IEEE 802.11 be: Doppler Effects on the Performance of Chase Combining HARQ Protocol

This paper analyzes performance gains, challenges and issues regarding the implementation of Chase Combining Hybrid Automatic Repeated Request (CC-HARQ) protocol in the IEEE 802.11 be physical layer (PHY) over channels with Doppler spread and feedback delay of the channel state information (CSI). The design and performance of the following transceivers architectures are taken into account: (1) downlink single-user multiple-input multiple-output with transmit beamforming (DL SU-MIMO TxBF); (2) DL SU-MIMO with spatial spreading (SS); (3) downlink multiuser MIMO (DL MU-MIMO); (4) uplink multi-user MIMO (UL MU-MIMO). The implementation of CC-HARQ protocol allows power gains between 3 to 5 dB over channels without Doppler spread. On the other hand, the performance of DL MU-MIMO transceivers has greater sensibility with Doppler spread and CSI feedback delay in relation to DL SU-MIMO TxBF transceivers. UL MU-MIMO transceivers have the greatest performance gains due to the implementation of CC-HARQ protocol and present no performance loss due to Doppler spread since the stations do not implement any precoding on the transmitted waveforms in the study cases analyzed in this industry-oriented research paper.