RF for 802.11 WLAN

Peter Welcher
Architect, Operations Technical Advisor

In October 2009, Dr. Pete Welcher presented these slides at a Bluesnet Network Advisory Group meeting in Santa Barbara, CA. This presentation covers RF (radio frequency) essentials you need to make Wireless LAN (WLAN, WiFi, 802.11) work well. Click this link to review the RF for 802.11 WLAN (784 KB) seminar PDF.

2 responses to “RF for 802.11 WLAN

  1. It has occurred to me that the slides are a bit literal, and that might lead some folks astray. Let me explain the issue. If you take the linear dimensions and put AP’s in a grid, you’ll end up with a good many more than if you take the total square feet and divide by the square feet per AP. Why the discrepancy?

    The answer is pretty simple. When you estimate the number of AP’s by square feet, you are in effect working with non-overlapping AP circles. But deployments overlap! So if you budgeted one AP per 3000 sq ft, for linear placement you have to adjust upwards, i.e. each AP is going to cover something more like 5000 sq ft, i.e. the spacing is NOT going to be what I have in the linear distance table for a "pure" 3000 sq ft circle calculation.

  2. If you’re measuring in the field you might wonder where I got the 43′ number from. That was from a Cisco VoWLAN doc where I apparently missed the qualifying portion a bit below there: they were turning the power down to 40 mW to match a 7921 G phone. So with lower power the 43′ number makes more sense. (Other Cisco docs show 54 Mbps at 80′ distances…, presumably at 100 mW power.)

    The VoWLAN deployment number of 1 AP per 3000 sq ft or so works out to an AP spacing around 60′, where the RRM power management will probably end up turning down the RF power a good bit, to avoid massive overlap. Due to wall materials and other factors, YMMV (Your Mileage May Vary).

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


John Cavanaugh

CCIE #1066, CCDE #20070002, CCAr
Chief Technology Officer, Practice Lead Security Services, NetCraftsmen

John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.