Cognitive radio sensing method and system

摘要

The cognitive radio system and method uses a wideband chirp signal for characterization of the spectra that a mobile radio may use. A cognitive radio base station broadcasts the low power reference wideband chirp signal with bandwidth covering the sensed spectrum. At the receiver, spectral resolution in the presence of white noise is achieved by cross-correlating the chirp signal with a locally generated copy of itself (i.e., matched filtering). A Fast Fourier Transform (FFT) is applied to the output of this matched filtering. The FFT output is fed to a decision circuitry, where a threshold value is set to decide the minimum amplitude of utilized frequencies. This process eases sensing computational complexity and improves the quality of sensing, thereby offering enhanced cognition at the cognitive radio receiver.

主权项

1. In a cognitive radio system having a cognitive radio base station and a plurality of cognitive radio users operating in a cognitive radio coverage area overlapping a primary users' radio system coverage area, wherein the cognitive radio base station generates a low power wideband linear reference chirp signal extending over all channels and frequencies within the cognitive radio spectrum in the cognitive radio coverage area according to predetermined reference chirp signal parameters, a cognitive radio sensing method comprising the steps of:
(a) receiving a signal in the cognitive radio spectrum in the cognitive radio coverage area at a cognitive radio user's receiver on a cognitive radio channel; (b) generating a local copy of the linear reference chirp signal in the cognitive radio user's receiver according to the predetermined reference chirp signal parameters; (c) correlating the received signal with the local copy of the linear reference chirp signal in a matched filter in the cognitive radio user's receiver, the matched filter producing a correlated chirp signal output; (d) transforming the correlated chirp signal output from a time domain representation into a frequency domain representation of the correlated chirp signal output; (e) detecting interfering signals from primary users with a processor programmed with a predetermined spectral threshold level above a flat top of the frequency domain representation of the transformed correlated chirp signal output, the threshold level being slightly above noise level in the channel; (f) increasing said predetermined spectral threshold level from a normalized value of approximately 0.2 to a normalized value of approximately 0.8 when a signal to interference plus noise ratio increases from a value of approximately −20 dB to a value of approximately 0 dB; (g) increasing said predetermined spectral threshold level from a normalized value of approximately 0.8 to a normalized value of approximately 1.0 when said signal to interference plus noise ratio increases from a value of approximately 0 dB to a value of approximately 10 dB; and (h) automatically changing frequencies at the cognitive user's receiver before transmitting when the processor detects frequency spikes above the threshold in the transformed correlated chirp signal output in order to avoid interference with primary users' signals.