Performance Analysis of Cooperative NOMA Networks with Imperfect CSI over Nakagamim Fading Channels In this paper, we investigate a downlink cooperative nonorthogonal multiple access (NOMA) network with decodeandforward relaying, where two scenarios of user relaying with direct link and user relaying without direct link are discussed in detail. More particularly, the performance of cooperative NOMA system under the assumption of imperfect channel state information (ipCSI) is studied over Nakagamim fading channels. To evaluate the outage performance of the above discussed two scenarios, the closedform expressions of outage probability for a pair of users are derived carefully. The diversity orders of users are achieved in the high signaltonoise region. An error floor appears in the outage probability owing to the existence of channel estimation errors under ipCSI conditions. Simulation results verify the validity of our analysis and show that: (1) NOMA is superior to conventional orthogonal multiple access; (2) The best user relaying location for cooperative NOMA networks should be near to the base station; and (3) The outage performance of distant user with direct link significantly outperforms distant user without direct link by comparing the two scenarios.

Performance Comparison Between NOMA and OMA Relaying Protocols in MultiHop Networks over Nakagamim Fading Channels under Impact of Hardware Impairments In this paper, we evaluate and compare performance of multihop relaying (MR) protocols under impact of hardware impairments, in terms of outage probability (OP) and throughput (TP). By applying nonorthogonal multiple access (NOMA) technique at each hop, the endtoend data ratethroughput of the MR protocol can be enhanced, as compared with the conventional one. Particularly, the transmitter at each hop combines two signals, and forwards the combined signal to the receiver which uses successive interference cancelation (SIC) to extract the data. For performance evaluation and comparison, we derive exact closedform expressions of OP and TP for the considered protocols over Nakagamim channel. Monte Carlo simulations are then performed to verify the theoretical derivations.