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)