One of the main obstacles in full-duplex radios is analog-to-digital converter (ADC) saturation on a receiver due to the strong self-interference (SI). To solve this issue, researchers have proposed two different types of analog self-interference cancellation (SIC) methods—i) passive suppression and ii) regeneration-and-subtraction of SI. For the latter case, the tunable RF component, such as a multi-tap circuit, reproduces and subtracts the SI. The resolutions of such RF components constitute the key factor of the analog SIC. Indeed, they are directly related to how well the SI is imitated. Another major issue in analog SIC is the inaccurate estimation of the SI channel due to the nonlinear distortions, which mainly come from the power amplifier (PA). In this paper, we derive a closed-form expression for the SIC performance of the multi-tap circuit; we consider how the RF components must overcome such practical impairments as digitally-controlled attenuators, phase shifters, and PA. For a realistic performance analysis, we exploit the measured PA characteristics and carry out a 3D ray-tracing-based, system-level throughput analysis. Our results confirm that the non-idealities of the RF components significantly affect the analog SIC performance. We believe our study provides insight into the design of the practical full-duplex system.

In this paper, we propose a novel wireless architecture, mounted on a high-altitude aerial platform, which is enabled by reconfigurable intelligent surface (RIS). By installing RIS on the aerial platform, rich line-of-sight and full-area coverage can be achieved, thereby, overcoming the limitations of the conventional terrestrial RIS. We consider a scenario where a sudden increase in traffic in an urban area triggers authorities to rapidly deploy unmanned-aerial vehicle base stations (UAV-BSs) to serve the ground users. In this scenario, since the direct backhaul link from the ground source can be blocked due to several obstacles from the urban area, we propose reflecting the backhaul signal using aerial-RIS so that it successfully reaches the UAV-BSs. We jointly optimize the placement and array-partition strategies of aerial-RIS and the phases of RIS elements, which leads to an increase in energy-efficiency of every UAV-BS. We show that the complexity of our algorithm can be bounded by the quadratic order, thus implying high computational efficiency. We verify the performance of the proposed algorithm via extensive numerical evaluations and show that our method achieves an outstanding performance in terms of energy-efficiency compared to benchmark schemes.

In this paper, we propose a novel wireless backhaul architecture, mounted on a high-altitude aerial platform, which is enabled by reconfigurable intelligent surface (RIS). We assume a sudden increase in traffic in an urban area, and to serve the ground users therein, authorities rapidly deploy unmanned-aerial-vehicle base-stations (UAV-BSs). In this scenario, since the direct backhaul link from the ground source can be blocked due to several obstacles from the urban area, we propose reflecting the backhaul signal using aerial-RIS and the phase of each RIS element, which leads to an increase in energy-efficiency ensuring the reliable backhaul link for every UAV-BS. We optimize the placement and array-partitioning strategy of aerial-RIS and the phase of each RIS element, which leads to an increase of energy-efficiency under guaranteeing the reliable backhaul link for every UAV-BS. We show that the complexity of our algorithm is upper-bounded by the quadratic order, thus implying high computational efficiency. We verify the performance of the proposed algorithm via extensive numerical evaluations and show that our method achieves an outstanding performance in terms of energy-efficiency compared to benchmark schemes.

In this paper, we analyze the outage probability and the long-term average throughput (LAT) of a decode-and-forward (DF) cooperative scheme with hybrid automatic repeat request (HARQ) over Nakagami-m fading channels. To derive the outage probability, the distribution of the weighted sum of two independent gamma random variables is needed. We approximately obtain the distribution by using gamma approximation and derive a closed-form expression of the outage probability of the DF cooperative scheme with high SNR assumption. By exploiting the outage probability, we obtain the LAT of the DF cooperative scheme. Numerical results show that the derived LAT of the DF cooperative scheme is able to predict the average throughput and the DF cooperative scheme achieves higher LAT than the direct transmission scheme because of higher diversity gains.

The multi-input multi-output (MIMO) system with a subcarrier intensity modulation (SIM) scheme in free-space optics (FSO) has a huge merit for ultra wide band communications mainly due to its diversity gain to be able to mitigate the signal scintillation caused by the atmospheric turbulence. In this study, we have analyzed the performance of the orthogonal space-time block codes (OSTBCs) in FSO links. In particular, the power series expressions of the outage probability and average bit error rate (BER) of the OSTBC for any number of antennas are derived in gamma-gamma fading channels using the SIM scheme. According to the analysis, the 3×2 OSTBC scheme could achieve a significantly high signal-to-noise ratio (SNR) gain of 62.5 dB in a strong turbulence regime, and also a moderately high SNR gain of 48 dB in a moderate turbulence regime over the no diversity at the BER of 10-6. Monte Carlo simulation results verify the accuracy of our analysis.