Zaghdoud, NesrineMnaouer, Adel BenAlouane, Wided HadjBoujemaa, Hatem2021-02-102021-02-10© 20202020-10-20Zaghdoud, N., Mnaouer, A. B., Alouane, W. H., Boujemaa, H., & Touat, F. (2020, October). Secrecy Performance of AF/DF relaying in NOMA Systems using Average and Instantaneous Channel gain for users’ ranking. In 2020 International Symposium on Networks, Computers and Communications (ISNCC) (pp. 1-7). IEEE. https://doi.or/10.1109/ISNCC49221.2020.9297172978-172815628-6https://doi.or/10.1109/ISNCC49221.2020.9297172http://hdl.handle.net/20.500.12519/334This conference paper is not available at CUD collection. The version of scholarly record of this conference paper is published in 2020 International Symposium on Networks, Computers and Communications (ISNCC) (2020), available online at: https://doi.org/10.1109/ISNCC49221.2020.9297172In this paper, we consider a downlink cooperative NOMA system where both Decode and Forward (DF) and Amplify and Forward (AF) strategies are studied in the presence of a malicious eavesdropper. First, the secrecy outage probability (SOP) is studied when users' ranking is based on either instantaneous or average channel gains. Next, the strictly positive secrecy capacity (SPSC) is derived for users ranking based on average and instantaneous channel gains. Under this setup, we also investigate the improvement of the system secrecy using optimal power allocation (OPA) coefficients. Numerical and simulation results are provided and demonstrate that Instantaneous channel gain users' ranking provide better results and its further improved with the use of OPA. © 2020 IEEE.enPermission to reuse abstract has been secured from Institute of Electrical and Electronics Engineers Inc.Average channel gainCooperative NOMAInstantaneous channel gainOptimal power allocationSecrecy outage probablityStrictly positive secrecy capacityInformation systemsAmplify-and-forwardChannel gainsDecode and forwardSecrecy outage probabilitiesComputer networksConference PaperCopyright : 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.