7,037 research outputs found
Performance Enhancements for Multiuser Detection for MC-CDMA
No full text在這篇論文中，我們首先提出適用於多載波分碼多工（multi-carrier code division multiple access, MC-CDMA）系統中多用戶偵測（multiuser detection, MUD）之相對門檻削樹（relative threshold tree pruning, RTTP）演算法. 相對門檻削樹較傳統的M-演算法（M-algorithm）俱淘選力和效率，並能在高訊雜比下達到較低的錯誤率。針對二維矩形傳輸符號，我們提出用戶分離（user partitioning, UP）來和好的用戶排序（user order sorting, UOS）結合以產生沒有用戶分離時無法達到的細緻的用戶順序。這當中，我們提出的DLUPS和DLUP-RMOPS適用於下傳通道及實數展頻碼，而UP-RMOPS則適用於所有的環境，其中RMOPS是一個前人提出的優良的用戶排序演算法，它也可以是任何其他有效的用戶排序。此外，在下傳系統中當各用戶都使用一維傳輸符號時，我們提出了一個簡單的下傳相位旋轉（downlink phase rotation, DLPHR），可以把任何實數展頻碼轉換成複數展頻碼以大幅降低多用戶干擾（multiple access interference, MAI）。下傳相位旋轉可視為一種在同樣有限的資源下增加傳輸維度的方法。
當正交分頻多工（orthogonal frequency division multiplexing, OFDM）系統因為載波頻率誤差而存在載波相互干擾（inter-carrier interference, ICI）時，所有我們提出的演算法都依然適用。模擬結果顯示這些演算法能獲致較低的錯誤率，也因此降低了多用戶偵測的複雜度。In this thesis, we rst proposed the relative threshold tree pruning (RTTP) al-
gorithm suitable for pre-whitening tree pruning (PWTP) multiuser detection
(MUD) for multi-carrier code-division multiple access (MC-CDMA). RTTP
is more e cient and selective than the conventional M-algorithm and achieves
relatively lower error rate at high signal-to-noise ratio (SNR). For rectangular
2-D symbols, user partitioning (UP) is proposed and, when combined with
good user order sorting (UOS) produces a softer UOS not obtainable with-
out UP. The proposed DLUPS and DLUP-RMOPS are applicable with the
downlink channel and real-valued spreading code, while the proposed UP-
RMOPS is suitable in the general cases; ROMPS is a previously proposed
UOS that can be replaced by any other good UOS. A simple downlink phase
rotation (DLPHR) is proposed to convert any real-valued spreading code
into complex-valued and to signi cantly reduce multiple access interference
(MAI) when 1-D symbols are used with downlink channel. DLPHR can be
viewed as an increase of transmit diversity with the same limited resource.
All proposed algorithms apply in the presence of carrier frequency o set
which causes inter-carrier interference (ICI) of orthogonal frequency division
multiplexing (OFDM). Simulation results show that the proposed algorithms
indeed achieve lower error rate and thus enable low complexity MUD ap-
proaching optimal performance.1 Introduction 1
2 Signal Model of MC-CDMA Systems 3
2.1 Signal Model of OFDM System . . . . . . . . . . . . . . . . . 3
2.2 Block Diagram and Signal Model of MC-CDMA . . . . . . . . 8
2.2.1 Viewpoint of Single User . . . . . . . . . . . . . . . . . 8
2.2.2 Uplink Quasi-Synchronous (ULQS) MC-CDMA . . . . 9
2.2.3 Downlink Synchronous (DL) MC-CDMA . . . . . . . . 10
3 Pre-Whitening Tree Pruning Multiuser Detection with User
Order Sorting and Real Field Operation 13
3.1 Pre-Whitening Tree Pruning Multiuser Detection . . . . . . . 13
3.2 Performance Enhancement By User Order Sorting (UOS) . . . 18
3.2.1 Reverse Minimum Orthogonal Power Sorting . . . . . . 19
3.3 Real Field Operation . . . . . . . . . . . . . . . . . . . . . . . 20
4 Threshold-Based Tree Pruning 25
4.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 Absolute Threshold Tree Pruning (ATTP) . . . . . . . . . . . 26
4.3 Relative Threshold Tree Pruning (RTTP) . . . . . . . . . . . 33
5 Achieving Transmit Diversity For 1-Dimensional Constella-
tion in Downlink Channel 41
5.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.2 Downlink Phase Rotation (DLPHR) . . . . . . . . . . . . . . . 42
5.3 Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.4 Optimal Rotation in Special Case . . . . . . . . . . . . . . . . 45
5.5 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
6 User Partitioning 55
6.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.2 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.3 User Partitioning with Reverse Minimum Orthogonal Power
Sorting (UP-RMOPS) . . . . . . . . . . . . . . . . . . . . . . 59
6.4 Downlink User Partitioning Sorting (DLUPS) . . . . . . . . . 62
6.5 Downlink User Partitioning With Reverse Minimum Orthog-
onal Power Sorting (DLUP-RMOPS) . . . . . . . . . . . . . . 71
7 Simulation Results 75
7.1 Signal Model and Parameters . . . . . . . . . . . . . . . . . . 75
7.2 Threshold-Base Tree Pruning . . . . . . . . . . . . . . . . . . 76
7.2.1 Absolute Threshold Tree Pruning (ATTP) . . . . . . . 76
7.2.2 Relative Threshold Tree Pruning (RTTP) . . . . . . . 80
7.3 Downlink Phase Rotation (DLPHR) . . . . . . . . . . . . . . . 85
7.4 User Partition (UP) . . . . . . . . . . . . . . . . . . . . . . . . 88
7.4.1 User Partition with Reverse Minimum Orthogonal Power
Sorting (UP-RMOPS) . . . . . . . . . . . . . . . . . . 88
7.4.2 Downlink User Partition Sorting (DLUPS) and Down-
link User Partition With Reverse Minimum Orthogo-
nal Power Sorting (DLUP-RMOPS) . . . . . . . . . . . 91
7.5 Joint Frequency O set Compensation and Multiuser Detection 95
8 Conclusions and Future Works 101
8.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
8.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Adaptive resource allocation for downlink grouped MC-CDMA systems with power and BER constraints
No full text[[abstract]]This paper proposes a complete solution to adaptively allocate resource for downlink Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with the power and bit error rate (BER) constraints. Under frequency-selective fading channels, the whole spectrum is divided into several groups and each user is allocated to a group based on its channel state information (CSI). After grouping, the adaptive modulation algorithm assigns the bit loading and allocates the transmission power for each user according to its effective channel response. Simulation results show that the proposed solution can achieve high throughput, guarantee the required BER, and reduce the blocking probability. (C) 2013 Elsevier GmbH. All rights reserved.[[note]]SC
Multirate Multiband Hybrid MC/MC-DS CDMA for Ultra Wideband Transmission
No full text最新的無線個人區域網路標準802.15 3a採用超寬頻技術來傳輸多媒體資訊。因應其高且多重速率的要求，促使我們考量如何在已開放的頻寬中作規劃。而多頻帶傳輸被視為可降低硬體複雜度的方法之一，並它同時充釵U種多重存取系統架構於其夠寬的子頻帶中。在本文中，我們建構一種混合多載波/多載波-直序展頻之分碼多工系統於每一子頻帶中，此系統除了利用時域展頻之外也用了頻域展頻。至於多速率傳輸則使用已知的多碼存取和可變展碼長度存取技術來達成。此外我們提出去相關和干擾消除多戶偵測接收機用以克服高速傳輸使用者所遭受到來自等效用戶的多重存取干擾。而這兩種接收機又分別可用結合時頻域和分離時頻域之方法來實現。從模擬結果得知，當我們在增加時域或頻域展碼時，建議使用多碼存取技術配合結合時頻域去相關接收機。若因考量硬體複雜度而採用分離時頻率接收機，則使用可變展碼長度存取技術將是較佳的方法。Ultra wideband (UWB) transmission is adopted in the specific of 802.15 3a for wireless personal area network (WPAN) and applied to multimedia communications. The requirement of high and multiple data rates motivates us to consider how to plan the feasible transceiver structure on available ultra wide bandwidth. Multiband trans-mission technology, which divides the available bandwidth into several conjunctional subbands and transmits information through one subband at one time, is presented here to simplify the hardware complexity and still offer enough wide subbands for multiple access schemes. The novel hybrid MC/MC-DS CDMA structure, which exploits joint time and frequency domain spreading, is constructed in each subband. In another de-signed consideration of multirate communication, we choose the known multirate ac-cess schemes – multicode access and variable spreading length access. Furthermore, we propose two kinds of multiuser detection receivers, to decorrelate and cancel MAI from the effective users of a high rate user due to multipath channel. Two possible imple-mentations, joint and separate TF-domain, are considered for each kind of proposed re-ceivers. From the simulation, we recommend adopting MCD access scheme using joint TF-domain decorrelating receiver whether increasing spreading code assignment on T-domain or F-domain and using joint TF-domain interference cancellation receiver to avoid arithmetic computations of crosscorrelation matrix of TF-domain spreading codes. Considering the issue of the complexity, which means to use separate TF-domain re-ceiver, we prefer adopting VSL access scheme whether increasing spreading code as-signment on T-domain or F-domain.Chapter 1 Introduction 1
Chapter 2 Background 3
2.1 Ultra Wideband Channel Description 3
2.2 UWB TH-PPM Impulse Radio 5
2.3 Multiband Transmission 6
2.3.1 Benefits 6
2.3.2 Design Considerations 7
2.4 Subband Multirate Multiple Access Schemes 8
2.4.1 Multirate DS CDMA 8
2.4.2 Multirate MC CDMA 10
2.4.3 Multirate MC DS CDMA 13
Chapter 3 Multirate Multiband Hybrid MC/MC DS CDMA 17
3.1 Multiband Hybrid MC/MC DS CDMA 17
3.2 Slowly Fading Frequency Selective Channel Model 19
3.3 Multirate Schemes 19
3.3.1 Multicode Access 20
3.3.2 Variable Spreading Length Access 22
3.4 Proposed High Rate Decorrelating Receiver Structures 24
3.4.1 Joint TF-Domain Decorrelating Receiver 25
3.4.2 Separate TF-Domain Decorrelating Receiver 27
3.4.3 Issue of Complexity 31
3.4.4 Performance Results 31
3.5 Proposed High Rate Interference Cancellation Structures 35
3.5.1 Joint TF-Domain Interference Cancellation Receiver 36
3.5.2 Separate TF-Domain Interference Cancellation Receiver 37
3.5.3 Issue of Complexity 39
3.5.4 Performance Results 39
Chapter 4 Overall System Simulations 45
4.1 Different Ratio of Multiband to Users 45
4.1.1 Decorrelating Receiver 46
4.1.2 Interference Cancellation Receiver 49
4.1.3 Tradeoff 51
4.2 Multiple TF-Domain code assignments 55
4.2.1 Decorrelating Receiver 55
4.2.2 Interference Cancellation Receiver 58
4.2.3 Tradeoff 61
Chapter 5 Conclusion and Future Works 65
Bibliography 6
Interactively using Semantic Web knowledge: Creating scalable abstractions with FacetOntology
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Growth Morphologies and Mechanisms of Non-Equilibrium Solidified MC Carbide
No full textGrowth morphologies and mechanisms of the carbide of group IVB and VB elements (MC carbide), a typical faceted crystal, were studied with an estimated cooling rate from 102 to 105 K/s. Results showed that although the growth morphologies of the MC carbide vary remarkably with solidification cooling rate, the solid/liquid interface is always atomically smooth, and the growth mechanisms are always lateral growth. The growth mechanism transition from lateral to continuous growth mode, which was predicted by the classic crystal growth theory, was not observed for the TiC type MC carbide within the estimated cooling rate range of 102?105 K/s
On symmetric matrices with exactly one positive eigenvalue
Full text linkWe present a class of nonsingular matrices, the MC′-matrices, and prove that the class of symmetric MC-matrices introduced by Shen, Huang and Jing [On inclusion and exclusion intervals for the real eigenvalues of real matrices. SIAM J. Matrix Anal. Appl., 31:816-830, 2009] and the class of symmetric MC′-matrices are both subsets of the class of symmetric matrices with exactly one positive eigenvalue. Some other sufficient conditions for a symmetric matrix to have exactly one positive eigenvalue are derived
Ruth Klüger: la creatività per non “smarrirsi strada facendo”
No full textR. Klüger, a jewish viennese, a US citizen and a germanist, is the Author of two autobiographies “weiter leben”and “unterwegs versore”. Written in a style which alternates between essay and poetry, account and recollection, they are the occasion for the Author to establish a dialogue with the women having as a focus the exchange of experiences and reflections over the status of the feminine emancipation
Hemophilia B with mutations at glycine-48 of factor IX exhibited delayed activation by the factor VIIa-tissue factor com
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