Lecture Series in Mobile Telecommunications and Networks (1583KB)

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To the edge of chaos? The complexity and the promise of a technology and service-neutral future DIGITAL SHELTER KIT Pedro Sepuiveda (1999) So as I said, there is an enormous amount of simplicity in the way I have described the initial diagram, which does not take into account the actual ‘mess’ that the signal actually creates. Most of the debate about anything to do with exclusive usage rights and the ‘propertising’ of spectrum has all been about how you define an entity, and how do you define those rights, in a way that takes those interference issues, this ‘spill over effect’ into account. Many of the papers you will read will discuss those various suggestions on how that might be achieved. The following diagram captures the complexity of neighbouring spectrum consumers further. If I am deaf, and I am living in a house where the person next door plays extremely loud music but I cannot hear it, is that interference? Whereas, if I put a sensitive array of microphones around my house and the person next to me is playing extremely quiet music, and I am annoyed by that really quiet music, which of those two scenarios is depicted here? When it comes to thinking about mobile communication devices and wireless communication systems, you have to think the kind of situation encapsulated in this slide. That is why in this very, very fluid world, it is harder to define what kind of things can live next to each other. The problems do not stop there. There are enormous problems when you step back and begin to look at the market issues. People worry about fragmentation of spectrum, and people worry about entities buying spectrum to block others using it, and people worry about the cost of any of these ideas. A lot of people would say today – and certainly I hear people in industry say, the infrastructure costs are so expensive that the whole idea of perhaps installing something new and thinking differently is a big problem. There is another huge problem, and I do not know whether you have come across this. In the UK, if you ask someone for directions, they will typically tell you to go down the M1, take a left at the second junction and go on to such-andsuch a route. In Ireland, they tend to say things like, ‘Go to O’Brien’s pub and, after that take a left until you get to O’Donohue’s pub, and then take the second left when you get to McCarthy’s pub.’ – they think like that. The other thing they will tell you, if you ask for directions in Ireland, is, ‘Well, I wouldn’t start from here’, which is a typical reaction. That is the point of some of these ideas: we are where we are with the regulatory system that we have and it can be quite difficult to imagine how we can start from where we are now. A typical reaction is, ‘Here is how we would like things to be, but I would not start from here.’ That is something that needs to be overcome in this field. There are big challenges concerning interference, in how to define spectrum usage rights, in defining the regulatory policies and in the economic and financial arena. However, there is also a good deal of hope, and that hope comes from much of the engineering advances that have taken place in the last little while. In this part of the talk, I will focus on various different aspects of the technology that feed into that hope for the future. As I see it, it is not true to say that, collectively, any of the pictures represented here have been dealt with, but there are bits of advancement all over the place that are contributing to this picture and beginning to push things forward, and build on where we are going. I would like to spend a little time talking about cognitive radio. Thsi slides shows different radios, static fixed frequency radio, a multi-band radio, a multi-mode radio that we are very used to and a cognitive (software defined) reconfigurable dynamic spectrum enabled radios that supposedly can do any mode, any band, over a wide range of frequencies. There are probably a number of people in the audience who are very familiar with cognitive radio, but the term ‘cognitive radio’ was coined by Joseph Mitola in the 1990s. He used this thing called the cognitive cycle, which depicts what cognitive radio was about. The whole idea is that you have a radio that has a brain, so that the radio has the capability of observing the outside world and then somehow making some decisions about how to react to that very changing and dynamic outside world. In this diagram from one of his papers, he particularly focuses on how you can react immediately and quickly, and how you can make long term plans about what to do next, make decisions and then act. There is a huge amount of research in the area of cognitive radio. The Royal Academy of Engineering 29
As an aside, I was reading a few of the transcripts of previous lectures before I came here. I noticed that in Joseph McGeehan’s lecture, he was talking about software radio and cognitive radio as well, and making very interesting points about how a great deal of the technologies , when he designed radios in the 70s and 80s, had that kind of configurability in them. He made the statement that there is very little that is new under the sun. To a large extent, much of the technology that we see emerging is based on ideas that have been around for a while, or there are now techniques that allow those ideas to be put into practice. Cognitive radio is definitely the buzzword of the moment. Another way that it is useful to think about it – and this is the terminology that was coined originally at Virginia Tech in the US – is to talk about radio that has meters and knobs. A cognitive radio has a whole load of knobs, which you can set anyway you want, and you have some meters that are used to observe the outside world. You then have the brain which makes some kind of decision about how to set those knobs in the best possible way and in line with whatever observations were made with the meters. If you look at the literature on cognitive radio, nine out of 10 times, people talk about cognitive radio being used for dynamic spectrum access techniques. When you go back to the measurements that I showed when we looked at the overlay and underlay techniques, most people are interested in how you create cognitive radio to sculpt the signal to fit into one of those holes, or sneak the signal underneath the others. Acknowledging that, I want to talk about cognitive radio a little and then bring this back to the wider discussion about spectrum. Here is a cognitive radio that has lots of knobs. This is a busy slide with a great deal of detail on it but, essentially, in recent years people have designed every and any kind of software radio, with all parameters up for grabs. In this particular case, it is a kind of generic, multi-carrier CDMA/OFDM radio. By setting various kinds of parameters, you can turn it from one to the other or, by adding new components, you can make it behave in different ways. You can see plenty of examples of this kind of thing and, in this particular case, it is again focused on dynamic spectrum access. In this case there is a primary user which transmits a DBPSK signal, and there is the secondary user which uses DS-CDMA signal. It, the secondary user, wants to co-exist with this primary user, so it notices that it cannot co-exist in its current form. It adds another block into this system and, through doing that, it is able to do what we call sub-carrier selective, multi-carrier CDMA – in other words, it sculpts itself into a different shape, to fit around the existing user. We see lots of examples of this kind of work. The main point to take from here is that a lot of software radio research that we see in the world today has come up with a great many different ways of making every single parameter of a radio a variable that can be set as desired and when desired. The other point is that there are better ways being developed all the time in the brain section of the radio. With all these parameters that can be set, there needs to be means of deciding how they should be set and this is where the brain of the cognitive radio comes in. On this slide I have referenced a piece of research by Tom Rondeau. Tom designed a cognitive engine based around genetic algorithms and case based reasoning, in order to be what he called ‘multi-objective’ optimisation. In other words his radio makes decisions on its performance characteristics using multi-objective optimisation. 30 The Royal Academy of Engineering
Page 1 and 2: Lecture Series in Mobile Telecommun
Page 3 and 4: Foreword This compilation brings to
Page 5 and 6: From wireless networks to sensor ne
Page 7 and 8: From wireless networks to sensor ne
Page 9 and 10: As far as the routing of packets is
Page 11 and 12: easons. In the internet, one never
Page 13 and 14: Implementation with laser pointers,
Page 15 and 16: here of laptops, and all these lapt
Page 17 and 18: adds a great deal of discrete compl
Page 19 and 20: Questions & Answers Mike Walker: Th
Page 21 and 22: Human beings will also evolve and w
Page 23 and 24: Welcome and introduction Professor
Page 25 and 26: ComReg Collection - Start 16/Apr/20
Page 27 and 28: evidence that people give in favour
Page 29: chunks of spectrum where you are in
Page 33 and 34: Of course, it is not just one mask,
Page 35 and 36: I apologise for hopping between top
Page 37 and 38: Questions & Answers Michael Walker:
Page 39 and 40: Nobody - believe you me, it came ou
Page 41 and 42: The second aspect of my comment is
Page 43 and 44: want to call it - that sits there a
Page 45 and 46: From plain old Telephony to flawles
Page 47 and 48: From plain old Telephony to flawles
Page 49 and 50: You can see that there is much room
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Page 57 and 58: Questions & Answers Michael Walker:
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Page 61 and 62: them and perhaps leave out some of

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