Lecture Series in Mobile Telecommunications and Networks (1583KB)

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From wireless networks to sensor networks and onward to networked embedded contrtol Power control affects all the layers and the question is, where should you address it? That is actually one of the most difficult problems there. It is not sufficient to say that you will address it all over the place because then different layers would be fighting with each other and turning knobs. We still do not have any satisfactory answer on that and, even in communication networks, we are still in research mode. Turning to these more sophisticated systems, they are in the very beginning stages of this and what I have just spelled out is one proposal. I think there will be further evolution of thinking and competing proposals and so on. However, it is true that I have suggested a kind of layered hierarchy, if you will. Sreebhusan Ghosh (AT Consultancy): I have one question for Professor Kumar with regard to the practical application in poor countries. He mentioned earlier that mobile phones have taken over like fireflies in India and China – I think that in China, 60 per cent of the population have mobile phones and it is rapidly progressing in India. I was very surprised at how quickly it has taken off because five years ago there were hardly any but now there is the better part of nearly 20 per cent, for which Mr Sarin of Vodafone spent a great deal of money for a network in India. The point in question is this. Seeing that the mobile phone technology works so well, despite the relative level of ignorance and lack of technological development, do you see any particular application with this networking, also without any land line involved, which will help the traffic system in major cities like Calcutta or Bombay, where at any given time 50 per cent of the traffic lights do not work because of communications alone? Or likewise, in big cities in China or elsewhere? Or do you think that the technology itself is so complicated, comparing from the mobile phone to mobile networking, that it is a long time before this takes place? PR Kumar: Interestingly, these new technologies that we are seeing allow countries to leapfrog the industrial revolution. Actually it is a paradox: less developed countries probably have more wireless infrastructure than developed countries, because developed countries have so many wires in the ground and the capital is already there and it is hard to compete with that. There are many applications, for example in remote medicine. In the villages in India, as you mentioned, if you can transmit the image of your skin or whatever, then a doctor could at least do some preliminary diagnosis. There is greater justification for using these kinds of technologies in less developed countries than in developed countries where there is an infrastructure. There are also other applications, which I should have mentioned in answer to Professor Walker’s question. In hospitals, every time you are hooked up to all these instruments in the emergency room, with these all these wires trailing around, we can start to interconnect things wirelessly. Those kinds of applications, regardless of whether it is the US or India or wherever, mean that there is a great deal of potential. For traffic, the answer would probably have to lie in mass transit. Professor Ralph Benjamin (University of Bristol and UCL): Early on in your talk, you pointed out that, in a cellular network, frequency reuse with minimum interference benefits from a rapid increase of attenuation with range. The scope for doing this is rather limited but one can do a little by choice of frequency. Do you have any views on an appropriate combination of frequency reuse and time reuse, in order to minimise interference? PR Kumar: At high levels, there is not much difference between the two, or even CDMA. These are all ways of orthoganalising your channel, that is breaking up your overall channel into pieces – whether you package them in blocks of frequency, blocks of time or blocks of codes or whatever. At a high level you are just partitioning your resources and so there is not that much of a difference. Of course, there may be differences in other kinds of ways, for example perhaps CDMA may allow softer entry into and exit from the system and so on. At a high level, however, there is not much of a difference between the two, fundamentally. Mike Walker: Your traffic control is fascinating. Do you think we will ever reach the stage where people will really trust systems that will enable them to zoom across crossroads, seemingly without paying any attention whatsoever? PR Kumar: Very often, what we are familiar with is very comfortable, while we think that what we are not familiar with is just impossible. We seem to be on that edge all the time. However, the technology is already coming where you have given up the longitudinal motion of your car with cruise control – so you already do such things. I guess that lateral motion is the next step. The Royal Academy of Engineering 19
Human beings will also evolve and we will have to adapt to these new technologies. Of course, there are all kinds of challenges and not just us adapting – there are also legal challenges and so on. I do not want to minimise the challenges that exist, but there is the potential. Mike Walker: They make superb games anyway. Your students must love them. Professor Fu-Chung Zheng (University of Reading): I would be interested in the clock synchronisation progress that you mentioned. Some of us know this phenomenon, which happens in the forest in some Far Eastern countries, which is that hundreds upon thousands of bats would flash together during in the night, like fire blocks, and they have a really, really intricate synchronisation mechanism between them while we, as human beings, have to use other tricks as you have just mentioned – averaging and so on. How are we doing compared with those bats? The real question is about the accuracy that we can achieve now – it is milliseconds or nanoseconds? PR Kumar: The last question is always easier. The most we can achieve is 6 microseconds. There are many things that biology does which we cannot begin to get close to, and vision is a good example of that. Even the way that bats can spatially locate something that is less than the resolution of the neural spike – I do not know. We still have much to learn from biology. Dr Graham Woodward (Toshiba): [Without microphone] This relates back to the shared bridge network. So much of our feedback system is motivated by underlying information theory and you made an interesting observation on capacity by taking a Maxwell view rather than a virtual view of the network. I have seen the result of experiments based on unicast users collaborations. Network coding shows that you can get enormous capacity by collaborative coding across the network, especially when there is unicasting and broadcast. Is there a network coding theory emerging for Maxwell’s view of the network, and what does that tell us about networks taking a Maxwell view rather than a virtual view PR Kumar: That is a good question. As far as unicast systems are concerned, the information theory allows for network cording or anything else. It is an absolute theory, but it is only up to three constants, as I mentioned. On the other hand, there are simple examples where, when you are relaying packets in opposite directions, then you can use network coding to give a certain factor improvement and so on. So network coding definitely buys you constant factors improvement. The one thing I did not touch upon is multicast, where network coding has a great deal of potential. Ralph Benjamin: Concerning the intelligent crossroad junction, to operate intelligently, clearly you have to monitor the traffic approaching from all sides, and have distinct lanes for turning and keeping straight on, or other indication of that. Subject to that, you could give each block of traffic a target velocity with tolerances, which normally allows continuous flow and, in a limited addition, these target velocities can go down to .… In the present system, the lower limit of intelligence can no longer improve things. PR Kumar: Our system works on something like that, with the added feature that there is a proof of safety. The proof of safety is impervious to whatever the car in front of you does, subject to the limitations of Newtonian mechanics. It is that kind of system. Mike Walker: If there are no further questions, I suggest that we move into the Marble Room for drinks. I would like to thank Professor for his excellent presentation and the very interesting discussion that followed. [Applause] 20 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: Questions & Answers Mike Walker: Th
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 and 30: chunks of spectrum where you are in
Page 31 and 32: As an aside, I was reading a few of
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
Page 51 and 52: 1024, we transmit 10 bits, so to sp
Page 53 and 54: Bandwidth extension with hidden sid
Page 55 and 56: 4 Vision: ambience audio communicat
Page 57 and 58: Questions & Answers Michael Walker:
Page 59 and 60: I said five years ago and what I he
Page 61 and 62: them and perhaps leave out some of

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