• 인터넷정보학회논문지
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• 제23권3호
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• pp.13-20
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• 2022

차세대 와이파이 표준기술인 IEEE 802.11ay는 밀리미터파 대역에서 AP (Access Point)가 다수의 STA (Station)로 동시에 데이터를 전송하도록 MU-MIMO (Multiple User Multiple Input Multiple Output) 통신을 지원한다. 이를 위해, 주기적으로 MU-MIMO 빔포밍 훈련을 수행해야 하고, 효율적인 빔포밍 훈련을 위해서는 AP가 다수의 안테나로 다수의 빔을 동시에 전송할 때, 각 STA에서 측정되는 신호 세기를 정확히 예측하는 것이 중요하다. 본 논문에서는 딥러닝 기반 다중 빔 전송링크 성능 예측기법을 제안한다. 제안한 예측기법은 특정 실내 또는 실외 환경에서 미리 학습된 딥러닝 모델을 이용하여 다수의 빔이 동시에 전송될 때 STA에서 측정되는 신호 세기 예측의 정확성을 높인다. 이때, 딥러닝의 입력으로 개별 빔이 전송될 때 STA에서 측정되는 신호 세기 정보를 이용하고, 개별 빔의 신호 세기 정보를 얻는 과정은 이미 기존의 빔포밍 훈련에 포함되어 있으므로 정보 수집을 위해 추가적인 비용을 발생하지 않는다. 성능평가를 위해 NIST (National Institute of Standards and Technology)에 의해 개발된 Q-D 채널구현 (Quasi-Deterministic Channel Realization) 오픈소스 소프트웨어를 활용하였고 실측 데이터 기반으로 밀리미터파 채널을 구현하였다. 실험결과에서는 제안한 예측기법이 다른 비교기법보다 향상된 예측성능을 보였다.

• Journal of Communications and Networks
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• 제16권1호
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• pp.18-25
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• 2014

In this paper, we propose a codebook-based interference alignment (IA) scheme in the constant multiple-input multiple-output (MIMO) interference channel especially for the uplink scenario. In our proposed scheme, we assume cooperation among base stations (BSs) through reliable backhaul links so that global channel knowledge is available for all BSs, which enables BS to compute he transmit precoder and inform its quantized index to the associated user via limited rate feedback link. We present an upper bound on the rate loss of the proposed scheme and derive the scaling law of the feedback load to maintain a constant rate loss relative to IA with perfect channel knowledge. Considering the impact of overhead due to training, cooperation, and feedback, we address the effective degrees of freedom (DOF) of the proposed scheme and derive the maximization of the effective DOF. From simulation results, we verify our analysis on the scaling law to preserve the multiplexing gain and confirm that the proposed scheme is more effective than the conventional IA scheme in terms of the effective DOF.

• Journal of Communications and Networks
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• 제11권1호
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• pp.20-25
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• 2009

The maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) has been presented as a suboptimum multiple-input multiple-output (MIMO) detection scheme which can provide almost the same performance as the optimum maximum likelihood (ML) MIMO detection scheme but with the reduced complexity. However, due to the lack of parallelism and the regularity in the decoding structure, the conventional QRM-MLD which uses the tree-structure still has very high complexity for the very large scale integration (VLSI) implementation. In this paper, we modify the tree-structure of conventional QRM-MLD into trellis-structure in order to obtain high operational parallelism and regularity and then apply the Viterbi algorithm to the QRM-MLD to ease the burden of the VLSI implementation.We show from our selected numerical examples that, by using the QRM-MLD with our proposed trellis-structure, we can reduce the complexity significantly compared to the tree-structure based QRM-MLD while the performance degradation of our proposed scheme is negligible.

• 전자공학회논문지
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• 제50권1호
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• pp.21-26
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• 2013

본 논문에서는 그룹(group)을 2개의 심볼(symbol)로 나누는 시스템을 제안하는데, 이 두 개의 더해진 심볼들은 다중화에 의해 분리된 후 역다중화 기술을 이용해 다시 합해진다. 제안된 시스템에서 간단한 PIC(Partial Interference Cancelation) 그룹 복호화 기술은 Double-ABBA(D-ABBA) 유사 직교(Quasi-Orthogonal) 시공간 부호(Space Time Code)를 위해 사용된다. 이 부호는 고차 MIMO(Multiple Input Multiple Output) 시공간 블록 부호화에서 복호화시에 복잡도를 줄여준다. 그리고 기존의 방법과 제안된 방법과의 성능을 비교한다.

• Journal of Communications and Networks
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• 제7권3호
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• pp.307-312
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• 2005

In this work, we study the performance of a serial concatenated scheme comprising a convolutional code (CC) and an orthogonal space-time block code (STBC) separated by an inter-leaver. Specifically, we derive performance bounds for this concatenated scheme, clearly quantify the impact of using a CC in conjunction with a STBC, and compare that to using a STBC code only. Furthermore, we examine the impact of performing antenna selection at the receiver on the diversity order and coding gain of the system. In performing antenna selection, we adopt a selection criterion that is based on maximizing the instantaneous signal-to­noise ratio (SNR) at the receiver. That is, we select a subset of the available receive antennas that maximizes the received SNR. Two channel models are considered in this study: Fast fading and quasi-static fading. For both cases, our analyses show that substantial coding gains can be achieved, which is confirmed through Monte-Carlo simulations. We demonstrate that the spatial diversity is maintained for all cases, whereas the coding gain deteriorates by no more than $10\;log_{10}$ (M / L) dB, all relative to the full complexity multiple-input multiple-output (MIMO) system.

• Journal of information and communication convergence engineering
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• 제18권1호
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• pp.1-7
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• 2020

This paper proposes a fast-processing and low-cost hardware multiple input multiple output (MIMO) channel emulator. The channel emulator is an important component of hardware-based simulation systems. The novelty of this work is the use of sharing and pipelining functions to reduce hardware resource utilization while maintaining a high sample rate. In our proposed emulator, the samples are created sequentially and interpolated to ensure the sample rate is equal to the base band rate. The proposed 4 × 4 MIMO requires low-cost hardware resource so that it can be implemented on a single field-programmable gate array (FPGA) chip. An implementation on Xilinx Virtex-7 VX980T was found to occupy 10.47% of the available configurable slice registers and 12.58% of the FPGA's slice lookup tables. The maximum frequency of the proposed emulator is 758.064 MHz, so up to 560 different paths can be processed simultaneously to generate 560 × 758 million × 2 × 32 bit complex-valued fading samples per second.

• 한국통신학회논문지
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• 제32권10A호
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• pp.958-964
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• 2007

이 논문은 maximum a posteriori (MAP) 비트 검출(bit detection)의 비트 오류 확률 (bit error probability: BEP)과 비트 최소 평균 제곱 오류(bit minimum mean square error: bit MMSE)사이의 관계를 유도한다. BEP는 bit MMSE의 1/4 보다 크고 1/2보다 작음을 유도한다. 이 결론을 이용하면 bit-linear linear-dispersion (BLLD) 부호를 적용한 다중 입출력 (multiple-input multiple-output: MIMO) 통신 시스템에서 가우시안 채널의 mutual information의 미분 값의 하한과 상한을 BEP로부터 얻을 수 있고 나아가서 mutual information의 하한과 상한을 구할 수 있다.

• 한국전자파학회논문지
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• 제24권9호
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• pp.922-927
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• 2013

본 논문에서는 다중 안테나 시스템(Multiple Input Multiple Output: MIMO)를 사용하는 상향 링크 다중 사용자 환경에서 공간 변조(Spatial Modulation: SM) 기법을 사용하고, 변조된 신호를 수신 신호와 모든 송신 신호 후보를 비교하는 최대 우도(Maximum Likelihood: ML) 기법으로 복조하는 방법을 사용하여 시스템의 성능을 평가한다. 같은 데이터 율(date rate)로 전송하였을 때 공간 변조 기법이 기존에 제안된 다중 사용자 환경에서의 공간편이 방식(Space Shift Keying: SSK)보다 비트오류율(Bit Error Rate: BER) 성능이 좋아졌다.

• ETRI Journal
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• 제26권5호
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• pp.375-383
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• 2004

This paper proposes a common interleaving method associated with independent channel-encoding among transmitter antenna branches in orthogonal frequency and code division multiplexing based on multiple-input multiple-output (MIMO) multiplexing to achieve an extremely high throughput such as 1 Gbps using a 100 MHz bandwidth. This paper also investigates the average packet error rate performance as a function of the average received signal energy per bit-to-background noise power spectrum density ratio $(E_b/N_0)$. We found that the loss in the required average received $E_b/N_0$ of the proposed method is only within approximately 0.3 dB in up to a 12-path Rayleigh fading channel, using 16QAM and Turbo coding with a coding rate of 5/6. We also clarify that even for a large fading correlation among antenna branches, 1 Gbps is still possible by increasing the transmission power. Therefore, the proposed method reduces the processing rate to 1/4 in the turbo decoder with only a slight loss in the required average received $E_b/N_0$.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.635-656
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• 2019

In this paper, we investigate the degrees of freedom (DoF) of a multi-cell multi-user multiple-input multiple-output (MIMO) interference broadcast channel (IBC) with non-cooperation distributed base stations (BS), where each BS serves users of its corresponding cell. When all BSs simultaneously transmit their own signals over the same frequency band in the MIMO IBC, the edge users in each cell will suffer the inter-cell interference (ICI) and inter-user interference (IUI) signals. In order to eliminate the ICI and IUI signals, a distributed space time interference alignment (DSTIA) approach is proposed where each BS has only limited access to distributed moderately-delay channel state information at the transmitter (CSIT). It is shown that the DSTIA scheme can obtain the appreciate DoF gains. In addition, the DoF upper bound is asymptotically achievable as the number of antenna at each BS increases. It is shown that the DSTIA method can get DoF gains over other interference alignment schemes with delayed CSIT in literature. Moreover, the DSTIA method can attain higher DoFs than the IA schemes with global CSIT for certain antenna configurations.