Jeong-Ahn Kwon

Utility-Based Subchannel Allocation for OFDMA Femtocell Networks

In femtocell networks, due to their small cell size, we can achieve higher spatial diversity from the channel reuse between multiple femtocells. In addition, if femtocells are operated on OFDMA systems, each subchannel can be reused separately among femtocells by carefully treating inter-cell interferences. However, due to a large number of femtocells and their uncoordinated and irregular deployment, we need to treat intercell interferences very carefully in OFDMA-based fmetocell networks, which make developing efficient resource allocation schemes more difficult. In this paper, we study a subchannel allocation problem that aims at maximizing the sum utility of the OFDMA-based femtocell network. Since the problem is formulated as a nonlinear integer programming, which is inherently difficult to solve, we propose a suboptimal subchannel allocation algorithm. The proposed subchannel allocation algorithm consists of two steps: calculating the number of subchannels that should be granted to each femtocell to maximize the sum utility and finding actual subchannel allocation that achieves the granted number of subchannels for each femtocell. Numerical results show that the proposed subchannel allocation algorithm provides near-optimal performance.

Subchannel allocation for the OFDMA-based femtocell system

In femtocell networks, due to their small cell size, we can achieve higher spatial diversity from the channel reuse between multiple femtocells. In addition, if femtocells operate on OFDMA systems, each subchannel can be reused separately among femtocells, improving system efficiency more significantly. However, due to a large number of femtocells and their uncoordinated and irregular deployment, we need to treat intercell interferences very carefully in OFDMA-based femtocell networks, which makes developing efficient resource allocation schemes more difficult.In this paper, we study a subchannel allocation problem that aims at maximizing the sum utility of the OFDMA-based femtocell network, which can be applied to both the dedicated channel and shared channel femtocell deployments. Since the problem is formulated as a nonlinear integer program, which is inherently difficult to solve, we propose a suboptimal subchannel allocation algorithm. The proposed subchannel allocation algorithm consists of two steps: calculating the number of subchannels that should be granted to each cell to maximize the sum utility and finding actual subchannel allocation that achieves the granted number of subchannels for each cell. Numerical results show that the proposed subchannel allocation algorithm provides near-optimal performance.

Utility-Based Power Allocation for Multiclass Wireless Systems

We study power-allocation problems in wireless systems through a network utility maximization framework. In this framework, the type of utility function represents the characteristics of each service. Hence, to deal with multiclass services in the system, it is important to accommodate various types of utility functions. In this paper, we consider four types of utility functions that can represent most of the services in wireless networks. We first develop a simple algorithm that solves a general optimization problem with those four types of utility function. We show that, even though the proposed algorithm might not provide the optimal solution, it provides an asymptotically optimal solution, which could be a good approximation to the optimal solution. The proposed algorithm can be applied to various resource-allocation problems in wireless systems. Among them, in this paper, we show that the proposed algorithm can be applied to both uplink and downlink power-allocation problems.

A unified framework for opportunistic fair scheduling in wireless networks: a dual approach

In this paper, we propose a unified framework for opportunistic fair scheduling in wireless systems. We consider a TDMA type of multiple access scheme, in which only one user can be scheduled in each time-slot. For opportunistic fair scheduling in such a system, some nice frameworks have been developed in the previous works, such as Agrawal and Subramanian (Allerton conference on communication, control and computing, 2002), Liu et al. (IEEE Journal of Selected Areas in Communications 19(10): 2053–2065, 2001) and Liu et al. (Computer Networks 41(4): 451–474, 2003). However, in this paper, we consider a more general problem that can accommodate more general types of fairness, and more general types of utility functions than those in the previous works. In addition to those generalizations, we develop a new framework for opportunistic fair scheduling based on the duality theory, which is different from those in the previous works. The duality theory is a well-defined theory in the mathematical optimization area. Hence, it can provide a unified framework for many different types of problems. In fact, we show that two different frameworks in Agrawal and Subramanian (Allerton conference on communication, control and computing, 2002), Liu et al. (IEEE Journal of Selected Areas in Communications 19(10): 2053–2065, 2001) and Liu et al. (Computer Networks 41(4): 451–474, 2003) are special cases of ours. In addition, by using the unified framework developed in this paper, we can not only develop various opportunistic fair scheduling schemes but also analyze the developed algorithm more rigorously and systematically.

Joint Cell Association and Resource Scheduling for Multi-cell HetNets

In this paper, we study a joint cell association and resource scheduling scheme for a multicell heterogeneous network (HetNet) in one integrated framework. In the multicell HetNet, the system becomes more complex. Especially, there are several heterogeneous cells that a user can associate. Also, the interference scenarios are complex. Therefore, finding an appropriate cell to each user and managing interference of each user efficiently are very important to utilize resource efficiently. To this end, the enhanced inter-cell interference coordination (eICIC) is proposed. Based on eICIC, we propose a joint cell association and resource scheduling algorithm considering the time-varying channel condition of wireless link and the quality of service (QoS) requirement of users represented by its minimum utility. Through simulations, we verify the appropriateness of our framework and show the performance of the proposed algorithm.

Optimal subchannel and power allocation for multi-cell OFDMA systems

Joint subchannel allocation and power control problems for multi-cell orthogonal frequency-division multiple access (OFDMA) systems have been extensively studied. However, due to the high complexity of the problems, only heuristic approaches are studied instead of the optimal approach for achieving the maximum system capacity. In this paper, we study this problem with a monotonic optimization approach, from the point of the optimal subchannel and power allocation aiming at maximizing the sum-rate of the multi-cell OFDMA system.

Network lifetime improvement by relaying node re-selection in the IEEE 802.15.6 BAN

In this paper, we study a relaying node re-selection problem in the IEEE 802.15.6 body area network (BAN) protocol, which requires to alleviate energy consumption burden of a relaying node and enhance the network life time. To this end, we develop a procedure for wake-up schedule control for a node that can be accommodated in the IEEE 802.15.6 standard. Numerical results show that by allowing a node to re-select its relaying node with our procedure, we can improve the network lifetime.

A new framework for opportunistic scheduling in wireless networks

In this paper, we propose a new framework for opportunistic scheduling in wireless systems. We consider a TDMA type of multiple access scheme, in which only one user can be scheduled in each time-slot. For opportunistic scheduling for such a system, a nice framework has been developed in. However, in this paper, we consider a more general system that has a probabilistic scheduling policy and more general fairness constraints. Moreover, in addition to this generalization, we develop a new framework for opportunistic scheduling based on the duality theory. The duality theory is a well-defined theory in the mathematical optimization area. Hence, by using the framework developed in this paper, we can analyze the developed algorithm more rigorously and systematically.

Joint cell association and resource scheduling for OFDMA multi-cell HetNets

In this paper, we study a joint cell association and opportunistic resource scheduling scheme for an OFDMA multicell heterogeneous network (HetNet) in an integrated and unified framework. To this end, we formulate the optimization problem and solve it with a dual approach to develop a scheduling scheme.

Study of optimal topology and routing in the BAN

In this paper, we study an optimal topology and routing problem in the body area network (BAN). Aiming at maximizing the network lifetime, we consider the guarantee of two important quality-of-service (QoS) requirements for BAN applications: the minimum bit error rate and the minimum data rate. Especially, we study the effect of the maximum number of hops that is allowed in routing to the system performance.