Ki-Dong Lee

Fair Allocation of Subcarrier and Power in an OFDMA Wireless Mesh Network

This paper presents a new fair scheduling scheme for orthogonal frequency-division multiple-access-based wireless mesh networks (WMNs), which fairly allocates subcarriers and power to mesh routers (MRs) and mesh clients to maximize the Nash bargaining solution fairness criterion. In WMNs, since not all the information necessary for scheduling is available at a central scheduler (e.g., MR), it is advantageous to involve the MR and as many mesh clients as possible in distributed scheduling based on the limited information that is available locally at each node. Instead of solving a single global control problem, we hierarchically decouple the subcarrier and power allocation problem into two subproblems, where the MR allocates groups of subcarriers to the mesh clients, and each mesh client allocates transmit power among its subcarriers to each of its outgoing links. We formulate the two subproblems by nonlinear integer programming and nonlinear mixed integer programming, respectively. A simple and efficient solution algorithm is developed for the MRs problem. Also, a closed-form solution is obtained by transforming the mesh clients problem into a time-division scheduling problem. Extensive simulation results demonstrate that the proposed scheme provides fair opportunities to the respective users (mesh clients) and a comparable overall end-to-end rate when the number of mesh clients increases

Dynamic resource allocation in OFDMA wireless metropolitan area networks [Radio Resource Management and Protocol Engineering for IEEE 802.16]

In this article we present important resource allocation problems in IEEE 802.16 wireless metropolitan area networks employing orthogonal frequency division multiple access. We first highlight the unique aspects of these networks and identify challenges and opportunities provided by the physical and medium access control layers. Next, we concentrate on four interrelated resource allocation problems: dynamic subcarrier allocation, adaptive power allocation, admission control, and capacity planning. We describe solution techniques, provide preliminary results, and discuss open problems for future research

Optimization for adaptive bandwidth reservation in wireless multimedia networks

In future wireless multimedia networks, user mobility management for seamless connection regarding realtime multimedia applications is one of the most important problems. In this paper we propose an opportunity-cost concept-based approach for adaptive bandwidth reservation with admission control for handover calls utilizing network traffic information. Excessive reservation guarantees low blocking probability of handover calls at the cost of high blocking probability of new calls. According to our survey, however, it may degrade bandwidth utilization while no prioritization for handover admissions degrades quality of service (QoS) for ongoing calls. We consider both QoS assurance and bandwidth utilization in order to optimize the amount of bandwidth to reserve for handover admissions. We believe that our scheme could be utilized as a guideline for cost-effective radio resource allocation in mobile multimedia networks.

A real-time algorithm for timeslot assignment in multirate return channels of interactive satellite multimedia networks

Since the digital video broadcast-return channel via satellite (DVB-RCS) standard was released in 2000, developing an interactive satellite multimedia (ISM) network has become a hot issue. In order to provide high-speed multimedia services using a DVB-RCS system, it is important to efficiently and dynamically assign the timeslots to a number of terminals according to their various demands. Also, it is imperative to improve the degradation of link quality due to rain-fade attenuation in Ka-band satellite communications. As a result, multirate superframe structures should be implemented for a relatively low data rate at the cost of stable connection to terminals in rain-fade regions and a relatively high data rate to terminals in clear-sky regions. Timeslot scheduling in this environment is studied in this paper. We mathematically formulate the timeslot assignment problem as a nonlinear integer programming problem and develop an efficient real-time solution algorithm. Extensive simulation results show that our algorithm successfully finds a feasible solution with optimality gap less than 0.05% within about 5 ms at Pentium III PC. We believe that our algorithm can be utilized as a guideline in developing real-time timeslot assignment algorithms for ISM networks.

Throughput-maximizing timeslot scheduling for interactive satellite multiclass services

We develop an efficient method for optimal timeslot scheduling in an interactive satellite multimedia network. We formulate the timeslot assignment problem as a binary integer programming (BIP) problem, where the throughput is maximized, and decompose this BIP problem into two sub-problems. With this decomposition, we promote the computational efficiency in finding the optimal solution of the original BIP problem.

Optimal scheduling for timeslot assignment in MF-TDMA broadband satellite communications

Recently, developing interactive satellite multimedia networks, such as digital video broadcasting (DVB) return channel via satellite (RCS) systems, has become important. We develop a dynamic resource allocation algorithm in a multifrequency time-division multiple access (MF-TDMA) basis for return link of an interactive satellite multimedia network. The proposed timeslot assignment algorithm, very efficient dynamic timeslot assignment (VEDTA) algorithm, gives an optimal assignment plan within a very short period of time. Owing to the optimality of the resulting solution and computational efficiency, we believe that our algorithm could be utilized in field applications.

Utility-Based Rate-Controlled Parallel Wireless Transmission of Multimedia Streams with Multiple Importance Levels

Multimedia data often have different levels of importance such that more important bits are less error-tolerant. A new rate control method for transporting such multimedia data over parallel wireless links with heterogeneous reliability is proposed. Rate-controlled parallel transmissions (RCPT) of different layers of a multimedia stream with different levels of importance over a wireless channel that support multiple links with heterogeneous reliability can improve the efficiency in resource allocation while satisfying the quality of service requirement of the multimedia connection. To exploit RCPT, we present and evaluate a novel dynamic resource allocation method that decomposes the available radio resources into multiple sets of links with different levels of reliability. We mathematically formulate a rate control problem for the flexible RCPT scheme and develop an efficient real-time resource allocation algorithm with a remarkably fast rate of convergence. Simulation results show that the proposed method improves the utility and reduces the power consumed for delivery of a multimedia stream at the required quality of service, in comparison with a previous scheme, where different layers of each multimedia class are scheduled with dependency, and two schemes that provide homogeneous high or low reliability over all parallel links.

An efficient real-time method for improving intrinsic delay of capacity allocation in interactive GEO Satellite networks

An interactive satellite network consists of a hub, a geostationary Earth orbit (GEO) satellite, and a group of terminals. Terminals in need of capacity send a capacity request (CR) message to the hub and the hub then makes a capacity-allocation schedule according to the CR and broadcasts that schedule to the terminals. Thus, it takes the round-trip time plus the scheduling time for a terminal to receive a response from the hub. Due to such intrinsic delay between capacity request and capacity allocation, it is difficult to promptly transmit user data via interactive channels of GEO satellites. The preferred solution to this problem is to have a prediction-based resource-allocation policy and to have as short a period of scheduling time as possible. As a solution to use such policies, we mathematically formulate a resource-allocation problem as a nonlinear integer programming problem considering uncertain future traffic conditions and we develop a real-time heuristic solution algorithm. Computational complexity analysis and extensive simulation results demonstrate the excellent performance of the proposed method on computational efficiency and heuristic solution quality.

Evaluations of Achievable Rate and Power Consumption in Cooperative Cellular Networks With Two Classes of Nodes

Previous work on cooperative cellular networks has mostly considered homogeneous relaying architectures where all nodes act as both sources and relays. In this paper, we examine the performance of heterogeneous cooperative cellular networks with the following two classes of nodes: source nodes (SNs) that do not act as relays and relaying agents that are dedicated to relaying functions with little concern about power consumption. In this architecture, SNs are able to reap the benefits of cooperative communications, such as improvements in the achievable data rate and reductions in the transmit power, while reducing the overall power consumption since they do not act as a relay. With an SN employing no more than two parallel relaying agents between itself and the base station, the proposed architecture achieves a 10%-80% improvement in the average achievable rate and a 15%-30% savings in the average amount of consumed power as compared to the situation where an SN can use, at most, a single relay agent.

Optimal timeslot and channel allocation considering fairness for multicell CDMA/TDD systems

The CDMA/TDD system is a highly attractive solution to support the next generation cellular mobile systems which provide unbalanced multimedia services between downlink and uplink. In this paper, we analyze the interference for downlink and uplink timeslots in a multicell CDMA/TDD system. We also mathematically formulate an optimal timeslot and channel allocation problem considering capacity fairness among cells, which is to maximize the system capacity under the given traffic unbalance, and propose an efficient algorithm based on the simulated annealing technique. Extensive experimental results show that the proposed scheme yields a good performance, and fairness among cells improves with a decrease in the system capacity.