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

1. Integrating Accurate Capacity
Planning into WLAN Design
Andrew von Nagy
@revolutionwifi
CWNE #84
CCIE #28298

2. 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!
Agenda:
!
1. Network Performance Concepts
2. WLAN Design Methodology
3. Introduction to the Revolution Wi-Fi
Capacity Planner Tool
4. Real-World Example

3. Network Performance
Source: Martin Geddes

4. Link Speeds Reaching Limits
Source: Martin Geddes

5. WLAN Capacity
Single Client Multiple Client Coordinated APs
All APs

6. Defining WLAN Capacity
Net WLAN Capacity
(-) (+)
Spectral Inventory
Spectral Efficiency
Medium Contention
RF Interference
Goal: Increase spectral inventory and efficiency,
decrease medium contention and RF interference

7. 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
42
58
106
138
106
58 138
One cell ‘buffer’ before
channel must be re-used
138 58
42
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
106

8. Medium Contention
Airtime Demand within a Channel / Frequency

9. Airtime Utilization
Where is the breaking point?

10. Airtime Utilization
Airtime saturation varies by WMM Access Category
3% airtime demand per-client in this example Source: Comsis

11. Measuring Capacity
Spatial
Streams
Channel
Width
Client Mix
Signal
Quality
Protocol
Version
Frequency
Bands
Application
Throughput
Airtime Demand

12. 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)

13. Design Methodology

14. Iterative Approach
RF
Design
Capacity
Design
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

15. Hands-On

16. 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)

17. 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!
Inflection!
Point

18. Capacity Plans
One for each unique use-case area (in this example 3)

19. Iteration between
Capacity and RF Planning
• Initial Capacity Plan
- Select initial variables using informed idea of what you think can be
achieved
- 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!)

20. 2.4 GHz RF Propagation

21. 5 GHz RF Propagation

22. 5 GHz AP Layout

23. 5 GHz CCI

24. 2.4 GHz AP Layout

25. 2.4 GHz CCI

26. Recap
1. 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

27. 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
• Don’t guess!!!
• I recommend an iterative design approach
6. Revolution Wi-Fi Capacity Planner:
http://www.revolutionwifi.net/capacity-planner