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Behind the iPhone Software 2.0.2 fix to reduce dropped calls

The recent iPhone 2.0.2 software update addressed a problem with the iPhone 3G's power control that was causing dropped calls, according to a new report.

Last week, Apple's Jennifer Bowcock told USAToday that “the software update improves communication with 3G networks.” However, Roughly Drafted is now reporting addition details from "a source close to AT&T" that explained what the real issue may have been, and why some users didn't notice any immediate impact after installing the iPhone 2.0.2 update.

The cited source said, “In [AT&T 3G] UMTS, power control is key to the mobile and network success. If the UE [phone set] 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.”

“The power control issue will also have an effect on the data throughput," the source said, "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.”

The source added that the issue had compelled AT&T to send iPhone 3G users an SMS text message about the availability of the new iPhone 2.0.2 software, and that, "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.”

Steve Jobs separately emailed one user with a tersely worded intent to fix unrelated problems in the iPhone's higher level software that concern instability and crashing in third party apps, writing, "This is a known iPhone bug that is being fixed in the next software update in September."