Full duplex (FD) communication is considered as a promising technology in the development of 5G-advanced and 6G systems as it theoretically doubles the capability of channel. However, this improvement relying on a simultaneously bidirectional manner of communication induces intrinsic self-interference (SI) demanding to be fully cancelled, which is generally intractable. This challenge is minimized in the scenario of integrated access and backhaul (IAB) networks operated in millimeter wave (mmW) band, as its transceivers are stationary and the complexity of SI is greatly reduced by beamforming technique. As a matter of fact, FD can be a pioneering technique to unlock the full potential mmW-based IAB network by releasing its suffering of the half-duplex inefficiency. This article presents the design principle and validation of a practical SI cancellation (SIC) technique in the case of high transmission power class in mmW-based IAB networks. The proposed technique sequentially eliminates SI from the spatial, RF, and digital domains that reduces the SI down to the noise floor. To validate the technique, a prototype system is developed in accordance with 5G IAB specifications and field tests are conducted. Results suggest that the designed mmW SIC transceiver significantly reduces residual-interference to noise ratio (R-INR) to 2.1 dB or less. Additionally, a system-level simulation is conducted in line with 5G IAB evaluation methodology, which explores the potential performance gain of the proposed technique in presence of cross-link interference (CLI). Results indicate that the method could yield a cell throughput gain of about 84%, compared to the current time division duplex deployment.

This paper emphasize the importance of the inter-sector self-interference (SI) cancellation to realize the full duplex (FD) for the practical three-sectored cell deployment scenario. We measure the inter-sector SI, the interference coming from the neighboring sector in the same site, using our FD enabled prototype testbed, and then we conduct the system-level simulation to validate the the impact of the inter-sector SI along with the intra-sector SI and cross link interference (CLI) in mmWave integrated access and backhaul (IAB) networks. From our extensive simulation results, the FD operation compared with the half duplex (HD) operation achieves throughput gain of 70% with inter-sector SI cancellation (SIC), while the FD operation achieves throughput gain of 20% without inter-sector SIC. Conclusively, the inter-sector SI should be effectively cancelled out to guarantee the meaningful FD gain over HD.

Dynamic time division duplex (D-TDD) maximizes resource utilization by dynamically allocating resources to the downlink and uplink according to variations in traffic conditions. The new 5th generation (5G) mobile communication standard has reflected D-TDD in the frame structure. However, D- TDD has inherent cross-link interference (CLI) problems. Although many CLI mitigation schemes have been proposed as part of the standardization of the 5G system, none of these schemes have solved the multifaceted CLI problem. In this paper, we analyze the CLI mitigation schemes by dividing them into proactive and reactive scheme categories considering operational principles. Through this categorization process, we found that combining CLI mitigation schemes can solve the CLI problem more effectively. The performance of the various CLI mitigation schemes and combinations thereof is evaluated using a system level simulator. The best combination of CLI mitigation schemes is also derived.

We consider a mixed numerology spectrum sharing (SS) system where the users have different subcarrier spacing (SCS). Unlike in single numerology SS systems, mixed numerology SS systems suffer from inter-numerology interference (INI). We first derive the interference pattern and find that the variance of interference energy increases due to the difference in SCS. This increase in variance negatively affects decoding performance, since the interference energy is unbalanced between subcarriers. However, previous works on this issue did not take this interference pattern into account for interference management. In order to suppress the increase in variance of the interference energy, we propose a transceiver structure for large SCS users by using simple cyclic shift and frequency shift operations. The proposed transceiver disperses the effect of INI, reducing the variance in the interference energy. From the derived distribution characteristics of the interference energy in closed-form expressions, we show that the proposed transceiver achieves better decoding performance.

Ultra-dense small cell networks have been proposed as a way of addressing the explosive growth of data traffic. However, this approach often results in empty cells which only end up causing interference instead of serving UEs because they do not have any associated UEs. In this paper, we investigate the empty cell problem using system-level simulation and propose a dual layer on/off strategy for solving the empty cell problem. Systemlevel simulation results verify that the proposed scheme achieves performance enhancement in terms of capacity compared with conventional ultra- dense small cell networks.

The dynamic time division duplex (TDD) system has been proposed as a way to meet today's asymmetrically and dynamically changing traffic demand. However, this approach causes cross-link interference, because neighboring base stations and user elements transmit in opposite directions. In this paper, we investigate and analyze the characteristics of cross-link interference in dynamic TDD systems. Based on this observation, we propose an aligned reverse frame structure to utilize and cancel the cross-link interference. Mathematical analysis and numerical results verify that the proposed scheme achieves performance enhancement in terms of capacity compared with conventional dynamic TDD systems.