I recently had the opportunity to provide commentary on the subject for an article written by Lee Badman in Network Computing. Lee did a superb job with the article, as he always does, and provides great insight for corporate WLAN network managers looking for advice.
I'd like to expand a little bit deeper on my viewpoints expressed in his article with this post, and to provide an assessment of the "real-world" impact that most enterprises should be considering.
802.11ac - Wi-Fi Just Keeps Getting Better!
The 802.11ac standard includes complex technology that will eventually allow multi-Gigabit data transfer, but not all aspects of the specification will be available on day one. Similar to 802.11n, which began with two spatial stream devices capable of 300 Mbps and eventually saw maturation to three spatial streams capable of 450 Mbps, 802.11ac will see an initial first wave of products that are capable of 1.3 Gbps with future maturation possibly up to 6.9 Gbps. Whether or not we will actually see 802.11ac products capable of 6.9 Gbps is dependent on hardware enhancements on both the access point and client that are not certain.
First generation 802.11ac products will achieve 1.3 Gbps through the use of three spatial streams, 80 MHz wide channels (double the largest 40 MHz channel width with 802.11n), and use of better hardware components that allow higher levels of modulation and encoding (256-QAM). The 802.11ac amendment also simplifies implementation of standards-based beamforming for manufacturers by focusing on a single form of explicit beamforming, and eliminating the complex number of beamforming methods detailed in 802.11n. This should allow AP and client manufacturers to align on a single interoperable method.
Future releases of 802.11ac will enable even higher bandwidth by allowing up to eight spatial streams, 160 MHz wide channels, and simultaneous transmission to multiple clients by an access point, called Multi-User MIMO (MU-MIMO). In a few years, the realistic benefits for enterprises will likely be four and five spatial stream products with network designs still primarily based around 20 MHz and 40 MHz wide channels. MU-MIMO deserves special attention because it will mark a significant milestone in wireless technology that will allow greater performance through the use of parallel transmissions to two different receivers from the same transmitter. For example, an AP that is capable of 3 spatial streams (3X3:3) could transmit 1 spatial stream to three different clients that are only capable of 1 spatial stream each, concurrently. This will allow enterprises to better-serve large client populations in high-density environments. As described in the Aerohive High-Density Wi-Fi Design and Configuration Guide, the increasing reliance on WLANs as the primary method of network connectivity and for mission-critical services is shifting the focus from designing Wi-Fi networks for coverage to designing them for capacity. MU-MIMO will be a critical enhancement that will allow Wi-Fi networks to scale larger and provide greater capacity to support growing demand.
Most of the current discussion on 802.11ac focuses on large bandwidth improvements that will not be available for several years to come. The short-term improvements are of bigger benefit in small WLAN deployments, such as SMB and consumer homes, where only a single Wi-Fi AP will be able to take advantage of the much wider channels.
First-generation enterprise 802.11ac products that will be available in 2013 represent an incremental evolution of Wi-Fi above current 802.11n products on the market. These first-generation products will outperform existing 11n products, but only marginally, especially in multi-AP enterprise deployments. This is because the majority of bandwidth gain with first generation 802.11ac products will rely on the use of wider channels, up to 80 MHz. Enterprises need to be cognizant of the limitations in spectral capacity when designing and deploying an enterprise WLAN network. Enterprises must be careful to deploy access points on non-overlapping channels, with sufficient signal attenuation between adjacent access points to prevent co-channel interference.
Here is a look at the data rates available with first-generation 802.11ac products capable of 1, 2, and 3 spatial streams. Note that 160 MHz channels are shown only for reference, and will not be available with the first wave of 11ac products.
|First-Generation 802.11ac Data Rates|
(Note - 160 MHz channels will not be available in first wave of products)
Arguably, the biggest benefit of first generation 802.11ac will be the adoption of 5 GHz bands by mobile devices. This will enable enterprise WLANs to serve mobile devices in greater quantity with better performance due to the mandatory support of 5 GHz frequency bands by all 802.11ac compliant equipment. Today, enterprise WLANs struggle to provide the capacity required to support the large influx of mobile devices like smartphones and tablets. Once mobile device manufacturers begin deploying 802.11ac capable devices, existing 802.11n and new 802.11ac WLAN deployments will be able to provide significantly better services to mobile devices. Due to the enormous popularity and market growth of mobile devices, they now represent a significant portion of the user-base in many enterprise WLAN networks. However, most mobile devices today are limited to the 2.4 GHz band, which is cluttered with interference and offers minimal capacity. This has resulted in under-performing WLANs and an often poor user experience. With the adoption of 802.11ac, mobile devices will be able to take advantage of the cleaner spectrum and the additional capacity available in the 5 GHz bands. In addition, chipset enhancements should allow mobile devices to operate at higher bandwidth and performance levels with better battery life.
The Massive Shift to 5 GHz and the Impact to Enterprise WLANs
802.11ac operates exclusively in the 5 GHz unlicensed bands. In the U.S. there are a total of 25 non-overlapping 20 MHz channels in the 5 GHz bands. While this appears sufficiently large to handle channel re-use in large enterprise deployments, it can be deceiving. When channel size is increased, the number of available channels decreases, constraining channel re-use and making the risk of co-channel interference and WLAN performance degradation higher. Only 10 non-overlapping channels will be available with 40 MHz channel width (similar to the 9 channels available with 802.11n; the difference is due to the addition of channel 144 with 802.11ac), and only 5 channels will be available with 80 MHz channel width. When DFS channels are avoided, which are not supported by a large percentage of client devices and are at higher risk of causing network stability issues, the number of remaining channels dwindles down the only 2. Therefore, it will not be practical for most enterprises to use of 80 MHz wide channels because it will significantly constrain channel re-use that is critical to a high-performance WLAN. This will limit practical performance of first-generation 802.11ac in enterprise environments to 600 Mbps using 40 MHz channels, a far cry from the 1.3 Gbps advertised.
|Spectral Capacity versus Channel Width|
Enterprises in multi-tenant buildings or in dense urban areas will likely see increased utilization of the 5 GHz spectrum bands, which could cause greater levels of interference and degrade WLAN performance. This is of significant concern if enterprises deploy 802.11ac equipment with 80 MHz wide channels, without recognizing the impact to neighboring businesses.
802.11ac also threatens to accelerate the utilization of 5 GHz spectrum bands by a large majority of enterprises. This could be a double-edged sword, providing the promise of increased performance for individual organizations, while simultaneously congesting the once interference-free 5 GHz bands. This may expose the need for more unlicensed spectrum sooner than anticipated. The timing is impeccable, as the FCC and Congress are currently considering allowing unlicensed use of two additional 5 GHz bands, devising rules for spectrum auctions in 2013-2014 of the 600 MHz TV white spaces, and spectrum-sharing plans in the federal 3550-3650 MHz band that would provide additional unlicensed spectrum for general use. While there may not be an "unlicensed spectrum crunch" today, there very well could be one in the not-to-distant future. More information on the current spectrum policy discussions can be found in my previous blog post about the need for a balanced spectrum policy.
When does it make sense to deploy 802.11ac?
Enterprises that have deployed the latest generation 802.11n equipment pervasively throughout their network can be confident in the investment they have made; first generation 802.11ac only offers incremental benefits over 3 spatial stream 802.11n.
First generation 802.11ac products will be of greater interest to enterprises that are purchasing a new "greenfield" WLAN deployment, growing an existing WLAN deployment with additional APs, or are running on older legacy WLAN equipment. 802.11ac is backwards-compatible with all previous versions of Wi-Fi, so it will be able to supplement existing WLAN deployments seamlessly while providing higher performance and investment protection versus 802.11n equipment. Enterprises that were early adopters of 802.11n may see greater appeal in moving to first generation 802.11ac because their existing 802.11n equipment has already been depreciated over a number of years and they have received their return on investment. In addition, 802.11ac can offer a substantial upgrade in performance to 600 Mbps over two spatial stream 802.11n (300 Mbps), allowing the enterprise to increase performance, capacity, and services offered over the WLAN.
Revolution or Evolution? - Andrew's Take
I'm bullish on 802.11ac. The technology holds a lot of promise to improve enterprise WLAN performance and capacity, especially for mobile devices which are accounting for a larger and larger percentage of our client base with BYOD and Consumerization of IT.
However, we need to temper our short-term expectations. The first wave of 802.11ac equipment will likely not prompt upgrades to existing WLAN deployments unless it is replacing older gear; it just won't provide enough value to justify the replacement of the latest generation of 802.11n equipment. Enterprises will also need to be careful to deploy 802.11ac equipment correctly to avoid harmful interference to their own network and neighboring networks - most notably limiting channel width to 20 MHz in high-density areas and 40 MHz maximum in other common-use areas.
Just as with 802.11n, we will see subsequent releases of 802.11ac that implement additional technology improvements detailed in the standard. This will include 4+ spatial streams (possibly up to 8 eventually), 160 MHz wide channels, and MU-MIMO.
Lastly, we need to ensure the value of unlicensed spectrum is recognized by regulatory agencies throughout the world. The 2.4 GHz unlicensed band is often joked about as being the "junk" band today due to rampant interference and over-crowding. The massive shift to 5 GHz is already underway which will only be accelerated by 802.11ac adoption. We run the risk of 5 GHz over-crowding very soon if more unlicensed spectrum isn't made available.
802.11ac Gigabit Wi-Fi Series: