Lecture Series in Mobile Telecommunications and Networks (1583KB)

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