The Green Radio Project studied how future mobile wireless networks and in particular radio base stations may be made more energy efficient. This project involved significant collaboration with the Universities of Bristol, Sheffield, Southampton along with Kings College London. There was also strong interaction with a number of major industrial companies, through the Mobile Virtual Centre of Excellence (MVCE) sponsoring company. At Edinburgh, there were five major strands of work carried out during the project.
The first part of the work studied adaptive sleep mode concepts for wireless base stations. The base station organises its data transmission in order that the transmitter power amplifier can be switched off temporarily when there is low levels of data traffic to be transmitted. Switching off the power amplifier when it is not needed, can achieve an energy reduction estimated at 10-20%.
The second item of the work studied how heterogeneous networks of radio base stations, femtocells and multihop relays can save energy consumption compared to today's networks which consist mainly of radio base stations. Mathematical models of radio equipment and power drain in different devices were developed to analyse a variety of different scenarios. The results are complex to interpret, but in some cases energy savings of 60-70% could be achieved by moving to heterogeneous networks.
The third topic studied energy efficient packet scheduling schemes for radio base station data transmission. These methods exploit bandwidth expansion techniques for energy saving under low traffic conditions and bandwidth compression techniques for high traffic scenarios. The results suggest modest savings of 5-10% in energy, but these gains are likely to increase in future when more efficient base stations are deployed.
The fourth element of the project studied techniques to improve the energy efficiency of video transmission techniques. A novel scheme called random network coding is used to make the data transmission more efficient and to reduce delays in transmission. Results suggest that for high traffic scenarios, energy savings of 25% are possible for users located far away from the base station.
Finally, the project has studied how multihop relays may cooperate with one another to improve the efficiency of data transmission in wireless networks. Through joint transmission techniques operating over short distances, energy savings of 20-30% are possible when compared to radio base station only networks.