1. November 18
WLAN Performance Prediction and Environments a framework for discussion
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Rick Denker, VeriWave Inc.

2. November 18
Introduction
This presentation builds on the presentation previously given at the Portland meeting (11-04/770r0)
That presentation has additional detail on Test Environments and Customer Environments that will only be summarized here.
Rick Denker, VeriWave Inc.

3. Importance of Environment
November 18
Importance of Environment
In Ethernet testing prediction was simple. Test the switch/router, test the cable, and the results could be easily predicted
In wireless the variation of customer environments is a critical factor to performance.
Interference
Interaction
Distance
Rick Denker, VeriWave Inc.

4. Three Types of Environments
November 18
Three Types of Environments
Test Environments
Created by equipment developers
Often artificial, not matching a customer use
High degree of control
Small number of types
“Real World Lab” Environments
Used for final evaluation
Small variation
Customer Environments
Any place equipment is used
Large variation
Rick Denker, VeriWave Inc.

5. Test Environments Four basic types of environments:
November 18
Test Environments
Four basic types of environments:
Open Air
Cabled
Test Boxes
Faraday Cages/Chambers
Each has different trade-offs
Almost all developers use a combination of the four basic types of environments
Rick Denker, VeriWave Inc.

6. Test Environments Open Air Cabled Test Boxes Faraday Cage
November 18
Test Environments
Open Air
Cabled
Test Boxes
Faraday Cage
Interference resistance
Least
High
Very High
Cost
Free
Very Low
Moderate
Size limits No
Yes
Use
Development, customer installations
Crowded development labs, manufacturing
Development labs
Shared resource in development lab
Antenna
Required for longer range tests
Not appropriate
Not appropriate for most antennas
Useful for antenna testing
Strengths
Matches customer usage, only solution for certain spatial tests
Very easy to set up
Clear environment
Weaknesses
Not appropriate for crowded test environments
Idealized results that do not match the randomness of open air
Near field effects, multiple chamber sizes required
Can only test 3-4 devices before traffic gets congested
Rick Denker, VeriWave Inc.

7. “Real World Lab” Environments
November 18
“Real World Lab” Environments
Possible Names
Prototype environments
System Test environments
Validation environments
Field Test environments
Used for final evaluation
Often the only place the complete product is assembled and tested before shipment (spatial, antennas, loading)
Not aware of any vendor that ships without some form of this, however limited.
A significant source of finding issues with equipment under development
Relatively controlled environment
Compared to customer environments it is controlled, compared to test environments it is uncontrolled (This is why is tends to cause disagreements.)
Limited interference
Limited repeatability - typically results cannot be exactly repeated
No where near the variation of customer environments
Methods vary significantly by vendor
Rick Denker, VeriWave Inc.

8. “Real World Lab” Environments
November 18
“Real World Lab” Environments
Methods vary significantly by vendor
Selected channels only used for validation
Use international channels
Off hours
Empty office buildings
Football fields
Attenuators
Rotating tables
Combinations of the above
Combinations with Chambers
Rigorousness depends on several factors
Application
Market
Complexity
Time
Rick Denker, VeriWave Inc.

9. Customer Use Environments
November 18
Customer Use Environments
Customer environments vary widely
Hard to create a small set of model environments
Very expensive
Implies an approach of characterizing an environment by a small set of key variables
Potential key summary variables are:
Amount of noise
Overlap with other traffic
Signal strength
Rick Denker, VeriWave Inc.

10. Customer Environment – Key Variables
November 18
Customer Environment – Key Variables
Amount of Noise
Overlap with other traffic
Signal Strength
Examples
Cordless phones, microwave ovens, bluetooth devices
APs placed close together,
Neighboring businesses
Distance,
Construction materials, Location of metal equipment
Nature
Dynamic,
Cannot be measured at a single point in time (average over a typical day)
Traffic could be measured at peak traffic times ,
Channel mapping issues
Mostly static
(but metal file cabinets can be moved)
Effect
Causes frames with CRC errors
Contention for the air
Poor signal strength
Measure of Variable
# CRC error over time
Duty cycle of background traffic,
Burstiness of background traffic
Range of signal strength levels
(typically contour map)
Rick Denker, VeriWave Inc.

11. Mapping Test Environments to Other Environments
November 18
Mapping Test Environments to Other Environments
Noise, Overlap, and Signal Strength can have a significant impact on performance for a given customer
Measurements in ideal test environments can set overly high false expectations
Ability to correlate the results between the different environments is important to productivity
Providing the user with a good understanding of how equipment will perform in their environment is key
Rick Denker, VeriWave Inc.