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This paper addresses the problem of Blind Signal Separation (BSS) as it pertains to Multiple Input Multiple Output (MIMO) systems utilizing Orthogonal Frequency Division Multiplexing (OFDM). In systems with N subcarriers affected by frequency selective channels, when sampling the received signals at the Nyquist rate, the original BSS is transformed into a set of N standard Independent Component Analysis (ICA) problems. In this paper, fractional sampling is employed to increase the number of received signals and improve diversity at the receiver. The up-sampling of the OFDM frames is analyzed in the frequency domain with an up-sampling factor of 2. This doubles the number of ICA problems which provide N new solutions to aid in the recovery of the original data symbols. The additional solutions using equal gain combining improve signal-to-noise ratio (SNR) and therefore the data recovery. To achieve convergence of the ICA algorithm for the over-sampled data symbols, a specialized rotation of constellations on adjacent subcarriers is introduced. The simulation results demonstrate effectiveness of the overall system in its resiliency to inter-carrier interference and the AWGN channel.
Date of Conference: July 30 2007-Aug. 2 2007