Spectrum Sensing Under RF Non-Linearities: Performance Analysis and DSP-Enhanced Receivers

Abstract

Intermodulation products arise as a result of low noise amplifier (LNA) and mixer non-linearities in wideband receivers. In the presence of strong blockers, the intermodulation distortion can deteriorate the spectrum sensing performance by causing false alarms and degrading the detection probability.We theoretically analyze the impact of third-order non-linearities on the detection and false alarm probabilities for both energy detectors and cyclostationary detectors under front-end LNA non-linearities.We show that degradation of the detection performance due to nonlinearities of both energy and cyclostationary detection is strongly dependent on the modulation type of the blockers. We then propose two DSP-enhanced receiver architectures to compensate the impact of nonlinearities. The first approach is a post-processing technique which compensates for nonlinearities effect on the test statistic by adapting the sensing time and detection threshold. The second approach is a pre-processing method that compensates by correcting received samples prior to computing the test statistic. This approach

Performance Analysis of the Effect of Nonlinear Low Noise Amplifier for Wideband Spectrum Sensing in the Poisson Field of Interferers

“…The effect of shadowing was clearly seen in the simulation results. The main contribution of this paper was to analyze the performance degradation in spectrum sensing due to inherent nonlinearity of an LNA in the Poisson field of interferer considering intranetwork interference, which models the more realistic scenarios than the ones in the existing literatures [10,15]. It was also shown that the noise model after LNA is more accurate by using the multivariate Gaussian mixture model.…”

“…This is due to the fact that increasing results in the increase in the effective SNR or SIMDR [15,20]. It is noted that the receiver operating under the high input power experiences more severe nonlinearity behavior.…”

“…These studies consider narrowband spectrum sensing and assume that the receiver operates in the linear region. References [14,15] consider wideband spectrum sensing and study the effect of third-order nonlinearity due to LNA in the performance degradation of the energy detector and the cyclostationary detector. These papers study only the effect of IMD terms in the frequency band.…”

“…A more realistic study would be to consider the situation where CRs may be transmitting either on either separate frequency bands or same frequency band considering the effect of strong in-band interfering signal. References [14,15] investigated effect of IMD on the performance of sensing node but they do not consider the scenario where the subband of interest may be degraded further by other interfering signals in a noncooperative environment which would be more realistic; for example, the subband at which the sensing node is detecting the PU signal is degraded not only by IMD but also by the interfering signal from other CRs in a noncooperative network.…”

“…Our contribution is to study the performance of detector in wideband spectrum sensing in noncooperative environment considering the effect not only of IMD but also due to the interfering signal from other CRs which has not been investigated before in [10,14,15]. We investigate the performance of energy detector for wideband spectrum sensing considering the effect of nonlinearity in LNA.…”