Great Wi-Fi Starts with Proper Design
I’m sure that we have all experienced poorly designed Wi-Fi networks. When a technology is so ubiquitous, so easily accessible, and is increasingly the most relied upon method of Internet access for mobile devices and cloud computing, then there are bound to be some issues. Unfortunately, the prevalence of underperforming Wi-Fi networks is still much too common for my liking.
Great Wi-Fi starts with proper design. There are various approaches to WLAN design that have evolved over time, ranging from providing basic coverage to maximum capacity and situations in-between.
At one end of the spectrum, we have a basic coverage oriented design. This was the historical way of designing a WLAN that simply involved ensuring adequate signal strength from access points was present in desired locations. At the other end of the spectrum is a design focusing on maximum capacity. This involves careful RF planning in order to integrate the most Wi-Fi cells as possible into a physical area.
The problem with both of these approaches is that they are the extremes and aren't applicable for many wireless networks. Basic coverage designs may still work for warehouses and some retailers and maximum capacity designs are great for stadiums and Continue reading
U-NII Unlicensed Spectrum Inventory in 5 GHz Bands
Given the recent FCC Report & Order on U-NII (Unlicensed National Information Infrastructure) rule changes in March/April of 2014, I thought it would be helpful to recap the new regulations in the United States regarding the 5 GHz unlicensed spectrum bands. I've put together the following table for quick reference: |
| U-NII Unlicensed Spectrum in 5 GHz (Click to Download PDF) |
Additionally, here is a graphic of the 5 GHz U-NII bands, both current and proposed, from the NTIA report made in January 2013 (note - this graphic does NOT reflect the change with regards to the extension of U-NII 3 up to 5.850 GHz).
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| NTIA Graphic of U-NII Unlicensed Spectrum in 5 GHz |
Cheers,
Andrew von Nagy
Wi-Fi SNR to MCS Data Rate Mapping Reference
I previously posted a picture of an SNR to MCS data rate mapping table that I have compiled based on various sources of credible research. Keith Parsons has kindly put this information into a printable format for reference. You can download them below.It should be noted that individual devices perform differently. These tables are simply generic estimates that are a good approximation for many Wi-Fi devices. In other words, it's not perfect.
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| Click to Download Full Version (PDF) |
This table maps client SNR values to MCS indexes for the purpose of determining the data rates that clients can achieve based on the signal quality of their connection to the AP.
SNR is also related to RSSI. Two RSSI values are of importance: the Minimum Receiver Sensitivity and the Expected Receiver Sensitivity. The 802.11 minimum receiver sensitivity tables often referenced in research and testing material are the required minimum RSSI values that a radio should be able to decode a given modulation type and encoding rate (MCS index) with a packet error rate (PER) less than 10%. Most 802.11 radios provide better receiver sensitivity than the minimum requirement. Therefore, the "Expected Receiver Sensitivity" reflects the typical receive sensitivity Continue reading
Quick Take: Wider Channel Widths Are Flashy but Not Efficient
I've been thinking of writing a well-articulated blog post on why the preference for high-density Wi-Fi networks is smaller channel width over larger channel width. This post is NOT that.Instead, I was on Twitter articulating some of the logical points why smaller channel widths provide better aggregate capacity than larger channel widths (assuming you deploy enough radios and take advantage of all the spectrum at your disposal). Here is a quick recap of those points.
You might want to reference my SNR to MCS Index Mapping Table, which shows why larger channels result in a reduction in modulation rate that can often offset the gain from using the wider bandwidth in the first place. And my 802.11ac Receiver Sensitivity charts show that you have to have a really great signal strength for wider channels to even be considered, but watch out in your design because overcompensating to achieve higher signal strength will increase co-channel interference (CCI) which travels a LONG ways! Finally, my post on 802.11ac Adjacent Channel Interference (ACI) shows that wider channels create more ACI than smaller channels, and ACI is even more detrimental and unfriendly than CCI. Therefore, radio receivers require greater adjacent channel Continue reading
802.11ac Receiver Sensitivity
Following my previous post regarding typical SNR to MCS rate mappings for Wi-Fi clients, an interesting discussion was held on Twitter regarding the effects of increased channel width on the ability of a client to decode frames at any given SNR. Long story short, wider channels increase the noise power captured by the receiving radio which reduces its SNR. For every doubling of channel width, you require 3dB better signal to achieve the same MCS rate.George Ou created a chart showing the relative range of each MCS rate based at various channel widths:
@revolutionwifi @vall_wifi @KeithRParsons The negative effects on effective range with wider channels http://t.co/wyg3qtQjJl
— George Ou (@GeorgeOu) August 20, 2014
Following up on his work, I thought it would be useful to provide some context around these coverage ranges by referencing it against a typical noise floor of -93 dBm found in many environments. Using this noise floor and the SNR to MCS rate mapping table, combined with the relative coverage ranges (based on RF signal propagation using the inverse square law) we can visualize what data rates a typical 802.11ac radio will experience at various RSSI and SNR signal levels for each channel Continue reading
Visualizing How Wi-Fi SNR Helps Determine the Achievable MCS Data Rate
If a Wi-Fi station has a better signal, you get more throughput. Everyone knows that. Here is a handy chart to help visualize it.This table shows the "typical" data rates that Wi-Fi stations can achieve based on their SNR (signal to noise ratio). I say "typical" because it actually varies based on the radio chipset receiver sensitivity, but these values are a good starting point for most devices.
The achievable data rate (MCS rate) varies based on a number of variables:
- The 802.11 protocol - really a function of the increasing maturity of chipsets over time to handle more complex modulation types even when SNR is a bit lower.
- The channel width - typically doubling the channel width increases the noise floor by 3 dB, which decreases SNR. So to get the same MCS rate on wider channels you need higher SNR.
- The complexity of the modulation - notice as you get into more complex modulations like 64-QAM and 256-QAM that it doesn't take much more SNR to move from the lower encoding rate to the higher encoding rate, and vice versa in the opposite direction.
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| Typical Wi-Fi SNR to MCS Data Rate Mappings (Download for full resolution Continue reading |
Optimized Roaming, RSSI Low Check, RX-SOP, Oh My!
In the Cisco landscape today, there are three features that usually come up in the same conversation. They all solve what I'd call "related" problems, but are not the same. They are incredibly useful features and do share one thing in common...you must know your RF environment before implementing them. I'll provide use-cases and examples below, but it should be noted that in the case of "Optimized Roaming", this is based on public information currently available and could change prior to the WLC AirOS version 8.0 release.Optimized Roaming
The problem:The well known "sticky client" issue. For the uninitiated, when a client refuses to roam to an assumedly "better" AP (closer, stronger RSSI, better SNR etc.) that client is being "sticky". Why is this bad? Consider the following example of a lecture hall:
As the client enters the room, it associates to AP-1. As it moves farther away from AP-1 it's RSSI gets weaker, SNR gets worse, retransmissions occur, dynamic rate-shifting happens, and you end up with a client communicating at a much lower data-rate. Lower data-rate consumes more air-time to transfer the same information, resulting in higher channel utilization. Ideally, the client would roam to Continue reading
Downloads
Here is a repository of Wi-Fi related documents and resources that WLAN administrators will find useful.
If you have a Wi-Fi related document, tool, or resource that you would like included on this list, please contact me for inclusion! My contact info is listed on the right column of this website.
Revolution Wi-Fi Downloads:
35 presentation slides, PDF format.
This presentation covers an approach and methodology to integrating WLAN capacity planning into the WLAN design process to allow network engineers to effectively meet growing capacity demands by clients on wireless networks. It defines what capacity means for a WLAN, what factors determine capacity, provides an approach to designing for capacity, and where capacity planning should be integrated into the overall WLAN design process.
Effective capacity planning is required for all WLANs, not just high-density environments.
This information was presented at the WLAN Professionals Conference (2014).
You can also
and download the
to help calculate capacity needs, which helps simplify the process and step the user through each step.
Wi-Fi SSID Overhead Calculator
Excel Spreadsheet format.
This tool allows WLAN administrators to assess the network performance impact that multiple SSIDs Continue reading
SSID Overhead Calculator
One of the most commonly cited best practices among Wi-Fi professionals is to the limit the number of SSIDs you have configured on your WLAN in order to reduce the amount of overhead on the network and to maintain high performance. But there is not a lot of public data out there to really drive home this point when explaining it to another engineer, management, or a customer. Simply telling someone that they shouldn't create more than 'X' number of SSIDs isn't very convincing.Therefore, I've created a visual tool to help you explain WHY too many SSIDs is a bad thing:
The Wi-Fi SSID Overhead Calculator
(Click Image to Download)
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| Wi-Fi SSID Overhead Calculator |
This tool calculates the percentage of airtime used by 802.11 beacon frames based on the following variables:
- Beacon Data Rate - beacon frames are sent at the lowest Basic / Mandatory data rate configured on the WLAN. Beacons must be sent at a "legacy" data rate, meaning only 802.11a/b/g rates. Select the beacon data rate from the drop-down menu within the tool.
- Beacon Frame Size - beacon frames can vary in size based on the version of the 802.11 standard implemented (802. Continue reading
802.11ac Adjacent Channel Interference (ACI)
I was reading this article on development of 5G cellular technologies when this bit on OFDM deficiencies and the need for new waveforms to support higher capacities and user densities caught my attention (emphasis added by me):4G and 4G+ networks employ a type of waveform called orthogonal frequency division multiplexing (OFDM) as the fundamental element in the physical layer (PHY). In fact, almost all modern communication networks are built on OFDM because OFDM improved data rates and network reliability significantly by taking advantage of multi-path a common artifact of wireless transmissions. However as time and demands progress, OFDM technology suffers from out-of-band spectrum regrowth resulting in high side lobes that limit spectral efficiency. In other words, network operators cannot efficiently use their available spectrum because two users on adjacent channels would interfere with one another. OFDM also suffers from high peak-to-average ratio of the power amplifier, resulting in lower battery life of the mobile device. To address OFDM deficiencies, researchers are investigating alternative methods including generalized frequency division multiplexing, filter bank multi-carrier, and universal filter multi-carrier. Researchers speculate that using one of these approaches over OFDM may improve network capacity by 30 percent Continue reading
Article Archives
Here are some of the most popular posts on Revolution Wi-Fi, grouped by topic.Note - This is NOT a comprehensive archive of articles on this blog.
802.11ac Gigabit Wi-Fi Series:
- The Impact of 802.11ac Gigabit Wi-Fi on Enterprise Networks
- 802.11ac Channel Planning
- Safely Using 80 MHz Channels with 802.11ac
- Ekahau Site Survey™ 6.0 Incorporates 802.11ac Channel and Capacity Planning
- First Look - 802.11ac Gigabit Wi-Fi Speed
- Presentation Video: Going Beyond RF Coverage and Designing for Capacity
- Design Your WLAN for High Capacity
- Video Blog: High-Density Wi-Fi Design Part 1 - Forecasting AP Capacity
- Video Blog: High-Density Wi-Fi Design Part 2 - RF Design
- Video Blog: High-Density Wi-Fi Design Part 3 - WLAN Configuration Best Practices
- Part 1 - Background Information
- Part 2 - IEEE 802.11e Principles
- Part 3 - User Priorities, Access Categories and Queues
- Part 4 - Arbitration Interframe Spacing
- Part 5 - Contention Window and Final Thoughts
The Economic Value of Unlicensed Spectrum $228 Billion Annually in the U.S.
According to a new report completed by Telecom Advisory Services, LLC (Raul Katz, Columbia Business School) commissioned by WiFiForward, the economic value of unlicensed spectrum is over $228 Billion per-year in the U.S. alone! |
| WiFiForward Value of Unlicensed Spectrum Infographic |
FINAL REPORT - ASSESSMENT OF THE ECONOMIC VALUE OF UNLICENSED SPECTRUM IN THE UNITED STATES
The Report Overview (1 page) highlights the use-cases and value of each. WiFiForward has also produced an infographic (shown at right) to highlight the various ways in which unlicensed spectrum provides economic value in the U.S.
The report details the value of unlicensed spectrum in the U.S. based on two different economic impacts:
- Gross Domestic Product (GDP) - direct sales of technologies, services and applications that run on unlicensed spectrum. This results in $6.7 Billion per-year in value ($4.559 Billion of which is attributed to Wi-Fi).
- Economic Surplus - use of technologies that rely on unlicensed spectrum that add value to the economy. This results in $222 Billion per-year in economic value ($91.474 Billion of which is attributed to Wi-Fi).
I am a bit confused since the value from enterprise Wi-Fi sales and resulting efficiencies appears Continue reading
Impact of the FCC 5 GHz U-NII Report & Order on Wi-Fi Networks
Following the news release of the FCC's actions to change some technical rules for the 5 GHz U-NII bands, the official Report and Order was released on Tuesday.I've read through the R&O, and here are the technical modifications that were approved:
- U-NII 1 band (5.150 - 5.250 GHz) indoor operation restriction is removed. This allows use of the band for outdoor hotspots, WISPs, and bridge links. The growth of public hotspots will clearly benefit from this change.
- U-NII 1 band (5.150 - 5.250 GHz) power level restrictions are changed.
- AP power levels at the Intentional Radiator may be 1W (previously 50mW) and the EIRP may be 4W using a 6dBi antenna (previously 200mW), and following the 1dB reduction rule in transmitter power for every 1dB of antenna gain above 6dBi.
- Client power levels at the IR may be 250mW and the EIRP may be 1W, following the 1:1 dB reduction rule for antenna gain above 6dBi.
- WISPs may use up to 23dBi antennas on fixed point-to-point links without any corresponding reduction in transmitter power.
These changes help to unify the U-NII 1 band with the U-NII 2A/2C and U-NII 3 bands so Continue reading
10 Wi-Fi Terms You’ve Probably Been Using Incorrectly
Sometimes we fall into bad habits. Unfortunately, the improper use of terminology is quite common in the Wi-Fi industry. This can cause a great deal of confusion when people discuss technical topics. Therefore, as a Wi-Fi industry, I think we should start referring to the following terms using more accurate terminology so we are all on the same page.Here goes:
- Over-the-Air Rogue APs - if it's not on your wired network, it's NOT a "Rogue AP" so let's start calling them Neighboring APs so we all know what someone is talking about rather than having to inquire each and every time someone mentions a rogue for clarification. And let's reserve using the term Rogue APs for when unauthorized APs are on the internal wired network.
Correct Term: Neighboring APs - Co-Channel Interference (CCI) - APs and clients that are operating on the same channel don't cause interference with one another, they contend for the same airtime and backoff if another one is transmitting. This is distinctly different from interference where a transmission cannot be properly decoded because the receiver can't distinguish the valid signal from noise.
Correct Term: Co-Channel Contention (CCC) - Collision - okay, here is one that most of Continue reading
FCC Eases Restrictions on 5GHz UNII-1 Band
The FCC just made an unofficial news release of pending action that was approved at today's commission hearing which eases restrictions on the existing 5 GHz UNII-1 frequency band (5.150-5.250 GHz, Wi-Fi channels 36-48).To quote from the news release (emphasis added by me):
By its action the Commission significantly increased the utility of the 100 megahertz of spectrum, and streamlined existing rules and equipment authorization procedures for devices throughout the 5 GHz band.This ruling makes the following changes to the UNII-1 band:
- Removes restriction on indoor use. Now the UNII-1 band can be used outdoors as well. This will allow use of the band by WISPs and for outdoor hotspot deployments which are rapidly growing with the support of telecommunications and cable operators.
- Increases the allowed power output. The power output had been lower in UNII-1 than other 5 GHz UNII bands due to indoor-only use (50mW IR, 200mW EIRP). Exact details of the new power limits have not been released, but it is fair to assume the UNII-1 band will have similarly capable power output as
UNII-2/2e bands (250mW IR, 1W EIRP)the UNII-3 band (1W IR, 4W EIRP). (Update after reviewing Commissioner Rosenworcel's Continue reading
WLAN Professionals Conference Videos Posted
Videos of presentations from the WLAN Professionals Conference that occurred Feb. 10-12th in Austin, TX have now been posted by Keith Parsons and the Prime Image Media team. The conference was chalk-full of great content, both technical and business focused, by some of the best experts in the industry!I had the honor of presenting a session titled "Going Beyond RF Coverage: Designing for Capacity." The topic is about how to define, measure, and plan for capacity needs for ALL wireless networks (not just high-density environments - for which no commonly accepted definition even exits). I provided a bit of background on why I decided to give my presentation on this topic in my previous blog "Mind the Gap in Your WLAN Design" and you can download the full presentation and related material.
Check it out!
WLAN Pros Summit 2014 | Andrew Von Nagy Beyond RF Coverage 1 from Keith R. Parsons on Vimeo.
Be sure to check out all of the great presentations from the event on the WLAN Pros website and Keith's Vimeo channel!
Cheers,
Andrew
Wi-Fi Tools
A good engineer takes pride in his tools.As with many things in IT, there are many options to choose from and most work equally well provided the engineer has a thorough understanding of how to use them. I happen to use and prefer the following tools, but your taste may be different. Use what you like and know as long as it gets the job done.
Items with an asterisk are my preferred tools for each category.
Information Gathering:
*AirMagnet Wi-Fi Analyzer Pro
*MetaGeek inSSIDer
Fluke AirCheck
Ekahau HeatMapper (Free)
Xirrus Wi-Fi Inspector
WiFi Scanner (Mac)
Kismet (Linux)
Predictive Site Surveys:
*Cisco Wireless Control System (WCS)
AirMagnet Planner
Ekahau Site Survey
Motorola LANPlanner
Aerohive Wi-Fi Planner (online - Free)
Post-Installation Site Surveys:
*AirMagnet Survey Pro
Ekahau Site Survey
TamoSoft TamoGraph Site Survey
Veriwave WaveDeploy
Protocol & Roaming Analysis:
*WildPackets OmniPeek
*MetaGeek Eye P.A. (protocol visualization)
*Wireshark with CACE AirPcapNx and Wi-Fi Pilot (now Riverbed Cascade Pilot Personal Edition)
Wireshark with Atheros Adapter (Linux)
AirMagnet Wi-Fi Analyzer Pro with multi-adapter kit
AirMagnet VoFi Analyzer
TamoSoft CommView for Wi-Fi
Spectrum Analysis:
*MetaGeek WiSpy DBx Continue reading
WLPC Conference Day 1 Highlights
I'm here at the WLAN Professionals Conference (#WLPC if you're following on Twitter). This is the first of what hopefully will turn into an annual conference dedicated to the Wi-Fi industry. But this conference is a bit different than what you might think a typical conference is. First and foremost, it's got a grassroots, peer-to-peer focus. It's engineers talking about Wi-Fi and gathering for discussion. It's not overly promoted by vendors or full of presentations with marketing drivel. Instead, it's just people who are passionate about this technology coming together to share their knowledge and experiences with each other to better everyone! What a great concept!There are over 100+ attendees, many of whom are also presenters. I hear there was more demand than seats available, so next year Keith Parsons, organizer of the event, should have a solid baseline to grow the conference and allow more of you (the community) to attend and get involved. What's also great is that many of the presentations have been interactive, with great questions and quality discussion fostering the entire group to share information. The focus on the technology instead of the marketing that so often surrounds the technology and products Continue reading