Comparison of Single User with Multi User Cooperative Spectrum Sensing for Energy Detector at Low SNR Wall

With rapidly increasing demand in wireless communication, available licensed spectrum resources should be utilized efficiently and actively. Cognitive radio is a device which learns from surrounding environment and transmit its signal when license spectrum is unutilized. Spectrum sensing is the need for Cognitive radio. In this paper, Energy detector is implemented though MATLAB software for single and multiusers. Region of Convergence (ROC) curve is plotted for both normal ED and Cooperative spectrum sensing ED. Results show while increasing number of samples from 1k to 100k, probability of detection is also achieved 0.9 maximum. Increasing SNR from -20dB, -15dB to -10 dB, probability of detection is improved in ROC curve. Also cooperative spectrum sensing with OR rule gives good probability of detection 0.9 to 1.

Substorm evolution of the auroral zone boundaries on the dawn and dusk flanks: DMSP and POES/MetOp observations

<p>We present a method for tracking the evolution of the auroral boundaries on the dawn and dusk flanks during magnetospheric substorms by using a combined database of auroral zone boundaries derived from DMSP and POES/MetOp satellite particle measurements. Auroral boundaries can be identified by the Kilcommons et al. (2017) algorithm which use electron energy fluxes from the DMSP spectrometer (SSJ instrument). We show how auroral boundaries may also be obtained from precipitating electron observations from the POES/MetOp Total Energy Detector (TED) instrument by subjecting the TED electron measurements to an algorithm similar to that presented by Kilcommons et al. (2017). Boundaries derived from the two satellite missions are similar, suggesting that the technique for auroral oval boundary identification is physically meaningful.</p>

Spectral Analysis of Individual Terrestrial Gamma-ray Flashes Detected by ASIM

<p>Terrestrial Gamma-ray Flashes (TGFs) are sub-millisecond bursts of high-energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.</p><p>The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.</p><p>Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecraft capable of detecting TGFs. By comparing Monte Carlo simulations to the energy spectrum from single ASIM TGFs we will aim to put stricter constraints on the production altitude and beaming geometry of TGFs. We will present the dataset, method, and some results of the spectral analysis of individual TGFs.</p><p>References:</p><p>1. Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848.</p><p>2. Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.</p>

An analysis of energy detector based on improved approximations of the chi-square distributions

Closed-form expressions for the detection probability, the false alarm probability and the energy detector constant threshold are derived using approximations of the central chi-square and non-central chi-square distributions. The approximations used show closer proximity to the original functions when compared to the expressions used in the literature. The novel expressions allow gains up to 6% and 16% in terms of measured false alarm and miss-detection probability, respectively, if compared to the Central Limit Theorem approach. The throughput of cognitive network is also enhanced when these novel expressions are implemented, providing gains up to 9%. New equations are also presented that minimize the total error rate to obtain the detection threshold and the optimal number of samples. The analytical results match the results of the simulation for a wide range of SNR values.