SungHoon Seo

An efficient power-saving mechanism for integration of WLAN and cellular networks

In this letter, we propose an efficient power-saving mechanism using paging of cellular networks for WLAN in heterogeneous wireless networks, where WLAN interface is turned off during idle state without any periodic wake-up in order to save power consumption while at the same time, the existing paging of cellular network is utilized in place of beacons in WLAN. For the proposed mechanism, the mean power consumption is investigated via analytical and simulation results.

An energy-efficient interface selection for multi-mode terminals by utilizing out-of-band paging channels

With the advent of a number of wireless network technologies such as WCDMA and WLAN, current mobiles are equipped with multiple network interfaces, so called Multi-Mode Terminal (MMT). MMTs are capable to access different kinds of networks by performing a vertical handover between heterogeneous wireless networks, where during the idle state, the MMTs consume a lot of energy since their WLAN interface must wake up for listening to periodical beacons. However, previous studies on the vertical handover did not address how to select the optimal interface taking into account the characteristics of MMTs, especially energy consumption. Therefore, in this paper, we propose an energy-efficient interface selection scheme for MMTs in the integrated WLAN and cellular networks. The proposed interface selection scheme takes advantage of existing out-of-band paging channel of cellular networks, so that the WLAN interface can be completely turned off during the idle state leading to reduction in energy consumption. Simulation results show that the proposed scheme outperforms conventional approaches in terms of energy consumption with reduced signaling overhead and handover delay.

Mobile-Velocity adaptive Vertical Handoff in Integrated WLAN and WiBro Networks

Integration of communication networks has been accelerated and is recognized as an important evolution plan of the existing networks such as WLAN (wireless local area network) and WiBro (wireless broadband Internet) networks. For the network integration, vertical handoff plays an important role to provide seamless connectivity between different networks. Mobile node (MN) performs the vertical handoff in the overlapped coverage of these networks. The vertical handoff can be useless if the MN moves at fast speed and penetrates the coverage in a short dwell-time (DT) so that it causes handoff oscillation which is known as a ping-pong effect. We therefore propose a new vertical handoff mechanism to prevent the ping-pong effect in the integrated WLAN and WiBro networks taking into account the MNs velocity. We called our proposed mechanism a mobile-velocity adaptive vertical hand-off. The proposed mechanism adaptively performs the vertical handoff according to the DT which denotes the time for MN dwelling in the coverage of the target network, and it is calculated by mobile-velocity and its coordinates. When the estimated DT is larger than the predefined threshold, DTthreshold, the MN performs handoff to WLAN. Since the short DT may cause the unnecessary handoff occurrence, it had better for the MN not to perform handoff and remain it connection in the current network. Simulation results show that the proposed handoff mechanism not only dramatically increases average throughput but also reduces the number of unnecessary handoff occurrence in comparison to typical RSS-based scheme. According to the channel rate setting on access point, our mechanism makes the throughput be differentiated, but the average throughput is improved for the entire network performance. Also the number of unnecessary handoff occurrence is remarkably reduced as the DTthreshold increases.

Policy Based Intelligent Vertical Handover Algorithm in Heterogeneous Wireless Networks

There are a few representative wireless network access technologies used widely. WCDMA is third generation technology of mobile communication technology supporting high mobility and broad service area. WLAN supports high data rate similar to wired network, and DVB-H supports both data and broadcasting services correspondingly. However, these technologies include some limitations especially on the mobility, data rate, transmission direction, and so on. In order to overcome these limitations, we propose the policy based intelligent vertical handover algorithm in heterogeneous wireless networks. Proposed scheme makes interface selection in the most appropriate way to maximize user throughput of activated service. Simulation results show that our proposed scheme outperforms the existing schemes in terms of energy efficiency and throughput improvement.

An Effective Codec Adaptation for MIH Based Vertical Handover in Heterogeneous Wireless Networks

The explosive demands of multimedia services have been grown up to support delay-sensitive applications, e.g., VoIP and streaming using codec. When a mobile node (MN) moves across different types of networks, the codec should be effectively adapted according to the significant change of network condition, i.e., throughput and delay. Therefore, in this paper, we propose a codec adaptation for vertical handover (ACAV), aiming not only to increase throughput but also to decrease delay at MNs. Using media independent information service (MIIS), the ACAV is able to proactively estimate network conditions of the target network then determine a proper type of codec for on-going multimedia services. The simulation results show that the proposed ACAV outperforms typical codec adaptation mechanism in terms of throughput and delay by determining a proper codec for the target network.

A New Soft Handover Mechanism Using DCHs in High-Speed Downlink Packet Access Networks

In 3GPP (Third Generation Partnership Project) Release5 (R5), HSDPA (High-Speed Downlink Packet Access) has been standardized to enhance the data rate of downlink packet transmission on top of WCDMA (Wideband CodeDivision Multiple Access) network. Even HSDPA supports up to 10 Mbps data rate through HS-DSCHs (High Speed-Downlink Shared Channels), an UE (User Equipment) suffers from significant handover latency since HSDPA standard does not supporting soft handover. Therefore, in this paper, we propose a new soft handover mechanism for HSDPA to reduce the handover latency by utilizing DCH (DedicatedChannel) instead of HS-DSCH. Simulation results show that the proposed soft handover mechanism reduces the packet IAT (Inter Arrival Time) less than 15 msec while HSDPA’s hard handover suffers from 190 msec packet IAT. It means that the proposed mechanism guarantees the minimum packet IAT requirement of the typical VoIP service in 20 msec. Furthermore, the proposed mechanism employees no service disruption for the data connection while an UE performs the soft handover procedure.

Location-Aware Signaling Protocol for WWAN and WLAN Interworking

With the rapid improvement of wireless networking technologies, current mobile devices can be potentially equipped with multiple interfaces to access different kinds of wireless networks. Thus, there have been many efforts to provide a seamless roaming between heterogeneous networks. However, most previous studies do not address how to select the best possible interface in terms of energy consumption. Therefore, in this paper, we propose to take advantage of accurate location positioning via WWAN interface, so that Mobile Nodes (MNs) obtain the information of hotspot range and completely turn off WLAN interface during idle state, leading to save energy consumption. Simulation results show that our mechanism outperforms existing approaches in terms of energy consumption and signaling overhead.

TSA: Time Series Adaptation for enhanced Cell Reselection in UMTS

Mobile Stations (MSs) operate in either idle mode or connected mode. However, previous studies have mainly focused on the connected mode even though the MSs remain their most of time in the idle mode. In this paper, we propose an efficient Cell Reselection algorithm, namely TSA (Time Series Adaptation), to decide the best cell in UMTS (Universal Mobile Telecommunication Systems). The proposed algorithm has the advantage of selecting the strongest RSCP cell out of neighboring cells for the cell reselection by utilizing time series parameters (e.g., β0 and β1). We evaluate the proposed cell reselection with TSA through the real-system testbed (Stand Alone Simulator). As a result, the TSA provides a proper decision for the cell reselection thereby avoiding the occurrence of unnecessary ping-pong cell reselection.

Achievable throughput-based MAC layer handoff in IEEE 802.11 wireless local area networks

We propose a MAC layer handoff mechanism for IEEE 802.11 Wireless Local Area Networks (WLAN) to give benefit to bandwidth-greedy applications at STAs. The proposed mechanism determines an optimal AP with the maximum achievable throughput rather than the best signal condition by estimating the APs bandwidth with a new on-the-fly measurement method, Transient Frame Capture (TFC), and predicting the actual throughput could be achieved at STAs. Since the TFC is employed based on the promiscuous mode of WLAN NIC, STAs can avoid the service degradation through the current associated AP. In addition, the proposed mechanism is a client-only solution which does not require any modification of network protocol on APs. To evaluate the performance of the proposed mechanism, we develop an analytic model to estimate reliable and accurate bandwidth of the AP and demonstrate through testbed measurement with various experimental study methods. We also validate the fairness of the proposed mechanism through simulation studies.