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For orthogonal frequency division multiplexing (OFDM) communication systems, the orthogonality among subcarriers is lost in mobile applications due to frequency offset resulting from either transmitter-receiver local oscillator differences or Doppler shift caused by mobility. As a direct result, inter-carrier interference (ICI) is observed on each and every subcarrier, leading to significant performance...
The limited time available for acquiring the channel state in mobile broadband wireless communication systems makes it crucial to count with channel estimation methods that attain the highest accuracy with a given preamble length. For the family of preambles that probe channels repeatedly at equispaced frequencies, we find that the shortest preamble that attains a given mean square error is a sequence...
In semi-blind channel estimation techniques, the choice of the regularizing parameter that weights the blind criterion when linearly combined to the training-based least square criterion has a great impact on channel estimation performance. If a scalar regularization is considered, it has been noted that the optimal value of the regularizing factor has no closed-form expression. In a recent work,...
We consider the problem of pilot-aided accurate least squares (LS) channel estimation in the presence of carrier frequency offset (CFO). We first formulate the mean square error (MSE) of the LS channel estimator in the presence of CFO and then show how to select the pilot sequence (with element values constrained to plus or minus one) that minimizes the MSE. Our main conclusion is that, in the presence...
By using a pilot sample from a selected time-slot in a time-domain orthogonal frequency division multiplexing (OFDM) block, we present a simple maximum-likelihood (ML) scheme for frequency tracking in OFDM systems over frequency-selective channels. The frequency offset estimator thus obtained is found to become unbiased and its mean square error (MSE) will approach the Cramer-Rao bound (CRB) as signal-to-noise...
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