• Journal of Korea Multimedia Society
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• v.16 no.7
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• pp.862-869
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• 2013

In order to support a cell-independent traffic asymmetry, the conventional TDD system cannot avoid crossed time slot (CTS) interference. Moreover, the TDD/FDD hierarchical overlay cellular systems is taken into account as a generally accepted cell model in a heterogeneous radio environment. In this paper, we propose an interference resolving radio resource allocation technique in a TDD-OFDMA cellular system that overlays a FDD-CDMA cell. In our proposed scheme, we exploit under-used FDD-CDMA uplink resource by TDD mobile abiding by a region based time slot(TS) allocation which in turn mitigates CTS interference considerably. It is demonstrated that combined with under-used resource utilization scheme based on mobile's location, the proposed technique can reduce CTS interference considerably and support the asymmetric traffic in TDD system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.11
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• pp.67-72
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• 2004

In this paper, we propose a downlink beamforming method which is considered common pilot channel for coherent detection and dedicated traffic channel for desired user in FDD/CDMA systems. The existing downlink beamforming system produces phase mismatch between traffic and pilot signals at desired mobile as well as interference to other mobiles. A new downlink beamforming method can solve above problem based on least squares method between reference function and beamforming function. A numerical analysis shows that the proposed downlink beamforming method matches well and gives low BER performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.32-36
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• 2008

In this paper, we investigate the capacity of CDMA/TDD in the inner zone of multimode scenario with dual-band operation where high frequency band is used for TDD in the inner zone and lower frequency band is utilized for FDD in the outer zone. The effects of various system parameters such as cell radius, date rate, and time slot allocation are analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.358-365
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• 2007

In this paper, the effects of transmit beamforming on downlink performance in DS-CDMA communication systems are investigated. The uplink and downlink in FDD systems use different carrier frequencies. If the downlink uses the same weighting vectors as the uplink, the antenna beam for downlink is formed with certain DOA shift and it thus affects the beamforming gain. So, the impacts of different frequencies on the downlink beam patterns are studied. One possible algorithm to convert uplink beamforming weights to downlink, which is called frequency-calibrated processing, is also evaluated to reduce the degradation of downlink performance due to different frequencies. Under frequency selective channels, the downlink chooses a PUPW beamforming scheme when the uplink employs a PPPW vectors. To form a beam pattern for a PUPW after combining the downlink PPPWs converted from the uplink PPPWs, three approaches are studied. One method is to consider only one dominant path and thus obtain a single main-beam. In the others, multiple-beams weighted with the magnitudes of all paths and equally weighted with all paths are constructed.

• The Magazine of the IEIE
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• v.29 no.4
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• pp.77-91
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• 2002

스마트 안테나 기술은 CDMA 이동통신 시스템에서 다른 사용자 간섭신호 및 무선 채널 특성에 의한 성능 열하 현상에 대해 효과적으로 성능 및 채널 용량을 개선할 수 있는 대표적인 해결 방법으로 알려지고 있다. 본 논문에서는 이러한 스마트 안테나 기술의 개요 및 국내외 기술동향에 대하여 기술하고, 단말기의 mobility를 고려한 스마트 안테나 채널 모델을 제안하였으며, W-CDMA FDD 상향 링크에서 칩 레벨 빔 형성 알고리즘을 적용한 스마트 안테나 기술의 성능을 분석하였다. 시뮬레이션 결과를 통하여 스마트 안테나 기술을 적용한 경우, 채널 용량이 증가함을 알 수 있으며, 특히 DD(Decision-Directed)모드의 칩 레벨 빔 형성 알고리즘을 적용했을 경우에 성능이 더욱 향상됨을 알 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.603-610
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• 2005

Beam-forming method based on the estimated channel information at the base station degrade the performance mismatching directional vector in case of systems which Frequency Division Duplex (FDD) center frequency of uplink and downlink are different. Also blind estimation technique which is to obtain directional vector of reverse link through received signal has disadvantage of hardware complexity increase. To solve these problems, in present paper, a smart antenna algorithm which is to improve the beam-forming complexity increase due to user number by appling the spatial fourier transform to be able to beam- forming toward a wanted direction through adjusting a obtained uplink weight function by estimating Angle-of-Arrival (AoA) to the competable form at the downlink is proposed. The proposed algorithm is integrated to the CDMA downlink transmitter and simulations are performed to confirm the performance as frame error rate at the receiver. As a result, the beam forming effect is confirmed and the performance gain with the proposed algorithm is comparable to ordinary smart antenna system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1648-1655
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• 2001

TD-CDMA is based on a combination of CDMA, TDMA, and TDD technologies, and it is proposed to support TDD mode for IMT-2000 service. To analyze the performance of TD-CDMA, we have to establish a modeling technique that takes into account the interference that can occur in each scheme. There is special interference in TDD mode, e.g. interference from base station to base station and from mobile to mobile. In this paper, we present an interference model for analyzing the performance of TD-CDMA systems and the slot allocation strategies. This model includes the cell synchronization error. As a result, this paper shows that almost equal slot allocation and low cell synchronization error guarantee desirable performance in TD-CDMA.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.57-61
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• 2006

As high speed internet users are tremendously increasing, three are keenly in need of development of high speed portable internet technology which can provide high quality wireless internet service cheaply even in the mobile. Unlike the FDD-CDMA, TDD-OFDMA has relatively poor wave environment with inducing interference, fading and delay because it agrees to multi-carrier modulation method and time-division radio telecommunication system. To solve this problem, it is necessary to develop repeater operating by digital signal processing method which have more strict wireless channel control and wave signal processing technology over TDD telecommunication equipments. This thesis is dealing with design and implementation of Digital RF Repeater which implemented 'Synchronization Acquisition Unit', 'TDD signal switching Unit', 'Feedback Signal Cancellation Unit'. Over this argument, we will develop digital RF repeater with more cheap, more adaptive in wave environment like oscillation control, adaptive wave monitoring and output increasing and having control function as a result it will be helpful for success in high speed portable internet service business.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.21-30
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• 2004

The capacity of WCDMA TDD system is limited mainly by the interference. So, to achieve the expected performance of WCDMA TDD system and to minimize the interference to cdma2000 system interferences, such as interference within WCDMA TDD system inter-cell interference, and interferences between cdma2000 systems, should be considered carefully. In this paper, by using System-level Simulation, we analyzed the interferences between WCDMA TDD system and cdma2000 system in practical situation based on the exact parameters of 3GPP TR 25.942 and by using System-level Simulation considering Link-level we analyze the interferences between WCDMA TDD system and cdam2000 system. From Simulation Results, we propose the condition for optimizing system capacity considering the interferences between WCDMA TDD system ＆ cdam2000 system

• The KIPS Transactions:PartC
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• v.14C no.6
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• pp.493-502
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• 2007

In this paper, we propose a handoff-aware DiffServ scheduler which intends to guarantee various QoS requirements of multimedia services for mobile nodes in TDD/CDMA based wireless networks. TDD is widely used duplexing mechanism in wireless communications. Unlike FDD, TDD allows a node to symmetrically communicate with a base station by using a single frequency band, resulting in high utilization of wireless resources. DiffServ is regarded as a relatively simple QoS support mechanism and thus it is easy to be extended. This is because DiffServ is not a per-flow based mechanisms and it does not require any signaling protocol. However, previously proposed DiffServ schedulers for wired networks can not be deployed directly into wireless networks since they do not consider properties of wireless networks. As a solution to the problem, DSS(DiffServ Supporting Scheduler) was proposed. DSS uses uplink channel, which is originally used for a node to require a base station to transmit packets, to support QoS efficiently. However, QoS does not consider handoff so that it can not support QoS for moving nodes from one cell to the other cell. Therefor. the proposed handoff support QoS mechanism is necessary for TCC/CDMA networks. The proposed scheme allows a mobile node to achieve seamless service without QoS degradation even for the handoff duration.