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. Source...