Absolute Power


Death Grip


This blog originally posted on the Low Power Engineering Community 12/1/11.

One of the areas I’ve been most interested in testing out on the new iPhone 4S is the effectiveness of the new dual antenna design, which is claimed to solve the now-infamous iPhone 4 “death grip” problem. Since we’ve already seen in previous experiments that battery life on these devices is strongly tied to communications and signal strength, any improvement in reception would have a direct impact on battery life whenever the radio is being used extensively. And with the addition of Siri, expanded notifications, and iCloud in iOS 5, it’s clear that the percentage of time our coveted smart phones will be spending connected (or connecting) to data networks is going to be increasing.

To get a picture of the effectiveness of the new antenna setup, I took data using the built-in Field Test mode (key in the string ‘*3001#12345#*’ without the beginning and ending apostrophes into the Phone application and then push “call”), which conveniently displays signal strength in dBm (power ratio in dB referenced to 1 mW). I compared the signal strength on the iPhone 4S with the iPhone 4, and also recorded signal strength for each device while using the “death grip” that Steve Jobs warned us about. It’s not as glamorous as the “Vulcan death grip” that Mr. Spock administered to Captain Kirk in “The Enterprise Incident,” but everyone knows there’s no such thing as a “Vulcan death grip” anyway!

The data chart below shows average signal strength data in 9 different locations, from “terrible signal” (1 bar or less) to “strong signal” (5 bars). Note, as we’ve mentioned before, signal strength for these kinds of transmissions is notoriously flaky. The variance in readings in each location over a period of around two minutes was between -4 dBm and -10 dBm. The “terrible signal” location was in my office in Mountain View. And just for grins, I’ll bet you can’t guess where, within a five-mile radius of Mountain View, you can reliably get a very “strong signal.” If you guessed a street address of “One Infinite Loop,” you’d be correct!

The top line (green) is the data for the new iPhone 4S. It signal reception is generally a couple of dBm better than the original iPhone 4 (orange). This is a measurable difference, but practically not too significant, especially given the large variations in the measurements. However, there is a big difference when comparing the signal strength of the two devices while applying the “death grip” (light green and light orange). The iPhone 4S shows a drop of less than -6 dBm on average using the “death grip”, but the original iPhone 4 shows a whopping drop of over -17 dBm, and that’s conservative because the Field Test numbers were “pegged” at -116 dBm. This would definitely result in dropped calls in any areas without a very strong signal to begin with.

So, the iPhone 4S does indeed solve the “death grip” problem. Its dynamically switching dual-antenna design (one on the bottom and another on top) is an effective solution that we’re sure to see in other smart phones as well. Just for the fun of it, I also applied a “double death grip” to the iPhone 4S, and saw about an additional -6 dBm of signal strength loss as a result. But don’t try this one at home (or at least not in public). It’s legitimately in Apple’s category of “you’re not supposed to hold the phone that way!”

Next time; we’ll try to use the data we’ve gathered to predict and measure the improvement in energy efficiency of the iPhone 4S over the iPhone 4 as a result of the new antenna design. Stay tuned.

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