WI-FI TECHNOLOGY DEEP DIVE: PART 1 WHAT YOU NEED TO KNOW TO DEPLOY A HIGH PERFORMANCE WIRELESS LAN

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1 WI-FI TECHNOLOGY DEEP DIVE: PART 1 WHAT YOU NEED TO KNOW TO DEPLOY A HIGH PERFORMANCE WIRELESS LAN Todd Savarese Sr. Wireless Architect Vamshi Doma Sr. Product Manager - WLAN 1

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5 FREQUENCY Frequency is the number of times a specified event occurs within a specified time interval. A standard measurement of frequency is hertz (Hz), which was named after the German physicist Heinrich Rudolf Hertz. Different metric prefixes can be applied to the hertz (Hz) measurement of radio frequencies: 1 hertz (Hz) = 1 cycle per second 1 kilohertz (KHz) = 1,000 cycles per second 1 megahertz (MHz) = 1,000,000 (million) cycles per second 1 gigahertz (GHz) = 1,000,000,000 (billion) cycles per second So when we are talking about 5 GHz WLAN radio cards, the RF signal is oscillating 5 billion times per second! 2016 Avaya Inc. All right reserved 5

6 AMPLITUDE Amplitude is defined as the maximum displacement of a continuous wave. With RF signals, the amplitude corresponds to the electrical field of the wave. When you look at an RF signal in an oscilloscope, the amplitude is represented by the positive crests and negative troughs of the sine wave. Note that although the signal strength (amplitude) is different, the frequency and wavelength of the signal remains constant. A variety of factors can cause an RF signal to lose amplitude, otherwise known as attenuation Avaya Inc. All right reserved 6

7 GAIN (AMPLIFICATION) Gain, also known as amplification, can best be described as the increase of amplitude, or signal strength. The two types of gain are known as active gain and passive gain. A signal s amplitude can be boosted by the use of external devices. Active gain is usually caused by the use of an amplifier on the wire that connects the transceiver to the antenna. The amplifier is usually bidirectional, meaning that it increases the AC voltage both inbound and outbound. Active gain devices require the use of an external power source. Passive gain is accomplished by focusing the RF signal with the use of an antenna. Antennas are passive devices that do not require an external power source. Instead, the internal workings of an antenna focus the signal more powerfully in one direction than another Avaya Inc. All right reserved 7

LOSS (ATTENUATION) Loss, also known as attenuation, is best described as the decrease of amplitude, or signal strength. A signal may lose strength while on a wire or in the air.

9 LOSS (ATTENUATION) Loss, also known as attenuation, is best described as the decrease of amplitude, or signal strength. A signal may lose strength while on a wire or in the air. On the wired portion of the communications (RF cable), the AC electrical signal will lose strength because of the electrical impedance of coaxial cabling and other components such as connectors. Attenuation is typically not desired; however, on rare occasions an RF engineer may add a hardware attenuator device on the wired side of an RF system to introduce attenuation to remain compliant with power regulations or for capacity design purposes Avaya Inc. All right reserved 9

10 ATTENUATION COMPARISON OF MATERIALS Material Interior wall Cubical Wall Wood Door (Hollow-Solid) Brick/Concrete Wall Hollow Block Wall (School) Glass/Window (non tinted) Double-pane Coated Glass Bullet-proof glass Steel/Fire exit Door 2.4 GHz 3-4 db 2-5 db 3-4 db 6-18 db 4-9 db 2-3 db 13 db 10 db db 5 GHz 3-5 db 4-9 db 6-7 db db 6-12 db 6-8 db 20 db 20 db db 2016 Avaya Inc. All right reserved 10

11 Rule of 3s and 10s For every 3 db of gain (relative), double the absolute power (mw). For every 3 db of loss (relative), halve the absolute power (mw). For every 10 db of gain (relative), multiply the absolute power (mw) by a factor of 10. For every 10 db of loss (relative), divide the absolute power (mw) by a factor of Avaya Inc. All right reserved 11

$diffraction, and so on. Free space path loss (FSPL) is the loss of signal strength caused by the natural broadening of the waves, often referred to as beam divergence.$ RF signal energy spreads over larger areas as the signal travels farther away from an antenna, and as a result, the strength of the signal attenuates. FSPL = 32.

RF signal energy spreads over larger areas as the signal travels farther away from an antenna, and as a result, the strength of the signal attenuates. FSPL = 32.

13 FREE SPACE PATH LOSS Because of the laws of physics, an electromagnetic signal will attenuate as it travels despite the lack of attenuation caused by obstructions, absorption, reflection, diffraction, and so on. Free space path loss (FSPL) is the loss of signal strength caused by the natural broadening of the waves, often referred to as beam divergence. RF signal energy spreads over larger areas as the signal travels farther away from an antenna, and as a result, the strength of the signal attenuates. FSPL = (20log10(f)) + (20log10(D)) FSPL = path loss in db f = frequency in MHz D = distance in kilometers between antennas or An online calculator for FSPL and other RF calculators can be found at Avaya Inc. All right reserved 13

14 LINK BUDGET When deploying radio communications, a link budget is the sum of all gains and losses from the transmitting radio, through the RF medium, to the receiver radio. The purpose of link budget calculations is to guarantee that the final received signal amplitude is above the receiver sensitivity threshold of the receiver radio. Link budget calculations include original transmit gain, passive antenna gain, and active gain from RF amplifiers. All gain must be accounted for, including RF amplifiers and antennas, and all losses must be accounted for, including attenuators, FSPL, and insertion loss. Any hardware device installed in a radio system adds a certain amount of signal attenuation called insertion loss. Cabling is rated for db loss per 100 feet, and connectors typically add about 0.5 db of insertion loss Avaya Inc. All right reserved 14

17 REFLECTION Reflection can be the cause of serious performance problems in a WLAN. As a wave radiates from an antenna, it broadens and disperses. If portions of this wave are reflected, new wave fronts will appear from the reflection points. If these multiple waves all reach the receiver, the multiple reflected signals cause an effect called multipath Avaya Inc. All right reserved Source: The Official CWNA Study Guide 17

SCATTERING Scattering can happen in two ways. The first type of scatter is on a smaller level and has a lesser effect on the signal quality and strength.

18 SCATTERING Scattering can happen in two ways. The first type of scatter is on a smaller level and has a lesser effect on the signal quality and strength. This type of scattering may manifest itself when the RF signal moves through a substance and the individual electromagnetic waves are reflected off the minute particles within the medium. Smog in our atmosphere and sandstorms in the desert can cause this type of scattering. Did you know that the color of the sky is blue because the wavelength of light is smaller than the molecules of the atmosphere? This blue sky phenomenon is known as Rayleigh scattering. The shorter blue wavelength light is absorbed by the gases in the atmosphere and radiated in all directions Avaya Inc. All right reserved 18 Source: The Official CWNA Study Guide

$behavior known as refraction.$ $change. RF refraction most commonly occurs as a result of atmospheric conditions.$

19 REFRACTION In addition to RF signals being absorbed or bounced (via reflection or scattering), if certain conditions exist, an RF signal can actually be bent in a behavior known as refraction. A straightforward definition of refraction is the bending of an RF signal as it passes through a medium with a different density, thus causing the direction of the wave to change. RF refraction most commonly occurs as a result of atmospheric conditions Avaya Inc. All right reserved 19 Source: The Official CWNA Study Guide

$DIFFRACTION Not to be confused with refraction, another RF propagation behavior exists that also bends the RF signal; it is called diffraction.$

20 DIFFRACTION Not to be confused with refraction, another RF propagation behavior exists that also bends the RF signal; it is called diffraction. Diffraction is the bending of an RF signal around an object (whereas refraction, as you recall, is the bending of a signal as it passes through a medium). Diffraction is the bending and the spreading of an RF signal when it encounters an obstruction. The conditions that must be met for diffraction to occur depend entirely on the shape, size, and material of the obstructing object as well as the exact characteristics of the RF signal, such as polarization, phase, and amplitude Avaya Inc. All right reserved 20 Source: The Official CWNA Study Guide

$Because of the natural broadening of the waves, the propagation behaviors of reflection, scattering, diffraction, and refraction will occur differently in dissimilar environments.$

21 MULTIPATH Multipath is a propagation phenomenon that results in two or more paths of a signal arriving at a receiving antenna at the same time or within nanoseconds of each other. Because of the natural broadening of the waves, the propagation behaviors of reflection, scattering, diffraction, and refraction will occur differently in dissimilar environments. A signal may reflect off an object or scatter, refract, or diffract. These propagation behaviors can all result in multiple paths of the same signal. In an indoor environment, reflected signals and echoes can be caused by long hallways, walls, desks, floors, file cabinets, and numerous other obstructions. Indoor environments with large amounts of metal surfaces such as airport hangers, warehouses, and factories are notoriously high multipath environments because of all the reflections Avaya Inc. All right reserved 21 Source: The Official CWNA Study Guide

22 RESULTS OF MULTIPATH Upfade - This is increased signal strength. When the multiple RF signal paths arrive at the receiver at the same time and are in phase or partially out of phase with the primary wave, the result is an increase in signal strength (amplitude). Smaller phase differences of between 0 and 120 degrees will cause upfade. Please understand, however, that the final received signal can never be stronger than the original transmitted signal because of free space path loss. Downfade - This is decreased signal strength. When the multiple RF signal paths arrive at the receiver at the same time and are out of phase with the primary wave, the result is a decrease in signal strength (amplitude). Phase differences of between 121 and 179 degrees will cause downfade. Nulling - This is signal cancellation. When the multiple RF signal paths arrive at the receiver at the same time and are 180 degrees out of phase with the primary wave, the result will be nulling. Nulling is the complete cancellation of the RF signal 2016 Avaya Inc. All right reserved 22 Source: The Official CWNA Study Guide

SPATIAL MULTIPLEXING/SU-MIMO 802.11N/802.11AC WAVE 1 Spatial Multiplexing Source data stream split Sent out over separate antennas at the same time.

23 SPATIAL MULTIPLEXING/SU-MIMO N/802.11AC WAVE 1 Spatial Multiplexing Source data stream split Sent out over separate antennas at the same time. Recombined at receiver using MIMO Signal Processing Doubles or triples the data rate SU-MIMO (aka MIMO) Multiple In Multiple Out Takes advantage of multiple antennas using multi path reflections to improve receiver sensitivity. The extra sensitivity is used for higher data rates and in some cases greater range Avaya Inc. All right reserved 23

26 RECEIVE SIGNAL STRENGTH INDICATOR (RSSI) RSSI is a receivers interpretation of a signal based on the devices receive sensitivity. Receive sensitivity refers to the power level of an RF signal required to be successfully received by the receiver radio. The lower the power level that the receiver can successfully process, the better the receive sensitivity. In WLAN equipment, receive sensitivity is usually defined as a function of network speed. WiFi vendors will usually specify their receive sensitivity thresholds at various data rates. Different speeds use different modulation techniques and encoding methods, and the higher data rates use encoding methods that are more susceptible to corruption TEST WITH THE DEVICES YOU ARE USING AS RSSI WILL VARY DEVICE TO DEVICE. What is good for one device isn t necessary good for another Avaya Inc. All right reserved 26

in the area non 802.11 traffic such as motors, lights, speaker systems, older in-building synchronized clocks, etc.

27 NOISE Noise is unwanted electrical or electromagnetic energy that degrades the quality of signals and data. Noise can be Co-Channel or Adjacent channel interference Bluetooth Cordless phones microwave ovens other wifi networks in the area non traffic such as motors, lights, speaker systems, older in-building synchronized clocks, etc. etc. Minimize all the noise you can and avoid what you can t for a successful wireless deployment Avaya Inc. All right reserved 27

28 Signal to Noise Ratio (SNR) THE RF LINK - SNR Indicates how much useable signal is available Higher data rates require higher SNR values **Maximize your SNR for successful wireless deployments** 2016 Avaya Inc. All right reserved 28

single cell Sensitive to co-channel interference (from other cells on the same channel) If

retards higher data rates Greatly reduces overall network capacity 802.

29 802.11b/g/n Channels Available = CHANNELS - CELL PLANNING Distance between cells on same channel is less than a across a single cell Sensitive to co-channel interference (from other cells on the same channel) If energy is weak, seen as interference If energy is strong, stations will defer Bleed-over retards higher data rates Greatly reduces overall network capacity a/n/ac Channels Available = 25 High Performance: 8 times the capacity Far less interference from cells on same channel More channels to avoid interference 2016 Avaya Inc. All right reserved 29

CHANNEL BONDING/SPECTRUM REUSE Bonding Channels Together Increasing the Bandwidth Bonds two-eight 20MHz channels to a make one larger channel Applies the use of several new

30 CHANNEL BONDING/SPECTRUM REUSE Bonding Channels Together Increasing the Bandwidth Bonds two-eight 20MHz channels to a make one larger channel Applies the use of several new efficiencies Increased bandwidth is only effective if clients need the bandwidth otherwise its possibly making your environment worse Avaya Inc. All right reserved 30

32 KNOW YOUR DEVICES, APPLICATIONS & BANDWIDTH NEEDS Enterprise Education LPVs Plan for 5-10 Mbps per user as a rule of thumb. Plan for 5 Mbps per user as a rule of thumb. Plan for 1-2 Mbps per user as a rule of thumb. Design for 25 users per radio (50 per AP) as a general rule when designing your wireless networks Wireless success in Enterprise is all about understanding the clients needs and bandwidth requirements upfront and not after the network is deployed Application Control can greatly help in identifying and managing the data on your wireless network. Design for users per radio (40-50 per AP) as a general rule when designing your wireless networks Wireless success in K-12 is measured in the 1st 10 minutes and last 5 minutes of class. This is when all machines will be moving the most data at the same time. Application Control can greatly help in identifying and managing the data on your wireless network. Discuss and agree on a take-rate prior to getting too far into the network design Wireless success in LPVs is minimizing your receive sensitivity, covering the right amount of clients based on your take rate, spectrum reuse and SNR. Application Control can greatly help in identifying and managing the data on your wireless network Avaya Inc. All right reserved 32

33 DYNAMIC FREQUENCY SELECTION (DFS) An AP must monitor configured DFS channel for 60 seconds before transmitting any packets. Once an AP is transmitting on a DFS channel and radar is detected then the AP has 10 seconds to change to another channel Once the AP changes channels the AP must stay off the original channel for a minimum of 30 minutes In the US, military and weather radar have mostly moved off the UNII-2 and UNII-2- Extended frequencies Avaya Inc. All right reserved 33

AUTO CHANNEL Auto channel is an algorithm built into your APs that TRIES to select the best channel given the variables it understands at that moment.

34 AUTO CHANNEL Auto channel is an algorithm built into your APs that TRIES to select the best channel given the variables it understands at that moment. Auto channel will work ok for 80% of office environments typically. I don t rely on auto channel however I will use it during deployments as a starting point and manually adjust further Avaya Inc. All right reserved 34

AUTO POWER/CELL The Avaya 9100 takes co-channel and adjacent channel interference into account when selecting power levels A wireless design built for capacity

Personally I don t use auto channel ever.

35 AUTO POWER/CELL The Avaya 9100 takes co-channel and adjacent channel interference into account when selecting power levels A wireless design built for capacity should never have a coverage hole if an AP fails Auto channel is a best guess and doesn t know your devices or user densities like you do. Personally I don t use auto channel ever. I set my power to the lowest device s output power (to avoid asynchronous power problems) and layout my APs with proper overlap from there. This is a proven method for deploying APs and it provides 1 less variable to cause issues long term Avaya Inc. All right reserved 35

37 AP PLACEMENTS Plan for the correct amount of clients per radio. Target 50% overlap. Don t confuse the clients. Make sure there are always 2 signals at a -65 or stronger for servicing clients and load balancing Optimize placements keeping in mind nulls, antenna patterns/orientation and use attenuation to your advantage Wireless success is measured as a system not how fast one client can do a speed test. 1 to 1 is the term used to define a school providing devices for every student. In reality 2+ to 1 is what you need to design your wireless network for regardless of the type of business Avaya Inc. All right reserved 37

HIDDEN NODE In a wireless network, it is likely that the node at the far edge of the access point's range, which is known as A, can see the access point, but it is unlikely that the same node can see

39 HIDDEN NODE In a wireless network, it is likely that the node at the far edge of the access point's range, which is known as A, can see the access point, but it is unlikely that the same node can see a node on the opposite end of the access point's range, C. These nodes are known as hidden. The problem is when nodes A and C start to send packets simultaneously to the access point B. Because the nodes A and C are out of range of each other and so cannot detect a collision while transmitting, Carrier sense multiple access with collision detection (CSMA/CD) does not work, and collisions occur, which then corrupt the data received by the access point Avaya Inc. All right reserved 39

1 AP per classroom APs are spread out further in office areas due to lower density of users AP PLACEMENTS CONT D Multiple APs in large/multipurpose rooms to accommodate higher

40 1 AP per classroom APs are spread out further in office areas due to lower density of users AP PLACEMENTS CONT D Multiple APs in large/multipurpose rooms to accommodate higher density Small cell sizes Wireless engineer attempts to place APs in corners of rooms to optimize spatial multiplexing and to minimize nulls Avaya Inc. All right reserved 40

THE IMPACT OF BEACONS Beacon size: 225 bytes in 11n and around 170 bytes in 11bg Usual beacon data rate in 2.4GHz: 1Mbps Beacon interval: 100ms Used bandwidth: 0.000001 x 225 x 8 x 10 = 0.

42 THE IMPACT OF BEACONS Beacon size: 225 bytes in 11n and around 170 bytes in 11bg Usual beacon data rate in 2.4GHz: 1Mbps Beacon interval: 100ms Used bandwidth: x 225 x 8 x 10 = sec Around 2% of the bandwidth is used If we now have 4 SSIDs configured and we can see 3 radios on the same channel from a particular location that means: 2% x 4 x 3 = 24% 2016 Avaya Inc. All right reserved 42

FRESNEL ZONE The Fresnel zone (pronounced FRUH-nel the s is silent) is an imaginary footballshaped area (American football) that surrounds the path of the visual LOS between two point-to-point

$In addition to the obvious reflection and scattering that can occur if there are obstructions between the two antennas, the RF signal can be diffracted or bent as it passes an obstruction of the$

43 FRESNEL ZONE The Fresnel zone (pronounced FRUH-nel the s is silent) is an imaginary footballshaped area (American football) that surrounds the path of the visual LOS between two point-to-point antennas. If the first Fresnel zone becomes even partly obstructed, the obstruction will negatively influence the integrity of the RF communication. In addition to the obvious reflection and scattering that can occur if there are obstructions between the two antennas, the RF signal can be diffracted or bent as it passes an obstruction of the Fresnel zone. This diffraction of the signal decreases the amount of RF energy that is received by the antenna and may even cause the communications link to fail. Calculator Avaya Inc. All right reserved 43

ITEMS TO REMEMBER WHEN DEPLOYING YOUR SUCCESSFUL 9100 WIRELESS SOLUTION Understand your users, their devices and the applications being used

) and keep APs close to the users. Bond Channels when it s needed not because it s the thing to do.

Do a post site survey to make sure you have proper power set and 50% overlap in all areas.

44 ITEMS TO REMEMBER WHEN DEPLOYING YOUR SUCCESSFUL 9100 WIRELESS SOLUTION Understand your users, their devices and the applications being used to ensure a great wireless experience. Maximize your SNR by lowering your noise (cochannel, adjacent channel, SSIDs, etc.) and keep APs close to the users. Bond Channels when it s needed not because it s the thing to do. Place/Mount APs in the optimal locations to minimize nulls, maximize spatial multiplexing and for optimal antenna orientation. Do a post site survey to make sure you have proper power set and 50% overlap in all areas. When troubleshooting, look at the RF for possible changes in the environment instead of assuming it s always your config or a code issue. If you know what to look for, problem resolution could be minutes instead hours/days or even weeks 2016 Avaya Inc. All right reserved 44

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CSNT 180 Wireless Networking. Chapter 4 Radio Frequency (RF) Fundamentals for Wireless LAN Technology

CSNT 180 Wireless Networking. Chapter 4 Radio Frequency (RF) Fundamentals for Wireless LAN Technology CSNT 180 Wireless Networking Chapter 4 Radio Frequency (RF) Fundamentals for Wireless LAN Technology Norman McEntire norman.mcentire@servin.com Founder, Servin Corporation, http://servin.com Technology