• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.733-742
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• 2008

In 3GPP LTE downlink system, initial cell search is essential for mobile station to connect to base station. In order to obtain information of the base station, the mobile station detects frame timing, frequency offset, and cell identification using primary synchronization channel(PSC) and secondary synchronization channel(SSC), which are defined in downlink OFDMA specification. In this paper, we analyze various detection algorithms in practical environment of inter-cell-interference, frequency offset, and multi-path fading channel and propose the optimal algorithm. Simulation results show that partial correlation method (for PSC acquisition) and interference cancellation method (for SSC detection) are the most superior algorithms among the applicable algorithms. Employ these two algorithms for receiver design, initial cell search is performed with 99% probability within 70ms in the channel environment considered.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.205-214
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• 2011

In 3rd generation project partnership long term evolution, wireless multicast techniques which send the same data to multiple users under single frequency networks have attracted much attention. In the multicast system, the transmission mode needs to be selected for efficient data transfer while satisfying the multicast coverage requirement. To achieve this, users' channel state information (CSI) should be available at the transmitter. However, it requires too much uplink feedback resource if all the users are allowed to transmit their CSI at all the time. To solve this problem, in this paper, the multicast coverage prediction is suggested. In the proposed algorithm, each user measures its transition probabilities between the success and the fail state of the decoding. Then, it periodically transmits its CSI to the basestation. Using these feedbacks, the basestation can predict the multicast coverage. From the simulation results, we demonstrate that the proposed scheme can predict the multicast system coverage.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.3
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• pp.28-35
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• 2011

Cooperative ARQ scheme is effective for better QoS guarantee for the next generation mobile communication systems where multimedia data transmission highly increases. In this paper, we propose a cooperative ARQ strategy in ad hoc cognitive relays for mobile multimedia communication for supporting instantaneous cooperation in MANET environment. In the proposed strategy, to support real time, delay-sensitive services, whenever a frame is transmitted from the source, each relay actively senses the SINR of the signal transmitted from the source, and determine whether to propose retransmission or not before the destination transmits feedback signal. To minimize the false retransmission decision or needless retransmission, we propose an adaptive sensing threshold optimization algorithm to maintain suboptimal sensing thresholds for each relay. By computer simulation, it is shown that the proposed cooperative ARQ retransmission scheme outperforms the conventional schemes with respect to frame transmission delay and frame loss probability in real time multimedia data transmission system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1479-1495
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• 2012

Spectrum scarcity seems to be the most challenging issue to be solved in new wireless telecommunication services. It is shown that spectrum unavailability is mainly due to spectrum inefficient utilization and inappropriate physical layer execution rather than spectrum shortage. Daily increasing demand for new wireless services with higher data rate and QoS level makes the upgrade of the physical layer modulation techniques inevitable. Orthogonal Frequency Division Multiple Access (OFDMA) which utilizes multicarrier modulation to provide higher data rates with the capability of flexible resource allocation, although has widely been used in current wireless systems and standards, seems not to be the best candidate for cognitive radio systems. Filter Bank based Multi-Carrier (FBMC) is an evolutionary scheme with some advantages over the widely-used OFDM multicarrier technique. In this paper, we focus on the total throughput improvement of a cognitive radio network using FBMC modulation. Along with this modulation scheme, we propose a novel uplink radio resource allocation algorithm in which fairness issue is also considered. Moreover, the average throughput of the proposed FBMC based cognitive radio is compared to a conventional OFDM system in order to illustrate the efficiency of using FBMC in future cognitive radio systems. Simulation results show that in comparison with the state of the art two algorithms (namely, Shaat and Wang) our proposed algorithm achieves higher throughputs and a better fairness for cognitive radio applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.1
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• pp.64-77
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• 2013

In this paper, we propose a joint bandwidth allocation and path selection scheme for IEEE 802.16j networks in uplink with cooperative relaying, and we evaluate the performance of the proposed scheme by using OPNET based simulation in hilly terrain with heavy tree density. The proposed scheme maximizes the system throughput in uplink with cooperative relaying in IEEE 802.16j networks. Then, we transform the proposed scheme into multi-dimensional multiple choice knapsack problem (MMKP) based scheme. We also propose uplink throughput maximization scheme and MMKP based scheme without cooperative relaying. We show that the system throughput of the proposed MMKP based scheme is higher than that of link quality based scheme, and cooperative relaying provides higher system throughput than the conventional case without cooperative relaying in uplink.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3C
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• pp.302-313
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• 2010

In this paper, we propose an enhanced AGC (Automatic Gain Control) structure and P-SCH detection method for initial cell search in 3GPP (3rdGenerationPartnershipProject) LTE (Long Term Evolution) FDD(Frequency Division Duplex) / TDD (Time Division Duplex) dual mode system. Since TDD frame structure consists of uplink subframe and downlink subframe, conventional AGC structure causes P-SCH detection performance degradation by increase of AGC variation due to signal power difference between uplink and downlink subframe. Also, P-SCH detection performance is degraded by distortion of P-SCH correlation characteristic in frequency offset and multipath fading channel environments. Therefore, we propose an AGC structure which can minimize P-SCH detection performance degradation with stable operation in 3GPP LTE TDD mode as well as FDD mode. Also we propose a P-SCH detection method which can reduce distortion of correlation chareteristics in frequency offset and multipath fading environments and obtain good P-SCH detection performance. Simulation results show that the proposed AGC structure and P-SCH detection method have stable AGC operation and excellent P-SCH detection performance for 3GPP LTE TDD / FDD dual mode downlink receiver in various channel environments.