| 1. |
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| 2. |
- de Graauw, Th., et al.
(författare)
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The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L6-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 3. |
- Middeldorp, Christel M., et al.
(författare)
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The Early Growth Genetics (EGG) and EArly Genetics and Lifecourse Epidemiology (EAGLE) consortia : design, results and future prospects
- 2019
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Ingår i: European Journal of Epidemiology. - : Springer Science and Business Media LLC. - 0393-2990 .- 1573-7284. ; 34:3, s. 279-300
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of many unfavorable childhood traits or diseases, such as low birth weight and mental disorders, is not limited to childhood and adolescence, as they are also associated with poor outcomes in adulthood, such as cardiovascular disease. Insight into the genetic etiology of childhood and adolescent traits and disorders may therefore provide new perspectives, not only on how to improve wellbeing during childhood, but also how to prevent later adverse outcomes. To achieve the sample sizes required for genetic research, the Early Growth Genetics (EGG) and EArly Genetics and Lifecourse Epidemiology (EAGLE) consortia were established. The majority of the participating cohorts are longitudinal population-based samples, but other cohorts with data on early childhood phenotypes are also involved. Cohorts often have a broad focus and collect(ed) data on various somatic and psychiatric traits as well as environmental factors. Genetic variants have been successfully identified for multiple traits, for example, birth weight, atopic dermatitis, childhood BMI, allergic sensitization, and pubertal growth. Furthermore, the results have shown that genetic factors also partly underlie the association with adult traits. As sample sizes are still increasing, it is expected that future analyses will identify additional variants. This, in combination with the development of innovative statistical methods, will provide detailed insight on the mechanisms underlying the transition from childhood to adult disorders. Both consortia welcome new collaborations. Policies and contact details are available from the corresponding authors of this manuscript and/or the consortium websites.
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| 4. |
- Zamora, Juan Carlos, et al.
(författare)
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Considerations and consequences of allowing DNA sequence data as types of fungal taxa
- 2018
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Ingår i: IMA Fungus. - : INT MYCOLOGICAL ASSOC. - 2210-6340 .- 2210-6359. ; 9:1, s. 167-185
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Tidskriftsartikel (refereegranskat)abstract
- Nomenclatural type definitions are one of the most important concepts in biological nomenclature. Being physical objects that can be re-studied by other researchers, types permanently link taxonomy (an artificial agreement to classify biological diversity) with nomenclature (an artificial agreement to name biological diversity). Two proposals to amend the International Code of Nomenclature for algae, fungi, and plants (ICN), allowing DNA sequences alone (of any region and extent) to serve as types of taxon names for voucherless fungi (mainly putative taxa from environmental DNA sequences), have been submitted to be voted on at the 11th International Mycological Congress (Puerto Rico, July 2018). We consider various genetic processes affecting the distribution of alleles among taxa and find that alleles may not consistently and uniquely represent the species within which they are contained. Should the proposals be accepted, the meaning of nomenclatural types would change in a fundamental way from physical objects as sources of data to the data themselves. Such changes are conducive to irreproducible science, the potential typification on artefactual data, and massive creation of names with low information content, ultimately causing nomenclatural instability and unnecessary work for future researchers that would stall future explorations of fungal diversity. We conclude that the acceptance of DNA sequences alone as types of names of taxa, under the terms used in the current proposals, is unnecessary and would not solve the problem of naming putative taxa known only from DNA sequences in a scientifically defensible way. As an alternative, we highlight the use of formulas for naming putative taxa (candidate taxa) that do not require any modification of the ICN.
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| 5. |
- Axell, Erik, et al.
(författare)
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On the Optimal K-term Approximation of a Sparse Parameter Vector MMSE Estimate
- 2009
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Ingår i: Proceedings of the 2009 IEEE Workshop on Statistical Signal Processing (SSP'09). - : IEEE. - 9781424427093 ; , s. 245-248
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Konferensbidrag (refereegranskat)abstract
- This paper considers approximations of marginalization sums thatarise in Bayesian inference problems. Optimal approximations ofsuch marginalization sums, using a fixed number of terms, are analyzedfor a simple model. The model under study is motivated byrecent studies of linear regression problems with sparse parametervectors, and of the problem of discriminating signal-plus-noise samplesfrom noise-only samples. It is shown that for the model understudy, if only one term is retained in the marginalization sum, thenthis term should be the one with the largest a posteriori probability.By contrast, if more than one (but not all) terms are to be retained,then these should generally not be the ones corresponding tothe components with largest a posteriori probabilities.
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| 6. |
- Axell, Erik
(författare)
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Spectrum Sensing Algorithms Based on Second-Order Statistics
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cognitive radio is a new concept of reusing spectrum in an opportunistic manner. Cognitive radio is motivated by recent measurements of spectrum utilization, showing unused resources in frequency, time and space. Introducing cognitive radios in a primary network inevitably creates increased interference to the primary users. Secondary users must sense the spectrum and detect primary users' signals at very low SNR, to avoid causing too much interference.This dissertation studies this detection problem, known as spectrum sensing.The fundamental problem of spectrum sensing is to discriminate an observation that contains only noise from an observation that contains a very weak signal embedded in noise. In this work, detectors are derived that exploit known properties of the second-order moments of the signal. In particular, known structures of the signal covariance are exploited to circumvent the problem of unknown parameters, such as noise and signal powers or channel coefficients.The dissertation is comprised of six papers, all in different ways related to spectrum sensing based on second-order statistics. In the first paper, we considerspectrum sensing of orthogonal frequency-division multiplexed (OFDM) signals in an additive white Gaussian noise channel. For the case of completely known noise and signal powers, we set up a vector-matrix model for an OFDM signal with a cyclic prefix and derive the optimal Neyman-Pearson detector from first principles. For the case of completely unknown noise and signal powers, we derive a generalized likelihood ratio test (GLRT) based on empirical second-order statistics of the received data. The proposed GLRT detector exploits the non-stationary correlation structure of the OFDM signal and does not require any knowledge of the noise or signal powers.In the second paper, we create a unified framework for spectrum sensing of signals which have covariance matrices with known eigenvalue multiplicities. We derive the GLRT for this problem, with arbitrary eigenvalue multiplicities under both hypotheses. We also show a number of applications to spectrum sensing for cognitive radio.The general result of the second paper is used as a building block, in the third and fourth papers, for spectrum sensing of second-order cyclostationary signals received at multiple antennas and orthogonal space-time block coded (OSTBC) signals respectively. The proposed detector of the third paper exploits both the spatial and the temporal correlation of the received signal, from knowledge of the fundamental period of the cyclostationary signal and the eigenvalue multiplicities of the temporal covariance matrix.In the fourth paper, we consider spectrum sensing of signals encoded with an OSTBC. We show how knowledge of the eigenvalue multiplicities of the covariance matrix are inherent owing to the OSTBC, and propose an algorithm that exploits that knowledge for detection. We also derive theoretical bounds on the performance of the proposed detector. In addition, we show that the proposed detector is robust to a carrier frequency offset, and propose another detector that deals with timing synchronization using the detector for the synchronized case as a building block.A slightly different approach to covariance matrix estmation is taken in the fifth paper. We consider spectrum sensing of Gaussian signals with structured covariance matrices, and propose to estimate the unknown parameters of the covariance matrices using covariance matching estimation techniques (COMET). We also derive the optimal detector based on a Gaussian approximation of the sample covariance matrix, and show that this is closely connected to COMET.The last paper deals with the problem of discriminating samples that containonly noise from samples that contain a signal embedded in noise, when the variance of the noise is unknown. We derive the optimal soft decision detector using a Bayesian approach. The complexity of this optimal detector grows exponentially with the number of observations and as a remedy, we propose a number of approximations to it. The problem under study is a fundamental one andit has applications in signal denoising, anomaly detection, and spectrum sensing for cognitive radio.
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| 7. |
- Carlström, Mattias, et al.
(författare)
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L-arginine or tempol supplementation improves renal and cardiovascular function in rats with reduced renal mass and chronic high salt intake
- 2013
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 207:4, s. 732-741
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Tidskriftsartikel (refereegranskat)abstract
- Aim Early life reduction in nephron number and chronic high salt intake cause development of renal and cardiovascular disease, which has been associated with oxidative stress and nitric oxide (NO) deficiency. We investigated the hypothesis that interventions stimulating NO signalling or reducing oxidative stress may restore renal autoregulation, attenuate hypertension and reduce renal and cardiovascular injuries following reduction in renal mass and chronic high salt intake. Methods Male SpragueDawley rats were uninephrectomized (UNX) or sham-operated at 3weeks of age and given either a normal-salt (NS) or high-salt (HS) diet. Effects on renal and cardiovascular functions were assessed in rats supplemented with substrate for NO synthase (L-Arg) or a superoxide dismutase mimetic (Tempol). Results Rats with UNX+HS developed hypertension and displayed increased renal NADPH oxidase activity, elevated levels of oxidative stress markers in plasma and urine, and reduced cGMP in plasma. Histological analysis showed signs of cardiac and renal inflammation and fibrosis. These changes were linked with abnormal renal autoregulation, measured as a stronger tubuloglomerular feedback (TGF) response. Simultaneous treatment with L-Arg or Tempol restored cGMP levels in plasma and increased markers of NO signalling in the kidney. This was associated with normalized TGF responses, attenuated hypertension and reduced signs of histopathological changes in the kidney and in the heart. Conclusion Reduction in nephron number during early life followed by chronic HS intake is associated with oxidative stress, impaired renal autoregulation and development of hypertension. Treatment strategies that increase NO bioavailability, or reduce levels of reactive oxygen species, were proven beneficial in this model of renal and cardiovascular disease.
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| 8. |
- Larsson, Erik G., et al.
(författare)
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The Cramer-Rao Bound for Continuous-Time Autoregressive Parameter Estimation with Irregular Sampling
- 2002
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Ingår i: Circuits, systems, and signal processing. - : Springer Science and Business Media LLC. - 0278-081X .- 1531-5878. ; 21:6, s. 581-601
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of estimating the parameters in a continuous-time autoregressive model given measurements taken at arbitrary time instants. This problem is of importance in applications ranging from time-series analysis to automatic control. We derive the Cramer-Rao bound (CRB) for this estimation problem by using a technique based on the Slepian-Bang's formula and residue calculus. Furthermore, we investigate by means of numerical experiments how different sampling schemes can affect the achievable estimation accuracy. We demonstrate that the achievable estimation accuracy is relatively insensitive to the choice of sampling strategy, even though it is generally not identical for different sampling schemes. This observation is also in line with recent results on parameter estimation for polynomial-phase signals. Finally, we discuss the asymptotic properties ofthe CRB.
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| 9. |
- Larsson, Erik K., et al.
(författare)
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Cramer-Rao bounds for continuous-time AR parameter estimation with irregular sampling
- 2001
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Ingår i: Proc. of IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2001. vol. 5. - 0780370414 ; , s. 3097-3100
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Konferensbidrag (refereegranskat)abstract
- Consider the problem of estimating the parameters in a continuous-time autoregressive (AR) model given measurements taken at arbitrary time instants. In this paper the Cramer-Rao bound for this problem is derived by using a technique based on the Slepian-Bang's formula and residue calculus. Furthermore, we investigate by means of numerical experiments how different sampling schemes can affect the accuracy. Interestingly enough, however, for the examples studied, the estimation accuracy is relatively insensitive to the choice of sampling strategy.
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| 10. |
- Larsson, Erik K., et al.
(författare)
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The CRB for parameter estimation in irregularly sampled continuous-time ARMA system
- 2003
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Ingår i: Proc. of IEEE International Symposium on Signal Processing and Information Technology, (Darmstadt, Germany), Dec. 2003. - 0780382927 ; , s. 110-113
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Konferensbidrag (refereegranskat)abstract
- We derive novel and compact formulas for the Cramer-Rao bound (CRB) associated with the identification of the parameters in a continuous-time autoregressive moving-average (ARMA) model, given the nonuniformity of the sampled data. Our approach is based on a state-space formulation of the ARMA model, which facilitates a derivation of the CRB in closed form. Numerical examples illustrate our results.
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| 11. |
- Larsson, Erik K., et al.
(författare)
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The CRB for Parameter Estimation in IrregularlySampled Continuous-Time ARMA Systems
- 2004
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Ingår i: IEEE Signal Processing Letters. - 1070-9908 .- 1558-2361. ; 11:2, s. 197-200
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Tidskriftsartikel (refereegranskat)abstract
- We derive novel and compact formulas for the Cramer-Rao bound (CRB) associated with the identification of the parameters in a continuous-time autoregressive moving-average (ARMA) model, given nonuniformly sampled data. Our approach is based on a state-space formulation of the ARMA model, which facilitates a derivation of the CRB in closed form. Numerical examples illustrate our results.
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| 12. |
- Nicholls, Thomas J., et al.
(författare)
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Topoisomerase 3α Is Required for Decatenation and Segregation of Human mtDNA
- 2018
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 69:1
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Tidskriftsartikel (refereegranskat)abstract
- How mtDNA replication is terminated and the newly formed genomes are separated remain unknown. We here demonstrate that the mitochondrial isoform of topoisomerase 3α (Top3α) fulfills this function, acting independently of its nuclear role as a component of the Holliday junction-resolving BLM-Top3α-RMI1-RMI2 (BTR) complex. Our data indicate that mtDNA replication termination occurs via a hemicatenane formed at the origin of H-strand replication and that Top3α is essential for resolving this structure. Decatenation is a prerequisite for separation of the segregating unit of mtDNA, the nucleoid, within the mitochondrial network. The importance of this process is highlighted in a patient with mitochondrial disease caused by biallelic pathogenic variants in TOP3A, characterized by muscle-restricted mtDNA deletions and chronic progressive external ophthalmoplegia (CPEO) plus syndrome. Our work establishes Top3α as an essential component of the mtDNA replication machinery and as the first component of the mtDNA separation machinery. Nicholls et al. identify a role for topoisomerase 3α in the separation of mtDNA following replication. Loss of Top3α activity impairs mtDNA segregation and, consequently, segregation of the mtDNA nucleoid within the mitochondrial network. Mutations in TOP3A cause human mitochondrial disease associated with mtDNA deletions and impaired mtDNA separation. © 2017 Elsevier Inc.
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| 13. |
- Abarenkov, Kessy, et al.
(författare)
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Annotating public fungal ITS sequences from the built environment according to the MIxS-Built Environment standard – a report from a May 23-24, 2016 workshop (Gothenburg, Sweden)
- 2016
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Ingår i: MycoKeys. - : Pensoft Publishers. - 1314-4057 .- 1314-4049. ; 16, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Recent molecular studies have identified substantial fungal diversity in indoor environments. Fungi and fungal particles have been linked to a range of potentially unwanted effects in the built environment, including asthma, decay of building materials, and food spoilage. The study of the built mycobiome is hampered by a number of constraints, one of which is the poor state of the metadata annotation of fungal DNA sequences from the built environment in public databases. In order to enable precise interrogation of such data – for example, “retrieve all fungal sequences recovered from bathrooms” – a workshop was organized at the University of Gothenburg (May 23-24, 2016) to annotate public fungal barcode (ITS) sequences according to the MIxS-Built Environment annotation standard (http://gensc.org/mixs/). The 36 participants assembled a total of 45,488 data points from the published literature, including the addition of 8,430 instances of countries of collection from a total of 83 countries, 5,801 instances of building types, and 3,876 instances of surface-air contaminants. The results were implemented in the UNITE database for molecular identification of fungi (http://unite.ut.ee) and were shared with other online resources. Data obtained from human/animal pathogenic fungi will furthermore be verified on culture based metadata for subsequent inclusion in the ISHAM-ITS database (http://its.mycologylab.org).
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| 14. |
- Abrahamsson, R., et al.
(författare)
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Elimination of leakage and ground-bounce effects in ground-penetrating radar data
- 2001
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Ingår i: Proceedings of the 11th IEEE Signal Processing Workshop on Statistical Signal Processing, 2001. - 0780370112 ; , s. 150-153
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Konferensbidrag (refereegranskat)abstract
- We address the problem of removing specular ground surface reflections and leakage/cross-talk from downward looking stepped frequency ground-penetrating radar (GPR) data. A new model for the ground-bounce and the leakage/cross-talk is introduced. An algorithm that jointly estimates these effects from collected data is presented. The algorithm has the sound foundation of a nonlinear least squares (LS) fit to the presented model. The minimization is performed in a cyclic manner where one step is a linear LS minimization and the other step is a non-linear LS minimization where the optimum can efficiently be found using, e.g., the chirp-transform algorithm. The results after applying the algorithm to measured GPR data, collected at a US army test range, are also shown
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| 15. |
- Axell, Erik, 1980-, et al.
(författare)
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A Bayesian Approach to Spectrum Sensing, Denoising and Anomaly Detection
- 2009
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Ingår i: Proceedings of the 34th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP'09). - 9781424423545 - 9781424423538 ; , s. 2333-2336
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with the problem of discriminating samples that contain only noise from samples that contain a signal embedded in noise. The focus is on the case when the variance of the noise is unknown. We derive the optimal soft decision detector using a Bayesian approach. The complexity of this optimal detector grows exponentially with the number of observations and as a remedy, we propose a number of approximations to it. The problem under study is a fundamental one and it has applications in signal denoising, anomaly detection, and spectrum sensing for cognitive radio. We illustrate the results in the context of the latter.
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| 16. |
- Axell, Erik, et al.
(författare)
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A Unified Framework for GLRT-Based Spectrum Sensing of Signals with Covariance Matrices with Known Eigenvalue Multiplicities
- 2011
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Ingår i: Proceedings of the IEEE International Conference on Acoustics, Speech and SignalProcessing (ICASSP). - : IEEE conference proceedings. ; , s. 2956-2959
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we create a unified framework for spectrum sensing of signals which have covariance matrices with known eigenvalue multiplicities. We derive the generalized likelihood-ratio test (GLRT) for this problem, with arbitrary eigenvalue multiplicities under both hypotheses. We also show a number of applications to spectrum sensing for cognitive radio and show that the GLRT for these applications, of which some are already known, are special cases of the general result.
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| 17. |
- Axell, Erik, et al.
(författare)
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Capacity Considerations for Uncoordinated Communication in Geographical Spectrum Holes
- 2009
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Ingår i: Physical Communication. - : Elsevier. - 1874-4907. ; 2:1-2, s. 3-9
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Tidskriftsartikel (refereegranskat)abstract
- Cognitive radio is a new concept of reusing a licensed spectrum in an unlicensed manner. The motivation for cognitive radio is various measurements of spectrum utilization, that generally show unused resources in frequency, time and space. These "spectrum holes" could be exploited by cognitive radios. Some studies suggest that the spectrum is extremely underutilized, and that these spectrum holes could provide ten times the capacity of all existing wireless devices together. The spectrum could be reused either during time periods where the primary system is not active, or in geographical positions where the primary system is not operating. In this paper, we deal primarily with the concept of geographical reuse, in a frequency-planned primary network. We perform an analysis of the potential for communication in a geographical spectrum hole, and in particular the achievable sum-rate for a secondary network, to some order of magnitude. Simulation results show that a substantial sum-rate could be achieved if the secondary users communicate over small distances. For a small number of secondary links, the sum-rate increases linearly with the number of links. However, the spectrum hole gets saturated quite fast, due to interference caused by the secondary users. A spectrum hole may look large, but it disappears as soon as someone starts using it.
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| 18. |
- Axell, Erik, et al.
(författare)
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Comments on "Multiple Antenna Spectrum Sensing in Cognitive Radios"
- 2011
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE. - 1536-1276 .- 1558-2248. ; 10:5, s. 1678-1680
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Tidskriftsartikel (refereegranskat)abstract
- We point out an error in a derivation in the recent paper [1], and provide a correct and much shorter calculation of the result in question. In passing, we also connect the results in [1] to the literature on array signal processing and on principal component analysis, and show that the main findings of [1] follow as special cases of standard results in these fields.
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| 19. |
- Axell, Erik, et al.
(författare)
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Eigenvalue-Based Spectrum Sensing of Orthogonal Space-Time Block Coded Signals
- 2012
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 60:12, s. 6724-6728
-
Tidskriftsartikel (refereegranskat)abstract
- We consider spectrum sensing of signals encoded with an orthogonal space-time block code (OSTBC). We propose a CFAR detector based on knowledge of the eigenvalue multiplicities of the covariance matrix which are inherent owing to the OSTBC and derive theoretical performance bounds. In addition, we show that the proposed detector is robust to a carrier frequency offset, and propose a detector that deals with timing synchronization using the detector for the synchronized case as a building block. The proposed detectors are shown numerically to perform well.
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| 20. |
- Axell, Erik, et al.
(författare)
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GNSS spoofing detection using multiple mobile COTS receivers
- 2015
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467369978 ; , s. 3192-3196
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Konferensbidrag (refereegranskat)abstract
- In this paper we deal with spoofing detection in GNSS receivers. We derive the optimal genie detector when the true positions are perfectly known, and the observation errors are Gaussian, as a benchmark for other detectors. The system model considers three dimensional positions, and includes correlated errors. In addition, we propose several detectors that do not need any position knowledge, that outperform recently proposed detectors in many interesting cases.
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| 21. |
- Axell, Erik, et al.
(författare)
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Multiantenna Spectrum Sensing of a Second-Order Cyclostationary Signal
- 2011
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Ingår i: Proceedings of the 4th IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP'11). - 9781457721038 ; , s. 329-332
-
Konferensbidrag (refereegranskat)abstract
- We consider spectrum sensing of a second-order cyclostationary signal receivedat multiple antennas. The proposed detector exploits both the spatial andthe temporal correlation of the received signal, from knowledge of thefundamental period of the cyclostationary signal and the eigenvaluemultiplicities of the temporal covariance matrix. All other parameters, suchas the channel gains or the noise power, are assumed to be unknown. The proposeddetector is shown numerically to outperform state-of-the-art detectors forspectrum sensing of anOFDM signal, both when using a single antenna and with multiple antennas.
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| 22. |
- Axell, Erik, et al.
(författare)
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Optimal and Near-Optimal Spectrum Sensing of OFDM Signals in AWGN Channels
- 2010
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Ingår i: Proceedings of the International Workshop on Cognitive Information Processing (CIP).
-
Konferensbidrag (refereegranskat)abstract
- We consider spectrum sensing of OFDM signals in an AWGN channel. For the case of completely unknown noise and signal powers, we derive a GLRT detector based on empirical second-order statistics of the received data. The proposed GLRT detector exploits the non-stationary correlation structure of the OFDM signal and does not require any knowledge of the noise power or the signal power. The GLRT detector is compared to state-of-the-art OFDM signal detectors, and shown to improve the detection performance with 5 dB SNR in relevant cases. For the case of completely known noise power and signal power, we present a brief derivation of the optimal Neyman-Pearson detector from first principles. We compare the optimal detector to the energy detector numerically, and show that the energy detector is near-optimal (within 0.2 dB SNR) when the noise variance is known. Thus, when the noise power is known, no substantial gain can be achieved by using any other detector than the energy detector.
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| 23. |
- Axell, Erik, et al.
(författare)
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Optimal and Sub-Optimal Spectrum Sensing of OFDM Signals in Known and Unknown Noise Variance
- 2011
-
Ingår i: IEEE Journal on Selected Areas in Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 29:2, s. 290-304
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Tidskriftsartikel (refereegranskat)abstract
- We consider spectrum sensing of OFDM signals in an AWGN channel. For the case of completely known noise and signal powers, we set up a vector-matrix model for an OFDM signal with a cyclic prefix and derive the optimal Neyman-Pearson detector from first principles. The optimal detector exploits the inherent correlation of the OFDM signal incurred by the repetition of data in the cyclic prefix, using knowledge of the length of the cyclic prefix and the length of the OFDM symbol. We compare the optimal detector to the energy detector numerically. We show that the energy detector is near-optimal (within 1 dB SNR) when the noise variance is known. Thus, when the noise power is known, no substantial gain can be achieved by using any other detector than the energy detector.For the case of completely unknown noise and signal powers, we derive a generalized likelihood ratio test (GLRT) based onempirical second-order statistics of the received data. The proposed GLRT detector exploits the non-stationary correlation structure of the OFDM signal and does not require any knowledge of the noise power or the signal power. The GLRT detector is compared to state-of-the-art OFDM signal detectors, and shown to improve the detection performance with 5 dB SNR in relevant cases.
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| 24. |
- Axell, Erik, et al.
(författare)
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Overview of Spectrum Sensing for Cognitive Radio
- 2010
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Ingår i: Proceedings of the International Workshop on Cognitive Information Processing (CIP). ; , s. 322-327
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Konferensbidrag (refereegranskat)abstract
- We present a survey of state-of-the-art algorithms for spectrum sensing in cognitive radio. The algorithms discussed range from energy detection to sophisticated feature detectors. The feature detectors that we present all have in common that they exploit some known structure of the transmitted signal. In particular we treat detectors that exploit cyclostationarity properties of the signal, and detectors that exploit a known eigenvalue structure of the signal covariance matrix. We also consider cooperative detection. Specifically we present data fusion rules for soft and hard combining, and discuss the energy efficiency of several different sensing, sleeping and censoring schemes in detail.
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| 25. |
- Axell, Erik, et al.
(författare)
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Spectrum sensing for cognitive radio: State-of-the-art and recent advances
- 2012
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Ingår i: IEEE signal processing magazine (Print). - : IEEE Signal Processing Society. - 1053-5888 .- 1558-0792. ; 29:3, s. 101-116
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Tidskriftsartikel (refereegranskat)abstract
- The ever-increasing demand for higher data rates in wireless communications in the face of limited or underutilized spectral resources has motivated the introduction of cognitive radio. Traditionally, licensed spectrum is allocated over relatively long time periods and is intended to be used only by licensees. Various measurements of spectrum utilization have shown substantial unused resources in frequency, time, and space [1], [2]. The concept behind cognitive radio is to exploit these underutilized spectral resources by reusing unused spectrum in an opportunistic manner [3], [4]. The phrase cognitive radio is usually attributed to Mitola [4], but the idea of using learning and sensing machines to probe the radio spectrum was envisioned several decades earlier (cf., [5]).
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