The Price of Self-sustainability for Block Transmission Systems

In this work, the self-sustainability of block transmission systems is analyzed. In particular, orthogonal frequency division multiple access (OFDMA) is taken as a reference, due to its popularity and rather simple signal model. More precisely, a generalized variant of this scheme in which the transmitted signal is obtained as the sum of an OFDMA and a cognitive interference alignment (CIA) component, acting as an energy bearer, is considered. In this scenario, the self-sustainability of the transmission is made possible by the flexibility of the adopted strategy and the introduction of a novel energy harvesting OFDMA receiver. Both the feasibility conditions for the self-sustainability and the optimal power allocation to maximize the effectiveness of the energy transfer performed through the CIA signal are derived. Numerical results show that full self-sustainability can be achieved for several system configurations and channel statistics. However, this comes at the cost of a rate penalty with respect to a standard classic OFDMA transmission, which is termed the price of self-sustainability. A study of the relationship between the performance of both the energy and the information transfer is carried out. A CP size that minimizes the price of self-sustainability can be found for all the considered configurations.