Opportunistic Techniques to Inject OFDM Subcarriers into Navigational Radar Spectral Guard Bands and Mainlobe for Spectrum Sharing

In this paper, we investigate the effects of an opportunistic spectrally shaped communications waveform impinging into the spectrum of a radar with practical spectral shape (e.g., commercial navigation radar). The communications signal employs orthogonal frequency-division multiplexing (OFDM) with the subcarriers modulated by quaternary phase shift keying (QPSK). We use waterfilling and adhoc waterfilling inversion (AWI) techniques to shape the communications spectrum to fill the spectral tails (i.e., guard bands) and to even inject subcarriers into the radar bandwidth. Unsurprisingly, the high-powered radar interferes with the communications waveform such that the symbol error rate (SER) is drastically degraded. We propose estimation and subtraction of the radar interference from the interfered subcarriers resulting in SERs that are vastly improved while the radar probability of detection P
_D
is minimally affected.