Cognitive radio sensing method and system
First Claim
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.
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Abstract
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.
20 Citations
12 Claims
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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:
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(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. - View Dependent Claims (2, 3)
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4. 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:
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(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 a conjugate of the linear reference chirp signal in the cognitive radio user'"'"'s receiver according to the predetermined reference chirp signal parameters; (c) cross-correlating the received signal with the local copy of the conjugate of the linear reference chirp signal in a matched filter in the cognitive radio user'"'"'s receiver, the matched filter producing a cross-correlated chirp signal output; (d) estimating times of interference and noise from the primary users with a processor programmed to detect times at which the chirp cross-correlation output exceeds a predetermined envelope threshold level above an envelope of the cross-correlated chirp signal output; (e) transforming the cross-correlated chirp signal output from a time domain representation into a frequency domain representation; (f) determining frequencies of interference and noise from the primary users with the processor by detecting spectral components of the frequency domain representation of the cross-correlated chirp signal output exceeding the predetermined spectral threshold level above a flat top of the frequency domain representation of the cross-correlated chirp signal output; (g) 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;(h) 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 (i) timing transmission and reception of the cognitive radio user'"'"'s radio to avoid the interference frequencies determined in step (f) at the interference times determined in step (d). - View Dependent Claims (5, 6, 7)
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8. A computer software product, comprising a non-transitory medium readable by a processor, the medium having stored thereon a set of instructions for performing a cognitive radio sensing method, the set of instructions including:
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(a) a first sequence of instructions which, when executed by the processor, causes said processor to receive a low power reference chirp signal broadcast by a cognitive radio base station, the chirp signal being received in the presence of noise and interference from primary users of a predetermined multi-channel spectrum overlapping a spectrum of a cognitive radio system, the low power reference chirp signal having a bandwidth covering the entire spectrum of the cognitive radio system; (b) a second sequence of instructions which, when executed by the processor, causes said processor to correlate the chirp signal in the presence of noise and said interference from said primary users with a locally stored copy of the chirp signal, said correlating step providing a chirp correlation output; (c) a third sequence of instructions which, when executed by the processor, causes said processor to transform said chirp correlation output into a frequency domain; (d) a fourth sequence of instructions which, when executed by the processor, causes said processor to determine frequencies of interference and noise from said primary users by observing spectral components of said frequency domain transformed chirp correlation output which exceed a predetermined spectral threshold level above an expected flat top of said frequency domain transformed chirp correlation output; (e) a fifth sequence of instructions which, when executed by the processor, causes said processor to tune said cognitive radio to transmission and reception frequencies that spectrally avoid the interference frequencies determined in step (d); (f) a sixth sequence of instructions which, when executed by the processor, causes said processor to increase 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; and(g) a seventh sequence of instructions which, when executed by the processor, causes said processor to increase 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. - View Dependent Claims (9, 10, 11, 12)
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Specification