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Space-time block code and spatial multiplexing are promising approaches that exploit the multiple input multiple output (MIMO) channel to provide high diversity and multiplexing gain without sacrifice in bandwidth. In this paper, a hybrid MIMO scheme for orthogonal frequency division multiplexing systems is proposed to achieve various multiplexing gains according to the channel condition. The existing hybrid MIMO schemes are appropriate for limited integer multiplexing rates without taking into account the channel condition, whereas the proposed scheme can attain various multiplexing rates according to the channel condition. [ABSTRACT FROM AUTHOR]

This paper proposes a computationally efficient approach of estimating a sampling frequency offset (SFO) in multi-band ultra wideband orthogonal frequency division multiplexing systems. In order to devise the post-FFT based SFO estimator with low complexity, the partial pilot subset is chosen such that it provides an equivalent estimation performance to the conventional SFO estimator using the full pilot symbols. Mean square error of the low-overhead frequency estimation scheme is derived and simulation results are provided to verify our analysis. [ABSTRACT FROM AUTHOR]

In this paper, a joint estimation of carrier frequency offset and sampling frequency offset is suggested for multi-band ultra-wideband orthogonal frequency division multiplexing (UWB-OFDM) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the UWB-OFDM system, thus removing the need of pilot symbols. The system performance of using our algorithm is demonstrated in terms of mean square error and bit error rate. [ABSTRACT FROM AUTHOR]

In orthogonal frequency division multiplexing (OFDM) systems, the loss of orthogonality between the subcarriers due to carrier frequency offset (CFO) can degrade the performance of the system. In this paper, a residual CFO synchronization method is proposed for ultra wideband OFDM (UWB-OFDM) systems. The proposed fine frequency synchronization scheme uses a channel estimation sequence and physical layer convergence protocol (PLCP) header information which are equipped with frequency-domain spreading. A UWB-OFDM receiver with algorithm for fine frequency error synchronization is simulated and is evaluated in terms of mean square error. [ABSTRACT FROM AUTHOR]

In this paper, a fine carrier frequency offset synchronizer is presented for ultra-wideband multi-band orthogonal frequency division multiplexing (UWB MB-OFDM) systems. The proposed scheme uses a channel estimation (CE) sequence provided in the current UWB MB-OFDM system and is designed to be insensitive to a sampling clock frequency offset. To demonstrate the efficiency of the proposed fine frequency synchronizer, comparisons are made with the conventional frequency synchronizer in terms of mean square error. [ABSTRACT FROM AUTHOR]

A combination of orthogonal frequency division multiplexing (OFDM) with multiband frequency hopping (FH) is regarded as a promising solution for realizing ultra-wideband (UWB) systems. This paper deals with a modified maximum likelihood approach for frequency ambiguity resolution in the multiband UWB system. By using computer simulation, the synchronization performance of the traditional and proposed methods is evaluated in terms of probability of synchronization failure. [ABSTRACT FROM AUTHOR]