Apple iPhone 4 WiFi proves a challenge for university

The iPhone 4 is the first to use 802.11n for Wi-Fi connectivity. But it runs only in the crowded 2.4GHz band. And that poses some complex challenges if you have 500 students trying to connect their iPhone 4 in a lecture hall.

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The iPhone 4 is the first to support 802.11n, which offers the highest Wi-Fi data rates and throughput. But it runs only on the crowded 2.4GHz band, and at one university, which is deploying hundreds of the new devices, that poses some big Wi-Fi challenges for IT.

The iPhone deployment at Abilene Christian University, in Abilene, Texas, is unusual, possibly unique: there can be up to 500 or more iPhone 4 handsets in a big lecture hall, all trying to connect to the hall's collection of wireless access points. It's especially frustrating because ACU's IT group had successfully deployed hundreds of 11g iPhones, in the same lecture hall, on the same 2.4GHz band with minimal problems.

For now, in the areas with 802.11n access points, 11n has in effect been turned off, and the new iPhone 4s will run as 11g clients, at least for a few weeks until the kinks get worked out. The WLAN setup based on ACU's 11g experience includes the unique idea of using the student's as RF signal attenuators.

At this point, it's not clear if the WLAN instability is an issue of: configuring the access points; the mix of 11g and 11n clients, which triggers 802.11 protection mechanisms adding overhead; the limited channel assignments; a possible iPhone 4 Wi-Fi bug; or some combination of these.

Other colleges and universities so far are reporting no similar problems, though iPhones are popular on nearly all of them. University of Washington, in Seattle, has seen iOS devices soar from 1,400 in the fall of 2007 to 17,000 as of July 2010, according to statistics tracked by David Morton, mobile strategies director for the university, on his blog. So far, he says, they've had no issues, though he's not run any tests on iPhone 4 (UW is just starting its 11n upgrade).

A university in Georgia has upgraded its residence halls to 11n, with classrooms to follow. So far, about two-thirds of students on the "ResNet" use 11n, evenly split between 2.4 and 5GHz, with no problems; the remaining third are still using 11b/g, according to a university RF engineer, who asked not to be identified.

Yet few of these other schools have the kinds of classroom concentrations that ACU does, since ACU courses increasingly are designed to require the use of iPhones in actual class work.

Three years ago, as part of a major mobile learning initiative, ACU decided to equip each successive incoming freshmen class with the current iPhone model, as part of systematic, campus-wide exploration of "mobile learning" course content and teaching methods. The project included a campus-wide 802.11abg WLAN, both 2.4 and 5GHz, based on Alcatel-Lucent products (which are from Aruba Networks). They persuaded AT&T to put a 3G cell site on campus.

When the iPhone 4 was announced, ACU decided to begin upgrading to 11n starting with dorms, the library and some lecture halls. The IT group assumed the new phones would support the 5 GHz band, which is much less crowded and supports 11 vs. three non-overlapping channels. The extra channels mean more channel assignment options, making deployment and management simpler, and give the option for merging two standard 20 MHz channels into one "fatter" 40 MHz channel, to boost throughput, with plenty of channel options remaining.

When they discovered the iPhone 4 only runs on the 2.4 band, "it was kind of deflating," says Arthur Brant, ACU's director, networking services. That meant the iPhone 4 would join its 3G and 3GS brethren on the same crowded frequency, contending for the same three channels. Of 1,000 incoming students, 800 chose iPhone 4 (roughly 300 faculty also have it), the remainder chose the existing 11g-only iPod touch (Apple’s just-announced new iPod touch has 11n).

The new phone's Wi-Fi chip is Broadcom's BCM4329, a low-power, single-chip system designed specifically for mobile devices. It can run in either Wi-Fi band.

It appears to be what's called a single-stream MIMO (multiple input multiple output) implementation, which sounds like a contradiction in terms. (Through a spokesperson, Broadcom declined to explain its products features or the implementation options for device makers like Apple. Apple also declined to comment on its 11n implementation.)

Basically, MIMO breaks up a data stream into two or more substreams, each which is usually but not necessarily associated with a corresponding antenna. These multiple inputs and outputs have a kind of multiplicative impact on data rates and throughput, and the same technology is part of mobile WiMAX and LTE.

Single-stream 11n can't achieve the same effect, but it does realize higher throughput, greater range, and more robust signals compared to 11a and 11g due to other optional features of the 11n specification, including space time block coding, which improves transmission redundancy and reliability. The Broadcom chip supports many of these options.

So what kind of 11n performance does iPhone 4 actually get? We asked WLAN test vendor VeriWave to run a simple trial, with its WaveDeploy product suite. 

The test was run at VeriWave on a separate but real 802.11n network, based on Cisco gear, designed to behave as a typical enterprise production WLAN. An iPhone 4 was tested for upstream and downstream throughput at 14 locations, sending and receiving TCP traffic, with 1,460-byte frames which are "representative of typical Web traffic," says Eran Karoly, VeriWave's vice president of marketing.

Upstream throughput ranged from 3.9Mbps (at one access point; the next lowest was 9.1Mbps) to 15.6Mbps, for an average of 12.3Mbps. Downstream throughput ranged from 9.4Mbps to nearly 13Mbps, for an average of 10.5Mbps. No significant changes were found using 20MHz or 40MHz channels, according to Karoly. For comparison, an iPod touch using 802.11g was also tested: "the results were more or less the same" as for iPhone 4, he says.

Some schools are reporting better results. Scripps College, in Claremont, Calif., finds that the iPhone 4 and iPad, which also has 11n, are averaging about 28Mbps according to various bandwidth testers, says Jeffrey Sessler, director, Information Technology.

So in terms of data rates and throughput, and depending on lots of variables, often there may not be too much difference between single-stream 11n and a well-designed 11g network. But, 11n still can increase the reliability of the signal, and the range at which a client can sustain a given data rate, both of which can have a big impact on the user's experience.

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