going beyond rf coverage: designing for capacitynoc.ucsc.edu/docs/misc/wlan-capacity-2014.pdf ·...
TRANSCRIPT
Going Beyond RF Coverage: Designing for Capacity
Revolution Wi-Fi
1997 1999 2003 2009 2011 2013
2.4 GHz5 GHz
Andrew von Nagy
+
Have you experienced this?
Hint: It’s NOT an RF coverage issue
How Many AP’s Do I Need?
Goal for Today:
1. Definition
2. Measurement
3. Methodology
4. Integration
Promote the use of capacity planning when designing EVERY WLAN
This is NOT a High-Density Session!
WLAN LifecycleDESIGN
DEPLOY
MONITOR & REPORT
TSHOOT & REMEDIATE
OPTIMIZE & GROW
Typical Design Process
Predictive Modeling Deployment Site Survey
Focus is on signal strength and coverage only
WLAN Requirements
• Coverage
• User Mobility
• Capacity
• High Availability
• Wired Integration
• AAA Services
• IP Addressing
• Security
• Proper Configuration
• Code Stability
• Monitoring & Visibility
• Troubleshooting Tools
What Determines 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
Spectral Inventory (+)
1. Unlicensed Spectrum (by region; growth)
2. Optimal Use of Spectrum:
- Wider Channels
- More Radios, Smaller Channels
- Channel Reuse
Medium Contention (-)1. Minimize # STA on same channel / AP radio
Medium Contention (-)• Optimize Link Efficiency
• Initial Contention Window size affects performance
Medium Contention (-)
DFS Non-DFS20 MHz 22 940 MHz 10 480 MHz 5 2160 MHz 1 0
United States Regulatory Domain
42
58
106
138
106
58 138
One cell ‘buffer’ before channel must be re-used
138 58
42
58 138
2. Minimize co-channel interference (APs & Clients)
• Typical WLAN (omni antennas, standard overlap for roaming)
• Need ≥4 non-overlapping channels to effectively minimize co-channel interference at -85dBm
106
High-DensityChannel Planning
• Higher radio density
• Spectrum re-use harder
• Clients still create CCI with omni
Always, Always, ALWAYS... use 20 MHz channels!
Spectral Efficiency (+)1. Packing More bits per MHz (Shannon’s Theorem)
• Modulation, Spatial Streams, MU-MIMO, (Wider Channels - very little gain from addtl subcarriers)
QAM-16 QAM-64 QAM-256
Spectral Efficiency (+)1. Packing More bits per MHz (Shannon’s Theorem)
• Modulation, Spatial Streams, MU-MIMO, (Wider Channels - very little gain from addtl subcarriers)
Spectral Efficiency (+)2. Client Airtime Efficiency
Highest Data Rate
Higher Data Rate
Lower Data Rate
Lowest Data Rate
RF Interference (-)
• Identify and Eliminate:
- Design: Site Survey
- Production: Network Monitoring
Measuring CapacityAirtime Utilization
Measuring CapacitySticky Situation, This Is!!!
Spatial Streams
ChannelWidth
Client Mix
SignalQuality
ProtocolVersion
FrequencyBands
ApplicationThroughput
Airtime Demand
Design MethodologyKey: Design for BOTH coverage and capacity!
Design Requirements:• Device - what type of device(s) are used?‣ Laptops vs. tablets vs. smartphones vs. embedded‣ Identify data rates and actual throughput
• Application - bandwidth demand, latency req.?• Quantity - how many total concurrent devices?
Forecasting Capacity:• Airtime - shared amongst all devices (in same contention domain)• Capacity - dependent on both client and AP capabilities
Method for Forecasting WLAN Capacity
1. Inventory Client Devices & Applications
Method for Forecasting WLAN Capacity
2. Calculate Airtime Consumption per Device
Method for Forecasting WLAN Capacity
3. Forecast AP Capacity
Method for Forecasting WLAN Capacity
3. Forecast AP Capacity
Y% airtime utilization (each)
Z% airtime utilization (each)
X Qty.
X Qty.
Total airtime utilization based on client mix
Example #1Scenario: 4 K-12 Classrooms in a Building Wing
Devices: 11n tablets (20 MHz, 1SS), 65 Mbps (30 actual)Application: 2 Mbps YouTube StreamsQuantity: 30 per classroom (120 total), only 50% concurrent
Airtime: 2 Mbps / 30 Mbps = 6.66%Total: 6.66% * 60 devices = 400% = 4 AP radios (2 dual-radio APs)
Example #2Scenario: 300 Seat University Auditorium
Devices: 11n tablets (20 MHz, 1SS), 65 Mbps (30 actual) 11n laptops (20 MHz, 2SS), 144 Mbps (70 actual)Application: 1 Mbps Web / Email / Social MediaQuantity: 100 tablets, 200 laptops 100% concurrent
Example #2Scenario: 300 Seat University Auditorium
Airtime: tablets 1 Mbps / 30 Mbps = 3.33% laptops 1 Mbps / 70 Mbps = 1.43%Total: tablets 3.33% * 100 devices = 333% + laptops 1.43% * 200 devices = 286% = 619% = 7 AP radios (4 dual-radio APs)
WLAN Design Process
Grab the Worksheets
http://www.revolutionwifi.net/p/downloads.html
Supplementary
Spectrum InventoryVaries by Region (Return)
Spectrum InventoryFCC proposal for additional unlicensed spectrum
(Return)