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Frequency injection interfacing: A novel method for delivering external information to an OFDM receiver physical layer

This work presents a novel method we call: Frequency Injection Interfacing (FII), for OFDM communication systems. With FII, an external system or observer can communicate to an OFDM receiver through a frequency encoder that injects additional frequency content into the received signal. Specifically, the null subcarriers at the edges of the OFDM waveform are turned on or off to represent a binary code word which references a lookup table. OFDM transmitters do not broadcast wireless energy in the OFDM sidebands in order to comply with regulatory policies. To avoid violating transmission laws, FII uses a direct connection between the frequency encoder and OFDM receiver. Because FII can deliver a unique code word per packet in real time, FII could potentially allow new applications and optimizations for OFDM systems, without requiring a separate application program interface. The FII method is validated through experimentation using software defined radios, a GNU Radio IEEE 802.11 receiver, and a COTS vehicle-to-vehicle radio. A packet reception rate above 95% proves FII operates transparently within existing OFDM architectures, furthermore the non-optimized implementation of FII presented in this work reveals that FII could reliably deliver up to 2047 code words with 67% success and zero false alarms.