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FAQ: iPhone 5 and 5GHz Wi-Fi

John Cox | Sept. 17, 2012
The iPhone 5 is Apple's first to support Wi-Fi connections on the 5GHz band. Here's what it means for you.

"The higher aggregate capacity is mostly a function of the much larger amount of bandwidth (e.g., the [much greater] number of channels) available in the 5GHz band as well as the more capacity-favorable propagation characteristics of the 5GHz spectrum," Kish says.

For example, an 802.11g network offers 54Mbps of capacity on each of three 2.4GHz channels, for a total capacity of 162Mbps. 802.11a offers the same 54Mbps, but in theory its capacity is much larger due to the larger number of 5GHz channels.

For 802.11n, the numbers are even greater: 150Mbps per channel, for 450Mbps in the 2.4GHz band, and 3.45Gbps in 5GHz. In all cases the actual throughput users get is much less.

What does that mean for throughput?

Kish was recently at the Time Warner Cable Arena in Charlotte, N.C., where a Ruckus Wi-Fi network had been installed, for a live event. He speed-tested his Samsung Galaxy S III smartphone in the network: 60.33Mbps download, and 58.78Mbps upload.

"60Mbps is a serious amount of throughput to a mobile device under real-world conditions!" he says. "I have my fingers crossed that the iPhone 5 delivers similar results."

Are there any drawback to 5GHz?

At the same power level, a 5GHz signal has a shorter wavelength than a 2.4GHz signal. That means it propagates shorter distances. From a client perspective, for example using a Starbucks hotspot or a well-designed hotzone or enterprise WLAN planned for 5GHz, users often may not be affected by either of those characteristics.

Higher-gain antennas and/or increased transmit power (though this is regulated by the Federal Communications Commission) can offset the 5GHz propagation.

Another issue is how the phone will decide which band to use: Will it be set (or settable) to "prefer" 5GHz over 2.4GHz, so the choice is automatic? Or will you be prompted for your preference? Or do you have to manually select one or other?

A June 2012 blog post at WLAN vendor Aruba Networks noted that the vendor's testing of 5GHz mobile devices found "that handover performance [from one access point to another] for a fast-moving device is not quite as good when both bands are enabled as it was for 2.4GHz only ... this is probably due to the larger number of channels that must be scanned. The chip vendors will need to tweak their probing and selection algorithms to tighten this up, and there are some new standard features coming that will help. But this is a minor concern."

What Wi-Fi chip is in the iPhone 5?

We don't know exactly, yet, until the phone is released and it gets the "tear-down" treatment. But historically, Apple has sourced the radio from Broadcom. The iPhone 4S uses the Broadcom BCM4330 -- at the time last year Broadcom's newest WLAN -- Bluetooth, and FM combo chip. It was also used in the Samsung Galaxy S II and, according to Kish, in the newer S III.


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