Jin-Yup Hwang

QoS-Based Vertical Handoff Decision Algorithm in Heterogeneous Systems

Vertical handoff is the switching process to provide seamless service among heterogeneous systems. An accurate estimation for utilities of target systems must precede a handoff for the efficient use of system resources. In this paper, we propose a vertical handoff decision algorithm based on the utility function to satisfy wireless QoS. Shannons capacity is used to maximize throughput and traffic load is considered to utilize systems evenly. The tradeoff between handoff rate and throughput is investigated based on users mobility. Simulation results show that the utility function effectively increases throughput

An Adaptive Traffic Allocation Scheduling for Mobile WiMAX

OFDMA is suitable for multiple access technique for packet- based wireless communication system. OFDMA-based system can achieve high system throughput by multi-user diversity in limited radio resource. One important technique to increase system performance is a scheduling supporting multi-traffic in the 4G system. The proposed algorithm provides priority regarding delay requirement and then allocates users packets in a frame according to required data rate of each traffic class. Simulation results show that proposed algorithm satisfies require data rate of real time and non-real time traffic class at large number of users and has low outage ratio.

A Periodic Frequency Band Rotation Scheme for Multi-Cell Coordination Clustering

Lots of attention to achieve cell edge performance has been made in future wireless networks. Through multi-cell coordination clustering, we can reduce co-channel interference, resulting in cell edge performance improvement. This letter proposes a periodic frequency band rotation clustering scheme for joint transmissions in multi-cell configuration. Through mathematical interference analysis, we show that the inter-cluster interference can be reduced and cell edge data rate is improved over existing schemes.

A Two-Step Vertical Handoff Algorithm in Heterogeneous Traffic and Systems

Vertical handoff is a switching process for seamless communication between heterogeneous wireless networks. By applying pre-handoff concept for the heterogeneous traffic, we propose a two-step vertical handoff algorithm, which can select the best suitable system to a user. From this point of view, we can get a better performance than existing vertical handoff algorithms. Simulation results show that the proposed algorithm increases the throughput and decreases the handoff rate and the connection time ratio with target systems.

Joint processing in multi-cell coordinated shared relay network

This paper investigates multi-cell coordinated shared relay with joint processing (JP) scheme in interference limited network. In general, multi-cell coordinated shared relay network increases the Signal to Interference-plus-Noise Ratio (SINR) in cell edge users, but resource usage efficiency is decreased by two-phase transmission of relay protocol. We propose JP of cooperating BSs and shared relay station (RS) in the relay transmission phase (second phase) to increase resource usage efficiency, and introduce the SVD precoding with phase correction based on the multi-cell coordinated shared RS network to mitigate other cell JP interference in the cluster. Simulation results show that the proposed scheme leads to network capacity enhancement.

Adaptive Frequency Reuse Scheme for Interference Reduction in Two-Hop Relay Networks

Multihop relay network can be adopted to increase cell edge data rate and extend cell coverage. Performance degradation, however, might be caused due to co-channel interference because of common frequency resource sharing among relay stations. In this paper, we propose an adaptive frequency reuse scheme among relay stations for interference reduction and enhancement spectral efficiency in orthogonal frequency division multiple access - time division duplex based location awareness two-hop relay networks. Our scheme is shown to achieve interference reduction and higher spectral efficiency through simulations.

Utility-Aware Network Coding in Wireless Butterfly Networks

This paper investigates the effect of combined network coding and power control based on network utility under wireless butterfly networks. Although it is well known that network coding improves network performances, it might not be always advantageous for a hostile wireless environment due to error propagation problem through relaying. Therefore, in this paper, the crossover point for profit-and-loss of network coding and non-network coding according to wireless link quality is derived, and then we show that network utility in terms of spectral efficiency per power is improved, and average power consumption is reduced by adaptively applying relay mode control and power control, which is of bang-bang type with a threshold in wireless butterfly networks.

Rate Control for Sum-Rate Maximization in Wireless Network Coding

For maximizing the benefit of network coding in two-way relay networks, the data rate of links from sources to a relay should be the same, since only the same number of received bits can be network-coded at a given time and the rate for broadcast at the relay is limited by the minimum rate over all links. Therefore, we investigate rate control scheme based on power control to maintain the link to be symmetrical while maximizing sum of data rates. We show the impact of rate asymmetry and formulate such problem as a max-min rate optimization problem. A simple iterative solution based on binary search algorithm is provided. Numerical results show the radio resource utilization in terms of bit/sec/Hz/watt is maximized by the proposed rate control scheme when the network coding is applied.

A Packet-by-Packet Scheduling Algorithm for Wireless Multimedia Systems

In this paper, we propose a packet-by-packet scheduling algorithm which grants priority to each packet instead of a user. The proposed scheduler classifies packets inside of each user into three classes such as emergency, near emergency, and non-emergency packets based on packet delay ratio, and applies different scheduling schemes to grant priority in each region respectively. It can be possible to manage packets more efficiently for guaranteeing various Quality of Services (QoS) in wireless multimedia systems. Simulation results show that the proposed scheme offers higher system throughput and lower packet drop rate than other scheduling algorithms.

Dynamic Subchannelization for Adaptation to Multipath Fading in Mobile WiMAX

In mobile WiMAX based on the IEEE 802.16e wireless MAN technologies using an OFDMA, the system throughput is improved by subchannelization schemes such as Diversity and AMC in multipath fading channel environment. Especially, in high mobility environment, mobile WiMAX systems uses FUSC which is one of the diversity subchannelization schemes, and get frequency diversity under multipath fading channel. However, the FUSC scheme is not flexible for channel variations inherent to users speed. In this paper, we propose dynamic subchannelization scheme under multipath fading channels which is varied with a users speed. Simulation results show that the proposed subchannelization algorithm leads to better the system throughput as compared to conventional subchannelization scheme such as FUSC in various channel environments.