Combined Effect of Transmit Diversity and Frequency Hopping for DFT-Precoded OFDMA in Uplink Frequency-Selective Fading Channels

This paper proposes a combination of open-loop (OL) transmit diversity and intra-subframe frequency hopping (FH) for a shared channel carrying user traffic data and investigates the potential performance of the combination compared to closed-loop (CL) transmit diversity for uplink discrete Fourier transform (DFT)-precoded OFDMA in frequency-selective fading channels. We apply FH to OL transmit diversity to mitigate the reduction in the diversity gain under high fading correlation conditions among antennas and decision-feedback channel estimation (DFCE) to improve the channel estimation accuracy. Computer simulation results show that the loss in the required average received signal-to-noise power ratio (SNR) at the average block error rate (BLER) of 10-2 of space-time block code (STBC), i.e., OL transmit diversity, with intra-subframe FH compared to codebook-based CL transmit diversity is reduced to within approximately 0.8 dB using DFCE at maximum Doppler frequency of fD = 5.55 Hz. Moreover, it is shown that STBC with FH and DFCE achieves much better BLER performance than CL transmit diversity when fD is higher than approximately 80 Hz due to the degradation in the tracking ability against fast fading variation in the feedback loop of CL transmit diversity.