• Journal of Communications and Networks
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• 제11권1호
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• pp.42-46
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• 2009

Superimposed training (SIT) design for estimating of time-varying multipath channels is investigated for mobile orthogonal frequency division multiplexing (OFDM) systems. The design of optimum SIT consists of two parts: The optimal SIT sequence is derived by minimizing the channel estimates' mean square error (MSE); the optimal power allocation between training and information data is developed by maximizing the averaged signal to interference plus noise ratio (SINR) under the condition of equal powered paths. The theoretical analysis is verified by simulations. For the metric of the averaged SINR against signal to noise ratio (SNR), the theoretical result matches the simulation result perfectly. In contrast to an interpolated frequency-multiplexing training (FMT) scheme or an SIT scheme with random pilot sequence, the SIT scheme with proposed optimal sequence achieves higher SINR. The analytical solution of the optimal power allocation is demonstrated by the simulation as well.

• 한국통신학회논문지
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• 제21권6호
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• pp.1501-1509
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• 1996

Mobile stations can be classified by the transmission power level in CDMA system. Different performance parameters will be given to each class of mobile stations so that the appropriate quality ofservices can be provided. In this paper, it is assumed that there are two clsses of mobile stations. with the classification of mobile stations, analytical models are presented for the estimates of the reverse link capacity and the blocking probability. From the model for the reverse link capacity, the maximum number of each class of mobile stations to be served is derived. It is shown that $E_{b/}$I reduction of 1 dB allows the capacity to be increased by 25% and the data transmission rate and the power control accuracy have a significant effect on the reverse link capacity and the blocking probability. Simulation results are provided for validating the anlaytical estimates of the blocking probability.ocking probability.y.

• 한국통신학회논문지
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• 제22권7호
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• pp.1448-1458
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• 1997

In this paper the reverse link of the GLOBALSTAR-the representative CDMA LEO satellite system and LEO mobile satellite channel are developed by the SPW software simulation tool. And the performance of the system is evaluated. GLOBALSTAR is designed to give cellular-type service to hand-held user terminals through a constellation of 48 LEO satellites in circular orbites with 1414 Km altitude. Since LEO mobile satellite system communicates with mobile unit, it is suffered from severe multipath fading and shadowing. The fast mobility of LEO satellites makes the channel condition time vering. So, the LEO mobile satellite channel is different from land mobile channels. In this unique LEO satellite channel, it is shown that the performance of the GLOBALSTAR reverse link is varied according to the elevational angle, but this variation is overcome by satellite path diversity.

• Journal of Communications and Networks
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• 제11권3호
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• pp.261-270
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• 2009

We propose a tree-based integration of infrastructure networks and MANETs (TUM) to efficiently extend the scope of mobile Internet protocol to mobile ad hoc networks and devise a tree-based routing protocol (TBRP) that is suitable for the TUM architecture. Infrastructure networks have a number of fixed Internet Gateways that connect two heterogeneous networks. Mobile nodes form a number of small trees named pMANETs, each of them growing from anchor node which can communicate directly with an Internet Gateway. A new node registers with foreign agent and home agent along the tree path without resorting to an inefficient flooding. Furthermore, the TBRP sets up a routing path efficiently by exploiting the tree information without relying on flooding. We show by resorting to simulation that our approach is competitive against the conventional AODV based approach.

• 한국통신학회논문지
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• 제28권3A호
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• pp.119-128
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• 2003

A space diversity technique was applied to the conventional optimal beamforming structure using antenna arrays at the base station receiver in the wireless mobile communication system to get performance enhancement due to interference rejection and fading resistance ability of it. To demonstrate the benefit of proposed system, we derived output signal to interference plus noise ratio (SINR) of combined signal from all sub-array groups considering the fading effects and compared with the beamforming-only system. From the analysis and simulation results, we showed that the proposed system can provide high performance gain under Rayleigh fading channel.

• 한국통신학회논문지
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• 제18권5호
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• pp.721-729
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• 1993

본 논문에서는 도심환경에서 채널 상태를 잘 나타내는 Aulin의 수학적 모델에 근거하여 육상 이동 통신 채널을 시뮬레이션하는 방법에 대하여 제안하였다. 본 방법은 하드웨어 구현이 용이하고, 다양한 채널 상태를 모사할 수 있는 Jakes 방식의 장점을 유지하면서 Jakes 방식의 전력 스펙트럼이 실제의 결과 일치하지 않는 문제점을 해결하였다. 제안된 방식으로 생성된 신호의 자기상관관계, LCR(Level crossing rate), ADF(average duration of fades)등을 시뮬레이션을 통하여 얻은 후 이론치와 비교함으로써 우수한 성능을 나타냄을 보였다. 또한 본 방법은 여러개의 독립적인 페이딩 신호를 쉽게 발생시킬 수 있음을 보였다.

• ETRI Journal
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• 제28권4호
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• pp.435-443
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• 2006

This paper presents an efficient carrier recovery algorithm combined with a turbo-coding technique in a mobile communication system. By using a block turbo code made up of independently decodable block codes, we can efficiently recover the fast time-varying carrier phase as well as correct channel errors. Our simulation results reveal that the proposed scheme can accommodate mobiles with high speed, and at the same time can reduce the number of iterations to lock the phase.

• 한국통신학회논문지
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• 제36권4A호
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• pp.380-387
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• 2011

While mobile IPTV services are supported through the mobile WiMAX networks, there must need some guaranteed bandwidth for the IPTV services especially if IPTV and non-IPTV services are simultaneously supported by the mobile WiMAX networks. The quality of an IPTV service definitely depends on the allocated bandwidth for that channel. However, due to the high quality IPTV services and to support of huge non-IPTV traffic over mobile WiMAX networks, it is not possible to guarantee the sufficient amount of the limited mobile WiMAX bandwidth for the mobile IPTV services every time. A Service Level Agreement (SLA) between the mobile IPTV service provider and mobile WiMAX network operator to reserve sufficient bandwidth for the IPTV calls can increase the satisfaction level of the mobile IPTV users. In this paper, we propose a SLA negotiation procedure for mobile IPTV users over mobile WiMAX networks. The Bandwidth Broker controls the allocated bandwidth for IPTV and non-IPTV users. The proposed dynamically reserved bandwidth for the IPTV services increases the IPTV user's satisfaction level. The simulation results state that, our proposed scheme is able to provide better user satisfaction level for the IPTV users.

• 한국통신학회논문지
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• 제31권11B호
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• pp.945-952
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• 2006

Hierarchical Mobile IPv6(HMIPv6) 네트워크에서 도메인간의 핸드오버(Inter-domain handover)가 발생할 때 Mobile Nodes(MNs)는 과도한 신호전달 트래픽과 긴 핸드오버 지연시간에 의해 영향을 받게 되고, 이로 인하여 유지하고 있는 연결들이 깨어질 수도 있다. 또, 전체적인 시스템 성능은 Mobile Anchor Point(MAP)의 선택 방법과 부하 상태에 따라 큰 영향을 받는다. 따라서 본 논문에서는 부하를 MAP들에 분산하면서 도메인간의 핸드오버를 감소시킬 수 있는 동적인 MAP 선택 알고리즘을 제안한다. 제안한 알고리즘의 성능 분석을 위하여 신호 전달 비용에 대한 분석적 모델을 수립하고 시뮬레이션을 수행하였다. 수치결과와 시뮬레이션 결과를 통하여 제안한 알고리즘이 IETF HMIPv6에 기반을 둔 기존의 방법에 비해 부하를 더 균형 있게 분산시키고, 도메인 간 핸드오버의 횟수와 평균 신호 전달 비용을 감소시킨다는 것을 확인할 수 있었다.

• 전자공학회논문지S
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• 제35S권1호
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• pp.1-13
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• 1998

The next generation of wireless network will be problably developed as a mobile communications which will support ATM-based multiMedium traffic. We need to develop an dffective MAC protocol in order to support multimedia traffic having variety of QoS characteristics on wireless neteworks. In this paper, we propose a MAC protocol a MAC protocol where mobile terminals having cells to transmit, request slots to base station through requested slot then the base station analyze parameters from mobile and allocate slots to mobile according to priority. The multimedia slot allocation(MSA) protocol divides multimedias applications into real-time/ variant and non real-time services. Entire slots of the frameare partitioned proportionallyby sizeof bandwidth according to types of services, so that related services can use allocated-slots in priority. The proposed algorithm guarantees real time operation since real-time service share slots allocated for non real-real services. The algorithm whih divides slots of the frame is called as an Algorithm A, otherwise as an Algorithm B. The simulation compares by average delay time and cell loss probability between Algorithm and Algorithm B by increasing number of mobile terminal using the proposed MAC protocol. the simulation result for real-time services shows that average delay time and cell loss probability of Algorithm A is better than those of Algorithm B.