Performance analysis of non-orthogonal multiple access systems in cognitive radio networks

In this thesis, system performance analysis of downlink non-orthogonal multiple access (NOMA) systems in relay-assisted cognitive radio networks is investigated. In the proposed system model with one source, one relay, and two users, information is exchanged with a relay with the exponential distribution channel model by using the decode-and-forward method (DF). The end-to-end signal-to-noise plus noise ratio (SINR) of this system is calculated for both the transmitter and receiver nodes. The mathematical inferences in the proposed system model are obtained by deriving the closed-form equations of the outage probability and exact and approximate ergodic capacity analysis for the near and far users, using the probability density function (PDF) and the cumulative distribution function (CDF) of the exponential distribution channel. In the relay and near user (NU) it is assumed that successive interference cancellation (SIC) is applied, the outage probability performances of the relay and secondary users, the distance between nodes, the power-allocation coefficient, the interference power, and the exponential distribution parameters are taken into account, and the total ergodic capacity performance is determined by the distance between nodes, power-allocation coefficient, transmission power, and path loss coefficient. The parameters are analyzed with Monte Carlo simulations with 10^6 repetition. The outage probability performance of the system for near and far users is observed with the signal-to-noise ratio (SNR). It is determined that the outage probability increases with the increase of the interference power, that is, the system performance worsens. The effect of the distance variation between the relay and the far user (FU) on the system performance is investigated. It is observed that the outage probability increases as the FU moves away from the relay. When the system performance of the power allocation coefficient is examined, it is determined that the system performance for NU and FU deteriorates when the power assigned to the NU decreases. Finally, when the system outage probability performance of the exponential distribution parameter in inter-node channels is examined, it is seen that as the exponential distribution parameter increases, the outage probability for NU and FU decreases. In the ergodic total capacity analysis, the variation of system analysis with SNR for NU and FU is examined. The performance of the system is analyzed with the change in the power allocation coefficient and the distance between nodes, and it is observed that as the SNR increases, the ergodic capacity increases, thus the system performance increases. The ergodic total capacity for the NU is investigated by the variation of the power allocation coefficient. It has been determined that the system performance increases with the increase of the power allocation coefficient assigned to the NU. Finally, the performance of the difference between the distance of the primary network (PN) transmitter to the relay and the distance between the relay and the source on the ergodic total capacity for the NU is investigated. It is found that removing the PN transmitter from the relay increases the ergodic total capacity. It is observed that the system performance deteriorates when the relay in the secondary network (SN) moves away from the source compared to the PN transmitter, and the increase in the power allocation coefficient assigned to the NU positively affects the ergodic total capacity. It is predicted that the analyzes made on the proposed system model and the results obtained will provide the desired performance and will guide the researchers in the selection of the distance between nodes, the power allocation coefficient, the transmission power, the path loss coefficient, the interference power, and the exponential distribution parameters.