Indoor environments with rich scatters and severe shadowing are very complicated today for wireless communications. The presence of metal surfaces and an overwhelming number of wireless devices further introduces challenges to the resilience of existing wireless links, especially in industrial scenarios. The existing single-transmitter links often suffer from the complex environment and thus cannot guarantee a stable performance; even with more transmitting antennas on a commercial multiple-input-multiple-output (MIMO) capable access point (AP), due to limited antenna number and positioning, it may not provide fair and satisfactory quality of service to all users. Distributed beamforming (D-BF) is a future upgrade for the existing collocated MIMO that allows individual APs to transmit coherently from multiple locations for improved link resilience. We analyze the main limiting factors of channel sounding for implementing D-BF with the current Wi-Fi standard. Our proposed synthetic multi-AP channel sounding approach overcomes the 8-antenna constraint posed by the standard and uses IEEE 802.11ax compliant Wi-Fi frames, enabling commercial single-receiver Wi-Fi station (STA) to benefit from distributed beamforming without additional upgrade. Our simulation result shows that the effective SNR can be boosted by roughly 26dB with D-BF of 64 APs against a commercial 8x1 beamforming link, alongside a 441.6µs sounding airtime which corresponds to less than 0.5% overhead under 100ms channel coherence time.
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