In this paper, we investigate a two-hop full-duplex wireless-powered relaying system consists of a source, a relay, and a destination in the presence of a passive eavesdropper. The relay assists the transmission of confidential information from the source to the destination, while simultaneously harvesting the energy with time switching scheme by the radio-frequency (RF) signals. Our goal is to maximize the physical-layer security under harvested energy constraints by designing the full-duplex wireless-powered relay, whose two relaying strategies are considered, namely amplify-and-forward (AF) and decode-and-forward (DF). The relay beamforming vector design is proposed for AF protocol, and is jointly optimized with the time ratio parameter in the case of DF protocol to maximize the physical-layer security under harvested energy constraints. Moreover, for the simultaneous energy and secure message transfer at the relay, a two-phase method is provided, which enables the relay to avoid the self-interference caused by full-duplex operation, and also to harvest the energy from the self-interference. The proposed algorithmic solutions leverage the rank relaxation, Majorization-Minimization (MM) programming, and line search method. Numerical results show that the proposed full-duplex relaying system outperforms the half-duplex relaying system in energy harvesting. Moreover, the trade-off between AF and DF protocols according to the occurrence probability of non-zero secrecy rate can be observed in terms of physical-layer security.

Channel state information (CSI) is known to play crucial role for downlink transmissions of multi-user multiple-input multiple-output (MU-MIMO) systems. The existing works have been widely researched on the CSI feedback problem for system throughput aspects. With limited available radio resources, system throughput and fairness are usually in conflict with each other, balancing system throughput and fairness with high resource efficiency is necessary. Also, the analysis of feedback-rate allocation considering these two performance measures is needed. Therefore, in this paper, we propose the non-cooperative feedback-rate control game for improving throughput fairness in MU-MIMO system. Based on the game theory, the utility function of each user is considered both throughput fairness and total throughput. Moreover, we investigate the existence of the Nash-equilibrium of the proposed game and outage probability in terms of CSI feedback-rate. Simulation results show that the proposed game improves throughput fairness, and thus achieves better outage performance, as compared to the conventional equal-sized feedback scheme.

Uncoded antijamming capability of the multicarrier direct-sequence spread-spectrum system proposed by Kondo and Milstein (see ibid. vol.44, p.238-46, 1996 ) is analyzed. Joint pulse/partial-band noise jamming is considered with various subcarrier demodulator output combining schemes. We find that full-band pulse jamming maximizes the error probability for all cases considered. With Rayleigh fading and maximal-ratio combining, the multicarrier system achieves performance very close to that of the single-carrier system without fading even with a very small number of subcarriers.