The Experts below are selected from a list of 16383 Experts worldwide ranked by ideXlab platform
Mohamed-slim Alouini - One of the best experts on this subject based on the ideXlab platform.
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VTC Spring - Dual Branch Transmit Switch-and-Stay Diversity for Underlay Cognitive Networks
2011 IEEE 73rd Vehicular Technology Conference (VTC Spring), 2011Co-Authors: Mostafa Sayed, Mohamed-slim Alouini, Mohamed Abdallah, Khalid A. QaraqeAbstract:In this paper, we study applying dual branch transmit switch-and-stay combining (SSC) technique for underlay cognitive radio (UCR) networks. In UCR, the secondary user is allowed to share the spectrum with the primary (licensed) user under the condition that interference at the primary receiver is below a predetermined Threshold. Assuming binary phase-shift keying (BPSK) modulation and Rayleigh fading channels, we develop a closed form expression for the average bit error rate (BER) of the secondary link as a function of the Switching Threshold. We then find a closed form expression for the optimal Switching Threshold in the sense of minimizing the average BER. For the sake of comparison we derive an expression for the average BER of the dual branch transmit selection combining (SC) technique. We finally investigate the effect of correlation between secondary and interference channels on the average BER and the associated optimal Switching Threshold.
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Optimization of multi-branch switched diversity systems
IEEE Transactions on Communications, 2009Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:A performance optimization based on the optimal Switching Threshold(s) for a multi-branch switched diversity system is discussed in this paper. For the conventional multi-branch switched diversity system with a single Switching Threshold, the optimal Switching Threshold is a function of both the average channel SNR and the number of diversity branches, where computing the optimal Switching Threshold is not a simple task when the number of diversity branches is high. The newly proposed multi-branch switched diversity system is based on a sequence of Switching Thresholds, instead of a single Switching Threshold, where a different diversity branch uses a different Switching Threshold for signal comparison. Thanks to the fact that each Switching Threshold in the sequence can be optimized only based on the number of the remaining diversity branches, the proposed system makes it easy to find these Switching Thresholds. Furthermore, some selected numerical and simulation results show that the proposed switched diversity system with the sequence of optimal Switching Thresholds outperforms the conventional system with the single optimal Switching Threshold.
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Multi-branch switched diversity with adaptive Switching Thresholds
2008 International Symposium on Information Theory and Its Applications, 2008Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:This paper investigates a simple analytical approach that yields the optimal Switching Thresholds for multi-branch switched diversity systems. It also presents a performance optimization based on these optimal Thresholds. For multi-branch switched diversity systems, the optimal fixed Switching Threshold is not only a function of the average channel SNR but also a function of the number of diversity branches. Conventional multi-branch switched diversity systems use a single fixed Switching Threshold, where computing this optimal Threshold is not a simple task when the number of diversity branches is high. We propose a novel multi-branch switched diversity system that is based on a set of adaptive Switching Thresholds instead of a single fixed Switching Threshold, where a different Switching Threshold is used every Switching. Thanks to the fact that each Switching Threshold in the set depends only on the remaining diversity branches, the proposed system allows a simple optimization for these Switching Thresholds. Furthermore, numerical and simulation results show that the proposed adaptive switched diversity system outperforms the conventional system.
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Performance analysis of joint switched diversity and adaptive modulation
IEEE Transactions on Wireless Communications, 2008Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:In this paper, a simple and practical system based on a switched diversity scheme with adaptive modulation is presented. This system provides a reduced number of channel estimation while offering the optimum spectral efficiency given by a selection diversity system. In addition, the Switching Threshold is easily manipulated so as to make an efficient use of the tradeoff between spectral efficiency and channel estimation overhead. An extension of switched diversity into a multiuser scheduling is later also considered. This switch-based multiuser access scheme results in a lower average feedback load than that for the optimal selection-based multiuser scheme. Numerical results show that we can obtain a trade-off between spectral efficiency and the feedback load by choosing the Switching Threshold appropriately.
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ISIT - Performance Analysis of Switch-based Multiuser Scheduling with Adaptive Modulation
2007 IEEE International Symposium on Information Theory, 2007Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:In this paper, a simple and practical multiuser scheduling based on switched diversity with adaptive modulation is presented. This switch-based multiuser scheduling scheme results in an average feedback load that is lower than using the optimal opportunistic multiuser scheduling scheme while offering the optimum overall system spectral efficiency when used with the highest Threshold in the adaptive modulation. Numerical results show we can obtain a trade-off between spectral efficiency and the feedback load by choosing the user Switching Threshold appropriately. In addition, system operation can be adaptively altered based on the optimization goal and the given resource budget by a user Switching Threshold change.
Norman C. Beaulieu - One of the best experts on this subject based on the ideXlab platform.
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ICC - BER of MFSK With Postdetection Switch-and-Stay Combining in Correlated Rayleigh and Rician Fading
2007 IEEE International Conference on Communications, 2007Co-Authors: Sasan Haghani, Norman C. BeaulieuAbstract:The performance of M-ary frequency shift keying (MFSK) with dual-branch postdetection switch-and-stay combining (SSC) in correlated Rayleigh and Rician fading is studied. Closed-form expressions are derived for the average bit error rate (BER) of MFSK with postdetection SSC in correlated Rayleigh and Rician fading. Optimum Switching Thresholds that minimize the average BER are obtained. Extensive Monte Carlo simulations are presented to test the validity of the analytical results. The performance of MFSK with dual-branch postdetection SSC is compared to the performance of MFSK with dual-branch predetection SSC. The effects of correlation, fading parameter, fading power imbalance and Switching Threshold on the relative performance of the postdetection SSC compared to predetection SSC are examined.
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Performance of Two Dual-Branch Postdetection Switch-and-Stay Combining Schemes in Correlated Rayleigh and Rician Fading
IEEE Transactions on Communications, 2007Co-Authors: Sasan Haghani, Norman C. BeaulieuAbstract:The performance of binary frequency-shift keying (BFSK) and M-ary frequency shift keying (MFSK) with dual-branch postdetection switch-and-stay combining (SSC) in correlated Rayleigh and Rician fading is studied. Two postdetection SSC receivers are considered and the performances of noncoherent BFSK and MFSK are analyzed. Closed-form expressions are derived for the average bit-error rate (BER) of BFSK and MFSK with postdetection SSC in correlated Rayleigh and Rician fading. Optimum Switching Thresholds that minimize the average BER are obtained. Extensive Monte Carlo simulations are presented to test the validity of the analytical results. The performance of dual-branch postdetection SSC is compared with the performance of dual-branch predetection SSC. The effects of correlation, fading parameter, average fading power imbalance, and Switching Threshold on the performances of postdetection SSC receivers are examined
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ICC - BER of BFSK with Postdetection Switched Combining in Correlated Rayleigh Fading
2006 IEEE International Conference on Communications, 2006Co-Authors: Sasan Haghani, Norman C. BeaulieuAbstract:The performance of binary frequency-shift keying (BFSK) with dual-branch postdetection switch and stay combining (SSC) in correlated Rayleigh fading is considered. A closedform expression for the average bit error rate (BER) of BFSK with dual-branch postdetection SSC is derived. Optimum Switching Thresholds that minimize the average BER are obtained. It is shown that, for a fixed value of average signal-to-noise ratio (SNR), the optimum Switching Threshold is a decreasing function of branch correlation. Our analytical results are validated using Monte Carlo simulation results. The performance of dual-branch postdetection SSC is compared to the performance of dual-branch predetection SSC in correlated Rayleigh fading and it is shown that postdetection SSC has superior performance over predetection SSC for all values of SNR.
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Switched diversity on microcellular Ricean channels
IEEE Transactions on Vehicular Technology, 1994Co-Authors: Adnan Abu-dayya, Norman C. BeaulieuAbstract:The performances of switched dual diversity systems operating on independent and correlated Ricean fading channels are analyzed using a discrete time model. The average bit error rate (BER) of the discrete time switched diversity system using binary noncoherent frequency shift keying (NCFSK) on slow, nonselective Ricean fading channels is derived. A closed form expression that gives the optimum Switching Threshold in a minimum error rate sense is derived for the case of independent branch signals. Results for the optimum Switching Threshold for the case of correlated branch signals, obtained numerically, are also presented. Results using selection diversity combining are obtained for comparison. The effects of fading severity on both the BER and on the optimum Switching Threshold are investigated. The Ricean fading model may be used to model both the microcellular radio environment and the mobile satellite fading channel. Hence, the results of the paper are useful for both of these areas. >
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Analysis of switched diversity systems on generalized-fading channels
IEEE Transactions on Communications, 1994Co-Authors: Adnan Abu-dayya, Norman C. BeaulieuAbstract:The performances of switched diversity systems operating on generalized (Nakagami)-fading channels are analyzed using a discrete-time model. The average bit error rate (BER) of binary noncoherent frequency shift keying (NCFSK) on slow, nonselective Nakagami-fading channels is derived. Closed-form expressions that can be used to determine optimum Switching Thresholds (in a minimum error rate sense) are also derived. In addition, the use of optimum fixed Thresholds is considered. It is found that a considerable amount of diversity gain can be obtained using an optimum fixed (rather than adaptive) Switching Threshold. Results are obtained for both independent and correlated Nakagami-fading branch signals. The effects of fading severity and the correlation coefficient on both the BER and on the optimum Switching Threshold are investigated. It is shown that useful diversity gain can be obtained with power correlation coefficients as high as 0.9 when the fading is strong. The results for a Rayleigh channel are obtained and presented as a special case of generalized-fading model. >
Alfonso Martinez Arias - One of the best experts on this subject based on the ideXlab platform.
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fgf mapk signaling sets the Switching Threshold of a bistable circuit controlling cell fate decisions in embryonic stem cells
Development, 2015Co-Authors: Christian Schröter, Jonathan Peter Mackenzie, Alfonso Martinez AriasAbstract:Intracellular transcriptional regulators and extracellular signaling pathways together regulate the allocation of cell fates during development, but how their molecular activities are integrated to establish the correct proportions of cells with particular fates is not known. Here we study this question in the context of the decision between the epiblast (Epi) and the primitive endoderm (PrE) fate that occurs in the mammalian preimplantation embryo. Using an embryonic stem cell (ESC) model, we discover two successive functions of FGF/MAPK signaling in this decision. First, the pathway needs to be inhibited to make the PrE-like gene expression program accessible for activation by GATA transcription factors in ESCs. In a second step, MAPK signaling levels determine the Threshold concentration of GATA factors required for PrE-like differentiation, and thereby control the proportion of cells differentiating along this lineage. Our findings can be explained by a simple mutual repression circuit modulated by FGF/MAPK signaling. This might be a general network architecture to integrate the activity of signal transduction pathways and transcriptional regulators, and serve to balance proportions of cell fates in several contexts.
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FGF/MAPK signaling sets the Switching Threshold of a bistable circuit controlling cell fate decisions in embryonic stem cells.
Development, 2015Co-Authors: Christian Schröter, Jonathan Peter Mackenzie, Alfonso Martinez AriasAbstract:Intracellular transcriptional regulators and extracellular signaling pathways together regulate the allocation of cell fates during development, but how their molecular activities are integrated to establish the correct proportions of cells with particular fates is not known. Here we study this question in the context of the decision between the epiblast (Epi) and the primitive endoderm (PrE) fate that occurs in the mammalian preimplantation embryo. Using an embryonic stem cell (ESC) model, we discover two successive functions of FGF/MAPK signaling in this decision. First, the pathway needs to be inhibited to make the PrE-like gene expression program accessible for activation by GATA transcription factors in ESCs. In a second step, MAPK signaling levels determine the Threshold concentration of GATA factors required for PrE-like differentiation, and thereby control the proportion of cells differentiating along this lineage. Our findings can be explained by a simple mutual repression circuit modulated by FGF/MAPK signaling. This might be a general network architecture to integrate the activity of signal transduction pathways and transcriptional regulators, and serve to balance proportions of cell fates in several contexts.
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fgf mapk signaling sets the Switching Threshold of a bistable circuit controlling cell fate decisions in es cells
bioRxiv, 2015Co-Authors: Christian Schröter, Jonathan Peter Mackenzie, Alfonso Martinez AriasAbstract:Intracellular transcriptional regulators and extracellular signaling pathways together regulate the allocation of cell fates during development, but how their molecular activities are integrated to establish the correct proportions of cells with particular fates is not known. Here we study this question in the context of the decision between the epiblast (Epi) and the primitive endoderm (PrE) fate that occurs in the mammalian preimplantation embryo. Using an embryonic stem (ES) cell model, we discover two successive functions of FGF/MAPK signaling in this decision. First, the pathway needs to be inhibited to make the PrE-like gene expression program accessible for activation by GATA transcription factors in ES cells. In a second step, MAPK signaling levels determine the Threshold concentration of GATA factors required for PrE-like differentiation, and thereby control the proportion of cells differentiating along this lineage. Our findings can be explained by a simple mutual repression circuit modulated by FGF/MAPK signaling. This may be a general network architecture to integrate the activity of signal transduction pathways and transcriptional regulators, and serve to balance proportions of cell fates in several contexts.
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FGF/MAPK signaling sets the Switching Threshold of a bistable circuit controlling cell fate decisions in ES cells
bioRxiv, 2015Co-Authors: Christian Schröter, Jonathan Peter Mackenzie, Alfonso Martinez AriasAbstract:Intracellular transcriptional regulators and extracellular signaling pathways together regulate the allocation of cell fates during development, but how their molecular activities are integrated to establish the correct proportions of cells with particular fates is not known. Here we study this question in the context of the decision between the epiblast (Epi) and the primitive endoderm (PrE) fate that occurs in the mammalian preimplantation embryo. Using an embryonic stem (ES) cell model, we discover two successive functions of FGF/MAPK signaling in this decision. First, the pathway needs to be inhibited to make the PrE-like gene expression program accessible for activation by GATA transcription factors in ES cells. In a second step, MAPK signaling levels determine the Threshold concentration of GATA factors required for PrE-like differentiation, and thereby control the proportion of cells differentiating along this lineage. Our findings can be explained by a simple mutual repression circuit modulated by FGF/MAPK signaling. This may be a general network architecture to integrate the activity of signal transduction pathways and transcriptional regulators, and serve to balance proportions of cell fates in several contexts.
Hidde De Jong - One of the best experts on this subject based on the ideXlab platform.
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The Switching Threshold Reconstruction Problem for Piecewise-Affine Models of Genetic Regulatory Networks
IEEE Transactions on Automatic Control, 2008Co-Authors: Samuel Drulhe, Giancarlo Ferrari-trecate, Hidde De JongAbstract:Recent advances of experimental techniques in biology have led to the production of enormous amounts of data on the dynamics of genetic regulatory networks. We present an approach for the identification of piecewise-affine (PWA) models of genetic regulatory networks from experimental data, focusing on the reconstruction of Switching Thresholds associated with regulatory interactions. In particular, our method takes into account geometric constraints specific to models of genetic regulatory networks. We show the feasibility of our approach by the reconstruction of Switching Thresholds in a PWA model of the carbon starvation response in the bacterium Escherichia coli.
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The Switching Threshold Reconstruction Problem for Piecewise-Affine Models of Genetic Regulatory Networks
IEEE Transactions on Automatic Control, 2008Co-Authors: Samuel Drulhe, Giancarlo Ferrari-trecate, Hidde De JongAbstract:International audienceRecent advances of experimental techniques in biology have led to the production of enormous amounts of data on the dynamics of genetic regulatory networks. We present an approach for the identification of piecewise-affine (PWA) models of genetic regulatory networks from experimental data, focusing on the reconstruction of Switching Thresholds associated with regulatory interactions. In particular, our method takes into account geometric constraints specific to models of genetic regulatory networks. We show the feasibility of our approach by the reconstruction of Switching Thresholds in a PWA model of the carbon starvation response in the bacterium Escherichia coli.
Haewoon Nam - One of the best experts on this subject based on the ideXlab platform.
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Optimization of multi-branch switched diversity systems
IEEE Transactions on Communications, 2009Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:A performance optimization based on the optimal Switching Threshold(s) for a multi-branch switched diversity system is discussed in this paper. For the conventional multi-branch switched diversity system with a single Switching Threshold, the optimal Switching Threshold is a function of both the average channel SNR and the number of diversity branches, where computing the optimal Switching Threshold is not a simple task when the number of diversity branches is high. The newly proposed multi-branch switched diversity system is based on a sequence of Switching Thresholds, instead of a single Switching Threshold, where a different diversity branch uses a different Switching Threshold for signal comparison. Thanks to the fact that each Switching Threshold in the sequence can be optimized only based on the number of the remaining diversity branches, the proposed system makes it easy to find these Switching Thresholds. Furthermore, some selected numerical and simulation results show that the proposed switched diversity system with the sequence of optimal Switching Thresholds outperforms the conventional system with the single optimal Switching Threshold.
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Multi-branch switched diversity with adaptive Switching Thresholds
2008 International Symposium on Information Theory and Its Applications, 2008Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:This paper investigates a simple analytical approach that yields the optimal Switching Thresholds for multi-branch switched diversity systems. It also presents a performance optimization based on these optimal Thresholds. For multi-branch switched diversity systems, the optimal fixed Switching Threshold is not only a function of the average channel SNR but also a function of the number of diversity branches. Conventional multi-branch switched diversity systems use a single fixed Switching Threshold, where computing this optimal Threshold is not a simple task when the number of diversity branches is high. We propose a novel multi-branch switched diversity system that is based on a set of adaptive Switching Thresholds instead of a single fixed Switching Threshold, where a different Switching Threshold is used every Switching. Thanks to the fact that each Switching Threshold in the set depends only on the remaining diversity branches, the proposed system allows a simple optimization for these Switching Thresholds. Furthermore, numerical and simulation results show that the proposed adaptive switched diversity system outperforms the conventional system.
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Performance analysis of joint switched diversity and adaptive modulation
IEEE Transactions on Wireless Communications, 2008Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:In this paper, a simple and practical system based on a switched diversity scheme with adaptive modulation is presented. This system provides a reduced number of channel estimation while offering the optimum spectral efficiency given by a selection diversity system. In addition, the Switching Threshold is easily manipulated so as to make an efficient use of the tradeoff between spectral efficiency and channel estimation overhead. An extension of switched diversity into a multiuser scheduling is later also considered. This switch-based multiuser access scheme results in a lower average feedback load than that for the optimal selection-based multiuser scheme. Numerical results show that we can obtain a trade-off between spectral efficiency and the feedback load by choosing the Switching Threshold appropriately.
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ISIT - Performance Analysis of Switch-based Multiuser Scheduling with Adaptive Modulation
2007 IEEE International Symposium on Information Theory, 2007Co-Authors: Haewoon Nam, Mohamed-slim AlouiniAbstract:In this paper, a simple and practical multiuser scheduling based on switched diversity with adaptive modulation is presented. This switch-based multiuser scheduling scheme results in an average feedback load that is lower than using the optimal opportunistic multiuser scheduling scheme while offering the optimum overall system spectral efficiency when used with the highest Threshold in the adaptive modulation. Numerical results show we can obtain a trade-off between spectral efficiency and the feedback load by choosing the user Switching Threshold appropriately. In addition, system operation can be adaptively altered based on the optimization goal and the given resource budget by a user Switching Threshold change.
