Aalborg University

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    167824 research outputs found

    Model-Based Detector for SSDs in the Presence of Inter-cell Interference

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    In this paper, we consider the problem of reducing the bit error rate of flash-based solid state drives (SSDs) when cells are subject to inter-cell interference (ICI). By observing that the outputs of adjacent victim cells can be correlated due to common aggressors, we propose a novel channel model to accurately represent the true flash channel. This model, equivalent to a finite-state Markov channel model, allows the use of the sum-product algorithm to calculate more accurate posterior distributions of individual cell inputs given the joint outputs of victim cells. These posteriors can be easily mapped to the log-likelihood ratios that are passed as inputs to the soft LDPC decoder. When the output is available with high precision, our simulation showed that a significant reduction in the bit-error rate can be obtained, reaching 99.99% reduction compared to current methods, when the diagonal coupling is very strong. In the realistic case of low-precision output, our scheme provides less impressive improvements due to information loss in the process of quantization. To improve the performance of the new detector in the quantized case, we propose a new iterative scheme that alternates multiple times between the detector and the decoder. Our simulations showed that the iterative scheme can significantly improve the bit error rate even in the quantized case

    Crusading in the North

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    The role of hydrogen in a net-zero emission economy under alternative policy scenarios

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    Low emission and green hydrogen as a carbon-free energy carrier has attracted worldwide attention in decarbonizing the energy system and meeting the Paris agreement target of limiting warming to 2 °C or below. This study investigates the contribution of different hydrogen pathways to the energy transition and sheds light on adopting different decarbonization scenarios for Quebec, Canada, while including biogenic emissions from forest-based biomass consumption. We assess various alternative policy scenarios using a TIMES model for North America (NATEM), a bottom-up techno-economic approach. This study examines the role of various hydrogen pathways in Quebec's energy transition by considering different net-zero policy scenarios and an additional set of “green” scenarios, which prohibit the use of fossil fuel-based hydrogen. The results show that varying the penetration of hydrogen provides a key trade-off between reliance on direct air capture, reliance on carbon storage, reliance on wind and solar buildout, the inter-sector allocation of residual emissions, and the overall cost of achieving emission targets. In particular, the use of hydrogen in the industrial sector, a sector known to be difficult to decarbonize, reduces industrial emissions and reliance on direct air capture (DAC). Clustering industrial plants to use captured CO2 as a feedstock for synthetic fuel production may not reduce industrial GHG emissions by 2050, but it offers the opportunity to use captured CO2 instead of sequestering it in deep saline aquifers. Even though increasing industrial green hydrogen penetration increases marginal GHG abatement costs in the green net-zero scenario by 2050, it further minimizes industrial GHG emissions and the need for DAC among all net-zero scenarios by 2050. Hydrogen plays a significant role in achieving ambitious net-zero emission target, especially where electrification is not feasible, or electricitystorage is required.</p

    Ny standard har fokus på brugeren som medborger

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    The mistreatment of time in planning:Towards planning without the clock in a world increasingly out-of-sync

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    How do we (re-)imagine planning in a world which is increasingly out-of-sync? This is an important question because as a field of knowledge, policy, and practice that regards time as absolute, linear, and tameable, planning has yet to seriously engage with contemporary social science debates conceiving time as not only relative, diverse, and variegated. Our provocation in this chapter is to argue that planning mistreats, and has a problem, with time. Drawing on ‘critical time studies’, we engage with nascent scholarship on time and temporalities in and of planning to argue for a new approach of ‘planning without the clock’. Assessing the degree of leverage of critical time approaches to theorising planning we then reflect on the prospective role of planning and planners in a world ‘out-of-sync’. In conclusion, we call for greater engagement with developing ‘temporal’ tools, methods, and vocabularies to enable planners to place time front and centre of planning deliberation

    Gaikwad, Sagar Dilip

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    Sum-Rate Maximization in Integrated Space-Air-Ground Networks Under Backhaul Capacity Constraints

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    Integrated space-air-ground (ISAG) networks have emerged as a promising technology for next-generation communication networks, which demand higher throughput and wider coverage. However, several challenges must be addressed, such as wireless resource and interference management, transmit power control, and optimal deployment of unmanned aerial vehicles (UAVs) to achieve higher throughput. To this end, in this paper, we propose the joint transmit power control and the deployment UAV problem in the ISAG network to maximize the sum-rate of devices while guaranteeing the minimum rate requirement ofeach device and the wireless backhaul link constraints betweenUAVs and the satellite. However, solving the resulting problemis challenging since it has a non-convex structure. As a solution,we propose to decompose the problem into two subproblems. Wethen transform the decomposed subproblems into convex formsand solve them using successive convex approximation (SCA).Finally, we conduct extensive simulations to show the effectivenessof the proposed method, and the numerical results show that theproposed method achieves a performance gain: up to 8.35%, and4.08% in comparison to FPA and C-UAVs schemes

    Toribio, Markus Heinrich

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