Optimization of Links With a Battery-Assisted Time-Switching Wireless Energy Harvesting Relay

On the Performance of Battery-Assisted PS-SWIPT Enabled DF Relaying

“…In our considered system, the relay not only runs out of the harvested energy, but also may extract the energy E b (E b ≥ 0) from its battery. Let us focus on the worst case scenario where Rayleigh fading is used to model small-scale fading over each channel [8,[10][11][12][16][17][18][19], and we assume that the small-scale fading follows a complex Gaussian distribution with zero mean and unit variance. Hence, the k-th The relay follows the PS scheme in which each transmission slot is divided into two equal sub-slots.…”

“…After solving the internal integral with respect to the variable y, (18) can be obtained. Since the integral is unbounded and there is no closed-form for (18), we use the variable substitution y = tanθ and adopt the Gaussian-Chebyshev quadrature (in this paper, we adopt the Gaussian-Chebyshev quadrature instead of other approximation methods because it can provide sufficient level of accuracy with very few terms; thanks to this advantage, the Gaussian-Chebyshev quadrature has been widely used in the state-of-the-art works [11,12,21]) to approximate Systems (18) as (19), where…”

“…In [15], the authors considered energy accumulation at the relay's battery and proposed a hybrid protocol. Recently, the authors in [16][17][18][19] proposed a battery-assisted SWIPT relay system, where the relay not only can use up the harvested energy, but also may draw energy from its battery. Compared with the "accumulated-then-forward" scheme, the battery-assisted SWIPT relaying is easier to implement since it does not require energy accumulation.…”

“…In [17], the authors compared the outage performance between the PS scheme and the TS scheme for a battery-assisted SWIPT amplify-and-forward (AF) relay system. Recently, this work was extended to battery-assisted TS-SWIPT DF relays [18,19]. While the recent works have shown that the joint usage of the harvested energy along with the battery energy can greatly enhance the outage performance, there are still open challenges that need to be tackled.…”

“…Firstly, the PS scheme for battery-assisted SWIPT DF relay systems has not been investigated yet and there is a lack of fundamental understanding of their performance, e.g., the outage and ergodic capacities. Secondly, we note that the existing works [17][18][19] focused on the static PS/TS scheme, where the PS/TS ratio is determined by the statistical channel state information (CSI). While it has been shown that the system performance can be further enhanced by using a dynamic PS ratio that can be adjusted based on the instantaneous CSI instead of the static one [8,11], the performance gain in battery-assisted SWIPT relay systems is not known yet.…”