Abstract

(ABSTRACT) Orthogonal Frequency Division Multiplexing (OFDM) has recently gained a lot of attention and is a potential candidate for Fourth Generation (4G) wireless systems because it promises data rates up to 10Mbps. A variation of OFDM is Multi-Carrier CDMA (MC-CDMA) which is an OFDM technique where the individual data symbols are spread using a spreading code in the frequency domain. The spreading code associated with MC-CDMA provides multiple access technique as well as interference suppression. Often times in cellular and military environments the desired signal can be buried below interference. In such conditions, the processing gain associated with the spreading cannot provide the needed interference suppression. This research work investigates multi-antenna receivers for OFDM and MC-CDMA systems; specifically this works investigates adaptive antenna algorithms for MC-CDMA for very different channel conditions. Frequency domain beamforming is studied in this research predominantly through simulation. As an alternative a time domain beamforming is also studied. Time variations in the channel can disrupt the orthogonality between subcarriers. Minimum Mean Square Error (MMSE) detection coupled with MMSE beamforming is proposed for time varying channels. Semi-analytic results are derived to study the Bit Error Rate (BER) performance. These results show significant performance improvement in the presence of interference. Joint MMSE weights in space and frequency is also investigated and semi-analytic results are derived to study their BER performance. iii ACKNOWLEDGEMENTS I would like to express my sincere appreciation and gratitude to my primary advisor Dr. Michael Buehrer. His vast experience and nice nature has given me a very great learning experience during the course of this research. While research contracts might be more alluring than the students' actual progress Dr. Buehrer gives more importance to the latter. I consider it a great honor to have Dr. Jeffrey Reed and Dr. Brian Woerner in my committee. I thank them for their review and comments on this work. A lot of times discussions with the colleagues in MPRG has helped me gain a lot of insight into very difficult issues. I would like to thank Jay Tsai, a Bell-Labs veteran, for his time and the numerous fruitful discussions we have had. Thanks are also due to other colleagues, though not in any particular order Nishant, Patrick, Mahesh and other MPRG colleagues. I would also like to thank the Raytheon Company and DARPA, the sponsors of this project, and the MPRG industrial affiliate program. I thank my parents and …

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Cite this paper

@inproceedings{Venkatasubramanian2003BeamformingFM, title={Beamforming for MC-CDMA}, author={Ramasamy Venkatasubramanian and Michael R. Buehrer and Brian D. Woerner and Jeffrey H. Reed}, year={2003} }