Secure degrees of freedom of two‐user X‐channel with synergistic alternating channel state information at transmitters

Abstract

In this study, a two-user single-input single-output X-channel with confidential messages is addressed. In this model, the authors assume that the transmitters have access to synergistic alternating channel state information. During different time slots, the channel state information at transmitters (CSIT) alternate between three states including perfect CSIT, delayed CSIT, and no CSIT. By using the eminent synergistic benefits of the CSIT pattern, some schemes capable of attaining the maximum achievable secure degrees of freedom (SDoF) are presented. Additionally, in devising the schemes, the minimal CSIT patterns required to achieve optimal SDoF are introduced. It is shown that for CSIT patterns which are weaker than minimal ones, using a half-duplex relay can assist the network in obtaining the optimal SDoF. Indeed, the relay alleviates the effects of the lack of knowledge at transmitters on achievable SDoF.