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Looking down the rabbit hole at the iPhone 3G's issues

The iPhone 3G is one of Apple's flagship products.  Many would argue it stands far above its most able competitors in terms of capabilities. Yet, the iPhone has been having some problems.

The iPhone's problems began when users started to become frustrated with dropped calls and poor call quality.  They took their frustrations and poured them out on Apple's message boards.  Sources in Apple said that CEO Steve Jobs was unconcerned with the problems as he said they likely only affected 2 percent of iPhone customers, or about 60,000 people.

Then came the report from Sweden's foremost tech weekly Ny Teknik, saying that it had test the iPhone's 3G and it fell well below the standards set for 3G, and should not be certified and as a 3G product.  Many, including sources inside Apple, seemed to place the blame on the Infineon chipset in the phone.

Further complicating the issue are new tests from Göteborgs-Posten, a Swedish newspaper, which show the phone to be only slightly short of its competitors in terms of quality.  So, barring wildly varying batches of hardware, these reports paint an unclear picture of what is wrong with the iPhone and how badly it is wrong.

The final bit of confusion was the update to the iPhone's firmware.  The 2.0.2 update said it had "bug fixes" for the iPhone, but gave no specific details.  Apple's Jennifer Bowcock did tell USA Today that "the software update improves communication with 3G networks".   With such a hazy picture, a new inside source from AT&T steps in to try to clarify exactly what the fix did according to Roughly Drafted.

Basically the update "fixed power control on the mobile" according to the source.  To understand what they're going to say next, you must first know a bit about AT&T's jargon for UMTS -- the technology it uses to deliver its 3G network.  In the technology, phones are referred to as user equipment, "UE" for short.  The base transceiver station towers are known as "Node B".

With this jargon in mind, the AT&T source explains:

In UMTS power control is key to the mobile and network success. If the UE requires too much downlink power then the base station or Node B can run out of transmitter power and this is what was happening. As you get more UEs on the cell, the noise floor rises and the cell has to compensate by ramping up its power to the UEs.  If the UE power control algorithm is faulty then they will demand more power from the cell than is necessary and with multiple users this can cause the cell transmitter to run out of power. The net result is that some UEs will drop their call. I have seen the dropped call graphs that correspond to the iPhone launch and when the 2.0.2 firmware was released. The increase in dropped calls, (were the result of) dropped calls due to a lack of downlink power.

In essence, the iPhone is asking for a stronger signal than it needs.  In areas with lots of users, some or all of whose phones are doing this, calls start to get dropped and signal quality drops.  This all follows with the conclusions the media had reached -- the problems were somehow correlated to user distribution and seemed puzzlingly to be both with AT&T's network, and with the hardware.

The source continues:

The power control issue will also have an effect on the data throughput, because the higher the data rate the more power the Node B transmitter requires to transmit. If the UEs have poor power control and are taking more power than is necessary then it will sap the network’s ability to deliver high speed data.  This is one of the reasons why AT&T has been sending text messages to users to persuade them to upgrade to the 2.0.2 software. In a mixed environment where users are running 2.0, 2.0.1, and 2.0.2, the power control problems of 2.0 and 2.0.1 will affect the 2.0.2 users.  It is not the network that is fault but the interaction of the bad power control algorithm in 2.0 and 2.0.1 software and the network that is at fault. The sooner everybody is running 2.0.2 software the better things will be. Having seen the graphs the 2.0.2 software has already started to make difference.

Since transmitting lots of data takes lots of transmission power, and transmission power was unnecessarily being raised above that necessary for the use levels on phones, the network in areas of heavy use was unable to handle high speed data.

This revelation offers up two key pieces of insight.  The first -- this explains why there was little difference seen among individual users in the news media who downloaded and tested the update.  The updates did not majorly change the phone on an individual basis; rather they changed how the phone interacted with the network in a small way. 

Secondly, the quality of the fix is directly proportional to how many users download it.  There are still many users running old firmware, so problems are continuing.  AT&T is going as far as to send users text messages to try to get them to download the fix.

With this latest update from within AT&T, we are presented with a picture of a company struggling with a serious technical issue.  It appears it is well on the way of solving the problems, but the rub is that the solution will only come if users are willing to cooperate.

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I'm confused...
By Diesel Donkey on 8/28/2008 9:20:39 AM , Rating: -1
Why does an iPhone running the old firmware affect anything more than other iPhones still running the old firmware and the cell company's electricity bills? Am I not understanding how the word power (usually P=IV) is being used here? It seems to me that if an iPhone with old firmware causes the tower to ramp up to full power, then yeah, the other old iPhones will have trouble with that because they will request even more power and not get it, but why should it affect any other phones? They'll be getting full power, which is the best scenario for phones with proper power management, is it not?

RE: I'm confused...
By JasonMick on 8/28/2008 9:39:13 AM , Rating: 4
Hmm. Maybe a simple example might illustrate it better.

iPhone A (broken) --> requests 4 units of signal power at peak capacity
iPhone B (fixed) --> requests 2 units of signal power at peak capacity.

There are four broken iPhone A's and four fixed iPhone B's on Tower X which has 18 units of signal power capacity.

If eight fixed iPhones were on it, it could handle all their traffic, with 2 units of flexibility.

However now there are broken ones as well. Together, the phones now are demanding 24 units of signal, more than twice what it can handle. In response it first tries to cut back the high speed data rates, to lower power. Maybe this lowers power to 20 units.

Still strapped, the tower then begins to lose calls. Now there's three broken iPhones and three fixed on the tower, which is at full capacity, and the other 2 can't get on it, until those phones end their chat with the tower.

Horribly simplified example, with some minor inaccuracies, but I hope it helps you understand AT&T's problems on a more basic level.

RE: I'm confused...
By Mitch101 on 8/28/2008 10:28:52 AM , Rating: 5
The train carrying Phone B arrives in Seattle at 7:30 while the train carrying Phone A arrives at 8:15.

Why do I always get these questions!!!

RE: I'm confused...
By daftrok on 8/28/2008 10:58:22 AM , Rating: 1
RE: I'm confused...
By Diesel Donkey on 8/28/2008 5:19:39 PM , Rating: 2
OK, that makes sense. Thanks for the clarification.

RE: I'm confused...
By mvpx02 on 8/28/2008 9:45:07 AM , Rating: 5
Think of your internet connection: No ISP has the capacity to provide every user with advertised data throughput at the same time. They bank on only a percentage of their subscribers usering 25-100% bandwidth at a time. This is evident particularly with cable ISP's when speeds slow down during peak times.

Now imagine if for some reason, due to some bug, every computer with Internet Explorer (people with old firmware) started constantly downloading (lets say) 50% of the user's available bandwidth when it really only needed 5% to perform its function. the overall performance of the network would drop significantly. Even firefox/opera/etc users (whos browser didn't have the bug, like the iphone's new firmware) would experience the slowdown.

The more people who upgrade their firmware, the less trouble the network/towers will have.

RE: I'm confused...
By jaydubya on 8/28/2008 9:45:59 AM , Rating: 5
This is actually an RF issue that deals with radiated power and interference. As the radiated power of a device increases so does its adjacent channel interference with relation to other devices within the spectrum - hence the reference to increasing the noise floor of the system. As the noise floor increases the Signal to Noise Ratio (SNR) decreases and the quality of the link therefore is affected detrimentally so.

Therefore the most optimum situation is to have all devices transmitting at the lowest power level necessary to establish a high link quality and not to exceed this. If devices are transmitting with higher power then they will interfere with other devices more and cause them to increase there power to establish better SNR (all cell phones have an adaptive power control algorithm) - thereby raising the noise floor of the entire spectrum.

It is then understandable to see why AT&T would like to remove these errant iPhone's from there network. It is reducing the number of available calls a station can handle at one time and also the individual quality of the calls in a high traffic environment. That is probably why they are so eager to remove the old firmware's from the network. Also with better power control you may see a slight increase in battery life from the device.

RE: I'm confused...
By RHITee05 on 8/28/2008 10:37:08 AM , Rating: 3
It's actually slightly worse than simple adjacent-channel interference (ACI). UMTS is not a channel-based system where each user has their own discrete slice of spectrum and ACI is due to spillover from other users.

UMTS is a system that uses CDMA-type spread spectrum technology. There are no discrete channels, instead each user's data is "spread" across the entire band by an unique code (thus the term code division multiple access - CDMA). To a particular user, other users' data appears just as noise.

So, if other users are requesting more transmit power, that directly increases the noise floor for all users in the channel. If that reduces SNR sufficiently, it might cause some users to request still more power, quickly causing positive feedback that has the tower blasting away at full power.

RE: I'm confused...
By jaydubya on 8/28/2008 11:39:40 AM , Rating: 2
You are indeed correct. In a PN spread CDMA system other transmitters with different PN codes will appear as uncorrelated broadband gaussian noise to the receiver. Thus power control is a very important part of a CDMA system - as it will be directly proportional to the number of units that can communicate with the base station.

I guess the most difficult problem then with a CDMA type system is controlling the output power of the tower and units and making fast adjustments to that power as channel conditions change. Also like you said controlling a positive feedback situation that can occur when the channel degrades from multiple interferers and determining when the channel has reached peak capacity - due to the non-deterministic nature of the traffic.

RE: I'm confused...
By joeld on 8/28/2008 9:53:29 AM , Rating: 2
Also, if the iPhones with older firmware are being affected because the TOWER is running out of transmission power because of multiple phones in the cell requesting too much power, why aren't all the other 3G phones in the cell also experiencing the same issues with call quality and dropped calls?

RE: I'm confused...
By heffeque on 8/28/2008 10:16:55 AM , Rating: 2
Who said that they aren't? It's just not as cool to ramble about a brand new N73 than to ramble about a brand new iPhone:

Repeat tests show iPhone 3G...

After reading that... now what.

RE: I'm confused...
By JustTom on 8/28/2008 11:59:11 AM , Rating: 2
After reading that I say the study itself is silly.

RE: I'm confused...
By heffeque on 8/28/2008 12:08:54 PM , Rating: 2
In what way is it silly. In the way that it doesn't tell you what you wanted to read?

RE: I'm confused...
By JustTom on 8/28/2008 12:24:12 PM , Rating: 2
Cause they tested 3 phones. Cause it does not address the issue AT&T highlighted. Cause there is potential bias in the fact that the researcher owns an iPhone. Cause the researcher himself states "I do not draw any conclusion from this, there is so many factors influencing the outcome," Wieselgren reported. "We can at least be certain of one thing. The three iphones we tested had nothing wrong with their antennas."

Frankly, I have no dog in this fight. I am locked into Verizon -due to work reasons- and couldn't own an iPhone if I wanted to. However I do own an iPod touch and love it.

RE: I'm confused...
By heffeque on 8/28/2008 12:36:11 PM , Rating: 2
Tested a iPhone that supposedly had 3G problems, a 2.0.0 iPhone and a 2.0.2 iPhone and all of them did ok.

Seeing that people that don't live in heavy usage places don't have problems just shows that the problem is AT&T, and seeing that BEFORE the iPhone existed AT&T was ALREADY the operator that had the most dropped calles = their network already had serious problems. It all indicates that the problem is that the iPhone is too much for AT&T to handle:

"A Citigroup analyst recently reported similar 3G problems with dropping to the slower EDGE network or even cutting out entirely when using RIM's new BlackBerry Bold on AT&T's 3G network. The Bold uses an entirely different cellular chipset than the iPhone 3G."

RE: I'm confused...
By JustTom on 8/28/2008 1:13:54 PM , Rating: 2
Seeing that people that don't live in heavy usage places don't have problems just shows that the problem is AT&T, and seeing that BEFORE the iPhone existed AT&T was ALREADY the operator that had the most dropped calles = their network already had serious problems. It all indicates that the problem is that the iPhone is too much for AT&T to handle:

You may be right. I even suspect you are. However, this study in no way proves anything. The sample size is ridiculously small. There is no mention of which facilities produced those phones, and whether phones from all factories manufacturing the phones were tested. There is no mention of whether they stressed the cell tower to determine performance at non-ideal conditions. It did not test in frequency used in the US, thus at best making any conclusion from this already flawed study specific to Europe. The phones very well may function perfectly at the frequency used in Europe while being substandard in the US.

RE: I'm confused...
By heffeque on 8/28/2008 2:39:29 PM , Rating: 2
Agreed there.

RE: I'm confused...
By JustTom on 8/28/2008 12:26:06 PM , Rating: 2
oops, forgot some other silly things...

"The testing did not also include the 850MHz band used by AT&T in the US and Telstra in Australia"

RE: I'm confused...
By heffeque on 8/28/2008 12:29:43 PM , Rating: 2
Obviously: the test was done in Europe.

RE: I'm confused...
By theapparition on 8/28/2008 12:06:39 PM , Rating: 2
Love how that report glosses over the fact that the phones they tested were consistantly a couple of dB's lower than competing models. Still witin the spec, but at the very low end.

RE: I'm confused...
By Diesel Donkey on 8/29/2008 11:46:11 PM , Rating: 2
Wow, that'll teach me for asking a question!

"We shipped it on Saturday. Then on Sunday, we rested." -- Steve Jobs on the iPad launch

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