Wireless for communications and this is what we're mostly interested in here. We have many many options and frequencies available we have many technologies we have wi-fi we have cellular mobile connect using satellite connection for wireless communications different frequency bands different standards how would we make the decision what to choose one is the range that we want how far is that while the signal is supposed to go what is the power consumption we can allow do we have stable power do we need to run on solar panels or wind turbines maybe next what is the bandwidth we are wanting to provide what is the requirements in terms of how much data i'm sending through this often the most important is my budget the cost of this how much can i spend on this for community networks and for campus network most of the time wi-fi will be our choice and why is this one very important reason is the spectrum considerations wi-fi uses something which is called ism frequencies industrial scientific and medical these are frequencies that are free for use in most places on this planet they are license exempt as a term we're using you don't have to apply for a license you don't have to buy a license this might still mean that you have to ask somebody for permission to do this depending on where you are but in general you don't have to pay to use a license and that's a main diff difference to cellular networks where it's frequencies that some companies bought in a typically in an auction and that they bought the right to use for so that is one reason why wi-fi wireless is so attractive to us not all spectrum is equal in terms of ownership and wi-fi is in the parts of the spectrum that are free to use wi-fi standards there are many of them they go at the time of this talk back a little bit more than 20 years in the beginning we used the terms 802 11 b a g and these were the three first ones historically the ones i just named b a g they're all part of the 802 11 standard a general wireless networking standard and they then came in as substandards b the first then a and g over time n a c a x and then just a couple of years ago somebody had the bright idea to make things a little bit easier and give them names that are more like what they're doing in mobile networks 3g 4g 5g let's give them numbers let's call them y5456 now that makes it a little bit easier maybe wi-fi 4 corresponds to to 11n 5 to ac 6 to ax the earlier ones didn't get an official name but we in officially call them wifi 1 2 and 3. and then immediately it got complicated again because just last year we opened 6 gigahertz as an additional ism frequency at least currently in some countries other countries are still on their way and then unluckily six gigahertz wasn't included in wi-fi six that would have been nice if those had matched so we now have wi-fi 6e which means wi-fi 6 with 6 gigahertz added so the attempt to make things simpler and immediately got kind of complicated again the main differences we are interested in here most of the time we're asking for speed now the way different wi-fi standards over time have reached faster speeds is mainly by doing three things one is channel access the modulation the way in which data is modulated into the carrier wave the way we get data into that frequency you could say there's different ways of doing that you might spread out evenly direct spread shad spectrum you might put it on different sub frequencies you might have hopping like using different frequencies over different times there's many certain ways these have improved over time and this is one contribution to higher data throughput another one is the mere bandwidth of the channels available we have made the bands within each frequency wider and wider and we've added more of them and then lastly we've worked with something called mimo multiple in multiple out that means instead of just having one or two antennas you have 4 8 16 you do multiplexing you could say multiple in multiple out with that speeds have gone from a few megabits per second in the early days to currently with wi-fi six something that reaches the gigabit per second class with a theoretical limit of around 10 gigabit per second i'm saying theoretical because that's not something you see on an end user device also remember protocols have an overhead when we're saying something has let's say the the oldest standard 802 11b we had 11 megabits per second but only five of that five and a little bit were available for data the rest is protocol overhead so this is the rough overview let me quickly get back to the question of data throughput and speed so yes most of the time we're asking how fast is it how much can we do already at this point though comment do i always have to go for the latest and fastest because it's funny the the second question that typically comes when building wireless networks is how can i limit people's usage of data how can i limit bandwidth so the two is sort of a bit funny together a we want a lot of speed and then we're asking how to limit that speed sometimes the latest and fastest and most expensive isn't the best choice.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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