An Experimental Study of Wi-Fi Joint Transmission With Multiple Openwifi Access Points

Multi-Access Point Collaboration (MAPC) envisioned in future Wi-Fi standards has the potential to provide reliable connectivity for time-critical IoT applications. The joint transmission (JT) concept strengthens the signals at the station transmitted from distributed APs, increasing its resilience against interference and multi-path fading to improve reliability and latency performance. There is no commercially available WiFi device capable of doing this since individual APs must be synchronized for time, RF carrier and packet data, and are required to share the medium access with each other. We present an experimental study of distributed dual-AP Wi-Fi network prototype with SDR platforms with openwifi. By synchronizing the clock source, packet transmission control and data, we demonstrate a successful constructive overlap of transmitted WiFi signals at the receiver from distributed APs. Specifically, we observe a 6 dB received signal power gain and a 4.4 dB SNR improvement from the decoded packets with two APs compared to a standalone transmission in the experiment.