We investigate the effect of outdated channel state information (CSI) on the secrecy performance of wireless-powered untrusted relay networks, in which the relay is a potential eavesdropper. To keep the information secret from this untrusted relay, the destination sends a jamming signal to the relay when the source transmits an information signal. At the same time, the relay harvests energy from the radio-frequency power, and forwards the received signals to the destination using this harvested energy. To determine the proportions of energy harvesting and information processing, the relay makes use of relaying based on power splitting or time switching policy. Although the destination tries to remove the jamming signal from the relaying signal, it cannot cancel out the jamming signal perfectly due to imperfect channel reciprocity caused by the outdated CSI; this residual jamming signal therefore has a negative impact on secrecy performance. In this scenario, we derive the closed-form expressions for the outage probability and average secrecy rate, and find the jamming power ratio, power splitting ratio, and time switching ratio to optimize these secrecy performance metrics. The numerical results demonstrate the accuracy of our analysis, and show that the proposed secure relaying protocols achieve a near-optimal secrecy performance, as well as outperforming the conventional scheme without the jamming power control.

In-band full-duplex (IBFD) radio system can potentially double the spectral efamp;#64257;ciency of wireless networks. For IBFD radio system, the residual self-interference (RSI) is a critical issue. In addition, in-band full-duplex cellular (FDC) networks, particularly when the cell size is small, inter-user interference (IUI) would be another key factor for the performance degradation. To overcome these issues, we propose the scheduling scheme which adaptively utilizes bidirectional FD (BFD) mode and unidirectional FD (UFD) mode in the halfduplex (HD) networks. This scheme is based on the RSI channels after interference cancellation and IUI channels for each carrier, in order to maximize the proportional fairness. Simulation results revealed that the use of BFD mode is extremely dominant for a small cell with few mobile stations (MSs) if self- interference is sufamp;#64257;ciently canceled since IUI could be large.

Cell edge performance in the handover has been recently researched in the development of mobile network systems since it can cause the significant degradation of the quality of service (QoS). We consider a novel adaptive multi input multi output (MIMO) semisoft handover technique. Semisoft handover permits both hard and soft handover advantages for OFDM networks. In this paper, we analyze the semisoft handover combined with the adaptive MIMO mode switching scheme. The downlink spectral efficiency is studied for the adaptive MIMO semisoft handover compared to the adaptive MIMO hard handover. The simulation and numerical results for each handover of the cellular systems are computed to validate the effectiveness of adaptive MIMO semisoft handover in the femtocell networks. Finally, it is also shown that the influence of the correlation between the signal qualities of the source and target base station (BS).