This paper proposes a symbol-by-symbol-based multilevel transmit power control (MTPC) scheme for orthogonal frequency division multiplexing (OFDM) based adaptive modulation system (AMS) to achieve high quality broadband wireless transmission for high mobility terminals. In the proposed system, delay profile for each OFDM symbol is estimated by linearly extrapolating previously received delay profile information (DPI) sequence to improve tracking ability of OFDM based AMS with MTPC to the fast fading variation. Moreover, 2-branch reception diversity is applied to reduce dynamic range and variation speed of the multipath fading. Computer simulation confirms that the proposed system is effective in supporting higher mobility terminals with keeping high transmission quality.

This paper proposes an adaptive modulation system with a punctured convolutional code for land mobile communications to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments. The proposed system adaptively controls the coding rate of the punctured convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. During good channel conditions, the modulation parameters are selected to increase the transmission rate as much as possible with satisfying a certain transmission quality. As channel conditions become worse, lower rate modulation parameters are applied or transmission is stopped. The performances in fading environments are evaluated theoretically and by computer simulations. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

This paper proposes a directive antenna diversity reception scheme for an adaptive modulation/time division multiple access (TDMA)/time division duplex (TDD) system to achieve high quality, high bit rate and high spectral efficient data transmission in high mobility land mobile communication environments. In mobile stations, a directive antenna is applied to equivalently reduce the observed variation speed of the fading channel. At each branch, the offset frequency (foff) and foff-canceled fading variation are estimated to improve accuracy of the propagation path characteristics estimation even in high maximum Doppler frequency (fd) environments. Computer simulation confirms that the proposed scheme can achieve successful variable rate transmission in fast fading environments.