A composite approach to self-sustainable transmissions : rethinking OFDM

This paper proposes two novel strategies to extend the battery life of an orthogonal frequency division multiplexing (OFDM) receiver, by exploiting the concept of wireless power transfer (WPT). First a new receiver architecture is devised that does not discard the cyclic prefix (CP), but instead, exploits it to extract power from the received signal, realizing a WPT between the transmitter and the receiver. Subsequently, a flexible composite transmit strategy is designed, in which the OFDM transmitter transmits to the receiver two independent signals coexisting in the same band. It is shown that, by means of this approach, the transmitter can arbitrarily increase the power concentrated within the CP at the OFDM receiver, without increasing the redundancy of the transmission. The feasibility conditions for the self-sustainability of the transmission are derived, in terms of power consumption at the receiver, for both legacy and composite transmission. Numerical findings show that, under reasonable conditions, the amount of power carried in the CP could be made sufficient to decode the information symbols, making the transmission fully self-sustainable. The potential of the proposed approach is confirmed by the encouraging results obtained when the full self-sustainability constraint is relaxed, and partially self-sustainable OFDM transmissions are analyzed

A Green Approach to Femtocells Capacity Improvement by Recycling Wasted Resources

Abstract—In this contribution we propose a method to increase the energy efficiency of orthogonal frequency division multiplexing (OFDM)-based femtocells. This is accomplished with no impact to the current power consumption, radio frequency (RF) circuitry, link adaptation strategies, bandwidth and transmit power. The proposed technique recycles redundant resources of OFDM transmissions (e.g., guard bands and cyclic prefixes), introduced to combat frequency selectivity. We borrow the underlying idea from a technique called cognitive interference alignment (CIA). Interestingly, our novel approach does not suffer from the same issues inherent to CIA, such as synchronization at the primary receiver and channel knowledge related complications. Nevertheless, it introduces a new issue related to the interference from the OFDM signal, which prompted the adoption of an adequate linear receiver at the femtocell user equipment. Numerical findings demonstrate that spectral efficiency gains are achieved, improving the energy efficiency of the femtocell by up to 20 % for the simulated scenario. Index Terms—Femtocells, green networks, energy efficiency, spectrum sharing, interference management, linear precoding I