Figure 3
From: Cross-layered resource allocation in UWB noise-OFDM-based ad hoc surveillance networks
Spectrum comparison for covertness. Spectrum: (a) OFDM signal, (b) band-limited UWB noise, (c) UWB notched noise, and (d) Coexistence: UWB noise-OFDM spectrum. Comparing (b) and (d), we note that the transmit waveform (d) also appears random & noise-like, thereby hiding the data message inside.