Abstract
In this work, a novel resource allocation scheme is proposed to find the optimal timeswitching and powersplitting factors in a SWIPT assisted nonorthogonal multiple access (NOMA) relay network with combined time switching and power splitting protocol. The system model consists of a source node broadcasting a multiplexed NOMA signal to the far and near user via an amplifyandforward energy harvesting relay node in a Rayleighflatfading channel environment. Here, effective SNR maximization at both the near and far users is formulated as an optimization problem under total transmit power constraint and to deal with this both the Lagrangian multiplier approach and differentialevolution algorithm have been exploited. Furthermore, performance study is presented about the comparison of proposed scheme with the fixed allocation scheme in terms of outage probability under the impact of distinct target rates, relay locations, and channel conditions. Finally, the simulation results signify the performance improvement in the system with the optimal values obtained from the proposed scheme over the fixed time and power splitting factors.
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Abbreviations
 NOMA:

Nonorthogonal multiple access
 SWIPT:

Simultaneous wireless information and power transfer
 AF:

Amplifyandforward
 CTSPS:

Combined time switching and power splitting
 DF:

Decodeandforward
 SIC:

Successive interference cancellation
 EH:

Energy harvesting
 DE:

Differentialevolution
 RF:

Radio frequency
 SNR:

Signaltonoise ratio
 AWGN:

AdditivewhiteGaussiannoise
 PS:

Powersplitting
 TS:

Timeswitching
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Appendix
Appendix
Derivation to acquire the optimal power allocation coefficients \(a_{1} , \, a_{2}\) of NOMA users using Lagrange method.
Solution to get the power allocation fractions \(a_{1} , \, a_{2}\) with regard to D_{1} can be derived as follows:
The Lagrange function (J) can be formulated as
where
By substituting \(\gamma_{{sr_{1} }}\) and \(\gamma {}_{rd1}\) in “(27)”, the effective SNR obtained as
where ‘λ’ is the Lagrangian multiplier.
By solving \(\frac{dJ}{{da_{1} }} = 0 \, and \, \frac{dJ}{{da_{2} }} = 0\)
Finally, the power allocation factor for D_{1} can be expressed as
where \(Z_{1} = \frac{{2.N_{0} }}{{P_{s} h_{sr} ^{2} }} + \frac{{N_{0}^{2} }}{{P_{s} P_{r} h_{sr} ^{2} h_{rd} ^{2} }} + \frac{{N_{0} }}{{P_{r} h_{rd} ^{2} }}\); \(z_{2} = \frac{{2.N_{0} }}{{P_{s} h_{sr} ^{2} }} + \frac{{N_{0} }}{{P_{r} h_{rd} ^{2} }} + \frac{{N_{0}^{2} }}{{P_{s} P_{r} h_{sr} ^{2} h_{rd} ^{2} }}\).
Similarly, by solving \(\frac{\partial J}{{\partial a_{1} }} = 0\)
Finally, the power allocation factor for near user (D_{2}) is given by
Optimal values of \(a_{1} , \, a_{2}\) can be formulated as
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Nayak, V.N., Gurrala, K.K. A Novel Resource Allocation for SWIPTNOMA Enabled AF Relay Based Cooperative Network. Wireless Pers Commun (2021). https://doi.org/10.1007/s11277021081507
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Keywords
 NOMA
 SWIPT
 AF protocol
 CTSPS
 Power allocation
 Lagrangian multiplier method
 DE algorithm