• 한국정보통신설비학회:학술대회논문집
• /
• 2009.08a
• /
• pp.275-280
• /
• 2009

Femtocells are viewed as a promising option for mobile operators to improve coverage and provide high-data-rate services in a cost-effective manner Femtocells can be used to serve indoor users, resulting in a powerful solution for ubiquitous indoor and outdoor coverage. TThe frequency accuracy and phase alignment is necessary for ensuring the quality of service (QoS) forapplications such as voice, real-time video, wireless hand-off, and data over a converged access medium at the femtocell. But, the GPS has some problem to be used at the femtocell, because it is difficult to set-up, depends on the satellite condition, and very expensive. The IEEE 1588 specification provides a low-cost means for clock synchronisation over a broadband Internet connection. The Time of Packet (ToP) specified in IEEE 1588 is able to synchronize distributed clocks with an accuracy of less than one microsecond in packet networks. However, the timing synchronization over packet switched networks is a difficult task because packet networks introduce large and highly variable packet delays. This paper proposes an enhanced filter algorithm to reduce ths packet delay variation effects and maintain ToP slave clock synchronization performance. The results are presented to demonstrate in the intra-networks and show the improved performance case when the efficient ToP filter algorithm is applied.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.9
• /
• pp.790-797
• /
• 2015

In this paper, We made the microwave polar transmitter based on the software to analyze the synchronization status between the phase signal and the amplitude signal of polar transmitter, and analyzed the result. In order to solve the time delay mismatch problem, we applied simplified compensation algorithm and compared the synchronization status between the two paths before and after compensation. Before compensation, the value of time delay mismatch was the maximum of 97 nsec at 9.3 GHz with the occupied bandwidth of 12 MHz, but after applying the compensation algorithm, the signals between the two paths were synchronized, and we identified the occupied bandwidth could recover to the previous 3.7 MHz.

• Journal of Korea Multimedia Society
• /
• v.9 no.2
• /
• pp.208-214
• /
• 2006

Participants of a NVE(networked virtual environment) may have different hardwares and network environments, and to guarantee the fairness, messages of participants should be synchronized. A solution for the synchronization problem is to wait for a certain amount of time until the server processes the message. It is not easy to determine a suitable waiting period because of the trade-off between the fairness and the responsiveness. In this paper we propose a method to decide a waiting period by considering only the participants with small network delays and perform experiments for the performance evaluation. Experiments show that the proposed method leads to significant improvement of responsiveness, while retaining fairness.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.26 no.9
• /
• pp.64-72
• /
• 2012

The interest in wind power generation area such as developing and operating wind-diesel pilot complex in remote and island regions that have difficulty in having power plant and connecting to power system is growing rapidly in the world. We have installed and researched the hybrid system in Sekgok Pilot Complex to meet the new generation system. From the monitored data of the system, the performance of each diesel power plant is outstanding. However, step out problem was detected with respect to load sharing and synchronization with decentralized power supply. An advanced controller design having better response time and stability is needed to solve such problem. In this paper, we proposed the algorithm, through digital controller of Governor, which is applied to hybrid system. As a result, we obtained the stable frequency value in variable loading conditions. Also, we proved the advanced response time and stability through the simulation and experiment by applying additional current signal to the control algorithm.

• Journal of Internet Computing and Services
• /
• v.3 no.1
• /
• pp.91-99
• /
• 2002

Many companies and departments are increasingly concerned of searching their business information in correct and faster way as they share the information through the internet. LDAP has been proposed for directory server standards which supports storing, searching and managing the business information, and it has become a global standard. Current LDAP, however, cannot solve problem; such as server overloads and data synchronization. This paper describes the history and characteristics of LDAP, and proposes an architecture for solving those problem;. Since the proposed architecture is designed based on the existing LDAP architecture, it guarantees extensibility and portability of server configuration.

• Journal of Drive and Control
• /
• v.13 no.2
• /
• pp.1-9
• /
• 2016

In this paper, an elementary force fighting problem was investigated. The problem is encountered when a double-rod type EHA(electro-hydrostatic actuator) is combined with a single-rod type EHA to build a redundant actuator system with synchronized motion. When the rod-side chambers of the two different types of EHAs have the same effective piston areas and are simultaneously pressurized by an external load, the two EHAs behave identically, sharing the external load equally. However, when the piston head-side chamber of the single rod type EHA, having a larger effective area than the rod-side chamber, is pressurized by the external load, an abnormal force fighting between the two EHAs occurs, unless their pump speeds are properly decoupled. In this study, the output drive forces of each EHA were obtained from the cylinder pressure signals and applied to the position control for each EHA to maintain the balance between their pump speeds. Adding minor force difference feedback loops to the position control, the force fighting phenomena could be eliminated and steady state synchronization errors were reduced. The power consumption of the pumps also could be remarkably reduced, avoiding unnecessarily high load pressures to the pumps.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.23 no.1
• /
• pp.37-43
• /
• 2023

Compressed still image or video bitstreams require protection from channel errors in a wireless channel. Embedded Zerotree Coding(EZW), SPIHT could have provided unprecedented high performance in image compression with low complexity. If bit error is generated by dint of wireless channel transmission problem, the loss of synchronization on between encoder and decoder causes serious performance degradation. But wavelet zerotree coding algorithms are producing variable-length codewords, extremely sensitive to bit errors. The idea is to partition the lifting coefficients. A many partition of lifting transform coefficients distributes channel error from wireless channel to each partition. Therefore synchronization problem that caused quality deterioration in still image and video stream was improved.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.12
• /
• pp.5049-5057
• /
• 2010

As communication technologies are developed and variety of services to mobile devices are provided, mobile users is rapidly increasing every year. However, mobile services running on wireless network environment are exposed to various security threats, such as illegal tampering, eavesdropping, and disguising identity. Accordingly, the secure mobile communications services to 3GPP were established that the standard for 3GPP-AKA specified authentication and key agreement. But in the standard, sequence number synchronization problem using false base station attack and privacy problem were discovered through related researches. In this paper, we propose an efficient authentication mechanism for enhanced privacy protection in the 3G network. We solve the sequence number synchronization existing 3GPP authentication scheme using timestamp and strengthen a privacy problem using secret token. In addition, the proposed scheme can improve the bandwidth consumption between serving network and home network and the problem of authentication data overhead for the serving network because it uses only one authentication vector.

• Journal of Communications and Networks
• /
• v.5 no.4
• /
• pp.319-327
• /
• 2003

We consider the problem of low-sampling rate high-resolution channel estimation and timing for digital ultrawideband (UWB) receivers. We extend some of our recent results in sampling of certain classes of parametric non-bandlimited signals and develop a frequency domain method for channel estimation and synchronization in ultra-wideband systems, which uses sub-Nyquist uniform sampling and well-studied computational procedures. In particular, the proposed method can be used for identification of more realistic channel models, where different propagation paths undergo different frequency-selective fading. Moreover, we show that it is possible to obtain high-resolution estimates of all relevant channel parameters by sampling a received signal below the traditional Nyquist rate. Our approach leads to faster acquisition compared to current digital solutions, allows for slower A/D converters, and potentially reduces power consumption of digital UWB receivers significantly.

• Journal of Information Technology Services
• /
• v.10 no.3
• /
• pp.203-212
• /
• 2011

In the every day life of the people, the Internet is widely used. Currently over 1.9 billion people have one or more email addresses and over 600 million people use the Facebook. People are collaborating via the Internet more and more. When people are collaborating through the Internet, the differences of the message delivery delay are the biggest problem that disturbs the collaborative work over the network. To solve the differences of the message delivery delay, we introduce the delay-gap method. An experimental code have been implemented and the efficiency of the delay-gap is presented through the results from the experiment that have many participants.