Leveraging physical-layer cooperation for energy conservation

Physical-layer (PHY) cooperation is a technique for achieving multiple-input-multiple-output (MIMO)-like performance improvements on small devices that cannot support antenna arrays. Devices in a network transmit on behalf of their neighbors to act as 'virtual MIMO' antennas. Since small devices are typically battery constrained, PHY cooperation immediately leads to the following question related to the energy efficiency (bits per joule) of devices: Is the performance improvement worth the extra energy costs of transmitting for others? Through an in-depth hardware test-bed study, we find that PHY cooperation can improve energy efficiency by as much as 320%, or it can reduce energy efficiency by as much as 25%, depending upon topology. With this performance gap in mind, we propose the distributed energy-conserving cooperation (DECC) protocol. DECC tunes the amount of effort that each device dedicates to providing cooperative assistance for others so that the energy that each device spends on cooperation is commensurate with the personal benefits that are received by that device. With DECC, users can tune their level of cooperation with completely node-localized decision-making. Thus, DECC allows nodes to tap into a large energy-efficiency benefit, suffering only a bounded preset loss when this benefit is not available.