To meet the rising demand of mobile data, IEEE 802.11ac was recently developed to offer better network performance than previous IEEE 802.11 standards, representing the 5G Wi-Fi technology. One of the new technologies added to IEEE 802.11ac is a dynamic bandwidth channel access scheme that supports channel bonding (CB) with an up to 160 MHz bandwidth. However, the use of CB increases the number of stations sharing the same medium, resulting in an increased collision rate and severe interference caused by overlapping sub-channels. This problem is further aggravated in densely deployed wireless networks where the service ranges of access points (APs) are likely to be highly overlapping. To resolve these issues, we present an analytical throughput model that considers the effect of both collisions and interference. With this analytical model, we formulate the CB problem to optimize the throughput along with the traffic demand and propose a genetic algorithm for solving the problem. Further, a dynamic channel bonding algorithm (named DCB) is proposed to solve the problem with lower complexity. Extensive simulation results demonstrate that our proposed algorithm provides a higher performance than other recent dynamic CB algorithms with respect to the throughput achieved for the traffic demand.

Skiing is one of the most popular winter sports in the world. Even though the equipment has been improved for preventing injuries during skiing, injury risks of the lower extremity are still high. It is necessary to investigate injury risk by motion analysis during skiing. The wearable motion capture system consisting of inertial sensors and insole pressure sensors can be utilized due to restrictions of conventional optical motion capture system. In this study, the motions for short-and middle-turns during skiing were analyzed using a wearable motion capture system and the multi-scale computer simulation technology. Seven male certified ski coaches participated in this study and their full body motion and foot pressure data were simultaneously recorded by the wearable motion capture system. Joint kinematics and kinetics in the hip, knee and ankle of the right lower extremity were analyzed during short- and middle-turns. Even though a slight difference in the joint kinematics between two turns was predicted, the joint forces and moments for middle-turn were higher than those for short-turn. Because these higher joint forces and moments can result in osteoarthritis or ligament injury at the joint, injury risk of the joint for middle-turn may be higher than that for short-turn. This study confirms that the wearable motion capture system is useful for measuring the motion and plantar pressure data in outdoor sports such as skiing.

Femur 3D reconstruction from x-ray images enables cost-effective and precise diagnosis of disease and surgery guidance. However, reconstructing accurate 3D model from sparse x-ray images are not a trivial task. In this paper, we propose a femur 3D reconstruction method from two x-ray images. We incorporate prior knowledge on the femur deformation such as twist distortion to improve reconstruction accuracy. We deform our generic 3D model optimizing global registration and twist correction parameters simultaneously. And then, non-rigid deformation is performed constructing dense 3d femur model of a patient. We have tested our method on real x-ray images and synthesized 3d femur models for quantitative and qualitative evaluations.

In IEEE 802.11 standard, the backoff parameters of its collision avoidance mechanism can be very inefficient and hence, the network becomes far from its optimal behavior. There have been several mechanisms to tune the Contention Window (CW) with the aim to achieve the optimal throughput in the IEEE 802.11 WLAN, however, the mechanisms do not specifically address a proper setting of the backoff parameters under non-saturated conditions. Noting that typical 802.11 networks are usually non-saturated, in this paper, we analytically derive the CW sizes that maximize the WLAN system throughput under both saturated and non-saturated conditions. Then, using the CW sizes derived, we propose a distributed algorithm that enables each station to dynamically adapt its CW according to the channel congestion status. The performance of the proposed algorithm is investigated through simulation. Simulation results indicate that our proposed backoff algorithm provides a remarkable performance improvement in terms of the delay experienced by a packet in the MAC layer, while maintaining an optimal throughput close to the theoretical throughput limit of the IEEE 802.11 Distributed Coordination Function (DCF) access scheme.

In an integrated WLAN and cellular network, if all mobile users whose connections originate in the cellular network migrate to the WLAN whenever they enter the double coverage area, the WLAN will be severely congested and its users will suffer from performance degradation. Therefore, we propose a Call Admission Control (CAC) algorithm that allows the WLAN to limit downward Vertical Handovers (VHOs) from the cellular network to reduce unnecessary VHO processing. Numerical and simulation results demonstrate that our CAC scheme reduces the unnecessary VHO processing while keeping the DVHO blocking rate within acceptable limits and maintaining reasonable throughput in the WLAN.

There are currently heterogeneous wireless access networks. A large variety of applications utilizing these networks will demand features such as real-time, high-availability and even instantaneous high-bandwidth in some cases. Therefore, it is imperative for network service providers to make the best possible use of the combined resources of available heterogeneous networks for connection support. Thus, with regard to vertical handoff performance, there is a critical need for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a vertical handoff decision algorithm that enables a wireless access network to not only balance the overall load among all attachment points but also to maximize the collective battery lifetime of mobile nodes (MNs). Simulation results are also presented to demonstrate the efficacy of the proposed algorithms.