Full-duplex (FD) communication is capable of simultaneously transmitting and receiving data on the same frequency band. To effectively utilize FD in a wireless local area network (WLAN), one must use medium access control (MAC) protocols that consider the characteristics of FD. Many researchers have proposed and analyzed FD MAC protocols for WLANs. Most of this work revealed that as the number of nodes increases, the overall throughput decreases due to collisions. We have found, however, that with a smart MAC protocol, the throughput actually improves as the number of nodes increases. In this paper, we propose an asymmetric FD MAC protocol and then design an FD WLAN analytical model to evaluate saturation throughput. In our analytical model, we consider FD pair probability-the probability that a node capable of FD communication exists. To validate our model, we calculate FD pair probability values based on the modulation and coding scheme (MCS) levels and self-interference cancellation (SIC). We then analyze the effect of the FD pair probability on throughput. Simulation results verify the accuracy of our analytical model. Moreover, we compare the fairness of the proposed and conventional FD MAC protocols. As demonstrated through extensive evaluations, the fairness of the proposed FD MAC protocol is improved.

Structural health monitoring provides significant and obvious potential in enhancing our life safety and extending the service life of systems. In practice, structures are often exposed to random excitations without knowing the exact characteristics of its source. This paper proposes a novel method of the implementation of LSTM and GRU models for characterizing anomalies in output-only random vibration signals. In the proposed approach, the time response of a 3D printed PLA beam is measured when subjected to a random excitation and used to train LSTM and GRU models. Healthy time response and four additional cases that contain a small mass at varied locations along the beam are used as model inputs. These inputs represent normal and abnormal signals which are then classified to diagnose the health state of the structure. In this study, the random vibration time responses with large amplitude (so-called signal caricature) were selectively employed for creating the output-only models. The results illustrate the signal caricature data set leading to both more accurate and efficient characterization of the structural health state, compared to utilizing the entire time response as an input to the models. Modal properties obtained by traditional vibration analysis support the effectiveness of utilizing the signal caricature with LSTM/GRU models, demonstrating great potential in identifying defects in practical applications.

Full-duplex (FD) radios can transmit and receive packets simultaneously in the same frequency band. Although this potentially doubles the spectral efficiency, it also causes inter-node interference, which was not an issue for half-duplex (HD) radios and can significantly reduce FD radio throughput. This paper proposes a hybrid transmission switching algorithm to reduce performance degradation due to inter-node interference. In contrast to previous studies that only considered channel capacity, we determine the transmission mode by considering the modulation and coding scheme (MCS). The access point compares the required transmission time for HD, FD, and hybrid mode and selects the mode with the best network throughput. We also designed an analytical model to evaluate network throughput for the proposed algorithm. In particular, we consider FD pair probability, which has not been addressed previously. Analytical and simulation results verify that the proposed algorithm improves network performance.

Additive manufacturing technologies have the potential to revolutionize the manufacturing industry by making it easier to fabricate complex structures, high value, and low volume parts in various contexts. Bio-additive manufacturing is particularly promising, as it has enabled the 3D printing of human organs. Researchers have made progress by developing novel materials and printing strategies for additively manufacturing complicated mission-critical geometries. On the other hand, assessing the structural integrity of these bio-printed structures has been challenging, as destructive contact-based approaches may interfere with the manufacturing process and affect the original dynamics and quality of the bio-prints, due to the relatively soft and lightweight nature of bio-prints. Furthermore, the repeatability of measurement is significantly dependent on the quality of how the sensor is attached to the part. Non-contact methods, such as laser and X-ray based techniques, can provide measurements without adding mass to the part. However, lasers may produce inaccuracies due to reflection and absorption in translucent materials, which are often found in bio-constructs. Although there have been significant advances in non-contact methods for reliably identifying damages in bio-printed structures, particularly embedded defects, implementing these approaches in a straightforward way has been challenging. To advance the state-of-the-art, this study proposes a novel method that can reliably assess the damage properties without contact by using video-based vibrometry. Vibration signals can provide a comprehensive response of the target structure, including material properties and geometry changes due to embedded defects in bioprinting. By analyzing the phase shift of the pixel intensity in the video, the vibration characteristics that indicate surface and/or embedded defects can be assessed for the entire structure captured in the camera angle, without the need for multiple sensors to be installed on the structure. This research focuses on analyzing the vibration characteristics of a cube that was manufactured by an extrusion-based bio-printer with pneumatic dispensing using sodium alginate based bioink. A high-speed camera and phase-based motion estimation technique are used to obtain experimental data on the vibration characteristics of the cube. Volumetric defects introduced by extrusion pressure irregularity and scaffolds with voids and their severities are identified by monitoring the vibration characteristics. These findings suggest that the proposed method could be utilized to effectively verify the structural integrity of additively manufactured organs during fabrication, which could enhance process optimization and operation safety. Future works include incorporating finite element model to compare its response characteristics for healthy and damaged models with the experimentally obtained results and identifying the detection sensitivity and limit with respect to parameters such as damage type and location.

본 논문에서는 전술 데이터 링크 표준인 Link-16의 정밀 시간 동기 과정에서 발생하는 JU(Joint Tactical Information Distribution System Unit)들 간의 충돌 확률을 분석하고 안정적인 통신을 위해 JU가 각 타임 슬롯에서 정밀 시간 동기를 시도할 확률과 전체 JU의 수에 따른 정밀 시간 동기 성공 확률을 계산한다. JU가 정밀 시간 동기에 성공할 확률, 여러 차례 정밀 시간 동기를 시도하였을 때 한 번 이상 성공할 확률, 그리고 모든 JU가 각각 일정 횟수 이내에 정밀 시간 동기를 성공할 확률을 유도하고, 유의수준 α에서 정밀 동기 성공확률이 1- α 이상이 되기 위해 필요한 파라미터 조건을 계산한다. 유도된 확률식을 컴퓨터 모의실험을 통해 검증하고 타당성을 입증하여, Link-16의 정밀 시간 동기 시스템의 안정성과 효율성을 최적화할 수 있는 정밀시간 동기 충돌 확률 분석 방법을 제안한다.