• Journal of Positioning, Navigation, and Timing
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• v.9 no.3
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• pp.229-236
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• 2020

The trend of water vapor contents in atmosphere is one of key elements for studying climate change. The tropospheric products, i.e., ZTD values achieved through GPS data processing can retrieve the amount of water vapor with higher temporal and spatial resolution than any other instruments. In this study, the tropospheric products of KASINET for a time period from 2001 to 2014 are reprocessed using PPP strategy and the products from the CODE's 2nd reprocessing campaign. For consistency with reprocessing activities of other networks like EPN, the VMF1 mapping function and non-tidal loading effect due to atmospheric pressure are applied in the process. The reprocessing results are investigated through comparing with the CODE's 2nd reprocessing products by including some IGS stations in the process and also calculating weekly coordinate repeatability to see the quality of the processing. After removing outliers based on the variation of averaged formal error, all processed stations have similar variations of formal error about 2 mm which is lower than that of the IGS final product. Comparison results with the CODE's 2nd reprocessing products show that the overall mean difference is found to be -0.28±5.54 mm which is similar level of the previous studies. Finally, the ZTD trends of all KASINET stations are calculated and the averaged trend is achieved as 0.19 mm/yr. However, the trend of each month shows different amounts and directions from -1.26 mm/yr in May to 1.18 mm/yr in August. In conclusion, the reprocessed tropospheric product and applied strategy of this study has enough quality as one of reliable solution for a reference product for Korean Peninsula which is needed to use GPSbased tropospheric product for climate change research.

• Journal of the Korea Computer Graphics Society
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• v.25 no.5
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• pp.11-20
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• 2019

With the development of deep learning technology, research is being actively carried out on user-friendly interfaces that are suitable for use in virtual reality or augmented reality applications. To support the interface using the user's hands, this paper proposes a deep learning-based fingertip detection method to enable the tracking of fingertip coordinates to select virtual objects, or to write or draw in the air. After cutting the approximate part of the corresponding fingertip object from the input image with the Grad-CAM, and perform the convolution neural network with Atrous Convolution for the cut image to detect fingertip location. This method is simpler and easier to implement than existing object detection algorithms without requiring a pre-processing for annotating objects. To verify this method we implemented an air writing application and showed that the recognition rate of 81% and the speed of 76 ms were able to write smoothly without delay in the air, making it possible to utilize the application in real time.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.313-324
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• 2005

The success of the IEEE 802.11 standard has prompted research into efficiency of the different medium access methods and their support for different traffic types. A modified version of the point coordination function (PCF) called modified PCF has been introduced as a way to improve the efficiency over the standard method. It has been shown through a simulation study and a mathematical analysis that channel utilization can be much improved compared to the standard, in case there is no so-called hidden station problem. However, under the hidden station problem, the efficiency of the modified PCF would obviously decrease. In this paper, some enhancements of the modified PCF are introduced. Firstly, we propose a retransmission process to allow frames involved in collisions to be retransmitted. Then, we propose a collision resolution mechanism to reduce the frame collision probability due to the hidden station problem. In addition, we propose a priority scheme to support prioritization for different traffic types such as interactive voice and video, and real-time data traffic in the modified PCF. To prevent the starvation of one low priority traffic, minimum transmission period is also guaranteed to each traffic type via an admission control algorithm. We study the performance of the modified PCF under the hidden station problem and the performance of the modified PCF with priority scheme through simulations. To illustrate the efficiency of the priority scheme, we therefore compare its simulation results with those of some standardized protocols: The distributed coordination function (DCF), the enhanced distributed channel access (EDCA), the PCF, and our previously proposed protocol: The modified PCF without priority scheme. The simulation results show that the increment of delay in the network due to the hidden station problem can be reduced using the proposed collision resolution mechanism. In addition, in a given scenario the modified PCF with priority scheme can provide better quality of service (QoS) support to different traffic types and also support a higher number of data stations than the previous proposals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1288-1296
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• 2006

This paper proposes a fast authentication scheme based on hierarchical key structure (HiFA) for roaming mobile nodes in both intra-domain and inter-domain. The full authentication procedure standardized in IEEE 802.11 and 802.16 is difficult to be applied to a handover since it needs a heavy operation and long delay time during a handover. Though a number of schemes were proposed to solve the problem, the existing schemes might degrade the security of authentication or impose heavy administrative burden on the Pome authentication server. The main contribution of this paper is to reduce the communication and computation overhead of the home authentication sewer without degrading the security strength of the fast roaming authentication using hierarchical authentication key structure. The proposed scheme iii this paper decentralizes the administrative burden of the home authentication server to other network entities such as a local authentication server or access point and supports the security separation of the authentication key among local authentication servers using hash key chain.

• Journal of Broadcast Engineering
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• v.16 no.5
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• pp.811-823
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• 2011

This paper proposes an efficient transmission method for the panoramic multimedia contents. The panoramic video provides wide sight and various view-point to the user. The traditional methods of the panoramic multimedia content transmission has several limitations, as follow; A client suffers a long initial delay time to play a panoramic video when it is transmitted through a limited bandwidth network, because the panoramic video has larger data size than a general video. And if a client's display device has limited resolution, such as mobile phone, laptop PC monitor, etc. it can not display the entire panoramic video that has a wide view video sequence. So, in order to overcome the obstacles, this paper proposes an efficient transmission of panoramic multimedia contents. This method will increase the transmission efficiency throughout the technique of the scene description in MPEG-4 system. Also we demonstrated the efficiency of the proposed method by comparison with existing methods.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.3
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• pp.351-355
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• 2010

The service which is required wide bandwidth is growing in these days, so building up High Speed communication system is being required. The Task Force team of IEEE 802.3ah set the EPON as a standard; next generation subscriber access network. For offering a high quality service, 10G EPON that is changed from 1Gbps uplink downlink bandwidth to 10Gbps is come up. Although Kramer had studied 10G EPON there was a QoS limitation, when load is low, End-to-End maximum delay is increased. This paper is suggesting time synch ronization method, resource reservation method, band width allocation method. We confirmed that 10EPON was able to offer quality service by the result of the OPNET.

• Journal of KIISE:Computing Practices and Letters
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• v.6 no.2
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• pp.244-253
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• 2000

Since no single routing-switching combination performs the best under various different types of applications, a flexible network is required to support a range of polices. This paper introduces an implementation of a look-up table routing engine offering flexible routing and switching polices without performance degradation unlike those based on microprocessors. By deciding contents of look-up tables, the engine can implement wormhole routing, virtual cut-through routing, and packet switching, as well as hybrid switching, under a variety of routing algorithms. Since the routing engine has a piplelined look-up table architecture, the routing delay is as small as one flit, and thus it can overlap multiple routing actions without performance degradation in comparison with hardwired routers dedicated to a specific policy. Because four pipeline stages do not induce a hazard, expensive forwarding logic is not required. The routing engine can accommodate four physical links with a time shared cut-through bus or single link with a cross-bar switch. It is implemented using Xilinx 4000 series FPGA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11B
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• pp.1178-1190
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• 2009

IEEE 802.11e proposed by IEEE 802.11 working group to guarantee QoS has contention based EDCA and contention free based HCCA. HCCA, a centralized polling based mechanism of 802.11e, needs a scheduling algorithm to allocate the network resource efficiently. The existing standard scheduler, however, is inefficient to support for QoS guarantee for real-time service having VBR traffic. To efficiently assign resource for VBR traffic, in this paper, we propose TXOP algorithm based on dual leaky bucket using average resource allocation and peak resource allocation. The minimum TXOP of each station is obtained by using statistical approach to maximize number of stations of which performance satisfy QoS target. Simulation results show that the proposed algorithm has much higher performance compared with reference scheduler in terms of throughput and delay.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.67-74
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• 2001

In this paper, we propose a new method to improve tile processing of route recovery of the existing DSR algorithm on detection of route error. In mobile ad hoc networks, mobile nodes themselves have routing capability. Thus, a well-defined routing protocol is required for route set-up between two mobile nodes. However, the existing DSR routing protocol has problem with dropping of packets due to the recovery delay when a route error occurs. In order to alleviate tile problem, we propose an enhanced DSR protocol to reduce the route error recovery tine and evaluate the protocol through simulation. As tile result of evaluation, we found the proposed DSR protocol provided about 4 to 30 times faster route error recovery time according to the test scenario than the existing DSR protocol.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1194-1203
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• 2004

The RR protocole, proposed in IETF mip6 WG and standardized by RFC 3775 at lune 2004, send a message 'Binding Update' that express MN's location information to CN safety and update location information. Standard RR protocole has some problems with initiating the protocol by the MN; it causes to increases in communication load in the home network, to increases communication delay between MN and CN. Also, is connoting vulnerability to against attacker who are on the path between CN and HA in security aspect. This paper proposes doing to delegate MN's location information update rights by HA new location information update method. That is, When update MN's location information to HA, Using MN's private key signed location information certificate use and this certificate using method that HA uses MN's location information at update to CN be. It decreases the route optimization overhead by reducing the number of messages as well as the using location information update time. Also, remove security weakness about against attacker who are on the path between CN and HA.