Research described with simple words

Here are some short introductions from our PhD students. The texts are written in an attempt to be easy to understand for people with some engineering background.

Make Use of Interference by Cooperation

High-speed wireless service such as web surfing and video streaming becomes more and more popular. Unlike wired cables, the broadcast nature of wireless channel spreads dedicated signals for one user to its neighborhood. Such signals appear destructively and hence are treated as interference.

My research in cooperative communication is to treat such "interference" as useful resource and utilize it to get extra information of the desired signal so that the quality of service can be improved and the communication range can be extended. How to achieve this? Cooperation, both among access points and among users. I focus on design of information combining methods and try to figure out theoretical limits as well as practical solutions. Cooperation makes "interference" helpful.

- Jinfeng Du

Networked Control Systems: A Joint Area of Communications and Control

My research area concerns networked control systems. It seems a complicated issue, but I will give you an example in order to understand it well. Imagine there is a big and modern green house. This green house has a lot of sensors to sense temperature, humidity, light, etc. Since it is big, we have to transfer sensors’ information over a medium to a monitoring unit to take the appropriate decision. These units are called controllers. So we understand the definition of networked control systems: controllers used in a communication network.

The main point which is interesting to me and what I am going to work on my research is how to change sensor information, or, scientifically, code information in order to have a better performance of networked control systems from both control and communication points of view.

- Amirpasha Shirazinia

Control over Low-Rate Noisy Channels

Networked embedded control systems are present almost everywhere. A recent
trend is to introduce radio communication in these systems to increase mobility and flexibility. Network nodes, such as the sensors, are often simple devices with limited computing and transmission power and low storage capacity, so an important problem concerns how to optimize the use of resources to provide sustained overall system performance. Our approach to this problem is to analyze and design the communication and control application layers in an integrated manner. We focus in particular on cross-layer design techniques for closed-loop control over non-ideal communication channels, motivated by future control systems with very low-rate and highly quantized sensor communication over noisy links. Among others, we study the problems such as: to jointly design encoder--controllers for linear plants, whose state feedback is transmitted over a finite-rate noisy channel; to optimize the rate allocation for state feedback control of linear plants over noisy channels.

- Lei Bao

Wireless Control: If you don’t have anything nice to say, don’t say it

To control a modern processing factory, one needs thousands of sensors, hundreds of controllers and dozens of computers. Traditionally the communication between these devices is managed with a lot of wires. Wiring, however, is expensive and time-consuming. During the last decade the wireless technique has significantly matured which has opened up for a solution to all the tedious wiring. But it is not so easy to replace all the wired communication with wireless as one first might think. Using the traditional technique, sending precise data at high data rates is not an issue, but when thousands of devices have to share the same communication medium, they need to limit themselves in order not to disturb the others. They can no longer send as accurate data because this demands a high communication rate. They can no longer use the channel any time they like because this might disturb an already ongoing communication. This typically means that the sensors need to be smarter and send information only when they have something important to report, and when they report, they do it with little data. Our research aims at finding clever solutions to these communication issues so that we hopefully in a close future can construct cheaper factories faster, which in the end will benefit the customer with cheaper products.

- Dennis Sundman

How do we measure information?

In the field of Communication theory we study the fundamental limits of communication, for example, how much information that can be transmitted with a given amount of energy, and we also study how we can build systems that achieve these limits. An important question is then - How do we measure information? It’s not straightforward to answer this.

60 years ago, a clever guy called Shannon answered this question by formulating a precise and meaningful measure of information and he also showed how to determine some important limits. Something very typical to communication theory is that it’s often possible to prove fundamental limits even though you cannot tell how to reach them. This applies to Shannon’s results as well, they were nonconstructive.

Today, thanks to the advances in Communication theory, there are techniques available that achieve these limits for several important cases. It’s therefore possible to have a high-speed connection to Internet wherever you are.

- Johannes Karlsson

Help your mobile phones work better

Suppose the time turns back 50 years, perhaps you would never imagine that one day you could talk to your friend who is thousands of miles away, see her smile on the screen of your little mobile phone. Most of us may know what made this possible: it's digital communication, where the voice, the images are conveyed in a long chain of 0's and 1's. They are called bits.

Now imagine you are in a party, talking with your friend. It's difficult since people around you are talking loudly to their partners. Of course, you can speak louder but then you distract your neighbors. Similarly, when you are using mobile phone, your bits might be heard by your neighbors' phones and spoil their bits. What I am doing now is to find the optimal solution for this problem. Precisely, I am finding the point where every phone can send and receive as much as possible without hurting the others. The solution promises to help future mobile phones and network work more efficiently than they are today.

- Hieu T. Do

Multiuser cooperative communication

Nowadays, smart phones connected to the internet attracted much interest and using them become important part of our daily life. People who are using such communication devices are looking for high speed connections which are reliable everywhere.

It would be interesting to know that there are some fundamental limits on the speed of reliable data transmission while there are some resource (e.g. transmitter power, channel bandwidth,…) constraints.

Characterizing such fundamental limit in different communication scenarios was the aim of researchers in the area of information theory for the last decades. Although, it has been found in the case of point to point communication, it is really a challenging problem to find such performance limits while more than two users are communicating at the same time. My current research mainly concerns with design and analyzing transmission schemes for the network of users which are cooperating to increase speead and reliability of communication.

- Farhadi Hamed

Saving Cooperation

Imagine a beautiful city of Amsterdam in XVII century. A Dutch ship-owner wants to trade with overseas countries. But the sea is full of dangers. His boat can be crashed or captured by pirates. Then all the business of this particular ship-owner dies in a moment. The brilliant idea Dutch ship-owners used was the following one. They said "Why don't we cooperate together? We can send 10 boats simultaneously and share all the benefits and expenses". The risk that several boats will be crashed or captured at the same time is not so high. Let's say they have sent 10 boats at the same time and one of them is captured by pirates. Other 9 still come back and the ship-owners lose just one tenth.

Now consider a Wireless Cellular Network. Mobile phones within one cell want to communicate with Base Station. Let them share the information among each other and send it simultaneously. Assume that one link is corrupted. Other links are still working and the communication remains reliable. The cooperation in such a way increases the robustness of the system. Such a Cooperative Communication is an interesting topic and what I am working on right now.

- Maksym Girnyk