• Journal of the Korea Society of Computer and Information
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• v.17 no.7
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• pp.77-86
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• 2012

Using OFDM(Orthogonal Frequency Division Multiplexing) provides the same diversity order as MRRC(Maximal Ratio Receiver Combining). It is assumed that fading channel is constant across two consecutive symbols. Unfortunately, when the channel condition is changed for the two consecutive symbols, the OFDM using STBC(Space Time Block Code) does not offer good performance due to the large doppler shift. In this paper, we have proposed a performance enhancement scheme for OFDM using STBC over time-selective fading channel. Simulation results for various doppler shift rates are presented to robust system performance of OFDM due to using our proposed scheme over time-selective fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.11A
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• pp.1244-1252
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• 2004

In this paper, we derive some properties of linear detectors (zero forcing or minimum mean square error) at spatial multiplexing systems with alamouti's space-time block code. Based on the derived properies, this paper proposes low-complexity receivers. Implementing MMSE detector adaptively, the number of weight vectors to be calculated and updated is greatly reduced with the derived properties compared to the conventional methods. In the case of recursive least square algorithm, with the proposed approach computational complexity is reduced to less than the half. We also identify that sorted QR decomposition detector, which reduces the complexity of V-Blast detector, has the same properties for unitary matrix Q and upper triangular matrix R. A complexity reduction of about 50%, for sorted QR decomposition detector, can be achieved by using those properties without the loss of performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.423-430
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• 2010

The performances of turbo-coded space-time block coding (STBC) schemes are subject to how soft decision detection (SDD) information are generated from the STBC decoder. For this reason, we have to pay particular attention to estimation of SDD. In this paper, we evaluate the performance of a turbo coded STBC scheme depending on the accuracy of the SDD. Recently, a new quasi orthogonal STBC (QO-STBC) scheme using a noise whitened filter was proposed in order to reduce noise enhancing effect of zero forcing detection process. This QO-STBC scheme was proven to be efficient in computational complexity compared to the other conventional QO-STBC schemes. In this paper, we first present detailed mathematical analysis on the noise whitened QO-STBC scheme, and by using the result we propose the optimum SDD method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.59-69
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• 2007

In this paper, we propose a MIMO-OFDMA (Multi Input Multi Output-Orthogonal Frequency Division Multiple Access) system based on Grassmannian beamforming for performance improvement of downlink real-time traffic transmission in harsh channel conditions with low CIR (Carrier-to-Interference Ratio). In the proposed system to reduce feedback information for the beamforming, we also apply Grassmannian Beamforming. Furthermore, we propose antenna selection scheme which performs the beamforming with more useful transmit antennas. In the proposed system, the optimal combination of transmit antennas with maximum MRT (Maximum Ratio Transmission) beamforming gain, is selected. Simulation results reveal that the proposed MIMO-OFDMA system achieves significant improvement of spectral efficiency in low CIR region as compared to a typical open-loop MIMO-OFDMA system using pseudo-orthogonal space time block code.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.547-554
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• 2010

Recently, the multi-band orthogonal frequency division multiplexing(MB-OFDM) system, one of UWB system, can satisfy the requirement and can be applied to various wireless communication services because ultra-wideband(UWB) is a wireless communication technique that supports high data rate with low power. In this paper, the method applying Alamouti's space time block code(STBC) and cyclic delay diversity(CDD) is proposed. The proposed method can be easily applied with arbitrary number of relays and only needs two time slots of quasi stationary assumption. And it is applied to the MB-OFDM system. Second, an optimal relaying scheme based on decode-and-forward(DF) method is proposed which is provides good error performance compared to conventional schemes.

• The KIPS Transactions:PartC
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• v.13C no.7 s.110
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• pp.865-872
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• 2006

Cooperative communications (CC) have received a great deal of attention recently as an efficient way to obtain the spatial diversity without physical arrays. Thus, space-time block codes (STBC) which are well-known for use in co-located multi-antenna systems can be still utilized for single-antenna users in a distributed fashion. In this paper, we propose a cooperative signaling structure using the $\frac{3}{4}$-rate STBC and derive closed-form BER expression which takes the effect of network geometry and transmit power constraint into account. A variety of simulated and numerical results demonstrated the cooperation considerably outperforms the direct transmission when partners are located in appropriate positions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.1
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• pp.93-113
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• 2020

According to information theory, non-orthogonal transmission can achieve the multiple-user channel capacity with an onion-peeling like successive interference cancellation (SIC) based detection followed by a capacity approaching channel code. However, in multiple antenna system, due to the unideal characteristic of the SIC detector, the residual interference propagated to the next detection stage will significantly degrade the detection performance of spatial data layers. To overcome this problem, we proposed a modified power-domain non-orthogonal multiple access (P-NOMA) scheme joint designed with space-time coding for multiple input multiple output (MIMO) NOMA system. First, with proper power allocation for each user, inter-user signals can be separated from each other for NOMA detection. Second, a well-designed quasi-orthogonal space-time block code (QO-STBC) was employed to facilitate the SIC-based MIMO detection of spatial data layers within each user. Last, we proposed an optimization algorithm to assign channel coding rates to balance the bit error rate (BER) performance of those spatial data layers for each user. Link-level performance simulation results demonstrate that the proposed time-space-power domain joint transmission scheme performs better than the traditional P-NOMA scheme. Furthermore, the proposed algorithm is of low complexity and easy to implement.

• Journal of Navigation and Port Research
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• v.38 no.4
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• pp.349-356
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• 2014

In the underwater communication, the performance of system is reduced because of the inter-symbol interference occur by the multi-path. In the recent years, to deal with poor channel environment and improve the throughput, the efficient concatenated structure of equalization, channel codes and Space Time Codes has been studied as MIMO system in the underwater communication. Space Time Codes include Space Time Block Codes and Space Time Trellis Codes in underwater communication. Space Time Trellis Codes are optimum for equalization and channel codes among the Space Time Codes to apply in the MIMO environment. Therefore, in this paper, turbo pi codes are used for the outer code to efficiently transmit in the multi-path channel environment. The inner codes consist of Space Time Trellis Codes with transmission diversity and coding gain in the MIMO system. And Zero Forcing method is used to remove inter-symbol interference. Finally, the performance of this model is simulated in the underwater channel.

• The Journal of the Korea Contents Association
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• v.5 no.1
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• pp.201-208
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• 2005

Tn this paper, we evaluate the peak-to-average power ratio (PAPR) performance in a space-time block code (STBC) multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system using selected mapping (SLM) and partial transmit sequences (PTS) approaches. SLM and PTS methods are used to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear high power amplifier(HPA) in the MIMO-OFDM system. In simulation result, when compared with the existing MIMO-OFDM system using QPSK, the PTS method reduces the PAPR about 5dB while the SLM method can reduce about 3.5 dB. Also, we find the BER performance of the MIMO-OFDM system with and without the predistorter in front of the HPA. When the predistorter is used, the input back-off (IBO) of 4 dB is required in the PTS method, and IBO of 6 dB in the SLM method to closely conform to the linear amplifier. If the method of improving the PAPR is not used, the value of IBO of 8 dB is required.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.3
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• pp.507-513
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• 2015

In this paper, we present the bit-error rate (BER) performance of quasi-orthogonal space-time block code (QOSTBC) massive multiple-input multiple-output (MIMO) system employing up to 32 transmit and receive antennas. The QOSTBC, due to its advantages in transmission rate and decoding complexity, is an important transmit diversity scheme for more than 2 transmit antennas. As massive MIMO implies very large number of antennas, practically at least more than 15 antennas, a different number of transmit and receive antennas (i.e. $2{\times}2$, $4{\times}4$, $8{\times}8$, $16{\times}16$ and $32{\times}32$) using QOSTBC for the massive MIMO system are considered. The BER performance of the massive MIMO with antennas up to $32{\times}32$ using BPSK modulation scheme is analyzed. Simulation results show that the full-rate massive MIMO systems with QOSTBC give a significant performance improvement due to increasing diversity effect, compared with previously considered massive MIMO systems.