What a difference a couple of years makes. In our first roundup of draft-802.11n Wi-Fi routers (see "Wireless Routers: The Truth About Superfast Draft-N"), we found so many problems, we couldn't recommend any of them: Firmware was buggy, interoperability between vendors was hit-and-miss, and performance was not as good as that of some enhanced, earlier-generation 802.11g routers.
As of this year, we're happy to report, those issues have largely gone away. Although the standard is still technically in draft form and final ratification of 802.11n by the IEEE isn't expected until next year, the Wi-Fi Alliance has been certifying draft-2.0 n routers for interoperability and compatibility since last year, and the final version should largely be a formality that at most may require a firmware upgrade.
And the Wi-Fi certified products are worthy updates. With link rates--the nominal connection speeds, as opposed to real-world throughput--of up to 300 megabits per second (compared with 54 mbps for standard 802.11g) and extended range (thanks to multiple smart antennas), 802.11n Wi-Fi is the first Wi-Fi technology that can rival wired 100-mbps ethernet in performance. Upgrading your home router to 802.11n is thus one of the quickest and easiest ways to improve your network.
But choosing a particular 802.11n router has become more complicated than ever because the standard covers a lot of ground that lets vendors issue a dizzying array of product options, with literally dozens of models ranging in price from $50 to $250. D-Link alone has six 802.11n routers.
To give an idea of the options, we chose two widely available models in each of three categories: under-$90 routers for people who don't need maximum performance, but who can nonetheless benefit from 802.11n's improved range and speed; midrange (about $150) models that offer top wireless speeds and gigabit ethernet; and dual-band routers ($180 to $200) that support both the crowded 2.4-GHz frequency range (used by all of the less-Expensive models and their 802.11b/g predecessors) and the relatively open 5-GHz band, with support for legacy 802.11a gear. These top-of-the-line units target users preparing for an expected influx of networked multimedia devices that need uncluttered bandwidth to stream media. (The 802.11n spec supports both frequencies.) Up to now, vendors have been focusing on the 2.4-GHz band in order to support the vast majority of legacy devices.
For a point-by-point comparison of the six routers we examined, see our chart, "Wi-Fi Draft-2.0 802.11N Routers: Good, Better, and Best."
Deconstructing the Technology
The 802.11n variant of Wi-Fi achieves its high through??put (typically four times that of 802.11g) in two ways. First, it uses MIMO (multiple input, multiple output) antenna technology to transmit more data at a time. Intelligent antennas combine streams of data arriving at different times from multi??path signals bouncing off walls, floors, and ceilings. Entry-level routers typically have two receiving and transmitting antennas; midrange and high-end models have three of each.
Second, draft-n uses channel bonding: Instead of the 20-MHz-wide channels found in previous Wi-Fi standards, 802.11n can use 40-MHz-wide channels, which in theory should double their data-carrying capacity.
Unfortunately, the limited bandwidth of the 2.4-GHz range means that just one 802.11n router using channel bonding will take up virtually the entire 2.4-GHz spectrum, leaving no room for neighboring routers, and causing severe interference. For this reason, draft-2.0's so-called good-neighbor policies require that routers ship in 20-MHz mode, and that, when in 40-MHz mode, they drop to 20-MHz operation if they sense nearby Wi-Fi nets or other 2.4-GHz devices. The top link rate in 20-MHz mode is only 150 mbps (rather than the much-advertised 300 mbps); since many users are likely to be within range of other 2.4-GHz traffic, we ran our 2.4-GHz tests with 20-MHz channels.
More Bandwidth, Less Range
The 5-GHz frequency range, however, has much more bandwidth to play with and can support multiple 40-MHz channels. It's also relatively unused (802.11a products appeared primarily in business environments), so interference is generally minimal to none. We therefore used 40-MHz channels in our 5-GHz testing of the two routers that support 5-GHz operations.
Interestingly, even with twice as much channel bandwidth, speeds in our 5-GHz testing at close range did not double; on average, they rose about 20 percent. But they were generally more consistent than the 2.4-GHz results, and throughput at close range never dropped below 40 mbps--well above the 25 mbps needed for top-quality HDTV streaming.
The downside to 5-GHz: Its higher frequency doesn't allow it to cover as large an area as 2.4-GHz draft-n. But its range is still generally far better than that of standard unenhanced 802.11g.
Another 5-GHz plus: While draft-n is backward-compatible with 802.11b and g gear in "mixed" 2.4-GHz mode, performance for n clients drops significantly on networks when b or g clients are present. But with a dual-band router, you can put newer draft-n gear that supports 5 GHz on the fast track while maintaining a slower 2.4-GHz network for older gear. We recommend a dual-band router if you need maximum performance for streaming media or networked storage--or if you can't get a good Wi-Fi signal at all due to interference from neighbors' networks.
source : http://www.pcworld.com
