• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.2
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• pp.27-34
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• 2013

We propose a simple power allocation scheme for an amplify-and-forward multiple relay system with multiple-input multiple-output antennas. Unlike the existing relay precoding matrix with full elements, proposed precoder is a diagonal matrix whose diagonal element is the relay gain for each stream. Furthermore, a weight vector is applied to streams, such that the mutual information of the system approaches that of the exhaustive search scheme, regardless of the number of antennas. Numerical results show that proposed scheme outperforms the conventional schemes with respect to mutual information.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.632-638
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• 2010

In this paper, we propose a fixed-complexity sphere encoder (FSE) for multi-user MIMO (MU-MIMO) systems. The Proposed FSE accomplishes a scalable tradeoff between performance and complexity. Also, because it has a parallel tree-search structure, the proposed encoder can be easily pipelined, leading to a tremendous reduction in the precoding latency. The complexity of the proposed encoder is also analyzed, and we propose two techniques that reduce it. Simulation and analytical results demonstrate that in a $4\times4$ MU-MIMO system, the complexity of the proposed FSE is 16% that of the conventional QRD-M encoder (QRDM-E). Also, the encoding throughput of the proposed endoder is 7.5 times that of the QRDM-E with tolerable degradation in the BER performance, while achieving the optimum diversity order.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.7
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• pp.431-436
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• 2014

In this paper, we propose a compressive sensing-based channel quantization feedback mechanism that is appropriate for practical massvie multiple-input multiple-output (MIMO) systems. We assume that the base station (BS) has a compact uniform square array that has a highly correlated channel. To serve multiple users, the BS uses a zero-forcing precoder. Our proposed channel feedback algorithm can reduce the feedback overhead as well as a codebook search complexity. Numerical simulations confirm our analytical results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.51-58
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• 2008

We propose a new duplex which does not require guard resources in MIMO environments. In the proposed duplex, two virtual channels in spatial domain are generated by preceding and postcoding MIMO channels, not to use guard resources in either the time or frequency domain. The capacity can be improved by properly selecting precoder and postcoder. We show the improved capacity of the proposed duplex outperforms conventional duplexes even without guard resources.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.10
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• pp.921-928
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• 2012

In this paper, we propose a novel interference alignment transceiver for multi-cell MIMO downlink channels with arbitrary number of cells and users per cell. We design the receive beamformer to align the interference from undesired base stations to the effective inter-cell interference (ICI) channels. Subsequently, we design the transmit precoder which can nulllify the interference from the corresponding base station. The proposed transceiver design can attain the degrees of freedom (DOF) equal to the number of streams per user. Accordingly, we investigate conditions for the antenna configuration. From numerical results, we confirm that the proposed transceiver design can achieve higher DOF than the conventional scheme under equal antenna configuration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10C
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• pp.929-936
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• 2009

In this paper, we consider designing a multi-input multi-output (MIMO) overlay system for fixed MIMO wireless link, where a frequency flat narrowband channel is shared by multiple transmitter and receiver pairs. Assuming the perfect knowledge of the second-order statistics of the received legacy signals and the composite channels from the overlay transmitter to the legacy receivers, the jointly optimal linear precoder and decoder matrices of the MIMO overlay system is derived to minimize the total mean squared error (MSE) of the data symbol vector, subject to total average transmission power and zero interference induced to legacy MIMO systems already existing in the frequency band of interest. Furthermore, the necessary and sufficient condition for the existence of the optimal solution is also derived.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.10
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• pp.879-882
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• 2021

The telemetry standard adopts SOQPSK-TG with excellent power and bandwidth efficiency as a modulation technique, and LDPC code with excellent performance as an error correction code. The SOQPSK-TG transmitter consists of a precoder and a CPM modulator. Rather than implementing each receiver separately, the reception performance is improved by combining the trellis and implementing it as a Viterbi decoder. In this paper, the reception performance of LDPC-encoded SOQPSK-TG was evaluated by replacing the Viterbi decoder with a max-log-map decoder capable of soft metric output. As a result of computer simulation in AWGN channel, there is an Eb/No performance gain of about more than 0.7~0.8dB compared to the conventional method.

• Journal of Broadcast Engineering
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• v.28 no.1
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• pp.141-144
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• 2023

Recently, a joint channel estimation, channel quantization, feedback, and precoding system based on deep-neural network (DNN) was proposed. The corresponding system achieved a joint optimization based on deep learning such that it achieved a higher sum rate than the existing codebook-based precoding systems. However, this DNN-based procoding system is not directly applicable for the environments with many users such that a specific user selection can potentially increase the sum rate of the system. Thus, in this letter, we study an appropriate user selection method suitable for DNN-based precoding.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.3
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• pp.16-21
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• 2010

In this paper, the linear source and relay precoders are designed for AF MIMO relay systems. In order to minimize mean squared error (MSE) of received symbol vector, the source and relay precoders are proposed, and MMSE receiver which is suitable to those precoders is utilized at the destination node. As the optimal precoders for source and relay nodes are not represented in closed form and induced by iterative method, we suggest a simple precoder design scheme. Simulation results show that the performance of the proposed precoding scheme is comparable with that of optimal scheme and outperforms other relay precoding schemes. Moreover, in high SNR region, it is revealed that SNR between source and relay node is more influential than SNR between relay and destination node in terms of bit error rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.3
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• pp.1098-1112
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• 2018

Achievable sum rate and energy efficiency (EE) are investigated for the massive multiple-input multiple-output (Massive MIMO) downlink with channel aging in the time varying Ricean fading channel. Specifically, the expression of the achievable sum rate of the system for the maximum ratio transmission (MRT) precoder with aged channel state information (CSI) in the time varying Ricean fading channel is first presented. Based on the expression, the effect of both channel aging and the Ricean factor on the power scaling law are studied. It is found that the transmit power of base station (BS) is scaled down by $1/{\sqrt{M}}$(where M is the number of the BS antennas) when the Ricean factor K is equal to zero (i.e., time varying Rayleigh fading channel), indicating that aged CSI does not affect the power scaling law. However, the transmit power of the BS is scaled down by 1/M for the time varying Ricean fading channel (where $K{\neq}0$) indicating that the Ricean factor affects the power scaling law and sum rate, and channel aging only leads to a reduction of the sum rate. Second, the EE of the system is analyzed based on the general power consumption model. Both the theoretical analysis and the simulations show that the channel aging could degrade the sum rate and the EE of the system, and it does not affect the power scaling law.