Cisco Aironet 2702i AIR-CAP2702I-E-K9 Folheto

 

 

© 2014 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information. 

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In some regulatory domains, new rules are needed to allow the transmission of waveforms across adjacent 
subbands where the rules presently don’t allow this (for example, below and above 5.725 GHz, also known 

as channel 144). 

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802.11ac devices (and other unlicensed devices) suffer from reduced access to spectrum containing time-

domain weather radars in and around 5.6 to 5.65 GHz. 

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Due to the wider bandwidth of 802.11ac, there are strong market desires to open up new spectrum, for 

instance, in the 5.35- to 5.47-GHz band (which enables two new 80-MHz channels and one new 160-MHz 

channel): 

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See, for instance, U.S. Act of Congress HR 3630, which empowers the National Telecommunications 

and Information Administration (NTIA) to study opening up this band to unlicensed use. 

Due to the fact that regulations around the world are continually evolving, it is difficult to comment on this topic in 

detail in this white paper. 

With 802.11n, a device can transmit multiple spatial streams at once, but only directed to a single address. For 

individually addressed frames, this means that only a single device (or user) gets data at a time. We call this 

single-user MIMO (SU-MIMO). With the advent of 802.11ac, a new technology is defined, called multiuser MIMO 

(MU-MIMO). Here an AP is able to use its antenna resources to transmit multiple frames to different clients, all at 

the same time and over the same frequency spectrum. If 802.11n is like a hub, 802.11ac can be thought of as a 

wireless switch (on the downlink). 

However, MU-MIMO is a challenging technology to implement correctly and wo

n’t be available in the first wave of 

AP products. And even when available, MU-MIMO does come with caveats. 

 shows one piece of the puzzle. To send data to user 1, the AP forms a strong beam toward user 1, shown 

as the top right lobe of the blue curve. At the same time the AP minimizes the energy for user 1 in the direction of 
user 2 and user 3. This is called “null steering” and is shown as the blue notches. In addition, the AP is sending 

data to user 2, forms a beam toward user 2, and forms notches toward users 1 and 3, as shown by the red curve. 

The yellow curve shows a similar beam toward user 3 and nulls toward users 1 and 2. In this way, each of users 1, 

2, and 3 receives a strong copy of the desired data that is only slightly degraded by interference from data for the 

other users.