Welcome back to the Cyber Underground. I'm your host Dave Stevens. I am the Cyber Guy. Welcome back. I've missed you. We had a break. Had to come back. December's a busy month. With me here today, president of the ISC Two Chapter in Hawaii, Jeff Milford. Thank you. Welcome, sir, my co-host today. Thanks for having me. We're going to be talking about all kinds of stuff. Let's get started with the title of the show, North Korea. North Korea. Again. Our favorite bad actor. That's true. We call these the people on the internet that do wrong things bad actors. Yeah, people on the network that you're always looking for to try to stop. North Korea's one of our favorites. Why? Because they have unlimited time and unlimited resources to do whatever they want. Yeah. Don't feed the citizens. Spend money on training bad actors. Exactly. And then you can... Because there's profit in that. And you can get Bitcoin. Yes. So they... My God. The stuff they do... Now, the reason I bring this up is because we get the warnings all the time from the U.S. Cybersecurity Emergency Response Team, my computer emergency response readiness team. Sorry, SIRT. And InfraGuard locally gives us these warnings. And one of the ones that came out with a new North Korea attack.  I don't know what camera to put to. Where am I pointing to? North Korea is known as Hidden Cobra to our intelligence community. So North Korea, Hidden Cobra came out with Bankshot, which is... It's hard to explain. You want to help me try to explain to our audience what an interproxy advanced persistent threat is? It uses obfuscation. So you have a network, right?  And you click on something and it installs a proxy. A proxy somewhere on your network, you know nothing about that has a passage in from the outside and usually has a passage to the outside from the inside. So it's a pivot point, but through your network. So they're using that proxy to obfuscate themselves or hide themselves from illegal activity as they exit your network. They're using you as the fingerprints in the crime. And they don't just do it once. They do it multiple times. And every time they go from network to network from proxy to proxy, that's one hop, a network hop. And there might be some other routers and switches in between. So those are all hops. But the more hops you get between the criminal and the crime, the harder it is to find forensically the criminal. And they're trying this. This is what's called bank shot. And it's also called an advanced persistent threat. Why don't you walk us through an advanced persistent threat and APT? Complex topic. Long live threats that are very, very difficult to find. And the bad actors have been upping their games.  And nowadays they're getting a lot more sophisticated. They're finding different ways to exfiltrate data. They're using Dropbox at times. I think I heard that they were using LinkedIn as a place where they could go to pick up the data that was exfiltrated by the malware that was written. The creativity is just absolutely amazing. And I wouldn't say we're defenseless for companies, not as, but for the people on the street. And granted, they're not typically targets of bad actors, advanced persistent threats. They're more the target of criminals and whatnot. But one of the things I've been thinking about with North Korea is, when are we going to strike back? Because at a certain point, you can't allow this to continue happening. So do we know that we have like an army? Do we know that we haven't though? It's not like the US would attack and tell us, Hey, guess what? We just attacked them. We don't we're not going to admit to what we do or do not have. Right. So we could be have that ability to be doing that now. Stuxnet. Stuxnet. Yeah. But that was we were we explain that to the audience because they might not be up on Stuxnet. Stuxnet was supposedly written by the Israelis. We had a hand in accomplishing the goal. But it went into, I can't remember Iran, the centrifuges on Iran's nuclear plant. And it spun them up so that they all blew up. Right. It spun them too fast. Right. Right. Unfortunately, it got into the wild, which is always a problem with these these things. You cannot control them. They jump from network to network. And Stuxnet caused some some difficulties for other people. You bring up a really good point. So when we're talking about just, you know, biomed, right, people want to know how to cure diseases. So they keep copies of the diseases samples, right in secure areas. So let's talk about, you know, anthrax, right, which just happened to accidentally get mailed to a lab that didn't order it a few years ago. So a virulent copy of this this anthrax went to a lab that said, Why are you sending us anthrax? Yeah, we're not equipped for anthrax. And that's a problem, right? So the same thing happens when we stockpile these viruses and these tools and pieces of malware that have been created. People break in the NSA tools, right? And they get posted by other bad actors on the internet. And then those tools get sold. And they can use they can be used for first strike weapons against anybody, not just companies and people, but countries. And so Stuxnet Stuxnet I think showed us that a piece of computer malware can get into a motorized device of PLC programmer, logic circuit or circuit logic, and, and also SCADA controls, right, which, which control things like hydraulics and doors and all the things that robots can do. And when malware power stations and power stations and water supplies and water supplies, right? And when when you talk about being able to knock out things like that with viruses, kind of scary. You know, we as humans, I think are inherently lazy. And we want everything done for us. So we will work all day and night to automate something. And to automate something, we also want to work from home. So we put it all on the internet. And now we've kind of made our bed and we have to sleep in it. And North Korea knows that. And other bad actors who I won't name right now, also know that.  So the way they get money is they go out and they steal it. And the internet is a perfect way to do this. So the last suspect we had was the Swift Network on between banks, right, how they move money back and forth. The latest theory from our intelligence communities that North Korea hacked that stuck, or stuck Swift and and made it so they took a few pennies out of every transaction. And they had planned on getting almost a trillion dollars, but they only got 80 billion before the whole thing was shut down. That's still a lot of money. That's a lot of coin for countries is not getting much money. And all of a sudden they got all this money. Coincidentally, right after that, they started making really good missiles, really good missiles and supposedly some payloads for them. Yeah, that makes me nervous. A little bit. Yeah, because our anti missile system, I think is only 50% accurate. I heard 25, one out of four. Really? So I got to flip the coin twice and pray. And wow, okay, well, thank goodness Hawaii is a little blip in the middle of the Pacific. And sorry, mainland. My wife, you're the target asking what we're going to do. If a missile comes in, and we keep a bottle of champagne in the refrigerator, pop open the champagne, go out to the forge, enjoy the sunrise, whatever's going on yet. Because really, you're on an island. Sorry to say. Yeah, very well defended island. True from most conventional attacks, not a missile. I don't think that's going to be the first the warfare though. I mean, everyone's talking about cyber war. Yeah. And truly, it could be happening right now, we could not know it. You know, it could happen because of these advanced persistent threats. The worst ones are, of course, they enter your network, they place something there that they can use later. It's completely innocuous to your sensors. So you don't pick it up until the time they activate it, and it goes to work for you. It's like a sleeper agent in all those old spy movies, right? They just sit there waiting for you or scanning your network. Yeah, to get the call. Like, Charles Bronson gives you a call, right? Right, right. Oh, that was great. You were now active. Destroyed. And you can use multiple networks together to perform something. So people like you and I, who do security were constantly scanning for what they call the signatures of these advanced. Signatures and the behaviors. Right, both port access. Signatures often are a reactive way to deal with things, because first somebody has to write the first somebody has to identify the threat, and find a way to usually hash a numerical. Let's explain that. That's a really good one. So we take like an exe file, the executable file that we know is malware, and we run an algorithm against it. And the result of that algorithm is called a hash, which is a numerical sequence of like 256 bytes. But it's unique to that particular executable file. So we can scan our network and do a hash algorithm against every single file we encounter with an exe on it. And if we match those two hashes, we know that is an advanced persistent threat, we can block it, we can destroy it, we can isolate it, right. But that's like you said, it's reactive, we have to know it's out there first, then create the signature for a for a company with intrusion detection systems and things like that, you have to subscribe to the feeds, so that you get that intelligence, the threat intelligence described that for us for audience again. So there are companies that are actively pursuing these threats and identifying them and creating the hashes and then pushing them out, you subscribe to a feed, pushing them out to companies, you import them into your appliances, your devices. And they then use those and those are still reactive, but they're usually pretty current. They're much better than what I want to say better than antivirus. Some companies are pretty good about that. But the whole thing is if somebody in England gets it, and you're on the network and you get the feed, you're ready for that signature before it hits your network. So it's better than nothing. Oh, it's way better than prevent what they call a zero day, which is the first time an attack happens and no one's seen it before and no one's been able to identify. It's never been reported, never been never reported. So this is not a zero day prevention, but it's better than nothing. And most of our systems, if you subscribe to their feed like Cisco, it's automatic, it's applied, right? And so the very next sweep that signatures added to that sweep, so you're checking again. Usually that doesn't even slow down your network. No, yeah, it allows traffic to continue while it sweeps constantly. These kind of automated systems save our bacon. Yeah, I've been working with with them a lot at this, the new job. And it all goes back to the defense in depth. You cannot depend on any one device you need multiple ones. It's like at home, I can use my anti virus, but I also have a malware program. And there are some things that one program finds that the other doesn't. And that's why you have security and layers defense in depth. So you have your perimeter fencing, you've got your front door with a lock, you've got door inside, you got Graham upstairs with a shotgun. Everybody's playing a part. And if you get through one layer, there's another layer waiting for you, right? And sometimes that doesn't prevent the attack. But is it deterrent? Yeah, it depends on how badly they want. It's like a thief breaking into your house. If you have lights on a dog nearby, the doors are all locked. They're going to move on to an easier target, typically. Yeah, your neighbor who's on vacation at the garage door, looking at all the newspapers on the porch, the house is dark. Typically, the thieves are going to go there.  It really has to be worth their while, which is why nation state attacks like hidden cobra can be so bad, because you have all the defenses in the world, but they have all the time, all the resources and all the resources throw out. And people I don't think realize that if you're just one person, you might not think of yourself as a target. But if you work for a company and you have a position of some kind of authority in that company, and you can do a key activity in that company, you might actually be a target. If someone wants to take down a power grid and you work at the power station, and you have access to the power grid controls through your network account, you might be a good target because it's easier to get malware onto your personal laptop or your cell phone than it is to attack the power station. Oh, very nice. Yeah, you don't want to storm the front gate to the castle. Yeah. You go get the cook on the outside and have him smuggle you in the back door, right? That's the best way. And a lot of what we hear about the big things like the target breach is hackers trying to get inside a company. But more often than not, it's these phishing attempts that are succeeding, whether you're an individual or a company. Because once you click on that link, you've brought the malware in for them. You bypassed the security system. It's exactly right. You know, when we come back from the break, we're going to discuss the phishing attacks, the difference between personal and corporate phishing attacks, spear phishing, whaling, and some of the new ones that the FBI just warned us about through our U.S. Cert and InfraGuard. Okay, we're going to take a break, pay some bills, we'll be right back until then, Stacy. Hi, guys. It's RV Kelly. I'm your host of Ad in the Comfort Zone, where I find cool people with cool solutions to problems that all of us face. Now, the thing is, we're really cool. And I only invite really cool people. But the thing is, I think you're kind of cool too. So I think you should come and watch that Thursdays at 11 a.m. here on OC16 television with Think Tech Hawaii. I'm RV Kelly, host of Ad in the Comfort Zone, and I will see you next Thursday. Welcome back. I hope you enjoyed the commercial break. I know I did. It was highly entertaining. I'm Dave Stevens. I'm your host of the Cyber Underground. And we're going to change topics now. We were talking about Hidden Cobra in North Korea and Bankshot, the latest North Korea bad state actor. And now we're going to shift into some email scamming, especially now during the holiday season, people are always victims of shopping scams. And a new one just came out as a warning from the FBI about three different shopping shipping attempts for phishing emails. Let's talk about that. You've got the same warning I did apparently. I haven't read it. I came out early this morning, I think, or yesterday morning. And it was apparently three different emails that they've identified that get sent to people. And this is the time you're doing shopping. So almost everybody is getting something shipped to them or to somebody else. And even UPS, I signed up for UPS, if someone's shipping something to me, I get notification. It's going to be here in this little window of time. Please be home because you have to sign for it because, you know, most of mine are alcohol, so I got to sign for it. So an ID. Hidden drunk, you know. And so I expect these emails anyway. So now I have to closely inspect them because all of them contain a link. Yeah. Click here to check on the status. And what can that do to us? That leads to very bad things. Describe some of the bad things for us. Some of the bad things. Keystroke lockers, maybe not as popular as some of the other malware, but if you want somebody to be able to tell everything that you type on your machine when you're logging into various banking accounts, all that gets captured and sent back to the mothership while aware of different types of ransom where, of course, that we've heard so much about. That's very popular now. Yeah, ransomware. So that was the want to cry attack, which is now being blamed on Tom. Is it bozzard? The Homeland Security Advisor to President Trump has actually come out publicly and said, No, that was North Korea. We have evidence. The UK has provided evidence. We're not going to show you, of course, but we have evidence. And so we need to believe. But that was apparently North Korea. And the funny thing about that want to cry is I was all ransomware and they all wanted you to pay a little bit of money to unlock your data. But it was like 300 bucks. So they only made maybe 20, 30, 40, 50 grand on the whole attack, but they got, you know, what, a couple of million computers in 150 different countries. Yeah, but that's just one variant. Just one variant of ransomware. Could it be that they were just testing this out? Probably. And the distraction was, Hey, it's a ransomware, but it really did take down the national healthcare system in the UK. Oh yeah, the NHS N8S. I can't even speak. If that happens again, take over for me. The entity that control right the entity that controls the medical services in the UK pretty much got taken down mostly because they were running Windows seven and Windows or Microsoft said, Oh, we know this is coming. So we're going to patch this in advance. But they didn't do the end of life computers. So Windows seven had already passed its prime. But NHS and HS and UK hadn't upgraded yet. Well, and remember what happened in China with all the should I call them bootleg machines unregistered? I think you could say that here. There's the thing about the ransomware to show what a threat it is is that there are criminal organizations that have a help desk. You can actually call them and say the encryption key I bought from you doesn't work. And sometimes it'll actually help you get your data back. So that's how much money there because they have a reputation to protect, right? They want people to know that if you pay us the ransom, we're going to give you your data back. Why is it the criminals have a better help desk system than AT&T? They get paid better. It's not about the stock price. Customer customer giving them money. So that shows how much money there is to be made by all these variants. But the thing that gets me is when WannaCry came out, Microsoft patched for that two months earlier. Yeah. The fact that people got hit by it as much Microsoft used to have a really bad reputation for patches. Sometimes patches would break things. Nowadays, it's not so much. That's a bad to me. It's a sucker bet not to do that. I mean, you can set it to automatic and it'll take care of that. Granted, there are end of life operating systems. Like if you've got a Windows XP system that's connected to the no more bad just coming out. Yeah. Why? Yeah. Why are you doing that? Well, it's good to do that because if you do not pay attention, accidentally, it happens to us all. We've only had a one cup of coffee in the morning and we click on that link and go. Yeah. But if you've patched your system, it's very likely that the ransomware will not get your computer. Do you have some defense and death? Mm hmm. But if you've already clicked on the link. Unplugging the network cable is not going to do anything for that machine. No, it's going to protect any other machines that you have in your house because it spreads because it spreads spreads via the network. Right. But it boggles my mind. I work with some vendors that I say, when do you issue patches as needed? Okay, how do you define as needed? Because Microsoft puts out at easily 10 security patches every patch Tuesday, the second Tuesday of every month. That's patched. Microsoft and Adobe is in the same date. They patch their stuff at the same time too. So I just, I look at these vendors and they say, well, you know, we look at them and we make a determination. And I'm looking at these vendors saying the determination is if it's hit mainstream media and everybody knows about WannaCry, then you say, ah, you know, maybe we should patch our application or something. The Microsoft is ahead of the game and you have to appreciate that. It is nice. And again, defense and depth will help with a lot of these things too. But the patching is one of the biggest. I think it's no longer a decision about when you should apply it. It's always, I should apply that as soon as I can. Exactly. I think, unfortunately, there's some people that run applications so long on their network, custom applications, they need to have Internet Explorer eight or nine. Otherwise, that web application fails. They have to have SQL Server 2008, you know, for that application to run. So they fail to update because they don't want to update their application. That costs a lot of money. So you gotta make a decision though, because especially if you're handling financial transactions, right? If you have credit card numbers, credit card companies will charge you, I think 75 cents. If you got breached, 75 cents for every credit card number that got taken off your network, X-filled, right? One person can have multiple numbers. And you're getting charged multiple times for each customer. And if you have a million customers, that's 75 cents. This is why one breach can wipe out a small business. And that's the thing. What's the mentality that, you know, let's bring in a contractor, somebody who knows his old stuff and have them fix it for us? Yeah. Or do we take a risk that we hose our business and it goes away? The one thing people can do for the ransomware is how many people back up their systems. That's the only way to recover. Oh, unless you're backing up. Here's the thing. If you're backing up and you have like an external hard drive or something like that, unplug that. Unplug it. Don't leave that plug. Ladies and gentlemen, do not leave your backup drive plugged in. I think mine's actually plugged in right now.  Don't do what I do. Unplug that drive. Unplug it only when you do the backups because if you get hit with ransomware and your drive is plugged in, what happens? It's going to treat it just like network drive and it's going to encrypt that drive. Right. And then there goes your backup. Then there goes your backup. Thankfully, I don't think that can happen in the cloud. So if you have an automatic cloud backup. No, that's not going to happen. No. So the cloud vendors are thank you, God, they're really doing a good job. Amazon, Google, Microsoft, Azure, they've come way up to speed. They're following the new NIST rules for the DOD, the 800-53 rules a lot of times, which is if you got there into your research, that's a lot of control checks to put on your network. They handle tempest controls and employment. They don't hire non-use citizens a lot of time. It's a pretty serious security and defense in depth. And it's reasonably priced. Nearly everybody has somebody in their family that understands this. Yeah. So that's not an excuse. You have automatic built-in tech support a lot of times. Exactly. As we both know. Yes. We're the tech support. But you know what? I have a 12-year-old person in my family who could probably do just as well with this cloud backup stuff. They understand it. It's like they grew up with this stuff. It's just magical. Oh yeah, I know what that is. My friend who had his business on a thumb drive. And the thumb drive crashed. Oh. It couldn't be read. Oh. So he took it to a local company. And they took it apart. Oh. There are no moving parts. Yes. There's no reason to take it apart. Just a circuit board. And a plug. Yeah. So he gave it to me and I'd mess with it and tried to do some tricks, you know, some drive utilities and stuff. Yeah. And I said, okay, here's a deal. You're an Apple guy. Right. Yeah. iCloud. Right. Yeah. iCloud comes automatically and for free. I'll set you guys up and you won't have to ever worry about it again. Yeah. And if you, they give you a certain amount of storage for free. But it's really inexpensive for the next, I think I pay 99 cents a month for my storage and I get 50 gigabytes. That's a heck of a lot of data. I mean, I gotta go way out of my way to put 50 gigabytes in the cloud and I do some experimental stuff with virtual machines. So, you know, I've got a lot of data. But yeah, it's a really good backup and they keep it somewhat secure and it's more secure than my system. Yeah. And I think people got to realize nothing's ever totally secure. Right. But they're more secure than others. People will store their tax returns, pictures that mean a lot to them. And this is valuable. It may not rise to the value of company Coke secret recipe or things like that. But to these individuals, it's really important to them. So, protect it. You know, that's, let's change gears and you got a good segue here. What's the difference between attacking a person versus a corporation in an email phishing attack? I don't see one. You're after individuals. Yeah. It's a psychological game. To see who's going to both click on the right. The goals, the same. It get malware or something on the computer. Maybe in a business, it's a little more aggressive malware designed to be a little more stealthy maybe. But it's still the same idea. It's to get people to click a link. And I, my mother-in-law told me about 15 years ago that her internet was slow. And I thought to myself, she was an older woman. And I thought, what does she know from slow internet? And my brother-in-law told me, he says, well, you know what happened is people got conditioned to a response time from the TV remote. When you use a TV remote, things happen immediately. So, when you are clicking around with your mouse, you expect that same kind of response time. And I thought, that's really reasonable. Yeah. I can see that. So, people have to take some of the responsibility, protect yourself, the defense in depth, run your updates, make sure your antivirus software is being updated, the malware signatures for the malware product you're using, that gets updated as well. Most of that is built into Microsoft, right? Take a minute. The defender, right? Yeah. Yeah, it's built in. Okay, we got to wrap it up. But let's go on a rant really quick. It does take 20 seconds and we're talking about cell phones. And I told you, I got caught in the whole Apple iPhone battery scam. Right, we're not guaranteeing you to update. No, we're protecting the battery. We're protecting the battery. So, if you see this episode on the web, everybody, please go in there and comment. Tell us what you think about Apple. Now, in lawsuits currently, already class action lawsuits filed in Chicago and a couple of other places against Apple for slowing down phones and they're calling it breach of contract because they didn't tell them, they didn't tell us, I had an iPhone 6 also, that they were going to slow down the iPhone. So, let us know what you think. We really want to know. And also, the point I was making with the mouse clicking is take a minute. Look at an email. Look at who it's from. Don't click right away. Hover over the link. See if it goes to what you think it says. Don't be in such a hurry. I still get phished from people I worked with 15 years ago who have hacked emails. They don't want to change their emails because they've had them forever. We got to come on two weeks from now. We're back on the show. Let's do this again. OK. All right. Sounds good. Thanks for being with us, everybody. More good news every time you watch. OK. We'll see you next week on the Cyber Underground. Until then, stay safe.


moment where that clicked for you and sort of served as an entry and I'm also curious because When you talk about sort of your work being collected is your performance work collected or is it object-based work collected? What is the relation between I never mentioned? Collected in your bio it talks about like your your work is in the life of your videos or videos or okay? So so the performance work is not collected per se well I I'm in the video so I perform in the videos Okay, I I Don't distinguish between I I mean my live performances. No Right, but the art world for the last number of years has figured out how to commodify those anyways So well, that's what I'm that's what I'm trying to I'm trying to I'm waiting a little what you're waiting. Yeah, okay But because yeah, like you know, that's that's something that very much interests me and we'll have to see how that unfolds collecting ephemeral performance So can you okay? Can you just talk a little bit? I'm like stand up to me is fascinating because of like the very rigid structure and the very like It's actually a very difficult performative discipline that gets undervalued because there's so much bad comedy out there. Well, I I Don't know how good I was and I don't know if I ever did it I I mean I I worked with this guy. It was my manager for a while and he He told me I never had five minutes. So I Don't know I I mean discovered comedy I mean television when I was a kid and a lot of the I mean television had a lot of The Ed Sullivan show you get people that had to do five minutes Right and then back then they didn't have the internet so people could travel for a couple years with those five minutes and do that Act over and over again At the time it was I had a lot of time on my hands when I went to this the club the stand-up club And it was also It was kind of interesting because it was not the setup or the situation was not that foreign from what it was in The gallery situation you had a lone performer standing up there and you had an audience and there was like trying to get some sort of Reaction a lot of times to be playing off the moment even though a lot of it was rehearsed and staged and A lot of or scripted and then a lot of it was like at the moment so I Don't know if I quite understood that then but it also sounded kind of interesting because the tenor of the art world was very serious So it sounded kind of you know made for interesting conversation at cocktail party. What do you do on the comic? It was bullshit, but it sounded good Okay, so Laura I wanted to ask I unfortunately I haven't seen your work So it's a little naive But you say that a lot of it you started in photography in that world and then sort of found that the body was very important I'm just curious what I'm trying to figure How does the body like tell me a little bit about that and do you work have you done Subsequently do you need to do training to for your body to do what you need it to do performatively or yes And no, I mean I'm a pretty athletic person, but if you're are you asking about artistic training? Yeah, like have you done choreography or like movement training or anything like that? I haven't until pretty recently. I did some viewpoints training, which is the Anne Bogart's theater Exercises paradigm So so in terms of you know, that's my main I mean, that's kind of the only formal theater training I have if you can call it that and other than that, I mean my My relationship to the physical my own physicality has been the way I've Been in been connected to performance though I would say that I I think for many creative people the body is really and The sensual is at the root of how we make things So it doesn't necessarily happen always happen in front of an audience, but there's something you know Visceral about most parts of the process though. I suppose you could argue that sitting in front of the computer Isn't very visceral I think most art forms, you know have that kind of Engagement Yeah, yeah, I'm just I'm just I'm trying to unpack it a little because one of the you know Interesting things that that I think is is happening at the moment is as artists move between disciplines or Across disciplines is that is this sort of idea of like what skills are required in different Media, right? I know and you you wrote about that and and And I wonder, you know, you have this you have this question about Like dancers choreographers people in the theater are have gone through this rigorous training and So for the visual artists who hasn't had that same Well theoretically that same physical training. They're somehow not Kind of prepared or maybe they don't have the discipline for the they can just do performance art And they don't have kind of the The integrity right to do it. That's what you suggested in your article Not so much but but but I but I'm but I'm curious about what it means like to you When you're putting your own body out there as part of the art process, you know in a very Just like what's the difference between sort of one and the other? between This my situation is very frustrating for me. Okay between Here All right Between performing and visual art or no, I'm saying I'm saying my question is is Yeah, I'm you're right like what I wrote in my essay is like it's like I want I wonder about that like, you know People who's trained artists whose training is body-based What they're what their presence is in front and engagement what that dynamic is versus an artist who is primarily visual-based And then using their body as a canvas if you will or a locus for aesthetic engagement You know, I don't know. Yeah, I mean, I think that that That binary can exist, but I think the question is more for me. Anyway, the way I think about it is more about Presence, you know and and there's something about You know someone who who hasn't has no experience drawing that the way they come to the paper is Can be really amazing if they if they are present and observing and I think that that happens You know with inexperienced performers in the way of performance art as well, you know, there there are different ways we embody ideas or Feelings or you know, whatever and and I don't know if it's necessarily the discipline that determines the virtuosity Okay, great Bill do you want to talk a little bit about? Well, we're a race of great things about sort of presence and your piece currently deals with presence very much because you have the The physical actor and then you have the virtual Captain Kirk Yeah, Captain Kirk and then also other pieces. I've seen of yours. Definitely deal with sort of people as sort of you know Well sit stand walk lie down definitely had presence in a totally different and in that you worked with a bunch of people the Variety of different skill levels in terms of physical Embodiment so could you talk a little bit about that? I think The issue well presence has been at the center of my work Since I began working on it, but I have found that it takes a tremendous amount of work to To empty the container so to speak That it is not I find that there is something that an amateur And I'll just I don't mean that in a pejorative sense I mean that in a person who has little to no experience as the people In sit stand walk lie down many of them were ranked amateurs and I never done any performing whatsoever When they first encounter something new Some exercises I might be doing there is a spark and that spark by accident can create some present fire But it is very short lived and so the practice of presence has become Something quite Compelling to me and difficult not that I know what it is, but I find I'm practicing it all the time sort of to how the I Think I would call it a consciousness about it, and I think the practice of making the work that I make is of developing a consciousness Consciousness about the act of doing what you're doing, which leads to some sort of presence So the I discovered in sit stand walk lie down that there was a moat on this island and People had walked by the moat. I had walked by the moat a million times, but to somehow Notice the presence of that moat became Something interesting to me and the moat took on the quality of a line seen sideways very painterly thing and By calling I could call attention to that moat its moatness by the placement or taking away of hands and Since you didn't know where the hands would appear Disappear the moat became very interesting. So the performance became a way of pointing at the presence of the physical Properties of the architecture and I think my directing skills also led to it knowing that the the presence of the hands became part of that dance, but Not the central part of that dance that makes any sense, you know, I Think directing is about figuring out what things go in front of what things when so I Don't know if I'm answering the question. I'm sort of talking about my practice a little and this these are the things I engage with Obsessively And whether I get paid or not No, I think no, I think it's I mean I actually think there's a wonderful Consonance between what the artists are saying because I think we're everyone everyone is talking that there is a visual element It's a sort of creating a visual environment and or a visual experience This question of presence it You know, I think it's it's not a valued of judgment. I think for me it's sort of and I think for the Field in general it's sort of how do we develop a framework that talks about the different modes of performance in these different contexts? It isn't that honors the different practices that lead to what happens in that ephemeral Moment and I want to talk to Hillary does okay. I want to talk to Hillary a little bit about how did you? like come to curate primarily performance art and sort of what do you You know, what have you seen over the past? I guess ten years that you've been curating and or however Five years, but talk a little bit about what you know Yeah, I was really lucky to work at the box gallery in Los Angeles that is the owner and is Mara McCarthy who is Paul McCarthy's daughter and so it was a good place to be and So the the premise of the gallery when they started it was that there would be they would show artists that Mainly performance artists and Older who had been around who didn't really get their dues and usually it was because their work was very sexual political they Intentionally took themselves out of the art world because they didn't want to be in it So I Was lucky to work with people like Barbara T. Smith Simone Forte People also with the states like Stan Van der Beek and others so that's sort of how I got my start and it was Also being in Los Angeles. I was there a lot of the artists that were still living But I mean we would interact with all the time and And so that's where my interest was struck. Also. I have an arts background I went to Cal Arts for studio art and so I've always had an interest in performance work Because it's harder to commodify even though We do So great. Well, I think yeah, I mean I think all of us at this table You know Michael talked about it. You just mentioned it You know is and this is this is if you know almost like an entire other discussion, which is that you know Theater performance has not done a very good job Especially in the new in new era of commodity commodifying itself and dance even less so You know, I think you know at one point, you know You would go see a play and then you could the author could sell the script and so you could have some sort of there would be an object that was sort of Referencing what happened on the stage and someone could make some money that way that sort of gone away now Because people don't make that kind of work so much and not so many you know, and that's as an income thing That on the streets all the time. They're selling scripts all the time where it's a cottage industry in New York Oh, yeah, yeah like those Yeah, but um, it's interesting. I mean you were like it's like Tino Saga all I guess, you know gets paid a lot of money to Sell, I don't know whispered instructions, which is sort of amazing and brilliant I Don't know I don't Michael just scoffs. Oh, okay Well, I mean it is so it's an interesting it's an interesting moment I think So actually I hi I feel like we've been having a very nice conversation up here. Can you guys have questions? Thoughts Yeah, Wayne Can you can you um? Yeah, come come come to the Yeah So so for those of you who can't hear and for those of you watching on the internet hi Wayne Ashley wanted to I was asking had we have we foregrounded this conversation in a discussion about sort of the market and capitalism and and consumption I Think there's various factors that Lead to that in terms of museums doing it I think a lot of it has to do with funding some of it has to do with funding education programs bringing in a public Trying to attract them so you have fly of events you bring people in you bring ticket holders You can get funding from that I also think it has to do with the economy and reaction to the economy in terms of artists and criticism Also, these things are circular and they're cyclical so these things come up over and over again It's every four years or three years. There's a there's a lifespan to these issues. So and then I In terms of like the people that are bringing these I Don't want to I mean not to get not getting personal or anything I just know that there's certain opportunities that are Attracting and when you're dealing with spectacle which a lot of the performance is which a lot of happens at Performa You're gonna get attention and attention doesn't necessarily You know lead to direct money, but it leads to influence. It's important. Yeah, I think To Wayne to address the sort of foreground. Yes, they're this whole chain of conversations started from an essay Series of essays one that I wrote one that Claire Bishop wrote And a bunch of stuff that came out of Performa where it was really where we're and I think that that's what We're trying to do over the next, you know ongoing is unpack these issues around commodification And and I agree like I'm I'm you know It's like the Whitney is building a performance venue in their new museum You know MoMA is like all these people are investing in something that I would imagine knowing the thought that world May be out of fashion in six years And I wonder what they're with these institutions are like are they and this is why the commodification is so interesting Or the collecting is so interesting because it's like they wouldn't be I wouldn't think that a major institution would invest in Building a performing Program a performance program unless they had a strategy for collecting the performance and creating value Or else to bring attention to it that they're doing it Who knows what that facility is gonna look like and how practical or how good it's gonna be right? Right gather a lot of you know generate a lot of interest and excitement around it And let's see how it sounds when you go in the room if you can actually understand what's being said in a video Yeah knows that well, that's a big that's a big and I actually want to talk to Phil about this a little because and this kind of gets to this like skill issue a little bit is that I You know, I know that you went to TCG to build this piece with Jim Finley Just so you can talk a little bit about that But it's about sort of are the places Building with the equipment to make the work that they're asking to make you know If you're gonna ask Sarah Mitchelson to create a dance piece is The Whitney building a facility that's going to allow her to actually build You know what she's or Richard Maxwell who was in the biennial, you know Are are are we creating a or are we creating a structure where the performing arts dedicated venues? We'll continue to be underfunded will serve as a sort of farm You know a petri dish to develop these artists that will then you know Move to the MoMA and get a claim for MoMA and not down the I'm sorry No, no, that's okay. Yeah Yeah, I I did spend upwards of two years at the center theater group These are very interesting questions you ask and I feel that I Will address Them through my own experience. It's probably the the the best way to do it. So I Did spend two years in a collaboration with Jim Finley at the center theater group in Los Angeles Which arguably is the flagship? regional theater in the country Billings this that would dwarf this room And I found the experience was locked in To certain preconceptions about how to build how to construct a piece that adversely Affected the creative process that Jim Finley and I were trying to engage him now You know, we're not Powerful guys, although I wouldn't mess with Jim.  We can't be written off that way Let me give an example the first Hurdle I had a jump was with playwriting. We were funneled within the institution into new play development The focus of the piece that we were building involved no written text No play You would think the conversation would end there and what are you working on and let's go to it but it didn't and it became the subject of a year's years worth of arguing to Make the people at the center theater group understand we weren't dealing with a play We were dealing with the experience of a performance so I come at theater from All the questions that you might ask about a play meaning The play as a map for Who are the characters? What's happening? What is the narrative? What is the set? But my solutions well, I should say that each of those What each of those areas became the subject of questions for me, which I then built a production around over many many years, so When I came to the center theater group I was not in a position to when I said I'm not going to work with play it wasn't To be a cool kid on the block. It was after years of work and research Enough said about that. So I Found that the institution could not it became a binary situation to quote myself that The institution could not handle the fact that we didn't have a play to work with Part one part two was that Jim Finley is known primarily as a video designer Jim and I met and talked and our We wanted to work with a very interesting question. What can we do with video that hasn't been done before? That's a really interesting question and then maybe an impossible one and a really difficult one So I think Jim and I decided well, let us start by we will light the entire space only with video light There will be no stage lighting only video light Great, let's start there. Let's start work Let's see how plastic is attracted to video light and all that Enter the center theater group video becomes within the institution becomes a Very problematic issue because you cannot videotape any actors who might enter Into the video frame while you're making something Because then you have to negotiate a contract with I think sag or aftra To a clear it to okay it so we had to go through this Probably nine month your long dance Contracts had to be signed In order to use video to do anything in the room so the creative energy went into bureaucratic nonsense in my opinion as opposed to The harder question of what can you do with this? I don't know So I found that The theater establishment What became an uphill battle all the way I'm not unfamiliar with those battles, and I don't think they're Unexpected or I Don't know what the word is it's hot But they're very familiar and Either you take them on or you don't But I think much too much energy gets wasted inside the theater establishment trying to make something exactly like the thing that was already made instead of there doesn't seem to be a Will inside of large institutions to do something that they don't know about and My interest is purely in doing something that you don't know about when you start and you keep your fingers crossed And you have faith that when you finish You will Make something that will be of interest I think were there another question Okay We're kind of getting up on it anyone closing remarks thoughts to share One last thing, you know you we started this part of the conversation with a question about commodification and I think that The example that you just spoke about is a really Good point about how about the I don't know if I could call it the commodification of theater But the reason that process exists is because for a long time people fought for unions and to do things in particular Ways so that all of those collaborators in the process could get paid right and it's the same thing that happens in museums There's a similar bureaucracy, so it's not I don't think that it's It's necessarily that the visual artists, you know can sell the painting and make money and that the theater person can't you know we're And when we're talking about the Whitney, we're talking about these number of artists We're not talking about all of these people who are doing lots of different kinds of work to you know to survive so it's And I think also and I'll give you this that the Whitney building a performance base Along with the economic Decisions that go behind that might also be a great sign of Genre crossing and breaking down that is really necessary and that has I think always been The experience of artists that you know we are asked to study study in a certain way, but there's a you know We're whole we do lots of things, you know, we listen to sound we feel the earth beneath our feet We draw even if I'm a theater artist, so It I think it's a good thing as well I just want to add that the Whitney was actually modeled after a series at the at the Whitney that happened 30 40 years ago and The curators are well aware of it And it's also was seen as a swan song to that building to you know sort of inhabit that building for a while I forgot what I was Also in terms of like, you know Organizing or unions, I mean a lot of the it's not about The discussion is not about money sometimes it is about money, but in terms of collaboration It's about credit, you know in term with artists, too And that's that becomes a talking point with them or a big part of it But they do have unions too. There's been unions in the trying to organize artists in terms of getting together It's not only in that world, but it's less. It's not as powerful Well, I think I think thank you. I mean, I think I wish we had like another hour Just because this is this is sort of I think that we're what you're talking about is I think it's exactly sort of like I'm looking at everyone here and looking at the program for this festival I'm like I'm seeing all these artists that are you know artists like fundamentally whether their primary in mode of engagement is choreography or Quote-unquote theater or visual or whatever and I mean and that's proud and that's always I think the way it's been to some extent But I think now more than ever That's always a horrible thing to say, but it feels like this moment embraces a multitude of creative expressions by self-identified artists and What I'm hearing from Philip and what I'm hearing also is that is that are the institutions a are the institutions sort of developing curatorial and production models that suit that mode of creativity and You know and and the issues you address around sort of labor and and equity and getting paid for your work I think are a huge issue regardless of discipline right now But when we did this in January, you know, it's interesting like I sort of feel like you know the the sort of Lord theater Model and the sort of like, you know, I think that the art is feels old And I think that you know the contemporary art center idea seems to be more relevant to this moment But you know where you have like, you know a performance program and a visual art program And it's all housed in one thing and you know, but even in those institutions, you know, I was talking to someone from a major contemporary art center who said, you know that you You know Even internally they have Communications issues between the people that create performance and the people that create the visual arts world and some of it's some of it's like just Logistics, it's like the prep time for an exhibit at a museum is like two years and the prep time for a performance is like, you know Six months nine months. So you have these so but I but um anyway Do you want to talk a little bit before we go just tell us about the show the artists that are here that we can come see at the gallery So tonight we're having two performances by math bass and dashel manly who are just want to wave so and Then and those will happen at seven o'clock tonight and tomorrow Barry McGregor Johnston, who's right there will be performing here at Seven and They're all very wonderful. I go on and on but you should really just come and see the performances Great. So I want to um, I want to thank all of the panelists. It's been a great discussion. Thank you guys for coming And continue it online. Yeah, send feedback. Thank you. Thank you run


There's this, found this woman that molested like, she was a nursery worker, she molested like babies when she was at work and I just thought, do you know what, I'm just gonna absolutely batter her and go to the block, at least I get out of here, at least that's one damn, do you know what I mean? Yeah, I don't condone violence but I condone that so well done. No regrets, do you know what I mean? But yeah. Yeah, what was it like battering her, someone who was abusing kids at name one fold? It was good. She earned it and they're so protected and stuff and there's disgusting. But yeah, and I, I don't care, I went to court for that and I said, Jay, I've done it and I've done it because she's a child molester and that's it, basically, what are you gonna say? Yeah. And who was that woman? Marie, Marie Raisin. Her name's Marie Raisin, she used like sending pictures and stuff online to people and just working in the nursery, absolutely wrong and scum, bad, but yeah, she was in a bad, she was in a bad shape.


Welcome to this lecture on digital communication using GNU radio. My name is Kumar Appaya and I belong to the department of electrical engineering IIT Bombay. This lecture will be a continuation of our discussion on orthogonal frequency division multiplexing wherein we will discuss how equalization is greatly simplified when using OFDM. To recall our previous discussion on OFDM what we concluded is that if you look at OFDM as repetition of symbols combined with frequency shift that is if you repeat B0 multiple times B the symbol B1 multiple times but multiply them by appropriate vectors then the resulting you know wave form so to speak in the frequency domain exhibits a characteristic wherein B0 occupies a spectrum that is close to 0 hertz B1 occupies a spectrum that is close to W upon 4 hertz B2 occupies a spectrum that is close to W by 2 or minus W by 2 hertz and B3 occupies somewhere close to minus W upon 4 hertz. These are called subcarriers and these subcarriers follow a sync like pattern in the frequency domain and carry data. One remark that I would like to make is that you have to sample in the frequency domain exactly at this particular point. If you think about it sampling in the frequency domain is basically in time domain getting your frequencies exactly right. In other words you must have performed your receiver carrier calibration and carrier recovery phase estimation correctly for OFDM to be very effective. Otherwise you may suffer from some inter symbol interference because if you do not sample at the right point you make a contribution from the neighbouring symbols. Let us now continue we were discussing that we can use the DFT or to be technically correct the inverse DFT matrix to take your symbols B0, B1, B2 etc. and convert them to a format where they occupy these narrow band subcarriers in the frequency domain. Now if you start increasing the number of subcarriers you will see that the spectral footprint of those sync like pulses become narrower and they occupy a much narrower bandwidth yet you are able to parallelize. In this current picture again we have split our bandwidth of minus W upon 2 to W upon 2 into 8 parallel OFDM streams and these 8 parallel OFDM streams are essentially allowing you to send you send this data at the same data rate you know your data rate is unchanged as it stands yet you are able to put your data in parallel frequency bands. So in other words B0 occupies close to 0 hertz B1 in this case will occupy I believe close to so if B5F4 is close to W by 2 then I believe this should be W by 16 this is 2W by 16 3W by 16 yeah I think it should be W by 8, B1 occupies W by 8, B2 occupies W by 4, B3 occupies 3W by 8, B4 occupies W by 2. So it is like this is like and so on and so in this particular instance you have 8 subcarriers these 8 subcarriers are reflecting narrow band transmissions in the frequency domain. If you increase the number of subcarriers to something like 16 then again the subcarriers become narrower and narrower they become very very close in the frequency domain one remark again this is something which we will not cover in this course but something you should remember is that getting the frequency sampling wrong meaning not calibrating the receiver frequency correctly can result in a significant amount of inter symbol interference that reflects in the frequency domain this inter symbol interference that reflects in the frequency domain can significantly hinder your performance that is something that you must remember. Now we will remember we will recall our DFT based picture technically what we said is you can use the inverse DFT matrix which was that 1 1 1 1 j minus 1 minus j and so on to enable this kind of modulation this should be n sorry enable the kind of modulation that you just saw wherein your symbols were put in parallel frequency bins. So how do you do that? So we will now slightly alter the way we looked at it it is the same thing but with just different rotation we will say that our data we will collate into B0 B1 B2 up to Bn minus 1 let us say we take a single block our idea was to repeat B0 repeat B0 multiple times that is why B0 is multiplying the B0 is multiplying the all 1s mid you know column B1 is also repeated n times but being multiplied by e power j omega naught n in this case it is e power j 2 power by n e power j 4 pi by n we are taking n point d f i d f t that is B2 is multiplied by e power j 4 pi by n e power j 8 pi by n and so on and finally, Bn minus 1 is being multiplied by this particular vector this is scaled by 1 by root n this 1 by root n scaling is to ensure that this matrix is unitary.  So, what I am going to do is I am going to just divide this by 1 by root 4 and divide this by 1 by root 4 and I get identity the 4 cross 4 identity this 1 by root 4 is very very useful because it scales w. So, that w Hermitian times w is identity another thing is that the scaling also has another important use this w Hermitian w being identity implies that you are not scaling the vectors energy. In other words if you are multiplying by b then the energy of b does not change how so let us go back and see. So, if you see our x is w times b where b is this particular vector which we have let us just work this out ok. So, suppose that my b vector is b 0 b 1 say b n minus 1 let us actually evaluate expectation of norm b vector square what will it be this is equal to expectation of b Hermitian times b which is equal to summation l runs from 0 to n minus 1 expectation of mod b l square why because b Hermitian b is just sum of the magnitude square of the elements. Now, since we assume that our symbols are generated IID with the same average energy this is going to be n times E s where E s is your signal energy n times E s is the signal energy. Now, our x is w times b the question which we are asking is after doing this IDFT operation are we using more power or less power. So, to do that let us evaluate expectation of this Hermitian x ok because that is summation of mod x i square this is equal to expectation of let us play a matrix trick x is w b Hermitian w b ok. Now, here this is equal to expectation of b Hermitian w Hermitian w times b, but w is a fixed matrix it is not statistical and what did you just show you said w Hermitian w is identity in fact identity n for the n cross n case. So, this is equal to expectation of p Hermitian b which not surprisingly is n times E s this is very very useful result because if you now use this scaled version of w with the 1 by root n we have ensured that the energy usage does not change. In other words the IDFT matrix in this particular form you ensure that the energy usage does not change I will give you a warning in GNU radio the IDFT matrix has a scaling related issue you know issue not issue it just scales the signal differently you have to account for it is very easy you just have to multiply by a factor, but just something to keep in mind that we will be using this particular IDFT matrix picture because if you then have this property w you can check w Hermitian w w Hermitian is identity n of course in the notation it is much more convenient for us to do our analysis. In other words if the budget for your signal power is E s in the transmitter then the x which you get by multiplying b by this particular w is also you going to use the same amount of energy per symbol. Now since w is a unitary matrix we just showed that x Hermitian x is equal to b Hermitian b actually expect in expectation sense of course ok will be equal to n times E s of course if you use a symbol like QPSK right for QPSK this will be true irrespective, but if you use something like quam 16 or something you have to put an expectation. Now x is the inverse DFT of b now here is the key we never spoke about how we can get back b from x at the receiver let us suppose that there is no channel and there is no noise then since x is the DFT of b all you need to do is x is the IDFT of b rather all you need to do is to take the DFT of x because the DFT and IDFT are lossless you know lossless reversible operations. So, at the receiver what you can do is you can just group n symbols take the DFT you will get back your b of course there are some issues you do not know what happens when there is noise you do not know what happens when there is a channel that is something which we will see the bandwidth usage is nominally the same the channel split into K or n narrow band sub channels or sub carriers, but now let us see what happens when we have a channel when we say channel we have a convolution and we have noise addition that is something which that we have to handle. So, we will take a small detour and aside and remember the connection between the discrete Fourier transform and convolution. If you remember from your DSP if you have two sequences let us say x n and h n if you take their n point DFT's and refer them to capital X k and capital H k respectively when we say n point DFT we take the n point DFT to be summation x n e power minus j 2 pi k n upon capital N. So, capital X k and capital H k are defined for numbers between 0 and capital N minus 1. Now, if your y k is h k times x k if you multiply the DFT's of two sequences then the sequence that corresponds to is not the convolution it is the so called circular convolution that is why I have put a C. That means that whenever you perform in the traditional sense if you use DTFT if you multiply DTFT's of two sequences then the inverse of that will be the convolution of those two sequences in the sequence domain unfortunately over here when you have DFT's that are being multiplied then your resulting sequence is something which is circularly convolved. That is your y n is going to be summation l is equal to 0 to n minus 1 x l h n minus l mod n or you just swap h and x is the same thing this is not the same as linear convolution. Now, let us go to our picture of OFDM in the OFDM case we took the IDFT we then it underwent convolution with a channel. Now, the problem is that if you want to exploit this particular property of single tap equalization or just division based equalization let us see I am just saying that suppose your you know h is known and your y is known then to get x you just need to y upon h at least at the for this you know something like a zero forcing equalizer that you just saw you can just do y upon h or for MMSE you can do y upon some you know function of h the problem however is that this is valid only if you have circular convolution, but any practical channel that you saw when we were dealing with this MMSE and zero forcing equalizers performs linear convolution and not circular convolution. So, what do we do? So, see since we want to use the DFT IDFT property we want y k is equal to x k times h k we want that, but the natural way the you know nature is not giving you that it just says I am going to do linear convolution. So, what can we do? The way to do it is we can actually fake circular convolution by including what is called a cyclic prefix that is we group our symbols in this manner b 0 b 1 b 2 up to b n minus 1 we take the IDFT and we what we get we call x 0 x 1 up to x n minus 1 this is your x vector so to speak and we had a cyclic prefix of for the form x n minus 3 x n minus 2 x n minus 1 what is this achieve? Let us actually analyze this. So, let us say that you have x 0 x 1 x 2 x 3 let us take this and let us suppose that you want to convolve this with h 0 h 1 h 2 and you want circular convolution how do we achieve this? To perform the circular convolution what we will do is we will write x 0 x 1 x 2 x 3 and we will write h 0 flipped h 0 h 1 h 2 and we will multiply and add. Now, sadly over here h 0 times h 0 you should the linear convolution give you h 0 times x 0 but the circular convolution will give you h 0 times x 0 plus h 2 times x 3 plus h 1 times x 2 unfortunately that is not there. So, what we can do is we can actually just modify our sequence to append this over here. If you append these over here and then perform the circular convolution in this region let us just look at the output in this region you are going to have h 0 x 0 plus h 1 x 3 plus h 2 x 2 this is exactly the output of the circular convolution that you want. Let us look at this one also we have to shift this by 1. So, you will get h 0 x 1 a linear convolution would also have given you h 1 x 0 no problem, but a circular convolution will need will give you h 2 times x 3. So, by pre-pending these you are able to get the circular convolution in this regime and we will ignore this part. Therefore, the way we achieve this circular convolution in the OFDM cases let us say you have x 0 x 1 x 2 x 3 then you have the next symbol and deliberately adding a gap let us say x prime 0 the next group of symbols you know next these x prime 1 x prime 2 x prime 3. What you do is you take you take these let us say 2 of these just for an example let us say you take these and you prepend them over here. Similarly, you take these x 2 prime x 3 prime and prepend them over here sorry about this then as you perform the convolution with h your h 2 h 1 h 0 moves move moves your h 0 h 1 h 2 you ignore the convolution result at these points just take these you again ignore the convolution result at these points and just take these these points will be circularly convolved. This is the trick that we play and by playing this trick of course you have to prepend some amount of data to the beginning this of course results in an overhead meaning you are repeating symbols it is not like you get something for free for OFDM if you are going to use the cyclic prefix let us say in this case we are using 3 symbols earlier in n time if you have n symbols you are sending them in n time instances. In this case for n symbols you are sending them in n plus 3 samples n plus 3 time instances. So, your overhead is actually n upon n plus 3 in or rather the efficiency is n upon n plus 3 because you are reducing the data rate ever so slightly. This is one of the reasons why if you look at the FFT size n in OFDM the n is essentially chosen to be as large as possible for supporting the data rate and you choose the cyclic prefix length to be close to or just slightly above the expected channel length in number of tabs. For example, we have a 3 tab channel head 0 h 1 h 2 the cyclic prefix needs to be at least 2 in length typically you will choose more because if you then have to run your system in an environment where there are more tabs needed then you do not want it to fail. So, the circular convolution produces overhead and in fact, let us say that you know I can define a term called let us say OFDM's efficiency this is not a very standard term this is equal to you can say n upon n plus c p length or alternately the overhead is c p length in you can think of this as a fraction or n percentage. So, the OFDM efficiency is n upon n plus c p length meaning you want your n to be much larger than c p length or c p length to be much smaller than n of course, c p length has to be chosen to be length of channel typically length of channel minus 1 that is something to keep in mind. So, the key idea that we are doing is we are taking the cyclic prefix and by taking the cyclic prefix even after you convolve with the channel you can ignore the part that comes out the y that comes out after convolution from the channel just previous to this actually this is let us say y prime n minus 2 n minus 3 and take only this part this part is circularly convolved that is within the part after the cyclic prefix at the receiver you have circular convolution what does that give you. If you do this then if you take the DFT of this part which I have highlighted then you are going to get y k which is h k times x k which as we promised is giving you a flat channel. In other words if you manage to do this cyclic prefix based you know extra effort the resulting y k you get has undergone just multiplication by h k which is a much simpler equalization problem because you just have to multiply or divide by a single number let us say it is MMSC or you know let us say it is a 0 to 0 forcing you can come with a simpler equalization in this particular approach that is the key idea. One thing we have not seen is the effect of noise that is something which we will address now the overall model is h n convolution w n sorry h n convolution x n plus w n is what we have if we consider vectors of the form w you know y is y is equal to y 0 y 1 up to y n minus 1 transpose and so on and similarly for x ok. If you assume an appropriate cyclic prefix so whenever we say appropriate cyclic prefix we say that the cyclic prefix length is long enough so that the impact of the channels has been converted to a circular convolution within the region of interest. Then if you now choose the w which we chose earlier the w was the IDFT matrix scaled so that w Hermitian w was identity at the receiver if you do w Hermitian y y is only the part after the cyclic prefix you get w Hermitian h circular convolution x now h circular convolution x if you take the DFT of that you get h k x k. Now what about w Hermitian w now that is something which we call w prime but let us look at what w Hermitian w is let us say our w is w 0 w 1 I will call it noise w n minus 1 and this is distributed as complex normal with mean 0 and let us say we will assume identity covariance it is scaled that is you do not have sigma square i because I have taken the sigma square as a scaling and just go to scale my E s so that E s by sigma square is my new E s. In this case my noise is w if I do w Hermitian times w and call it w prime let us look at the covariance of w prime expectation of w times w prime times w prime Hermitian is equal to we will play the same trick as we did earlier w prime w w Hermitian sorry this will be w Hermitian w w Hermitian w ok let me just redo this carefully yeah w prime is w Hermitian w. So, this is w Hermitian w w Hermitian ok now since this w is a fixed matrix this is equal to w Hermitian times expectation of w Hermitian times w, but this is identity as we saw here. So, this is equal to w Hermitian w which is equal to identity of the same size in other words taking the DFT of the noise results in a noise sequence that is the same distribution in other words because of the fact that this scale DFT matrix is just a circular you know it is it is just like a rotation matrix the noise variance does not change. Therefore, this w k are actually IID because why chose my w is IID they have the same variance as w this is the key this is true only in the case where your w has a covariance which has some scale version of identity which is what we are going to consider. So, w prime k has the same variance of w n and it is IID just like w n. Therefore, this is actually something like a very plain single tab scaling additive white Gaussian noise channel and it is very very easy and simple to handle. Therefore, you are able to now bring back all the tools that you learnt except that it is very very simplified because you just have a single tab it is not a filter your OFDM is converted this convolution filter to a channel like this. Of course, there are some prices you have paid for like cyclic prefix and you know a stranger kind of frequency footprint, but it is very very easy to implement a receiver for this if you look at the tradeoffs. So, let us summarize what we have learnt white band channels can be paralyzed for simple equalization you just want to put your data in parallel frequency bands and using the DFT or an IDFT is a nice way to make the channels parallel channels parallel one key requirement is that we need circular convolution and this is enabled by using the cyclic prefix that is an overhead and because of its ease of implementation and several advantages OFDM is used in several modern wireless standards and in fact all standard like Wi-Fi, LTE use some variant of OFDM and several wired communication also such as ADSL use a variant of OFDM called discrete multi tone and OFDM has seen a lot of success in several wireless standards as well. In the next lecture, we will go through a couple of examples of implementing OFDM on GNU radio that will make the concepts very clear. Thank you.


Howdy guys, IndiePixel here. And in this video, I wanted to cover the latest and greatest sweep node that comes with Houdini 18. And the reason why I'm doing this is because, well, I made the procedural racetrack course up on Udemy a few months ago. And a lot of things have changed since that course with regards to the sweep node specifically. And so I've had a lot of questions of individuals asking me how to use the new sweep node. And so I thought might as well just make a really quick video and show you guys some of the basics and how to get used to it and understand its new functionality, which is really slick. It has lots of new features that really just remove a lot of the steps we used to have to do. So let's go and start out by dropping down a geometry node here. And I'm just going to call this my rope generator. We're going to make just a really simple rope generator. So to get this started, let's just focus on the basics first. So I'm just going to drop down a line, just a simple line. Currently just has two points. And then I'm going to go ahead and drop down a sweep node. And then we're just going to wire in the line. This is basically going to be our path. And we're going to wire it into the first input. Now the inputs for the sweep node have basically been swapped. So the first input here is for your path. The second input is for your cross sections. Or as before, or in previous versions of Houdini, it was the other way around. So you put in the cross section here in the path and the second input. And the reason why they have it in the first input is because the sweep node basically allows you now to change the surface shape type. So if you don't need to provide any other cross section, or let's just say you're doing something really simple like a tube or just a box, the surface shape has a bunch of options built into it. So we can select a round tube. And it automatically just makes a round tube for us. We can come up here and select the square tube. And that makes a square tube for us. So if you've watched any of the other tutorials or courses that I've put out, you'll remember that we actually had to go through and do quite a bit of work where we had to define our, in this case, we would create a grid. And we would have to set it to 2 by 2. And then we'd drop down the sweep node and feed in those two options there. Now we don't have to do that. Now we just change the surface shape. And for the last one here, we have the ribbon option. So if you just need a ribbon shape, so beforehand you would drop down some sort of curve and then align to make a ribbon shape. But it's built into it now. So let's take a look. Let's set this to the round tube here first. Now our next options here, our next parameters that we have are the columns and the radius. So this allows me to increase the amount of columns for my tube. And it works the same way for the square tube. So this can increase or decrease your columns there. All right, and then we also have the radius. So this allows me to control that radius. So really cool, really fast. And I actually think the sweep node does run faster. It feels faster. Maybe it's just because it feels new. We could come in and we can reverse it. If you remember from past versions of the sweep node in Houdini, a lot of times your geometry would come out reversed. And so now there's just an option to allow you to reverse it here, which again removes another node. Literally just in two nodes, we already have a tube. All right, so then we also have the stretch around turns. Now this basically replaces the functionality where it would automatically scale the corner profiles or cross sections so that it would fit. So basically as the shape was coming around a particular turn, the volume would be preserved. All right, so that's what this does here. The cool thing too is that they also built in the end caps. All right, so if we come down to the end caps here, I can go and select single polygon now and it'll cap it off with me. You can also cap it off with the grid. In this case, we get this more pill-like version. All right, and you can change the cap divisions. You can change the scale of that. You can change the roundness of it. Really cool stuff. Let's do single side polygon, which I don't think actually works for this particular one. Let's put it onto the square tube. Yeah, we're just gonna leave it there. But really cool thing about this, now we have a single polygon. And we can go and put it into a group. So again, this removes a whole nother step where we used to have to drop down the polyfill node. All right, so you just drop down this guy and select single polygon. So now we don't have to do that anymore. It's all built in. And now that we have this option to put it into a group, all right, you can see now, if we select our attribute list and group list here, we can see that those two caps are in this group. So you can go and then drop down the split node or a blast node, and you can select it from that list. So you can get just the caps if you need it. Pretty cool. All right, so let's take a look at some more of this stuff. I'm actually going to keep the end caps off for this particular project here. All right, and then we have apply scale along curve. All right, this allows us to apply scale, but currently I don't have any cross section. So in order to take advantage of this particular curve here, we need more points like that. All right, and so let's just do something like this. That's pretty cool. All right, so that allows us to control the scale. Beforehand, we would put in a value based off of the resampled values. So in this case, if I actually had this guy like that, I would do a resample. This is all what we would have to do before hooting the 18. That would give me a bunch of new points, and then I would pump out the Curve U value, which gave me a value from zero to one. Or we would do it in a wrangle node as well, and then apply that to the p scale. Now we just have the curve or the scale ramp available to us right off the bat. Just need to make sure that we add some points to our profile or our path, I should say. And then we have our rotation down here. All right, this allows us to control the pitch yaw roll. So if I put in some roll, you can see I can turn the whole object. We can twist all this stuff. And we can do a full twist based off the length of the curve. All right, and you have options here too to control that. Really cool stuff. So you also can come down here and control the yaw and the pitch individually. All right, so you can come down here and control the yaw there. Or you can do it based off of the length of the curve as well. Same for the pitch. And change it based off the length of the curve there. So lots of power in all of this. So what I wanna do now is I wanna move on over. So there's lots more other things here that we can talk about when it comes to the construction of this. All right, but usually this stuff comes into play when you actually provide something like a curve, not just a straight line. All right, currently we have just a straight line, which is really basic. So let's move on to the UVs and attributes over here. All right, and I'm actually going to turn off the scale along curve just for this particular demonstration. So let's go to the UVs and attributes tab here. And I'm gonna hit five on the keyboard. All right, currently we don't have any UVs for this particular node. Well, the cool thing is, is we can just check this compute UVs. And voila, we get some UVs. And by default what it's gonna do is it's going to actually normalize our UVs to the zero to one space inside of your UV view over here. And that's all coming from these particular options down here, okay? And so if you don't want that, and a lot of times I really don't, there are cases where you would want to have it normalized like that. So what I'm gonna do is I'm actually going to turn off normalize computed use there. And I'm gonna come down to the UV seams. And you'll notice that these two toggles here allow us to snap the U to the nearest tile boundary or the V to the nearest tile boundary. And that is what's actually snapping it. So if I uncheck these, we're gonna get the actual size. Now if you recall beforehand, we had to use the UV texture node to do all that. And we'd have to take the arc length, spline right here, and then we'd have to actually measure the length. You know, it was a lot of work beforehand. And that's why I really, really love this new version that I came up with because it just really speeds things up. So if I come down here and drop down a labs UV visualize node and just set my grid time to one, you can see we have perfect UVs. And if I change the length of my line, they scale appropriately. And if we were to switch back over to our UV view, you can see it's scaling perfectly. All right, and if I were to change something like the radius over here, look at that, super cool. All right, and let's check it out over here. So you can see it's scaling perfectly as well. Awesome. All right, so let's have a little fun with this now and take a look at some practical use case of this. So I'm gonna delete the UV visualize node there. And what I wanna do for this first sweep node here, let's go and instead of producing the quadrilaterals, this time let's just do the rows. This will give me basically a disk for each one of those points on the line. All right, so really useful. You don't always have to just produce some geometry for all this stuff. All right, so with those particular pieces, let's actually, and you know what? Now that I'm thinking about it, let's just do the columns here. Yeah, because what I wanna do is make a rope with this just by using sweep nodes, really, all UV and everything. So just to show you the power of this new node, we can make a piece of rope literally in like three nodes basically. And so let's go now and let's do some twists. So I'm gonna apply a full twist here. All right, that's looking pretty good too. Yeah, so that's gonna basically be each profile or path for our rope. So then what I wanna do is I wanna feed those particular curves into another sweep node like so. All right, notice I'm not having to use anything else other than just sweep nodes for all this stuff. And this time I'm gonna do a round cube and boom, rope, it's so awesome that way. All right, you can control the cross sections of this and the radius of all this stuff. You can then control the amount of strands that you have and the overall radius of that as well. Look at that, so now we have a rope. And we can come down here and do our scale as well. And I think I'm just gonna keep it, let's just do something like it's a little skinnier in the middle there. That's pretty cool. And then let's come into our second sweep node and do another radius like so. And there we go. And we can also control the twisting of it with this guy. You know, we should probably also in the middle here. So I lied, we're gonna use four nodes to make this rope. Let's put in a resample node to resample our individual strands here. And I'm going to set this to subdivision curves. And yeah, I think this will work out nicely for us. There we go. So we got something that's a little bit smoother now. How cool is that? So hopefully that helps out. Let's go and finish this up by making some UVs and then maybe let's put in a different curve instead of a line for this. So let's go down to our last sweep node here and let's go to UVs and attributes. I'm gonna compute the UVs. So let's just save this. I'm just gonna save it to my desktop here. I'll let you guys have this file. So we'll just call this sweep or sweep rope like so. So let's switch back over to that UV view. And you'll notice that we're getting UVs, but what's happening is because this first sweep node was actually producing UVs, it's trying to use that data as well. So if I turn that off, we get our UVs back, right? Or you can come into the sweep node down here and say override any existing UVs, which is another way to do that. So if you remember, I'm gonna keep it on length weighted and we're gonna turn off normalize. And this is just because I want the UV to actually match the dimensions of my rope. All right, so there we go. So now we have UVs for each of our rope strands. So if I were to put down that UV visualize node again and just take a look, let's actually put that grid tiling into one and there you go. We now have a rope. It's pretty cool. So I'm gonna actually close this off. Let's just really quickly make a curve. So I'm gonna go into my top view here and let's just make a really quick curve. Let's drop down the curve node like so and let's hit enter on the keyboard so we can start drawing and let's just make some rope like curve. There we go. Then let's do a resample on that just so we make it nice and clean. All right, and let's just put it to one and let's do subdivision curves. That was a little bit too harsh on the length there. There we go. Cool. So now we can just feed that into that first input over here and we'll take a look. Look at that. We have a rope. Pretty awesome stuff. When you come down here, we can control the twisting from the first node. If you wanna get more twists in there, pretty cool. All right, and so the second input, just remember the second input is for your own custom profile. All right, so far to put in some circle here that would basically replicate the same thing. All right, so let's just pump that guy in there and you can see we get the same results. All right, so hopefully that clears things up for you guys and that was a fun little exercise in learning how to use the new sweep node in Houdini 18. Thanks so much.