• Journal of Communications and Networks
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• v.2 no.1
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• pp.76-84
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• 2000

Communication systems, including cell-based mobile communication systems, multiple satellite communication systems of multi-beam satellite systems, require reliable handoff methods between cell-to-cell, satellite-to-satellite of beam-to-team, respectively. Recent measurement of a CDMA cellular system indicates that the system is in handoff at about 35% to 70% of an average call period. Therefore, system reliability during handoff is one of the major system performance parameters and eventually becomes a factor in the overall system capacity. This paper presents novel and improved techniques for handoff in cellular communications, multi-beam and multi-satellite systems that require handoff during a session. this new handoff system combines the soft handoff mechanism currently implemented in the IS-95 CDMA with code and packet diversity combining techniques and an iterative decoding algorithm (Turbo Coding). the Turbo code introduced by Berrou et all. has been demonstrated its remarkable performance achieving the near Shannon channel capacity [1]. Recently. Turbo codes have been adapted as the coding scheme for the data transmission of the third generation international cellular communication standards : UTRA and CDMA 2000. Our proposed encoder and decoder schemes modified from the original Turbo code is suitable for the code and packet diversity combining techniques. this proposed system provides not only an unprecedented coding gain from the Turbo code and it iterative decoding, but also gain induced by the code and packet diversity combining technique which is similar to the hybrid Type II ARQ. We demonstrate performance improvements in AWGN channel and Rayleigh fading channel with perfect channel state information (CSI) through simulations for at low signal to noise ratio and analysis using exact upper bounding techniques for medium to high signal to noise ratio.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.53-57
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• 2013

The quality of service for the voice and data communication is one of the most important elements in the mobile cellular networks. This quality has the time varying characteristics depending on the wireless network environments. In order to guarantee the quality of service at the predefined level, the mobile service provider needs to collect all the information about the level of quality served by the local base stations. In the conventional method the information on the service quality is measured and collected by the moving vehicle adopting the global positioning device. However this method requires relatively high cost and does not cover all the service areas. In this paper a new method is proposed utilizing a measurement node with local area communication transceiver and the mobile user equipment. In the proposed method the node communicates with the user equipment periodically to monitor the information on the service quality. The resulting information is reported to the measurement server in the mobile network. This method could be applied to either the circuit or the packet based networks. It also has an advantage in terms of the cost efficiency compared to the conventional method considering the required the equipment and the human resources.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1807-1816
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• 1998

The interference probability between non-geostationary-statellite orbit mobile station is calculated when the two systems are sharing the frquency band below 1 GHz. The probability density function of a mobile earth station(MES) is calculated based on the established propagation model and then, a probability of exceeding the threshold level is derived. By changing the average transimission per unit time of total MSS(Moblie satellite service) area and the ratio of transmitters for specific area, we obtain the average transmission per unit time for the area under consideration. From this, the exceedance probability for the given pfd threshold level is evaluated. The exceedance probability is increased as the average transmissio per unit time and ratio become larger. Also the effect of filter isolation between channels is accounted for.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.51-59
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• 2011

To support seamless IPTV services in IP-based wireless network, delay or interruption time must be minimized because noticeable interruption will make IPTV service users unhappy. A number of protocols have been proposed for solving mobility problem. However effective seamless handover mechanism to support mobile IPTV services yet to be solved. Mobile WiMAX offers a wireless solution in the access networks that can support IPTV services. Goal of this paper is to identify some reasons of delay time during handover process in an IPv6 capable Mobile WiMAX and to perform handover delay of some optimization scenarios given by existing standardization and proposed improvement.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.285-288
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• 1998

Viterbi docoder is a maximum likelihood decoding method for convolution coding used in satellite and mobile communications. In this paper, a Viterbi decoder with constraint length of K=7, 3-soft decision and traceback depth of $\Gamma$=96 for convolution code is implemented using VHDL. The hardware size of designed decoder is reduced by 4 bit pre-traceback in the survivor memory.

• Electronics and Telecommunications Trends
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• v.21 no.4 s.100
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• pp.97-106
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• 2006

이동통신과 인터넷 사용에 대한 사용자의 요구는 집이나 회사 등 도심지역에 국한되지 않고 언제 어디서나 그 사용을 요구하고 있다. 하지만 이런 요구를 충족시키기에 지상망의 제한된 서비스 영역은 그 한계를 가진다. 이에 반해 위성은 광역 서비스가 가능하여 이런 욕구를 충족시키기에 좋은 장점을 가진다. 이런 특징에 기반하여 유럽에서는 현재 열차, 항공기 및 선박에 이동 인터넷 서비스 지원을 위한 연구가 활발히 이루어지고 있으며 이에 대한 동향을 알아보고자 한다. 동시에 지상망이 미치지 않는 외각지역에 대해 위성을 이용한 3G 서비스와 함께 MBMS 제공을 위한 연구에 대해서도 알아보고자 한다.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.8-14
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• 2017

In 4G mobile communication, data services of mobile communication began to be provided in earnest. As a result, services such as the internet and multimedia including the video have become the main contents in the recent wireless traffic. Accordingly, research on 5G mobile communication with higher transmission rate has been actively carried out. 5G mobile communication is expected to be based on 4G for compatibility with existing terminals. Therefore, the simulation of this paper is based on 4G and we propose a new user scheduling scheme based on the Max throughput scheduling algorithm to improve system performance. This paper derives the frequency efficiency and fairness to compare the existing user scheduling algorithm with the proposed user scheduling algorithm. The proposed scheme shows better frequency efficiency and fairness than Max throughput in all situations. This paper contributes to the research for improving the system performance of 5G mobile communication technology, and I hope that it will help some of the ongoing standardization work.

• Journal of Satellite, Information and Communications
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• v.9 no.3
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• pp.22-26
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• 2014

This paper introduces homogeneous liquid crystal (LC) orientations on chemically modulated polystyrene (PS) surfaces using various ion beam (IB) exposure time. Transparent PS was replaced with conventional polyimde material. Especially, PS has higher transparent property than conventional polyimide thin film and it means PS is more suitable material for producing high brightness mobile LCD. As a non-contact process, IB bombardment process induced LC orientation in the direction parallel to the IB process. Through x-ray photoelectron spectroscopy, it was shown that the chemical compositional changes of the IB-irradiated PS surfaces were determined as a function of IB exposure time. Using this analysis, the optimal IB bombardment condition was determined at IB exposure time of up to 15 s. Moreover, thermal stability on IB-irradiated PS surfaces were carried out which showed that a relatively high IB exposure time induced a thermally stable LC alignment property. And it has a highly potential of mobile high transparent mobile LCD such as smart phone display and mobile information device.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.78-83
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• 2015

In this paper, when WLAN repeater of satellite communication package system as a novel wireless disaster communication network connected to LTE D2D mobile terminal, we analyzed radio channel interference from WLAN and WPAN system of adjacent same ISM band using Monte-Carlo method. In this study, WLAN cell radius was determined using Extended Hata Model considering practical environment, and simulated physical protection distance and density in the dense-mode to minimize interference from WLAN, Bluetooth, and ZigBee. Simulation results, WLAN repeater can be operated with 15 WLAN interferer over 130m distance, 23 Bluetooth interferer over 100m distance, and with 62 ZigBee interferer over 83m distance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.140-150
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• 2003

In this paper, we propose a novel code sharing method for downlink transmission of mobile satellite communication systems using a multibeam geosynchronous-orbit satellite. In the proposed system, spreading codes are shared among downlink beams in order to increase the system capacity. We also propose efficient radio resource and transmit power allocation schemes for the proposed system. Simplified analysis and simulation results on the system capacity show the capacity improvement by the proposed scheme. The simulation results show that the capacity of the proposed system is more than 2 times as large as that of a conventional multibeam satellite system. In the frequency-selective fading channel, the capacity improvement increases as the interference between orthogonal spreading codes decrease.