Jinyoung Oh

Cell selection for range expansion with almost blank subframe in heterogeneous networks

To encourage data offloading in heterogeneous networks, range expansion techniques have been introduced in LTE-Advanced system. By adding a positive bias in cell selection process, more users can select picocells as their serving cells even the picocell is not of the strongest signal. Also, to protect offloaded users from severe macrocell interference, a specific subframe called almost blank subframe (ABS) is introduced. Since macrocell is kept silent during ABSs, the offloaded users can be allocated without strong macrocell interference within ABSs. It is noted that the offloaded users average data rate highly depends on the amount of ABSs rather than the bias value because the scheduling opportunities of offloaded users are limited within ABSs. And from the users point of view, the cell which is expected to give high data rate should be selected as a serving cell. In this paper, we propose a cell selection scheme based on expected user data rate which is a function of the ABS ratio. Simulation results show that the performance of our proposed cell selection scheme can improve average user rate and increase the number of offloaded users as the ABS ratio increases.

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.

A dynamic transmission mode selection scheme for CoMP systems

In this paper, we address the issue of resource management for coordinated multi-point transmission/reception (CoMP) systems. We propose a dynamic transmission mode selection scheme combined with proportional fair (PF) scheduling, where each cell performs scheduling in a consecutive order. Based on the prior user selection information, each cell decides transmission mode, and makes user scheduling according to the selected transmission mode. Furthermore, we extend precoding matrix indicator (PMI) coordination in order to mitigate intra-cluster interference. The proposed scheme provides adequate resource allocation in JT-CoMP systems without central scheduling unit. Simulation results show that the proposed algorithm provides significant edge user throughput gain without any loss in average throughput.

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.

Opportunistic Relay Selection Protocol under Multi-User Environment

In this paper, a relay selection issue is studied to improve data rate performance in a multi-user environment. Previous opportunistic relay selection protocols only consider channel condition in relay selection. However, the target performance is affected by other system attributes, such as delay and load in relay node (RN). The proposed relay selection scheme, which is based on analytic hierarchy process (AHP), adopts signal-to-noise ratio (SNR), switching, and the number of connections to RN as a selection criteria. Also, a special form of eigenvector is proposed and proved analytically. From the proposed eigenvector, the computational complexity is obviously reduced. Target system performance is examined under different weighting parameter values to the above attributes. This work shows that average data rate can be maximized corresponding to the number of RN. Simulation results reveal the benefits of the proposed scheme over the conventional opportunistic relay selection scheme and the threshold-based relay switching selection scheme. The performance of our scheme is verified in terms of average data rate and distribution of the data rate.

Efficient CQI feedback via network coding for wireless relay networks

For the efficacy of radio resource management in downlink wireless relay networks, the channel quality indicator (CQI) between a mobile station (MS) and a relay station (RS) should be fed back from the RS to its base station (BS), at the cost of additional feedback overhead. In this letter, we propose an efficient feedback scheme based on network coding between a pilot sequence and the CQI of MS-RS link, through which the BS can have both CQIs of MS-RS and RS-BS links without overhead. Numerical results reveal that the proposed CQI reporting scheme has as good feedback performance as conventional one which generally requires additional feedback burden.

AHP-Based Relay Selection Protocol for Flexible Resource Management

In this paper, we deal with a relay selection issue to improve throughput performance under signaling overhead and delay constrained system. The proposed relay selection protocol, which is based on analytic hierarchy process (AHP), adopts signal-to- noise ratio (SNR), system delay, and switching weight as selection criteria. We examined target system performance under various weighting to the above attributes. Also, average throughput can be maximized adaptively in various system environments. The proposed protocol entirely realizes the feature of opportunistic relaying (OR) protocol by totally weighting the SNR criterion. The performance of our protocol is verified in terms of average throughput, average delay and average relay switching counts.

Congestion Control based on AMC Scheme for WLAN Mesh Networks

Recently, Wireless Local Area Network (WLAN) mesh networks are attracting significant attention. Because the Institute of Electrical and Electronics Engineers (IEEE) 802.11 Medium Access Control (MAC) protocol has been designed for single- hop networks, the performance of WLAN mesh networks degrades due to congestion, and buffer overflow in intermediate Mesh Nodes (MNs). In this article, we propose new congestion control scheme which applies Adaptive Modulation and Coding (AMC) scheme and effective buffer usage to enhance the performance. AMC scheme uses multiple fragmentation thresholds, modulation levels and coding rates for various data sizes according to Channel State Information (CSI). Because CSI can be used more effectively to squeeze more bits into the medium, the throughput is enhanced. Simulation results show that the proposed scheme achieves much higher throughput than other congestion control schemes.