• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.6
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• pp.1848-1868
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• 2014

Multiple-in multiple-out (MIMO) in long-term evolution (LTE) is an essential factor in achieving high speed data rates and spectral efficiency. The unexpected growth in data rate demand has pushed researchers to extend the benefits of multi-user MIMO. The multi-user MIMO system can take full advantage of channel conditions by employing efficient adjustment techniques for scheduling, and by assigning different modulation and coding rates. However, one of the critical issues affecting this feature is the appropriate estimation of channel quality indicator (CQI) to manage the allocated resources to users. Therefore, an accurate CQI estimation scheme is required for the multi-user MIMO transmission to obtain significant improvements on spectral efficiency. This paper presents overviews of multi-user MIMO in LTE/LTE-advanced systems. The link adaptation, scheduling process, and different factors that affect the reliability of CQI measurements are discussed. State-of-the-art schemes for the post-processing CQI estimation, and the comparisons of various CQI estimation schemes to support multi-user MIMO are also addressed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.613-619
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• 2012

The Long Term Evolution (LTE) system is already able to provide a background of variety services for mobile users with multimedia services such as audio, video, and data. In fact, the High Speed Packet Access plus (HSPA+) solution can greatly enhance bit rates on down-link. However, the supporting for multimedia applications with different QoS (Quality of Service) requirements is not devised yet. Hence, in this paper we propose an effective packet scheduling algorithm based on Proportional Fairness (PF) scheduling algorithms for the LTE. In this proposed packet scheduling scheme, we optimized instantaneous user data rates and the traffic class weight which prioritize user's packets. Finally, we evaluated and showed the performance of the proposed scheduling algorithm through simulations of multimedia traffics being transmitted to users over LTE links in a multi-cell environment.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.5
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• pp.43-49
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• 2017

In this paper, we propose the scheduling scheme of IEEE802.15.4e TSCH which is not specified in standard specification. The proposed scheme schedules the link by cooperating among the devices. A new device scans EBs(Enhanced Beacons) from network. An advertiser device broadcasts an enhanced beacon frame including links information on allocated channel offset and time-slots, and a new device can determine its own channel offset and time-slot. It's performance on maximum throughput and minimum delay is evaluated by comparing the proposed approach with a typical single channel IEEE802.15.4.

• Journal of Communications and Networks
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• v.13 no.3
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• pp.221-231
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• 2011

A joint multipath routing algorithm and channel allocation and scheduling for wireless multihop and multichannel systems is discussed. In packet transmission, distribution of packets to multiroutes makes it possible to reduce the transmission cost of the channels. Cross-layer cooperation of routing, channel allocation, and scheduling is an effective method of packet distribution. As a framework for the cooperation, we propose a multiroute distance vector routing (MDVR) scheme. In the MDVR scheme, the routing table is logically placed in between the routing and link layers, and the table plays the role of a service access point between these two layers. To evaluate the performance of MDVR, simulation is performed in a multichannel, multihop environment. The simulation results show that the MDVR framework can be efficiently implemented in the form of a distributed routing algorithm. It is also shown that in MDVR, the system-wise channel efficiency is almost 25% higher than that in a conventional single-route routing approach.

• Journal of Communications and Networks
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• v.13 no.2
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• pp.160-166
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• 2011

In u-healthcare services based on wireless body sensor networks, reliable connection is very important as many types of information, including vital signals, are transmitted through the networks. The transmit power requirements are very stringent in the case of in-body networks for implant communication. Furthermore, the wireless link in an in-body environment has a high degree of path loss (e.g., the path loss exponent is around 6.2 for deep tissue). Because of such inherently bad settings of the communication nodes, a multi-hop network topology is preferred in order to meet the transmit power requirements and to increase the battery lifetime of sensor nodes. This will ensure that the live body of a patient receiving the healthcare service has a reduced level of specific absorption ratio (SAR) when exposed to long-lasting radiation. We propose an efficientmethod for delivering delay-intolerant data packets over multiple hops. We consider forward error correction (FEC) in an erasure correction mode and develop a mathematical formulation for packet-level scheduling of delay-intolerant FEC packets over multiple hops. The proposed method can be used as a simple guideline for applications to setting up a topology for a medical body sensor network of each individual patient, which is connected to a remote server for u-healthcare service applications.

• Asia pacific journal of information systems
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• v.24 no.4
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• pp.417-441
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• 2014

Organizations need to exhibit characteristics of agility to stay ahead of their competitors and to survive in dynamic environments. One major concern for organizations is how to implement Information Systems (ISs) to enhance their agility. Organizations tend to spend too many resources to change their entire IS instead of only the components that cause problems without exactly knowing whether it enables or suppress organizational agility. To address these shortcomings and practical issues, we provide a framework to assess organizational agility and to diagnose a problem related to IS. By applying this prototype of the Agility Framework, we were able to diagnose a problem that the department of Management Control and Information Systems at the Universidad de Chile had and planned actions for them to improve its organizational agility with a course scheduling system, eClasSkeduler. This action research, which took more than 25-month for the first cycle, further develops the Agility Framework, which not only provides a way to link IS with organizational functions but also illustrates how to use it to diagnose a situation and plan actions for improving organizational agility through an information system.

• Journal of Information Processing Systems
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• v.13 no.5
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• pp.1320-1330
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• 2017

Wireless sensor networks for forest monitoring are typically deployed in fields in which manual intervention cannot be easily accessed. An interesting approach to extending the lifetime of sensor nodes is the use of energy harvested from the environment. Design constraints are application-dependent and based on the monitored environment in which the energy harvesting takes place. To reduce energy consumption, we designed a power management scheme that combines dynamic duty cycle scheduling at the network layer to plan node duty time. The dynamic duty cycle scheduling is realized based on a tier structure in which the network is concentrically organized around the sink node. In addition, the multi-paths preserved in the tier structure can be used to deliver residual packets when a path failure occurs. Experimental results show that the proposed method has a better performance.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.1080-1082
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• 2016

In a multi-hop CR (Cognitive Radio) network, each node find a path to destination node through several links. If links have the same frequency channel, there can be a serious interference among the links and it can reduce the network capacity. In multi-channel CR networks, each channel has different capacity according to the inter-link interference, and each channel has different traffic properties of primary users. In this paper, we propose channel scheduling scheme to minimize channel interferences and collision with primary users. Simulation results show the improvement of channel capacity and collision rate with primary users.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.7
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• pp.569-576
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• 2003

The data link layer of Foundation Fieldbus provides both token-passing and scheduling services for periodic, time-critical and time-available data. This study developed an analytical model that evaluates the delay performance of urgent data when the data link layer of Foundation Fieldbus provides token-passing service. The validity of analytical model is verified using an experimental model that consists of network interface boards of Foundation Fieldbus. Comparison of analytical and experimental models shows that the analytical model can be utilized in the approximate analysis of the delay characteristics of time-critical data in the Foundation Fieldbus. The analytical model can also be used in the basic design stage of Foundation Fieldbus network system.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.05a
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• pp.79-81
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• 2019

Collecting data in wireless sensor networks in minimum time is a traditional problem which is known NP-hard. Previous studies built the schedule using the node-based or link-based metrics to prioritize the transmissions. In this work, we combine the effect of both metrics to obtain a smaller aggregation time. We compare our work with state of the art schemes and report the improvement.