Cyclic Prefix Noise Reduction for Digital Self Interference Cancellation in OFDM-Based In-Band Full-Duplex Wireless Systems

Orthogonal frequency division multiplexing (OFDM) is the pertinent waveform for current and next generation wireless systems, whose spectral efficiency can be potentially doubled by in-band full-duplex (IBFD) communication. However, in OFDM based IBFD systems, digital self-interference cancellation (DSIC) employed at baseband does not provide sufficient cancellation in the cyclic prefix (CP) region. When the propagation delay between two communicating radios is non-zero, the CP noise affects the data region of the desired signal. In this work, we propose CP noise reduction (CPNR) technique for OFDM based IBFD radios. We have evaluated CPNR with time and frequency domain DSIC schemes via both simulations and MATLAB and FPGA implementations on our Software Defined Radio based IBFD radio. In the laboratory tests, the total suppression of the IBFD radio is improved by 6 dB by employing CPNR in frequency-domain DSIC and EVM for bidirectional communication is improved by up to 5%, allowing realistic propagation delays. In addition to improving the total suppression and EVM performance, CPNR is also shown to enhance the multi-path resiliency of DSIC techniques.