• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.519-536
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• 2007

In this paper, we combine the Hybrid-Automatic Repeat reQuest (HARQ) algorithm with joint Tx and Rx antenna selection based on the reliability of the individual antennas links. The cyclic redundancy check (CRC) is applied on the data before being encoded using the Turbo encoder. In the receiver the CRC is used to detect errors of each antenna stream and to decide whether a retransmission is required or not. The receiver feeds back the transmitter with the Tx antennas ordering and the acknowledgement of each antenna (ACK or NACK). If the number of ACK antennas is higher than the NACK antennas, then the retransmission takes place from the ACK antennas using the Chase Combining (CC). If the number of the NACK antennas is higher than the ACK antennas then the ACK antennas are used to retransmit the data streams using the CC algorithm and additional NACK antennas are used to retransmit the remaining streams using Incremental Redundancy (IR, i.e. the encoder rate is reduced). Furthermore, the HARQ is used with the I-BLAST (Iterative-BLAST) which grantees a high transmission rate.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.4
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• pp.729-736
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• 2018

Due to the frequency offset, interchannel interference (ICI) is occurred in the received symbols of the orthogonal frequency division multiplexing (OFDM) systems. The ICI self-cancellation (ICI-SC) technique appropriately adjusts the subchannel signal assignment of the OFDM symbols, thereby canceling the interference caused by other subchannels. The conventional adjacent symbol repetition (ASR) method can reduce the interference caused by remote subchannels. However, it may not mitigate or even increases the ICI produced by some nearest subchannels. To solve the problem, a new ASR based ICI-SC technique is proposed and its performance is analyzed in this paper. Here, a t-parameter obtained by the interference coefficients of 3 successive subchannels is applied. As a result, the proposed method has the same capability to reduce the influence of remote subchannels. However, it can reduce the ICI caused by the nearest subchannels significantly.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.523-523
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• 2006

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.23-23
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• 2004

• 한국ITS학회:학술대회논문집
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• 2004.11a
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• pp.252-256
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• 2004

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.9-12
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• 2002

In this paper, we analyze high-rate wireless LAN system based on Orthogonal Frequency Division Multiplexing(OFBM) transmission method. For this analysis, actual channcl measurement model of indoor office areas such as JTC model was adopted, and cllanncl coding of IEEE 502.11 and channel equalizer over multipath environment are also considered.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.2
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• pp.288-307
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• 2013

This paper formulates resource allocation for decode-and-forward (DF) relay assisted multi-cell orthogonal frequency division multiple (OFDM) networks as an optimization problem taking into account of inter-cell interference and users fairness. To maximize the transmit rate of system we propose a joint interference coordination, subcarrier and power allocation algorithm. To reduce the complexity, this semi-distributed algorithm divides the primal optimization into three sub-optimization problems, which transforms the mixed binary nonlinear programming problem (BNLP) into standard convex optimization problems. The first layer optimization problem is used to get the optimal subcarrier distribution index. The second is to solve the problem that how to allocate power optimally in a certain subcarrier distribution order. Based on the concept of equivalent channel gain (ECG) we transform the max-min function into standard closed expression. Subsequently, with the aid of dual decomposition, water-filling theorem and iterative power allocation algorithm the optimal solution of the original problem can be got with acceptable complexity. The third sub-problem considers dynamic co-channel interference caused by adjacent cells and redistributes resources to achieve the goal of maximizing system throughput. Finally, simulation results are provided to corroborate the proposed algorithm.

• ETRI Journal
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• v.34 no.1
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• pp.9-16
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• 2012

Precoding in the multiple-input multiple-output orthogonal frequency division multiplexing system is investigated. In conventional wideband precoding (WBP), only one precoder, obtained from the decomposition of the subcarrier independent channel matrix, is used for all subcarriers. With an investigation of the relationship between the subcarrier independent channel matrix and the temporal/frequency channels, an improved WBP scheme is proposed for practical scenarios in which a part of subcarriers are allocated to a user. The improved WBP scheme is a generalized scheme of which narrow-band precoding and conventional WBP schemes are special modes. Simulation results demonstrate that the improved WBP scheme almost achieves the optimum performance of a single precoder and outperforms the conventional WBP scheme in terms of the bit error ratio and ergodic capacity with slight complexity increase. The largest advantage of the improved WBP scheme on signal-to-noise ratio in simulation results is over 2.1 dB.

• Journal of the Korea Society of Computer and Information
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• v.16 no.10
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• pp.137-145
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• 2011

In this paper, we modeled digital M/W transmission channel by frequency non-selective fading channel and analyzed the power spectrum magnitude of digital M/W transmission systems adopting OFDM modulation scheme through simulation. From the simulation results, it was found that deep does not appear in the specified fixed bandwidth under the AWGN environment. Also, lower power spectrum magnitude was shown in frequency non-selective fading channel than that in AWGN channel. Futhermore, the power spectrum magnitude value became more lowered when carrier frequency and vehicle speed became higher.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.5
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• pp.1286-1302
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• 2012

In this paper, the resource allocation problem with proportional fairness rate in cognitive OFDM-based wireless network is studied. It aims to maximize the total system throughput subject to constraints that include total transmit power for secondary users, maximum tolerable interferences of primary users, bit error rate, and proportional fairness rate among secondary users. It is a nonlinear optimization problem, for which obtaining the optimal solution is known to be NP-hard. An efficient bio-inspired suboptimal algorithm called immune clonal optimization is proposed to solve the resource allocation problem in two steps. That is, subcarriers are firstly allocated to secondary users assuming equal power assignment and then the power allocation is performed with an improved immune clonal algorithm. Suitable immune operators such as matrix encoding and adaptive mutation are designed for resource allocation problem. Simulation results show that the proposed algorithm achieves near-optimal throughput and more satisfying proportional fairness rate among secondary users with lower computational complexity.