Apple has confessed that it has discovered that every iPhone uses the wrong formula to calculate how strong a signal it is receiving — meaning that it seems to show good reception when the signal is weak. It has promised a software fix for the problem “within a few weeks” which will match that used in other phones.
The explanation, in which the company says it used “totally wrong” calculations to work out the strength of the signal, seems to explain why some people have complained to the company that they see a dramatic drop-off in the signal strength displayed when they hold the iPhone 4 in a particular way. Within hours of the phone being delivered to customers last month, dozens had posted videos on YouTube showing that the number of “bars” indicating reception strength fell abruptly when they picked the phone up from a desk.
Apple says in a press release on its site that it was “surprised” after the launch of the phone to read reports of reception problems, especially those who reported that the signal strength dropped completely — from five “bars” (the strongest reception) to none when held in a way that covers the antenna on the bottom of the phone.
But after getting “hundreds of emails from users” and seeing articles about the problem, it took the phones back to its laboratories — and discovered, it says, that it has been measuring signal strength wrongly since the very first iPhone, in a development it calls “simple and surprising”.
The company explains: “Upon investigation, we were stunned to find that the formula we use to calculate how many bars of signal strength to display is totally wrong. Our formula, in many instances, mistakenly displays two more bars than it should for a given signal strength. For example, we sometimes display four bars when we should be displaying as few as two bars. Users observing a drop of several bars when they grip their iPhone in a certain way are most likely in an area with very weak signal strength, but they don’t know it because we are erroneously displaying four or five bars. Their big drop in bars is because their high bars were never real in the first place.”
That would mean that the apparently strong reception that vanished when the phone was picked up was a mirage — and that the abrupt fall-off was because the signal strength dipped below the normal levels for a lower range of bars.
The review site Anandtech investigated the iPhone 4’s reception earlier this week, and found that there is comparatively little difference between the signal strength needed to get four “bars” and one: a difference of 12 decibels’ signal strength is enough to boost the apparent reception from one to four bars. A difference of 10dB is equivalent to a tenfold difference in the power of the signal, and a 3dB difference equates to a factor of two in the signal power.
Other phones use different measures to indicate signal strength: different versions of RIM’s BlackBerry, for example, will show only two bars out of five with a signal strength of -80dB — which would be enough on the iPhone to show five bars.
Apple says it intends to fix the problem with a software update which will mean that the displayed signal strength matches the formula recommended by AT&T, the sole phone provider for iPhones in the US. There is no comment yet from UK phone providers as to whether the formula they recommend for signal strength is the same as AT&T’s. Nor is AT&T’s measurement system available online: the phrase “recommended formula” does not appear in any of its developer documentation, and an AT&T representative said that “You will need to speak to Apple about its letter.”
But Apple insists that the iPhone 4’s wireless performance is “the best we have ever shipped” and that for the vast majority of users, “this software update will only make your bars more accurate”.
The company is facing a class action in the US from angry buyers of the iPhone 4 who have complained that Apple knew about the issues with the antennas before the phone was released. The company has not yet responded to the lawsuit, though in its letter it points out that dissatisfied customers can return their phones for a refund. – guardian.co.uk