Feasibility of transmit diversity for IS-136 TDMA systems
In this paper, we investigate the performance of transmit diversity technique operating in IS-136 TDMA systems where the Doppler frequency can be as high as 184 Hz. Transmit diversity transforms a flat fading channel into a frequency selective fading channel, thus we use finite length decision feedback equalizers to estimate the desired signal at the receiver. The channel parameters are trained via the training symbols and tracked using decision-directed symbols. It is shown that systems with transmit diversity can provide a significant performance improvement over systems without transmit diversity for Rayleigh flat fading channels when the Doppler frequency is less than 40 Hz; however for systems with high Doppler frequency, transmit diversity alone cannot totally mitigate the fast fading effect since the effects of the channel estimation errors may cancel the benefit of the transmit diversity.