• KIPS Transactions on Computer and Communication Systems
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• v.9 no.6
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• pp.131-136
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• 2020

In vehicular communications environment, content pre-caching can reduce the delay time from the user to the content server. However, the problem of where and how much pre-caching is still not solved. In this paper, based on the movement probability of the vehicle, we propose a method for pre-caching by distributing the optimized amount of content to each base station candidate that the vehicle will move as follows. First, the movement probability of each vehicle was learned using Markov Model. And the amount of content to be distributed and pre-cached was optimized based on the wireless environment. In experiments based on NS-3, the proposed strategy maintained the least delay compared to the existing protocol, leading to the most traffic-saving results.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11b
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• pp.1261-1264
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• 2002

Ad-hoc 무선망은 각자의 이동 노드에 대한 제약이 없고, 유선망이나 기지국과 같은 기반구조를 필요로 하지 않기 때문에 병원, 전시장, 생산 현장과 같은 곳에서 사용되는 자치분산 네트워크이다. 최근 들어 이동 Ad-hoc 네트워크에서 사용되는 AODV, DSR, TORA, ZRP등의 라우팅 프로토콜 연구가 활발히 이루어지고 있는 실정이다. 따라서 본 논문에서는 AODV 라우팅 프로토콜을 사용하여 다양한 네트워크 환경에서 성능평가와 라우팅 프로토콜의 문제점을 수정, 개선하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7B
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• pp.659-667
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• 2009

Mobile Ad-hoc Network consists of mobile nodes without immobile base station. In mobile ad-hoc network, network cutting has occurred frequently in node because of energy restriction and frequent transfer of node. Therefore, it requires research for certain techniques that react softly in topology alteration in order to improve reliability of transmission path. This paper proposes path selection techniques to consider mobility of node that respond when search path using AOMDV routing protocol. As applying proposed techniques, We can improve reliability and reduce re-searching number of times caused by path cutting.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11A
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• pp.1068-1075
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• 2006

An adaptive ranging technique for Orthogonal Frequency Division Multiple Access(OFDMA) uplink transmission is proposed for timing synchronization of multiple mobile stations located different distances from a base station. By combining the Timing Phase Compensated Frequency Domain Cross-correlation(TPCFDC) and Frequency Domain Differential Cross-correlation(FDDC), the proposed scheme reduces the number of correlators used in ordinary TPCFDC. Repeated initial ranging attempt with the FDDC in the proposed scheme greatly reduces the hardware implementation complexity. Simulation results for ranging success probability and average ranging attempts count show that the proposed algorithm performs similarly with the ordinary TPCFDC even with the 10 times reduced complexity.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.689-692
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• 2005

In this paper, we have developed a retrodirective active array operating in the 2 GHz LS band. The retrodirective array has the property of re-directing any electromagnetic wave back to the incoming direction without any priory informations. The system is consisted of frequency mixers and antenna array. The mixer is acting as a phase conjugator. In this research, 2-port gate mixers using pHEMT and 1${\times}$4 monopole array have been used. The retrodirective array developed in this research can be applied in the base station facilities for the wireless mobile communications and RFID transponders.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.561-564
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• 2005

This paper proposes an access control algorithm for guaranteeing fair packet transmissions in CDMA-based slotted ALOHA systems. In the proposed algorithm, the base station calculates the packet transmission and retransmission probabilities based on the offered loads and then broadcasts these probabilities to all mobile stations. Mobile stations, which have a packet to transmit, attempt to transmit a packet with the received probabilities. Simulation results show that the proposed algorithm can offer better system throughput and average delay than the conventional algorithm. Results also show that the proposed algorithm can guarantee a good fairness among all mobile stations regardless of the offered loads.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.872-875
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• 2005

Portable Internet extended from wireless LAN has a large cell size, similar to a wireless mobile communication, and can provides the seamless service which offers middle-low speed mobility. IEEE 802.16e, the international standard of Portable Internet, uses PKMv2(Privacy Key Management) protocol for authorization and key exchange between a MSS(Mobile Subscriber Station) and a BS(Base Station). This paper first reviews and studies overall security architecture of TTA HPi standard and IEEE 802.16e which supports mobility based on WMAN(Wireless Metropolitan Area Network) standard(IEEE 802.16)

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1649-1655
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• 2005

For systems with coexisting cellular and hot-spot cells in broadband orhogonal frequency and code division multiplexing (OFCDM) systems, a suitable cell search algorithm is proposed fur the common pilot channel (CPICH) in the forward link using separated I/Q channel cell specific codes(CSSC), in which the cellular cell specific scrambling code (CCSSC) is assigned to the in-phase (Q) pilot channel of all cellular cells, and the exclusive hot-spot cell specific scrambling code (HSCSSC) group is assigned to the quadrature (Q) pilot channel of all hot-spot cells. Therefore, the proposed algorithm enables a mobile station (MS) to search quickly for the most desirable hot-spot cell due to reducing the effect of CCSSC, when a MS wants to use a mobile internet. The computer simulation results show that the proposed cell search algorithm can achieve faster cell search time performance, compared to conventional cell search methods.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.7
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• pp.1399-1405
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• 2003

This paper proposes an MAC protocol for fair packet data services in stoned CDMA system. In slotted CDMA system, the packets transmitted in the same slot act as multiple access interference, so that unsuccessful packet transmissions are entirely caused by multiple access interference. Therefore, in order to get the optimal system throughput, the number of simultaneously transmitted Packets should be kept at a proper level. In the proposed protocol, the base station calculates the new and retransmitted packet transmission probability of mobile stations according to the offered load and then broadcasts these probabilities. Mobile stations, which have a packet, attempt to transmit packet with the received probabilities. Simulation results show that the proposed scheme can offer better system throughput than the conventional scheme, and guarantee a good fairness among all mobile stations regardless of the offered load.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.7
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• pp.1415-1420
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• 2003

The mobile radio networks can be divided into networks that has the base station or the infrastructures like AP(Access Point) and Ad Hoc network that hasn't any infrastructures. As there aren't any fixed infrastructures in Ad Hoc Networks, mobile nodes should transmit the data oかy among mobile nodes themselves. To supplement these weakpoints of the two networks, many studies about Ad Hon based on the 802.11 are in progress. In this thesis, we try to propose the efficiency of the suggested protocols by comparing and analyzing power saving protocols according to the Beacon intervals in multi hop Ad Hoc Networks based on IEEE 802.11.