• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.3
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• pp.167-167
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• 2004

The system combined layered space-time processing and space-time trellis codes (STTC) provide high transmission rate as well as diversity and coding gain without bandwidth expansion. In this paper, two layered receiver structures are proposed. One is the LSTT-MMSE in which received bit streams are decoupled by interference nulling and then decoded by separate STTC decoders. The decoded outputs are cancelled from the received signal before advancing to the next layer detection. The other is LSTT-Whitening employing whitening rather than nulling. The receiver employing whitening process shows several advantages on diversity gain and the required number of receive antennas compare to the convolutional coded space-time processing. The proposed receivers use different decoding order scheme according to each interference suwression. The (4, 3) LSTT-Whitening receiver still achieves 1㏈ gain over the (4, 4) LSTT-MMSE and the (4, 4) coded layered space-time processing.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.3
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• pp.9-14
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• 2004

The system combined layered space-time processing and space-time trellis codes (STTC) provide high transmission rate as well as diversity and coding gain without bandwidth expansion. In this paper, two layered receiver structures are proposed. One is the LSTT-MMSE in which received bit streams are decoupled by interference nulling and then decoded by separate STTC decoders. The decoded outputs are cancelled from the received signal before advancing to the next layer detection. The other is LSTT-Whitening employing whitening rather than nulling. The receiver employing whitening process shows several advantages on diversity gain and the required number of receive antennas compare to the convolutional coded space-time processing. The proposed receivers use different decoding order scheme according to each interference suwression. The (4, 3) LSTT-Whitening receiver still achieves 1㏈ gain over the (4, 4) LSTT-MMSE and the (4, 4) coded layered space-time processing.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.3
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• pp.41-50
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• 2010

In this paper, an area-efficient symbol detector is proposed for MIMO communication systems with two transmit and two receive antennas. The proposed symbol detector can support both the spatial multiplexing mode and spatial diversity mode for MIMO transmission technique, and shows the optimal maximum likelihood (ML) performance. Also, by sharing the hardware block with multi-stage pipeline structure and using the complex multiplier based on polar-coordinate，the complexity of the proposed architecture is dramatically decreased. The proposed symbol detector was designed in hardware description language (HDL) and implemented with Xilinx Virtex-5 FPGA. With the proposed architecture, the number of logic slices for the proposed symbol detection is 52490 and the number of DSP48s (dedicated multiplier) is 52, which are reduced by 35.3% and 85.3%, respectively, compared with the conventional architecture.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.25-33
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• 2012

Random beamforming (RBF) uses the signal to interference plus noise ratio (SINR) feedback to select users in multiple-input multiple-output (MIMO) systems. A large number of users are required to obtain the gain of multi-user diversity for a downlink transmission. However, if the number is not large enough, it may be difficult to obtain multi-user diversity, leading to a rapid degradation in performance. To resolve this problem, we propose the beamforming matrix transformation and the user scheduling method. The beamforming matrix transformation scheme uses the SINRs of each users and have a better performance than conventional schemes over a small number of users. In addition, we propose the user scheduling scheme corresponding to the beamforming matrix transformation. In simulation results, we demonstrate that the sum-rate can be improved according to the number of users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.1889-1899
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• 2015

In this paper, we propose a multiple slot reservation scheme to transmit data rapidly in the satellite random access channel. In the R-CRDSA (Reservation scheme with Contention Resolution Diversity Slotted ALOHA), each satellite terminal can use only one slot in a frame. Therefore, many slots are wasting in the low traffic load and the satellite terminals which have large date needs many frame to transmit their data although there are unused slots. In the multiple slot reservation scheme, each satellite terminal transmits a packet with their data size and reserves many slots in the light of data size and slot reservation status. Therefore, each satellite terminal transmits their data faster than R-CRDSA. This is because they can reserve many slots in a frame. Furthermore, we simulate proposed scheme and validate the performance of proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.191-197
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• 2008

For the efficient transmission of burst data in the time varying wireless channel, opportunistic scheduling is one of the important techniques to maximize multiuser diversity gain. In this paper, we propose a distributed opportunistic scheduling scheme for wireless LAN network. A proportional fair scheduling, which is one of the opportunistic scheduling schemes, is used for centralized networks, whereas we design distributed proportional fair scheduling (DPFS) scheme and medium access control with distributed manner. In the proposed DPFS scheme, each receiver estimates channel condition and calculates independently its own priority with probabilistic manner, which can reduce excessive probing overhead required to gather the channel conditions of all receivers. We evaluate the proposed DPFS using extensive simulation and simulation results show that DPFS obtains higher network throughput than conventional scheduling schemes and has a flexibility to control the fairness and throughput by controlling the system parameter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.3
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• pp.291-297
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• 2014

Due to the rapid increase in demand for transportation of human and freight in modern railway systems, the CBTC system has been proposed, which is the solution for improvement of the line capacity that has been limited by the conventional track circuit based train control system. In the CBTC system, higher reliability of the communication system should be guaranteed for the safety of passengers and trains. However, due to the inherent characteristics of the wireless channel environment, performance degradations are inevitable. The diversity techniques can increase the reliability of data transmission using multiple antennas. In this paper, we investigate the performance of the STBC in the railway channel environment. Rician fading model is used for the viaduct scenarios which take important roles in the railway system. Also, considered is the Doppler effect which is an important factor in the mobile communication system. Simulations are performed to analyze the performance of the STBC in various channel environments. Results show that the performance degradation due to the phase error in viaduct scenarios is independent of the diversity order but is affected by the constellation of the modulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.25-32
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• 2007

This paper proposes a distributed space-frequency block code (SFBC) for relay-assisted single carrier frequency-domain equalization (SC-FDE). The proposed technique achieves spatial diversity gain over fast fading channels without the complexity of multiple antennas. The mobile equipment of the proposed system has a very simple transmitter structure with constant amplitude transmit sequences, which is desirable especially for uplink communications. In order to obtain spatial diversity, the transmit sequence of relay is efficiently generated in the time domain, which is equivalent to the SFBC. Further, efficient implementation of relay and destination structures is also presented. Extensive simulation results show that the proposed system significantly outperforms the distributed space-time block code (D-STBC) SC-FDE over fast fading channels.

• 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 Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.51-56
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• 2007

Unitary matrix modulation (UMM) is investigated in multiple antennas system that is called unitary space-time modulation (USTM). When we consider only diagonal components of UMM with splitting over the coherence bandwidth, the system can obtain frequency diversity in a single antenna system. In Rayleigh fading channel, we compared USTM/OFDM with 2Tx-antenna with UMM-S/OFDM with 1Tx-antenna, conventional multi-level OFDM and UMM-S/OFDM with changing bit rate per Hz. Also, we analyzed SNR for between multi-level modulation STBC/OFDM and multi-level modulation UMM-S/OFDM with changing transmission rate. When it was adaptive multi-level modulation to improve SNR, we did the UMM-S/OFDM system performance analysis of N-ary PSK and M-ary QAM.