On the use of time-reversal for packet switching in green communications

With the data explosion coming, research on green communications experiences a growing interest in the Information and Communication Technologies (ICTs) world. At the same time, Time Reversal (TR) has been identified as a good green candidate owing to its low-complexity and its ability to focus energy in both spatial and temporal domains allowing for reduction of interference between users and to improve Signal to Noise Ratio (SNR) gains. Nevertheless, applying TR requires channel estimation at the transmitter side and therefore induces overhead in packet-switched system because of the sounding frames transmission. In this paper, we propose a very simple method to apply TR for packet switching under green constraints. We demonstrate that the proposed system offers a good compromise between the physical layer energy-efficiency gains owing to focusing properties of TR and the Medium Access Control (MAC) layer additional consumption due to the overhead caused by the sounding frames. The influence of different channel estimation protocols and medium access methods are studied leading to some recommendations. We also describe the application of TR to Multi-Users Multiple-Input Multiple Output (MU-MISO) Orthogonal Frequency Division Multiplex (OFDM) packet-switching system. The expected green performance of TR is then confirmed by link level simulations.