, interact with each other, or an In-Band signal, to produce other undesired In-Band signals.  Such undesired In-Band signals constitute interference with the desired In-Band signals.

Blocking is fairly obvious, but Intermod. deserves further explanation:

-  No amplifier is perfect; there is always some degree of non-linearity.

-  Such Non-Linearity usually increases dramatically above a certain threshold i.e. the upper limit of the Dynamic Range.

-  If you think in terms of an Audio Amplifier, non-linearity produces objectionable distortion when you have the volume set too loud i.e. above the upper limit that the amp. or speakers are designed to handle.  The distortion you are hearing is due to unwanted harmonics of the original signals.

-  In the case of a wideband RF amplifier, the non-linearity above the upper limit of the Dynamic Range causes unwanted harmonics, as well as Sum and Difference signals of the original two or more signals.

-  As the number of signals being handled concurrently increases, and as their relative strengths increase, clearly there is a much higher potential for one or more of the unwanted harmonics or sum and difference signals to fall In-Band i.e. on top of a weaker desired signal from a customer's distant mobile phone.  That is when the real problems start to occur.

140 posts

Master Geek


  Reply # 212863 6-May-2009 14:34
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jpollock ?
That would be Jackson Pollock if your drawings are anything to go by.
Thanx, clear as mud now.
;-)

69 posts

Master Geek


  Reply # 212873 6-May-2009 15:45
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Undecided Very disappointing.

I thought there would be at least 1 representative from Geekzone at the hearing able to post what was going on.

Still, there is always the 6 o'clock news I guess.

1240 posts

Uber Geek

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  Reply # 212879 6-May-2009 15:54
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Nobody has anymore info yet?


oh yes, 6 o clock news will be a great source of entertainment :P

'The telecom wireless gsm network is interfering with the vodafone wireless cell network. Whether it be through crossing of wires or malicious tampering, we are not yet sure.'.

*video clip of cell expert/engineer talking about something not related to the topic*


..who knows....

600 posts

Ultimate Geek
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  Reply # 212883 6-May-2009 16:17
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Old Grey Geek: jpollock ?

That would be Jackson Pollock if your drawings are anything to go by.

Thanx, clear as mud now.

;-)


Heh, I used the [pre] tag, so if the pictures look goofy, stretch the browser window wider. :)

I'm amazed that it is readable at all. :)




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