
Type of Document Dissertation Author Wu, Zhongshan Author's Email Address zwu1@lsu.edu URN etd04042006144949 Title MIMOOFDM Communication Systems: Channel Estimation and Wireless Location Degree Doctor of Philosophy (Ph.D.) Department Electrical & Computer Engineering Advisory Committee
Advisor Name Title Guoxiang Gu Committee Chair Kemin Zhou Committee Member Peter Wolenski Committee Member Shuangqing Wei Committee Member John M. Tyler Dean's Representative Keywords
 OFDM
 MIMO
 channel estimation
 location
 AOA
 TDOA
Date of Defense 20060328 Availability unrestricted Abstract In this new information age, high data rate and strong reliability features our wireless communication systems and is becoming the dominant factor for a successful deployment of commercial networks. MIMOOFDM (multiple input multiple outputorthogonal frequency division multiplexing), a new wireless broadband technology, has gained great popularity for its capability of high rate transmission and its robustness against multipath fading and other channel impairments.
A major challenge to MIMOOFDM systems is how to obtain the channel state information accurately and promptly for coherent detection of information symbols and channel synchronization. In the first part, this dissertation formulates the channel estimation problem for MIMOOFDM systems and proposes a pilottone based estimation algorithm. A complex equivalent baseband MIMOOFDM signal model is presented by matrix representation. By choosing equallyspaced and equallypowered pilot tones from subcarriers in one OFDM symbol, a downsampled version of the original signal model is obtained. Furthermore, this signal model is transformed into a linear form solvable for the LS (leastsquare) estimation algorithm. Based on the resultant model, a simple pilottone design is proposed in the form of a unitary matrix, whose rows stand for different pilottone sets in the frequency domain and whose columns represent distinct transmit antennas in the spatial domain. From the analysis and synthesis of the pilottone design in this dissertation, our estimation algorithm can reduce the computational complexity inherited in MIMO systems by the fact that the pilottone matrix is essentially a unitary matrix, and is proven an optimal channel estimator in the sense of achieving the minimum MSE (mean squared error) of channel estimation for a fixed power of pilot tones.
In the second part, this dissertation addresses the wireless location problem in WiMax (worldwide interoperability for microwave access) networks, which is mainly based on the MIMOOFDM technology. From the measurement data of TDOA (time difference of arrival), AOA (angle of arrival) or a combination of those two, a quasilinear form is formulated for an LStype solution. It is assumed that the observation data is corrupted by a zeromean AWGN (additive white Gaussian noise) with a very small variance. Under this assumption, the noise term in the quasiliner form is proved to hold a normal distribution approximately. Hence the ML (maximumlikelihood) estimation and the LStype solution are equivalent. But the ML estimation technique is not feasible here due to its computational complexity and the possible nonexistence of the optimal solution. Our proposed method is capable of estimating the MS location very accurately with a much less amount of computations. A final result of the MS (mobile station) location estimation, however, cannot be obtained directly from the LStype solution without bringing in another independent constraint. To solve this problem, the Lagrange multiplier is explored to find the optimal solution to the constrained LStype optimization problem.
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