Daniel Eran Dilger
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The Inside Deets on iPhone 2.0.2 and Dropped Calls

Daniel Eran Dilger
The mysteriously terse synopsis of the improvements made in iPhone 2.0.2, listed only as “bug fixes,” didn’t shed much light on why Apple’s Jennifer Bowcock could tell USAToday that “the software update improves communication with 3G networks.” However, our source close to AT&T helped illuminate why the update was necessary, what the problem was, and why the update didn’t immediately impact users equally.
The iPhone 2.0.2 update “fixed power control on the mobile,” the source told RoughlyDrafted. UMTS, the technology used to deliver AT&T’s 3G network, refers to phones and other client devices as “UE” for user equipment, and the base transceiver station towers as “Node B.”

Why the iPhone 3G dropped calls.

“In UMTS,” the source said, “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,” the source said, were the result of “dropped calls due to a lack of downlink power.”

Why the iPhone 3G suffered poor data throughput.

“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.”

That explains why some users saw no immediate impact after installing iPhone 2.0.2, and why tests of individual iPhone 3G models showed no significant difference between the 2.0 and 2.0.2 software: the problem was only evident when a critical mass of phones all acted in concert to run a given cell tower out of power. This also explains why users in locations such as San Francisco and New York were seeing bigger problems than users in less densely populated areas where fewer iPhone 3Gs were in use.

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  • alansky

    “A bit late?!! I sync it every day but just got the upgrade notice today and installed it right away.” –Brau

    The iPhone 2.0.2 update has been available since 18 Aug. iTunes doesn’t always notify users of an available update. You need to click “Check for Update” on the Summary page. Apple should really fix this.

  • alansky

    “Being the best phone ever made, it will speak for itself. Apple will blow away all estimates of iPhone sales.” –Realtosh

    Agreed. Being the best doesn’t require perfection. If it did, the title of “the best” would never be conferred on anyone or anything because perfection does not exist–except in the befuddled fantasies of individuals who are seriously out-of-touch with the world as-it-is.

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  • axc4466

    The explanation about the phone asking for too much power is shaky for the following reasons:

    1. The “calls dropped due to downlik power” occurs when the bases station exhusts all the power available to serve the active users, i.e. when it reaches the capacity. This can happen when there are too many active users at one time. Since iPhone clearly caused a spike in AT&T network load, this issue does not have anything to do with the iuPhone per se.

    2. Phones are thoroughly tested by the operator before they are “accepted” into the network. The amount of power the phone sucks out of the network is of course one of the most important aspects of the testing. The phones caught “cheating” are not allowed into the service.

    3. Power control works only for voice calls. For data calls, threre is no power control. The bases station spreads all the power left over from voice users across data users and the more power is available per data user the better throughput they will get.

    It is more likely that there are more than one issue that were more tricky tha that and that could not be discovered durig the testing. This is very typical for a combination of a complicated techology, such as 3G, and an immature product, such as Infenion chipset. Think of it as a Beta version of Vista.

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  • Frohike

    While this may or may not be in some way related although I’m sure there is a proportion of these drops that are related to the context of the calls being made. I live in Spain where there is a far more mature 3G market which has probably played its part on the network impact as iPhone usage is still very small when compared to the overall 3G market. For AT&T the iPhone 3G has caused a huge leap in 3G usage.

    An example of context was my playing with the GPS. I decided to see how well it would keep up with me driving at 160km/h (~100mph). Given the reports I was extremely happy to find that the little blue dot kept in place, correctly passing over-passes at the right time, for the whole 20 minute ride. The interesting thing was the streaming of the Google maps data. For the most part it streamed beautifully with the one exception… when you change cell towers the map streaming stopped altogether and I got a blue dot against a fast moving grey checker pattern until the new tower caught up with itself. Going back the other way a few days later confirmed this with the same dropouts in the same places (but in the other direction not to mention going much slower).

    I don’t profess to know anything about UE/Node B interactions for voice and data but maybe the issues are a combination of factors which includes UE power management, AT&T’s immature 3G network along with the call context in some instances. Apple may be making updates in order to help cope with AT&T’s 3G rollout and their problems. This is not to say Apple is “blameless” (if there’s anything to point fingers over at all) here but it’s possible it’s not just the iPhone 3G.

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