Lecture Series in Mobile Telecommunications and Networks (1583KB)

From wireless networks to sensor networks and
onward to networked embedded contrtol
Professor PR Kumar
Franklin W. Woeltge, Professor of Electrical and Computer Engineering, University of Illinois
Thank you, Professor Walker, for that kind introduction. I must say that it is a great honour to be present in such an
illustrious place in front of such a distinguished audience. Thank you for inviting me.
I shall be talking about three things: wireless networks, sensor networks and network embedded control.
The oncoming wireless era: from communication to sensing control
6 The Royal Academy of Engineering
The underlying key is that we may be on the cusp of a
wireless era. Let me sketch the elements of what that era
could be. As Professor Walker pointed out, we are very
much in the cellular systems era and countries like India
and China are adding 8 million or so phones per month.
I will look a little into the future, to see what else may be
coming down the road.
I will be talking about wireless networks where there is no
need for any infrastructure. In cellular systems, there is a
wired infrastructure and your telephone makes one wireless
hop to the infrastructure and then it travels with the wired
network. In the future, however, we may all be talking to
each other without any infrastructure.
It is not just communications. Already, we have these small gadgets. This is what is called a moat and it comes out of
the University of California, Berkeley. You can connect your favourite sensor to that – it could be temperature sensor, or
a light sensor, or a magnetic sensor or whatever. That gives you the ability to sense the environment, in addition to
communication and computing – but it does not stop there. None of us is content with sensing and, the moment we
sense something, we want to take action. I am not content with just knowing the speed of my car, but I want to go
faster or slower. Once we have sensing and acting, that is called control and we may be exercising control
over networks.
In the US, since last year people have been talking about a new phrase, ‘cyberphysical systems’, and these are computers
interacting with the environment, the cyber and the physical worlds coming together. This is really the convergence of
communication, computation and control, and that is what I want to talk about.
Ad hoc wireless networks
There are several themes, the first of which is wireless networks. The type of wireless networks I shall be talking about
are what are called ‘ad hoc wireless networks’. These are things that you can set up spontaneously, anywhere. A bunch
of us could open up our laptops in this room or on a campus and then we could start interacting with each other.
The current proposal for operating such wireless networks is what is called multi-hop relaying. How does that work?
Let us say that this node wants to send packets of information to that node. This thing here says, ‘I want to talk’, and the
nodes which hear it agree to keep quiet. Then this node says, ‘Okay, go ahead and talk to me’, and any node which
hears that also keeps quiet. At this point, the neighbours of both these nodes have kept quiet and that facilitates a
packet from here being sent to there, and being received without nearby interference. We can also send an
acknowledgement back, saying ‘I received your packet’. So this four-phase handshake takes place and the packet of
information makes one hop. It then continues on in a similar fashion until it reaches its destination, and that is a multihop
wireless network.