Lecture 15: WRAN And WiMAX

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  • May 7, 2021
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Talha Ibn Aziz – Lecturer at Department of CSE, IUT

Hello everyone so this is the 15th lecture and probably this will be the last lecture where we learn protocols and in the next lecture we’ll be learning about more specifics for example like congestion control and routing metrics and so on so the topic for today’s lecture are two specific protocols uh which are pretty well known and one is wireless regional area network and other is ymax okay so let’s see what uh the contents are so the protocol for uh w ran our wireless regional area network is 802.22 so what it does is it uses frequencies from the television frequency bands which are not used locally so there is obviously a frequency band allocated for every wireless application and uh televisions also have frequency bands uh which of uh and all of which are not used okay so there are spaces in that spectrum which are unused those are called the white spaces of tv or television spectrum so uh i 802.22 uses cognitive radio techniques to provide network facilities to hard to reach rural and low population areas okay so what special about it is in rural and low population areas and places where uh high internet speed is difficult to achieve uh those places you usually have some unused frequency bands especially in case of television okay so uh they do not use or they rarely use the full capacity of the frequency bands for television as a result those are unused so cognitive radio techniques are used to actually detect those and transmit using those gaps in the frequency so cr is a technique or cognitive radius technique dynamically i use available frequencies as i’ve already said so the advantages are it provides congestion free and interference free connections because uh those wire spaces are not used by anyone else and there is no cost usually there is a cost of buying or you know using a dedicated spectrum but as it’s already using a spectrum for television uh the spectrum is already bought for television so the spaces can be used without any cost so this protocol was finalized in 2011 okay so why is uh it easy to use compared to let’s say other radio waves which might also be used to reach those hard to reach places right so we’re going to see that now so uh what is cognitive sensing so wran is found by two things the first one is base stations or bs which is sort of like a tower that you all usually see in wide area networks for example you know uh the cells have base stations right so this these base stations are similar to that and the other is customer premises equipment or cpe okay so these cp can be compared to the mobile station so just like a wider network where the mobile stations uh use the or connect to the network using the base station here the cp is connect to the base station in a similar way okay so it’s a wireless connection so the base station controls all the cps attached to it and it allocates uh you know communication slots accordingly but in this case the cps also have some uh job to do okay so cognitive sensing is performed by the bss but with the help of cpes so cpe sends the spectrum in their location okay so they find the white spaces uh where it is not being used okay so those spectrum or those spaces are detected by the cpes and they report this information periodically to the base stations okay so once the base stations get the information or uh the periodic reports from the cpes about what they’re sensing then the base stations have an idea of which frequencies they can use to communicate with the cps okay so using those frequencies the base stations uh keep transmitting for example let’s say it selects a frequency bandwidth and it keeps transmitting in that bandwidth unless it gets a report which states that someone else is using that frequency in that case it switches over to another white space or another free space okay so this information is collected from the cps and from the reports so this is an example of uh uh example figure so you can see uh these okay let me just turn on the uh what what is it called the laser so what you can see here these are the uh base stations okay and these homes okay so you can consider that all these homes contain uh cpes okay or any devices which may contain uh cognitive radio sensing okay so this figure i have actually collected it from a very recent paper so this is just the reference of the figure so you don’t have to you know study details about this paper it’s just a reference so based on cognitive radio technology the wran mclare has been built because this is the main thing that we need so without cognitive radio technology it will be difficult or it will be actually impossible to implement this technology because or this protocol because what this protocol does is it uses the unused spectrum okay so without any way to sense those spectrums there is no use of you know using this protocol so that the cognitive radio technology allows uh sensing that the medium um without you know much uh battery usage okay so it consists of two structures uh the w rand mech layer one is the frame and is the super frame so each super frame is actually built of many frames and super frame also has a preamble so super frame contains frames and preamble so so each super film also has a control header which is called a super frame control header or sch okay so bs or the base station sends super frames to every possible channel uh which are free actually uh while avoiding interference by using the cpu readings just as i have told you before so it communicates using all the free channels and whenever it receives a report that okay this channel is being used and again a new channel is free then it shifts from that channel to the new one okay so this is how actually it controls which channels are being used so cpu performs uh spectrum measurement as i have said because without measuring the spectrum they will not be able to understand uh which parts of the spectrum are free and according to that they cannot send the report so they uh measure the spectrum in two ways one is in band and one is outband so in band means con inband consists of sensing actual channel that is being used so that means uh sensing the channel which is currently being used by the base station to communicate with the cpe okay and outband means uh consists of sensing the rest of the channels okay so if you are you know uh checking the inbent channel that means you are checking for information that is being sent to you and on at the same on the same hand you have to also check whether uh that frequency is being used by someone else or not so whenever someone else is transmitting then you have to notify uh or give the report to the base station so this is inband and in case of outband that means you are actually keeping track of the channels which are not uh being used by the base stations okay so if one of those channels are free again then that free channel can be used by the base station right so that is when the report will contain the information and will be sent to the base station so these are the two types of uh spectrum measurement and the macular also performs two types of sensing so this means this is different of from spectrum management so there are two types of sensing fast sensing and fine sensing so both of these can be used in in-band or outband so basically there can be four types of you know spectrum management if you consider sensing so in in-band there can be fast sensing and fine sensing and in outbound also there can be fast sensing and fine sensing okay so what are these two things fast sensing and fine sensing so fast sensing means uh you the when the cp only tries to detect whether the channel is free or not very quickly and it requires about let’s say one um per channel so if you want to check for 25 channels it requires only about 25 milliseconds okay so this is just to do a quick uh let’s say overview of what which channels are free and then that is uh sent to the base station okay afterwards if the base station wants to specifically check a channel whether that can be uh you know transferred to or that can be used or not then it asks for a fine sensing so fine sensing is a much more thorough sensing but comparatively it’s slower so it’s actually 25 times slower approximately because it requires 25 milliseconds per channel to you know check whether that channel is being used or not so the bs can decide or the base station can decide which sensing to use but usually fine sensing is used after fast sensing so after fast sensing is used and when you know which channels might be free then fine sensing is used to properly you know understand the details of the channel the frequencies and everything so sensing and wn transmissions are performed simultaneously that means the base stations and the cpu together perform these two things at the same time so that means they are checking whether the other channels are free or not or whether the current channel is being used by someone else or not so they’re doing this thing and they’re also communicating or using the internet at the same time so without wren transmission so without communicating uh then there is no use of sensing right the main reason for sensing and finding white spaces is so that you can use the internet or you can use that bandwidth to communicate so this is how wran works so there are many applications of wran the first thing is it provides cost effective and rural broadband okay so what does it mean it means that it is very cost effective especially in in rural areas because the the bandwidth is much unused in those areas and also they do not have much resources to buy expensive materials so adapter and applications can be used in the in that scenario so that it provides a very uh cost effective solution okay and another is the second uh so application is uh there are many un used uh frequency bands so which actually reduces the overall efficiency efficiency so whenever you have a spectrum of frequency bands it’s best if all of it is being used but as in rural areas much of it much of it is not being used so wn applications can actually solve the problem of of unusually utilized spectrum by you using those uh unused white spaces for communication so advantages of tv white spaces are so here we we’re going to see why we can use this to actually reach far away places so the frequency or the signal is three to five times better compared to microwave in terms of coverage so it means that they are broader so whenever you use uh let’s say microwave uh they travel in a specific direction but in case of uh tv white spaces or television spectrum uh the coverage is broader that means you can reach a larger area or you can cover a larger area and then again the range is also higher compared to microwaves so it has both uh facilities or it has both advantages that can cover a larger area and it can go further okay so this is the solution which uh which which can be provided when you are talking about rural places because they are usually far away from the towers or base stations okay so if we are using uh tv white spaces then we can go uh three times or five times the signals can travel three to five times more compared to the regular microwaves so the cost is also reduced because uh there is need of fewer access points so if the range is higher that means you need less access points to cover the same area so this also reduces the cost and uh the use of clean spectrum at no cost because you’re not buying any spectrum uh you’re using on an already existing spectrum and it is free of cost and it’s also very clean way so these three are the advantages of tv white spaces or using tv white spaces okay so they can be used in developed areas as well not only in rural areas for example they can be used for environment or critical infrastructure monitoring because in those areas as well uh for example in let’s say environment where there is less technology or maybe forests or maybe infrastructure which is currently being built so in those areas also there are frequencies unused and can also be used in border protection and providing emergency broadband okay so these are all places where there is unused spectrum which can be put to good use okay so that was eight zero two point two two so the second one that we’re going to learn in this lecture is i triple eight zero two point one six so this family of standards is officially called wireless man or wireless metropolitan area network and the commercial name for this one is very well known which is ymax so this name was coined by the ymax forum industry alliance and the full form of ymx is worldwide interoperability for microwave access okay so the original standard was published in 2001 and was called or it is still called fixed y max because that that has not changed but a lot of other changes have been uh uh incorporated into the standard and eventually it was deployed in 2005. the version was 802.16e 2005 amendment version okay so after even after that a lot of uh let’s say standards were proposed or amendments were done but that was the uh first large-scale deployment so the protocol or this specific protocol standardizes the physical and mac layer just like the previous uh protocols that we learned this protocol also you know works with the last and the second last layer that means the physical and the mac layer so the macula is actually part of the data link layer so it works with the part of the data link layer and the physical layer the protocol mainly deals with providing far end wireless broadband access okay so that means it tries to provide internet to far away places where you know usually a wireless network does not reach and usually cables or wired connections are used so it is let’s say alternative of cable and dsl okay and it is also let’s say last mile use okay or last mile means uh the end users so cable and dsl is used to provide internet to the end users that means the the normal people at homes at residences at universities okay things like that so this y max also works as a alternative 2k cable and dsl in that respect so 80 2.16 describes a few convergence layers for wireline technologies okay so what are wireline technologies ethernet then atm okay so these are examples of wireline technologies that means they use wired connection uh to provide internet or network facilities so uh what is your 2.16e does it provides a few convergence layer which encapsulates all those wireless technologies so that they can also be used in sorry wire line technology so that they can also be used in wireless medium okay so that’s how wimax can cover a lot of other protocols or uh the facilities of those protocols so it is a connection oriented technology so what does connection oriented technology mean connection or into technology means the the subscriber needs a permission from the base station to use the channel or to communicate with the base station okay so even in this scenario in wi-max also there is a tower uh or the base station which allocates a channel to the subscriber station so the subscriber station can again be compared to uh the mobile uh mobile station of wide area network and as the channel is allocated specifically to a subscriber station without the providing this channel the subscriber station cannot use that medium as a result it provides a quality of service because the slots are fixed and the slots are given in a centralized manner okay so ymax is based on the ieee 802.16 standard which is why it is unofficially also called ymax and another import import information here is wireless man or wireless metropolitan area network has an advanced version and lt also has an advanced version so these uh these two uh competed with each other for application in 4g but now as you know lte is being used okay so this is just to show how much importance uh ymax or wireless man has or how much improved it is or how much usability it has so these are the ymax applications so portable a mobile broadband across cities and countries okay so this time is this point is very important so providing broadband wirelessly was a difficult issue before even providing to wired was uh is uh quite recent so now it can be provided across cities and countries that means the range has been increased by a lot so this is one application of ymax and the names kind of suggests that also right uh even even without the you know a full form the abbreviation suggests that it has maximum capability compared to wi-fi okay so y max is even though the architecture looks similar to mobile or wide area networks it is actually much more similar to wi-fi hence the name uh ymx also uh you know corresponds to that okay so it’s an alternative to wired last mile access like dsl and cable i’ve already said what last smile access means it means the let’s say the technology which are used to reach the end users and next is it provides data telecommunication and iptv services okay so data means the regular internet that we use to you know connect and telecommunication means you know audio connection that means when you want to communicate with someone uh using the internet that is called the voice over internet protocol so it also provides the telecommunications facilities and the iptv services this is the internet protocol television services okay so all these three services are provided over the internet but there are different kinds of services and other applications include smart grids and metering okay so these are let’s say uh electronic or electric applications smart kids are smart applications which allow let’s say controlling of energy and providing of energy uh resources and metering is you know measuring that energy even meters are present in some homes okay so wi-max applications also use are also used to connect smart grids and metering applications so that was it about this uh lecture and it was a very short lecture so i have not you know gone into details about it and most of the information i’ve collected from wikipedia and some from papers so if you have any questions regarding this please feel free to ask and with this i’m going to end the lecture for today assalamu alaikum everyone


Lecture 14: WSN MAC Part 2

Lecture 16: Routing Metrics

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