802.11ac Wi-Fi Part 2: Wave 1 and Wave 2 Products
January 30, 2014
In my last article, I discussed the major enhancements in the 802.11ac Wi-Fi standard. In this post, I'll examine the first wave of 802.11ac products as well as what the industry expects with 11ac Wave 2 products.
From July to December 2013, 262 WLAN products passed Wi-Fi Alliance tests, earning them the right to wear the Wi-Fi Certified ac logo. These Wave 1 products are based on a draft of the 802.11ac standard, supporting a then-stable subset of defined building blocks.
If you’re looking at today’s Wave 1 Wi-Fi Certified ac products, here’s what you can expect.
First off, Wave 1 products support 11ac using 20-, 40-, and 80-MHz channels in the 5-GHz band, usually combined with 11n in the 2.4-GHz band for backward-compatibility with older products. This alone accounts for much of the improvement early adopters experience with Wi-Fi Certified ac products.
Using 11ac to lure more clients into the 5-GHz band reduces competition, while freeing up the 2.4-GHz band for laggards. Clients moving to the 5-GHz band get to play in a far bigger, less crowded sandbox, with 11ac clients consuming less airtime by speaking three times as fast. New clients are no longer forced to wait for old clients to stop talking slowly. Even dual-band 11n clients benefit from this to some degree, primarily at coverage edges where rates were previously too low to maintain connectivity.
Second, 11ac products can use eight to nine 40-MHz channels, or four to five non-overlapping 80-MHz channels, or a mix of both. In fact, the least well-known 11ac feature is dynamic channel widths that can change per-frame. Like a carpool lane that sits empty while single-rider cars go nowhere in jammed adjacent lanes, bands statically divided into faster, wider channels are often underutilized. 11ac starts with primary channel assignments, but can expand and contract channel widths on each transmission, sending larger frames faster by borrowing otherwise idle airtime from adjacent channels.
Third, Wave 1 products may also support 256 QAM, but this higher-density modulation can only be used in very-high-quality, low-interference environments, such as between devices in the same room. For this reason, 256 QAM has limited utility in business WLANs, filling mostly niche needs such as HD video streaming between server and Wi-Fi displays.
Like many 11n APs, Wave 1 APs tend to support three spatial streams, using 3x3 SU-MIMO. However, many new 11ac clients are single-stream devices such as tablets and smartphones, and today’s Wi-Fi population is still dominated by 11n clients.
This dichotomy results in a wide range of real-world data rates. A single-stream 11n client using a 40-MHz channel can at best reach 150 Mbps, while a single-stream 11ac client using an 80-MHz channel can hit 433 Mbps. At the opposite end of the spectrum, an 11ac notebook that connects to an 11n AP at 450 Mbps might connect to an 11ac AP at 1.3 Gbps under similar circumstances. (Note: Just as for all previous generations of Wi-Fi, application throughputs are still roughly two-thirds data rate.)
Finally, Wave 1 Wi-Fi Certified ac products support a litany of required capabilities that improve business mobility, including enterprise-class WPA2 security, WMM quality-of-service, and power management. A sample certificate for one of the first Wave 1 smartphones is illustrated below.
802.11ac : Wave 2 Products
At International CES 2014, Quantenna released what may become the first Wave 2 11ac chipset: the 4x4 QSR1000. What capabilities place this product in Wave 2? Primarily the inclusion of MU-MIMO, a key 11ac enhancement unlikely to become Wi-Fi certified or commonplace in enterprise-class APs or clients until 2015 or 2016.
MU-MIMO is a novel technology that might double or even quadruple WLAN user density by increasing the number of simultaneously supported clients. Wave 2 APs with MU-MIMO may use up to 8x8 antennas and transmit/receive streams, conversing with clients that support between one and four streams. This mismatch is intentional; MU-MIMO lets APs leverage beamforming to not only serve one user better, but to serve multiple users at once. For example, a Wave 2 AP might communicate with four single-stream smartphones on the same channel, or with two 4x4 notebooks.
Because MU-MIMO depends on interoperable beamforming, Wave 2 APs and clients must both support this. In fact, some Wave 1 products already use beamforming to improve SU-MIMO performance. The more that 11ac standard beamforming works its way into the installed base in wave one, the more useful Wave 2 APs will be upon release.
Finally, Wave 2 products may include 80+80 and 160-MHz channels. This is of interest in residential WLANs, where a single AP can freely utilize most of the 5-GHz band for one very-high-throughput application such as HDTV. However, few businesses are likely to allocate this much airspace to one channel.