ASK THE EXPERTS : High Density Wireless Deployments and CleanAir Technology

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Welcome to the Cisco Support Community Ask the Expert conversation. This is an opportunity to get an update on High Density Wireless Deployments and CleanAir technology with Cisco expert Fred Niehaus. Fred is a technical marketing engineer for the Wireless Networking Business Unit at Cisco, where he is responsible for developing and marketing enterprise wireless solutions using Cisco wireless LAN products. In addition to his participation in major deployments, Fred has served as technical editor for several Cisco Press books including the "Cisco 802.11 Wireless Networking Reference Guide" and "The Business Case for Enterprise-Class Wireless LANs." Prior to joining Cisco with the acquisition of Aironet, Fred was a support engineer for Telxon Corporation, supporting some of the very first wireless implementations for major corporate customers. Fred has been in the data communications and networking industry for more than 20 years and holds a Radio Amateur (Ham) License "N8CPI."
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Answer 1

You are correct, between the higher numbers of users with multiple devices the bandwidth requirements keep increasing.
The limitation of three non-overlapping channels in the 2.4 GHz space is driving more customers to 5 GHz, it is important to have both bands when high density deployments are needed.  While many older devices only support 2.4 GHz, we are now seeing far more devices with 5 GHz as well.
The recomendation of 20-25 clients and 8 voice calls on a given 2.4 GHz channel is still a good "rule of thumb" with actual customer data requirements driving those numbers higher or lower. You are right when you say "throwing Access Points" at the problem can degrade the wireless quality as co-channel interference and overall noise floor can rise with multiple Access Points that can all hear each other.
A better approach to the problem is to throw more spectrum at this issue (using 5 GHz channels) and elements of 802.11n (20 MHz) bandwidth on 2.4 GHz.
What we have been doing in high density deployments is to try to minimize the propagation of a cell and focus it in a given direction.  This can be done by
1. Managing the RF power of the radios (Access Points) and in some cases the client's power (using elements of CCX).
2. Using the right antennas to shape both Tx and Rx cell size to help isolate, we have recently introduced a new high gain antenna for stadiums that does this well.
3. Limit supported rates, obviously the higher the data rate the less sensitive the receiver is and the smaller the cell size becomes.
4. Enable 5 GHz (that adds far more channels for data throughput)
5. Limit the number of SSIDs in use as each requires a separate beacon (adding to RF utilization)
6. Co-locating access points with non-overlapping channels
There are some challenges, for example; many dual -band clients prefer to connect to 2.4 GHz, and 2.4 GHz is more likely to be busier and subject to interference, so we also enable Cisco "Band-Select" which basically "nudges" those clients off 2.4 GHz and pushes them to 5 GHz so as to free up the 2.4 GHz band when we can determine the client has 5 GHz capability.
So how is this done? well, we do this by listening to the clients and if we detect that the client is sending out probe requests on both bands we know the client can use 5 GHz so we essentially make the 5 GHz band "appear more attractive" to that client.
Note: Client load balancing and Band select are features in the Cisco Unified controller menu.
Also enabling client link (intelligent beam forming) helps direct the signal directly at the client and reduces same channel interference.