• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.362-362
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• 2004

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.1076-1081
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• 2007

In this paper, we propose a new switch structure for time division duplex(TDD) system. The existing TDD structure utilizes a circulator fur isolation characteristic between ports. However, the circulator produces intermodulation distortion signals which are undesired signal because of its nonlinear properties. The proposed circuit is composed of a modified branch-line hybrid coupler which controls the signal flow while the isolated port is open-/short- terminated. In order to prove the validity of the presented structure, the switch circuit is fabricated and measured at 2.3GHz, the center frequency of Wibro service system.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2001.10a
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• pp.119-123
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• 2001

The CDMA system with time division duplex mode (CDMA/TDD system) is a highly attractive solution to support the next generation cellular mobile systems providing multimedia services where the traffic unbalance between downlink and uplink exists. In this paper, the capacity of the CDMA/TDD system is analyzed in general multicell environments. For this analysis, the interference for a time slot is analyzed, and a time slot and channel allocation problem is mathematically formulated and solved using simulated annealing technique. Computational experiments provide a promising result.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.113-122
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• 2010

In this paper, we propose a CP (Cyclic Prefix) detection based SSS (Secondary Synchronization Signal) detection method for initial cell search in 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) FDD/TDD (Frequency Division Duplex/Time Division Duplex) dual mode downlink receiver. In general, a blind coherent SSS detection method which can detect SSS without CP detection is applied. However, coherent detection method caused performance degradation by channel compensation error at high speed environment because it uses estimated CFR (Channel Frequency Response) at PSS (Primary Synchronization Signal), and it can be more serious problem in TDD mode due to increased distance between PSS and SSS. Also blind detectionhas the drawback of high computational complexity. Therefore, we proposed a CP type pre-decision structure with non-coherent SSS detection which has stable operation in high speed channel environments for 3GPP LTE TDD mode as well as FDD mode, and can reduce computational complexity by applying CP detection before SSS detection. Simulation results show that the proposed method has stable operation for 3GPP LTE TDD/FDD dual mode downlink receiver in various channel environments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.410-414
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• 2006

In the present, Orthogonal Frequency Division Multiple Access (OFDMA) that wireless access scheme for high speed data transmission is noticed in mobile communication market and OFDMA/TDD scheme will be used combining Time Division Duplex (TDD) scheme based on OFDMA. The Base Station's receiver synchronizes the symbol timing to anyone user's symbol and the other user's symbols have some Symbol Timing Offset (STO). Linear phase shift is occurred by each user's STO in an OFDMA symbol and the Multiple Access Interference (MAI) caused by the summation of each user's linear phase shift degrades the performance of ranging code detection. In this paper, we analyze the ranging code detection performance for each users STO in OFDMA/TDD system. Simulation results show that the more users access and mobile speed increase, the more ranging code detection performance degrades.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11A
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• pp.1076-1084
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• 2006

In this paper, we first review a concept of hybrid division duplexing (HDD) scheme, which has been proposed as a new type of duplexing scheme useful for a next generation mobile communication system and its implementation issues, including the unified radio resource management for HDD scheme. The HDD scheme maintains the advantages of both TDD and FDD at the same time while providing a useful structure to control the inter-cell interference, caused by an asymmetric traffic load of multimedia services over uplink and downlink in the TDD scheme. Employing two frequency bands, one for TDD scheme and the other for FDD scheme, uplink is operating under the TDD scheme only, while downlink is operating under the TDD or FDD scheme, depending on the location of mobile station. In the HDD scheme, therefore, it must determine a type of duplexing scheme to employ in the downlink and futhermore, a ratio of uplink and downlink duration to meet a given traffic load of asymmetric service, which requires some unified radio resource management for handling the subsequent inter-cell interference. In this paper, we propose a distributed adaptive control approach as a means of unified radio resource management for a HDD system that maximizes the overall system efficiency by fully utilizing the resource in TDD band, while minimizing the inter-cell interference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.7
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• pp.1244-1255
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• 1994

The wireless-LAN(Local Area Network), which is emerged as a solution to cable problem and increasing requirement for communication network, has a several problem when it transmit information MAN protocol by used wired-LAN`s MAC protocol. Media Access protocol in Wireless-LAN has great effect on system performance and much studies are processing now. The PRMA(Packet Reservation Multiple Aeecss) of reservation method has a disadvantage that the system performance was degraded become of delay time in the reservation step as a resulting of collision. In this paper, using the TDD(Time Division Duplex) method amd modified PRMA method wireless-LAN modelled to overcome disadvantage, that id delay time due to collision in reservation step. The performance evaluation fo the model was done using M/M/1//M process model and this was simulation using SLAM.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.118-126
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• 2008

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.125-133
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• 2007

In this paper, the frequency sharing issue between cellular time division duplex-orthogonal frequency division multiple access (TDD-OFDMA) Systems and terrestrial Fixed Systems has been studied. The conventional advanced minimum coupling loss (A-MCL) includes only the formulation to calculate the interference from one interfering system. Therefore, A-MCL must be modified to assess the aggregated interference from base stations(BS) and mobile stations(MS). By applying the modified model, the coexistence analysis are done according to the average number of MS per sector, BS-to-BS distance, and the main beam direction of the terrestrial fixed system. In the case of 20 MS per sector, the BS-to-BS distance and the minimum distance between a terrestrial fixed system and BS are 5.8 km and 2.5 km, respectively. It is about 25dB that the difference between maximum and minimum interference signal power which varies with the main beam direction of the terrestrial fixed system. Moreover, for 40% of the main beam direction of the terrestrial fixed system, interference signal power is less than the maximum permissible interference.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.5 s.108
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• pp.440-450
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• 2006

In this paper, the frequency sharing issue between time division duplex-orthogonal frequency division multiplexing/orthogonal frequency division multiple access(TDD-OFDM/OFDMA) based systems beyond third generation(B3G) and fixed Satellite Service(FSS) earth station has been studied. The conventional advanced minimum coupling loss(A-MCL) is adopted to assess the interference from a single base station(BS) of B3G systems. The aggregated interferences from base stations and mobile stations(MS) are evaluated by applying the extended A-MCL and analysed with a cumulative density function(CDF). The minimum distances that enable a single FSS earth station to sharing the frequency with a single BS are between 4 and 53.3 km. In the case of 20 MS per sector, the BS-to-BS distance and the minimum distance between a ES and BS are 6.5 and 2.8 km, respectively.