The future of WiFi: gigabit speeds and beyond

Wi-Fi logoNow that 802.11n has been officially ratified, attention is turning to the next big thing in wireless networking: gigabit WiFi. Ars explores the future of WiFi and how it may give gigabit Ethernet a run for its money.

In a couple of years, crossing the 1Gbps threshold with a WiFi access point will be routine. That access point will likely have two radios, one for each major spectrum band, and support a host of older flavors for compatibility. Eventually, WiFi will approach the robustness and speed needed to make it a completely viable replacement for Ethernet for most users.

In today's pipeline are optional enhancements to 802.11n that have been in the works since the standard stabilized at the IEEE engineering group nearly three years ago. These enhancements will increase range and performance by up to a couple orders of magnitude, offering raw data rates of 450 Mbps and 600 Mbps.

The slated improvements will also correct for black holes, where current 802.11n gear's signals don't reach unless an excessive amount of overlapping devices are installed at relatively high expense. Even better, the boosts to 802.11n are just the start. A new IEEE committee is working on fast WiFi that will hit a raw encoding rate of 1 gigabit per second (Gbps).

All these higher speeds will be eminently affordable and reasonable choices for small-to-medium-sized businesses. It may even be possible to achieve higher performance (both for speed and network consistency) by spending less than a network upgrade would cost today: fewer, more powerful access points with better coverage may wind up saving money.

The need isn't always for speed: it may be better to have a network that works in the worst circumstances, with tons of users moving lots of data, than to move additional raw data. With the popularity of watching video (for business purposes, no less), the growth in the size of standard document files, continuous network backups, and other network loads, network capacity, quality, and support for simultaneous users and heavy-load applications will become increasingly important.

Faster WiFi paradoxically also means that more wired infrastructure is needed. With individual access points able to pump out a dual-band total of several hundreds Mbps, and future dual-band devices topping 1 Gbps, more robust and higher-performance backhaul will also be needed.

From a tiny nut, a great oak

The 802.11n standard has come a long way from its contentious origins, when MIMO (multiple in, multiple out) antenna arrays were seen as impractical, expensive, and beside the point of pushing data over the air. Now, in addition to 802.11n, all 3.5G and 4G cellular wireless standards either require or allow the use of MIMO for better coverage and performance.

At a time when 802.11g could only deliver 20 to 30 Mbps of real throughput out of a potential 54Mbps raw data or "symbol" rate, the idea of 150Mbps with 75 to 100 Mbps of actual throughput was pretty stunning.

But it got better. By the time manufacturers coalesced their efforts—after a cantankerous process—around a single approach for 802.11n, it was clear that all access points and adapters would support two radio streams, each of which would be able to handle a raw rate of 150 Mbps, for a combined 300 Mbps.

Each stream is a chain of radio components that share antennas. For sending, each stream transmits uniquely and simultaneously across space, using signal reflection in the environment in the same way that a billiards player uses bumpers to strike a ball. This is called spatial multiplexing: multiple signals encoded using space as a parameter. A receiver decodes the signals across multiple antennas, dumping each stream into a unique radio chain.

A receiver with a like number of radio chains, and often a similar number of antennas, can interpret the directionality of signals, sifting out separate streams to reconstruct the original message.

For instance, a 2x2 (two transmit, two receive) antenna array is often paired with two radio streams, or a 3x3 with three radio streams. Some devices with two radio streams might have 2x3 arrays, in which three receive antennas are used to improve signal differentiation and range.

Two chains is good. But what about three? Or four? These optional enhancements to 802.11n were eminently possible, but with the exception of wireless chipmaker Marvell and startup Quantenna, most firms sat out the dance, waiting for a shoe to drop: interoperable certification from the WiFi Alliance.

The WiFi Alliance is a trade group that popularizes wireless networking as a technology to use while also setting certification testing for companies that want to use the WiFi label and branding on products. Apple, Cisco, Intel, Microsoft, Nokia, and many similar firms sit on the group's board.

WiFi has managed the neat task of herding cats for a decade, even as standards have proliferated into an alphabet soup of a, b, g, e, i, aa, and more—and as the IEEE 802.11n proceedings threatened to scuttle industry-wide compatibility. The group persevered, ultimately offering a Draft N certification that was an interim brand while the 802.11n spec was being finished, and which has now transition to just "N."

With the ratification of 802.11n as a finished spec earlier this year by the IEEE, the WiFi Alliance released an updated certification program designed to standardize several more obscure elements of 802.11n that weren't fixed in stone until near the end.

The most important of these were multi-stream 802.11n devices, starting with three-stream radios. The certification process seems to have taken the brakes off the industry besides Marvell, all of which are now looking to three-stream radios and beyond. For instance, Atheros announced its 2010 series of 3x3 three-stream chips shortly after the WiFi Alliance's certification news. The chips have to exist before the alliance can create a certification standard, which is why these evolutions all come together at once.

Likewise, while four-stream devices are defined in the 802.11n spec, the WiFi Alliance won't be able to approve such devices until chipmakers have them available.

So far, it's difficult to tell what hardware is shipping with 3x3 antenna arrays and three-stream systems installed. Apple's October 2009 update to the AirPort Extreme Base Station and Time Capsule access point and network-attached storage device include three-stream radios, but Apple isn't advertising the feature. On its base station pages, the company says only that the latest revision "gives[s] you up to 50 percent better WiFi performance and up to 25 percent better range" than its immediate predecessor. This conforms with 3x3 antenna arrays, which, even with a two-stream radio, carry data further at higher speeds.

However, the device has the capability of higher speed, too, several industry sources confirmed who declined to be identified. Apple didn't respond to multiple requests for clarification.

The three streams in Apple's base stations require 3x3, three-stream adapters to reach higher speeds. This means redesigned WiFi adapters in Apple gear or those made by other companies; so far, only Intel seems to have a three-stream laptop radio available, found in only a few computers.

Source: ars technica

Tags: Wi-Fi

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