Five Fundamentals of RF You Must Know for WLAN Success

good afternoon and welcome to our webinar on the five fundamentals of RF you must know for wireless LAN success my name is Tom carpenter and I'm the CTO here at CW NP before we get started into the content today let me make sure that you can hear me if you could just either chat in or in the Q&A panel just let me know that you're able to hear me that'll be great and we'll continue on with the presentation excellent thank you for that feedback so we're going to go ahead and get started today with this topic which is a Foundation's topic and it is really targeted at two groups of people those are the people studying for C WTS and or C wna however these foundational concepts are absolutely essential to implementing an effective Wireless LAN if we don't know how RF works we can't make RF work the way we want it to and so it's very important to understand these foundations therefore even if you've been around Wi-Fi for a while I'm sure you'll hear some tips and tricks that will help you better optimize your networks as well now before we get into the technical content of today's presentation I do want to remind you that of course CW NP is all about certifying your knowledge and capabilities in relation to wireless networking this means that we provide different certifications focused on different specialty areas of wireless networking of course we have the CWA the certified wireless network administrator which is the foundation of all of our other professional level certifications and even our expert level certification here you're going to learn about the basics of RF which is partly what we're talking about today you'll learn about Wireless LAN hardware and the basics of planning and implementing a wireless network and then at the professional level there are three certifications the security professional the design professional and the analysis professional and these focus on three very important key areas of wireless lans first of all of course security making sure that our network is secure and only those who should have access do have access and that all of the data is protected from eavesdropping and other attacks and then of course design is about planning and implementing an effective wireless LAN that meets your needs key component there is meeting your needs and that's why one big part of CWD P is needs analysis and then of course the analysis professional is focused on looking at an existing wireless land and finding out how to make it perform better how to resolve different problems that might be happening in the wireless land and so forth so it's really a troubleshooting master class and then once you have your CW NAC WS p CW d p + CW AP if you choose you can apply for the certified wireless network expert the four before it all have an exam associated so you have to pass an exam to gain the certifications with the CW n/a instead of passing an exam you submit an application to the Board of Advisors which is six different CW knees that are going to look at the application evaluated and determine your qualification to become a certified wireless network expert it requires three years of enterprise experience and having passed all four of the other exams mentioned here on the screen so it is an elite certification that nearly a couple hundred people now have and it's certainly one well worth pursuing additionally before we get into the specific topics of today I want to remind you about our Wi-Fi Trek conferences coming up in the next few months first of all we'll be in Prague on June the 8th through the 10th at the Radisson Blu Alcorn hotel very nice location there and we'll be excited to see those of you who can attend that event and then we'll be in New Orleans later in the year September 28th through the 30th at the Hilton Riverside and you can of course find more information at the website at CW NP comm to go directly to the prague registration page go to CW m p comm slash 2016 conference slash prague okay so let's talk about our agenda for today and what we'll be talking about first of all we're going to be looking at our F basics so before we get into the 5rf fundamentals I do want to review some basics with you to make sure you have the terminology down then we'll get into the 5 RF fundamentals which are channels behaviors measurements interference and analysis and we'll look at those one by one our webinar will run until about 1:30 Eastern Standard Time and so we try to keep them to about a half hour to not take too much time out of your day and yet provide you this valuable technical information so first of all RF basics what we need to understand is frequencies waves and radios the frequencies are the specific locations within the RF spectrum that we actually use to transmit our data or to pass signals on the waves of course are the actual medium that we manipulate in order to modulate data and therefore transmit data and then the radios do the transmission so let's talk about this a little bit more first of all when we look at frequencies the two primary frequency bands that we use for 802 11 wireless networks are the 2.4 gigahertz frequency band and the 5 gigahertz frequency band now 2.4 gigahertz many years ago kind of won a battle because of being first to market that is with the original 802 11 standard that came out in 1997 sometimes called 8o 2.11 prime did not specify any operations in 5 gigahertz it only specified operations in 2.4 gigahertz and since that was first these were the devices that existed we then had a rolling effect that has stuck with us to this very day and that is that because 2.4 gigahertz client devices already existed even when a piece came out that could support both 2.4 and 5 gigahertz we still kept supporting 2.4 gigahertz because 2.4 gigahertz clients existed and so therefore we still find ourselves in that space today which is not a good space to be in 2.4 gigahertz is very cluttered some have said in recent months the 2.4 gigahertz is dead this is of course completely untrue how can you say that something that is alive and utilized more than anything else is dead it's not dead but it's certainly crippled its crippled because of the fact that so many devices operate they're not just our wireless networking devices but many other devices as well so 2.4 gigahertz is not an effective band for enterprise wireless lans when we have control over the client devices that are going to be used if we can dictate that 5 gigahertz clients will be used then we want to use 5 gigahertz clients why what we'll see later there are many more channels in 5 gigahertz because we have much more frequency space so the first thing to realize is that the frequencies matter and the frequency is really just how often RF wave cycles per second so how many waves per second are we creating 20 Hertz would be 20 cycles 900 megahertz would be 900 million cycles 2.4 gigahertz is 2.4 billion cycles per second so higher frequency waves have shorter wavelengths and lower frequency waves have longer wavelengths now the other factors the wave itself so the wavelength is an entire 360-degree movement of an RF wave this is 1 Hertz and waves have characteristics that are important like the amplitude of the wave this is the strength or power of the wave how strong is it and the strength or power of the wave attenuates or weakens as it travels through free space and as it passes through materials like walls and doors and floors the period is the distance between two identical points on an RF wave and a phase is really not a feature of a wave but it is the characteristic when two waves are compared with one another that is two waves can be in phase or they can be some degree out of phase when two waves are in phase if they are the same wave they strengthen the signal received when two waves are 180 degrees out of phase they can completely cancel the signals but certainly out of phase waves arriving at a receiver caused a weakening of the signal now how can you have multiple phases of the same signal well you do that because of the RF behaviors we'll talk about later the reflection that causes the signal to move around within a space so that you get multiple copies of the signal at the receiver at slightly different times which means they're slightly out of phase or possibly completely out of phase this is an important thing to consider and it's one thing that we actually take advantage of in our modern wireless lans with 802 11 N and 802 dot 11ac using what is called MIMO multiple-input multiple-output we're actually taking advantage of these phase variations and using it to transmit multiple spatial streams now the last thing I mentioned for RF basics is the radio so the radios are the transmitters and receivers of RF signals the antenna is not actually the transmitter the antenna is the radiator the antenna simply allows the electromagnetic waves to go out of it into free space and propagate but it's not the actual transmitter the transmitter you could say is the entire radio chain the combination of the radio any cables or connectors the antenna all of it together become a transmitter it's also called an intentional radiator now many devices have multiple radio chains so when you see 3 by 3 by 3 that means there are three radio chains and we can send out 3 spatial streams and this is an important thing to consider when you're implementing modern wireless lans so now let's begin talking about the 5 RF fundamentals or the five fundamentals of RF that you have to know for wireless LAN success the first one is channels and we have different channels depending on whether we're in 2.4 gigahertz or 5 gigahertz and we're about to see why I said that 5 gigahertz is so much better for implementing wireless LANs in 2.4 gigahertz you have a total of 14 channels however these 14 channels are spaced only 5 megahertz apart based on their center frequency so you'll notice in the screen that channel 1 centers on 2.4 1 2 gigahertz and channel 2 centers on 2.4 one 7 gigahertz so notice they're only 5 megahertz apart however the channels are 20 megahertz wide for OFDM which would be 802 11 B or rather I'm sorry 802 11 G and 802 1011 a and 5 gigahertz but we're focused on 2.4 years here and also 802 11 n so 802 dot 11 N and 802 11 G use OFDM and they use 20 megahertz channels 802 11 B and the original 802 dot 11 use 22 megahertz channels so the point is that because the channels are 20 or 22 megahertz wide when we actually transmit and they're centered on the center frequency and these numbered channels are only 5 megahertz apart that tells you that you channel one the actual signal itself is going to span channels one two and three and then the side bands the extra energy that is just radiated as we generate signal is going to go even up to four and possibly five depending on the output power this is why we say in 2.4 gigahertz when you only have eleven channels which is all we have in the US and in many other regions of the world you only have three real channels that you can use even though there are 11 we can only use three of them channel 1 channel 6 and channel 11 this is why hopefully in your enterprise wireless LAN on 2.4 gigahertz when you do a scan of the environment you see a lot of ApS on channels 1 channel 6 and channel 11 hopefully you don't see any ApS on channels 2 3 4 5 7 8 9 and 10 sadly in mixed environments particularly in shared spaces like office spaces and things like that where multiple companies are represented you see nearly all of these channels utilize and this causes a lot of what we call adjacent channel interference the channels are stepping on each other because their signals invade the other channel bandwidth so 2.4 gigahertz here's why it is so cluttered we really only have 3 channels and then add onto that all of the many many many devices that are actually they're operating in 2.4 gigahertz now we get to 5 gigahertz things are much improved in 5 gigahertz we have 20 megahertz OFDM channels we have other channel widths as well so you can bond to 20 megahertz channels for 40 megahertz 802 dot 11 n or AC channel you can also have 80 megahertz 802 11 ac channels and 160 megahertz 802 11 ac channels now I don't recommend using 160 megahertz channels even if they're available and when they're available in any enterprise deployment ever 80 megahertz channels are still up for debate in some enterprise deployments based on the fact that it has some dynamic channel capabilities built into 802 11 AC so that it can only use a 40 megahertz channel if that's all that's clear or a 20 megahertz channel if that's all that's clear or conversed it the entire a team a Hertz channel if all clear so there are some capabilities there but because we haven't really been implementing it we don't really see the efficiency gains that it might bring us yet in any practical real-world implementation so at this time we're still generally recommending 20 and 40 megahertz channels 40 megahertz channels for standard data networks that are medium to low density when you get into high density and certainly very high density we want to stick with 20 megahertz channels now we don't really have the depth of time to get into all of the details about channel selection today but just note that many of the five gigahertz channels are what we call DFS channels dynamic frequency selection and what that means is the channels may have to monitor for radar and if they detect radar activity they have to move off channel and so DFS channels if they can be used should be used but you have to make sure you understand your environment and you also have to understand your clients if the vast majority of your clients do not support the DFS channels then there's not a whole lot of reason to take advantage of them but you can always be sure that 36 40 44 48 149 153 157 and 161 are pretty much available everywhere so even if nothing else we automatically know we have eight channels nearly all clients will support those and most clients will also support channels 52 through 64 and some clients will support some of the channels from 100 to 140 now 144 is actually a channel just introduced in 802 11 AC so we don't see full support for it out there yet and just as a note channel 165 we used to refer to that as the is M band channel in the US but it's been integrated to uni 3 now it really doesn't matter on all of our exams today you are no longer tested on terms like uni 1 uni to uni 2 e uni 3 or is M because those are us specific and our exams are global so instead you're just tested on your awareness of the frequencies and the channels that are used and are available now the next thing that is one of the five fundamentals of RF you must know is RF behavior RF as it moves Brewis space has a particular behavior set and and these behavior sets include scattering diffraction reflection refraction and absorption now we don't have to get too fancy enough into all the technicalities of it today you just need to understand these basics and the most important ones we see in doors are reflection and absorption with some refraction and diffraction as well but mostly reflection and absorption is what we think about so reflection is the RF signal reflecting or bouncing off of some kind of reflective material that has a size greater than the wavelength and so we're talking here about metal objects like filing cabinets things like that these can all cause reflection and many other objects cause some level of reflection it's reflectivity factor may be higher or lower but some level of reflection occurs absorption is when technically speaking the RF energy is converted to heat and so what happens is the RF energy converts to heat as it is absorbed and therefore it is lost this is why your microwave oven works ok you close the door you start it up and all of a sudden 2.4 gigahertz radio waves are blasted into the microwave oven these radio waves are absorbed very well by water and so the absorption is the converting of the electromagnetic waves into heat and the end result is that your liquid heats up or anything that has moisture in it that's in the microwave think about it like this have you ever noticed that you can take a glass of water sit it outside and if the light waves pass through the glass it will actually heat up the water more than just contacting water directly well this is in part because of absorption and refraction behaviors now refraction is where the RF wave bends as it moves through a material so it's going to change slightly in the example I like to use with this is take a clear glass put some water in it and take a butter knife place it in the glass and look at it from the side it will appear to you that the knife breaks in two at the point of the water and so you'll see the part of the knife that is in the water appears to be in a different location than where it really entered the water there's this kind of illusion that occurs that's because the light waves are refracting as they pass through the water and so refraction can also occur slightly changing the path of an RF wave and of course some absorption as well diffraction is how an RF wave may move around a large object in sometimes change direction and then scattering is when an RF wave hits something a little different than reflection that is smaller than the wave and breaks it up and sends it in multiple directions it's really many many reflections of the RF wave so why are these behaviors important well they're the reason that when you put an ap in a room in a building those radio frequency waves can get to nearly every place in the room and also other rooms because they're reflecting around as they move throughout the space and of course they're passing through some materials as well now the interesting thing is that this can be bad for old type of networks like 11 B G and 11 a but it can be very good for new networks like 11 and 11 AC because these multiple signals give us this reflectivity that allows us to have multiple spatial streams separation of data based on phases and other factors so RF behaviors key to understand the next of the five fundamentals of RF you must know the third is RF measurements so we need to know how we look at an RF signal measure it and understand how strong it is now we can measure RF signals in absolute and relative units we'll talk about absolute first milliwatts is a common measurement in milliwatt is one one thousandth of a what so if we say we have a 1000 milliwatts signal then that means we have a 1 watt signal okay usually we're looking at milliwatts in indoor wireless lans at a range somewhere between 5 and 50 milliwatts of output power so these are the actual power levels in milliwatts now the issue is that we don't use really very high output power levels but we do use very low output power levels or at least very low received power levels and because of that it's good to have another absolute measurement and that is what we call DBM decibels to milliwatts now a decibel itself is a relative measurement a DB that's a relative measurement but DBM is an absolute measurement because it's a decibel relative to milliwatts 0 DBM equals 1 milliwatt so when we talk about negative DBM values we're not talking about something like we have negative power we have less than some power no we're not saying we have less than some power we're saying we have a certain amount less than 1 milliwatt we always have something positive so our power received at the antenna is always positive but it's somewhere between zero and one milla one well that range can go to many many decimal places so rather than saying point 0 0 0 0 0 0 0 0 0 0 37 milliwatts we would instead use a DBM value so for example notice that when we look at negative 40 DBM we're talking about 100 nano watts so obviously we don't want to have to do all of the decimal places to get to that point so you'll see these DBM values in tools when you look at RF signal strength it'll tell you the power level in DBM in many cases and the reason it's doing that is to avoid having to put some field of dot 0 0 0 0 0 and who knows who would understand it anyway so it makes it more human-friendly when we're dealing with power levels now we also have relative power levels and I'll talk about that in a moment but first some terms RF measurements we have this term called RSSI it stands for received signal strength indicator and it can be a bit complex because technically according to the 802 dot 11 standard it's a value that different vendors end up specifying differently and many tools today don't even say our SSR RSSI they'll just say signal strength or something like that and oftentimes they're reporting it in DBM instead of reporting it as some arbitrary value so our SSI has kind of evolved over time and today people will use the term in direct exchange for DBM but technically according to the standard our SSI is not equal to DBM and DBM is not equal to our SSI but you'll see them used interchangeably a lot when people are talking about signal strength probably the better term to use is more generic signal strength rather than saying our SSI if you're going to equate it to DBM directly or you need some way to map what an RSSI is to a DBM so sometimes the common vernacular can get a bit confusing out there but for now just know that our SSI is a factor of your signal strength and signal strength is often reported in DBM these days the noise floor is just the signal strength of the RF noise in the frequency space that you're using within that environment usually we're looking at somewhere between neg 2 neg 103 or 104 DBM and that would be your noise floor the difference between the received signal strength and the noise floor is what we call SNR and we represent it in decibels DB so if the noise floor for example is negging is neg 70 DBM then that means your SNR is 25 DB not DBM it's 25 dB there's 25 decibels difference between the signal and the noise floor okay so we want to use the right term DBM the signal strength DBM the noise floor but SNR is just dB okay so this is a relative value because it's the difference between two absolute values so it's going to change depending on what the two absolute values are now we also have a little chart here for you 1 milliwatt equals 0 DBM 10 milliwatts 10 DBM 100 milliwatt equals 20 DBM and one water 1000 milliwatts equals 30 DBM these can be some good starting points to memorize because many times when you're doing RF math calculations you can go ahead and jump to a number you already know and then go from there so for example if you already know that 20 DBM is 100 milliwatts and you're trying to figure out well then what would 23 DBM be well if you already know what 20 DBM is you don't have to start with 0 DBM as one milliwatts because normally if you're going to try to figure out what is 23 DBM you could use the rules of tens and threes that I'm going to talk about momentarily and calculated but you first have to do 10 then another 10 then a 3 but if you already know 20 DBM is 100 milliwatts then all you have to do is add 3 DB and that's going to double it so it'll be 200 Watts let me talk to you about that here in the screen notice where it says gain and loss examples when we're talking about the rules of tens and threes what we mean is that if you add 3 DB of power you double the power if you subtract 3 DB of power you have the power so this is the 3 rule so if I have 50 milliwatts and I add 3 DB of gain I now have 100 milliwatts but if I have 50 milliwatts and I lose 3 DB or I have 3 DB of loss now I have 25 milliwatts ok so the 3 rule add 3 multiplied by 2 subtract 3 divided by 2 then there's the 10 rule if you add 10 DB of power the signal strength is 10 times stronger if you subtract 10 DB the signal strength is one-tenth or 10 percent so let's go back to our 50 example 50 milliwatts + 10 DB is 500 milliwatts 50 milliwatts minus 10 DB is 5 milliwatts okay so these rules of tens and threes can be used to calculate your power levels and we're not going to get into complex examples today but I want to make sure that that's introduced and understood here so again going back to our example of I need to know what 23 DBM really is in milliwatts if I already know 20 DBM is 100 milliwatts then all I have to do is add 3 DB right and when I add 3 DB what do I do I double it therefore what we have is that our 100 milliwatts becomes 200 milliwatts now the fourth RF fundamental or of the five fundamentals you need to know for wire design success is that interference is real RF interference occurs when an external modulated or unmodulated influence affects the ability of an RF receiver to interpret a data signal this is important because higher data rates use more complex waveforms and because they're more complex it's more susceptible to error so we see here on the screen an example of a constellation chart it's called 464 km and that's quadrature amplitude modulation now this is not even the highest data rate modulation we have 256 km now in 802 11 AC and we're going to go higher in the future so the point is that the higher modulation data rates use more complex waveforms and the result is we need a very good signal then to be able to process that waveform and that's why RF interference can become a key factor in getting good data rates low signal strength and external RF interference sources are problematic now it's important to know RF interference happens at the receiver it doesn't happen at the transmitter or in between the transmitter and receiver that is to say if I'm sending a signal on channel 1 and 2.4 gigahertz to a receiver that's 200 meters away and in the middle there's another network on 2.4 gigahertz but it has very weak signal strength that network is not going to interfere with my signal it's going to go right on ahead and pass through so the point is that interference happens at the receiver and that's where you need to look for it now low duty cycle interference can often be tolerated low duty cycle interference means the interference is not existing say 40 50 60 70 percent of the time on the medium it just comes up maybe 5 to 20 percent of the time in these cases you may still be able to communicate but you're going to find your retry rate will probably go up for your 802 dot 11 devices high duty cycle interference can wreak havoc on a channel there are some devices out there that have a near 100 percent duty cycle particular some of the 802 11 channel video devices they're not really 802 11 but they use the 802 thousand channels and they can have very high utilization we're seeing several of these now come in the five gigahertz range as well so it's important to understand interference and then the fifth of the five fundamentals of RF you must know for wireless LAN success is analysis so all this other stuff we've talked about channels RF interference RF measurements all of these things we need to understand how do we look at it how do we analyze it and see what's going on in our environment well the answer to that at the pure RF level is something called spectrum analysis with spectrum analysis or spectrum analyzer we can actually capture the RF energy and represent it in a lot of different ways on the screen here you can see the meta geek channel Iser and the Y spy DB x adapter that's used with it and you can see air magnet spectrum expert and the spectrum adapter that's used with that these are two very popular tools today because they're still updated and maintained and you can still buy the devices to do the spectrum analysis and they operate of course in 2.4 and 5 gigahertz so what they'll do is they'll show you the frequencies in fast Fourier transform mode which is where I like to say it like this think of it as if the waveform is coming right at you and you're looking at the individual frequencies and what's being modulated on them and then you can also see things like swept spectrogram and these types of views that are going to show you the RF energy over time and visual representations usually using color to represent the strength of the signal so if you're having what you think might be interference problems because of high retry rates or something like that a spectrum analyzer will show you devices that are not 802 11 whereas a protocol analyzer is only going to show you 802 11 frames with a spectrum analyzer you can see video devices you can see cameras you can see phones you can see microwave oven interference you can see motor interference anything like this that might be radiated in the environment and you can also use them to move around until you find the signal is at its strongest to find the area where the actual radiator exists so RF analysis is key of course we talked about it in C wna but it's a key factor in CWAP as well okay so we're gonna have some time here for any questions that you might have here at the end of the presentation and if you do not have questions let me just say to you thank you for attending and hope to see you on a future webinar or at one of our conferences coming up either in June or September

Channel: CWNPTV

Views: 253,951

Keywords: cwnp, wifi, 802.11, wireless, wlan, RF, radio frequency, channels, interference

Id: dwDRAqfA7GI

Length: 31min 31sec (1891 seconds)

Published: Thu Mar 17 2016