| 1. |
- 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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| 2. |
- Alty, Stephen R., et al.
(författare)
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Efficient implementation of the time-recursive Capon and APES spectral estimators
- 2004
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Ingår i: EUSIPCO <em>2004</em>. - 3200001658 ; , s. 1269-1272
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Konferensbidrag (refereegranskat)abstract
- A method for the computationally efficient sliding window time-updating of the Capon and APES spectral estimators based on the time-variant displacement structure of the data covariance matrix is presented. The proposed algorithm forms a natural extension of the computationally most efficient algorithm to date, and offers a significant computationalgain as compared to the computational complexity associated with the batch re-evaluation of the spectral estimates for each time-update.
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| 3. |
- Avazkonandeh Gharavol, Ebrahim, 1980-, et al.
(författare)
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Robust Joint Optimization of MIMO Interfering Relay Channels with Imperfect CSI
- 2011
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Ingår i: 2001 4th IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP). - Piscataway, NJ, USA : IEEE. - 9781457721045 ; , s. 209-212
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Konferensbidrag (refereegranskat)abstract
- In this paper we deal with the problem of the joint optimization of the precoders, equalizers and relay beamformer of a multiple-input multiple-output interfering relay channel. This network can be regarded az a generalized model for both one-way and two-way relay channels with/without direct interfering links. Unlike the conventional design procedures, we assume that the Channel State Information (CSI) is not known perfectly. The imperfect CSI is described using the norm bounded error framework. We use a system-wide Sum Mean Square Error (SMSE) based problem formulation which is constrained using the transmit power of the terminals and the relay node. The problem at hand, from a worst-case design perspective, is a multilinear, and hence, a nonconvex problem which is also semiinfinite in its constraints. We use a generalized version of the Peterson’s lemma to handle the semi-infiniteness and reduce the original problem to a single Linear Matrix Inequality (LMI). However, this LMI is not convex, and to resolve this issue we propose an iterative algorithm based on the alternating convex search methodology to solve the aforementioned problem. Finally simulation results, i.e., the convergence of the proposed algorithm and the SMSE properties, are included to asses the performance of the proposed algorithm.
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| 4. |
- 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
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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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| 5. |
- 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
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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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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
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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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| 9. |
- 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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| 10. |
- 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).
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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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