Myeongyu Kim

Real-time white spectrum recognition for cognitive radio networks over TV white spaces

A key technical challenge in TV white spaces is the efficient spectrum usage without interfering with primary users. This paper considers available spectrum discovery scheme using in-band sensing signal to support super Wi-Fi services effectively. The proposed scheme in this paper adopts non-contiguous orthogonal frequency-division multiplexing (NC-OFDM) to utilize the fragmented channel in TV white space due to microphones while this channel cannot be used in IEEE 802.11af. The proposed solution is a novel available spectrum discovery scheme by exploiting the advantages of a sensing signaling. The proposed method achieves considerable improvement in throughput and delay time. The proposed method can use more subcarriers for transmission by applying NC-OFDM in contrast with the conventional IEEE 802.11af standard. Moreover, the increased number of wireless microphones (WMs) hardly affects the throughput of the proposed method because our proposal only excludes some subcarriers used by WMs. Additionally, the proposed method can cut discovery time down to under 10 ms because it can find available channels in real time by exchanging sensing signal without interference to the WM.

A seamless channel handover method for service continuity in super Wi-Fi

A key technical challenge in the Super Wi-Fi applications is how to provide a seamless Internet service even when a Super Wi-Fi user should give up the channel in use due to an active incumbent user. In this paper, we propose a channel handover method to support service continuity of Super Wi-Fi, in which AP selects an available channel and provides the channel information to MSs. Performance evaluation shows that the proposed scheme is superior to the conventional Wi-Fi in channel handover delay.

Scalable wireless-optical broadband access network using reconfigurable optical backhaul and gateway selection method

We propose a scalable optical-wireless access network that is composed of reconfigurable passive optical network and wireless mesh network architectures, which is to flexibly adapt to a large scale of traffic variation in the mobile networks. The reconfigurable PON is equipped with dynamic bandwidth reallocation capability by the arrayed waveguide grating, so that it can provide improved bandwidth efficiency and graceful scalability. Furthermore, a selection method of optical-wireless integrated gateway is included to balance the network load between the two architectures. The proposed network can enhance the network capacity and decrease the congestion probability of optical-wireless access network.

Rotation multiple-channel allocation scheme for seamless handoff in IEEE 802.11 WLANs

IEEE 802.11 Wireless LANs can provide broadband wireless data services without dealing with a cable in a limited area. However, when a MS moves to a neighboring AP, it has significant constraints on seamless mobile services. In this paper, we propose a rotational multiple-channel allocation scheme to manage mobility between APs that are equipped with multiple wireless interfaces, prohibiting from using the same channel as neighboring APs simultaneously. Performance evaluations show that the proposed scheme can achieve low handoff delay.

Seamless mobility provisioning by dual cross-linking method in WLAN

While the wireless local area network (WLAN) has been the most common technology for static indoor wireless services, its applications has limited performance in seamless mobile services because of its inherent static service transaction mechanisms. In this paper, we propose a mobility provisioning handoff method called dual cross-linking method to support seamless services in WLAN. A mobile node (MN) has two wireless interfaces and access points (APs) are controlled by a mobility management (MM) agent. In the area where the service areas of two adjacent APs are overlapped, one wireless interface is used to maintain the wireless services while the other interface searches for a next available AP. After finding a new AP, MN forms dual communication path from the MM to the MN so that the MN is ready to move to a newly found AP service area without service loss. Once the MN is moved to a new AP area, the first interface is disconnected leaving only one interface connection. It was proved that the proposed method can effectively reduce the handoff delay and packet loss through the analysis.