Tips and Considerations for 802.11ac Wireless
If you're currently looking to deploy 802.11ac wireless, or plan to in the future, there are many things to understand and consider. Along with the dramatically higher data rates-of 1.3 Gbps or more-come many caveats and additional technical aspects to understand. And here I'll share some tips and considerations, giving you a better understanding of the technical aspects. As you'll see, the data rates you'll see with 802.11ac-especially the higher rates-depend upon the particular APs and clients used and how the APs are configured.
The Supported Streams
The Multiple Input, Multiple Output (MIMO) technology was introduced with 802.11n to help increase performance on Wi-Fi networks. Basically MIMO allows the Wi-Fi radios to simultaneously send and receive multiple streams of data among a single client via multiple antennas, increasing the data rates, total throughput, and even signal range. While 802.11n was designed to handle up to four spatial streams, 802.11ac is designed to allow up to eight streams. And with 802.11ac we should see Multi-User MIMO. With this the Wi-Fi radios can simultaneously send and receive multiple streams of data among multiple clients instead of just a single client. Most 802.11n products support only up to three streams, with design constraints and economics preventing the use of all streams. The same issues apply to 802.11ac. It will take time for vendors to be able to manufacturer products that support more than three streams. Some vendors advertise the MIMO details, including the amount of streams, of their products openly in their product details while others you may have to do some digging on the Internet. When looking for this you may see the MIMO numbers listed in this format: number of transmit chains by the number of receive chains, a colon, and then the number of data streams supported. So a three stream device would be listed as 3x3:3.
With 802.11n the use of 5GHz channels was optional whereas with 802.11ac it's required. 802.11ac is backward compatible and can connect via the earlier standards in the 2.4GHz band as well, but for a true 802.11ac connection the 5GHz band must be used. In the 2.4GHz band there are only three non-overlapping regular 20MHz channels and only one channel if a 40MHz wide channel was used with 802.11n for maximum throughput. In the 5 GHz band there are 24 non-overlapping regular 20MHz channels supported in the US. And if 40MHz wide channels are used for increased throughput with 802.11n or 802.11ac there would be 11 non-overlapping channels. And if 80MHz channels are used with 802.11ac for additional throughput, five channels would be available. And in the future we'll see 160MHz wide channels for 802.11ac, minimizing the non-overlapping channels even more. Keep in mind although we'll see more channel options with the 5GHz band, it generally offers shorter useful ranges as the 5GHz signals don't penetrate obstructions as well as 2.4GHz signals. Plus with 802.11ac, the higher Quadrature Amplitude (QAM) rate-which helps increase the data rates-is very sensitive to signal strength and interference; thus requiring a great signal in order to get the great rates.
When looking to deploy 802.11ac in an existing network, consider the existing infrastructure. Ensure your router, switches, and other network components can handle the higher data rates and other technical aspects. For instance, most 802.11ac APs will require support of the higher-power 802.3at Power-over-Ethernet (PoE) standard if you plan to use PoE to power your APs.
Although 802.11ac is supposed to be compatible with the previous wireless standards, current 802.11ac APs and clients from different vendors may not work well together. The Wi-Fi Alliance just recently started testing 802.11ac products, so consider waiting for products that will be Wi-Fi Certified.
Consider Support for Future Updates
When choosing an 802.11ac solution, consider the vendors support for future updates/upgrades. This is especially important for the APs since the 802.11ac standard is not fully finalized and upgrading the APs on a larger network would require significant resources. Check with the vendor if Draft 802.11ac products could later be upgraded to the finalized standard by firmware upgrades. Or consider modular APs that could run 802.11n for now that are upgradable later with an 802.11ac module.
USB 3.0 Support for Clients
Keep in mind for end-users using USB 802.11ac adapters, it's best that the PC or laptop support USB version 3.0. The maximum data rates of USB 2.0 is 480 Mbps while 802.11ac has maximum data rates of 1,300 Mbps or more, thus using a USB 2.0 wireless adapter or plugging into a USB 2.0 port can cause a bottleneck and reduce the throughput of the 802.11ac connection. USB 3.0 supports up to 5,000 Mbps, providing a high enough data rate to fully take advantage of the high data rates of 802.11ac.
Remember, when looking for 802.11ac APs and clients consider those that are Wi-Fi Certified for best chances of interoperability. Before deploying, evaluate your existing infrastructure to see if it will support the higher data rates and new technologies like 802.3at PoE. We choosing 802.11ac products, consider the amount of streams they can handle. The more streams, the faster the connection. And when using USB wireless adapters, it's best that the PC or laptop supports USB 3.0 to get the maximum data rates of 802.11ac. Consider if and how the APs will be upgradable in the future when the final 802.11ac standard is released. And when configuring your APs, keep in mind that to get the higher data rates you need to set larger channel-widths.