Kalantari, AshkanZheng, GanGao, ZhenHan, ZhuOttersten, Björn2020-05-112020-05-115/12/2015Copyright 2015 IEEE Transactions on Information Forensics and Security. This is a pre-print version of a published paper that is avilable at:https://ieeexplore.ieee.org/abstract/document/7105916. Recommended citation: Kalantari, Ashkan, Gan Zheng, Zhen Gao, Zhu Han, and Björn Ottersten. "Secrecy analysis on network coding in bidirectional multibeam satellite communications." IEEE Transactions on Information Forensics and Security 10, no. 9 (2015): 1862-1874. doi: 10.1109/TIFS.2015.2432732. This item has been deposited in accordance with pbulisher copyright and licensing terms and with the author's permission.https://hdl.handle.net/10657/6463Network coding is an efficient means to improve the spectrum efficiency of satellite communications. However, its resilience to eavesdropping attacks is not well understood. This paper studies the confidentiality issue in a bidirectional satellite network consisting of two mobile users who want to exchange message via a multibeam satellite using the XOR network coding protocol. We aim to maximize the sum secrecy rate by designing the optimal beamforming vector along with optimizing the return and forward link time allocation. The problem is nonconvex, and we find its optimal solution using semidefinite programming together with a 1-D search. For comparison, we also solve the sum secrecy rate maximization problem for a conventional reference scheme without using network coding. Simulation results using realistic system parameters demonstrate that the bidirectional scheme using network coding provides considerably higher secrecy rate compared with that of the conventional scheme.Physical layer securitynetwork codingbidirectional satellite communicationssecrecy ratesemidefinite programmingArticle