Many enterprise wireless LANs are victims of their own success, challenged to serve a skyrocketing population of...
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wireless devices and bandwidth-thirsty applications. To meet escalating demand, WLAN administrators can take a two-prong approach: more efficiently use existing channels and tap new frequencies to offload bandwidth hogs. Together, these strategies offer hope to enterprises already approaching the limits of 802.11n.
Increasing enterprise WLAN capacity with draft 802.11ac
The most immediate step enterprises can take to boost enterprise WLAN capacity is to migrate existing access points (APs) to 802.11ac. Commonly known as Gigabit Wi-Fi, the draft 802.11ac standard further refines advances introduced by 802.11n, combining them to significantly boost total WLAN capacity.
Wi-Fi certified ac products use faster data rates, more tightly-packed transmissions, cleaner 5 GHz channels and wider channels to support very high throughput applications such as HD video. Specifically, enterprises can obtain the following improvements by migrating to 802.11ac:
Speed: 802.11n data rates top out at 450 Mbps to 600 Mbps, using three to four spatial streams to deliver traffic. The first wave of 802.11ac products uses the same spatial streams to reach speeds up to 1.3 Gbps. By late 2014, the next wave of 802.11ac products will top out at 6.93 Gbps. But real-world results still depend on client capability and distance. For example, you can expect a single-stream smartphone that transmits at 150 Mbps with 802.11n to hit 433 Mbps with 802.11ac. Because sending data faster requires one-third as much airtime, 802.11ac may permit administrators to see a corresponding increase in the maximum number of users per AP.
Spectral efficiency: Both 802.11n and 802.11ac use quadrature amplitude modulation (QAM) to send data, but 802.11ac can pack four times as much data into each transmission. Unfortunately, 256-QAM only works over short distances and thus will only quadruple capacity for clients within about 20 feet.
5 GHz only: Unlike 802.11n, which operates over channels chosen from both the noisy crowded 2.4 GHz band and the less-congested 5 GHz band, 802.11ac serves clients in the 5 GHz band only. Due to reduced interference at 5 GHz and related RF engineering advances, 802.11ac devices are likely to experience a better rate over range than their 802.11n counterparts, again increasing total enterprise WLAN capacity.
Wider channels: 802.11n doubled throughput by combining two 20 MHz-wide channels into one 40 MHz-wide channel. The first wave of 802.11ac products repeats this by adding 80 MHz-wide channels; next year's second wave will add 160 MHz-wide channels. Fatter channels do not increase available spectrum -- the 5 GHz band is roughly 1 GHz wide, no matter how it's divvied into channels. But doublewide channels give high-throughput applications their own express lane in which to move faster without being impeded by or sapping bandwidth from slower, latency-sensitive applications.
For these reasons, enterprises replacing older 802.11a/g or 802.11n APs with Wi-Fi certified ac APs are likely to see an immediate increase in WLAN capacity, especially when used by newer smartphones, tablets and notebooks now shipping with 802.11ac. Legacy clients won't reap all of the standard's benefits but may still see some improvement, enabling administrators to increase the total number of devices each WLAN can support. When the second wave of 802.11ac products emerge in late 2014, multi-user multiple-input, multiple-output will let each access point converse simultaneously with up to four clients, further boosting WLAN capacity.
Adding more WLAN capacity with 802.11ad
Migrating existing WLANs to 802.11ac benefits all Wi-Fi devices and applications. However, certain devices and applications -- most notably tablets and video -- are very demanding, guzzling limited shared bandwidth. While Quality-of-Service methods like Wi-Fi Multimedia (WMM) help to prioritize traffic and avoid starvation, all 802.11ac devices ultimately compete for the same finite patch of 5 GHz channels.
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Fortunately, enterprises will soon be able to slake escalating bandwidth thirst by using 802.11ad to relocate bandwidth hogs onto unused 60 GHz channels. The emerging 802.11ad standard -- commonly called WiGig -- leverages many of the same technologies used by 802.11ac to reach data rates up to 7 Gbps. However, 802.11ad works its magic over a completely different set of channels, thereby increasing the total spectrum available for WLAN use by nearly an order of magnitude.
That said, the 60 GHz channels used by 802.11ad are far more limited in range and penetrating power. But its properties make 802.11ad suited for very high throughput communication between nearby devices, preferably in the same room. Enterprise WLAN administrators may therefore use 802.11ad to expand capacity by offloading devices and applications that thrive under such conditions. Examples include HD video transmission to wall-mounted wireless displays, and sustained communication between desktop-replacement tablets and external monitors.
Planning for capacity
Wi-Fi certified ad products are expected to become available in early 2014. At that point, a growing number of devices will support both 802.11ac and 802.11ad, enabling both short-distance and long-distance high-throughput communication. Enterprise administrators should therefore start thinking about how and where to best use 802.11ad in the workplace -- for example, to offload edge-video traffic from increasingly-consumed 802.11ac APs.
Ultimately, combining 802.11ac and 802.11ad is like repaving a highway while adding lanes: Both strategies make it possible for more vehicles to move faster, increasing total capacity. Together, these two standards can help enterprise WLAN administrators design and deploy new and upgraded networks that deliver significantly higher data rates and amplified user density.
About the author:
Lisa Phifer owns Core Competence Inc., a consulting firm specializing in business use of emerging Internet technologies. She has been involved in the design, implementation and evaluation of networking, security and management products for nearly 30 years. She is a recognized industry expert on wireless security, mobile device security and VPNs.