Aufwandsgünstige Realisierung von hochperformanten OFDM-Systemen mit partieller Kanalkenntnis. Interzellinterferenzreduktion mit reduzierter Kanalkenntnis
Zusammenfassung der Projektergebnisse
Future mobile radio wireless comniunication systems aim to provide high quality of service (QoS) with high spectrum efliciency. The remarkable capacity potential of wireless communication systems applying the multiple-input multiple-output (MIMO) technique has been indicated by pioneering work. In interference-limited cellular systems which can be considered as multiuser MIMO systems, interference management has already become the central task to achieve spectrally efficient communications. Applying the orthogonal frequency-division multiplexing (OFDM) transmission technique in our project, interference management is performed based on available channel-state information (CSI) of the investigated multiuser MIMO-OFDM system. System concept based on the perfect full CSI is almost infeasible in realistic cellular systems due to the implementation complexity and the limited ability to track the CSI. Considering the above practical issues, in this project we have proposed a cooperative communication scheme based on partial CSI with respect to significant CSl and imperfect CSI as a promising candidate for interference management. In this scheme, base stations (BSs) cooperate with each other to perform joint detection (JD) in the uplink (UL) and joint transmission (JT) in the downlink (DL). As compared to the state of the art JD and JT techniques, our contributions in this project are shown as follows. JD and JT can be performed based on the CSI in subsysteius of the cellular system such as service areas (SAs) or group cells selected according to the static geographic architecture. However, the MSs close to the boundary of the subsystem still suffer strong interference from the MSs in other subsystems in the UL and cause strong interference to the MSs in other subsystems in the DL. In this project, we have dynamically selected the significant CSI from the point of view of each MS in the form of significant useful channels and significant interference channels according to the functionality of the channels. In order to make full use of the selected significant CSI and to implement the cooperative communication in an efficient way, an iterative algorithm for JD and JT with significant CSI following the ideas of the zero-forcing (ZF) algorithm is implemented in a decentralized way. The implementation complexity is reduced since no CU is needed and only local significant CSI is required at each BS. Additionally, alternative BS antenna layouts with omnidirectional or sector antennas in combination with different transmission techniques are also investigated. Although a lot of research work has been done on investigating the influence of imperfect CSI on multiuser MIMO systems considering full CSI, the impact of imperfect CSI on multiuser MIMO systems considering only significant CSl has rarely been mentioned in the literature, and our work in this project have contributed to this point. The performance degradation caused by the imperfectness of the CSI used in the significant channel selection and in the JD/JT with partial CSI has been investigated. The question about how much CSI should be considered in JD/JT as a function of the extent of imperfectness of CSI to obtain optimum system performance has been answered based on numerical results. Additionally, we have proposed an advanced detection algorithm based on the statistical knowledge of the imperfect CSI, from which optimum detection results can be obtained following the rationale of maximum-likelihood (ML). Our project partner from TU Darmstadt has investigated the impact of imperfect CSI on adaptive subcarrier allocation techniques, adaptive transmit antennas selection techniques and adaptive modulation techniques in a single cell scenario with one BS and multiple MSs. These adaptive techniques can be integrated in our cooperative communication scheme for cellular networks to select one MS in each cell in the considered subcarrier. In this joint project with TU Darmstadt, a system concept based on different levels of knowledge of CSI is proposed for future mobile radio systems. Diversity techniques can be applied with no CSI, and adaptive techniques have to be performed based on imperfect CSI. JD/JT interference cancellation techniques are performed based on imperfect significant CSI. In future work, further improvements and complements are expected to the current system concept based on the cooperative communication scheme with partial CSL Based on the present investigations on adaptive significant CSI selection algorithms with respect to various criteria, e.g., channel energy, log-likelihood ratio (LLR) of the detected data bits, and signal-to-noise-plus-interference ratio (SNIR), further applications of these criteria in realistic cellular systems can be performed and compared. A more practical significant CSI selection algorithm can be found according to the requirements of system performance or practical implementation complexity. Further studies of the system performance of the proposed advanced JD/JT algorithms in this project, e.g., successive interference cancellation (SIC) with quantization and Tomlinson-Harashima precoding (THP), with partial CSI can be performed with respect to numerical results and analytical assessment. Further combinations of resource allocation or power control with the cooperative communication schemes based on interference cancellation signal processing techniques could be applied. This project and its future work are expected to provide promising and practical solutions for interference management in next generation mobile radio networks. Concepts similar to our cooperative communication scheme are being investigated by many researchers all over the world, and cooperations in this field can be expected.
Projektbezogene Publikationen (Auswahl)
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"A novel decentralized MIMO-OFDM uplink detection scheme," Proc. International ITG/IEEE Workshop on Smart Antennas (WSA), February 2007, Vienna
A. Ahrens, X. Wei, T . Weber and S. Deng
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"Decentralized interference cancellation in mobile radio networks," Proc. IEEE Wireless Communications and Networking Conference (WCNC), March 2007, Hong Kong
T . Weber, A. Ahrens and S. Deng
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"Decentralized interference management in mobile radio networks," Frequenz, vol.61, pp . 259-269, Dec , 2007
X. Wei, T . Weber, A. Ahrens, and S. Deng
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"Decentralized signal processing for intercell interference cancellation with partial CSI," Froc. 12-th International OFDM-Workshop (InOWo), Hamburg, August 2007
X. Wei, T. Weber and A. Ahrens
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"Distributed organization of cooperative antenna system". H. Hu, Y. Zhang , and J. Luo (Hrsg.), Distributed Antenna Systems: Open Architecture for Future Wireless Communications. S. 279-312. Boca Raton : Auerbach Publications, 2007
W. Zirwas, J. H. Kim, V. Jungnickel, M. Schubert, T. Weber, A. Ahrens, and M. Haardt
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"MMSE Detection based on Noise Statistics with Random Noise Variance," Proc. IEEE Vehicular Technology Conference (VTC'08-Fall), Calgary, Canada, September 2008
X. Wei and T. Weber
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"Optimum MMSE Detection with Correlated Random Noise Variance in OFDM Systems," Proc. 13-th International OFDM-Workshop (InOWo), Hamburg, August 2008
X. Wei, T. Weber, A. Kühne, and A. Klein
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"Transmit Antenna Selection with imperfect CQI feedback in Multi-user OFDMA systems," Proc. 13-th International OFDM-Workshop (InOWo), Hamburg, August 2008
A. Kühne, A. Klein, X. Wei, and T. Weber
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"Joint Transmission with Imperfect Partial Channel State Information," Proc. IEEE Vehicular Technology Conference (VTC'09-Spring) , Barcelona, April 2009
X. Wei, T . Weber, A. Kühne, and A. Klein
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"Joint Transmission with Significant CSI in the Downlink of Distributed Antenna Systems," Proc. IEEE International Conference on Communications (ICC'09), Dresden, June 2009
X. Wei, T. Weber, A. Wolfgang, and N. Seifi
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"Partial Channel-State Information in Multiuser MIMO Cooperative Transmission," Proc. 13. Diskussionssitzung der ITC-Fachgruppe Angewandte Informationstheorie., Rostock, March 2009
X. Wei and T . Weber
