Ohyun Jo

Cooperative Resource Allocation for Guaranteeing Intercell Fairness in Femtocell Networks

In this letter, we focus on intercell fairness in OFDM femtocell networks. Serious degradation of any cell cannot ensure fairness for entire network, thus, intercell fairness is important for the satisfaction of all users. In order to improve intercell fairness, we devise a cooperative resource-allocation algorithm, which is an enhanced modified iterative water-filling (EMIWF). The proposed algorithm takes account into cell capacity and traffic load at the same time in power allocation. So, each femto base station allocates power in order to reduce the interference that it causes to a femtocell which experiences severe capacity degradation or has heavy traffic load. Through intensive simulations, we show that the EMIWF enhances intercell fairness with negligible degradation in view of system capacity.

Efficient spectrum matching based on spectrum characteristics in cognitive radio systems

QoS is a very important issue in cognitive radio systems. We present and discuss spectrum matching algorithms to support QoS for cognitive radio users. This work is carried out in the context of a dynamic changing spectrum. In this paper, we propose efficient spectrum matching algorithms, which have low-complexity and quite good performance, based on statistical characteristics of spectrum bands. Those are classified random matching algorithm and greedy algorithm. The classified random matching algorithms would match the most suitable spectrum class to a proper user and randomly choose a spectrum within the class. And, using greedy algorithm, the best spectrum out of available spectrum bands will be chosen whenever a new user joins. The proposed algorithms provide QoS for cognitive radio systems through the reduction of spectrum handoff probability and improvement of fairness. Performance analysis and simulation results validate the efficiency of the proposed algorithms.

QoS Provisioning Spectrum Management Based on Intelligent Matching and Reservation for Cognitive Radio System

To improve spectrum utilization, cognitive radio attempts to use temporarily unoccupied spectrum which is referred to spectrum hole in cognitive radio. In this paper, we introduce novel spectrum management algorithms for cognitive radio. We introduce a heuristic matching algorithms which is named cost minimized matching. The heuristic algorithm proposed in this paper outperforms the general random matching algorithm with respect to the expected number of handovers and handover probability fairness. Also, the spectrum hole reservation algorithm minimizes service dropping while using optimum amount of resource, and it realizes seamless service by eliminating delay generated due to spectrum change. Performance analysis and computer simulations validate the efficiency of the proposed algorithms. The proposed algorithms can be efficiently used in cognitive radio systems.

Seamless spectrum handover considering differential path-loss in cognitive radio systems

In cognitive radio systems, spectrum handover occurs when a secondary user changes frequency due to the appearance of a primary user. Spectrum handover may result in degraded system performance because of the different propagation loss of the different frequency. In this case, data transmission is disrupted and it is more difficult to provide seamless service. Here, we propose a seamless handover scheme based on the prediction of cell coverage. The proposed handover scheme can avoid service disruption and can reduce redundant handovers. The efficiency of the scheme is validated by simulation results.

An enhanced packet scheduling algorithm combined with HARQ for HSDPA system

High speed downlink packet access (HSDPA) is a packet-based data service that supports downlink data rates of up to 14 Mbps in the WCDMA (wideband code division multiple access) system. In HSDPA, the packet scheduler is a key element for high-speed and efficient transmissions. In addition, hybrid automatic request (HARQ) plays a significant role in improving system performance. We propose an enhanced scheduling algorithm combined with HARQ to reduce transfer delay without the degradation of system throughput.

Traffic Adaptive Uplink Scheduling Scheme for Relay Station in IEEE 802.16 Based Multi-Hop System

To improve system throughput and extend coverage, multi-hop relaying is a promising technology in wireless communication systems. Thus, multi-hop relaying is world-widely gaining huge attention as a key research item. Nevertheless, it may cause longer delay and degrade resource efficiency at the cost of the benefits due to multi-hop relaying. In this paper, we propose a traffic adaptive uplink scheduling algorithm for relay station, which could be applied to the centralized multi-hop system such as IEEE 802.16 MMR efficiently. The proposed algorithm can overcome those defects of multi-hop relaying technology and enhance system performance.

Seamless spectrum handover improving cell outage in cognitive radio systems

In cognitive radio systems, there is a concern of service disruption because of spectrum handover. Spectrum handover occurs when a secondary user changes frequency due to the appearance of a primary user. Spectrum handover can be frequent if a cognitive radio system operates in a wide spectrum band. In this case, spectrum handover may drastically degrade the performance of cognitive radio systems because of the different propagation loss according to the usage of different frequency. Here, we propose a seamless spectrum handover scheme. The proposed handover scheme can avoid service disruption and can reduce redundant handovers. The efficiency of the proposed scheme is validated by simulation results.

Enhanced Packet Scheduling Algorithm Providing QoS in High Speed Downlink Packet Access

In high speed downlink packet access (HSDPA), packet scheduler is a key element for high-speed and efficient transmissions. In this paper, we propose an enhanced packet scheduling algorithm which computes the priority according to the proportional fair algorithm. That is, for users to need hybrid ARQ retransmission in case of erroneous packets, the priority of the proportional fair algorithm is elegantly modified to reduce the transfer delay without degradation of system throughput.