Combining a layered space-time receiver with the OFDM for high-rate transmissions requires the multi-channel estimation process. Therefore, this letter highlights a design of a preamble structure for OFDM-based layered space-time receiver. The new proposed preamble can estimate the multi-channel up to the 8 transmit antennas using two long preambles in the WLAN standards.

In this letter, an algorithm that estimates one of the most important channel parameters, maximum Doppler frequency, fD, is proposed. The algorithm uses phase variations of received pilot signals, which is strongly related with fD in a fading environment. In addition, a phase variation measurement method for binary phase shift keying (BPSK) modulated signals is also proposed and it makes possible to estimate fD from BPSK modulated information signals as well as unmodulated pilot signals. The results show that the proposed algorithm is very simple and shows good performance over wide Doppler frequency range.

In this letter, a robust pilot-assisted synchronization scheme is proposed for estimation of residual frequency offset (RFO) in OFDM-based digital radio mondiale (DRM) system. The RFO estimator uses the gain reference pilots mainly reserved for the channel tracking in the DRM standard. To demonstrate the efficiency of the proposed RFO estimator, comparisons are made with the conventional RFO estimator using the frequency reference pilots in terms of mean square error (MSE) performance.

This letter presents the performance of ultra-wideband multi-band orthogonal frequency division multiplexing (UWB MB-OFDM) systems with an extra diversity. To fully obtain diversity gain in the current MB-OFDM system when a time-domain spreading (TDS) is adopted, two consecutive OFDM symbols are designed to be cyclic shifted against each other. Simulation results indicate that the MB-OFDM system using additional frequency diversity outperforms conventional MB-OFDM system.

This letter proposes a modified orthogonal frequency division multiplexing (OFDM) system with low peak-to-average power ratio (PAPR) and reduced complexity. To do this, OFDM system exploits a frequency diversity equipped with a simple symbol repetition. From the presented results, we can see that the investigated OFDM system with one transmit antenna gives the same diversity gain to two-branch transmit diversity and can be implemented with reduced transmitter complexity and low peak power at the cost of decoding delay.

In this letter, the effect of an imperfect channel estimation and carrier frequency offset on the performance of transmit diversity OFDM systems is investigated. For the performance evaluation, the average bit error rate (BER) expression is derived in the presence of the imperfect channel information including both the inherent estimation error and the imperfect windowing error derived in a mismatched channel separation.