Lecture Series in Mobile Telecommunications and Networks (1583KB)

Questions & Answers
Michael Walker: Now is the time for everyone to participate in the question session. Our speaker has agreed that she
is happy to take questions and the floor is open.
Mr Jim Munro (Intellect): That was a very interesting talk. The party line from very senior researchers at Ofcom and
elsewhere has been that cognitive radio is still over the horizon. You seem to be painting a somewhat different picture.
How would you reconcile these two viewpoints?
Linda Doyle: First, I am certainly not saying that cognitive radio will be here tomorrow. Secondly, the definition of
cognitive radio is widely varied and there are some people who talk about the all-singing, all-dancing, everythingunder-the-sun
cognitive radio. It is easy to say that that is still some way away.
However, Ofcom themselves to a certain extent are contradictory because their press statement about the interleaved
spaces on the TV bands was very supportive of the idea of supporting devices that would do no harm there, and that
included cognitive devices. What I have seen in Ofcom itself is a change – although I do not know the senior people in
Ofcom perhaps as you do – from ‘it’s miles and miles away’, to ‘it’s actually nearer than we think’. That is MIMO’s
evidence, that they are beginning to take a slightly nearer term view of where it goes.
Mr Brian Levy (Hewlett Packard Ltd): Dr Doyle, that was a very interesting talk but you did not mention a few things.
Propagation: you indicated, or tended to indicate, that all frequencies were the same, with very different propagation at
different frequencies, linked budgets and all those things. You talked about signal morphing and that that affects
spectral efficiency. Then there is the linkage to applications, because applications require certain bit rates, certain
parameters. How, in the chaos world, can we deal with all of that?
Linda Doyle: You are very true in saying that not all spectrum is equal and it is the case that, when you present some
of these ideas, and certainly when you draw them in the way that I do, this comes across. You will often hear the term
‘beach fun property’, when they talk about certain spectrum being more desirable than others.
I agree 100 per cent with what you say but I look at this in two ways. You are not dictating what people should use
which frequencies for. Certainly, users of certain services and certain kinds of applications will cluster around certain
frequencies. The economist’s viewpoint is that if everyone wants the same frequencies, then the people who put the
greatest value on them and are willing to pay the most should then have them. That is secondary, I suppose, to what
you are asking. It is not the case that I am saying that anything can be used for anything under the sun; I am saying
what is most appropriate and what is driven by the market, and what the consumer of that spectrum chooses to use, is
up to them, while acknowledging the fact that not everything is necessarily suitable for everything, and of course it is
not because you sometimes want really long coverage areas. Sometimes you want the complete opposite and you
don’t want your signal to go very far. There are all sorts of other issues that you need to take into account.
I agree with what you say, but that is and can be part of the picture.
Professor Ralph Benjamin (Bristol University): You talked of monitoring spectral occupancy and responding to it
adaptively but, in fact, as you rightly recognised, you are really concerned not with spectrum but with transmission
capacity, which is multi-dimensional, frequency, time, space and in fact the fourth dimension, modulation pattern.
It is that total space that you want to use in the best way.
If you use dynamic spectrum allocation, based on some form of marketing or bidding, then you need a cost function.
Cost function cannot just be commercial cost, because there are also such things as social value and social need and
you have to find a way of combining those in the bidding process.
When you use software reconfigured radios, at the same time you have to reconfigure or adapt the user’s mode of
operation to the changing cost of capacity. If you have achieved all of this, it means that there is all the mechanism and
incentive to exploit gaps and to equalise the use of capacity in frequency, time and space overall. Therefore, the only
36 The Royal Academy of Engineering