Читать книгу Dynamic Spectrum Access Decisions - George F. Elmasry - Страница 39

With some commercial OFDM signals, waveforms are altered by the transmitter to add signatures in the form of cycle frequencies at certain frequencies. These signatures can increase the robustness against multipath fading. Spectrum sensors can leverage these features for signal sensing. These signatures introduce periodicity features. The introduced cyclic frequencies and the periodicity make the signal cyclostationary. Cyclostationary signals follow a spectral density (cyclic spectral density function, CSDF) that is leveraged by the detection process and is used to differentiate noise from the sensed signal. This differentiation happens because the modulated signal has cyclostationary characteristics while the noise has wide‐sense stationary characteristics with no correlation. Cyclostationarity characteristics can also be used for distinguishing among different types of sensed signal.

Chapter 3 shows a type of cyclic autocorrelation function used with same‐channel in‐band signal sensing which estimates the noise spectral density separate from estimating the in‐band signal spectral density.