wifi design

WN Video 006 – Ekahau Pro

In this video Matt from WiFi Ninjas gives you a brief overview of one of his favourite WiFi tools – Ekahau Pro.

He takes a look at the WiFi data on his MacBook that he collected on the Ekahau App for iOS on his iPhone.

You can see how Matt use the Ekahau iOS App in this video: https://youtu.be/XgS3avplip8

You can find out more about Ekahau and their products at: https://www.ekahau.com

If you want to learn more about WiFi and how to use the suite of Ekahau design tools you can find out more here: https://www.ekahau.com/training/ecse-design/

WN Video 005 – Ekahau Survey App

In this video Matt from WiFi Ninjas shows you how to use the Ekahau Survey App for iOS & the multiple ways that you can carry out a WiFi Survey using the application.

Matt also shows you the different heat map visualisations that you can see on the app and how you sync your project files with the Ekahau cloud.

Find out more about Ekahau over at their website: https://www.ekahau.com

WN Podcast 031 – Surveys, Design & Teaching Tips with Ferney Munoz

Welcome to our new WiFi Ninjas Podcast
episode!

Today we talk about WiFi design and teaching tips and some crazy, unconventional surveys using GPS & Segways in quite niche verticals like slums, city outdoors and mining. Welcome our special guest and a great teacher – Ferney Munoz!

Enjoy!

Tons of love x,

WiFi Ninjas

WN Blog 022 – Distance Between 802.11 Radios – How Close Is Too Close?

We have recently come across few production networks, where distance between two APs or APs and a client stations was much closer than I was comfortable with.

Natural reaction was to suggest moving radios at least few metres apart. But why exactly? What happens when two or more transmitting radios are too close to one another? How would placing a laptop next to the AP affect wireless network quality?

Intrigued and eager to answer questions that, interestingly, no one was asking, I have decided to lab it up, research it more deeply and document my findings. I quickly realised that there is not one, but two issues potentially affecting wireless transmission, where distances between radios were too short. Let’s discuss Channel Leakage and Near-Field Interference.

Structure:

  • Channel Leakage
  • Near-Field Interference
  • Literature

Channel Leakage

Few months after a successful design and refresh of a WiFi estate for a financial institution in London, I came back to work on a periodic wireless survey and to assess if there is anything that would be potentially stopping them from introducing more agile working heavily relying on the new WiFi deployment.

I was told that there is a separate company that is working closely with my client in the same offices and that they use their own, separate WiFi network. They have decided to put their own APs next (few inches away) to our APs convinced that since it worked perfectly for my client, it would continue working when two overlaid networks operate simultaneously. This is how the new original vs new deployment looked like:

Having completed the survey, we have concluded that city centre location inside a multi-tenant building with multiple WiFi networks leaking from the outside and adjacent floors combined with two separate, overlaid WiFi networks contributed to very high CCI averaging at 10 or sometimes more. RF tuning across both networks has helped a lot with the contention but the overall quality of the WiFi was still not great. It felt slow despite having strong underlying infrastructure, little CCI and fast Internet pipe. Quick wireless capture has revealed excessive retransmissions rates peaking at 30% in some areas even when there were not too many clients (maybe 10 per radio, often less) competing for the airtime, channel utilisation peaking at 10% and with no obvious faults with the configuration.

Lab

Next step was to reproduce the issue in the lab, where I wanted to show how channel separation and AP-to-AP distance impacts percentage of retries in the wireless transmission.

Setup

  • 2x Cisco 3702i APs registered to C9800-CL WLC broadcasting separate BSSIDs on 5GHz only
  • 20MHz static non-overlapping, clean channels (100 & 104 and 100 & 140) and max Tx power (1) set
  • One mobile station associated to each BSSID, running external speed test in the loop
  • Ekahau Sidekick used for wireless captures

Tests

4 different tests were performed, each test involved wireless capture over 30 seconds and was repeated 5 times to minimise measurement errors:

  • Channels 100 & 104 (no channel spacing)
    • Test 1: APs 0 metres away from one another
    • Test 2: APs 3 metres away from one another
  • Channels 100 & 140 (200MHz channel spacing)
    • Test 3: APs 0 metres away from one another
    • Test 4: APs 3 metres away from one another

Conclusion

We can clearly see in Test 1, that close physical distance between radios combined with no channel separation resulted in 15.4% retries.

Introducing 200MHz channel separation (Test 3) without extending distance between radios has reduced retries ratio by about half, to 8.2%.

Moving APs 3 metres away from one another has further reduced the retries to 3.9% (Test2; no channel separation) and 2.3% (Test 4; 200MHz channel separation).

Unplanned channel leakage really is an adjacent-channel interference, even though our channels theoretically don’t overlap. ACI will naturally cause increased number of retries, and therefore decrease the throughput and contribute to the slow WiFi perception.

Note: we used flagship Cisco APs with great quality of components providing great RF accuracy. Using cheaper APs that pack cheaper antennas and radios would result in less stellar performance of spectral masks (algorithms applied to the levels of radio transmissions used to reduce main channel leaking to adjacent channels) and amplify the effects of intermodulation (signal modulation on two or more different, non-harmonic, frequencies), increasing effects of ACI and percentage of retries when reasonable channel separation and physical distance between AP radios are not maintained.

Near-Field Interference

Another distance issue that I have frequently seen in an enterprise environment is placing receivers too close to transmitters.

Let’s start with a quick definition of what near-field is in wireless.

Near-field is a 1 wavelength region, where electromagnetic field EM charges and electric charge effects are extensively produced, potentially negatively affecting quality of the received transmission within this region.

Near-field interference decreases drastically, in a logarithmic fashion, when the receiver is moved farther away from the transmitter. It is normally considered enough to be 1 wavelength away from the transmitter to negate the impact of near-field interference. Near-field also affects reflected signal for Rx antennas.

Based on the above, we can conclude that:

  • Radios should never be positioned closer than 1 wavelength apart from one another
  • Receive antennas should not be positioned closer than one wavelength to any reflecting obstacle due to reflection indicted multi-path phase cancellation

How far is 1 wavelength? It depends on the frequency. The higher the frequency the shorter the wavelength. Here are the wavelength calculations for our beloved 802.11 bands:

2.4GHz frequency wavelength = 12.5cm

5GHz frequency wavelength = 6cm

Now we know, that when we position 2.4GHz radios closer than 12.5cm away from one another (or 6cm in 5GHz) we would suffer from extensive near-field interference and that the situation would improve greatly when we start increasing this distance. Bear in mind, that unwanted channel leakage might contribute to packets corruption here too, so it typically is recommended to keep at least few metres distance between the radios!

Couple of examples, where near-field interference can affect quality of WiFi transmission:

  • Enterprise-class AP placed on a small desk with few people sitting around it and their laptops virtually adjacent to the AP; note, that external antennas can increase the negative effect of a near-field interference
  • Capturing wireless packets with a capturing device positioned to close to a client or an AP

We must remember that WiFi is not NFC! ????

Lab

In this test I targeted impact of near-field interference on wireless receive quality, where receiver (AP in a sniffing mode) was within 1 wavelength of a transmitter (AP serving clients).

Setup

  • 2x Cisco 3702i APs registered to Cisco 3504 WLC and one test client associated to client serving AP
  • AP with blue LED is serving clients
  • AP with green LED is running as a sniffer and capturing packets on the same channel as the AP serving clients
  • Below tests are based on 5GHz, but in my tests I could have easily reproduced them across both 5GHz and 2.4GHz bands

Tests

It was enough to perform a very simple test here – check captured packets integrity in two scenarios:

  • Test 1: AP sniffer placed 60 centimetres away from a client-serving AP (more than 1 wavelength distance between radios)
  • Test 2: AP sniffer placed on top of a client-serving AP (less than 1 wavelength distance between radios)

Here are the results:

Test 1 captures, where APs are fairly far away from one another, are clean. Putting transmitting and receiving radios very close together (Test 2) results in corruption of almost all packets transmitted by client-serving AP.

Conclusion

When receiver is placed too close to transmitter (especially true when the distance is less than 1 wavelength apart), near field interference will cause packets to lose integrity and result in failed Frames Check Sequence (FCS).

Summary

As shown in the above tests, unwanted channel leakage can seriously affect the transmission quality over distances less than few metres, especially without proper channel separation on the neighbouring BSSIDs. Near-field interference can cause corruption of most of the transmitted frames, where distance between transmitting and receiving radios is less than 1 wavelength apart. Finally, after having a chat with my friend Nigel (Twitter @WiFiNigel), we have concluded that the Rx overdrive might also play a role in the frames corruption. Unfortunately, it is difficult to ascertain which phenomena impacts the frames corruption most using the home lab, so I’ll just conclude with this: don’t stack APs! 🙂 And put them away from strong reflectors. All above issues can be easily avoided by using good quality enterprise equipment, solid RF design and having a high-level understanding of how the distance induced interference can affect the quality of the wireless transmission.

Literature

WN Podcast 014 – WiFi Design for Retail

Welcome to our new WiFi Ninjas Podcast episode! We continue our Design Series with a discussion around WiFi Design for Retail.

Design recap (see episode 12):

  • Understand the purpose (data, high density, location, etc.)
  • Capture success criteria (capacity, coverage, other RF elements, roaming)
  • Always go on site before and after (attenuation, RF condition, interferers, DFS, visual check)

Retail design challenges:

  • Often very high ceilings
  • Often large open spaces (food court areas etc.) so not much to attenuate WiFi
  • A lot of 2.4GHz CCI/ ACI from there being so many wireless devices in every store or concession stand
  • pretty much guarantee that 2.4GHz spectrum is near enough unusable
  • Legacy guest devices
  • So retail providers usually want you to still support 2.4GHz
  • Large amount of devices
  • Can you bring concessions WiFi under yours by giving them an SSID and VLAN on your wireless network in a certain area controlled by AP Groups – reduce the amount of rogue WAPs and contention! 

Retail design essentials:

  • What is the wireless design for?
    • Data? Voice?
    • Guest Location Analytics
    • Anything else?
  • Who is it for?
    • Guest only
    • Guest & Corp
  • Capacity in different times of year – ever seen a popular mall over Christmas period?
  • Mobility is key but it’s challenging
  • Security vs compatibility vs user friendliness
    • P2P block
    • Onboarding must be easy
      • Ask too many questions and users won’t connect
      • Keep it simple – use Facebook, Instagram etc.
      • Stick to basic email form for users with no social media
  • Value of cutting edge WiFi without apps
    • Challenging to get users to install apps
    • Easier with WiFi than with BLE due to randomisation

Drivers behind having a sleek WiFi in retail:

  • Goal: increase sales
    • Understand the customers needs
    • Adjust the displays, stock, presentation, promotions, online presence, etc.
  • Customers expect proper connectivity
    • If mobile coverage drops, they will check WiFi out
    • If it’s not there, it’s bad. If it is there but it’s slow or user-unfriendly, it’s even worse
  • All things considered, WiFi is not the most expensive part of running a store, but it can massively help business:
    • Built email list (login via form)
    • Built demographic stats (login via social network)
    • Understand basic customers presence in store (zone based analytics)
    • Understand routes client take (basic location analytics with WiFi triangulation and presence)
    • Understand exact clients location behaviour with high tracking accuracy (hyperlocation, BLE, vBLE)
    • Chance to push loyalty apps
    • Wayfinding
    • Grabbing attendant attention
    • Users engagement
  • ‘physical’ stores experience tough times – use tech to steer users towards own online shops instead of closing businesses

Wireless Coverage Areas and different requirements?

  • Front of House
    • Areas where guests will be traversing through the centre
  • Back of House
    • Service corridors
    • Offices
    • Service yards
  • External
    • Outdoor shopping areas
    • Outdoor entertainment areas
  • Car Parks
    • People locating themselves back to where their car is parked

What Vendors for wireless analytics

  • Cisco + CMX + DNA Spaces
  • Meraki + Purple
  • Mist

Pick your AP wisely

  • Internal or external?
  • Needs more ruggedness?

Think about the config

  • Its hard to get to know the devices you design for as there could be any kind of legacy device a guest user could bring in – agree upfront with the retail management what the worst device you are willing to cater for.
  • Guest is usually open / open or open with captive portal
  • Can you / should you use just UNII1 and UNII2 channels?
  • Monitor mode WAPs
  • Watch the Tx power and data rates
  • Stick to 20Mhz wide channels
    • Bonded channels = more interference = lower SNR
    • Normally throughput is not a concern in retail
  • RX-SOP can mean drop offs mid roam for stickier
  • Devices might not like 802.11v – clients don’t like to be disassociated and v sends client a proposition to associate with other best AP, followed by a threat of disassociation if STA doesn’t jump on its own and a big chunk of clients don’t support it
  • Devices might not like 802.11r at all or some flavour of it

Mounting and positioning

  • Often very high
  • Concessions may not let you install WAPs in front of their shop fronts as it will not make it aesthetically pleasing
  • Most important after coverage is no CCI / ACI and fast roaming
  • Service yards – WAPs can get covered in a lot of crap quite easily so may need to consider IP rated boxes to protect them or external / ruggedized WAPs

Other standard considerations

  • Distance to the switch
  • PoE
  • Mounting restrictions
  • Obstructions, metal
  • Other networks
  • Interferers
  • Vendor choice
  • Architecture

Thanks for listening and please don’t hesitate to leave a comment, feedback, subscribe or follow us on social media!

Join us at Natilik HQ in London, where we’ll be hosting an 802.11ax focused event with juicy theory hands on demos. Drinks and food on us! Register here:

https://www.eventbrite.co.uk/e/network-nomads-all-eyes-on-wifi-6-tickets-62909569215?aff=eac2

Cheers!

WN Podcast 013 – WiFi Design for Warehouse

Welcome to our new WiFi Ninjas Podcast episode!

In this episode Mac and Matt discuss at a high level how they design WiFi for the warehouse as they look to share their personal experience and tips with you.

Design recap (see episode 12):

  • Understand the purpose (data, high density, voice, scanners, etc.)
  • Capture success criteria (capacity, coverage, other RF elements, roaming)
  • Always go on site before and after (attenuation, RF condition, interferers, DFS, visual check)

Warehouse design challenges:

  • Often very high ceilings
  • Moving forklift trucks knocking off APs and antennas
  • Changing stock
    • Amazing WiFi during holidays season can go ‘tits up’ before Christmas
  • Changing racks layout
    • Matt can say something about it 😉
  • Changing requirements and purpose
    • Those scanners from 1999 might now be upgraded and need to support voice
  • Tons of obstructions
  • Legacy devices
    • Tendency to use old scanners forever
  • Weird devices (especially true for legacy ones)
    • Using specific channels only
      • 2.4 or 5GHz only
      • Limited 5GHz channels, in most cases UNII-1 only
    • Using specific data rates only
      • AP tries 54, fails, tries 48, fails, (…), settles on 2 Mbps – difficult to tshoot
    • Battery operated devices with failed implementation of battery saving mechanisms
      • Drops off
      • Doesn’t roam properly or quickly enough
  • Preferred authentication is often not supported
    • Security team crying about having to use PSK
  • Can be difficult to get to the AP or antenna if needed

Warehouse design essentials:

  • Choose the right antenna type for the job
    • Cover what needs to be covered
      • Coverage on the ground level, 15m up where the forklifts operate or both?
      • Propagation pattern
    • Reduce overlapping
      • Use the environment
      • Position antennas wisely
    • Environment can dictate antenna type
      • Omnidirectional won’t be great at 20m
      • Overlapping can be substantial with omnis in vast open spaces
      • Not always possible to put omni in the middle of the rack
  • Pick your AP wisely:
    • Cold or hot? Dust?
    • Internal or external?
    • Needs more ruggedness?
  • Think about the config:
    • Normally you’d have a different SSID for WH offices and WH packing / production / shifting
    • For WH offices design, listen to our previous episode
    • For WH production, keep it simple
    • Get to know the devices you design for – sometimes warehouses use very capable tablets or a mix or modern tablets and very old scanners
    • Roaming (quick one!) is extremely important
    • Can you / should you stick to PSK?
    • Can you / should you use just UNII1 and UNII2 channels?
    • Watch the Tx power and data rates
    • Will you survive on 20MHz? Normally WH capacity needs are low
    • Do you really need those bells and whistles for often very limited number of devices?
      • Bonded channels = more interference = lower SNR
      • RX-SOP can mean drop offs mid roam for stickier
      • Devices might not like 802.11v – clients don’t like to be disassociated and v sends client a proposition to associate with other best AP, followed by a threat of disassociation if STA doesn’t jump on its own and a big chunk of clients don’t support it
      • Devices might not like 802.11r at all or some flavour of it
    • Even old scanners normally support 802.11a and 2.4GHz is often noisy from both WiFi and non-WiFi interference; stick to 5GHz whenever possible
  • Mounting and positioning
    • Often very high
    • Few examples:
      • Patch or sector on the walls, covering entire or most of the aisle, tilted down, pointing towards the aisle’s end
        • Sometimes one AP per aisle is enough (up to 80-100m), sometimes two at both ends (more than 100m)
      • Patch or sector cone of coverage with antenna pointing down, antenna mounted to the ceiling, duct or suspended
      • Omni with external antennas pointed up or down, mounted to the wall, beam or column, away from the metal surfaces
      • AP/antenna placed in a heated or cooled Nema enclosure
    • Ensure basic AP redundancy – it’s not easy nor quick to replace one
    • Most important after coverage is no CCI / ACI and fast roaming
    • Ensure speeding clients, both human on forklifts and robots (have you seen automated warehouses yet?), are associated with the AP you want them to be associated with and that they roam where and when we want

Other standard considerations

  • Distance to the switch
  • PoE
  • Mounting restrictions
  • Obstructions, metal
  • Other networks
  • Interferers
  • Vendor choice
  • Architecture

Thanks for listening and please don’t hesitate to leave a comment, feedback, subscribe or follow us on social media.

WN Podcast 012 – WiFi Design for Enterprise

Welcome to our new WiFi Ninjas Podcast episode!

In this episode Mac and Matt discuss at a high level how they design WiFi for the enterprise as they look to share their personal experience and tips with you.

Capture requirements:

  • High Density / data (to be covered in more details in future episode)
  • Voice (see episode 11 with Andy)
  • RTLS (to be covered in more details in future episode)
    • Zone analytics
    • Location tracking or wayfinding
      • Trilateration
      • Hyperlocation
      • BLE / vBLE
      • Asset tracking / tags
      • Apps or no apps

Capture success criteria:

  • Capacity
    • Apps in use
    • Head count
    • Devices in use
    • Device count
  • Physical
    • SNR
    • RSSI
    • Overlapping

Make basics right:

  • Do a proper survey (see episode 3 – predictive survey)
  • Go to the site
    • Measure walls and ceilings attenuation
    • Understand mounting limitations
    • Check RF
    • Check DFS
  • APs count, model, antenna and placement for different use case
    • Omni vs directional
    • Aesthetic considerations
      • Visible or not
      • Flat antenna under the ceiling and AP in plenum?
      • Colour
    • Architectural considerations
      • Listed buildings
      • Custom requirements – lifts, landlord owned staircases, steel beams etc.
    • High density / basic data
      • Focus on capacity and coverage
    • Voice
      • Focus on roaming
    • RTLS
      • Focus on location accuracy
  • Physical APs mounting considerations
    • Obstructions
      • Reflectors
      • Absorbers
      • Scaterers (is that a word?)
    • Consider wavelength if mounting really close to the obstructions, especially if they’re highly reflective
      • AP at least 1 wavelength away
      • 2.4GHz wavelength: 12.5cm
      • 5GHz wavelength: 6cm
    • Consider close field interference
    • Consider overlaid wireless (not only WiFi) networks
    • Consider other interferers

Vendor / partner choice:

  • Staff skills
  • Managed services?
  • Fit for purpose
    • Is on-prem or cloud a preference?
    • Consider the complexity of the solution vs benefits

Architecture:  (to be covered in more details in future episode)

  • All the above will dictate architecture choices
  • Management
  • Data switching
  • Authentication

Keith Parson AP Power Level Chart:

Thanks for listening and please don’t hesitate to leave a comment, feedback, subscribe or follow us on social media.