Won Jin Lee

Selection of relay UE with energy harvesting capabilities in public safety environment

Relaying is a widely proposed solution for multi-hop communication in PS environments. However, the selected relay is energy constrained and cannot go on indefinitely. Energy harvesting can solve this problem and make multi-hop D2D communication a viable solution for PS services. In this paper, selection of energy harvesting relay has been studied for device-to-device (D2D) communications. Public safety environment has been considered, where some user equipments (UE) are located out of the coverage area of eNodeB (eNB). For out of the coverage UEs, communication with the eNB is possible through an intermediate relay UE and selection of those intermediate relay UEs is the main focus of this work. Based on D2D link between potential relay UE and out of coverage UEs and estimated harvested energy at potential relay UE, a relay UE is selected to support out of coverage UEs. The relay-based approach enables D2D communications to incorporate cellular and ad hoc operations based on the network availability. The energy harvesting parameter at the relay UE make it unique, which is used to extend the life of rapidly drained battery of a relay UE. The effect of energy harvesting and D2D link quality on the selection of a relay UE has been topics of focus in this work. The proposed scheme is evaluated through system level simulations.

Natural course of spontaneous pneumothorax without bullae or blebs under high-resolution computed tomography.

BACKGROUND The cause of primary spontaneous pneumothorax (PSP) is known as rupture of some bullae or blebs. OBJECTIVE The aim of this study is to clarify the natural course of spontaneous pneumothorax in the absence of bullae or blebs under high-resolution chest computed tomography (HRCT). PATIENTS AND METHOD From January 2006 to December 2010, 854 patients with PSP were enrolled in the study group. All subjects received a chest CT scan and were reviewed retrospectively. RESULT There were 56 PSP cases (6.5%) without bullae or blebs under HRCT. Treatments included oxygen therapy in 16 (28.5%) cases, arrow catheter insertion in 22 (39.2%) cases, closed thoracostomy in 17 (30.3%) cases, and 1 (1.7%) case received a video-assisted thoracoscopic surgery (VATS) operation. There were nine recurrent cases (16%). Of the nine cases, eight cases were treated with VATS operation. Several bullae or blebs were found in five of those nine operated cases, and there were severe inflammatory fibrotic changes on the apex of one of the nine operated cases. CONCLUSION Several bullae and blebs were revealed upon operation of PSP without previously detected bullae and blebs on HRCT. We cautiously recommend operating on PSP regardless of whether bullae and blebs are detected by HRCT as long as there are no contraindications to the operation.

Low-power backscatter relay network

This paper proposes a full duplex relay scheme for ambient backscatter devices which require little or no power for operation. The ambient backscatter devices reflect radio signals from ambient sources such as TV tower, FM radio station, etc. Because of the backscattering of radio signals, such devices have small coverage range. To extend the network coverage of such devices, relaying is the most conventional way, which is previously used for extending the coverage range of radio networks such as LTE, WiFi and so on. In this paper, the backscatter devices assist other backscatter devices to relay the information to their destination nodes. Because of the full duplex characteristics at the relaying node, they can send their own information while receiving signals from the source node. We propose the relaying procedure for full duplex backscatter nodes and investigate the its performance in terms of throughput by performing simulations.

Access control with ONOS controller in the SDN based WLAN testbed

Nowadays, software-defined networking (SDN) has attracted a lot of interest. Therefore, many research works have introduced the new concepts and architecture to SDN-based network. However, most of existing research studies in wireless network area mainly introduce the theoretical concepts and face a difficulty to implement on the testbed. In addition, useful network applications with SDN controller is essential to improve SDN-based network. In order to overcome these limitations, we propose the access control mechanism on the SDN-based network by using SDN controller. Moreover, we introduce the system architecture and testbed for the proposed scheme. Therefore, we guarantee quality of service (QoS) for the high-priority user group and manage the WLAN AP dynamically.

Testbed implementation for routing WLAN traffic in software defined wireless mesh network

Software defined network (SDN) is a promising network technology that separates the control plane from data plane. The network function can be defined by using open application programming interface (Open API) in the SDN. Therefore, the network operator can embed the network function in the SDN controller by developing the application source code. Since the SDN brings benefit of network especially in management perspective, it is considered applying SDN to the wireless mesh network (WMN) which has to manage a lot of routers in the networks. In this paper, the implementation of software defined-wireless mesh network (SD-WMN) is introduced. We develops both the AP (Access Point) on the open source wireless router (OpenWRT) platform. We also develops the open virtual switch (OVS) on the Raspbian platform in order to provide the interface between SDN controller and AP. Using SDN controller, the WMN topology can be seem in the graphic user interface (GUI) of SDN. Finally, we measure the performance of AP in our WMN testbed environment.

Channel allocation and transmission power management scheme in software defined network-based WLAN environments

Wireless local area network (WLAN) uses carrier sens multiple access with collision avoidance (CSMA/CA) to share wireless medium. However, in dense WLAN environment, it occurs interference between WLAN nodes such as access points (APs) and stations (STAs). For resolving this problem, we propose management of WLAN APs by using open network operating system (ONOS) controller which is one of software defined network (SDN) controller. Based on this, we propose a channel and transmission power control of WLAN AP in order to optimize the channel. Experimental results shows that our proposed scheme can improve performance of WLAN in terms of data rate.

A Mechanism on Energy Harvesting and Data Communications in Wi-Fi Network

RF energy harvesting is a novel technology which is used for harvesting energy from the ambient RF resources. In energy harvesting, harvested energy is converted into useful electrical energy to recharge battery of electronic devices. With energy harvesting scheme, there is no need to replace battery, and the device can be recharged without cable line. Although the energy harvesting technique brings the convenience for recharging the devices, the amount of harvested energy is too small to operate device without supplying energy from the wired resource. In this paper, we consider Wi-Fi signals as energy harvesting resource, where Wi-Fi nodes can harvest energy from ambient signals that are being transmitted by the other users. Not only energy harvesting but also data transmission is considered in this paper. In order to achieve simultaneous wireless information and power transfer (SWIPT) switching circuit is proposed. We measure the received signal strength of Wi-Fi signals in the real environment, and our simulation results show harvested energy and throughput of the nodes in Wi-Fi network.

A multiple beam management scheme on 5G mobile communication systems for supporting high mobility

Due to the consistently increasing data traffic, current fourth generation (4G) mobile communication systems have been rapidly congested. To accommodate the emerging data traffic, the fifth generation (5G) mobile communication systems have been developed based on the introduction of millimeter-wave bands and adoption of beamforming and massive antenna structure. However, due to the structural features of the 5G mobile communication systems operating a lot of narrow beams, it is difficult for high-speed mobile users to provide stable service environments. Therefore, In this paper, we propose a novel handover and radio resource management concept for overcoming the limitations. Our simulation results indicate that the proposed scheme can improve performances of the users with high mobility.