In the faster stream

Ultra-fast 4G mobile handsets and mobile systems that can stream live video and music at extremely high data rates are to move a step closer, thanks to research at Cardiff University.

The three-year project, in collaboration with Telecom Modus, aims to use a variety of advanced digital processing techniques to allow wireless services to reach the same levels of data capacity as fixed broadband systems such as cable modems or ADSL.

The amount of data that can be sent over wireless systems such as WiFi and WiMax is currently substantially lower than in these fixed systems, according to one of the project’s leaders, Prof Jonathon Chambers, director of the university’s Centre of Digital Signal Processing.

The team aims to increase the ability of wireless systems to carry data by an order of magnitude, so increasing the data-rates beyond 100Mb/s and even up to 1Gb/s. At present wireless services can only carry up to around 25Mb/s. One of the key techniques the team will employ is the addition of multiple antennas at both the transmitter and receiver. These are known as multiple input multiple output (MIMO) systems.

‘The great thing about MIMO is that, provided the environment is right, they have the potential to increase capacity in direct proportion to the number of additional antennas,’ said Chambers. ‘By using additional antennas, plus advanced signal processing, we should be able to reach these improved data rates.’

The project’s most innovative concept is the use of ‘feedback’ between the mobile handset and the base station. Feedback in this sense means extra information about the data sent from the station to the transmitter, and which tells the handset the channels available and so how best to transmit the data. For Chambers, this technique is an important step in improving mobile data rates.

‘It’s a tremendously exciting new concept and is the beginning of what is known as “collaborative radio processing” which in turn will eventually lead to full “cognitive radio”,’ he said.

In existing mobile networks the range of frequencies over which a system may operate is defined very precisely by standards. cognitive radio will be able to sense the available spectrum without being restricted by limits of pre-defined bands. It will also be able to operate over any part of the radio spectrum.

Using feedback between the transmitter and receiver will be crucial to reach this stage, said Chambers. He explained that the main reason this technique has not been used before in this context is because the processing power has not been available. Now, the benefits of Moore’s Law holding true mean that the computing power of both the handsets and at the base stations is beginning to approach the level at which it can be exploited.

The final technology that will be used to improve data rates is known as Orthogonal Frequency Division Multiplexing (OFDN). This technique — used in fixed broadband networks — uses algorithms to divide frequencies into smaller sub-units within which the channel operates most efficiently. According to Chambers it is this complex combination of MIMO antennae, OFDN and feedback that will eventually lead to upping the data-rate for systems such as WiFi and WiMax. While these mobile systems are the project’s primary focus the underpinning technologies that will be developed could one day be applied to 4G mobile networks, he added.

‘People are becoming evermore demanding in terms of multimedia applications and want video streaming — watching Manchester United on your handset, for example — without any degradation. Being able to listen to high-quality music and other online services will only become possible by pushing up the data rates,’ said Chambers.

He estimates that handsets capable of reaching these ambitious data rate targets will be available within the next five to 10 years.