• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.147-155
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• 2005

For the last several decades, many researches have been performed to distribute bandwidth fairly between sessions. In this problem, the most important challenge is to realize a scalable implementation and high fairness simultaneously. Here high fairness means that bandwidth is distributed fairly even in short time intervals. Unfortunately, existing scheduling algorithms either are lack of scalable implementation or can achieve low fairness. In this paper, we propose a scheduling algorithm that can achieve feasible fairness without losing scalability. The proposed algorithm is a Hierarchical Deficit Round-Robin (H-DRR). While H-DRR requires a constant time for implementation, the achievable fairness is similar to that of Packet-by-Packet Generalized Processor Sharing(PGPS) algorithm. PGPS has worse scalability since it uses a sorted-priority queue requiring O(log N) implementation complexity where N is the number of sessions.

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.254-260
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• 2005

In the guaranteed service, a real-time scheduling algorithm must achieve both high level of network utilization and scalable implementation. Here, network utilization indicates the number of admitted real-time sessions. Unfortunately, existing scheduling algorithms either are lack of scalable implementation or can achieve low network utilization. For example, scheduling algorithms based on time-stamps have the problem of O(log N) scheduling complexity where N is the number of sessions. On the contrary, round-robin algorithms require O(1) complexity. but can achieve just a low level of network utilization. In this paper, we propose a scheduling algorithm that can achieve high network utilization without losing scalability. The proposed algorithm is a Hierarchical Round-Robin (H-RR) algorithm that utilizes multiple rounds with different interval sizes. It provides latency bounds similar to those by Packet-by-Packet Generalized Processor Sharing (PGPS) algorithm using a sorted-Priority queue. However, H-RR requires a constant time for implementation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.12
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• pp.2811-2817
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• 2010

In this paper we propose the QAC-MAC that supports Quality of Service(QoS) and saves energy resources of the sensor node, and hence prolonging the lifetime of the sensor network with multiple sink nodes. Generally, the nodes nearest to the sink node often experience heavy congestion since all data is forwarded toward the sink through those nodes. So this critically effects on the delay-constraint data traffics. QAC-MAC uses a hybrid mechanism that adapts scheduled scheme for medium access and scheduling and unscheduled scheme based on TDMA for no data collision transmission. Generally speaking, characteristics of the real-time traffic with higher priority tends to be bursty and has same destination. QAC-MAC adapts cross-layer concept to rearrange the data transmission order in each sensor node's queue, saves energy consumption by allowing few nodes in data transmission, and prolongs the network lifetime.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1A
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• pp.44-53
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• 2010

This paper proposes a traffic management policy for delay control in the wireless networks. The so-called EDD(Earliest Due Date) scheme is adopted as the packet scheduling policy, so that the service provision is performed in the order of the transmission urgency of the backlogged packets. In addition, we derive a formula to determine the contention window, one of the MAC parameters, with the goal of minimizing the non-work conserving characteristics of the traditional MAC scheme. This method eliminates the burden of the class-wise parameter settings which is typically required for the priority control. Simulations are performed to show the validity of the proposed scheme in comparison with the policy that adopts the class-level queue management such as the IEEE 802.11e standard. Smaller delays and higher rates of delay guarantees are observed throughout the experiments.

• The KIPS Transactions:PartD
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• v.16D no.2
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• pp.161-168
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• 2009

Recently, use of various position base servicesthat collect position information for moving object and utilize in real life is increasing by the development of wireless network technology. Accordingly, new index structures are required to efficiently retrieve the consecutive positions of moving objects. This paper addresses an improved trajectory split algorithm for the purpose of efficiently supporting spatio-temporal range queries using index structures that use Minimum Bounding Rectangles(MBR) as trajectory approximations. We consider volume of Extended Minimum Bounding Rectangles (EMBR) to be determined by average size of range queries. Also, Use a priority queue to speed up our process. This algorithm gives in general sub-optimal solutions with respect to search space. Our improved trajectory split algorithm is going to derive minimizing volume of EMBRs better than previously proposed split algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1492-1512
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• 2011

Due to multiple hops, mobility and time-varying channel, supporting delay sensitive real-time traffic in wireless local area network-based (WLAN) mesh networks is a challenging task. In particular for real-time traffic subject to medium access control (MAC) layer control overhead, such as preamble, carrier sense waiting time and the random backoff period, the performance of real-time flows will be degraded greatly. In order to support real-time traffic, an efficient adaptive packet scheduling (APS) scheme is proposed, which aims to improve the system performance by guaranteeing inter-class, intra-class service differentiation and adaptively adjusting the packet length. APS classifies incoming packets by the IEEE 802.11e access class and then queued into a suitable buffer queue. APS employs strict priority service discipline for resource allocation among different service classes to achieve inter-class fairness. By estimating the received signal to interference plus noise ratio (SINR) per bit and current link condition, APS is able to calculate the optimized packet length with bi-dimensional markov MAC model to improve system performance. To achieve the fairness of intra-class, APS also takes maximum tolerable packet delay, transmission requests, and average allocation transmission into consideration to allocate transmission opportunity to the corresponding traffic. Detailed simulation results and comparison with IEEE 802.11e enhanced distributed channel access (EDCA) scheme show that the proposed APS scheme is able to effectively provide inter-class and intra-class differentiate services and improve QoS for real-time traffic in terms of throughput, end-to-end delay, packet loss rate and fairness.

• Journal of Korea Spatial Information System Society
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• v.12 no.1
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• pp.18-27
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• 2010

In u-GIS environment, GeoSensor environment requires that dynamic data captured from various sensors and static information in terms of features in 2D or 3D are fused together. GeoSensors, the core of this environment, are distributed over a wide area sporadically, and are collected in any size constantly. As a result, storage space could be exceeded because of restricted memory in DSMS. To solve this kind of problems, a lot of related studies are being researched actively. There are typically 3 different methods - Random Load Shedding, Semantic Load Shedding, and Sampling. Random Load Shedding chooses and deletes data in random. Semantic Load Shedding prioritizes data, then deletes it first which has lower priority. Sampling uses statistical operation, computes sampling rate, and sheds load. However, they are not high accuracy because traditional ones do not consider spatial characteristics. In this paper 'Pre-Filtering based Post Load Shedding' are suggested to improve the accuracy of spatial query and to restrict load shedding in DSMS. This method, at first, limits unnecessarily increased loads in stream queue with 'Pre-Filtering'. And then, it processes 'Post-Load Shedding', considering data and spatial status to guarantee the accuracy of result. The suggested method effectively reduces the number of the performance of load shedding, and improves the accuracy of spatial query.

• The KIPS Transactions:PartD
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• v.8D no.5
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• pp.533-542
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• 2001

In this paper, we present a scheduling method for real-time mobile transaction manager in mobile computing environment. The proposed method checks whether a transaction is executable or not. It is able to by considering not only the deadline of real-time data in mobile hosts. And then, it schedules the real-time mobile transactions by making optimal execution window based on the priority queue, while considering transaction value and deadline. Disconnection with mobile hosts is monitored in selecting the transaction for execution. Using the proposed method reduces the number of restarting times after transaction aborts which is caused by the violation of the validity constraints of real-time data. And in has merits of maximizing the sum of values of real-time mobile transactions which meet the deadline. The performance evaluation demonstrates that the number of committed real-time transactions within the deadline is improved by 20%. This method can be used in real-time mobile transaction manager is such environments as cellular communications, emergency medicine information system and so on.

• Journal of Internet Computing and Services
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• v.16 no.5
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• pp.19-27
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• 2015

Due to the advantages of fast read/write operation and low power consumption, SSD(Solid State Drive) is now widely adopted as storage device of smart phone, laptop computer, server, etc. However, the shortcomings of SSD such as limited number of write operations and asymmetric read/write operation lead to the problem of shortened life span of SSD. Therefore, the block replacement policy of SSD used as cache for HDD is very important. The existing solutions for improving the lifespan of SSD including the LARC scheme typically employ the LRU algorithm to manage the SSD blocks, which may increase the miss rate in SSD due to the replacement of frequently used block instead of rarely used block. In this paper we propose a novel block replacement scheme which considers the block reuse interval to effectively handle various data read/write patterns. The proposed scheme replaces the block in SSD based on the recency decided by reuse interval and age along with hit ratio. Computer simulation using workload trace files reveals that the proposed scheme consistently improves the performance and lifespan of SSD by increasing the hit ratio and decreasing the number of write operations compared to the existing schemes including LARC.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.6
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• pp.15-22
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• 2012

A performance index of singalized intersections is a standard to optimize signal control variables and to manage traffic flow. Traffic delays is generally used to minimize the average delay time on intersections or networks, progression efficiency is used to improve travel speed of main cooridors or to provide transit signal priority. We manage traffic flows with only selecting one index between delays and progression according to the objective of traffic management and field characteristics. In real field, the driver's satisfaction is high in any performance criteria when the waiting time is shorter and the unnecessary stop in front of traffic is smaller. This paper aims to develop simulation model to represent real progression with concurrently considering delays and progression. In order to reflect an effect of level of traffic volumes and residual queues which don't be considered in prior progression model, we apply shockwave model with flow-density diagram. We derive Cell Transmission Model of Daganzo in order to develop the delay index and the progression index for the macroscopic simulation model. In order to validate the effect, we analysis traffic delays and progression efficiency with comparing this model to Transyt-7F and PASSER V.