• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.2
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• pp.61-74
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• 2014

In recent years, development of femtocells are receiving considerable attention towards increasing the network coverage, capacity, and improvement in the quality of service for users. In 3GPP LTE-Advanced (LTE-A) system, to efficiently utilize the bandwidth, femtocell and macro cell uses the same frequency band, but this deployment poses a technical challenge of cross-tier interference to macro users. In this paper, the novel quality of service based fractional power control (QoS-FPC) scheme under the heterogeneous networks environment is proposed, which considers the users priority and QoS-requirements during the power allocation. The proposed QoS-FPC scheme has two focal points: firs, it protects the macrocell users uplink communication by limiting the cross-tier interference at eNB below a given threshold, and second, it ensures the optimization of femtocell users power allocation at each power adjustment phase. Performance gain is demonstrated with extensive system-level simulations to show that the proposed QoS-FPC scheme significantly decreases the cross-tier intereference and improves the overall users throughput.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.12
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• pp.3274-3292
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• 2013

Unsupervised methods for image segmentation are recently drawing attention because most images do not have labels or tags. A topic model is such an unsupervised probabilistic method that captures latent aspects of data, where each latent aspect, or a topic, is associated with one homogeneous region. The results of topic models, however, usually have noises, which decreases the overall segmentation performance. In this paper, to improve the performance of image segmentation using topic models, we propose two topic masks applicable to topic assignments of homogeneous regions obtained from topic models. The topic masks capture the noises among the assigned topic assignments or topic labels, and remove the noises by replacements, just like image masks for pixels. However, as the nature of topic assignments is different from image pixels, the topic masks have properties that are different from the existing image masks for pixels. There are two contributions of this paper. First, the topic masks can be used to reduce the noises of topic assignments obtained from topic models for image segmentation tasks. Second, we test the effectiveness of the topic masks by applying them to segmented images obtained from the Latent Dirichlet Allocation model and the Spatial Latent Dirichlet Allocation model upon the MSRC image dataset. The empirical results show that one of the masks successfully reduces the topic noises.

• Journal of Communications and Networks
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• v.16 no.4
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• pp.378-384
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• 2014

Replication routing can greatly improve the data delivery performance by enabling multiple replicas of the same packet to be transmitted towards its destination simultaneously. It has been studied extensively recently and is now a widely accepted routing paradigm in delay tolerant networks (DTNs). However, in this field, the issue of how to maximize the utilization efficiency of limited replication quota in a resource-saving manner and therefore making replication routing to be more efficient in networks with limited resources has not received enough attention. In this paper, we propose a DTN routing protocol with back-pressure based replica distribution. Our protocol models the replica distribution problem from a resource allocation perspective and it utilizes the idea of back-pressure algorithm, which can be used for providing efficient network resource allocation for replication quota assignment among encountered nodes. Simulation results demonstrate that the proposed protocol significantly outperforms existing replication routing protocols in terms of packet delay and delivery ratio.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.7
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• pp.2668-2717
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• 2021

Demands for high-speed wireless data services grow rapidly. It is a big challenge to increasing the network capacity operating on licensed spectrum resources. Unlicensed spectrum cellular networks have been proposed as a solution in response to severe spectrum shortage. Licensed Assisted Access (LAA) was standardized by 3GPP, aiming to deliver data services through unlicensed 5 GHz spectrum. Furthermore, the 3GPP proposed 5G New Radio-Unlicensed (NR-U) study item. On the other hand, artificial intelligence (AI) has attracted enormous attention to implement 5G and beyond systems, which is known as Intelligent Radio (IR). To tackle the challenges of unlicensed spectrum networks in 4G/5G/B5G systems, a lot of works have been done, focusing on using Machine Learning (ML) to support resource allocation in LTE-LAA/NR-U and Wi-Fi coexistence environments. Generally speaking, ML techniques are used in IR based on statistical models established for solving specific optimization problems. In this paper, we aim to conduct a comprehensive survey on the recent research efforts related to unlicensed cellular networks and IR technologies, which work jointly to implement 5G and beyond wireless networks. Furthermore, we introduce a positioning assisted LTE-LAA system based on the difference in received signal strength (DRSS) to allocate resources among UEs. We will also discuss some open issues and challenges for future research on the IR applications in unlicensed cellular networks.

• Journal of Platform Technology
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• v.11 no.1
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• pp.3-10
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• 2023

Unmanned Aerial Vehicles (UAVs) have gained significant attention in 5G and 6G wireless networks due to their high flexibility and low hardware costs. However, UAV communication is still challenged by blockage and energy consumption issues. Reconfigurable Intelligent Surfaces (RISs) have emerged as a promising solution to these challenges, enabling improved spectral efficiency and reduced energy consumption by transmitting signals to users who cannot receive signals because of the obstacles. Many previous studies have focused on minimizing power consumption and data transmission delay through phase shift and power optimization. This paper proposes an algorithm that maximizes the sum rate by including bandwidth optimization. Simulation results demonstrate the effectiveness of the proposed algorithm.

• Korean Journal of Psychosomatic Medicine
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• v.19 no.2
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• pp.74-82
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• 2011

Objective:The aim of this study was to evaluate the relationship between sustained attention deficits in Attention-Deficit/Hyperactivity Disorder(ADHD) children and short-term Heart Rate Variability(HRV) parameters. In addition, we evaluate the relationship between The ADHD rating scale(ARS), the computerized ADHD diagnostic system(ADS) and Parenting stress index- short form(PSI-SF). Methods:This study was performed in the department of children and Adolescent psychiatry, Korea university Guro hospital from august 2008 to January 2009. We evaluated HRV parameters by short-term recordings of 5 minutes. K-ARS and ADS are used for screening and identifying ADHD children. Intelligence was measured using Korean educational Developmental Institute-wechsler Intelligence Scale for Children. The caregivers Complete Parenting Stress Index scale for evaluation parent stress. Results:The low frequency(LF) was significantly correlated with response variability of ADS. However, the other variables of ARS and ADS were not significantly correlated with LF. Hyperactivity subscale of ARS was significantly correlated with parental distress subscale and difficult child subscale of PSI-SF and inattention subscale of ARS was also significantly correlated with dysfunctional interaction and difficult child subscale of PSI-SF. Conclusion:The LF, 0.10-Hz component of HRV is known to measure effort allocation. This study shows that the LF component of HRV is significantly correlated with the response variability of ADS. This means that more severe symptoms of ADHD were correlated with the increase in the LF that means decreased effort allocation. These results also support the clinical usability of HRV in the assessment of ADHD. Furthermore, PSI-SF is correlated with hyperactivity and inattention variables of ARS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12C
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• pp.1020-1028
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• 2010

Relay has attracted great attention due to its inherent capability to extend the service coverage and combat shadowing in next generation mobile communication systems. So far, most relay technologies have been developed under the half-duplex (HD) constraint that prevents relays from transmitting and receiving at the same time. Although half-duplex relay (HDR) is easy to implement, it requires partitioning of resource for transmission and reception, reducing the whole system capacity. In this paper, we propose a multinser precoding and power control scheme with sum rate matching for a full-duplex (FD) multiple-input multiple-output (MIMO) relay. Full-duplex relay (FDR) can overcome the drawback of HDR by transmitting and receiving on the same frequency at the same time, while it is crucial to reduce the effect of self-interference that is caused by its own transmitter to its own receiver. The proposed precoding scheme cancels the self-interference of the FDR as well as to support multiuser MIMO. Moreover, we suggest a power allocation scheme for FD MIMO relay with the constraint that the sum rate of the relay's received data streams is equal to that of the relay's transmit data streams.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.11B
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• pp.891-899
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• 2004

Ethernet passive optical network (EPON) has drawn many attention as a promising access network technology because it can provide a high bandwidth with a low cost. Since the uplink in the EPON system is shared by many users, it is necessary for an EPON system to have an efficient bandwidth allocation mechanism. In addition, as the users demand more QoS-oriented applications, it is necessary for an EPON system to have an efficient mechanism supporting QoS. In this paper, we propose a variable window dynamic bandwidth allocation (DBA) algorithm for the EPON system. Unlike the previously proposed DBA algorithms, the variable window algorithm guarantees the QoS for the highest priority class, and at the same time provides more enhanced QoS for the lower priority classes by dynamically allocating bandwidth if necessary. It is verified through the simulations that the variable window algorithm can provide more enhanced QoS performance than other DBA algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7B
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• pp.422-430
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• 2007

WDM-PON has been receiving much attention as a key technology to FTTH. As the cost of WDM-PON heavily depends on the number of transceivers implemented at ONU, one of its shortcomings comes from the fixed provision of wavelength resource, which is tightly coupled with costly transceivers. In this paper, we propose a cost-effective WDM-PON architecture for dynamic resource provision. The proposed architecture is based on hierarchical grouping of multiple ONUs into a logical group and hierarchical sharing the resource. For high utilization of dynamic resource, the dynamic resource allocation algorithm is also proposed. We analyze the system efficiency in term of dynamism of system resource and system cost. We also verify that the proposed resource allocation algorithm achieves a high dynamism on resource allocation, and at the same time maintains the fairness between ONUs.

• Journal of Broadcast Engineering
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• v.17 no.1
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• pp.95-107
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• 2012

Network coding was proposed to increase the achievable throughput of multicast in a network. Recently, combining network coding into user cooperation has attracted research attention. For cooperative transmission schemes with network coding, users combine their own and their partners messages by network coding. In previous works, it was shown that adaptive DF with network coding can achieve diversity gain and additional throughput gain. In this paper, to improve performance of conventional protocols and maximize advantage of using network coding, we propose a new network coding based user cooperation scheme which uses adaptively amplify-and-forward and decode-and-forward according to interuser channel status. We derive outage probability bound of proposed scheme and prove that it has full diversity order in the high SNR regime. Moreover, based on the outage bound, we compute optimal power allocation for the proposed scheme.