Datong Xu

Design in Power-Domain NOMA: Eavesdropping Suppression in the Two-User Relay Network with Compensation for the Relay User

Non-orthogonal multiple access (NOMA) is becoming important in 5G, therefore, it is widely researched. Note that the users served in NOMA are often paired to prevent excessive interference. However, if the channel condition of direct downlink from the service node to one user is serious, the node may require the other user with better channel condition to relay this user’s signals, especially when the pure relay is difficult to deploy. This relay transmission is helpful for NOMA communication, but two problems should be considered: (i) how to persuade the relay user (i.e., the user with better channel condition) to expend extra resources for relay; (ii) how to suppress eavesdropping in the relay transmission, especially for the signals of indirect communication user (i.e., the user with worse channel condition). To solve these problems, we propose a novel signal-level scheme. In this scheme, on one hand, the node increases the spectral efficiency of relay user, and does the wireless power transfer to make the relay user supplement his/her energy by energy harvesting. On the other hand, a signal transformation method is designed to deal with each signal of indirect communication user. This transformation hides privacy information of indirect communication user, but does not disrupt the relay transmission. Utilizing the proposed scheme, the above problems are effectively solved by the compensation for the relay user and the signal protection for the indirect communication user.

Signal Conversion: Combat Eavesdropping for Physical Layer Security Improvement

Eavesdropping in wireless communication environment should be suppressed. However, most existing schemes ordinarily focus on secrecy rate enhancement, which may not be achieved with the non-Gaussian signals. Therefore, we consider this security problem from the actual signal point of view. On the basis of this premise, a novel scheme is proposed. In our scheme, each original signal in one constellation is converted as a transmitted signal in another constellation, and the principle of this variation can be safely told to the user without being learned by others. With this conversion, the eavesdropper is difficult to restore the original signals. Performance analysis and simulation results illustrate that the proposed scheme is efficient for physical layer security improvement.

Information Security Enhancement with Actual Access Statuses of Users in the Multi-User System

In the new generation wireless communication systems, when multiple users are served, information security among them should be considered to protect each user’s privacy. In this case, physical layer security techniques can be adopted for this mutual confidence problem. Unlike other traditional physical layer security methods, the proposed scheme improves secrecy rate with the information of users’ access statuses (i.e., being served or idle), and it is denoted as SRT-AS. In the SRT-AS, appropriate parameters expressing users’ actual access statuses are introduced, and an adaptive transmitter and receiver design strategy is used to increase security. It can be found that no iterative process is included in the SRT-AS, moreover, performance analysis and simulation results illustrate that the SRT-AS is feasible for the multi-user system.