SPECTRAL SHAPING AND SYMBOL ERROR MITIGATION TECHNIQUES TO INJECT OFDM SUBCARRIERS INTO NAVIGATIONAL RADAR GUARD BANDS AND MAINLOBE FOR SPECTRUM SHARING

Abstract

In this work, we investigate the effects of spectrally opportunistic shaped communications waveforms impinging into the spectrum of a radar. To simulate the radar, we first use a Hamming-based spectral shape and a more realistic spectrum from a commercial navigation (COMNAV) radar. The communications system employs orthogonal frequency-division multiplexing (OFDM) with the subcarriers modulated by quaternary phase-shift keying (QPSK). We utilize waterfilling, adhoc waterfilling inversion, and uniform energy distribution techniques to shape the communications spectrum, fill the spectral tails (i.e., guard bands), and even inject subcarriers into the radar bandwidth. Unsurprisingly, the high-powered radar interferes with the communications signal such that the symbol error ratio (SER) is drastically degraded. In addition to the spectral shaping techniques on transmit, we propose estimation and subtraction of the radar interference from the interfered subcarriers. The combination results in SERs that are vastly improved, while the radar probability of detection is minimally or slightly affected.