Researchers bank on chaos theory to clean up wireless signals

Wireless communications comes in many forms, from the mobile phone to the automatic garage door-opener. All share a common problem: how to guarantee a clean signal.

Services are improving all the time but problems remain. What mobile phone user hasn't experienced a dropped call or a lack of service because the signal can't reach?

Researchers at University College Cork are working with European partners in Finland, Switzerland, Italy, Hungary and Greece to make blank spots a thing of the past. The EU-funded project is developing a new type of communications system that is cheap but also reliable.

The system relies on chaos theory, the science of randomness, explained Prof Peter Kennedy, professor of microelectronics engineering at UCC. This spring, Prof Kennedy received the inaugural Royal Irish Academy Parsons Award in the Engineering Sciences, a distinction given to an outstanding researcher under 40 years of age for work in engineering.

Prof Kennedy led UCC's involvement in the EU-funded research project and is a world expert in wireless communications and circuit design. He was one of the early researchers in oscillation and chaos theory, doing his PhD at the University of California, Berkeley.

The chaos-based system is radically different from conventional wireless communications, he explained. Existing technology relies on using a tightly-defined broadcast frequency and sending a relatively powerful signal as a way to overcome both interference caused by other signals but also disturbance caused when the signal bounces off objects and interferes with itself.

The chaos approach is completely different and is known as "spread spectrum communications", Prof Kennedy explained. Instead of using a tight frequency it uses a wide band spread over a predetermined range of frequencies. "We essentially wander randomly around the band. Our system automatically wanders around," he explained. The signal's wave-shape is also very different. Most broadcast waves are very regular, adopting a typical shape with the same sized peaks and valleys like ripples on the surface of a pond. The wave-generator that sends out this new signal is controlled using chaos mathematics so the wave shapes are all over the place. "It just means the wave forms are not sinusoidal, they don't repeat themselves," Prof Kennedy explained.

The signal is chaotic and it ranges over a wide band of frequencies, but because of this the signal can be much weaker. A weaker signal means there is less chance of interference caused by other signals. "We use the space more efficiently," Prof Kennedy said. "You have to make the best possible use of the spectrum that is available. We have a way of designing that spectrum using the chaotic signal source."

Their system is being developed and tested over an experimental frequency band that is shared by other researchers called the ISM (industrial, scientific, medical) Band. "In that band anybody can operate. If you want to do something different you have to work in one of the bands where standards are still being set."

The ISM band uses what is known as Bluetooth technology and has the dubious honour of being named after a Viking pirate of the same name. A requirement with Bluetooth technology is that everybody working in that band does so at low power.

The key to the chaos approach and the thing that makes the system both very cheap to operate and very reliable is that two streams of digital data are sent out together. One is a reference signal and the other is an information signal. The research team developed a special receiver that takes the two signals and correlates them. Like all digital data, be it the signal to a garage door opener, a mobile phone or an automated pay-toll system, it is sent as zeros and ones. It is very simple for the system to interpret the data because two similar wave forms represents a one, and a wave form and its inversion represents a zero. The signal is low-power but highly resistant to interference because of the reference signal, Prof Kennedy said.

"No matter what the interference, you are always seeing the reference."

This, he said, was particularly important, say, in an office application where there was a high potential for the signal to degrade due to interference. The chaos signal is insensitive to this problem.

A robust, low-cost system of this kind is "the holy grail" for many commercial applications, he said. The reliability of the low-power signal also means that inexpensive and less sensitive electronics can be used to receive the signal.

The research group has completed the initial €1.5 million (£1.2 million) project and is now seeking funds to commercialise the system. Possible products to use the system include electronic stocktagging, automated toll-booths, industrial applications where high-voltage electrical interference is possible, and communications using the electrical wiring in homes or offices.

Prof Kennedy will present a lecture next week explaining his research. Entitled Oscillators: Why are they so?, it takes place on Wednesday May 30th at 4 p.m. at the Boole I lecture theatre on the UCC campus. The event is free and open to the public.