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Getting More Out of Wave 2 of 802.11ac

By Linda Hui, Managing Director, Ruckus Wireless

Historically, Wi-Fi was only capable of serving clients one-at-a-time. Slow devices consume extra airtime, and all devices served by that AP suffer as a result. This is especially true in mobile-rich deployments.

Wave 2 802.11ac-capable access points make more efficient use of the RF spectrum by getting clients on and off the medium faster, leaving more airtime for clients, even those that don't support Wave 2 capabilities. By reducing the time to serve even some clients will benefit ALL clients.

The above is possible because MU-MIMO allow an AP to send downlink frames to multiple stations at the same time. This increases capacity compared with single user MIMO. Every MU-capable client in the network ultimately benefits legacy clients even for single-user, or non-MU as well. With 2-3x greater efficiency from MU, every extra bit of productivity gained is added to the airtime pool for other clients to utilize. When multi-user MIMO clients hit Wi-Fi networks, Wave 2 is capable of serving those clients simultaneously—allowing others the opportunity to access the RF spectrum sooner and hence increased Wi-Fi capacity.

Better Transmit and Receive Performance

Adding more receive radio chains improves uplink performance. Using maximal ratio combining (MRC), Wave 2 AP has the ability better hear signals on multiple antennas and in different polarizations (not all AP supports dual polarization), therefore, combining those signals to ensure better reception. This is especially useful for single- or dual-stream clients with small antennas and weak transmit power like smart phones. There may not be many 4x4 clients on the market now, but adding radio chains helps improve reliability even if you have 1x1, 2x2, or 3x3 clients.

To improve downlink speed, adding more transmit radio chains, especially for MU-MIMO. That extra transmitter provides more signal steering control and higher data rates with less interference. Hence, the high density venue would find it most useful.

Wave 2 provides more spatial streams to use, this provides incremental value in the form of spatial diversity, regardless if the clients have one, two, or three spatial streams. More antennas improve MIMO by increasing reliability and signal quality, pushing data throughput closer to data rates.

The number of spatial streams and the transmission bandwidth together indicate potential throughput performance and number of devices supported. Initial Wave 2 radio chips are 4x4:4 (4 transmit and 4 receive radio chains with support for 4 spatial streams), while most Wave 1 chips were 3x3:3.

With four- stream Wi-Fi devices, the additional spatial streams provide wireless meshing. Wi-Fi meshing has always suffered from multi-hop throughput loss. With additional, higher bandwidth streams, APs should now be able to connected wirelessly at true gigabit wireless speeds.

Investment Protection

Committing Wave 2 AP NOW actually gives you an investment protection; it extends the Wi-fi refresh cycles, saving you from architect and re-architects the Wi-Fi networks to accommodate the barrage of new devices with new features and functions that can’t benefit from your existing networks.

In fact, MU-MIMO client support is happening. MU-capable clients are already on the market, many of the mobile device chipsets in devices used today are actually “multi-user ready” with a firmware upgrade. MU-MIMO does require client support, so, not all 11ac clients can use it. Hence, MU-ready APs protects your 4 or 5-year AP investment.

Furthermore, MU-MIMO allows you to fine-tune the combination of spectral efficiency, proper channel reuse, Tx power, antenna choice based on the budget, time, building layout, and business requirement to give user the best experience.

Efficiency and Performance Gains

Every new generation of Wi-Fi chips comes with efficiency and performance improvements. Every new AP hardware revision is an opportunity to improve radio components, fine-tune the layout, enhance antenna subsystems, and generally improve performance. For all clients, expect new APs to enhance speed. Hence, upgrade now will bring efficiency and performance gains now.

While it enhances speed, don’t be fooled by some vendors claiming to their AP is the fastest AP ever and it offers data rates of 160 MHz. In fact, wide channels are the enemy of spectral efficiency in the enterprise and most client devices won’t support 160 MHz.

But, would the new APs require more power? When you add more radio chains, APs require more power unless the AP is designed to provide full GHz 802.11ac functionality on 802.3at power. Some AP can reduce 2.4 GHz radio output power to 25 dBm and disable the USB and second Ethernet port to increase power efficiency and some can even be powered up to provide full features with just a PoE switch rather than PoE+, reducing the cost of upgrading all existing PoE switch.

Summary

Indeed, the earlier you deploy Wave 2, the more benefits you can see it today, whether it is increasing wi-fi capacity or improving efficiency and performance, you should be able to find a good reason to invest it now and enjoy the benefits sooner.

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