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Network World - Is iPhone 5 the first smartphone to support 5GHz?
What is 5GHz Wi-Fi?
5GHz is the "other frequency" that Wi-Fi client radios can use, besides 2.4GHz, to connect to an access point or hotspot.
Why would I want to use it?
First, because the 2.4GHz band is crowded, and therefore has a greater chance of interference. There are lots of devices are using it: Lots of other Wi-Fi devices, including embedded Wi-Fi radios, but also non-Wi-Fi radios like Bluetooth, cordless phones, baby monitors, and stuff like microwave ovens.
Client Wi-Fi radios that support only 802.11g can only connect on 2.4GHz. 802.11a, which so far has not been widely used, runs on 5GHz. 802.11n, which has much higher data rates, can run on either band but most smartphones today that have 11n, such as iPhone 4 and 4S, only run it on 2.4GHz.
And even when the client radio could run on either band, a lot of them today still "decide" to connect on 2.4GHz and stick with it, even when a better connection is available. Vendors and IEEE are working on various technologies to address this, including shifting more control over the connection, and optimizing it to the access point/network, instead of the client.
Second, the 2.4GHz band has only three non-overlapping, 20MHz-wide channels: In crowded environments -- lots of access points, lots of clients -- that can make it hard to get a channel connection. And fewer channels means lower aggregate capacity on the network side.
So what's different about 5GHz?
By contrast, the 5GHz band has, for now, many fewer Wi-Fi clients, and 23 20MHz-wide, non-overlapping channels.
In the 802.11n radio standard, one way that data rates increase dramatically is by combining (or "bonding") two of these channels into a wider 40MHz wireless "pipe." In 2.4GHz, you only have the three channels, and can create only one 40MHz channel.
Apple says that iPhone 5 will deliver a maximum 150Mbps data rate. This would mean using 802.11n, with a single data stream, and a 40MHz channel. Actual throughput will be much less.
How does 5GHz affect network capacity?
"5GHz support on an iPhone is a wonderful thing for Wi-Fi," says William Kish, CTO and co-founder of Ruckus Wireless. "It increases aggregate capacity in challenging environments by something like a factor of 10-12 compared to 11n on 2.4GHz."
Kish defines aggregate capacity as "the total capacity available to all simultaneous users across all of the APs in a given area."
"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.