Back-Channel Wireless Communication Embedded in WiFi-Compliant OFDM Packets

This paper presents innovative back-channel wireless communication techniques for ultra-low power (ULP) devices. The concept of embedded back-channel communication is proposed to enable a variety of new applications by inter-connecting heterogeneous ULP devices through existing orthogonal frequency division multiplexing (OFDM)-based WiFi (IEEE 802.11a/g/n/ac) networks. The proposed back-channel communication allows ULP devices to decode messages embedded in WiFi OFDM packets even if these ULP devices are incapable of demodulating OFDM. The proposed back-channel signaling has unique properties that are easily detectable by non-WiFi ULP receivers consuming sub- $mW$ of active power. The proposed scheme eliminates the need for specialized transmitter hardware or dedicated channel resources for embedded back-channel signal transmission. Instead, carefully sequenced data bit streams will generate back-channel messages from already-deployed WiFi infrastructure without any hardware modification. This paper demonstrates that WiFi OFDM back-channel communication is feasible in various modulation formats, such as pulse position modulation, pulse phase shift keying, or frequency shift keying. Systematic algorithms are unveiled to create back-channel messages in various modulation formats from a WiFi standard compliant datapath. Comprehensive bit error rate performance analysis of various WiFi back-channel communication schemes is derived and validated in realistic multi-path frequency selective fading channels.