802.11n Delivers Better Range

802.11n Delivers Better Range

Informal tests indicate Draft N, even mixed with with legacy 802.11g products, connects faster at longer distances.

The concept of range for wireless LANs is pretty basic. Range is usually thought of as a measure of distance — the distance between two wireless stations at which they can effectively communicate. For typical Wi-Fi systems, range is the distance between a laptop client and the access point (AP) it is using.

Any discussion of wireless range also has to include data rate (not to be confused with the actual, physical throughput). In wireless systems, you can trade off data rate for range – at lower data rates, it is possible to communicate at greater distances. The 802.11 standard supports multiple data rates at the physical layer. 802.11 has an automatic rate fallback mechanism that reduces the data rate when communication degrades in order to maintain a better link between a wireless client and AP.

802.11n extends the original concepts of 802.11 and includes many new options to improve the quality of the wireless link and thereby to increase both data rate and range. The coding scheme for 802.11n is better than earlier versions of the standard, and that results in more data bits being transmitted in the same size channel. The most significant new feature of 802.11n is MIMO (multiple in, multiple out) , which transmits multiple streams of data on different antennas in the same channel at the same time and then recombines the streams at a receiver that also has multiple antennas and radios. There are different combinations of radios and antennas supported, resulting in different numbers of spatial streams and therefore different data rates. In addition to all these improvements, 802.11n allows channel bonding that will essentially double the data rate again.

Most first generation draft 802.11n (Draft N) systems support two spatial streams. Combining all of the enhancements, we can expect 144 Mbps as the highest data rate in a single 20 MHz channel, and 300 Mbps with channel bonding. Future 802.11n systems that incorporate additional spatial streams will deliver up to 600 Mbps with channel bonding. Can these systems deliver those data rates at a reasonable range?

Getting a precise range specification for 802.11n systems is difficult, since there are so many optional configurations possible. Like many questions about radio-based systems, the answer to the question, “What is the range of 802.11n?” is, “It depends.” Range will vary depending on the environment and on the capability of the client and access point.

The marketing claims on the current round of Draft N products are “twice the range of 802.11g products.” In order to fulfill that promise, an 802.11n client should be able to communicate at the same data rate from twice the distance, or a client should be able to communicate at twice the data rate from the same distance. Our early experience with Apple’s AirPort Extreme (a first gen Draft N system) goes way beyond doubling the range. Upgrading from an 802.11g AP to the AirPort Extreme improved the performance of all of the Wi-Fi clients in the house. With the new AP, 11g clients connected at 54 Mbps throughout the house. Previously, with an enterprise class 802.11g AP, the 11g clients would fall back to lower data rates when operating on different floors on the other side of house from the AP.

Based on this informal testing, our perception is that the Draft N AP doubled the range when communicating with legacy 802.11b/g clients. It seems clear that 802.11n APs have improved radio performance that delivers better range even when operating in backward compatibility mode and supporting legacy clients.

Using a Draft N client (a MacBook Pro with built-in AirPort Extreme) with the 11n AP was even better. In the best part of the coverage area where the 11g clients used to deliver 54 Mbps, the 11n client provided more than double that, at 144 Mbps. The Draft N client never shifted to a lower data rate, even at the farthest locations in the house.

And taking that same 11n client and using it with legacy 11g access points continued the good news. While not delivering the 144 Mbps possible with the 11n AP, it consistently delivered 54 Mbps over the entire house to the old AP.

Your mileage may vary. Range is very dependent on the environment, but these informal results are certainly promising. This is one case where the product exceeds the marketing hype. There appears to be no downside for home users to upgrade to 802.11n. (Conservative consumers may want to wait for products that are Wi-Fi Certified Draft N. These are coming in the next few months.) A new 802.11n home router may be worth the price premium just for the improved range it brings to legacy Wi-Fi clients around the house. And 802.11n clients appear to operate as “better 11g” on legacy Wi-Fi infrastructure.

What about 802.11n in the enterprise? How will we use the improved range capabilities of 802.11n? Can we reduce the number of APs required to cover an entire office building? Not exactly. We will address that in the next article.



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