Cooperative radio: together we can

Felipe Gómez Cuba | Researcher

One of the main limitations of wireless networks is spectrum scarcity. Systems are planned for different devices in the same neighborhood to employ different frequencies. This planning is limited by the bounded range of frequencies. How can we keep improving wireless communications if frequency ranges remain the same? We need devices that, for a fixed amount of spectrum, transmit more information. This is the reason behind the expression spectral efficiency.

The immediate method for achieving it is improving transmitters and receivers. Thanks to constant advancements in computing technology, radio devices can perform more complex calculations every day. One of the most important recent advancements has been including several antennas in each device, allowing very sophisticated transmissions. Among the most outstanding techniques are beamforming and space-time coding (STC).

In addition, the fact that our wireless gadgets belong to communication networks may be taken into account. Can the members of a network contribute somehow to improve efficiency? Let us imagine a daily life example: two persons are chatting in a crowded room and one of them cannot hear part of the conversation. A third one nearby overhears that part and helps.

A wireless network should work the same: if a third user is close to the destination peer, the former could decode packets missed by the latter and re transmit them, since this is more economic than a complete retransmission by the source. However, this is usually not the case nowadays: until recently, computing was not sufficiently powerful to enable devices that could pay attention to their surroundings. This is about to change.

We know that the capacity of a wireless network can be greater than that of a point to point model, but we ignore the limitations of this potential. We can find examples like the one above, demonstrations that there exists more capacity thanks to cooperation; but there is no formula in information theory for the exact capacity of a generalized wireless network.

Achieving the advantages of cooperative networks is not easy, but it is the moment to try.

Gradiant is currently working in this type of technologies in the framework of project Mefisto, (Page 72, Activity Report 2011) funded by Xunta de Galicia.