Soo-Yong Jeon

An enhanced channel-quality indication (CQI) reporting scheme for HSDPA systems

A major evolution of UMTS standard is the high speed downlink packet access (HSDPA). One of key techniques supporting HSDPA is the adaptive modulation and coding (AMC) in which the modulation scheme and the coding rate are adaptively changed according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. This letter proposes an enhanced CQI reporting scheme that can be used when a proportional fair scheduling algorithm (PFA) is used as a packet scheduling algorithm. The proposed scheme uses a dynamic threshold to filter off redundant CQI reports. With the proposed scheme, the battery capacity of UK can be conserved, maintaining the performance of traditional CQI reporting scheme.

Efficient resource allocation for rapid link recovery and visibility in visible-light local area networks

Visible-light communication provides many advantages over other forms of communications, such as visibility, high SNR (Signal to Noise Ratio), easy installation, freedom of interference from radio or electromagnetic waves, usage of license free frequency band, and high security. Furthermore, the exponentially increasing requirements and quality of LEDs (Light Emitting Diodes) have encouraged the development of visible-light communication that makes use of LEDs. In a visible-light communication system, an LOS (Line of Sight) link between two transceivers should be guaranteed due to the straightness of the visible-light signal. However, link failure caused by temporary blocking or poor orientation of a transmitter frequently occurs, causing burst frame errors. In this paper, we focus on how to let a user know about link failure as quickly as possible, in order that the link failure problem may be solved by realigning the transmission signal towards the receiver. This is furthermore a relatively straightforward matter, by the very nature of this system being a visible means of communication. It is also required that the visibility should be supported when a user attempts initial access procedure. Nevertheless, by supporting visibility, system performance can be degraded because some additional resources are required for the visibility to be enabled. In this paper, we propose three schemes for supporting visibility without reducing system performance in a visible-light local area network.

Channel adaptive CQI reporting schemes for HSDPA systems

HSDPA (high-speed downlink packet access) is an evolved UMTS packet scheme that delivers increased user peak data rates and quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. This letter proposes channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently by using information about channel quality. With the proposed schemes, the battery capacity of UE can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports

Channel Adaptive CQI Reporting Schemes for UMTS High-Speed Downlink Packet Access

HSDPA (high-speed downlink packet access) is an evolved UMTS packet scheme that delivers increased user peak data rates and supports quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. In the current specification of HSDPA, each UE must periodically report to Node B the CQI. Hence, UE must report the same CQI value repeatedly when the channel quality is unchanged. Obviously, this is the waste of the UEs battery power. To solve this problem, we propose channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently using information about channel quality. With the proposed schemes, the battery capacity of UEs can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports.

An Efficient ARQ mechanism in Multi-Hop Relay Systems Based on IEEE 802.16 OFDMA

A Mobile Multi-hop Relay (MMR) Task Group was created to achieve coverage extension and throughput enhancement by introducing a relay station (RS) in the IEEE 802.16 system. If the RS is introduced in the 802.16 system, the reliability of data transmission is worsen, since data transmission failures occur more frequently due to several wireless links establishing end-to-end connection and an ARQ mechanism used in the 802.16 system is not optimized for multi-hop environment. In this paper, we propose an ARQ mechanism focused on the 802.16 MMR system. The proposed ARQ mechanism introduces a new ARQ feedback message made by the RS for fast and efficient data transmission. The numerical analysis and simulation results show that transmission delay is reduced and transmission efficiency is enhanced by the aid of the RS with the proposed ARQ mechanism.

Modelling and Analysis of ARQ Mechanisms for Wireless Multi-Hop Relay System

Multi-hop relaying has attracted considerable attention recently as a key technique for improving cell coverage and throughput in wireless communication. We modelled various ARQ mechanisms that have been proposed for wireless multi-hop relay systems based on a Discrete Time Markov Chain(DTMC) technique. We analyzed the performance of the ARQ mechanisms with respect to delay and throughput. We also validated the proposed ARQ model and the performance analysis by comparing the analysis with simulation results.

Energy-efficient channel quality indication (CQI) feedback scheme for UMTS high-speed downlink packet access

A major evolution of UMTS standard is the High Speed Downlink Packet Access (HSDPA). Several new tech- nologies are applied to HSDPA system. One of key techniques supporting HSDPA is the adaptive modulation and coding (AMC) in which the modulation scheme and the coding rate are adaptively changed according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) feedback scheme is directly related to the accuracy of AMC and the performance of HSDPA. This paper proposes an enhanced CQI feedback scheme that can be used when a proportional fair scheduling algorithm (PFA) is used as a packet scheduling algorithm. The enhanced CQI feedback scheme uses a dynamic threshold to filter off redundant CQI feedbacks. With the proposed scheme, the battery capacity of UE can be conserved, maintaining the performance of traditional CQI feedback scheme.

An ARQ mechanism considering resource and traffic priorities in cognitive radio systems

In multi-hop relaying systems that have many relay stations (RSs), a cognitive radio (CR) technique can improve system performance greatly, due to an efficient resource sharing between the RSs. In this letter, the performance of an ARQ mechanism for CR-based multi-hop relaying systems is studied, using Markov chain and matrix signal flow graph (MSFG) techniques. Also, a priority-based resource allocation scheme is proposed to prevent performance degradation caused by the usage of unstable resources acquired by the CR technique.

An ARQ Mechanism with Rate Control for Two-Hop Relaying Systems

Wireless multi-hop relaying has been attracting considerable attention as a promising technique for future communication systems. The multi-hop relaying technique has many benefits, but many problems must be overcome if it is to be used successfully. One of the biggest is a degradation of system reliability that is caused by data being transmitted through many wireless links. Many automatic repeat request (ARQ) mechanisms have been proposed to improve system reliability. We propose an analytical model of hop-by-hop ARQ mechanisms and analyze performances using a discrete-time Markov chain (DTMC) technique. The proposed analytical model considers Poisson packet arrival, packet error rate, and channel capacity in a two-hop chain topology. In addition, we propose a rate control algorithm to compensate the weak point of the hop-by-hop ARQ mechanism. We evaluate the performance of the proposed ARQ mechanism with the rate control algorithm by comparing numerical analysis with simulation results.

Energy-efficient caching strategy using probability-based data request for mobile environments

In mobile environments, where data is broadcasted, the caching of frequently accessed data in the battery-powered mobile terminals is a very attractive technique in terms of the energy and bandwidth efficiency. The invalidation report (IR) based caching strategy is one of the popular caching strategies by its scalability. In the IR-based caching strategy, the data consistency is maintained by using the IR which has the information of updated data. In this paper, we approach the IR-based caching strategy in view of the energy efficiency and propose the energy-efficient caching strategy. With the proposed caching strategy, redundant data request messages for the identical data decrease significantly. Simulation results show that the proposed caching strategy has a great effect on the conservation of the battery capacity of mobile terminals and the uplink bandwidth compared with the conventional IR-based caching strategy.