Implicit MU-MIMO Sounding Procedures Performance Study

The multiuser multiple-input multiple-output (MU-MIMO) mechanism is a key component of modern Wi–Fi networks, enabling substantial performance gains in dense multiuser scenarios. Current generation Wi-Fi relies on explicit channel sounding, which involves a lengthy transmission of channel state information. To reduce this overhead, implicit sounding is considered. This work develops a Wi-Fi prototype based on software-defined radio that supports explicit sounding and two implicit sounding methods: one with sequential and one with simultaneous (multiplexed) pilot transmission from the stations. The latter shortens the sounding procedure, but our experiments show that it reduces the signal-to-interference-plus-noise ratio of the channel estimate by up to 4 dB compared with the sequential method. Due to the degradation in implicit channel-sounding quality, reciprocity-calibration errors arise, and the throughput of MU-MIMO transmissions decreases by 20–25