10,828 research outputs found
Generic Reduced-Complexity MMSE Channel Estimation for OFDM and MC-CDMA
No full textThe performance of a decision-directed channel estimation scheme is analyzed in the context of both OFDM and MC-CDMA systems. A difficulty associated with the employment of the Least Squares (LS) approach to the problem of a posteriori channel estimation in the context of a MC-CDMA system is described and a suitable MMSE-based estimator is proposed instead. It is demonstrated that the computational complexity associated with the MMSE estimation method proposed is relatively high in comparison to that of the conventional LS technique. Thus a low-complexity version of the MMSE estimator is proposed. The MC-CDMA system using a low-complexity MMSE estimator proposed is shown to outperform the corresponding OFDM-based scheme
Generic MMSE Decision Directed Channel Estimation for OFDM and MC-CDMA
No full textIn this letter we propose a Minimum Mean Square Error (MMSE) Channel Impulse Response (CIR) estimator-aided Decision Directed Channel Estimation (DDCE) method, which is suitable for employment in both OFDM and MC-CDMA systems. Firstly, we outline the difficulty associated with the employment of the Least Squares (LS) approach to the problem of a posteriori Frequency Domain Channel Transfer Function (FDCTF) estimation in the context of a MC-CDMA system and derive a suitable MMSE-based CIR estimator, which circumvents the LS method’s deficiencies. Secondly, we demonstrate that the computational complexity associated with the conventional MMSE estimation method is relatively high compared to that of the LS method. Thus a reduced-complexity version of the MMSE estimator is proposed, which has a complexity similar to that exhibited by the LS-aided estimator. The MC-CDMA system using the reduced-complexity MMSE estimator proposed is shown to outperform the corresponding OFDM-based scheme
Reduced-complexity timing detectors for MC-CDMA signals
No full textIn this paper, two reduced-complexity timing detectors for MC-CDMA signals based on incorporating the on-time arm in timing error signal update are proposed and analyzed. By theoretical analysis and simulations, it is shown that the simplified approaches provide superior performance for low E h/N0 with respect to the classical non-coherent early-late gate detector. ? 2006 IEEE.EI
Functional outcome of patients with brain tumor after comprehensive rehabilitation – a comparison with stroke patients.
No full text
Real-time control performance of a model-reference adaptive structural control system under earthquake excitation
No full text[[abstract]]Recent publications have presented Successful implementations of adaptive control techniques in various applications whereas its application on vibration suppression of civil infrastructures under adverse conditions is not well developed. The advantage of a model-reference adaptive structural control (MRASC) algorithm is to adjust the control command signal and to force the controlled system follow the trajectory of designed reference model while estimating properties of the controlled structure in real time. An adaptive control application based on Lyapunov stability theory is presented in this paper. The Lyapunov equation used to define the adaptation law is designed based oil a quadratic Lyapunov function candidate. This energy-like scalar function comprises weighted tracking-error states and parameter estimating error matrix. The adaptive feedback control force is calculated from both measured states and adjustable parameters estimated from the adaptation law. The tracking-error states illustrate the trajectory tracking performance between reference model and controlled system. The global asymptotical stability is guaranteed by choosing a pair of positive-definite weighting matrices for the time-invariant linear system. Systematic procedures based on fast convergence rate of the adjustable parameters are proposed to determine appropriate combination of coefficients embedded in the weighing matrices of Lyapunov function. A series of control performance investigation is performed on a single degree-of-freedom active tendon structure Subjected to different earthquake excitations. Copyright (C) 2008 John Wiley & Sons, Ltd.[[note]]SC
A Spreading Sequence Allocation Optimal to Mitigate MAI for MC-CDMA Communication System
No full textMC-CDMA系統在經過傳輸通道後，由於通道的影響，失去正交性，使得不同使用者間彼此產生干擾，稱之為MAI(Multiple Access Interferences)。本篇論文主要是藉由MAI功率的數學式，了解通訊碼選取對MAI功率的影響，再經由反覆過濾影響MAI功率的因素，找出最佳的通訊碼以降低MAI的干擾。Because of the channel effect, the MC-CDMA signals will lose orthogonality and result in the Multiple Access Interference (MAI). This thesis will derive the MAI formula to get the correlation between the spreading sequence and MAI. According to this correlation, we can find the optimal spreading sequence sets to mitigate MAI.目錄
誌謝.....................................................ii
中文摘要................................................iii
英文摘要.................................................iv
圖目錄.................................................viii
表目錄...................................................xi
第一章 緒論..........................................1
1.1 研究背景與動機...................................1
1.2 文獻回顧.........................................1
1.3 論文章節介紹.....................................2
第二章 OFDM系統的原理與架構..........................3
2.1 OFDM的特性.......................................3
2.1.1 正交性......................................4
2.2 傳統OFDM系統的架構..............................6
2.3 離散傅立葉OFDM系統的架構........................8
2.4 OFDM系統的傳輸與接收.............................9
2.5 保護區間與循環字首..............................10
2.6 OFDM的優缺點....................................12
第三章 結合OFDM與CDMA之系統........................14
3.1 Walsh Code......................................14
3.2 MC/DS-CDMA......................................15
3.3 MT-CDMA.........................................17
3.4 MC-CDMA.........................................18
3.5 系統比較........................................23
3.6 無線通道模型....................................24
3.6.1 小尺度衰落.................................25
3.6.2 Rayleigh分布...............................28
3.6.3 Rician分布.................................28
3.6.4 頻率選擇性衰落通道模型.....................29
第四章 MC-CDMA降低MAI之通訊碼選取最佳化............30
4.1 MC-CDMA系統描述.................................30
4.2 MAI數學式.......................................31
4.3 MAI 功率........................................33
4.4 通訊碼選取最佳化................................34
4.4.1 文獻方法...................................35
4.4.2 本論文提出之改善方法.......................36
第五章 模擬架構.....................................40
5.1 領航訊號........................................40
5.2 通道估測........................................42
5.3 組合法..........................................44
5.3.1 MRC........................................45
5.3.2 EGC........................................45
5.3.3 ORC........................................46
5.3.4 MMSEC......................................47
5.3.5 組合法整理.................................48
5.4 COST 259 通道模型...............................49
第六章 模擬結果與討論...............................54
6.1 文獻方法與改善方法效能比較.......................54
6.2 最佳化通訊碼相對於組合法.........................55
6.3 最佳化通訊碼相對於使用者人數......................58
第七章 結論.........................................66
參考文獻.................................................6
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