• Title/Summary/Keyword: Adaptive MIMO-OFDM

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A Study on the Adaptive Hybrid MIMO Scheme for MIMO-OFDM Systems (MIMO-OFDM 시스템에서의 적응적 하이브리드 MIMO 기법에 관한 연구)

  • Yu, Seung-Jun;You, Young-Hwan;Song, Hyoung-Kyu
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • 2013.06a
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    • pp.217-218
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    • 2013
  • 본 논문에서는 기존의 하이브리드 MIMO 기법들이 정수 배의 멀티플렉싱 이득만 달성할 수 있는 단점을 해결하기 위해서 임의의 멀티플렉싱 이득을 달성할 수 있는 하이브리드 MIMO 기법을 제안한다. 제안된 기법은 다양한 멀티플렉싱 이득을 달성하기 위해서 전송 matrix 의 구성을 기존의 MIMO 기법들과 다르게 구성함으로써 멀티플렉싱 이득의 조절이 가능하다.

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Performance Analysis of MIMO-OFDM Systems using Adaptive Bitloading Algorithm (적응비트로딩 알고리즘을 이용한 MIMO-OFDM시스템의 성능평가)

  • Jung, Dae-Hun;Byon, Kun-Sik
    • Proceedings of the Korea Institute of Convergence Signal Processing
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    • 2005.11a
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    • pp.331-334
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    • 2005
  • 현재 무선 이동통신의 발달로 고속 신뢰성 높은 데이터 전송을 요구하고 있다. 그러나 무선 이동통신 환경은 데이터 전송 시 지연과 간섭 등에 의해 주파수 선택성 페이딩을 가진다. OFDM은 주파수 선택성 페이딩에 영향을 받는 통신 시스템에서 채용되는 강력한 기술이다. OFDM에 적응 변조와 함께 송수신기에 다중의 안테나를 설치함으로서 채널 지연 확산에 강력히 대응한다. 본 논문의 연구는 MIMO 시스템에 적용된 적응 변조를 가진 OFDM이다. OFDM 각 서브채널의 상태에 따라 최적의 비트값을 할당하고 전력을 제어한다. 본 논문에서 제안한 적응비트로딩 MIMO-OFDM 시스템을 사용하면 현재의 시스템보다 더 좋은 BER을 가지며 고속 통신할 수 있다.

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Computationally Efficient Lattice Reduction Aided Detection for MIMO-OFDM Systems under Correlated Fading Channels

  • Liu, Wei;Choi, Kwonhue;Liu, Huaping
    • ETRI Journal
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    • v.34 no.4
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    • pp.503-510
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    • 2012
  • We analyze the relationship between channel coherence bandwidth and two complexity-reduced lattice reduction aided detection (LRAD) algorithms for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in correlated fading channels. In both the adaptive LR algorithm and the fixed interval LR algorithm, we exploit the inherent feature of unimodular transformation matrix P that remains the same for the adjacent highly correlated subcarriers. Complexity simulations demonstrate that the adaptive LR algorithm could eliminate up to approximately 90 percent of the multiplications and 95 percent of the divisions of the brute-force LR algorithm with large coherence bandwidth. The results also show that the adaptive algorithm with both optimum and globally suboptimum initial interval settings could significantly reduce the LR complexity, compared with the brute-force LR and fixed interval LR algorithms, while maintaining the system performance.

On the improved MIMO-OFDM system for the wireless environments (무선 환경에서 OFDM 성능향상을 위한 MIMO System)

  • 박창현;권혁일;양윤기
    • Proceedings of the IEEK Conference
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    • 2003.07a
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    • pp.481-484
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    • 2003
  • OFDM(Orthogonall Frequency Division Multiplexing) is an efficient transmission techniques for the frequency selective fading wireless channel where conventional modulations suffer from severe performance degradation. Recently, more efficient techniques for the OFDM are paid much attention such as adaptive modulation for each subcarrier, since more bit rate has been required for the wireless data network [1-3]. The proposed system employs the adaptive modulation between transmitter and receiver in each subcarrier, where the bit and power is properly allocated. Also multiple antenna system called MIMO is considered, which result in robustness in channel delay, improved power efficiency and improved bit SNR for the given BER.

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Symbol Based Rate Adaptation in Coded MIMO-OFDM Systems (심볼 기반의 적응 변조 기법을 이용한 채널 부호화된 MIMO-OFDM 시스템)

  • Sung, Chang-Kyung;Kim, Ji-Hoon;Lee, In-Kyu
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.1A
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    • pp.50-58
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    • 2008
  • The use of space-division multiple access(SDMA) in the downlink of multiuser multi-input/multi-output(MIMO) wireless transmission systems can provide substantial gains in system throughput. When the channel state information(CSI) is available at the transmitter, a considerable performance improvement can be attained by adapting the transmission rates to the reported CSI. In addition, to combat frequency selective fadings in wideband wireless channels, bit-interleaved coded OFDM(BIC-OFDM) modulation schemes are employed to provide reliable packet delivery by utilizing frequency diversity through channel coding. In this paper, we propose an adaptive modulation and coding(AMC) scheme combined with an opportunistic scheduling technique for the MIMO BIC-OFDM with bandwidth-limited feedback channels. The proposed scheme enhances the link performance by exploiting both the frequency diversity and the multiuser diversity. To reduce the feedback information, the proposed AMC scheme employs rate adaptation methods based on an OFDM symbol rather than on the whole subchannels. Simulation results show that the proposed scheme exhibits a substantial performance gain with a reasonable complexity over single antenna systems.

Channel Estimation Based on LMS Algorithm for MIMO-OFDM System (MIMO-OFDM을 위한 LMS 알고리즘 기반의 채널추정)

  • Hwang, Suk-Seung
    • The Journal of the Korea institute of electronic communication sciences
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    • v.7 no.6
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    • pp.1455-1461
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    • 2012
  • MIMO-OFDM which is one of core techniques for the high-speed mobile communication system requires the efficient channel estimation method with low estimation error and computational complexity, for accurately receiving data. In this paper, we propose a channel estimation algorithm with low channel estimation error comparing with LS which is primarily employed to the MIMO-OFDM system, and with low computational complexity comparing with MMSE. The proposed algorithm estimates channel vectors based on the LMS adaptive algorithm in the time domain, and the estimated channel vector is sent to the detector after FFT. We also suggest a preamble architecture for the proposed MIMO-OFDM channel estimation algorithm. The computer simulation example is provided to illustrate the performance of the proposed algorithm.

Enhanced Bit-Loading Techniques for Adaptive MIMO Bit-Interleaved Coded OFDM Systems (적응 다중 안테나 Bit-Interleaved Coded OFDM 시스템을 위한 향상된 Bit-Loading 기법)

  • Cho, Jung-Ho;Sung, Chang-Kyung;Moon, Sung-Hyun;Lee, In-Kyu
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.46 no.2
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    • pp.18-26
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    • 2009
  • When channel state information (CSI) is available at the transmitter, the system throughput can be enhanced by adaptive transmissions and opportunistic multiuser scheduling. In this paper, we consider multiple-input multiple-output (MIMO) systems employing bit-interleaved coded orthogonal frequency division multiplexing (BIC-OFDM). We first propose a bit-loading algorithm based on the Levin-Campello algorithm for the BIC-OFDM. Then we will apply this algorithm to the MIMO system with a finite set of constellations, by reassigning residual power on each stream Simulation results show that proposed bit-loading scheme which takes the residual power into account improves the system performance especially at high signal-to-noise ratio (SNR) range.

Adaptive Group Loading and Weighted Loading for MIMO OFDM Systems

  • Shrestha, Robin;Kim, Jae-Moung
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.5 no.11
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    • pp.1959-1975
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    • 2011
  • Adaptive Bit Loading (ABL) in Multiple-Input Multiple-Output Orthogonal Frequency-Division Multiplexing (MIMO-OFDM) is often used to achieve the desired Bit Error Rate (BER) performance in wireless systems. In this paper, we discuss some of the bit loading algorithms, compare them in terms of the BER performance, and present an effective and concise Adaptive Grouped Loading (AGL) algorithm. Furthermore, we propose a "weight factor" for loading algorithm to converge rapidly to the final solution for various data rate with variable Signal to Noise Ratio (SNR) gaps. In particular, we consider the bit loading in near optimal Singular Value Decomposition (SVD) based MIMO-OFDM system. While using SVD based system, the system requires perfect Channel State Information (CSI) of channel transfer function at the transmitter. This scenario of SVD based system is taken as an ideal case for the comparison of loading algorithms and to show the actual enhancement achievable by our AGL algorithm. Irrespective of the CSI requirement imposed by the mode of the system itself, ABL demands high level of feedback. Grouped Loading (GL) would reduce the feedback requirement depending upon the group size. However, this also leads to considerable degradation in BER performance. In our AGL algorithm, groups are formed with a number of consecutive sub-channels belonging to the same transmit antenna, with individual gains satisfying predefined criteria. Simulation results show that the proposed "weight factor" leads a loading algorithm to rapid convergence for various data rates with variable SNR gap values and AGL requires much lesser CSI compared to GL for the same BER performance.

A Simple AMC Technique using ARQ for a MIMO-OFDM System based on IEEE 802.11a WLANs (IEEE 802.11a WLAN 기반 MIMO-OFDM 시스템에서 ARQ를 이용한 간단한 적응변조 기법)

  • 유승연;김경연;이충용;홍대식;박현철
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.7
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    • pp.1-8
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    • 2004
  • A simple AMC (Adaptive Modulation and Coding) technique using ARQ (Automatic Repeat Request) for a MIMO (Multiple Input Multiple Output) system is proposed which does not require the additional feedback. In addition, the proposed AMC technique is different from the conventional technique in the aspect of considering the MCS (Modulation and Coding Scheme) level from the previous packet. The proposed technique can discard fewer amounts of unsuitable packets than the conventional technique. In the proposed system not only same rate control method for transmit antennas but also individual rate control method can be applied. The performance of the proposed technique is verified under a MIMO-OFDM (Orthogonal Frequency Division Multiplexing) system based on WLAN (Wireless Local Area Network), IEEE 802.11a. The results of the computer simulation show that a MIMO system with the proposed technique achieves higher throughput than one with a fixed transmission rate.

Turbo MIMO-OFDM Receiver in Time-Varying Channels

  • Chang, Yu-Kuan;Ueng, Fang-Biau;Jhang, Yi-Wei
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.12 no.8
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    • pp.3704-3724
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    • 2018
  • This paper proposes an advanced turbo receiver with joint inter-carrier interference (ICI) self cancellation and channel equalization for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over rapidly time-varying channel environment. The ICI caused by impairment of local oscillators and carrier frequency offset (CFO) is the major problem for MIMO-OFDM communication systems. The existing schemes (conjugate cancellation (CC) and phase rotated conjugate cancellation (PRCC)) that deal with the ICI cancellation and channel equalization can't provide satisfactory performance over time-varying channels. In term of error rate performance and low computational complexity, ICI self cancellation is the best choice. So, this paper proposes a turbo receiver to deal with the problem of joint ICI self cancellation and channel equalization. We employ the adaptive phase rotations in the receiver to effectively track the CFO variations without feeding back the CFO estimate to the transmitter as required in traditional existing scheme. We also give some simulations to verify the proposed scheme. The proposed schene outperforms the existing schemes.