Multiuser Detection in Space-Time Coded MIMO/ SDMA Systems

论文题目: Multiuser Detection in Space-Time Coded MIMO/ SDMA Systems

论文类型: 硕士论文

论文专业: 射频通信

作者: 喻斌

文献来源: University of Southampton

发表年度: 2005

论文摘要: Recently, Multiple-Input Multiple-Output (MIMO) assisted Space-Division Multiple-Access(SDMA) systems (MIMO/SDMA) have drawn wide research interests, in order for meetingthe demands of high spectral efficiency and for providing high speed wireless transmissionservices. In this thesis, the performance of MIMO/SDMA systems using Space-Time BlockCoding (STBC) is investigated, when the MIMO/SDMA signals are transmitted over Rayleighfading channels. In the considered MIMO/SDMA systems, each mobile user employs two orfour transmit antennas and transmits symbols with the aid of their corresponding Space-TimeBlock Codes (STBCs), while the base-station (BS) receiver is equipped with multiple antennasfor achieving the objectives of spatial diversity, multipath fading mitigation, and/or supportingmultiple-access communications. For the purpose of efficiently suppressing the multiple accessinterference (MAI), which may result in severe near-far problem in multiple-access systems in-cluding the considered MIMO/SDMA, in this thesis the received MIMO/SDMA signals at theBS are detected with the aid of various multiuser detectors (MUDs) associated with advancedspace-time processing algorithms.In the context of the detection in the considered MIMO/SDMA systems, in this thesis a rangeof sub-optimal MUDs are investigated, since the sub-optimum MUDs have relatively lowercomplexity in comparison to the optimal MUD, which is originally derived for code-divisionmultiple-access (CDMA) systems based on the maximum likelihood principles. Specifically,both linear MUDs and decision-feedback MUDs (DFD) are considered. The linear MUDsinclude the linear decorrelating MUD and the linear minimum-mean squared-error (MMSE)MUD. By contrast, the DFDs considered include the decorrelating DFD, MMSE-DFD, modi-fied versions of decorrelating DFD as well as multistage DFD. Furthermore, the direct matrixinversion (DMI) MMSE MUD is proposed for the case, where the a-priori channel knowledgeis unavailable at the receiver.In this thesis, a range of adaptive MUDs are also investigated with emphasis on the adaptiveMMSE-assisted MUDs. This is because the MMSE-assisted MUD facilitates the implementa-tion using adaptive techniques. Specifically, we first consider the adaptive MMSE MUDs basedon gradient techniques. Then, three types of reduced-rank MMSE MUDs are investigated in con-junction with the MIMO/SDMA systems for the purpose of achieving low detection complexity.From our study and results, it can be shown that the reduced-rank MMSE MUDs constitute arange of low-complexity MUDs with high-efficiency in comparison with the full-rank MMSEMUDs.In this thesis, a range of simulation results are provided in order to characterise the perfor-mance of the MIMO/SDMA systems, which may employ various detection schemes. Our studyand simulation results show that the considered sub-optimal MUDs conventionally employed inCDMA systems are near-far resistant and potentially capable of achieving significant improve-ment of BER performance over the correlation-based single-user detector in the MIMO/SDMAsystems. The considered MUDs are capable of facilitating joint space-time processing and re-ceiver diversity combining, while simultaneously suppressing the multiuser interfering signals.In the context of the adaptive MUDs, our simulation results demonstrate that the adaptive MUDassisted by the steepest-descent algorithm is capable of approaching to the ideal MMSE solution.When the BS has no a-priori knowledge about the communication channels, the MIMO/SDMAsystems can achieve satisfactory BER performance by employing the DMI-assisted MMSEMUD or the adaptive MMSE MUDs based on the LMS family of algorithms. Our results showthat the adaptive MMSE MUD based on sliding-window LMS outperforms the adaptive MMSEMUD that is based on the conventional LMS algorithm, at the expense of an increase in com-putational complexity. Furthermore, our simulation results demonstrate that, in time-varyingMIMO channels, there exists an optimal window-length in DMI-based MMSE MUD, whichresults in that the corresponding DMI-based MMSE MUD achieves the best BER performance.This observation is very different from that observed in conventional CDMA systems, where theperformance of the DMI-based MMSE MUD becomes better when increasing the length of thesliding-window. Finally, our study and results show that the MIMO/SDMA systems utilising thereduced-rank MMSE detection can be capable of achieving a satisfactory trade-off between theaffordable detection complexity and the attained BER performance.

论文目录:

Abstract

Acknowledgements

List of Figures

1 Introduction

1.1 MIMO System

1.2 Spatial diversity of MIMO systems

1.2.1 Why using Transmit Diversity

1.2.2 Space-Time Block Coding

1.3 SDMA System

1.4 Multiuser Detection

1.5 Outline of this thesis

1.6 conclusion

2 Fundamental Techniques and System Model of the STBC assisted MIMO/SDMA Systems

2.1 Representation of MIMO Model

2.2 Signal Model of MIMO Systems using Space-Time Block Coding

2.2.1 Two-Branch Transmit Diversity

2.2.2 Four-Branch Transmit Diversity

2.3 System Model of STBC assisted MIMO

2.4 Performance Analysis of the MIMO

2.4.1 Common assumptions for performance simulations in this thesis

2.4.2 Simulation results of different spatial diversity schemes

2.5 Conclusion

3 Classical Linear Multiuser Detection in the STBC assisted MIMO/SDMA systems

3.1 Correlation Detection

3.2 Decorrelating Multiuser Detection

3.3 Full-Rank MMSE Multiuser Detection

3.4 Simulation Results and Performance Analysis

3.5 Conclusion

4 Decision Feedback Multiuser Detection in the STBC assisted MIMO/SDMA sys-tems

4.1 Decorrelating Decision-Feedback Multiuser Detection

4.2 MMSE Decision-Feedback Multiuser Detection

4.3 Modified Decorrelating Decision-Feedback Multiuser Detection

4.4 Multi-stage Decision-Feedback Multiuser Detection

4.5 Simulation Results and Discussion

4.6 Conclusion

5 Adaptive Multiuser detection in the STBC assisted MIMO/SDMA Systems

5.1 Direct Matrix Inversion MMSE Multiuser Detection

5.2 Adaptive MMSE MUD based on the Steepest Descent Algorithm

5.3 Adaptive MMSE MUD based on the Least-Mean-Square Algorithm

5.4 Adaptive MMSE MUD based on the SW-LMS Algorithm

5.5 Adaptive MMSE MUD based on the NLMS Algorithm

5.6 Simulation Results and Discussion

5.7 Conclusion

6 Reduced-Rank MMSE Multiuser Detection in the STBC assisted MIMO/SDMA Systems

6.1 Representation of the reduced-rank MMSE detection

6.2 Principal Components based rank reduction algorithm

6.3 Cross-Spectral Metric based rank reduction algorithm

6.4 Taylor Polynomial Approximation based rank reduction algorithm

6.5 Simulation results and performance analysis

6.6 Conclusion

7 Conclusions and future work

7.1 Conclusions

7.2 Future work

Bibliography

发布时间: 2007-01-26

参考文献

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