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How To: Converting Path Loss to Distance

Tim Higgins

August 15, 2007

Introduction

Our new wireless performance test method using Azimuth's ACE 400NB Channel Emulator provides the most detailed look at wireless throughput vs. range performance that you'll find anywhere. Our Wireless Charts plot throughput vs. path loss, which relates speed to signal level. However, most purchasers of wireless gear really want to know how a product will perform over distance, which is not directly provided by our charts.

The actual performance range of a wireless LAN product depends on many factors—too many to provide a simple conversion from path loss to range. But what we can do is relate signal loss to range for a specific environment, which will help provide some feel for what the Throughput vs. Path Loss plots mean for real-world performance.

The basic approach taken is to measure signal strength in multiple test locations, convert the signal strength to relative signal loss and then overlay the results onto throughput vs. path loss plots.

Test Environment

The test environment is a 3300 square foot two-level home with 2x6 wood-frame exterior walls, 2x4 wood-frame sheetrock interior walls, and metal and metalized plastic ducting for the heating and air conditioning system.

Figure 1 shows a simplified layout of the lower level and two of the five test locations. Figure 2 shows the upper level layout and the other three test locations. Table 1 provides distance and materials details of each location.

Lower Level Test Locations

Figure 1: Lower Level Test Locations

Upper Level Test Locations

Figure 2: Upper Level Test Locations

Test Location	Description
Location 1	AP and wireless client in same room, approximately 3 feet apart.
Location 2	Client in room on same level, approximately 45 feet away from AP. Two sheetrock walls between AP and Client.
Location 3	Client in upper level, approximately 25 feet away (direct path) from AP. One wood floor, sheetrock ceiling, no walls between AP and Client.
Location 4	Client on upper level, approximately 55 feet away (direct path) from AP. Two to three interior walls, one wood floor, one sheetrock ceiling and stainless-steel refrigerator, between AP and Client.
Location 5	Client on upper level, approximately 65 feet away (direct path) from AP. Four to five interior walls, one wood floor, one sheetrock ceiling, between AP and Client.