What you ought to know before deploying an 802.11n Wireless Network

We all know that the IEEE 802.11n standard for Wi-Fi supports up to 600 Mbps for creating a wireless network. But are all 802.11n compliant devices same? Is the 600 Mbps throughput feasible as of today? What other network/ device considerations do we need to account for, to achieve maximum 802.11n throughput levels? These are some of the questions that will be answered in this article.

salient points and features of 802.11n MIMO Wi-Fi networks

Gone are the good old days of the 802.11a/b/g wireless networks where the throughput levels were simple and consistent for the entire standard. All the 802.11b compliant devices (clients and access points) could achieve 11 Mbps throughput (theoretically). All the 802.11a/g compliant devices could achieve 54 Mbps throughput (theoretically). This can be compared to the black and white era, where there were only two shades – black or white!

But in the coloured world of 802.11n, there are various options and configurations possible. For example, each 802.11n compliant device (access point or client adapter) could have unique T x R : S configurations. In addition to the 1×1, 2×2, 3×3, 4×4 configurations and throughput levels shown in the above diagram, there could even be configurations like 1×2, 2×3, 3×2 etc. Each transmit and receive antenna comes with its own radio. Each 802.11n compliant device can support a certain number of spatial streams (transmitted data streams, that have different amplitude and phase, each of which can be independently received at the receiver end). 802.11n compliant devices can work at 20 Mhz or 40 Mhz (bonded channels) and each gives a different throughput. Some of the 802.11n compliant devices work in both 2.4Ghz band as well as 5 Ghz band, while some of them work in either of the two.

So, next time you want to buy a laptop or access point that supports the latest wireless standard, don’t just ask for 802.11n compliance! Below are some of the common configurations of laptops/ home access points/ business access points that support 802.11n.

Common configurations for 802.11n compliant Laptop / Desktop wireless clients (adapters):

1×2 MIMO – Works in 2.4 or 5 Ghz (single band) – Supports up to 150/300 Mbps.

2×2 MIMO – Works in 2.4 and 5 Ghz (dual band) – Supports up to 300 Mbps.

3×3 MIMO – Works in 2.4 and 5 Ghz (dual band) – Supports up to 450 Mbps.

Common 802.11n compliant Access Point configurations:

Business: 2×2 MIMO (single band) – Supports 2.4 or 5 Ghz; 2×2 MIMO (dual band) – Supports 2.4 Ghz and 5 Ghz; 3×3 MIMO (dual band) – Supports 2.4 Ghz and 5 Ghz.

Home: There are no common configurations in this segment and the MIMO diversity could range from 1×1 to 3×3 configurations.

Note: 4×4 configurations (that support 600 Mbps, in theory) are not yet available, meaning they may not provide a significant performance improvement over 3×3 (if deployed currently, at the time of writing this article) and hence are not very popular. But very soon, they are expected to become available; 1×1 is not actually a MIMO but SISO (Single Input / Single Output) configuration and some of them support bandwidths in the range of 65 Mbps, which is only a slight improvement over the current 802.11a/g standards that support 54 Mbps.

Still, all the above devices are referred to as Wireless ‘n’ compliant devices! But cost varies with each product, and perhaps its good to have options!

Some suggestions for achieving highest possible throughput/bandwidth with 802.11n wireless implementations:

  • The wired (backbone) network to which each of these 802.11n access points are connected should be end to end Gigabit (1GE) network (Switch ports, cables, patch panels, patch cords, fiber transceivers, etc).
  • Access Points and client wireless adapters should support at least two spatial streams (three might be even better).
  • If access points are going to be used in 2.4 Ghz band, and channel bonding is applied (recommended for 802.11n performance), out of the three non overlapping channels (20 Mhz each), two would be bonded (to achieve a 40 Mhz channel for use in 802.11n networks) and only one would be left out for legacy 802.11b/g clients. Any network today would definitely have some legacy wireless b/g devices and hence those devices would be prone to higher interference – hence poor connectivity.
  • Hence it is suggested that, for effective 802.11n performance, it better for access points and clients to operate in 5 Ghz spectrum which has many more non over lapping channels. In fact using 40 Mhz channels in 5 Ghz would provide the best performance for 802.11n wireless networks.
  • Its even better if both wireless clients (laptops, etc) and wireless access points support both 2.4 Ghz and 5 Ghz spectrum. The legacy clients could operate in the 2.4 Ghz spectrum (most of todays legacy clients are 802.11g and hence operate in 2.4 Ghz) and the newer 802.11n clients could operate in the 5 Ghz spectrum (preferably).
  • By the way, 5 Ghz spectrum is cleaner and does not suffer from interference with blue-tooth devices, Microwave Owens, etc.
  • In dense wireless access point deployments in the 2.4 Ghz spectrum (for the legacy clients), channel bonding could be disabled as otherwise there would be a lot of interference from neighboring access points operating in the same channel.
  • The POE (Power Over Ethernet) standard – 802.3af supplies around 12.95 Watts or slightly higher per port (POE Switches or Power over Ethernet Injectors). This may not be sufficient for 802.11n access points. If the 802.11n access points are still used with them, some of the additional radios might be turned off and hence there would be lower throughputs. Either the POE Plus (802.3at) standard switches/ POE injectors could be used (or) multiple cables/shorter cables could be run to the 802.11n compliant access point from existing POE switches. But some vendors support 802.11n operation with 802.3af or equivalent power supplies. Hence its better to check the vendor specifications on this.
  • The RF Survey tool (used to predict the number of access points required in a wireless network, before implementation) should be specifically designed for 802.11n and should take in to consideration all the interfering objects on the way (as the reflections from these objects are critical for multiple path propagation) in order to come up with the right network sizing.
  • Though a network can be designed exclusively for 802.11n, there will be a number of legacy devices that operate in 802.11a/b/g, which needs to be taken in to account during the design stage itself. Probably, the 802.11n access points could co-exist with legacy access points, in certain cases.
  • In the 5 Ghz spectrum, wireless signals travel lesser distances than the 2.4 Ghz spectrum. Also, the signal strength for any client near the access point is always high and it decreases with client’s increasing distance from the access point.
  • It may be better to dis-allow the legacy 802.11b clients in the 802.11n network as they might slow down the performance of all the clients considerably. Generally, the more the number of legacy devices(802.11b,g) lesser is the performance of 802.11n network.
  • Integrated client adapters for 802.11n based clients (laptops, etc) perform better than the external adapters (USB based, etc).
  • Since encryption is a tedious process that can slow down the performance, its better if a 802.11n client can perform encryption at chip level than at the software level.
  • Similar type of network adapters for all the clients (as far as possible), increases the performance of 802.11n networks.
  • Some client adapters (and even access points) prefer to connect in the 2.4 Ghz spectrum by default, even though 5 Ghz spectrum might be available. In such cases, it might be better to disable the 2.4 Ghz spectrum operations in the client adapters so that they operate in 5 Ghz spectrum only.

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