Joo-Young Baek

Network-Initiated Handover Based on IEEE 802.21 Framework for QoS Service Continuity in UMTS/802.16e Networks

In the next-generation networks, guaranteeing QoS is one of the important factors, which allows QoS supportable networks such as UMTS and 802.16e to be deployed together. Under such networks, a mobile node (MN) with multiple interfaces demands for the QoS service continuity during a handover. The 802.21 framework enables MNs to freely move in multiple networks. However, supporting QoS service continuity remains as a problem to be solved. In this paper, we propose a network-initiated handover based on the 802.21 framework to provide the QoS service continuity in UMTS/802.16e networks. To support the QoS service continuity, we design a detailed handover procedure that consists of three steps; QoS measurement, passive reservation, and activation. Through our performance evaluation, we show that the proposed handover scheme provides the QoS service continuity of MNs during a handover in terms of guaranteed data rates and latency.

Efficient Uplink Resource Allocation for Power Saving in IEEE 802.16 OFDMA Systems

In this paper, we define a resource allocation problem focusing on the scheme minimizing energy consumption of subscribers in uplink subframe of the IEEE 802.16 OFDMA systems. In order to clearly formulate the relation between the uplink resource allocation and energy efficiency of subscribers, we use the multiple choice knapsack (MCK) problem, which is proved to be an NP-hard problem. Instead of finding an optimal solution, we seek a suboptimal solution. Based on the problem formulation, we adopt the existing solution of the Multiple Choice Knapsack problem to solve the resource allocation problem. The suboptimal solution adaptively uses the modulation and coding scheme defined in the IEEE 802.16 systems to minimize the required transmission power while guaranteeing QoS. Our simulation results show that the suboptimal algorithm can reduce the energy consumption up to 53% compared to the channel state information (CSI) scheme, which determines the modulation and coding level only considering the channel state information.

Efficient uplink scheduler architecture of subscriber station in IEEE 802.16 system

The IEEE 802.16, broadband fixed wireless access standard, defines four service classes, USG, rtPS, nrtPS and BE on high speed wireless networks. To guarantee the QoS requirement of these classes, the subscriber station and base station require scheduling architecture and algorithm. However, the IEEE 802.16 does not define any scheduling architecture or algorithm, and the most existing scheduling mechanisms only focus on working at the BS. In this paper, we propose two types of scheduling architecture working at the SS. In the one-level scheduler, we use a flow queue and class queue by differentiating flows with their class priority. The two-level scheduler can provide more organized QoS service with complementing the one-level scheduler. Adapting these architectures makes scheduler efficiently control all types of traffic defined in the IEEE 802.16. In the proposed architecture, any scheduling algorithms such as SCFQ and EDF can be applied. We evaluate the proposed scheduling architecture by simulation. The results of the simulation show that our proposed architecture can use the bandwidth efficiently.

Heuristic Burst Construction Algorithm for Improving Downlink Capacity in IEEE 802.16 OFDMA Systems

IEEE 802.16 OFDMA systems have gained much attention for their ability to support high transmission rates and broadband access services. For multiuser environments, IEEE 802.16 OFDMA systems require a resource allocation algorithm to use the limited downlink resource efficiently. The IEEE 802.16 standard defines that resource allocation should be performed with a rectangle region of slots, called a burst. However, the standard does not specify how to construct bursts. In this paper, we propose a heuristic burst construction algorithm, called HuB, to improve the downlink capacity in IEEE 802.16 OFDMA systems. To increase the downlink capacity, during burst constructions HuB reduces resource wastage by considering padded slots and unused slots and reduces resource usage by considering the power boosting possibility. For simple burst constructions, HuB makes a HuB-tree, in which a node represents an available downlink resource and edges of a node represent a burst rectangle region. Thus, making child nodes of a parent node is the same as constructing a burst in a given downlink resource. We analyzed the proposed algorithm and performed simulations to compare the performance of the proposed algorithm with existing algorithms. Our simulation study results show that HuB shows improved downlink capacity over existing algorithms.

An adaptive ARQ-HARQ interworking scheme in WiMAX systems

For reliable data transmissions, WiMAX systems support automatic repeat query (ARQ) that operates at the upper MAC and hybrid automatic repeat query (HARQ) that operates at the lower MAC and PHY. ARQ and HARQ schemes have their own weakness that results in low throughput and high delay in WiMAX systems. Although ARQ and HARQ schemes can complement with each other, they operate independently. Some studies focus on the benefits of the interaction between ARQ and HARQ schemes, but these studies have limitations. In this paper, we propose an adaptive ARQ and HARQ interworking scheme to provide reliable transmissions without performance degradation in WiMAX systems. The proposed scheme has five features that are designed to solve the weaknesses of the ARQ and HARQ schemes. We compare the proposed scheme with existing schemes that utilize the ARQ and HARQ interaction through simulations, and the simulation results show that the proposed scheme shows improved performance over existing schemes.

An efficient multi-dimensional handover scheme for next-generation networks

In next-generation mobile networks, consisting of multiple heterogeneous wireless networks, the vertical handover procedure is a difficult but important task. In the vertical handover procedure, the methods on which and how handover triggering factors are considered are not standardized. There are many research results considering a single or multiple handover triggering factors, but most of them select the handover network considering multiple factors at the same level. In this paper, we propose a new vertical handover architecture which considers multiple handover triggering factors with multi-dimension. The multiple handover triggering factors are classified and normalized according to their characteristics. The proposed scheme can be easily implemented in real systems because each part of the proposed architecture can be mapped to the corresponding protocol layer. We evaluate the performance of the multi-dimensional architecture using simulations. The simulation results show that our scheme can provide more throughputs with less end-to-end delay compared to other schemes.

The Compensation Model for Utilizing a Frame-Based Scheduling Algorithm in High-speed Wireless Networks

Designing scheduling algorithms that are simple to implement along with the process for servicing packets with low computation complexity is necessary to provide Quality- of-Service (QoS) for high-speed wireless networks. The ordinary frame-based scheduling algorithms are well-known for providing fair service with constant time complexity (O(l)), however, they have limitations of not being able to properly handle location-dependent burst errors in wireless networks. To utilize the advantage of frame-based scheduling algorithms, we propose a new Compensation Model which is based on Lead-lag Model, to provide smooth compensation, so that frame-based scheduling algorithms can guarantee fairness and reduce delay in error-prone wireless channels. Through the analytical model and simulation studies, we show that frame-based scheduling algorithms with Compensation Model can provide smaller delay bound and better fairness in wireless networks. Our belief is that the proposed frame-based scheduling algorithm (WFRR) based on the graceful Compensation Model can be a strong candidate for the scheduling algorithm in high speed wireless networks since the proposed algorithm has low computational complexity, is simple to implement, and has the ability to handle channel errors.

An elastic compensation model for frame-based scheduling algorithms in wireless networks

Scheduling algorithms for high-speed wireless networks need to be simple to implement for serving packets while ensuring quality-of-service (QoS). The ordinary frame-based scheduling principle is well-known for providing fair service with low implementation complexity. However, existing frame-based scheduling algorithms cannot properly handle location-dependent burst errors in wireless networks. To utilize the advantages of frame-based scheduling algorithms in error-prone wireless networks, we propose an elastic compensation model that provides not only smooth compensations without any service disruptions of flows but also flexible compensations to flows that experience frequent errors to provide flows with fairness of service. From our analysis and simulation studies, we found that the proposed compensation model shows smooth compensation performance without any service disruption periods and good fairness performance when channel errors occur.

Directory-Hopping Based Service Discovery for Dynamic Large-Scale Wireless Networks

With the rapid growth of wireless communication technologies, the demands for large-scale wireless networks have been emerged. One promising solution is the hierarchical architecture that consists of global and local wireless networks. The service discovery is a key issue to meet a vast amount of service demands from mobile nodes. However, under dynamic wireless networks, node failures severely affect the performance of service discovery protocols. Therefore, in this paper, we propose the directory hopping (DH) protocol for efficient service discoveries in dynamic large-scale networks. Basically, DH utilizes the directory for low-overhead service discoveries and periodically moves the directory to other operating nodes. In addition, it provides a fast and efficient recovery mechanism for node failures in dynamic network environments. Through extensive simulations, we show that the proposed DH protocol outperforms existing service discovery schemes.