RF planning for high-densities of mobile devices and bandwidth-hungry mobile apps

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  • Integrating Accurate Capacity Planning into WLAN Design

    Andrew von Nagy


    CWNE #84 CCIE #28298

  • Goal of this Presentation:To share my methodology for integrating capacity planning into

    WLAN design with the community !

    What works for me might work for you!



    1. Network Performance Concepts

    2. WLAN Design Methodology

    3. Introduction to the Revolution Wi-Fi

    Capacity Planner Tool

    4. Real-World Example

  • Network Performance

    Source: Martin Geddes

  • Link Speeds Reaching Limits

    Source: Martin Geddes

  • WLAN Capacity

    Single Client Multiple Client Coordinated APs

    All APs

  • Defining WLAN Capacity

    Net WLAN Capacity

    (-) (+)Spectral InventorySpectral Efficiency

    Medium ContentionRF Interference

    Goal: Increase spectral inventory and efficiency, decrease medium contention and RF interference

  • Medium Contention

    DFS Non-DFS

    20 MHz 22 9

    40 MHz 10 4

    80 MHz 5 2

    160 MHz 1-2* 0-1*

    United States Regulatory Domain

    * 80+80 MHz Channels






    58 138

    One cell buffer before

    channel must be re-used

    138 58


    58 138

    Co-channel Interference (CCI)

    Typical WLAN (omni antennas, standard overlap for roaming)

    Need 4 non-overlapping channels to effectively minimize co-channel interference at -85dBm


  • Medium ContentionAirtime Demand within a Channel / Frequency

  • Airtime UtilizationWhere is the breaking point?

  • Airtime UtilizationAirtime saturation varies by WMM Access Category

    3% airtime demand per-client in this example Source: Comsis

  • Measuring Capacity





    Client Mix









    Airtime Demand

  • Airtime Demand

    Y% airtime utilization (each)

    Z% airtime utilization (each)

    X Qty.

    X Qty.

    Total airtime utilization based on client mix

    Aggregate of individual client demands !

    Dependent on application requirements, packet sizing & timing. (Remember that airtime saturation is dependent on WMM AC)

  • Design Methodology

  • Iterative ApproachRF



    Input AP / Radio Quantities;

    Revise RF Design to Provide Required

    Frequency Re-Use (e.g. Antennas, Power)

    1. AP / Radio Quantities Required to

    Provide Coverage in All Areas

    2. Channel Planning & Frequency Re-Use

    Revise Capacity Design if Frequency Re-Use Cannot be Obtained

    (e.g. per-device throughput, 5 GHz channel width,

    capacity distribution across bands vs. channel inventory)

    1. AP / Radio Quantities Required for Capacity

    2. Throughput Required for WAN / Backhaul

  • Hands-On

  • Real-World Example Advertising Firm in Manhattan

    Apple-centric computing environment

    MacBook Air/Pro (3yr lifecycle)

    BYOD (tablets, smartphones)

    Some Windows (Finance Dept.)

    Heavy graphics and media content

    Open / Collaborative floorplan

    Large Event Space (e.g. TED Events)

  • Floor Layout

    Open Office (~36k sq ft)!350 Seats!20 Conference Rooms!!Graphic Designers!- 1 Apple Laptop ea.!- 1 BYOD ea.!

    !Existing WLAN:!- 66% concurrent online!- 50% concurrent active

    Event Space (~15k sq ft)!300 Seats (inside room)!200 Seats (overflow area)!!Large Events:!- 500 mobile devices!

    !Internal Meetings:!- 300 laptops!


  • Capacity Plans

    One for each unique use-case area (in this example 3)

  • Iteration between

    Capacity and RF Planning

    Initial Capacity Plan

    - Select initial variables using informed idea of what you think can be


    - Channel width, dual-band APs (no radios disabled)

    RF planning - use capacity results as starting point

    - Can you fit the AP radios into the space without CCI?

    - Determine if adjustments are necessary (directional antennas,

    different channel widths, disable some 2.4 GHz radios, etc.)

    Revise capacity plan, perform RF planning again ( iterate!)

  • 2.4 GHz RF Propagation

  • 5 GHz RF Propagation

  • 5 GHz AP Layout

  • 5 GHz CCI

  • 2.4 GHz AP Layout

  • 2.4 GHz CCI

  • Recap1. Network performance is increasingly reliant on

    minimizing contention delay

    2. Wi-Fi medium contention is dependent upon two causes:

    Co-Channel Interference (CCI)

    Airtime Demand (within a channel)

    3. Airtime saturation occurs at different points based on WMM Access Category

  • Recap (cont.)4. WLAN capacity is measured by airtime demand of

    clients within a channel

    5. WLAN design should account for BOTH capacity and coverage

    Dont guess!!!

    I recommend an iterative design approach

    6. Revolution Wi-Fi Capacity Planner: http://www.revolutionwifi.net/capacity-planner