In relay-based cooperative communications (RBCC) system, the energy problem of relays is a significant issue needs to be addressed. In the last few years, the simultaneous wireless information and power transfer (SWIFT) technique has been introduced to solve that matter. SWIFT technique aims to carry data and power over the wireless signals from the source node to the destination for the relays system. The SWIFT technique can be implemented utilizing two protocols. The first one has been introduced as time switch relay (TSR) protocol, which is time division between energy harvesting and data transmission. The second one has been introduced as power switch relay (PSR) protocol based on power division between two mentioned processes. The time or power fraction directly affects the quality of service (QoS) parameters in SWIFT-based cooperative communication systems. This paper aims to maximize effective capacity by implementing an optimization to find the optimum time or power fraction of energy harvesting in relays system utilizing TSR or PSR protocols. The optimization is applied using Lagrange multipliers while simulation results are used to verify the theoretical results obtained from the optimization process. In addition, outage probability of the source-relay-destination link is analyzed in both TSR and PSR protocols. (C) 2019 Elsevier GmbH. All rights reserved.